SCHOOL OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF INDUSTRIAL AND MANUFACTURING ENGINEERING
CAPSTONE DESIGN PROJECT
OPTIMIZATION OF THE GOLD LEACHING PROCESS IN LEACHING AGITATION
TANKS: CASE STUDY ( SABI GOLD MINE)
BY
MUGANHU RONALD FARAI
(H180287E)
SUPERVISOR:
ENG. T KANYOWA
A FINAL YEAR PROJECT REPORT SUBMITTED IN PARTIAL FULFILMENT OF
THE REQUIREMENTS OF THE BACHELOR OF TECHNOLOGY (HONS) DEGREE
IN INDUSTRIAL AND MANUFACTURING ENGINEERING
May 2023
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Copyright
All rights reserved. No part of this project may be reproduced, stored in any retrieval system or
transmitted in any form or by means of electronic, mechanical, photocopying, or otherwise,
without the prior written permission of the author or of Harare Institute of Technology on behalf
of the author.
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Declaration
This design project is my original effort except where sources have been acknowledged. The
work has never been submitted anywhere, nor will it ever be, to another University/Institute in
the awarding of a degree in any faculty.
RF MUGANHU
H180287E
Signature……………….
Date Signed…………………………………..
SUPERVISOR………………………………………………..
Date Signed………………………………………………………….
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Dedication
This project is dedicated to my family, supervisor and friends who sacrificed their precious time
until completion this project. Finally, I would like to dedicate this project to the all mighty God
for leading me throughout this Capstone project. It was not easy but through Him, all things
made possible.
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Acknowledgements
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Abstract
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TABLE OF CONTENTS
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LIST OF FIGURES
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LIST OF TABLES
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CHAPTER ONE: INTRODUCTION
1.0 Introduction
Gold mining in Zimbabwe is a major mainstay for millions in the southern African country.
There are over 4 000 recorded gold deposits in Zimbabwe of which nearly all of them are located
on ancient workings (Keith Sungiso, 2022). Mineral exports account for about 60 percent of
Zimbabwe’s export earnings and the mining sector contributes around 16 percent of the national
GDP. Gold continues to dominate as Zimbabwe’s single biggest export commodity after the
yellow metal accounted for about 30.1 percent of the total volume of goods exported by the
country in 2022.
The mineral is expected to generate at least US$4 Billion by 2023 in line with the country’s
vision of a US$12 billion mining industry by 2023. Deliveries to Fidelity Printers and Refineries,
the country’s authorized buyer of the yellow metal, jumped 55,5% in 2021 to 29,6 tonnes from
19 tonnes in 2020 (Oliver Kazunga, 2022). Sabi Gold mine is one of the large scale mines in
Zimbabwe. It is one of the largest producers of the yellow metal.
1.1 Problem Background
The gold mining sector is faced by a myriad of challenges such as outdated equipment, shortage
of foreign currency to import modern machinery and high cost of upgrading technology
according to (Rachel Mujaya, 2023). The Zimbabwe local miners do have a mammoth task in
acquiring machinery and equipment as a lot of money is required hence the miner will be
juggling between daily operations, taxes and equipment required ( Priviledge Moyo, 2019).
Sabi Gold mine is one of the large scale mines in Zimbabwe. Following the closure of the
company in 2014 due to debts according to the (Business reporter, 2014), the company resumed
operations in 2017. With the emergency of the Fourth Industrial revolution (Industry 4.0) and
current technological advancements, the current system at Sabi Mine legs behind in many ways,
for example, the monitoring of parameters like temperature and pH which are essential in the
gold leaching process is done manually. Cyanide which is used as a catalyst in the gold leaching
process is a deadly chemical and exposure to it may lead to one developing chest pains,
headaches, dizziness, nausea etc. The current system is slow and requires a worker to constantly
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measure parameters like temperature and pH at various intervals manually. If there is an
anomaly, for example a drop in pH, there is no immediate notification to the process engineers,
the anomaly will only be discovered when an employee takes readings at different intervals. This
means for that period, no significant recovery of gold was achieved from the system since pH
will be for example, below the optimal value required. This will mean the leaching hours will be
increased and the plant will be consuming electricity in the process with no significant output.
