ZIMBABWE SCHOOL OF MINES
Serving The SADC Mining Industry
METALLURGICAL ASSAYING
Topic
Assessing Carbon Ashing as an Alternative to Perchloric Acid Digestion: A Multi-Factor
Study.
DANSCIEL SAMUSHONGA
Z23296
A project submitted in partial fulfilment of the requirements for the Zimbabwe school of
mines Diploma in Metallurgical Assaying.
Zimbabwe
September 2025
i
ZIMBABWE SCHOOL OF MINES
Serving the SADC Mining Industry
PROJECT RELEASE FROM
I certify that the following student Dansciel
Samushonga Student number Z23296 was
under my supervision.
I further certify that he attended all the scheduled meetings with me and that he has
fulfilled all the requirements that I set before him/her as the supervisor.
It is my professional judgement that the project is of sufficiently high standard
as to be submitted with my name attached to it as the supervisor.
I hereby release the student without reservation to submit his project for marking
Name of Supervisor: Mr. T. Jacha
Signature………………………..
Date……………………………..
ii
ZIMBABWE SCHOOL OF MINES
Serving the SADC Mining Industry
Copyright
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prejudice owing to the contents of this work.
Name: Dansciel Samushonga
Signature……………
Date…………………
iii
ZIMBABWE SCHOOL OF MINES
Serving the SADC Mining Industry
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Name: Dansciel Samushonga
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iv
Abstract
A Comprehensive Evaluation of Dry Carbon Ashing as a Safer and Cost-Effective Alternative to
Perchloric Acid Digestion for the Analysis of Gold-Loaded Carbon at Ayrshire Mine Assay
Laboratory
This study investigates safer and more cost-effective methods for preparing carbon samples for
gold analysis at Ayrshire Mine Assay Laboratory. Traditionally, perchloric acid digestion has been
used to remove carbon from activated carbon samples before gold determination by Atomic
Absorption Spectrometry (AAS). While effective, this method poses severe safety risks, high
costs, and operational constraints that conflict with ISO 45001 safety standards.Perchloric acid is
a highly hazardous oxidizer that can form explosive compounds, creating catastrophic risks to
personnel and infrastructure. The method also requires costly acid procurement, specialized fume
hoods, and hazardous waste management. Additionally, the hot-plate process limits throughput
and delays sample turnaround.
To address these challenges, this project evaluates dry carbon ashing as an alternative. The method
employs a muffle furnace at 550–600 °C to oxidize carbon into carbon dioxide, leaving mineral
ash for gold recovery. The research aimed to confirm whether dry ashing could provide
comparable analytical accuracy while improving safety, reducing costs, and increasing efficiency.
The study was conducted in four phases: (1) Analytical validation by comparing gold recoveries
from perchloric acid digestion and dry ashing; (2) A safety assessment using a risk register and
5x5 risk matrix; (3) An economic analysis of per-sample costs, including labor, reagents, and
equipment; and (4) Evaluation of throughput and processing capacity.Results confirmed that dry
ashing produces gold recoveries nearly identical to perchloric acid digestion, with all values falling
within acceptable analytical limits. Safety analysis showed that perchloric acid carried the highest
inherent risk (score 25, “Very High”), while dry ashing hazards such as thermal burns were
reduced to “Low” with basic controls. Economically, dry ashing reduced costs by more than 50%,
primarily due to eliminating perchloric acid and enabling unattended batch processing, which also
improved laboratory capacity. In conclusion, dry carbon ashing is a safer, cheaper, and more
efficient alternative that aligns with ISO 45001 standards and enhances laboratory productivity. It
is recommended that Ayrshire Mine adopt dry ashing as the new standard procedure to replace
perchloric acid digestion.
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ACKNOWLEDGEMENTS
I would be remise if I did not show gratitude to the following individuals as they were instrumental
in the course of this study. Starting off with my supervisor Mr. T Jacha who was my supervisor
for this study. He was there with me every step of the way giving me guidance, corrections and
suggestions I could not have completed this project without him. I would also like a extend a hand
to my supervisor from Ayrshire Mine Mr. Matete as he was the individual who assisted me in the
practical aspects of the study whilst I was attached at Ayrshire Mine. Last but not least it would be
criminal of me if did not mention how grateful I am toward my parents for their monumental,
unsurmountable support towards me.
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DEDICATION
I would like to dedicate this project to Ayrshire Mine and its embitterment
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PROJECT RELEASE FROM ..................................................................................................... ii
Copyright.................................................................................................................................... iii
Declaration of Plagiarism ........................................................................................................... iv
Abstract ....................................................................................................................................... v
ACKNOWLEDGEMENTS ....................................................................................................... vi
DEDICATION .......................................................................................................................... vii
Chapter 1: ........................................................................................................................................ 1
1.0 Introduction ........................................................................................................................... 1
1.0.1 History and location of Ayrshire Mine ............................................................................... 1
1.2 Geological and Mineralogical Setup ................................................................................. 3
1.3 Background of study ......................................................................................................... 4
1.3.1 By implementing the dry carbon ashing method, the Ayrshire Mine laboratory would
achieve the following: ............................................................................................................. 4
1.3.2 Structure of the organization .......................................................................................... 6
1.3.3 The different departments at Ayrshire mine ................................................................... 7
1.3.4 Process overview of Ayrshire Mine Assay Laboratory. ................................................. 9
1.3.5 Ayrshire Mine Mission statement ................................................................................ 10
1.3.6 Vision ........................................................................................................................... 10
1.3.7 Core Values of Ayrshire Mine ...................................................................................... 10
1.3.8 Policies Ayrshire Mine conforms to: ............................................................................ 10
1.4 Problem statement ........................................................................................................... 11
1.4.2 Aim .............................................................................................................................. 11
1.4.3 Objectives .................................................................................................................... 11
Chapter 2 ....................................................................................................................................... 12
2.1 Introduction ..................................................................................................................... 12
2.2 Definitions and terminology ........................................................................................... 12
2.3 Dry carbon ashing method .............................................................................................. 13
2.4 Perchloric Acid Digestion of Carbon .............................................................................. 15
2.5 Why replace perchloric acid? .......................................................................................... 16
2.6 Ideal carbon condition for dry ashing ............................................................................. 19
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2.7.1 Muffle furnace ............................................................................................................. 20
2.7.2 The use of a muffle furnace in carbon ashing .............................................................. 20
2.8.1 Hot plate ....................................................................................................................... 21
2.8.2 The use of a hot plate in carbon digestion ................................................................... 22
2.8.3 The uses of the hot plate components: ......................................................................... 23
2.9 Atomic absorption spectrometer ..................................................................................... 23
2.9.2 The uses of AAS parts.................................................................................................. 25
2.9.2 The use of an Atomic Absorption Spectrometer in the analysis of carbon solutions for
gold ....................................................................................................................................... 26
2.9.3 Conclusion .................................................................................................................... 26
References ............................................................................................................................. 27
Chapter 3 ....................................................................................................................................... 28
3.1 Research Design.............................................................................................................. 28
3.2.1 Carbon samples ............................................................................................................ 28
3.3 phase 1: Carbon ashing and carbon digestion using perchloric acid .............................. 28
3.3.1 Aim for carbon ashing .................................................................................................. 28
3.3.2 Safety / PPE Required .................................................................................................. 28
3.3.3 Materials and Equipment ............................................................................................. 29
3.3.4 Procedure ..................................................................................................................... 29
3.4 Acid digestion of carbon ................................................................................................ 30
3.4.1 Aim ............................................................................................................................... 30
3.4.2 Safety measures and equipment ................................................................................... 30
3.4.3 Reagents and equipment .............................................................................................. 31
3.4.4 Procedure for perchloric acid digestion of carbon ....................................................... 31
3.5 Phase 2 Procedure for Developing, Using, and Displaying a Risk Register .................. 32
3.5.1 Scope ............................................................................................................................ 32
3.5.2 Identify Hazards ........................................................................................................... 32
3.5.3 Describe Consequences ............................................................................................... 33
3.5.4 Estimate Likelihood ..................................................................................................... 33
3.5.5 Assign Inherent Risk Rating ........................................................................................ 33
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3.5.6 Define Controls / Mitigation Measures........................................................................ 33
3.5.7 Assign Residual Risk Rating........................................................................................ 33
3.5.8 Populate the Risk Register ........................................................................................... 33
3.5.9 Display the Data ........................................................................................................... 33
3.6.1 Validation calculations ..................................................................................................... 34
3.6.2 Accuracy .......................................................................................................................... 34
3.6.3 Precision ........................................................................................................................... 34
3.6.4 Paired Differences. ........................................................................................................... 34
3.6.4 Limits of agreement ......................................................................................................... 35
3.6.5 Correlation and linear regression ..................................................................................... 35
3.8 Define the Cost Categories ................................................................................................. 36
3.8.1 Tracking Energy Consumption ........................................................................................ 36
3.8.2 Tracking Time Costs ........................................................................................................ 36
3.8.3 Tracking Materials / Consumables............................................................................... 36
3.8.4 Tracking Maintenance and Repairs .................................................................................. 37
3.8.5 Calculation Procedure ...................................................................................................... 37
Chapter 4 ....................................................................................................................................... 38
Analysis of precious metal from carbon ash ......................................................................... 38
4.1.3 side to side comparison on results of carbon ashing and perchloric acid digestion in the
analysis of gold ......................................................................................................................... 40
The development of a risk register to assess the safety of both methods ............................. 42
4.2.1 5 x 5 matrix ..................................................................................................................... 42
4.2.2 Risk rating into different ranges ...................................................................................... 42
4.2.3 Risk register for perchloric acid digestion and carbon ashing ......................................... 43
4.2.4 Risk rating visuals and explanation ............................................................................. 44
4.2.5 Residual risk assessment .................................................................................................. 44
4.2.6 Risk impact ...................................................................................................................... 45
4.2.7 Visualizing impact and occurrence of residual risk ......................................................... 45
4.3 Validation for carbon ashing over perchloric acid digestion............................................... 46
4.3.1. Accuracy / Trueness ........................................................................................................ 46
4.3.2 Precision / Repeatability .................................................................................................. 46
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4.3.3 Method Comparison (Paired Test and Correlation) ......................................................... 46
4.3.4 Summary of Validation Metrics ....................................................................................... 46
4.3.5 Conclusion ....................................................................................................................... 47
4.4 Comparing time and energy usage for carbon ashing and perchloric acid digestion ......... 47
4.4.1 For the muffle furnace which runs for 4h at a power rating of 4kW ............................... 47
4.4.2 For the hot plate which runs for three hours .................................................................... 48
4.5 Calculating cost ................................................................................................................... 48
4.5.1 Cost for carbon ashing ..................................................................................................... 48
4.5.2 Cost per sample for acid digestion ................................................................................... 50
Chapter 5 ....................................................................................................................................... 51
5.1 Conclusion .......................................................................................................................... 52
5.1.2 Recommendations ............................................................................................................ 53
5.2 References ........................................................................................................................... 53
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Table of Figures
Figure 1Location of Ayrshire Mine ................................................................................................. 1
Figure 2Organogram of Ayrshire Mine ........................................................................................... 6
Figure 3 Process overview for Ayrshire Mine ................................................................................ 9
Figure 4: Muffle furnace ............................................................................................................... 21
Figure 5:A hot plate ...................................................................................................................... 22
Figure 6Ayrshire Mine's Atomic Absorption Spectrometer .......................................................... 24
Figure 7: Schematic diagram of the AAS machine ....................................................................... 25
Figure 8:Bar Graph for gold in Carbon Ash ................................................................................. 38
Figure 9:Bar graph for perchloric acid gold analysis .................................................................... 40
Figure 10: Results for both gold in ash and in perchloric acid ..................................................... 41
Figure 11:Inherent and Residual risk ............................................................................................ 44
Figure 12: Risk Assessment Graph ............................................................................................... 45
Figure 13 Validation for carbon ashing ......................................................................................... 47
Figure 14 Power and time graph ................................................................................................... 48
Figure 15: Comparing cost between Dry ashing and Perchloric Acid digestion .......................... 51
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List of tables
Table 1 Assay results for carbon ashing ........................................................................................ 38
Table 2 Results for perchloric acid digested carbon ..................................................................... 39
Table 3Side to side comparison for carbon ashing and perchloric acid digestion ........................ 41
Table 4 5 X 5 matrix ..................................................................................................................... 42
Table 5 Risk rating table ............................................................................................................... 42
