New Projects:
Conventional or High
Density Tailings?
David Romo
Paterson & Cooke, Chile
Ray Martinson
Paterson & Cooke, Chile
The challenges of new mining projects
Every new mining project has to define the most important aspects for the business:
• Mineral resources model
• Mine explotation design
• Methallurgicall process
After that, the main consumptions of the process have to be evaluated:
• Water consumption
• Energy consumption
At the end, the projects have to define what to do with the waste of the
process:
• Sterile material
• Tailings
Aim of the study
In this case Paterson & Cooke office in Santiago was in charge of the
definition of tailings management system of the project.
The aim of this presentation is to show the issues we had to face and
what we did to deal with them, in order to support the definitions of
the Client.
“What we have to do is to look at the whole picture of the problem”
Content
1. Project overview
2. Tailings deposit location
3. Bench scale tests
4. Conceptual trade off: conventional or thickened tailings?
5. Semi pilot test work
6. Reviewing the solution
7. Conclusion
1. Project Overview
The study adresses a new project of Sociedad Punta del Cobre, the greatest
medium copper mining company in Chile.
• It is a gold-copper mine located at the IV region of Chile, around 300 km
north of Santiago
• It is located in a desert area, the annual rainfall is less than 200 mm.
• The project considers a plant to process over 15,000 tpd
• The tailings deposit considers a capacity over 100 million tonnes
1. Project overview
Paterson & Cooke led a consulting team to design the tailings system for the project
PROFILE PREFEASIBILITY TRANSITION
STUDY
STUDY ENGINEERING
2010
2011
FEASIBILITY
STUDY
2012
2013
DEPOSIT
LOCATION
BENCH SCALE
TESTS
SEMI PILOT
TESTS
PRELIMINARY
ARRANGEMENT
CONCEPTUAL
TRADE OFF
UPDATE THE
SOLUTION
PATERSON & COOKE LED THE TAILINGS
CONSULTING TEAM
PUMPING
TAILINGS
SYSTEM
DESIGN
SUB-CONTRATOR
OF AMEC CHILE
CONSTRUCTION
2014-15
2016
COMMISIONING
2. Tailings Deposit Location
• Based on satellite survey,
11 potential sites were
identified closer than 30
km to the plant.
Alt. 11
Alt. 10
• The storage target was 150
million tonnes.
Alt. 8
• A comparison was done
considering:
Alt. 9
•
Alt. 6
PLANT
•
Alt. 1
Alt. 5
Alt. 2
Alt. 4
Alt. 7
Alt. 3
•
•
Conventional tailings pumping
head
Recovered water pumping
head
Dam wall volume
Existing human activity
• Three alternatives were
selected to complete the
trade off comparison
2. Tailings Deposit Location
The evaluation of each alternative
considered:
PLANT
LOCATION
• Storage capacity of 80 million
tonnes
Alternative 5
• Processing plant of 17,000 tpd
Alternative 2
• Conventional tailings with 55%cw
• Sand wall from cycloned tailings
Alternative 4
The results were the following:
Parameter
Unit
Alternative 2
Alternative 4
Alternative 5
Starting wall volume
Mm³
1.5
1.3
0.8
Final wall volume
Mm³
11.1
5.0
4.4
Final wall height
m
102
81
85
Slurries and water pipeline length
m
8.4
36.2
56.1
Total installed power
kW
1,249
6,669
7,759
Plant make-up water
m³/t
0.54
0.55
0.64
Due to lower Capex and
Opex, lower installed
power, best plant makeup water and lower
environmental impact,
Alternative
2
was
selected.
3. Bench Scale Tailings Tests
In order to get slurry design parameters,
bench scale tests were done on samples
of each UGM and on a composite.
100
from
• The average p80 was 148 μm, 61% less
than 75 μm and Sg of 3.03
% Passing
• The
samples
were
got
metallurgical bench scale tests.
Tailings Particle Size Distribution
90
SF UGM1
80
SF UGM2
70
SF UGM4
60
SF UGM5
50
SF UGM6
40
Composite Sample
Sedimentation tests were done by Delkor:
30
• Magnafloc 338 was the best floculant,
floc dose between 6-12 g/t and
dilution of 13%cw
20
• Depending on the sample, a paste
thickener could produce tailings
between 68.5% - 74.1%cw, being the
expected average equals to 71.5%cw.