Gold leaching occurs in the agitation tanks after the ore is crushed into small particles using jaw
crushers. Real time monitoring systems are faster than humans, compute data faster, less prone to
errors, and data analysis is possible which enables feedback to be given to Engineers. By
monitoring these parameters, Engineers can analyze the performance of the system to determine
the recovery rate of gold from the ore. According to (Asghar Azizi and Reza Ghaedrahmati,
2015), the highest rate recovery rate is high as 91,5% of gold from its ore through leaching if
parameters such as temperature, leaching time and pH are maintained at the optimum level and
can be low as 45% if the parameters are not at optimum. Currently, the agitation tanks at Sabi
Gold mine do not have real time monitoring systems to enable monitoring of the process in the
agitation tanks automatically. Therefore, there is need to optimize the current system to enable
accurate and automatic monitoring of parameters in the leaching tanks, eliminate exposure to
cyanide by workers and enable the system to provide feedback to engineers in real time.
1.2 Problem Statement
The manual measurement and monitoring of parameters like temperature and pH in leaching
agitation tanks is slow, prone to errors and exposes employees to deadly cyanide.
1.3 Aim
To develop a real time monitoring and control system for temperature and pH in gold leaching
agitation tanks.
1.4 Objectives
 To develop a real time monitoring system for temperature and pH during the leaching
process.
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 To develop an automated temperature control circuit, to regulate the temperature in the
leaching tanks.
 To develop a mobile application to notify the user of any fluctuations in pH and
temperature during the process.
1.5 Justification
The emergency of smart manufacturing and cyber physical systems has led to greater seamless
data exchange, maximized plant efficiency and better safety and control. Digital technology has
revolutionized manufacturing and ushered in a myriad of changes that boost efficiency and
growth (Sasha llyukhin, 2023). The project seeks to optimize the current gold leaching elution
process by incorporating real time monitoring and control to the current system, this enables
seamless data exchange, greater control over the production process, minimizes exposure to
cyanide by employees and increase quality of decision making.
Real time monitoring and control enables data exchange thus there is feedback which enables
Engineers to make adjustments to the system where necessary. Without feedback and real time
monitoring, there are a number of drawbacks such as poor decision making, human error and
duplication of efforts. For efficient recovery of gold from the leaching tanks, temperature,
pressure, leaching time, pH and agitation speeds should be kept at optimum levels, therefore,
without real time monitoring and control, there is no real time feedback from the system to
effectively monitor these parameters in real time. Therefore, the project seeks to optimize the
current elution system by providing real time monitoring and control to fully maximize
productivity and have greater control over the process.
1.6 Scope
The project will focus on developing a real time monitoring and control system for temperature
and pH in the gold leaching agitation tanks.
1.7 Research Questions
 How does particle size affect the leaching process?
 What is the effect of temperature on the leaching process?
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 What mechanisms are there for separating gold from its ores?
 What speed of the agitation tank is required to optimum leaching of gold?
 What is the effect of pH on the leaching process?

1.8 Conclusion
The chapter highlighted the background of the problem, stated the research problem which
prompted the researcher to carry out the study. It also covered the objectives, research questions,
justification and scope of the study.
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CHAPTER TWO: LITERATURE REVIEW
2.0 Introduction
This chapter discusses related literature gathered from various sources. Citation is included as the
discussion progress. Views from the literature, concerning the subject matter are outlined and
analyzed prior to the researcher’s opinion. As this information is gathered, the researcher seeks
to find gaps and shortcomings in the current devices and systems used.
2.1 Review of the gold leaching process.
The gold industry has seen intense activity in the areas of exploration and metallurgy in recent
years. Many developments have taken place through which ore bodies that were once considered
uneconomical to exploit are becoming economical grade. Even the traditional cyanidation
process has been modified during the course of time to make it more economical and efficient
according to (A.R.Udupa et al, 2007). Developments such as heap leaching, in-situ leaching,
carbon in pulp (CIP) and pretreatment of refractory ores have already made an impact on gold
industries. Research and development work is also being carried out on less toxic, more efficient,
lixiviants which may eventually replace the toxic cyanide, solving disposing problems facing the
industry.