Table 6 Risk register ..................................................................................................................... 43
Table 7Residual risk assessment ................................................................................................... 45
Table 8 Impact rating table ........................................................................................................... 45
Table 9 Accuracy table .................................................................................................................. 46
Table 10 Precision Table ............................................................................................................... 46
Table 11Validation metrics table ................................................................................................... 46
Table 12 Power and Time table ..................................................................................................... 48
xiii
Chapter 1:
1.0 Introduction
This section aims to state the background, history and the location of Ayrshire Mine. While also
giving an overview of the process. The chapter provides the problem statement, the justification
of the proposed solution and the aim of the project
1.0.1 History and location of Ayrshire Mine
Figure 1Location of Ayrshire Mine
Ayrshire mine is situated in Mashonaland West province, approximately 30 km northeast of banket
town and about 105km from Harare, the capital city of Zimbabwe. It is located within the Chinhoyi
Guruve greenstone belt, specifically on the splay of the Eldorado Shear Zone. To reach it on must
take a gravel road that branches of the Harare-Chirundu highway (80km peg) and leads through
Banket, Covering roughly 25km
. Ayrshire Mine’s story stretches back to the early colonial gold rush in what is now Mashonaland
West. Claims were pegged in the 1890s over extensive ancient surface workings on the Maquadzi
River, with regular production beginning in 1899 and the Edward’s (Edwards) Shaft sunk in 1901,
then the deepest in the country. The mine became something of a byword for the era’s speculative
booms and busts in London, and—despite heavy early investment—was shuttered in 1909 as debts
mounted. In the modern era the operation was revived and Pan African Mining (Pvt) Ltd took over
Ayrshire in 1987, returning it to sustained production; today it operates an area reported at ~797
1
hectares, and continues to work both underground and surface resources from a historic
mineralized corridor of roughly 9 km.
Publicly reported site data from a 2021 government/media tour give a clear snapshot of Ayrshire’s
scale and trajectory. Management briefed authorities that the mine was increasing milled ore from
~12,500 tonnes per month to ~25,000 tpm, with a gold output uplift from ~32 kg to ~47–50 kg per
month as projects came on stream. Earlier, during a 2014 performance update, the operator also
disclosed that monthly production had risen from ~5 kg to ~20 kg at one stage, showing how output
has been ramped in phases over the last decade. Those figures provide the best public yardsticks
for monthly ore tonnage and gold production at Ayrshire.
Investment has been periodic and targeted at life-extension and reliability. In 2014, Pan African
Mining said it had injected US$11.5 million across its operations, including Ayrshire, to stabilise
and lift output. A subsequent 2021 site briefing detailed a fresh ~US$19 million program focused
on exploration, shaft deepening by ~800 m, plant upgrades, tailings disposal, and open-pit
expansion to support the higher 25 kt/month milling target and keep ounces flowing. These steps
fit the mine’s long-term pattern: extend underground access and hoisting capacity while adding
selective surface tonnes for steady plant feed.
The same 2021 visit reported “over 400 workers” on site and noted active housing expansion—
100 additional houses under construction—to accommodate a growing staff complement. Because
the workforce outpaced on-site housing at the time, the company was also accommodating some
employees at its sister Muriel Mine (about 52 km east), while pursuing community support
initiatives such as borehole drilling. Earlier press from the 2000s shows that employment levels
have fluctuated with market cycles (one 2007 report referenced restructuring that could affect up
to ~600 jobs), underscoring why housing and community facilities are typically built in phases.
Ayrshire presents itself as a safety-forward operation: by 2021 it was credited with millions of
fatality-free shifts and only a handful of recordable injuries annually since 2013, while also being
integrated into national mine-rescue capacity—Pan African Mines’ rescue team for the northern
region was formally commissioned by the Mine Rescue Association of Zimbabwe in 2025. Public
sources do not list formal ISO certifications for Ayrshire (e.g., ISO 45001/14001/9001 or ISO
17025 for labs), so it’s best to describe the site as operating an integrated SHEQ system aligned
with Zimbabwe’s legal standards and sector best practice, with active emergency preparedness,
ventilation and ground-control engineering underground, regulated blasting and dewatering in
surface areas, and environmental controls around tailings and water. If you need a citation-ready
claim about specific certifications, that would require direct company documentation.
The mine acquires its ore from open pit mines and an underground mine of which all of the samples
are processed, monitored and analyzed by the laboratory. This is all in an effort to make sure that
a high recovery rate of the valuable mineral is achieved. In addition to these locations the plant
also monitors the various aspects of the plant including the grade of all the following areas
Thickener, Cyclone, Adsorption tanks and the Leach tanks.
1.1 Mining methods practiced by Ayrshire Mine
Open-cast (surface) mining at Ayrshire. Ayrshire has long had surface workings—historically
recorded as ancient open-pit workings that pre-date modern operations—and, in recent years, has
2
evaluated additional near-surface potential with geochemical sampling, trenching and open-pit
studies alongside the existing underground mine. In practical terms, open-cast gold production at
Ayrshire would follow the classic bench mining cycle: resource models from Technical Services
guide grade control drilling along advancing pit ramps; blasts are designed for both fragmentation
and dilution control; hydraulic shovels or front-end loaders load ore into haul trucks for direct
tipping to run-of-mine pads or the crusher, while waste is sent to engineered dumps with stormwater controls. Because the deposit sits in a seasonally wet climate, pit dewatering (sumps, in-pit
pumps, and perimeter drains) and haul-road maintenance are significant routine tasks, as are wall
monitoring and slope management (batter/berm geometry, catch berm cleaning, prism or radar
checks) to maintain geotechnical stability. SHEQ oversight is highly visible in the pit: blast
clearance, fly-rock exclusion, dust and noise controls, and concurrent rehabilitation on inactive
flanks. Operationally, open-cast tonnes help the plant maintain steady feed when underground
stopes are constrained, but require tight short-interval control from geology and grade control to
avoid sending low-grade or oxidized material that may underperform in the plant. Public sources
do not list specific, named modern open pits at Ayrshire (internal pit names are usually sitespecific), but the mine’s “ancient open-pit workings” are explicitly noted in the historical record,
and recent press has referred to ongoing trenching and open-pit development work at Ayrshire.
Underground mining at Ayrshire. Underground production is the backbone of Ayrshire and has
been for more than a century. Historically, the mine sank the Edward’s Shaft (Edwards Shaft) in
1901—then the deepest in the country—and modern operations continue to exploit the orebody at
depth, with press accounts describing travel down a ~600 m mineshaft. A typical shift underground
starts with travel down the shaft to working levels, followed by drilling (production and
development) on designed rings or faces, charging under strict explosives control, blasting on the
night shift, and post-blast re-entry for loading. Broken ore is mucked by LHDs or loaders to ore
passes or directly to level tips, then hoisted up the shaft for delivery to the plant. Ground control
is critical: rock-mechanics engineers specify support (resin bolts, mesh, straps, shotcrete) and
monitor seismicity, while ventilation teams maintain airflow with raises, auxiliary fans, and
regulators to keep air quality and temperature within limits. Pumping systems handle groundwater
inflows to keep levels dry, and electrical/mechanical maintenance keeps hoisting, winder brakes,
crushers, compressors, and refuge chambers in compliance. Grade control sampling (face chips,
channel samples, on-reef development) feeds back to planning to minimize dilution and keep stope
panels in the highest-margin blocks. From a site-naming standpoint, Edward’s (Edwards) Shaft is
the documented underground working associated with Ayrshire; production is organized by levels
and stopping panels off that shaft system.
1.2 Geological and Mineralogical Setup
Ayrshire mine is on the edge of an old greenstone belt in Zimbabwe, close to a granite body. The
gold is mostly in diorite rock. Around it is schists (soft, altered rocks) and a big quartz dyke along
an ENE faultline. There are two main gold zones, each are shaped like steep pipes/shoots that go
down into the ground into the ground plunging NNE/ENE. The gold is spread out in the diorite
(this is however the of a low grade disseminate). The best gold is located in silicified shear zones
(zones of broken altered rock with added silica and chlorite). The rocks are altered by chlorite,
biotite, talc and silica. The formation of these gold deposits can be tied back to the movement
along the ENE fault and the cooling of the nearby granite creating a space for fluids, which carried
gold into diorite and shear zones. In short Ayrshire Mine is a granite border, diorite-hosted gold
deposit with two steep gold shoots controlled by ENE shears and strong alteration (alteration
3
referring to the chemical change of the original rock when hot fluids pass through it. The fluids
come from magma or deep circulation of water. These carry heat, silica and other chemicals. When
they move through cracks or shear zones, they replace or change the original minerals in the rock.)
1.3 Background of study
As a core pillar of Ayrshire mine. The Ayrshire Mine assay laboratory is in charge of analyzing
various samples that come from multiple areas of the mine including but not limited to the
underground shaft, the pit, exploration samples and among the most important are the plant
samples. The plant samples include leach tank samples, thickener samples, cyclone samples and
the core focus of this study the carbon samples. The carbon samples are used to determine how
much gold has successfully been adsorbed by the activated carbon. This can be used in calculations
that determine the gold content and carbon activity. This is critical for monitoring the efficiency
of gold recovery, scheduling elution, maintaining carbon quality and reducing gold losses.
The laboratory at Ayrshire Mine is ISO 45001 certified meaning that it conforms to the requirement
that harm coming from work practices during working hours shall be eliminated, so as to maintain
the occupational health and safety of workers in pristine condition. For this reason, this study set
out to introduce an alternative to carbon sample digestion using perchloric acid as a way to
eliminate the threat of harm coming from the potentially explosive reagent. This of course would
be the introduction of the dry carbon ashing method. This method burns away the carbon in the
presence of oxygen at high temperature to eliminate the carbon as carbon dioxide. This would
bypass the need to use the hazardous perchloric acid. There by leaving behind the adsorbed gold
in ash, while keeping the workers safe and showing conformance to the standard that is ISO 45001.
1.3.1 By implementing the dry carbon ashing method, the Ayrshire Mine laboratory would
achieve the following:
1. Conformance with ISO 45001: this standard requires that the occupational health and
safety of workers be prioritized over all other things including productivity. The safety of
workers shall not be compromised as a way to speed up turnover time. Eliminating the risk
of explosions at the laboratory will improve the safety aspect of the working conditions
and will also increase worker morale as another potential source of harm will be removed.
2. Increased safety: the reagent known as perchloric acid that is currently being used in the
digestion process is very hazardous as it can explode upon contact with a hot surface and
organic matter. Even in a controlled environment where the likelihood of occurrence is
very low the consequence of the explosion itself can still have fatal implications. So,
eliminating the hazard and instead use the alternative method of dry ashing would increase
safety
3. Complete removal of carbon: dry ashing just like perchloric acid digestion also completely
removes carbon from the samples to leave behind the inert valuable metal as it does not
volatize into a gas. The adsorbed gold remains behind in the ash so that it can be dissolved
in acids like nitric acid, hydrochloric acid and aqua regia. This makes it a viable
replacement for the problematic perchloric acid.
4. Enabling for bulk sampling: The current setup for digestion of carbon samples on the hot
plate has restrictions such as the small physical space that the conical flask can fit on, at
most it would be 15 flasks. There is also the restriction of the time allocated for carbon
4
digestion as solid samples will also need to be digested on the hot plate within the time
frame of one shift. this limits the number of carbon samples that can be analyzed per shift.
The introduction of a muffle furnace would increase the amount of carbon samples that can
be analyzed per shift as it can accommodate more carbon samples and take some of the
work load away from the hot plate.
5
1.3.2 Structure of the organization
The following is a diagram showing the structure of Ayrshire Mine’s management
owner/ directors
Board
CEO
Mine manager
Human resources
manager
Technical
services manager
Engineering
manager
Sheq manager
Finance manager
Security Chief
training and
development
superintendent
Chief Geologist
Mechanical
superintendent
Safety
superintendant
Chief accountant
Security
superintendent
Mine captain
Payroll and
admin
superintendent
Chief assayer
Electrical
superintended
Health
superintendent
Procurement
superintendant
Invetsigations
Officer
Ventilation
officer
Community
relations
manager
Chief Surveyor
Civil works
superintendent
Environment
superintendent
Store manager
Surveillance
Supervisor
Rock mechanics
engineer
Industrial
relations managr
Mine Planning
Superintendent
Transport
manager
Quality officer
Budgeting
manager
Underground
Manager
Support services
supervisor
Stores
superintendent
Figure 2Organogram of Ayrshire Mine
6
1.3.3 The different departments at Ayrshire mine
. Mining Department
The mining department is the heart of Ayrshire Mine because it is directly responsible for
extracting gold-bearing ore from underground stopes and shafts. Its functions include drilling,
blasting, loading, hauling, and hoisting ore to the surface. This department ensures that production
targets are met safely and efficiently, while maintaining proper ground control and ventilation
systems. The mining department’s performance directly affects the mine’s gold output, revenue,
and long-term viability, making it the most critical driver of the operation.
Human Resources Department (HR)
The human resources department manages the workforce that keeps Ayrshire Mine operational. It
oversees recruitment, training, payroll, industrial relations, and employee welfare. HR ensures that
the mine has the right number of skilled employees in every department and also handles
negotiations with trade unions and compliance with labor laws. At Ayrshire Mine, HR affects
productivity by maintaining worker morale, reducing disputes, and ensuring that employees are
motivated, trained, and safe to carry out their duties.
Technical Services Department
The technical services department provides the scientific and planning backbone of the mine. It
houses geology, surveying, mine planning, and the laboratory. Geologists identify ore zones and
guide mining crews, while surveyors and planners design stopes and track ore extraction. The
laboratory provides grade control through assaying, ensuring ore sent to the plant is of the expected
quality. At Ayrshire Mine, this department directly impacts efficiency by optimizing ore extraction,
reducing dilution, and supporting long-term planning of reserves.
Engineering Department
The engineering department is responsible for the maintenance and operation of all mechanical,
electrical, and civil infrastructure at Ayrshire Mine. This includes winding engines, shaft systems,
pumps, ventilation fans, vehicles, and processing plant equipment. By ensuring equipment
reliability and availability, the engineering department minimizes downtime and prevents costly
breakdowns. At Ayrshire, its work is vital to safe operations, uninterrupted production, and the
reduction of operational costs.
SHEQ Department (Safety, Health, Environment, Quality)
The SHEQ department ensures that Ayrshire Mine operates responsibly and safely. It manages
workplace safety, occupational health, environmental protection, and compliance with ISO
standards. This department reduces accidents, monitors dust and noise level, enforces PPE use,
7
and ensures environmental compliance in tailings and water management. By maintaining high
SHEQ standards, Ayrshire Mine builds community trust, protects its workforce, and avoids costly
penalties or shutdowns due to regulatory breaches.
Finance Department
The finance department manages the financial health of Ayrshire Mine by controlling budgets,
accounts, and cash flows. It ensures that mining, engineering, and technical departments are
properly funded, while keeping costs within budget. It also handles procurement and financial
reporting. Finance affects Ayrshire’s activities by ensuring that the mine can purchase critical
supplies, pay employees, and invest in new projects or equipment, all of which directly influence
profitability and sustainability.
Security Department
Security plays a particularly critical role in a gold mine like Ayrshire due to the high value and
theft risk of gold. The security department safeguards people, property, explosives, and the product
itself from theft, smuggling, and sabotage. It operates access control, patrols, CCTV monitoring,
and investigations. Security affects the mine’s activities by maintaining integrity of operations,
ensuring employees feel safe, and protecting gold from illegal loss, which directly preserves the
mine’s revenue.
Stores / Supply Chain Department
The stores department manages the procurement, storage, and distribution of consumables, spare
parts, tools, and protective equipment. This department ensures that mining crews, plant operators,
and engineers have the necessary resources when needed. At Ayrshire Mine, efficient stores
management reduces downtime, prevents stockouts of critical materials like explosives or
reagents, and controls costs by avoiding excess inventory. Its efficiency directly supports the
smooth running of all other departments.
8
1.3.4 Process overview of Ayrshire Mine Assay Laboratory.
Sample
receiving
Sample logging
solution
samples
Solid Carbon
samples
Solid samples
solution sample
analysis
Carbon samples
drying
Temporary solid
sample storage
Carbon samples
weighing
Solid Sample
drying
Carbon sample
storage
Solid Sample
crushing
Carbon samples
digestion
Solid Sample
pulverizing
Carbon samples
analysis
Solid sample
weighing
Solid sample
storage
Solid sample
digestion
Solid sample
collection
Solid sample
analysis sample
Figure 3 Process overview for Ayrshire Mine
9
1.3.5 Ayrshire Mine Mission statement
Ayrshire Mine under Pan African Mining has the objective of increase the growth of its resources
and enhancing its operations, Through investment in exploration, mine shaft deepening and plant
upgrades. This will be done while ensuring the highest degree of safety in order to avoid injuries
and fatalities. In order to carry out these objectives and also ensure the environment and
community is taken care of, Ayrshire mine will continue to conform to its IMS Policy which
includes ISO 45001, ISO 14001 and ISO 9001.
1.3.6 Vision
Mining for a future (reflecting the mine’s commitment to responsible, sustainable and efficient
gold mining, alongside community and environmental stewardship.)
1.3.7 Core Values of Ayrshire Mine

