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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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acknowledgements
Acknowledgements

OceanaGold

GRD Minproc

Brent Hill

Tony Frater

David King

Quenton Johnston

Nevin Scagliotta

Adrian Marin

presentation outline
Presentation Outline
  • Background
  • Macraes POX circuit
  • Integration of Reefton concentrates
  • Modelling
  • Metsim model calibration
  • Model prediction of increased throughput
  • Conclusion/Recommendation
slide4

Belo Horizonte Office

Johannesburg Office

slide7

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
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
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
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
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
slide13

Autoclave

Scaled Agitator

reefton processing
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
slide15

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
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 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
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 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
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 high throughput trials in 07 05
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%
model to predict various scenarios
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
scenario modelling results
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
scenario modelling results28
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
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