According to (Graham J et at, 2010) the selection of a leaching system for gold involves
consideration of ore texture and mineralogy, chemical requirements, leaching techniques, the
development of flow sheets, and environmental management. All systems require an oxidant to
oxidize gold and a ligand to complex with gold in solution. Adjustment of pH is usually
necessary. Alkaline systems with pH above 10 include cyanide, ammonia-cyanide, ammonia,
sulphide and a few other minor possibilities. Cyanide which is the main ligand in these systems,
forms anionic complex, Au(CN)2. Gold dissolution rates are controlled by oxygen solubility in
solution. Acid leaching systems with pH greater or equal to 3 may contain chlorine, thiourea and
thiocyanate. Chloride is the ligand in the acid leaching systems which produces Au(III) anionic
complexes eg (AuCl). Most non-cyanide leaching systems appear to have little wide-spread
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practical application. Possible niche applications include the use of chlorine or aqua regia to
dissolve coarse gold from gravity concentrates.
Various operational factors affect the cyanide leaching process. Research on the optimization
and evaluation of factors affecting the leaching process has been carried out recently. According
to (Asghar Azii et al, 2015) the use of CCD models has been done to evaluate various factors
affecting the leaching process. A response surface method using a central composite design was
employed to evaluate, model and optimize the influence of five main factors in the gold
cyanidation process. These factors were pH, solid percentage, NaCN concentration, particle size
and leaching time. The modeling results indicated that these factors influencing the degree of
cyanide leaching of gold were in the order of leaching time> NaCN concentration> particle size>
pH. The optimal condition was found to be a pH of 10-11 and 23.2 hrs of leaching time. Under
these conditions, the highest recovery of gold was achieved of approximately 91.5%.
According to (Reza Ghaedrahmati et at, 2015), cyanidation remains the most important and
widely used hydrometallurgical technology in the extraction of gold and silver from the primary
ores and concentrates. Used for over 100 years, the popularity of cyanidation is based mostly on
the simplicity of the process, yet, despite this fact, the reactions involved are not fully
understood. In fact, today, cyanidation is the only choice for the recovery of gold from low-grade
and finely disseminated gold ores in both technological and economic aspects.
Further research has been carried out on the use of more environmentally friendly processes
instead of cyanide on the recovery of gold from ores, scraps and jewellary. According to (S Beste
Aydin et at, 2020), nowadays the production and exploration of gold has an increased importance
all over the world. Recycling is a significant source for the supply of gold and has a pronounced
effect on its price. The flotation method which is more economical and more environmentally
friendly than cyanide leaching has been investigated for recycling gold and silver from jewellery
slag.
Recently, advances in the treatment of refractory gold ores have been done. According to
(A.J.Monhemius), the past decade has seen a renascence in research and development into new
gold extraction processes. This has been brought about primarily by the increase in the price of
gold since the abolition of the gold standard at the beginning of the millennium. Much of the
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development activity in gold extraction has been directed towards reducing the capital
investment required in the application of the standard cyanide process to free milling gold ores.
The development of carbon in pulp processing has had a major impact on costs in agitation leach
plants by eliminating the expensive liquid-solid separation requirements of the traditional
processes. The introduction of heap leaching into gold metallurgy is a major innovation. Various
methods such as pressure oxidation, pressure cyanidation, bacterial oxidation and use of thiourea
are some of the advancements in the processing of gold from its ores.