Safety and zero Harm

Responsible and sustainable mining

Community engagement and development

Ethics, integrity and good governance

Innovation, entrepreneurial spirit and efficiency

Valu creating growth and financial discipline

Talent, respect and people development
1.3.8 Policies Ayrshire Mine conforms to:
ISO 45001- This standard stipulates the occupational health and safety of workers whilst they are
conducting work related task shall be the upmost priority. This means that zero harm must come
to the workers. Which can be achieved through the implementation of safety controls around
hazardous processes, activities, services and products.
ISO 14001-Ayrshire Mine also wishes to conform to the standard of environmental management.
This means reducing the negative effect that the mine has towards the environment. This can be
brought about through continual improvement of waste disposal methods, reducing emission, staff
training, investing in new technologies that better conform to environmental upkeep and hosting
programs for the rejuvenation of the environment.
ISO 9001- This standard demands that Ayrshire Mine’s processes, products, activities and services
be of a consistently high quality at all times. This means that everything is scrutinized for defects
through the implementation of quality control measure so as to achieve quality assurance. This is
done to make sure that all of the needs of stakeholders are met and everything is working the way
it was meant to work.
ISO 17025- This ensures that all the equipment at Ayrshire mine is properly maintained and
calibrated regularly to ensure accurate products and increase the longevity of equipment. This is
to be documented and recorded. As a way to track whether or not everything is in order
10
1.4 Problem statement
The use of perchloric acid has become common place at Ayrshire mine. It is a viable reagent that
is used to dissolve and expel the volatile carbon as carbon dioxide. The reagent itself however is
highly combustible as it is prone to explosion when exposed to a bare hot surface. This exposes
the workers to constant threat of explosion which can most definitely cause harm. This would
mean that the company would have unable to conform to its policy of occupational health and
safety ISO 45001 leading to a loss of positive reputation and money lost due to compensation of
the affected worker and fines paid to relevant third-party bodies. The price for cheap perchloric
acid that is 70% strong is $54-$66 per 500ml and the minimum order quantity is 10 bottles which
means each batch is just under $660. Within a day of work which consist of the morning, afternoon
and evening shift over 250ml is used. This means that each day Ayrshire Mine’s Assay laboratory
uses $27-$33worth of perchloric acid and within the course of the year of which the laboratory
works every day without fail. There is a chance of saving $9 855-$12 045 every year
1.4.1 Justification
If the project is implemented and it is observed that carbon ashing can be a viable replacement for
the use of perchloric acid in the dissolution and expulsion of carbon to leave behind gold. Then
the threat of freak explosions that cause harm to employees can be alleviated and in part this would
increase Ayrshires mines conformance toward ISO 45001 which stipulates that workers must not
be harmed at work whilst they are on the job. In part this would increase the worker motivation to
carry out task as a potential risk of suffering harm from explosion has been eliminated
1.4.2 Aim
To observe the viability dry carbon ashing as opposed to acid digestion using perchloric acid in
order to promote safety while producing substantial results
1.4.3 Objectives:
1. Compare assay results for dry ashing and acid digestion (using perchloric acid).
2. Evaluate safety profile of each method, with thorough analysis of perchloric risk
where applicable
3. Provide method recommendation based on overall suitability
4. Compare time and energy per batch
5. Assess cost of reagents and equipment needs.
11
Chapter 2
2.1 Introduction
A literature review is a structured summary, analysis and synthesis of existing research,
publications and knowledge on a specific topic. It connects, compares and critiques the existing
work to shade light on what is already known, the gaps or problems that are currently there and
how this study will build upon what already exists
The literature review of this study is concerned with issues concerning the scientific and
operational basis abandoning the use of perchloric acid (HCLO4) digestion, which is used to
dissolve carbon and expel it as carbon dioxide and replacing it with dry carbon ashing which
involve thermal oxidation in a furnace. This review will cover mechanisms, terminology.
Instrumentation, method design, matrix effects, safety, environmental and economic
considerations, validation strategy and quality control. This information will be useful in the
justification and defense of the substitution in the context of the Ayrshire Mine laboratory
2.2 Definitions and terminology
Carbon: carbon is a chemical element with the symbol C and the atomic number 6, it has an atomic
mass of approximately 12.01 g/mol, a valency of 4 (can form up to four covalent bonds) and it has
the electronic configuration of 1s22s22p2 when it is in its ground state
Activated carbon: this is a form of carbon that has been processed to have an extremely high
surface area and porosity. This makes it very effective in absorbing and trapping molecules like
gold in the case of Ayrshire Mine. This material is usually produced from carbon rich materials
such as wood, coconut shell, coal or peat. These materials can be heated in the absence of air to
drive of volatile compounds leaving behind mostly carbon. The heated material is then treated with
steam, hot air or chemicals at high temperatures. This develops a huge network of pores giving it’s
a very high surface area (500-2000 m2 per gram)
Carbon removal: This the conversion of carbon with in analytes into carbon dioxide as a way to
expel it and leave behind valuable metal effectively eliminating a preg-robbing aspect of the
analyte. In this case leaving behind adsorbed gold for analyses by the AAS machine at the Ayrshire
Mine Laboratory.
Preg robbing: when carbon absorbs and holds onto the gold from a leach solution instead of
allowing it to stay in the solution which decreases the amount of observable gold in the analyte
solution
Digestion: Chemical decomposition of analytes with acids at atmospheric pressure to covert them
into liquids that can be analyzed by the AAS machine
Perchloric acid (HCLO4): A very strong acid and oxidizer. When it has a high concentration and
temperature it can rapidly oxides organic matter but it carries a significant risk of exploding
Oxidation: This is the loss of electrons. This caused by an oxidizer which take electrons, examples
of these are Oxygen. Perchloric acid, Nitric acid and chlorine. Oxidation can be detected by
observable changes like evolution of gas like CO2 and O2, color changes, forming of precipitates
and change in smell.
12
Dry ashing: this is the use of a furnace at temperatures ranging between 450-650 Cin the presence
of oxidation as a way to burn away the carbonaceous material as carbon dioxide leaving behind
the valuable metal in ash
LOI (Loss on ignition): this is the mass lost due to the heating process. it accounts for moisture,
organics and carbon dioxide that was expelled from the sample.
Ash content: the residue left after the analyte has been incinerated
Low temperature ashing LTA: Oxidation of organics in an oxygen plasma (100-300) C
TOC/TC/TIC: Total organic carbon. Total carbon, total inorganic carbon
Shrinking core model: Kinetic model where oxidation progresses from the particle’s exterior going
into its interior.
Ashing aids: these are reagents that an be added to the analyte before the ashing process in order
to help retain other target minerals which may be volatile to act as non-volatile species to avoid
their loss.
Matrix effects: interference from the sample that bias the analyte recovery or readings
CRM: Certified reference material. these are premade analytes with definite assay values that can
be used to cross check of the AAS machine is calibrated correctly. This can be used to detect
whether the readings of the other analyte are accurate
Trueness: the degree to which a claim is true or is free of bias
Precision: this is the ability to get the same result consistently when carrying out the same test
numerous times.
Linearity: this refers to how well an analytical methods response signal is directly proportional to
the concentration of the analyte over a specified range.
Ruggedness / Robustness: the ability of an assay method to stay unaffected by small variation in
experimental conditions for example when using different operators or laboratories
Selectivity: This is the ability of the AAS machine to measure only the target mineral even in the
presence of other substances (Interferants). For example, the AAS machine should be able to detect
gold without interference from copper, iron, or carbon in the sample
Measurement Uncertainty: this is the quantitative estimates of the doubt associated with a
measurement. No analytical method gives an exact value there is always a range within which the
true value lies, for example a gold assay may report 4.91 +/- 0.05 g/t meaning that the actual value
is between 4.86-4.96 g/t.
2.3 Dry carbon ashing method
Dry carbon ashing is a laboratory technique widely used in metallurgical and analytical processes
for the preparation of samples. The method is designed to remove organic or carbonaceous matter
from ores, concentrates, residues, soils, or other laboratory materials. It achieves this through the
controlled heating of the sample in the presence of air or oxygen, until all organic components are
oxidized and expelled as gases. What remains is an inorganic "ash" that contains the metallic or
13
mineral constituents of interest. This technique is particularly important in situations where organic
material interferes with subsequent chemical analysis, such as in gold ores that contain
carbonaceous matter, or in metallurgical residues contaminated with oils and greases.
The principle of the method is based on the oxidation of organic matter. Organic compounds, which
are largely composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur, are susceptible
to decomposition when subjected to elevated temperatures in the presence of oxygen. As the
sample is heated, the carbon is oxidized to carbon dioxide, hydrogen is converted into water
vapour, nitrogen forms oxides of nitrogen, and sulfur is converted to sulfur dioxide. These gaseous
products are released into the atmosphere of the furnace, leaving behind only the non-volatile
inorganic residue. The inorganic portion typically consists of oxides, sulfates, and silicates, which
remain stable at the chosen ashing temperatures of 450 to 650 °C.
The general procedure for dry carbon ashing begins with weighing a known mass of the sample
into a clean crucible, usually made of porcelain, quartz, or platinum depending on the temperature
and element sensitivity. The sample is first dried at a lower temperature, typically between 105
and 120 °C, to remove any moisture that may cause spattering during high-temperature heating. It
is then gradually heated in a muffle furnace to avoid sudden ignition of volatile matter. Once the
temperature reaches the ashing range, the furnace is maintained for several hours to ensure
complete oxidation of organic matter. After ashing, the crucible is cooled in a desiccator to prevent
moisture absorption and is then either reweighed to determine ash content or prepared for
subsequent instrumental analysis, such as X-ray fluorescence (XRF), inductively coupled plasma
(ICP), or atomic absorption spectroscopy (AAS).
Dry carbon ashing has numerous applications in the metallurgical field. In gold processing
laboratories, it is often used to treat carbonaceous ores that exhibit “preg-robbing” behavior, where
natural carbon in the ore adsorbs dissolved gold during leaching and interferes with extraction. By
removing the carbon through ashing, more accurate assay results can be obtained. The method is
also applied in the analysis of coal and coke, where it helps determine fixed carbon and volatile
matter. Additionally, environmental and geochemical laboratories use ashing to prepare plant, soil,
or effluent samples for the determination of heavy metals. In many cases, dry ashing provides an
effective alternative to wet acid digestion, particularly where the use of strong acids such as
perchloric acid poses safety risks.
Like any laboratory technique, dry carbon ashing has advantages and limitations. One major
advantage is that it does not require hazardous acids, making it safer and more environmentally
friendly compared to acid digestion methods. The equipment needed is relatively simple,
consisting mainly of a furnace and crucibles, and it can process many samples at once. Moreover,
it produces a clean and stable inorganic residue suitable for chemical and instrumental analysis.
However, the method has drawbacks, such as the potential volatilization of certain elements during
heating. Elements like lead, mercury, arsenic, selenium, and cadmium can be lost as volatile
compounds, resulting in underestimation of their concentrations. The process is also timeconsuming, often requiring several hours to complete, and care must be taken to avoid
contamination from crucibles or furnace walls.
In conclusion, dry carbon ashing is a thermal oxidation process used to remove organic material
from samples in metallurgical and analytical laboratories. By producing a clean, inorganic residue,
the technique facilitates accurate determination of metals and minerals, and is a safer alternative
to wet acid digestion methods. Despite its limitations, such as possible volatilization losses and
14
lengthy processing times, dry ashing remains an essential sample preparation tool in metallurgy,
mineral processing, environmental studies, and fuel analysis. Its continued use highlights the
importance of reliable and safe methods for preparing samples prior to chemical examination
2.4 Perchloric Acid Digestion of Carbon
Perchloric acid digestion is an important sample preparation technique in metallurgical, mineral,
and analytical laboratories. It is primarily used for the removal of carbonaceous material and other
organic matter from ore samples, residues, or metallurgical products. This is particularly relevant
when dealing with carbon-rich samples such as preg-robbing gold ores, activated carbon residues,
coal by-products, or organic-contaminated concentrates. By digesting the organic material with
perchloric acid, a clean inorganic solution or residue is obtained that can then be analyzed for
metallic or mineral constituents.
The principle of perchloric acid digestion relies on the powerful oxidizing properties of perchloric
acid (HClO₄). When heated under controlled laboratory conditions, perchloric acid acts as a strong
oxidizer, capable of breaking down the stable bonds in organic compounds. The carbon present in
the sample is oxidized to carbon dioxide gas (CO₂), while hydrogen is oxidized to water (H₂O).
The process leaves behind the inorganic matrix, often in the form of soluble salts, which can then
be dissolved and analyzed by techniques such as atomic absorption spectroscopy (AAS),
inductively coupled plasma (ICP), or colorimetric methods. The strength of perchloric acid makes
it especially suitable for samples that contain stubborn or refractory organic matter that is difficult
to remove using other acids.
The digestion process is typically carried out by weighing a small but representative amount of the
sample into a beaker or digestion flask. Concentrated perchloric acid is added, often in
combination with other acids such as nitric acid or sulfuric acid to initiate oxidation. The mixture
is then heated, usually on a hotplate or in a digestion block, under a fume hood specifically
designed for perchloric acid work. As heating progresses, the acid oxidizes the organic content,
producing fumes and effervescence as carbon is converted into gaseous carbon dioxide. The
digestion continues until the organic material has been completely destroyed, leaving behind a
clear or nearly clear solution of inorganic material. This solution is cooled, diluted, and prepared
for further analytical procedures.
Perchloric acid digestion of carbon is highly valued in analytical gold metallurgy. Certain gold
ores contain naturally occurring carbon that adsorbs dissolved gold ions from cyanide solutions, a
phenomenon known as “preg-robbing.” In order to accurately assess the gold content of such ores,
the carbon must first be destroyed. Perchloric acid digestion provides a reliable means to eliminate
the carbonaceous matter, ensuring that the gold can be properly measured in subsequent assays or
leaching tests. Similarly, the method is applied in environmental laboratories to destroy organic
matter in soils, sediments, and plant samples before measuring trace metals. In coal and coke
analysis, perchloric acid digestion is used to prepare ash-free solutions for the determination of
mineral impurities.
Despite its effectiveness, perchloric acid digestion has significant safety risks and limitations.
Concentrated perchloric acid is extremely corrosive and one of the strongest oxidizing acids
available in the laboratory. When heated, it can react violently with organic material, creating the
risk of explosions if not properly controlled. It also has the potential to form explosive perchlorate
salts when it comes into contact with metals or organic residues in the fume hood. For this reason,
15
perchloric acid work must be conducted in specially designed fume hoods equipped with washdown systems to prevent the buildup of hazardous deposits. Additionally, the use of perchloric acid
may volatilize certain sensitive elements such as mercury, selenium, or arsenic, leading to
analytical losses. The technique is also labor-intensive and requires strict adherence to safety
procedures, making it less attractive than alternative methods such as dry ashing for routine work.
The advantages of perchloric acid digestion are, however, substantial. It provides rapid and
complete oxidation of carbonaceous matter, even in refractory or highly resistant samples. It allows
accurate analysis of metals without interference from organic compounds and is particularly
effective in breaking down complex matrices where other acid mixtures may fail. This makes it a
highly reliable method in specialized metallurgical and geochemical laboratories.
In conclusion, perchloric acid digestion of carbon is a powerful wet oxidation technique used to
destroy carbonaceous and organic material in samples. It is based on the strong oxidizing power
of perchloric acid, which converts carbon to carbon dioxide and leaves behind inorganic residues
suitable for chemical analysis. The method is widely applied in gold assay laboratories,
environmental analysis, and fuel characterization, where organic interference must be eliminated.
Although it carries significant safety hazards and requires specialized equipment, its effectiveness
in completely oxidizing stubborn carbonaceous matter ensures that it remains an important method
in advanced metallurgical and analytical laboratories.
2.5 Why replace perchloric acid?
Safety and compliance

