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Modelling of Macraes POX Circuit

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

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Modelling of Macraes POX Circuit

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  1. Modelling of Macraes POX Circuit May 2006

  2. Acknowledgements OceanaGold GRD Minproc Brent Hill Tony Frater David King Quenton Johnston Nevin Scagliotta Adrian Marin

  3. Presentation Outline • Background • Macraes POX circuit • Integration of Reefton concentrates • Modelling • Metsim model calibration • Model prediction of increased throughput • Conclusion/Recommendation

  4. Belo Horizonte Office Johannesburg Office

  5. 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

  6. 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

  7. 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

  8. Macraes Processing Issues 2 • Newmont technology required for “controlled” POX • Limestone for free acid control • Washing for chlorides • Scale formation in autoclave

  9. 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

  10. Autoclave Scaled Agitator

  11. 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

  12. Reefton / Macraes Integration • Additional S oxidation requirement • Oxygen plant constraint • Autoclave retention time constraint • Differing POX conditions • Requirement for modelling to optimise capacity

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. Plant Trials in 10/04 and 01/05

  19. 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%

  20. Plant Trials in 07/05

  21. 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

  22. The Final Kinetic Curve Used for Scenario Modelling

  23. 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

  24. Scenario Modelling Results

  25. 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%

  26. 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

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