Post on 31-Mar-2015
transcript
Modelling of Macraes POX Circuit
May 2006
Acknowledgements
OceanaGold
GRD Minproc
Brent Hill
Tony Frater
David King
Quenton Johnston
Nevin Scagliotta
Adrian Marin
Presentation Outline
Background
• Macraes POX circuit
• Integration of Reefton concentrates
Modelling
• Metsim model calibration
• Model prediction of increased throughput
Conclusion/Recommendation
Johannesburg Office
Belo Horizonte Office
Macraes Processing Background
Historical Processing
• Small scale operation from 1862 until 1950
• 15 000 oz gold and 100 t scheelite recovered
Modern Processing (Since 1990)
• Crush / Grind / Flotation / CIL
• Crush / Grind / Flotation / Fine grind / CIL
• Crush / Grind / Flotation / Fine grind / POX / CIL
Modern Project History
Major Projects• 1.5 Mt/a sulphide treatment plant – 1990• 3.0 Mt/a expansion – 1994• MREP 4.5 Mt/a - 1999• Increase for sulphide and oxide capacity • Newmont POX technology• 170 t/d BOC cryogenic oxygen plant
Smaller Projects• Unit cell installation• Reclaim circuit• 0.5 Mt/a oxide mill• Autoclave optimisation
Current capacity approximately 6 Mt/a
Macraes Processing Issues 1
• Massive sulphide orebody hosting FeS2 / FeAsS
• Muscovite / quartz/ chlorite / siderite in gangue
• Presence of organic carbon, double refractory
• Variability. Low and high preg-robbing ore types
• 50% to 80% CIL recovery without POX
• Poor recovery with “conventional” POX
Macraes Processing Issues 2
• Newmont technology required for “controlled” POX
• Limestone for free acid control
• Washing for chlorides
• Scale formation in autoclave
Macraes POX Circuit Design
• Concentrate grade 8 - 12 % S
• 3.5 m dia. x 12.6 m
• 2:1 semi-elliptical ends
• 4 agitator, 3 compartment vessel
• 225°C and 3,140 kPag
• Koch Pyroflex membrane and AP302
Autoclave
Scaled Agitator
Reefton Processing
Orebody
• Native gold with minor sulphides in quartz veins
• Gold in FeS2, FeAsS, Sb2S3
Processing
• Crush / Grind / Flotation / Filtration / Transport
• Concentrate at 17.1 % S
• No organic carbon
• Highly refractory, complete oxidation required
Reefton / Macraes Integration
• Additional S oxidation requirement
• Oxygen plant constraint
• Autoclave retention time constraint
• Differing POX conditions
• Requirement for modelling to optimise capacity
History of Macraes POX Modelling
• Spreadsheet POX model developed and verified
• Single-compartment Metsim model developed
• Three-compartment Metsim model developed
• POX chemistry modified based on XRD results
• Thermodynamic data sources consolidated
Plant Trials and Model Calibration
• Plant trial in March 04 generated 23 data sets
• Solids and solution assays recorded
• Operating conditions recorded:
• Autoclave Pressure
• Temperatures in C1, C2 and C3
• Cooling water to C1 ,C2 and C3• Oxygen flow rate and purity
• Overall oxidation from feed and discharge assays
• Compartment oxidation inferred from heat balance
Sulphur Analysis Discrepancy
• Trial data:for 98% oxidation, 20 t/h CW added
• Model results:for 98% oxidation, 16 t/h CW added
• Site assay 10% of the total S (TS) is sulphate S
• No TS reported for the trial data
• No free acid in discharge reported
• Can not do overall S balance calculation
MLA Mineralogy Investigation
• MLA used for quantitative mineralogy investigation
• MLA results 2% of TS is sulfate S
• Site assay 15% sulfate S for the same sample
• Revised S and gangue mineralogy according to MLA
Plant Trials in 10/04 and 01/05
• Updated trial data collection template
• Additional data for heat/mass balance
• Updated mineralogy data used
• Good correlation between models and assays
• No heat adjustment factor required
Plant Trials in 10/04 and 01/05
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RT, min
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21/10/04 data set1
21/10/04 data set2
28/01/05 data set
Plant High Throughput Trials in 07/05
• In July 2005 eight plant trials run
• Four data sets from scaled autoclave and
• Four sets from “clean” autoclave
• Scaled agitators show poorer oxygen dispersion
• Scaled sets average oxygen utilisation is 79%
• “Clean” sets average oxygen utilisation is 85%
Plant Trials in 07/05
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oxi
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Set 8
Model to Predict Various Scenarios
• Plot leach kinetics for all plant trials
• Use average kinetic curve for further modelling
• Scenarios modelled:
• Grade: 10%, 12% and 14% total S
• Throughput: 2.7, 2.8, 2.9, 3.0, 3.1 and 3.3 t/h TS
• Constant oxygen partial pressure
• Oxygen: 7 t/h
The Final Kinetic Curve Used for Scenario Modelling
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RT, min
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oxi
dat
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21/10/04 data set1 21/10/04 data set228/01/05 data setSet 2Set 3Set 4Set 5Set 6Set 7Metsim input
Scenario Modelling Results
• For 10% S and 12% S- C1 temp drops with higher throughput
• For 14% S- C1 maintains 225°C for all scenarios modelled
S throughput, t/h 2.7 2.8 2.9 3.0 3.1 3.3
10% S 225 224 223 220 218 214
12% S 225 225 225 224 220 218
Compartment 1 Temperature
Scenario Modelling ResultsHigh throughput trials DCS data
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20/06/2004 19:12 21/06/2004 0:00 21/06/2004 4:48 21/06/2004 9:36 21/06/2004 14:24 21/06/2004 19:12 22/06/2004 0:00 22/06/2004 4:48
Time
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Scenario Modelling Results
• Above 2.7 t/h TS, oxygen constrained
• Increasing throughput, decreases RT for ≤ 12% S
• Increasing throughput, increases RT for ≥ 14% S
• For 14% S the RT is over 50 mins
• The autoclave is not constrained by RT at 14%
Conclusions
• Metsim a useful framework for plant optimisation/design
• Careful selection of chemistry and thermodynamic data
• Plant trial data for model calibration
• Modelling can assist in plant optimisation and future design