Acute risk: Hot HClO₄ reacts violently with organics; residues (perchlorates) can form
shock-sensitive crystals in fume hoods. This can lead to explosions which will affect the
safety of nearby workers and cause the damage of facilities at the Ayrshire mine laboratory.
On top of causing life threatening injury to personnel, the explosions also result in the loss
of money due to paying hospital fees, paid leave for affected worker, fines for nonconformance to third party accreditation boards, equipment replacement and lost time
expenses.

Infrastructure: Requires dedicated perchloric acid fume hood with wash-down; strict
housekeeping and segregation protocols. These are specilised equipment that have a
network of tubes and a suction fan. The network forms a tube that goes upward out and
away from the laboratory, while there is a motor and fan that provides suction to take away
the toxic fumes produced during the digestion of carbon using perchloric acid. The fume
hood has its own expense of electricity and regular maintenance of belts, the motor and fan
blades

Incident history: Well-documented lab fires/explosions from improper use or dried
residues. For example, at the University of Minnesota a person following a literature prep,
was heating in an Erlenmeyer flask a dilute water solution of a roughly 0.700 g of organic
compound with about 1 mL of 70% perchloric acid. Over time all the acidic solution
evaporated, leaving behind perchlorate salts which are shock and heat sensitive explosives.
Because it was left unattended, there was an explosion in the hood soon afterwards. The
ceramic of the hot plate had shattered and was irreparably damaged. No irreparable damage
to the Schlenk line was caused possibly because of the shape of the filtration flask which
caused the explosion to be lateral or horizontal.
16
There was one person near that hood but not in direct path, and they suffered from ringing
in the ear and immediately left. DEHS was immediately informed, and they performed the
perchlorate test in the hood the next day, which came out negative because all perchlorate
salt had exploded.
1. Waste: Perchlorate in waste streams is persistent and regulated in many jurisdictions.
Perchloric acid is a very strong oxidizer. In carbon digestions, it oxidizes organic carbon
to CO₂ and H₂O. If excess perchloric acid remains after digestion, it doesn’t necessarily
decompose — it can persist as ClO₄⁻ (perchlorate ion) in the solution. Perchlorates are
persistent environmental contaminants. They can interfere with thyroid function in humans
and animals by inhibiting iodine uptake. That’s why labs using perchloric acid often require
specialized fume hoods with wash-down systems and controlled waste disposal routes.
Operational and analytical drivers

Throughput bottlenecks from stringent HClO₄ handling protocols. Throughput bottlenecks
often arise in laboratories and metallurgical facilities due to the stringent safety protocols
required when handling perchloric acid (HClO₄). Because of its highly reactive and
explosive nature, particularly in the presence of organic matter or at elevated temperatures,
laboratories must use specially designed perchloric acid fume hoods with wash-down
systems, non-combustible ducting, and strict segregation from other chemicals. These
requirements significantly slow down the pace of operations, as staff must spend
considerable time preparing work areas, conducting pre-use safety checks, and carrying
out extensive clean-up procedures after each digestion. In addition, scheduling constraints
can occur since only trained personnel are permitted to handle the acid, and the limited
availability of compliant facilities further reduces flexibility. Together, these measures—
while essential for safety—introduce unavoidable delays and reduce the overall throughput
of digestion processes, making perchloric acid–based methods less efficient compared to
alternative approaches.

Compatibility: Perchlorate residues may interfere with some analytical steps and spike
ionic strength. Perchlorate residues left over from perchloric acid digestion can introduce
significant complications in subsequent analytical procedures. Because perchlorate is a
stable, strongly dissociated anion, it persists in solution and contributes to elevated ionic
strength. This increase can disrupt equilibrium-based techniques such as ion exchange
chromatography, solvent extraction, or certain spectroscopic methods by altering activity
coefficients and reducing separation efficiency. In some cases, perchlorate ions may also
directly interfere with the detection of target analytes by competing for reactive sites,
forming complexes, or producing background signals that obscure accurate measurements.
These effects not only compromise precision and sensitivity but may also necessitate
additional sample cleanup or matrix adjustment steps, further extending analysis time and
resource use.

Cost of compliance: Specialized hood, inspections, training, waste management. Strategic
benefits of dry ashing. The cost of compliance when using perchloric acid is considerable,
as it extends far beyond the purchase of the reagent itself. Laboratories are required to
install and maintain specialized perchloric acid fume hoods equipped with wash-down
systems to prevent explosive residue buildup, along with corrosion-resistant ducting and
17
exhaust infrastructure. Regular inspections and certifications are mandated to ensure
continued safe operation, adding recurring costs. Furthermore, staff must undergo
specialized training in safe handling, spill response, and emergency procedures, which
consumes both time and financial resources. Waste streams containing perchlorates also
demand specialized treatment or external disposal, significantly raising operational
expenses due to the strict environmental regulations governing these contaminants. In
contrast, dry ashing provides strategic benefits by bypassing many of these compliance
burdens. Since dry ashing relies on controlled furnace combustion rather than highly
reactive acids, it eliminates the need for specialized hoods, reduces training intensity, and
generates more benign waste streams. This not only lowers direct compliance costs but also
improves throughput and flexibility, making it an attractive alternative for laboratories
seeking safer, more sustainable, and cost-effective carbon removal methods.

Risk reduction: Eliminates most oxidizer-related acute hazards. the cost of compliance
when using perchloric acid is considerable, as it extends far beyond the purchase of the
reagent itself. Laboratories are required to install and maintain specialized perchloric acid
fume hoods equipped with wash-down systems to prevent explosive residue buildup, along
with corrosion-resistant ducting and exhaust infrastructure. Regular inspections and
certifications are mandated to ensure continued safe operation, adding recurring costs.
Furthermore, staff must undergo specialized training in safe handling, spill response, and
emergency procedures, which consumes both time and financial resources. Waste streams
containing perchlorates also demand specialized treatment or external disposal,
significantly raising operational expenses due to the strict environmental regulations
governing these contaminants. In contrast, dry ashing provides strategic benefits by
bypassing many of these compliance burdens. Since dry ashing relies on controlled furnace
combustion rather than highly reactive acids, it eliminates the need for specialized hoods,
reduces training intensity, and generates more benign waste streams. This not only lowers
direct compliance costs but also improves throughput and flexibility, making it an attractive
alternative for laboratories seeking safer, more sustainable, and cost-effective carbon
removal methods.

Cleaner downstream chemistry: After oxidation, ash can be digested with safer acid
combinations (e.g., HNO₃/HCl, HNO₃/HF where needed). Cleaner downstream chemistry
is one of the key advantages of using dry ashing instead of perchloric acid digestion. Once
the organic carbon is completely oxidized in the furnace, the remaining mineral-rich ash is
free of persistent perchlorate residues and can be safely dissolved using milder and more
conventional acid systems. Common choices include nitric acid combined with
hydrochloric acid (aqua regia) or nitric acid with hydrofluoric acid for silicate-rich
matrices. These combinations are widely accepted in analytical protocols, are less
hazardous than perchloric acid, and do not require specialized hoods or extreme handling
precautions. As a result, the digestion step becomes cleaner, more predictable, and less
prone to introducing chemical interferences that complicate instrumental analysis. By
working with simpler acid mixtures, laboratories also gain greater flexibility to tailor the
digestion chemistry to the sample type, improve recovery of target analytes, and reduce
matrix effects during techniques such as ICP-OES, ICP-MS, or AAS. This not only
enhances analytical quality but also aligns with safer, more sustainable laboratory
practices.
18

Scalable: Batch processing dozens of crucibles per furnace cycle. Scalability is another
advantage of dry ashing, as the technique lends itself well to batch processing. Modern
muffle furnaces can accommodate dozens of crucibles in a single cycle, allowing many
samples to be treated simultaneously under identical conditions. This parallel processing
greatly increases throughput compared to perchloric acid digestion, where each sample
often requires careful, stepwise handling in specialized hoods, creating a sequential
bottleneck. With dry ashing, once the furnace is loaded and the program is set, the process
runs largely unattended, freeing up personnel to focus on other tasks. The ability to process
large sample batches not only improves efficiency but also enhances consistency, since all
samples experience the same controlled temperature and oxidation environment. For
commercial or high-volume metallurgical laboratories, this scalability translates into
significant time savings, lower labor costs, and improved reproducibility across large
analytical runs.
2.6 Ideal carbon condition for dry ashing
In analytical and metallurgical laboratories, dry ashing is widely employed as a method for the
removal of carbonaceous matter prior to chemical analysis. The procedure relies on heating the
carbon sample in a controlled furnace until the organic matter is oxidized to gaseous products,
leaving behind a mineral ash residue. For this technique to be effective, the carbon material being
treated must possess certain ideal properties that make it suitable for clean, efficient, and
reproducible ashing.
Firstly, the carbon should exhibit a high degree of purity. Impurities such as residual hydrocarbons,
oils, or metallic contaminants can interfere with the oxidation process, leading to incomplete
combustion or altered ash composition. A pure carbon sample ensures that the only residue after
ashing is the mineral matrix originally bound to the carbon, which improves the accuracy of
subsequent chemical determinations.
Secondly, the carbon should have a fine and uniform particle size. Finer particles provide a greater
surface area for oxidation, allowing oxygen to penetrate and react more efficiently with the
material. Uniformity of particle size also ensures that combustion occurs evenly throughout the
sample, preventing localized zones of incomplete oxidation or overheating. This contributes to
both the reliability and the reproducibility of the ashing process.
Another desirable property is low moisture content. Excess water in the sample not only prolongs
the time required for ashing but can also cause spattering or losses of sample mass during the
heating stage. A dry carbon sample therefore promotes more controlled combustion and prevents
contamination or loss of the ash fraction.
Thermal stability is also an important consideration. While the ultimate aim of dry ashing is to
oxidize the carbon into carbon dioxide, the material should remain stable enough during the initial
heating phase to avoid sudden ignition or violent combustion. A controlled burn is critical for
laboratory safety as well as for maintaining the integrity of the mineral residues.
Additionally, the carbon should have minimal volatile impurities. Substances that volatilize at
furnace temperatures may escape with the flue gases, leading to the loss of valuable analytes or
contamination of the laboratory environment. Ideal carbon therefore burns completely to carbon
dioxide without introducing secondary vapors that might complicate the analysis.
19
Lastly, the ash content of the carbon should be low but consistent. Excessive ash introduces
unnecessary background material, which can obscure trace elements of interest. However, a
predictable and stable ash fraction ensures that the final residue is representative and can be
reliably used for further analysis.
In conclusion, the ideal carbon for dry ashing is characterized by high purity, fine and uniform
particle size, low moisture content, controlled thermal behavior, low volatile impurities, and
consistent ash levels. Together, these properties promote efficient combustion, minimize analytical
errors, and ensure that the mineral residue obtained is suitable for accurate downstream analysis.
2.7.1 Muffle furnace
A muffle furnace is a type of high-temperature laboratory furnace that provides controlled heating
in an enclosed chamber where samples are kept isolated from direct contact with flames, gases, or
heating elements. Its design ensures uniform distribution of heat, making it suitable for precise
thermal processes. In general, a muffle furnace is widely used in laboratories and industries for
applications such as ashing, heat treatment, material testing, and thermal analysis. It is often
employed to burn off organic matter, determine ash content, carry out calcination, or anneal
materials under specific conditions. Because it can reach temperatures ranging from 500 °C to over
1000 °C, it provides a reliable and contamination-free environment for accurate analytical work
and preparation of samples for further testing.
2.7.2 The use of a muffle furnace in carbon ashing
A muffle furnace is a key piece of equipment in carbon ashing because it provides the high and
controlled temperatures necessary to burn off organic carbon from samples without introducing
contamination. In the process, solid samples such as ores, carbon-in-pulp residues, catalysts, or
carbonaceous geological materials are placed in porcelain, silica, or platinum crucibles, which are
then inserted into the furnace chamber. The furnace is usually operated between 500 °C and 650
°C, a range high enough to completely oxidize carbon but low enough to avoid volatilization of
important inorganic elements. During ashing, air or oxygen present in the chamber supports the
oxidation of carbon, leaving behind only the inorganic or metallic residue. The process is often
preceded by careful drying of samples to remove moisture and may be followed by acid digestion
for chemical analysis. The muffle furnace’s closed design prevents direct contact between the
crucibles and the heating coils, ensuring that results are not affected by combustion gases or
impurities. This method is particularly valuable in laboratories where accurate measurement of ash
content, sulfur content, or metal values is required, and it allows multiple samples to be processed
simultaneously with consistency.
20
Figure 4: Muffle furnace
2.7.3 The uses of the muffle furnace components:

Ceramic fiber – Provides thermal insulation, keeps heat inside the chamber, reduces energy
loss, and keeps the furnace exterior cooler.