2.2 Review of gold leaching tanks and agitators
The mixing of solids suspended in a fluid medium is still largely an art. The development of
fundamental laws governing the operation is complicated by the large number of variables
involved, some of which can be hardly evaluated in mathematical terms. According to (L D
Michaud, 2017), in cyanidation leaching work, however, it is evident agitation has two purposes
only, to keep solids in suspension while dissolution is taking place and to supply the required
amount of oxygen. Violet agitation has no recognized value in itself, but ample oxygen supply is
essential to promote the reaction between gold, cyanide. Control of aeration during agitation is
essential, since excessive aeration usually results in greater consumption of lime and sometimes
of cyanide, with no increase in extraction. Length of contact between and dilution during
agitation vary considerably for different ores. For gold ores agitation periods vary from 16 to 48
hrs probably averaging 30hours.
Various agitators has been developed of late each based on a different work principle. The first
agitators used in industry were of simple rotating paddle type. These, however, required large a
large amount of power and didn’t give uniform suspension or satisfactory means for controlling
aeration in cyanidation leaching. Of late, the Dorr agitator is in use today, it is a combination of
mechanical and air agitator designed for use in round, flat-bottomed tanks as large as 50ft in
diameter and 25ft in depth. Further research is being done to determine the impact, for example
of using two agitators in series in a leaching agitation tank. In practice, an economic balance
covering costs for various combinations of agitators would have to worked out and the most
favorable selected.
.2.3 Current trends in Real time monitoring and control
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Industrial automation and control systems have become an integral part of industries and hence
Real Time Monitoring and Control System is an important system. According to (IJSRD, 2013),
Real Time Monitoring and Control Systems aims to monitor the environmental parameters like
temperature, humidity, pressure in any factory. Rahul D. Chavhan et al, 2013, asserts that
industries are the biggest workplace all over the world, there are many systems for industrial
workplace, some of them, monitors machine processes and some do monitoring and control of
machine parameters. Various process parameters have been measured and monitored of late in
various industrial applications.
2.3.1 Review of temperature monitoring and control systems
Temperature is an important parameter in gold leaching process. The optimal temperature for
cyanide leaching gold in industrial processes is 25-30 degrees Celsius. Although higher
temperatures can improve the efficiency of leaching, it will take large amounts of energy to heat
large gold cyanidation systems according to (Shimin Yu et al, 2020).
According to (Nor Alina Khairi et al, 2013) wireless devices will be important in future
monitoring applications such as automobiles, industrial machines and processes etc. In order to
monitor and maintain a process at a specific temperature, information must first be gathered from
a temperature sensor device. By using an effective temperature monitoring system, temperature
values can be recorded in real time or displayed on a monitor. The recorded temperatures can be
used further to analyze the performance of the process during a specific period of time. Building
a wireless temperature monitoring system will be expensive especially when continuous real
time is needed. Typically, a wireless temperature sensor system can be designed using Zigbee
sensor tag or Bluetooth devices to transmit and receive data.
As industries continue to grow and expand, so is the effort required to maintain them. According
to (Revathi R et al, 2020), the power of IoT can be used to simplify these growing demands. IoT
based temperature monitoring systems can be used alongside machines to monitor and control
their temperature 24/7 and raise an alarm should there be any discrepancy thus preventing any
accidents and ensuring that the temperature conditions are optimal for a process.
2.3.2 Review of pH monitoring and control systems
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pH is an important parameter in gold leaching processes, according to (M.G.Aylmore, 2016),
greatly increasing pH values has a beneficial effect on gold extraction for both oxide and sulfide
ores. However the outcome will vary depending on the nature of the gold background mineral
matrix. Jeffrey et al, 2008, observed that increasing the pH value from 8.5 to 10.5 increased the
gold leaching efficiency from 7% to 70%. However, leaching of gold after 24hrs at pH 8.5 was
similar to that observed at higher pH value, but the leaching rate was slower.
According to (Malusi Sibiya et al, 2020), the use of Fuzzy logic on arduino for the control of
acidity or alkalinity has been done, the system involves effectively calculating the amount of
acidic or alkalinity in a solution using fuzzy logic techniques programmed on an arduino mega.
(Narendra Khatri et al, 2018), did a research on an IoT based innovative real time pH monitoring
for municipal wastewater. The paper describes a smart solution through which IoT based systems
can be used in conjunction with pH sensors to monitor and control pH from a particular solution.