10
0
1
10
100
Particle size (micron)
1000
3. Bench Scale Tailings Tests
Bingham Yield Stress vs Solids Concentration
80
UGM1 (F)
UGM2 (F)
UGM4 (F)
UGM5 (F)
UGM 6 (F)
Composite Sample (F)
Design Curve
60
50
70
Yield Stress (Pa)
70
Yield Stress (Pa)
Bingham Yield Stress vs Solids Concentration
80
40
30
60
50
30
20
10
10
67%
68%
69%
70%
71%
72%
Solids Concentration (Cw)
73%
74%
75%
76%
Maximum
Rheology
40
20
0
66%
Minimum
Rheology
0
66%
68%
70%
72%
Solids Concentration (Cw)
74%
76%
• A range of rheology was measured in rotational viscometer.
• The unsheared yield stress, for the expected operational thickening points, was
determined between 15 and 40 Pa, which is considered a low rheology.
• The rheology reduction was measured at 30%, so the expected fully sheared yield
stress was between 10 – 28 Pa. At the average thickening point the expected fully
sheared yield stress was 19 Pa.
3. Bench Scale Tailings Tests
In order to estimate the beach slope at the deposit, a flume test was done on the
composite sample.
The limitations of flume tests for predicting beach slopes are well known, so the
measured values were reduced by considering two reduction factors: evaluating the
average slope in the middle of the flume and also considering a reduction of 30%.
Estimated Beach Slope vs Yield Stress (Fully Sheared)
Estimated Beach Slope (%)
6%
Middle Profile
Slope
5%
5.1%
Recommended
Curve
4%
3.6%
3%
2.2%
2%
1.5%
1%
0%
0
5
10
15
20
25
30
Yield Stress (Pa)
35
40
45
50
With those considerations,
at the average fully sheared
yield stress of 19 to 20 Pa at
the deposit, a beach slope
of 1.5% was estimated for
the
purpose
of
prefeasibility engineering
4. Conceptual Trade off: Conventional or
Thickened Tailings?
The main aspects to figure out in the project in terms of the prefeasibility study were
as follows:
• Deposit location
• Tailings management system
• Dam wall and storm water system design
The dam wall and storm water system design were undertaken by Knight Piesold Chile.
Two different options for tailings management system were evaluated:
• Conventional tailings option: low density tailings, cyclons operation, slimes
transport, tailings sand wall and tailings discharge at the deposit from the wall.
• Thickened tailings option: high density tailings, wall constructed with borrowed
material and tailings discharge at the end of the deposit.
4. Conceptual Trade off:
Parameter
Solids concentration
Conventional tailings system
64%CW
Thickened tailings system
70%CW
Thickener
(1) × Ø48 m high rate thickener, yield
stress < 15 pa
Gravitational flow through 4,300 m
HDPE pipeline
(1) × Ø48 m paste thickener,
yield stress < 80 Pa
Gravitational flow through
700 m HDPE pipeline
Tailings transport
Tailings classification
Sand transport
Slimes transport
Recovered water transport
Starting dam wall
Final dam wall
Beach slope
Plant make-up water
Installed power
3 + 3 cyclones
2 + 2 slurry pumps TDH 20 m
Gravitational flow through 1,475 m
steel pipeline
2 + 2 barge pumps and 4 + 2 water
pumps TDH 230 m
No cyclones or pumping slurries
systems were considered
1.8 Mm³
1.0 Mm³
12.5 Mm³
6.5 Mm³
0.3%
1.5%
0.46 m³/t
0.40 m³/t
3,100 kW
1,700 kW
4. Conceptual Trade off
The thickened tailings system was selected because of:
•
Lower capex
•
Lower installed power
•
Lower plant make up water
•
Lower volume of water within the
deposit
•
Greater opportunities to improve the
using of the deposit facilities
Tailings
discharge
Plant
Location
Wall
Thickener
5. Semi Pilot Tailings Tests
• The p80 was 218 μm - 192 μm
• Fine fraction less than 75 μm was
56%-60%
Slurry behaviour tests were done by
P&C Johannesburg:
• Natural pH 7.8
• Slurry conductivity over 40 mS/cm
(sea water)
• Slurry naturally settling
Particle Size Distribution - Semi Pilot Samples
100
90
80
70
60
50
40
30
20
10
0
M1
M2
% Passing
Semi pilot tailings tests were done in
order to improve the knowledge of
tailings on a larger scale.