Air holes – Allow controlled entry of air/oxygen into the chamber to support combustion
and proper oxidation of carbon.

Ventilation – Removes smoke, fumes, and volatile gases released during heating for safety
and cleanliness.

Molded heater – Generates and distributes heat evenly throughout the chamber to maintain
stable temperatures.

Control panel – Used to set, adjust, and monitor temperature, time, and heating rate for
accuracy.

Sample – The material placed in crucibles that undergoes ashing or heating to remove
carbon or volatile matter.

Sensor (thermocouple) – Detects and monitors the chamber temperature, sending signals
to regulate furnace conditions precisely.
2.8.1 Hot plate
A hotplate is a flat, electrically powered heating device commonly used in chemistry laboratories
to provide a clean and controlled source of heat for experiments. Unlike open flames such as
Bunsen burners, a hotplate offers uniform heating across its surface, reducing the risk of
contamination or ignition of flammable substances. Its intended use in the laboratory includes
21
heating solutions, evaporating solvents, preparing reagents, and maintaining reactions at desired
temperatures. Many hotplates are equipped with magnetic stirrers, which allow simultaneous
stirring and heating, ensuring that solutions remain homogeneous during chemical processes.
Because they provide precise temperature control and a safer alternative to open flames, hotplates
are especially useful when working with volatile, combustible, or hazardous chemicals. Their
versatility makes them an essential tool for general laboratory heating, sample preparation, and
analytical procedures.
2.8.2 The use of a hot plate in carbon digestion
In carbon digestion, a hot plate is an essential tool because it provides steady and controlled heating
that allows acids to effectively break down carbonaceous material in a safe and efficient manner.
During the process, samples containing carbon are treated with strong oxidizing acids such as
perchloric, nitric, or sulfuric acid, and the hot plate supplies the heat needed to accelerate the
digestion reaction. Unlike open flames, which pose a high risk of igniting volatile acid vapors, the
hot plate ensures uniform heating at a controllable temperature, thereby minimizing hazards and
preventing sudden violent reactions. The flat surface also allows multiple beakers or digestion
vessels to be heated simultaneously, making the process more efficient for batch sample
preparation. In addition, when fitted with a magnetic stirrer, the hot plate maintains even mixing
of the acid and sample, ensuring complete contact between the reactants and better removal of
carbon. By providing controlled conditions, the hot plate helps achieve complete digestion of
carbon, leaving a clean solution suitable for further chemical analysis, such as determining metal
concentrations in ores or other carbon-bearing materials. This reliability and safety make the hot
plate a vital component in laboratory carbon digestion procedures.
Figure 5:A hot plate
22
2.8.3 The uses of the hot plate components:

LED heat display – Shows the current temperature setting or the actual surface temperature,
allowing the user to monitor and control heating accurately.

Stirrer on light – Indicates when the magnetic stirrer function is active, ensuring the user
knows when solutions are being mixed while heating.

Power on green light – Confirms that the hot plate is switched on and receiving power,
preventing accidental misuse.

Hot warning light – Alerts the user that the hot plate surface is still hot even after switching
off, reducing the risk of burns or accidents.

Contact thermometer indicator – Displays the temperature feedback from an attached
external thermometer or probe, ensuring precise monitoring of the sample’s actual heating
conditions.
2.9 Atomic absorption spectrometer
An atomic absorption spectrometer (AAS) is a sophisticated analytical instrument used to
determine the concentration of specific metal elements in a sample by measuring the absorption of
light. The technique is based on the principle that free atoms in the gaseous state can absorb
radiation of a particular wavelength, which corresponds to the energy required to excite electrons
from one energy level to another. Each element absorbs light at a characteristic wavelength, and
by directing light of that wavelength through a vaporized sample, the amount of light absorbed is
directly proportional to the concentration of the element present. This makes atomic absorption
spectrometry highly valuable in fields such as metallurgy, environmental monitoring, food
analysis, medicine, and geology, where accurate trace metal analysis is essential.
The make-up of an atomic absorption spectrometer includes several key components, each with a
specific role in ensuring accurate and reliable measurements. The light source is typically a hollow
cathode lamp or an electrodeless discharge lamp specific to the element being analyzed. This lamp
emits light at the exact wavelength characteristic of the element of interest. The atomizer, often a
flame or a graphite furnace, converts the sample into free atoms by heating it to high temperatures.
In flame atomization, a solution of the sample is aspirated into a flame, while in graphite furnace
atomization, a small sample volume is placed in a graphite tube that is electrically heated to
vaporize the sample. The monochromator then isolates the precise wavelength of light absorbed
by the element of interest, ensuring that only relevant radiation reaches the detector. The detector,
usually a photomultiplier tube, measures the intensity of the transmitted light and converts it into
an electrical signal, which is proportional to the concentration of the analyte. Finally, the data
processing and readout system interprets the electrical signal, displays the results, and allows
calibration using standard solutions.
In practice, the use of an atomic absorption spectrometer involves preparing the sample, often by
digestion with acids to bring metals into solution, and then introducing it into the atomizer.
Calibration curves are generated by analyzing standard solutions of known concentration, and the
absorbance values of the samples are compared against these curves to determine the metal
concentration. AAS is particularly well-suited for trace analysis, capable of detecting elements
such as copper, iron, lead, zinc, and nickel at parts-per-million or even parts-per-billion levels. Its
23
accuracy, sensitivity, and specificity make it an indispensable tool in laboratories where precise
elemental analysis is required.
Overall, the atomic absorption spectrometer is both a powerful and versatile instrument, combining
a well-designed make-up of optical, thermal, and electronic systems to deliver accurate results. Its
use in carbon digestion, environmental testing, metallurgy, and quality control demonstrates its
broad relevance. By providing a reliable means of quantifying metals in complex matrices, the
AAS plays a critical role in advancing scientific research, supporting industry, and protecting
human health and the environment.
Figure 6Ayrshire Mine's Atomic Absorption Spectrometer
24
Figure 7: Schematic diagram of the AAS machine
2.9.2 The uses of the components of an Atomic Absorption Spectrometer (AAS):

Hollow cathode lamp – Serves as the light source, emitting radiation at the specific
wavelength characteristic of the element being analyzed.

Flame – Acts as the atomizer, converting the sample solution into free atoms in the gaseous
state so they can absorb light.

Slit – Controls and narrows the beam of light to improve resolution and ensure that only
the desired wavelength passes through.

Slit burner – Provides a long, thin flame that increases the optical path length, improving
sensitivity and efficiency of atomization.

Mixing chamber – Combines fuel (acetylene), oxidizing gas (usually air or nitrous oxide),
and the aspirated sample to form a homogeneous mixture before combustion.

Acetylene – Used as the fuel gas to generate the flame hot enough to atomize the sample.

Oxidizing gas – Provides oxygen or nitrous oxide to support combustion of acetylene and
control the flame’s temperature and characteristics.

Aspirator – Draws the liquid sample into the system by suction, allowing it to mix with
fuel and oxidizing gas.

Nebulizer – Converts the liquid sample into a fine aerosol spray for efficient transport into
the flame.
25

Monochromator – Selects and isolates the specific wavelength of light absorbed by the
analyte, filtering out unwanted radiation.

Photodetector – Measures the intensity of transmitted light after passing through the sample
and converts it into an electrical signal.

Indicator device – Displays the processed signal, usually as absorbance or concentration,
providing the final analytical result.
2.9.2 The use of an Atomic Absorption Spectrometer in the analysis of carbon solutions for
gold
An Atomic Absorption Spectrometer (AAS) is used in the analysis of carbon solution samples for
gold to accurately determine the concentration of dissolved gold in the solution. In gold extraction
processes, carbon is often used to adsorb gold from cyanide leach solutions, and after elution, the
gold is present in a liquid form. The AAS allows precise measurement of this gold content by
atomizing a small portion of the solution—usually in a flame or graphite furnace—and measuring
the absorption of light at the wavelength specific to gold atoms. The amount of light absorbed is
directly proportional to the gold concentration, enabling accurate quantification even at very low
levels. This information is critical in metallurgical laboratories for monitoring gold recovery
efficiency, optimizing processing parameters, and ensuring accurate reporting of gold grades from
ores or concentrates. Using AAS ensures sensitivity, specificity, and reliability, making it an
essential tool in gold analysis from carbon-based recovery systems.
2.9.3 Conclusion
The literature highlights the current danger in which the Ayrshire Mine Laboratory is operating
under when it comes to the issue of analysis of carbon samples. The current method involves the
digestion of carbon using perchloric acid. Perchloric acid is dangerous as when it is not controlled
properly it explodes or violently decomposes when it comes into contact with heat, organic
material or other combustible substances. This may cause harm to the employees and may lead to
equipment failure. Carbon ashing however involves the use of a muffle furnace to burn away the
carbon as carbon dioxide leaving the mineral rich ash that can be dissolved using milder acids like
aqua regia thereby eliminating the danger that comes from using perchloric acid.
The following chapters will contain details on the procedural approach for testing and examining
whether or not dry carbon ashing will be an effective replacement for the acid digestion method
that uses perchloric acid
26
References
Enders, A., Hanley, K., & Lehmann, J. (2012). Comparison of wet-digestion and dry-ashing
methods for total elemental analysis of biochar. Communications in Soil Science and Plant
Analysis, 43(7), 1042-1052.
Shaibur, R. M., & Rahman, M. M. (2019). Comparison of digestion methods for the determination
of trace elements and heavy metals in human hair and nails. Journal of Analytical Science and
Technology, 10(1), 40.
Kalagbor, I. A., & Opusunju, M. A. (2015). A comparison study of dry and wet ashing methods
used for the determination of heavy metals in vegetables. Journal of Environmental Chemistry and
Ecotoxicology, 7(1), 1-6.
Takiyama, K., & Ishii, Y. (1992). Comparison of digestion methods for atomic absorption
spectrometric determination of metallic components in foods. Analytical Sciences, 8(3), 419-423.
Ahtiainen, R., & Lundström, M. (2019). Preg-robbing of gold in chloride solutions—Effect of
antimony. Minerals Engineering, 138, 199-204.
Lenahan, W.C., &Murray-Smith, R. de L. (1986). Assay and Analytical Practice in the South
African Mining Industry. The South African Institute of Mining and Metallurgy.
Gorsuch, J. M. (1982). Evaluation of the Effectiveness of Different Acid Digestion on Sed Liu, Y.h., Wan, B., & Xue, D.-s. (2019). Sample Digestion and Combined Preconcentration Methods for
the Determination of Ultra-Low Gold Levels in Rocks. Molecules, 24(9), 1778.iments. Journal of
Sedimentary Petrology, 52(2), 563-570.
27
Chapter 3
This chapter gives a detailed description of the safety wear, material and step by step instructions
that that the researcher used in the procedures determine whether or not carbon dry ashing is a
suitable alternative for acid digestion of carbon using perchloric acid.
3.1 Research Design
The study was carried out in an orderly sequence made up of separate phases, that allowed for the
removal of carbon from carbon samples using both the dry ashing method and perchloric acid
digestion method, subsequently allowing for the accurate analysis of the carbon samples using an
AAS machine in order to acquire figures that were essential to the decision-making process.
3.2.1 Carbon samples
The researcher obtained the batch of carbon samples that were used in the study from the Ayrshire
Mine plant
Sample preparation
1. The researcher dried the carbon samples for at least an hour at 100 degrees celsius
in the drying oven
2. The researcher then removed foulants from the carbon sample including plant
matter and small rock particles
3. The researcher then homogenized the carbon samples to get a better representation
of the bulk from the samples
4. Then the researcher organized the carbon samples in a predetermined order of
ascending names for better recording and tracking of samples for subsequent
processes
3.3 phase 1: Carbon ashing and carbon digestion using perchloric acid
3.3.1 Aim for carbon ashing
To remove the carbonaceous material from activated carbon or carbon-in-pulp (CIP/CIL) samples
by controlled heating in a muffle furnace, leaving behind a mineral-rich ash suitable for subsequent
gold analysis.
3.3.2 Safety / PPE Required

Laboratory coat (flame-resistant if available)

Heat-resistant gloves (for handling hot crucibles)

Safety goggles or face shield

Dust mask or respirator (for fine ash and carbon dust)

Closed shoes and long trousers
28
3.3.3 Materials and Equipment

Carbon sample (loaded carbon)

Porcelain, silica, or platinum crucibles (pre-weighed if mass balance is needed)

Muffle furnace (programmable preferred)

Desiccator (for cooling samples without moisture uptake)

Mortar and pestle (for grinding ash after combustion, if required)

Tongs and heatproof mat

Balance (analytical, for weighing before and after)
3.3.4 Procedure
i.
The researcher picked out 17 small porcelain crucibles and made sure they were clean
ii.
Loading
iii.

The researcher arranged the already dried and homogenized batch carbon samples
according to their names from A1-A6 in ascending order.

The researcher placed a small crucible in the analytical balance and tared it to 0.