With the emergency of the Industry 4.0, more and systems are integrating IoT and sensor
technology to aid in monitoring and control systems.
2.4 Research Position
The author reviewed various literature on the gold leaching processes. The research enabled the
author to gather information on the current trends and literature done by various authors in
relation to the subject matter. From the authors research and point of view, few work has done as
far as monitoring and control of parameters in gold leaching processes is concerned. Although
real time monitoring and control has been applied in various manufacturing and automobile
industries, less research has done as far gold leaching is concerned, the author will use the
various information from different authors in his research project.
.
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CHAPTER THREE: METHODOLOGY
3.1 Introduction
This chapter serves to articulate on the methods and techniques employed to gather data, process
and represent research information properly. Engineering tools, data collecting techniques and
computer software will be used for analysis and presentation of results.
3.2 Process Flow Chart
Figure 3.1 Methodology Flow Chart
As applied to this thesis, the above design approach has been adopted in solving the problem.
3.3 Problem Identification
The researcher did a research in order to study and analyze the current gold leaching system used
at Sabi Gold Mine. The company seeks to increase its gold output from 240 to 384 kilograms of
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gold annually (Tamary Chikiwa, 2021). However, in order to achieve this target, there is need to
invest in new technology in order to maximize productivity and efficiency. The current system is
lagging behind in terms of technological advancement. With the transition to the fourth industrial
revolution, smarter manufacturing systems and data analytics have revolutionized the industry.
There is need to upgrade or optimize the current leaching process to maximize productivity.
Lack of real time monitoring and control means the engineers and technicians do not have full
control over the leaching process, there is no data analysis or feedback to enable corrective
measures.
3.4 Data Collection
Most of the data was obtained from various sources in order to see previous achievements that
were achieved by others. This would give the researcher what gaps need to be exploited. As a
result, academic journals, and related articles were used in coming up with different information.
The information will be used for designing and coming up with different concepts which will
lead to the development of the prototype.
3.4.1 Primary Data Sources
Primary data was collected by the researcher for the purpose of detailed study. Methods
employed include observations. For example the researcher had a visit to Sabi Gold mine where
he analyzed the current leaching process and ways to optimize it.
3.4.2 Secondary Data Sources
This method involved the use of data which was previously published by other researchers or
companies in relation to the topic of the research. The methods used involve the use of library
sources, academic journals, books, articles, newspapers and scientific research papers to come up
with information. The researcher will use statistical tools in order to analyze the data collected.
3.5 Literature Review
The results which were obtained from all the research and different literature will be analyzed in
order to come up with conceptual designs.
3.6 Conceptual Design
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After the analysis of results and literature review, different concepts were generated so as to
solve the problem as stated by the problem statement. The concept development helps in coming
up with possible solutions. The author began by coming up with concepts and then screening
them. The concept with the highest score was selected and detailed design was done on it.
3.9 Prototype Development
Having done the conceptual design, the prototype was developed. This involved integrating the
hardware and software together so that the prototype functions as projected.
3.10 Prototype Testing
This was done in order to find out if the prototype is performing as expected. The results were
satisfactory. If the results were not in sync with the expectation, the researcher would’ve gone
back to the prototype development and conceptual design to make some changes.
3.10 Results and Recommendation.
The author recorded the results from the functionality of the prototype. The author also made
recommendations for further research
3.11 Engineering Tools
According to (Hooper, 2017) engineering tools are specialized software or applications that are
used for research and development of new products. Therefore, to accomplish the tasks, the
researcher identified and incorporated various engineering tools that were relevant to the tasks at
hand. Such tools include Proteus for circuit designing, Arduino IDE as the source code for real
time monitoring and control of the system and AutoCAD for drawing of the mainframe of the
prototype and Microsoft Excel which was used for flowchart and table creation
3.12 Conclusion
This chapter was aimed at outlining the methodology the researcher will adopt in executing the
identified problem. An integrated hardware and software system was developed and the
researcher used them in result validation at the end. Following this approach, primary and
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secondary data collection techniques were used in conjunction with various engineering tools for
data processing and analysis
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