1
10
100
Particle size (micron)
1000
5. Semi Pilot Tailings Tests
Semi pilot thickening tests were done
by Outotec in a Ø190mm x 4 m
thickener:
• Magnafloc 338 was the one of the
best floculants, floc dose grew up to
17 g/t and dilution was 12%cw
• Optimum flux rate was 0.4 t/m².h
• Expected U/F solids concentration
65%-73%cw
• Unsheared yield stress between 50180 Pa
• Two options were proposed:
•
•
One 55Øm high compression thickener
Two 38Øm high compression/paste
thickeners
5. Semi Pilot Tailings Tests
Bingham Yield Stress vs Cw
200
Bingham Yield Stress (Pa)
180
160
140
Sample 1 Fully Sheared
Sample 2 Fully Sheared
Sample 1 Unsheared
Sample 2 Unsheared
Paste
120
100
80
Thickened
60
40
20
Conventional
0
50% 52% 54% 56% 58% 60% 62% 64% 66% 68% 70% 72% 74%
Solids Concentration (Cw)
• A range of rheology was measured in rotational and tube viscometer.
• A great difference between the rheology of both samples was measured. Even the
rheology was 6 times greater than the measured one at the PFS study.
• A rheology reduction of 60% was measured on these samples
5. Semi Pilot Tailings Tests
Estimated Beach Slope vs Solids Concentration
Estimated Beach Slope %
3,0%
2,5%
2,0%
1,6%
Estimated Beach
Slope M1
Estimated Beach
Slope M2
Operational Point
1,5%
1,0%
0,5%
0,0%
64%
66%
68%
70%
72%
74%
76%
Solids Concentration Cw %
• 4 m flume tests were done to estimate the beach slope. The experience and test
data analysis were done with the support of Professor Andy Fourie.
• Both samples showed different behaviour, due to the different lithology. The beach
slope estimation considered a safety factor of 50% over the measured slope.
• At the average solids content for the thickener operation of 70%CW, the average
beach slope was estimated on 1.6%
6. Reviewing the Solution
6.1 Tailings Pumping
Because of the higher rheologies measured at semi pilot test work, pump
stations are required for tailings transportation from thickener(s) to the deposit.
Depending on the option of thickening circuit the pumping system is as follows:
Pump station
(1) × Ø55 m
thickener
(2) × Ø38 m
thickener
Underflow discharge
(1 + 1) 20 m/15 m
250 kW centrifugal
pumps
2 × (1 + 1) 20 m /15
m 200 kW
centrifugal pumps
Transport to deposit
(1 + 1) 25 m/20 m 200 kW centrifugal
pumps
6. Reviewing the solution
6.2 Filtered tailings
Bench top filtering tests were done by Delkor, but the filtration rates were very
poor for vacuum and pressure technologies. In spite of those results, an evaluation
of filtered tailings system was done.
The area of the deposit is not suitable to dispose tailings in stock piles. This is
because of the maximum expected value for the hydrographic basin storm flow
which reaches 211 m³/s. As a result, a water dam as well as an evacuation tunnel
had to be considered in this evaluation.
Finally the filtered tailings option resulted into a Capex over 2.4 times the
thickened tailings option.
7. Conclusion
The study developed for this new project of Sociedad Punta del Cobre ended
into the following conclusions:
• The site conditions are the most important aspects that define which type
of dewatering system is the best. The topography and the hydrographic
basin storm determine the design of the deposit and the tailings
management system. The other very important aspect are the pumping
distances.
• If the material presents good conditions to be thickened or filtrated, a
complete test plan must be done to support every engineering evaluation.
Bench scale or pilot tests are recommended to be done for each stage of
engineering.
• In this case, thickened tailings clearly has technical advantages over
conventional and filtered tailings systems. The expected plant make-up
water is 0.4 m³/t and the installed power is 2,700 kW
• For feasibility engineering, the final selection of the thickening circuit and
the study of disposal strategies will be important issues to address.
Acknowledgements
We want to acknowledge to all people who worked with us, from Knight
Piesold Chile, Multical, Delkor, Outotec, Mr. Andy Fourie and to Pucobre S.A.