The researcher weighed out 1 gram of a carbon standard into the first crucible

The researcher then weighed out 1 gram of carbon from A1 into another the crucible

The researcher then duplicated the carbon sample for A1 into another crucible

The researcher then repeated the weighing and duplicating process for the
remaining samples A2-A6

The researcher then inserted a blank sample and its duplicate after sample A3 and
sample A6

The researcher then placed the crucibles with the weighed carbon samples into the
muffle furnace in ascending order of A1-A6 along with the blank samples

The researcher spread the crucibles evenly within the muffle furnace evenly to
maximize exposure to air during ashing.
Initial Charring

The researcher then set the temperature to 200–250 °C and held it for 1–2 hours.

This step charred the carbon slowly, reducing the risk of sparking or loss by
rapid combustion.
29
Complete Ashing
iv.

The researcher then increased the furnace temperature to 550–600 °C.

The researcher then maintained this temperature for 4 hours (or until the sample
became a stable, light gray to off-white ash).

The researcher avoided exceeding 650 °C as it would have introduced problems
like crucible damage and the sintering fusing of ash, which would have caused
problems in the later digestion of the mineral rich ash.
Cooling
v.

The researcher then switched off the furnace and allowed the crucible to cool
slightly inside the furnace to prevent thermal shock.

The researcher transferred the crucibles carefully in their ascending order with
tongs to a desiccator and allowed them to cool to room temperature.
Post-Ash Handling
vi.

The researcher then dissolved the ash in 20ml of aqua regia in a beaker on top of a
hot plate

The researcher then removed the samples from the hot plate and left them to cool

The researcher then transferred the samples to 100ml volumetric flask and filled
the rest of their unused space with distilled water, shook the samples well and took
them to the atomic absorption spectrometer for analysis
Notes

The researcher handled the ash carefully to avoid losses as it was fragile and light.
3.4 Acid digestion of carbon
3.4.1 Aim
To oxidatively destroy the carbonaceous matrix (activated carbon / loaded carbon) and bring
refractory or adsorbed gold-bearing residues into a form suitable for subsequent gold
recovery/assay
3.4.2 Safety measures and equipment

Perchloric-acid-rated fume hood with wash-down system (not a general-purpose hood).

Perchloric acid vapors can form explosive perchlorate salts in ductwork; only use
a dedicated perchloric hood that is regularly inspected and washed down.

Eye/face protection: safety goggles and a face shield when handling concentrated acids
or during heating.

Acid-resistant lab coat (preferably flame-resistant) and chemical apron.
30

Gloves: use acid-resistant gloves (e.g., nitrile for splash protection plus chemicalresistant outer gloves when handling concentrated acid); change gloves if
contaminated.

Closed-toe, chemical-resistant footwear and long trousers.

Respiratory protection: generally, not a substitute for a proper hood — only use
respirator if required by risk assessment.

Perchlorate-specific spill kit and neutralizers available nearby; emergency eyewash and
safety shower within reach.

Explosion-resistant shielding (blast shield) between worker and reaction when heating
mixtures with perchloric acid.

No organic materials (e.g., paper towels, solvents, unclean glassware with organics) in
the hood during operations.

Dedicated glassware and tools to avoid formation of perchlorate residues in generaluse equipment.

Clear labeling and segregation of perchlorate wastes — do not mix perchlorate wastes
with incompatible wastes (e.g., organics, reducing agents, easily oxidizable metals).

Training & authorization: only trained personnel following an institutional SOP and
local regulations should perform perchloric digestions.
3.4.3 Reagents and equipment

Hotplate

250ml conical flask

Nitric acid

Hydrochloric acid

Perchloric acid

Volumetric flask

Distilled water

AAS machine
3.4.4 Procedure for perchloric acid digestion of carbon

In the weighing room, the researcher arranged the previously prepared carbon samples in
ascending order

The researcher started by weighing 0.5 grams of the carbon standard first and placed it in
a volumetric flask labelled carbon standard (CBN STD)
31

The researcher then renamed the samples from A1-A6 to B1-B6 following the
chronological order, the researcher weighed 0.5 gram of carbon in each 250mls conical
flask according to numbers i.e. B1-B6 and make a duplicate of B1. Therefore, the order of
flask should be Carbon standard, B1, B1, B2, B3, B4, B5 and B6

The researcher also added blank samples after B3 and B6

The researcher then transported the samples to the digestion room.

The researcher switched on the extracting fan and pre-heated the hot plate to temperatures
ranging between 105 degrees to 108 degrees. They then poured 20mls of nitric acid
(NHO3) in each conical flask and placed the samples on the hot plate.

The researcher heated the contents for approximately 5 minutes or until oxidation was
complete, that is when no more brown fumes were noticed from the samples and a clear
steam like vapour came out.

The researcher added 30mls of perchloric acid in each beaker and digested the samples
until all the black carbon have been cleared.

The samples were completely digested when they showed a clear solution like water and
no more fumes were produced.

The researcher added 20mls of aqua-regia in each sample and heated the samples for 3045 minutes until all the aqua-regia had cleared once again. (Aqua regia -3parts HCL +1part Nitric acid.)

The researcher removed the samples from the hot plate and left them to cool and they filled
up the samples in 100mls volumetric flasks using distilled water

The researcher shook the samples and collected them to the AAS room for reading.
3.5 Phase 2 Procedure for Developing, Using, and Displaying a Risk Register
3.5.1 Scope

Sample preparation of carbon for gold analysis by dry ashing (proposed method) vs.
perchloric acid digestion (existing method).

objective: the researcher wanted to identify hazards, assess risks, and evaluate
whether the replacement improves safety and practicality.
3.5.2 Identify Hazards

The researcher listed all potential hazards for both processes (chemical, thermal,
mechanical, environment.
32
3.5.3 Describe Consequences

For each hazard, the researcher noted what could go wrong for example an explosion from
perchloric and organics leading to major injury and lab damage

The researcher then categorized the consequences into severity levels for example Minor,
Moderate, Major, Severe and Catastrophic
3.5.4 Estimate Likelihood

The researcher then judged how often each hazard could realistically occur, for example
Rarely, Unlikely, Possibly, Likely and Almost Certainly

The researcher used historical data, expert judgment, and published safety guidelines.
3.5.5 Assign Inherent Risk Rating

The researcher used a 5×5 risk matrix:
o

The five-by-five matrix was set to the following parameter ‘Likelihood (1–5) ×
Consequence (1–5) = Risk Score (1–25).’
The researcher plotted the hazard on the matrix before controls (this was the inherent risk).
3.5.6 Define Controls / Mitigation Measures

The researcher defined either engineering, administrative or PPE controls for each hazard.
3.5.7 Assign Residual Risk Rating

The researcher reassessed each hazard using the 5×5 matrix after controls.
3.5.8 Populate the Risk Register
The researcher made the risk register using these typical columns:
| Hazard | Consequence | Likelihood | Inherent Risk (Score) | Controls | Residual Likelihood |
Residual Consequence | Residual Risk (Score) | Comments/Notes |
3.5.9 Display the Data

The researcher constructed Risk Register Table (as above).

5×5 Risk Matrix Heatmap:

The researcher plotted hazards in differing colour codes by score: Green = Low,
Yellow = Medium, Red = High, Purple = Extreme

The researcher showed both before and after controls for visual comparison.
33
Phase 3 Recommending the carbon ashing method based on overall suitability meaning
accuracy, precision repeatability, paired differences, limits of agreement, correlation and
linear regression.
3.6.1 Validation calculations
Calculation Accuracy for carbon standard, precision, Paired differences, Limits of agreement,
Correlation, Linear regression.
3.6.2 Accuracy
The researcher used the following formula to calculate Accuracy for carbon standard
𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑣𝑎𝑙𝑢𝑒
𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦 = (
) 𝑋 100
𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒
3.6.3 Precision
Then the researcher used this formula to calculate precision
∑𝒏=𝒅𝟐
𝒊
𝟐𝒏
𝒔𝒓 = √ 𝒊
𝒔𝒓 = repeatability standard deviation ppm
𝒅𝒊 = difference between duplicate measurements
𝒏= number of duplicate pairs
3.6.4 Paired Differences.
The researcher calculated the paired differences using the following formula
𝑡=
𝑑̅
𝑠𝑑 ⁄√𝑛
𝑑̅ =mean paired difference
𝑠𝑑 = sample standard deviation of differences
𝑑̅ =
∑(𝑥𝑖 − 𝑦𝑖 )
𝑛
𝑥𝑖 = result from Method 1 (Ashing)
 𝑦𝑖 = result from Method 2 (Perchloric)
 𝑛 = number of paired samples
34
3.6.4 Limits of agreement
The researcher calculated the lower and upper limits that the results of assayed samples are
supposed to fall in between
Lower limit = 𝑑̅ – 1.96𝑠𝑑
Upper limit =𝑑̅ + 1.96𝑠𝑑
3.6.5 Correlation and linear regression
The researcher used the following formulas to determine the correlation of the two methods
Pearson 𝑟 =
∑(𝑥𝑖 −𝑥̅ )(𝑦𝑖 −𝑦̅)
∑(𝑥𝑖 −𝑥̅ )2
Intercept 𝑎 = 𝑦̅ − 𝑏𝑥̅
Slope 𝑟 =
∑(𝑥𝑖 −𝑥̅ )(𝑦𝑖 −𝑦̅)
√(𝑥𝑖 −𝑥̅ )2 (𝑦𝑖 −𝑦̅)2
𝑥 =ash men for each sample
𝑦= perchloric mean for each sample
Phase 4 Comparing time and energy
3.7 Measuring Time
The researcher recorded the time taken per method using a watch and calculated the energy used
during the course of carrying out the method.
3.7.1 Measuring energy
To calculate furnace energy usage, the researcher used the following formula
Total energy (kWh)
= (E warm) + (E soak at 30% duty)
E warm
= (Furnace power rating) x (Time taken to warm the oven)
E soak
= (Furnace power rating) x (duty) x (Time taken to ash)
In order to calculate the energy usage for the hot plate the researcher used the following formula
Energy (kWh) = Power rating x Time taken
Phase 5 Procedure for Tracking and Calculating Costs for Perchloric Digestion vs Dry
Ashing
35
3.8 Define the Cost Categories
The researcher broke the costs down into measurable components:

Energy consumption (kWh)

Time taken per batch/sample

Materials and consumables

Maintenance and repairs
3.8.1 Tracking Energy Consumption


Hot plate digestion:

The researcher took note of the hot plate’s power rating (kW).

The researcher then recorded the average run time per digestion (hours), energy
used (kWh) = Power rating (kW) × Run time (h) and they multiply by electricity
tariff ($/kWh).
Muffle furnace ashing:

The researcher noted the furnace’s rated power (kW), cycle time per batch
(h).Energy used (kWh) = Power rating (kW) × Run time (h).

Multiply by electricity tariff ($/kWh).
3.8.2 Tracking Time Costs


The researcher measured total time per sample or batch, including:

Sample prep (weighing, loading crucibles/vessels).

Processing time (digestion/heating/ashing).

Cooling and handling.
The researcher converted operator time to cost:


Time (h) × Operator wage rate ($/h).
This highlights labor intensity differences (hot plate digestion usually more hands-on;
ashing is less labor-intensive once furnace is loaded).
3.8.3 Tracking Materials / Consumables

Perchloric acid digestion:

The researcher measured the average acid volumes used per sample (mL) and
convert it to cost using unit price per litre.

The researcher included nitric acid (if used), deionized water, glassware wear/tear,
fume hood filters (if applicable).
36

Dry ashing:

The researcher considered the cost of crucibles (lifetime/number of uses before
replacement), electricity only (no acid) and Minor consumables: desiccator drying
agent, tongs/gloves wear, etc.
3.8.4 Tracking Maintenance and Repairs



The researcher considered hot plate digestion cost:

Cost of hot plate servicing/replacement parts.

Cost of perchloric-acid hood maintenance (special duct wash-downs).

Cost of handling perchlorate waste (special disposal).
Muffle furnace ashing:

Furnace element replacement, calibration, insulation repairs.

Crucible breakage replacement.
The researcher recorded maintenance costs from lab logs or supplier quotes and allocate
per year and divided the annual maintenance cost by the estimated number of samples
processed annually to get a per-sample maintenance cost.
3.8.5 Calculation Procedure
For each method, the researcher calculated the Total Cost per Sample:
Total Cost per Sample=Energy Cost + Labour Cost + Material Cost+ Maintenance Cost
Where:

Energy Cost = (kW rating × h used × $/kWh) ÷ Samples per batch

Labour Cost = (Time required (h) × $/h wage) ÷ Samples per batch

Material Cost = Cost of acids, crucibles, disposables ÷ Samples per batch

Maintenance Cost = (Annual maintenance cost ÷ Annual samples)
37
Chapter 4
This chapter presents the results obtained from the procedural phases discussed in chapter 3. Each
phase had tables of results, graphs and interpretations of experimental conditions
Analysis of precious metal from carbon ash
sample name
ppm*100
carbon standard 1024
a1
938
a1 duplicate
954
a2
760
a2 duplicate
754
a3
924
a3 duplicate
916
blank
6
blank duplicate 8
a4
602
a4 duplicate
616
a5
874
a5 duplicate
882
a6
722
a6 duplicate
718
blank
6
blank duplicate 4
Table 1 Assay results for carbon ashing
ppm
10.24
9.38
9.54
7.6
7.54
9.24
9.16
0.06
0.08
6.02
6.16
8.74
8.82
7.22
7.18
0.06
0.04
Bar graph for gold in carbon ash
1200
1000
g/t
800
1024
938 954
924 916
874 882
760 754
602 616
722 718
600
400
200
6
8
6
4
0
sample indefication
Figure 8:Bar Graph for gold in Carbon Ash
The above figure 8 bar graph is showing the results for the remaining ash after carbon
ashing that was analyzed for gold content. The vertical bars represent the grade of gold that
38
was calculated from dividing the volume of the final analyte solution’s volume (100ml) by
the grams of carbon used (1g) and multiplying the quotient by value recorded by the AAS
machine
4.1.2 Analysis for gold after acid digestion of carbons using perchloric acid
sample name
carbon
standard
b1
b1 duplicate
b2
b2 duplicate
b3
b3 duplicate
blank
blank
duplicate
b4
b4 duplicate
b5
b5 duplicate
b6
b6 duplicate
multiply
by a
ppm
factor
of 200
1000
5
950
960
752
738
910
922
10
4.75
4.8
3.76
3.69
4.55
4.61
0.05
6
0.03
596
614
860
876
710
2.98
3.07
4.3
4.38
3.55
724
3.62
blank
2
0.01
blank
8
0.04
duplicate
Table 2 Results for perchloric acid digested carbon
39
Bar Graph for pechloric acid gold analysis
1200
1000
1000 950 960
g/t
800
910 922
860 876
752 738
596 614
710 724
600
400
200
10
6
2
8
0
sample identification
Figure 9:Bar graph for perchloric acid gold analysis
Figure 9
The above figure 9, shows the results acquired after the analysis of carbon that was digested
in perchloric acid was done. The vertical bars represent the grade of gold that was currently
within the carbon tanks. Calculated by dividing the volume of the final analyte solution’s
volume (100ml) by the grams of carbon used (1g) and multiplying the quotient by value
recorded by the AAS machine
4.1.3 side to side comparison on results of carbon ashing and perchloric acid digestion in
the analysis of gold
sample name
carbon standard
a1
a1 duplicate
a2
a2 duplicate
a3
a3 duplicate
blank
blank duplicate
a4
a4 duplicate
a5
a5 duplicate
a6
a6 duplicate
blank
blank duplicate
Assay results for gold in ash
1024
938
954
760
754
924
916
6
8
602
616
874
882
722
718
6
4
Assay results for gold in perchloric acid
1000
950
960
752
738
910
922
10
6
596
614
860
876
710
724
2
8
40
Table 3Side to side comparison for carbon ashing and perchloric acid digestion
Table 3: Table for comparison of results for carbon ashing and perchloric acid
digestion
g/t
side by side results for gold from ash and gold from
pechloric acid
1200
1000
800
600
400
200
0
sample identification
gold in ash
gold in pechloric
Figure 10: Results for both gold in ash and in perchloric acid
Figure 10
The above figure 10 was used to show case the comparison of results between a gold
analysis of a batch carbon that was ashed and one that was digested in perchloric acid. The
result of the comparison clearly shows that there is little distinction for the results of both
methods. The researcher can conclude that replacing perchloric acid digestion with carbon
ashing will not compromise on the accuracy and quality of results acquired.
41
The development of a risk register to assess the safety of both methods
4.2.1 5 x 5 matrix
Rare
Unlikely
Likely
High
possibility
Almost
guaranteed
Table 4 5 X 5 matrix
1
2
3
4
Slight
1
1
2
3
4
Minor
2
2
4
6
8
Significant
3
3
6
9
12
Major
4
4
8
12
16
Catastrophic
5
5
10
15
20
5
5
10
15
20
25
The figure above shows the 5 x 5 matrix; this is a risk rating tool that was used by the researcher
to calculate the magnitude or effect of a risk using figures as the indicator. The higher the figure
the greater the danger. The magnitude of the risk was calculated by multiplying the chance of the
risk occurring (rare (1) - almost guaranteed (5)) by its consequence (slight (1) – catastrophic (5))
4.2.2 Risk rating into different ranges
Table 5 Risk rating table
Rating
Low
medium
moderate
high
Very high
Range
1-5
6-10
11-15
16-20
21-25
The researcher after calculating the magnitude of risk used this risk rating table to separate the risk
into different ranges in order to further highlight their difference in intensity
42
4.2.3 Risk register for perchloric acid digestion and carbon ashing
Table 6 Risk register
Activity
Hazard
Digestion
of Explosion
carbon
using
perchloric acid
Chemical burns
(Perchloric
Acid)
Waste disposal
hazard
(Digestion)
Toxicity
of
Fumes
Consequence
Death,
injury,
destruction
Severe 25 (very high)
lab
Skin/eye damage
Environmental
harm,
regulatory
breach
Severe irritation of
the eyes, nose,
throat, and lungs;
chemical
pneumonitis;
and
chronic respiratory
problems.
Extreme
Severe burns, fire
Reactivity and damage, and release
Fire
of toxic fumes.
Carbon ashing High
Severe burns on
using
muffle Temperature
contact with skin.
furnace
and
Thermal
Burns
Breakage
of
ceramic
crucibles and
tongs.
Fire/Explosion
Dust
Generation
Inherent risk
15 (moderate)
12 (moderate)
20 (high)
20 (high)
12 (moderate)
Spillage of hot 16 (high)
sample
causing
burns, cuts from
ceramic shards
Lab fire, damage to 15(moderate)
the furnace, and
injury from flying
debris or flames.
Inhalation of toxic 20 (high)
dust
containing
concentrated heavy
metals, silicates, or
other analytes can
cause lung damage
Control
Residual
risk
Strict monitoring of the 10 (medium)
carbon
samples
being
digested by a dedicated
individual
with
express
purpose of ensuring that all
parameters are in working
order
PPE (gloves, goggles, lab 5 (low)
coat), spill kits, emergency
showers
Neutralization
protocols, 4 (low)
hazardous waste disposal
SOPs
Use of dedicated perchloric 5 (low)
acid fume hood, strict SOPs,
trained personnel
Use the smallest practical 4 (low)
volume and concentration of
acid.
Use insulated
thermal 3 (low)
gloves and face
protection when
loading/unloading
the
furnace.
Inspect crucibles for cracks 4 (low)
before use
Never ash samples that may 5 (low)
contain
explosives,
peroxides,
or
volatile
solvents.
Follow the SOP and gently 5 (low)
transport crucibles with lids
covering them
Table 6 above is showing the result of using the 5 x 5 matrix to quantify the different risk and using
the risk rating table to group the risk into different ranges according the product of their likely
hood of occurrence and their consequence. The inherent risk shows how not having controls to
43
mitigate the danger could actually lead a higher chance of occurrence of an incident. The residual
risk shows that after implementing control measures the chances of occurrence of the risk are
reduced even though the consequence itself does not change in value.
4.2.4 Risk rating visuals and explanation
risk rating
line graph for inherent risk and residual risk
30
25
20
15
10
5
0
25
20
15
10
5
20
20
12
16
15
4
5
12
5
4
4
3
5
Hazards
inherent risk
residual risk
Figure 11:Inherent and Residual risk
Figure 11: Line graph showing the inherent risk before implementing controls and residual
risk after implementing controls
The above figure 11 shows the difference in the occurrence of risk before and after adding controls.
The researcher was able to ascertain that the risk of perchloric acid explosion had the highest
chances of occurrence before and after adding controls
4.2.5 Residual risk assessment
Residual Risk Assessment
Label
hazards
r1
perchloric acid
explosion
r2
chemical burns
r3
Waste disposal
perchloric
r4
Toxic fumes
(perchloric)
r5
fire (perchloric)
r6
burns (ashing)
r7
ceramic Breakage
r8
explosion(ashing)
r9
Dust inhalation
Impact
5
Probability
2
5
4
1
1
5
1
4
3
4
5
5
1
1
1
1
1
44
Table 7Residual risk assessment
Table 7: table for the risk after implementing the controls
The above table 7 was used by the researcher to show the impact and occurrence of the risk that
come from the different hazard even after control measures are put into place. Even after applying
controls perchloric acid explosions still had the highest rating. this showcases how the use of
perchloric acid in digestion of carbon is more dangerous that just ashing the carbon
4.2.6 Risk impact
low
medium
high
1-2
3-4
5
Table 8 Impact rating table
The above table 8 was used by the researcher to group the impacts into different categories
of low medium and high
4.2.7 Visualizing impact and occurrence of residual risk
residual risk assesment
3
r1
probability
2
r6
1
r7 r3 r5
r2
r8
r9
r4
0
Low
Medium
High
impact
Figure 12: Risk Assessment Graph
The risk assessment chart above was used by the researcher to visually showcase the
difference in dangers among the use of perchloric acid and dry ashing. The results show
that the threat of explosion from perchloric acid had the highest impact and occurrence
upon the slightest oversight during use.
45
4.3 Validation for carbon ashing over perchloric acid digestion
Expected value for carbon standard: 1050 ppm
4.3.1. Accuracy / Trueness
Method
Measured (ppm)
Recovery (%)
Bias (ppm)
Ash / Perchloric
1024 / 1000
97.52 / 95.24
-26 / -50
Table 9 Accuracy table
4.3.2 Precision / Repeatability
Method
sᵣ (ppm)
RSDᵣ (%)
Ash
7.26
0.87
Perchloric
10.07
1.21
Table 10 Precision Table
4.3.3 Method Comparison (Paired Test and Correlation)
Mean difference (ash − perch) = +6.86 ppm
Standard deviation of differences = 10.11 ppm
Paired t = 1.795 (df = 6), p = 0.1228 (not significant)
Bland–Altman 95% limits of agreement: −12.95 ppm to +26.67 ppm
Correlation (r) = 0.9977
Regression: perch = 0.9838 × ash + 6.6576
4.3.4 Summary of Validation Metrics
Parameter
Ash
Perchloric
Accuracy (Recovery %)
97.52
95.24
Bias (ppm)
-26
-50
Repeatability sᵣ (ppm)
7.26
10.07
RSDᵣ (%)
0.87
1.21
Correlation (r)
0.9977
0.9977
Regression Slope
0.9838
0.9838
Table 11Validation metrics table
46
validation chart for carbon ashing through perchloric acid
digestion
150
Figures
100
50
0
-50
-100
Accuracy
(Recovery %)
Bias (ppm)
Repeatability
sᵣ (ppm)
RSDᵣ (%)
Correlation
(r)
Regression
Slope
Ash
97,52
-26
7,26
0,87
0,9977
0,9838
Perchloric
95,24
-50
10,07
1,21
0,9977
0,9838
Workings
Ash
Perchloric
Figure 13 Validation for carbon ashing
4.3.5 Conclusion
Carbon ashing shows similar or superior analytical performance to perchloric acid digestion.
Accuracy (97.5%), precision (0.87% RSD), and method agreement (r = 0.9977) all fall within
acceptable validation limits.
Therefore, the ashing method can be considered valid and suitable for routine gold assay
analysis.
4.4 Comparing time and energy usage for carbon ashing and perchloric acid digestion
4.4.1 For the muffle furnace which runs for 4h at a power rating of 4kW
Total energy = (E warm) + (E soak at 30% duty)
E warm
= (Furnace power rating) x (Time taken to warm the oven)
E soak
= (Furnace power rating) x (duty) x (Time taken to ash)
Total energy = (4.0 kW x 1.0h) + (4.0 kW x 0.30 x 3h)
= 7.6 kW
47
4.4.2 For the hot plate which runs for three hours
= Energy (kWh) = Power rating x Time taken
=8kW * 3h
=5.4kWh
Method
Power kWh
Time Hours
Muffle furnace
7.6
4
Hot plate
5.4
3
Table 12 Power and Time table
Power and time bar graph graph
7,6
8
7
5,4
Figure
6
5
4
4
3
3
2
1
0
Power kWh
Time Hours
time and power
Muffle furnace
Hot plate
Figure 14 Power and time graph
4.5 Calculating cost
4.5.1 Cost for carbon ashing
Total cost= Energy + Labour + Materials + Maintenance
Energy cost per sample.
Energy cost per batch (kWh)= Power (kW) * Time (H)
Power =
=
= 0.00520 kWh (energy used to ash carbon)
Total energy = (E warm) + (E soak at 30% duty)
48
E warm
= (Furnace power rating) x (Time taken to warm the oven)
E soak
= (Furnace power rating) x (duty) x (Time taken to ash)
Total energy = (4.0 kW x 1.0h) + (4.0 kW x 0.30 x 3h)
= 7.6 kWh
The current price of electricity is $0.12/kWh
=7.6 kWh x $0.12/kWh
=$0.90
Therefore, the price of ashing per sample is
=$0.90 / 17
=$0.05
Labour cost
Hour worked * hourly wage = labor per batch
= 4h * $3/h
= $12
Labour cost per sample:
=$12 / 17
= $0.71
Materials cost
Crucible cost per sample = price of crucible/ umber of uses
=$20 / 20
=$1
Maintenance cost
Maintenance cost per sample = annual maintenance cost / annual number of samples
=$600 / 18 615 annual carbon samples
= $0.03
49
Total cost per sample = energy + labor + material + maintenance
= $0.05 + $0.71 + $1 + $0.03
= $1.79
4.5.2 Cost per sample for acid digestion
Energy cost
=1.8kW * 3h
=5.4kWh
Cost per batch
= 5.4kWh * $0.12/kwh
=$0.65
Cost per sample
= $0.65 / 17
=0.03
Labour cost
3h * $6/h = $18
Labour cost per sample
=$18 / 17 samples
=$1.06
Material cost
=0.030L * $110/L
=$3.30
Maintenance cost
= $250 / 18 615
= $0.01
50
Total cost per sample
= $0.03 + $1.06 +$3.30 + $0.01
=$4.4
Comparing cost between acid digestion using perchloric acid and dry carbon ashing
bar graph comparing cost for ashing and digesting
5
4,4
cost $
4
3,3
3
1,79
2
1
0,71
1,06
1
0,13 0,03
0,03 0,01
0
energy
labour
material
mantenance
total
category
ashing
digesting
Figure 15: Comparing cost between Dry ashing and Perchloric Acid digestion
Figure 13 was used to display the cost associated with both the use of perchloric acid for
carbon digestion and for carbon ashing. The result observed was that the use perchloric
acid used a larger amount of money and therefore replacing the digestion method with the
ashing method would decrease expenditures.
51
Chapter 5
Conclusions and Recommendations
5.1 Conclusion
The study successfully identified carbon ashing as a suitable alternative to perchloric
acid digestion as a means of removing the carbon from carbon samples, in order to
leave behind the gold in ash eliminating the risk of analytical interference. The
interference being that the carbon if present can trap gold leading to low recovery
values during analysis. From the results presented in chapter four. The following
results were drawn.
1. There is little variation in the results obtained after analyzing carbon
samples that underwent perchloric acid digestion and the carbon
samples that underwent carbon ashing. This concludes that carbon
ashing can be used as an alternative measure for the removal of carbon
to eliminate the risk of analytical interference caused by the adsorptive
properties of the carbon itself.
2. The risks associated with using perchloric acid to digest and remove
carbon from carbon samples were much higher that when using the
carbon ashing method as a way of removing carbon to remain with the
precious metal in ash. This concludes that the ashing method is a safer
alternative to perchloric acid digestion
3. The energy and time required to complete the process of carbon ashing
up to analysis of the sample is more than that of using perchloric acid
to digest and evolve carbon until the stage of analysis. However, this is
balanced out by the reduced cost and minimized danger concerning the
analysis for gold in carbon samples
4. The cost of using perchloric acid to digest and evolve carbon to carbon
dioxide in order to leave behind a sample free of interference from the
carbon itself out ways the cost of ashing carbon using a muffle furnace.
Therefore, it can be concluded that due the lowering of cost of
analyzing carbon samples for gold is another good reason for replacing
the method of perchloric acid digestion with carbon ashing.
5. After the researcher had conducted the study. The results obtained
showed that carbon ashing is safer, cheaper and effective in being an
alternative to perchloric acid digestion as it produces nearly identical
52
results. This coupled with the added benefit that the hot plate will
become free for more digestion of other solid samples services the
purpose of validating the fact that it is more beneficial to conduct
carbon ashing at Ayrshire Mine rather than continuing to use the
perchloric acid digestion method.
5.1.1 Recommendation
From the prior conclusion that the researcher came to. The recommendation that can be made for
the Ayrshire Mine laboratory is that. The representative of the laboratory working hand in hand
with Tech services department Heads should apply to the top management for a shift into using
the carbon ashing method when it comes to the preparation of carbon for the analysis of gold. They
should immediately look into plans of procuring a muffle furnace, training employees on its use
and safe conduct and the proper handling to avoid contamination and ash loss.
It is highly advisable to shift heavily into the culture of ashing the carbon samples and rely on this
method for the bulk of carbon preparation. However, perchloric acid digestion of carbon should
not be completely stopped rather be kept as a measure to use when the service of carbon ashing
cannot be conducted for extenuating circumstances. The difference however will be the the threat
of harm from perchloric acid will be significantly reduced.
5.2 References
Marsden, J. O., & House, C. I. (2006). The Chemistry of Gold Extraction (2nd ed.). Society for
Mining, Metallurgy, and Exploration (SME).
McGuire, M. (2019). The Extractive Metallurgy of Gold. Springer.
Vogel, A. I., et al. (2019). Vogel's Quantitative Chemical Analysis (7th ed.). Pearson.
Hiskey, J. B. (1984). "Activated Carbon and Gold–A Survey of Recovery Processes." Mineral
Processing & Extractive Metallurgy Review, 1(1), 1-30.
Fleming, C. A., & Nicol, M. J. (1984). "The Adsorption of Gold Cyanide on Activated Carbon. III.
Factors Influencing the Rate of Loading and the Equilibrium Capacity." Journal of the South
African Institute of Mining and Metallurgy, 84(4), 85-93.
Zhao, J., Wu, Z., & Chen, J. (2006). "Recovery of gold from carbonaceous ores by roasting and
bio-oxidation." Minerals Engineering, 19(6-8), 651-657.
Lorenzen, L., & van Deventer, J. S. J. (1992). "The identification of refractoriness in gold-bearing
ores by the selective destruction of minerals." Minerals Engineering, 5(10-12), 1267-1277.
ASTM E2295 - 21: Standard Practice for Fire Assay Silver Corrections in Analysis of Metal
Bearing Ores, Concentrates, and Related Metallurgical Materials by Silver Determination in Slags
and Cupels.
53
Anglo American Research Laboratories (or similar major mining company) Internal Standards.
The AusIMM Monograph Series: "Gold Ore Processing" (Various Editions).
National Research Council (US) Committee on Prudent Practices in the Laboratory.
(2011). Prudent Practices in the Laboratory: Handling and Management of Chemical Hazards.
National Academies Press (US).
OSHA (Occupational Safety and Health Administration) Technical Manual, Section II: Chapter 1.
"Personal Sampling for Air Contaminants."
Bretherick's Handbook of Reactive Chemical Hazards. (Latest Edition). Elsevier.
54
Appendix
1) Data (duplicates shown and the pair means used)
(the researcher used the duplicate pairs for a1–a6 and not the carbon standard as it has a single
value)
Ash duplicates and means:







carbon standard: 1024 (single)
a1: 938, 954 → mean = (938 + 954) / 2 = 1892 / 2 = 946.0
a2: 760, 754 → mean = (760 + 754) / 2 = 1514 / 2 = 757.0
a3: 924, 916 → mean = (924 + 916) / 2 = 1840 / 2 = 920.0
a4: 602, 616 → mean = (602 + 616) / 2 = 1218 / 2 = 609.0
a5: 874, 882 → mean = (874 + 882) / 2 = 1756 / 2 = 878.0
a6: 722, 718 → mean = (722 + 718) / 2 = 1440 / 2 = 720.0
Perchloric duplicates and means:







carbon standard: 1000 (single)
a1: 950, 960 → mean = (950 + 960) / 2 = 1910 / 2 = 955.0
a2: 752, 738 → mean = (752 + 738) / 2 = 1490 / 2 = 745.0
a3: 910, 922 → mean = (910 + 922) / 2 = 1832 / 2 = 916.0
a4: 596, 614 → mean = (596 + 614) / 2 = 1210 / 2 = 605.0
a5: 860, 876 → mean = (860 + 876) / 2 = 1736 / 2 = 868.0
a6: 710, 724 → mean = (710 + 724) / 2 = 1434 / 2 = 717.0
The researcher compared the seven paired means (carbon standard, a1..a6).
2) Accuracy / Trueness for the carbon standard (explicit workings)
Formula:
𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑣𝑎𝑙𝑢𝑒
𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦 = (
) 𝑋 100
𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒
Symbols:


measured value = the assay result for the carbon standard (ppm)
expected value = 1050 ppm (specified target)
Ash (measured = 1024):
xiv

Recovery = (1024 / 1050) × 100
= 0.9752 × 100
= 97.52% ≈ 97.52 %
Bias (ppm) = measured − expected = 1024 − 1050 = −26 ppm (negative = under-recovery)
Perchloric (measured = 1000):

Recovery = (1000 / 1050) × 100
= 0.95 × 100
= 95.23 % ≈ 95.24 %
Bias (ppm) = 1000 − 1050 = −50 ppm
Interpretation: both under-recover relative to 1050 ppm; ash is closer (smaller absolute bias).
3) Precision (repeatability) from duplicate pairs — full working
The researcher used the standard duplicate-pair repeatability estimator:
Formula:
∑𝒏=𝒅𝟐𝒊
𝒔𝒓 = √ 𝒊
𝟐𝒏
Symbols:
𝒔𝒓 = repeatability standard deviation ppm
𝒅𝒊 = difference between duplicate measurements
𝒏= number of duplicate pairs
The researcher used the six duplicate pairs a1..a6 for each method (not the single carbon standard).
Ash duplicate differences (x1 − x2):
1. a1: 938 − 954 = −16
2. a2: 760 − 754 = 6
3. a3: 924 − 916 = 8
xv
4. a4: 602 − 616 = −14
5. a5: 874 − 882 = −8
6. a6: 722 − 718 = 4
the researcher computed and sum:






(−16)² = 256
6² = 36
8² = 64
(−14)² = 196
(−8)² = 64
4²
Sum ∑=256+36+64+196+64+16=632
=
16
The researcher plugged into formula (n = 6):
632
𝑠𝑟,𝑎𝑠ℎ = √
2𝑋6
So sᵣ (ash) = 7.2572 ppm (rounded).
Perchloric duplicate differences :
1.
2.
3.
4.
5.
6.
a1: 950 − 960 = −10
a2: 752 − 738 = 14
a3: 910 − 922 = −12
a4: 596 − 614 = −18
a5: 860 − 876 = −16
a6: 710 − 724 = −14
the researcher computed squares and sum:






(−10)² = 100
14² = 196
(−12)² = 144
(−18)² = 324
(−16)² = 256
(−14)²
=
Sum ∑=100+196+144+324+256+196=1216
196
Now:
xvi
1216
𝑠𝑟,𝑝𝑒𝑟𝑐ℎ = √
2𝑋6
So sᵣ (perch) = 10.0664 ppm (rounded).
Relative repeatability (RSDᵣ, %)
the researcher expressed sᵣ relative to the overall mean of sample means (excluding blanks).
Overall mean of the seven paired means:


mean(ash_means) = (1024 + 946.0 + 757.0 + 920.0 + 609.0 + 878.0 + 720.0) / 7
= 5854 / 7 = 836.2857142857143 ppm
mean(perch_means) = (1000 + 955.0 + 745.0 + 916.0 + 605.0 + 868.0 + 717.0) / 7
= 5806 / 7 = 829.4285714285714 ppm
RSDᵣ_ash = (sᵣ_ash / mean_ash) × 100
= (7.25 / 836.28) × 100
= 0.0086 × 100 = 0.86 % ≈ 0.868 %
RSDᵣ_perch = (10.06 / 829.42) × 100
= 0.012× 100 = 1.21 % ≈ 1.21 %
Interpretation: both methods show excellent within-pair repeatability; ash is a bit better (lower
RSD).
4) Paired differences (method comparison) — full working
The researcher compared the seven paired means (ash mean − perch mean) and test whether the
mean difference is significantly different from zero.
Paired differences =ash −perch meanj for j = 1..7:
1.
2.
3.
4.
5.
6.
7.
carbon standard: 1024 − 1000 = 24
a1: 946.0 − 955.0 = −9.0
a2: 757.0 − 745.0 = 12.0
a3: 920.0 − 916.0 = 4.0
a4: 609.0 − 605.0 = 4.0
a5: 878.0 − 868.0 = 10.0
a6: 720.0 − 717.0 = 3.0
the researcher computed the mean of these differences :
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𝑑̅ =
24 + (−9) + 12 + 4 + 4 + 10 + 3
48
=
=6
7
7
So mean difference = +6.8571 ppm (ash minus perch).
( samples SD, ddof=1)
The researcher computed the squared deviations from mean:







(24 − 6.85)² = (17.14)² = 293.87
(−9 − 6.85)² = (−15.85)² = 251.47
(12 − 6.85)² = (5.14)² = 26.44
(4 − 6.85)² = (−2.85)² = 8.16
(4 − 6.85)² = 8.16 (same as above)
(10 − 6.85)² = (3.14)² = 9.87
(3 − 6.85)² = (−3.85)² = 14.
Sum of squared deviations = 293.87 + 251.47+ 26.44 + 8.16 + 8.16 + 9.87 + 14.01 = 611.02
Sample variance (ddof=1) = sum / (n − 1) = 611.02/ (7 − 1) = 101.83
Sample standard deviation sd =
=√101.837
So sd of differences = 10.1066 ppm.
Paired t-test (two-sided)
Test statistic:
𝑡=
𝑑̅
𝑠𝑑 ⁄√𝑛
Symbols:



𝑑̅ = mean of the paired differences = 6.85 ppm
𝑠𝑑 = sample standard deviation of differences = 10.10 ppm
𝑛 = number of pairs = 7
The researcher computed the denominator:

𝑠𝑑 ⁄√𝑛=10.10 /√7 =3.81
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Then:
t=6.85/3.81
Degrees of freedom = n – 1 = 6
Two-sided p-value (from t distribution with df = 6) ≈ 0.12278.
Interpretation: p ≈ 0.123 > 0.05 → fail to reject H₀: mean difference = 0. There is no statistically
significant systematic difference between the methods at α = 0.05 on this dataset.
5) Bland–Altman limits of agreement (full working)
Bland–Altman uses mean difference 𝑑̅ ± 1.96 ×𝑠𝑑 (differences).


mean difference 𝑑̅ =6.85ppm
sd of differences 𝑠𝑑 =10.10ppm
the researcher computed:


Lower limit=𝑑̅ −1.96𝑠𝑑 =6.85−1.96×10.1 = −12.95ppm
Upper limit = 𝑑̅ + 1.96𝑠𝑑 = 6.85 + 19.80 = 26.67 ppm.
So 95% limits of agreement: −12.95 ppm to +26.67 ppm.
Interpretation: about 95% of ash − perch differences should lie between −12.95 and +26.67 ppm.
You must judge whether that range is acceptable for your decisions (e.g., payable gold thresholds).
6) Correlation and linear regression (full working)
We fit a simple linear regression of perch (y) on ash (x) using the 7 paired means.
Symbols:
Pearson 𝑟 =
∑(𝑥𝑖 −𝑥̅ )(𝑦𝑖 −𝑦̅)
∑(𝑥𝑖 −𝑥̅ )2
Intercept 𝑎 = 𝑦̅ − 𝑏𝑥̅
Slope 𝑟 =
∑(𝑥𝑖 −𝑥̅ )(𝑦𝑖 −𝑦̅)
√(𝑥𝑖 −𝑥̅ )2 (𝑦𝑖 −𝑦̅)2
𝑥 =ash men for each sample
𝑦= perchloric mean for each sample
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Computed numbers:


mean(x) = mean(ash_means) = 836.28
mean(y) = mean(perch_means) = 829.42
Sum calculations (performed exactly in code) give:


Pearson r = 0.99(very high linear correlation)
slopeb=0.98
intercept a=6.65
So regression equation (approx):
perch=0.98384 × ash + 6.6576
Interpretation: slope ≈ 0.984 (close to 1), intercept ≈ +6.66 — methods track closely across the
measured range.
7) Summary table of the most important numeric results (rounded sensibly)






Carbon standard recovery: Ash 97.52% (bias −26 ppm); Perchloric 95.24% (bias −50 ppm)
Repeatability sᵣ: Ash 7.26 ppm; Perchloric 10.07 ppm
Relative repeatability (RSDᵣ): Ash 0.87%; Perchloric 1.21%
Paired mean difference (ash − perch): +6.86 ppm (sd = 10.11 ppm), paired t = 1.795, p =
0.1228
Bland–Altman 95% limits: −12.95 ppm to +26.67 ppm
Pearson r = 0.99766; regression perch = 0.98384 × ash + 6.6576
8) Practical interpretation (concise)




Accuracy: both methods under-measure vs expected 1050 ppm; ash is closer.
Precision: ash shows slightly better repeatability.
Agreement: very high correlation, non-significant mean difference (p ≈ 0.123). Bland–
Altman limits are narrow compared with sample magnitudes — decide if ±13 to +27 ppm
is acceptable for your use.
Since those acceptance ranges meet Ayrshire Mines laboratory criteria, the math supports
replacing perchloric digestion with carbon ashing using the data.
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