The gold processing industry is experiencing change. As free-milling and oxide ores become depleted, more complex polymetallic and refractory ores are being processed, coupled with increasing pressure for stricter environmental compliance. Recent years have also seen a steady reduction in mineral processing and metallurgy graduates and a gradual loss of older operating experience. A contribution to documenting current and future best practice in gold ore processing seems timely.
The focus of this volume is on advances in current gold plant operation, from conception to closure, chapters also cover innovations at the bench and pilot-scale level that would be expected to find commercial application at some stage. Sufficient coverage is also given to the chemistry and engineering aspects. The general principle behind the structure of the volume is that of flowsheeting based on unit operations and applied to a mineralogical classification of gold ore types. From concept to closure, this book covers all unit operations, mineralogies and processes that are relevant to dealing with today's complex orebodies.
Practical experience is vital to the successful development, operation and closure of any operation. The 42 chapters have been contributed by a total of 66 authors and co-authors who are experts from countries spanning the globe, and representing exhaustive practical knowledge covering many disciplines relevant to gold processing.
* Current best practice as elucidated by a select panel of experts in the field
* Innovations at the bench and pilot-scale level that would be expected to find commercial application at some stage
* Mineralogical-based approach to flowsheeting
The gold processing industry is experiencing change. As free-milling and oxide ores become depleted, more complex polymetallic and refractory ores are being processed, coupled with increasing pressure for stricter environmental compliance. Recent years have also seen a steady reduction in mineral processing and metallurgy graduates and a gradual loss of older operating experience. A contribution to documenting current and future best practice in gold ore processing seems timely.The focus of this volume is on advances in current gold plant operation, from conception to closure; chapters also cover innovations at the bench and pilot-scale level that would be expected to find commercial application at some stage. Sufficient coverage is also given to the chemistry and engineering aspects. The general principle behind the structure of the volume is that of flowsheeting based on unit operations and applied to a mineralogical classification of gold ore types. From concept to closure, this book covers all unit operations, mineralogies and processes that are relevant to dealing with today's complex orebodies.Practical experience is vital to the successful development, operation and closure of any operation. The 42 chapters have been contributed by a total of 66 authors and co-authors who are experts from countries spanning the globe, and representing exhaustive practical knowledge covering many disciplines relevant to gold processing.* Current best practice as elucidated by a select panel of experts in the field* Innovations at the bench and pilot-scale level that would be expected to find commercial application at some stage* Mineralogical-based approach to flowsheeting
Cover 2
Advances in Gold Ore Processing 4
Contributors 6
Table of Contents 10
Preface 14
Acknowledgements 18
List of Acronyms 20
List of Mineral Formulae 24
Gold – An historical introduction 26
Gold in Ancient Egypt 26
Early Gold-Mining Centers 27
Gold and Alchemy 29
Uses of Gold 30
Gilding 31
Gilding of metals 33
Gilding of glass and porcelain 33
Gold in the glass industry 34
Occurrence of Gold 35
Processing of Gold Ores 35
Gold panning 35
Amalgamation 36
Chlorination 38
Cyanidation 38
Refining of gold 42
Some recent trends in gold ore processing 42
Gold Standards and Assaying 43
Gold in Currency 44
Banks 45
Gold Museums 47
Suggested Reading 47
Part I. Project Development 50
I.1 Feasibility Study Management 51
Sampling procedures 52
Introduction 52
Sampling Basics 52
Importance of minimizing bias 53
Overall precision 53
Components of Sampling Error 54
Preparation error 54
Delimitation and extraction errors 55
Weighting and periodic quality fluctuation errors 55
Fundamental error and minimum sample mass 56
Percussion Hole Sampling 56
Blast-Hole Sampling 58
Plant Sampling 60
Sampling from Stationary Situations 65
Sampling from stockpiles 65
Sampling from trucks and railway wagons 65
Sampling from holding tanks and vessels 65
Sample Processing 67
Conclusions 67
References 68
Mineralogical investigation of gold ores 70
Gold Mineralogy 71
Gold minerals and alloys 71
Solid-solution gold 71
Colloidal gold 75
Surface gold 78
Forms and carriers of gold 79
Process Mineralogy of Gold 79
Gravity concentration 79
Floatability of gold minerals and carriers 80
Size and shape of gold grains 81
Silver content of native gold 82
Activators and depressants 84
Collector loading 85
Composition of gold mineral 85
Leachability of gold minerals 88
Cyanidation in leach tanks 88
Heap leaching 92
Other lixiviants 93
Response to oxidative pretreatment 94
Process mineralogy of gold from autoclave-CIL circuits 94
Process mineralogy of gold from roaster-CIL circuits 95
Process mineralogy of gold from bio-oxidized leach circuits 100
Response to ultrafine grinding CIL 102
Methodology for Studying Gold Minerals 104
Instrumental Analysis for Gold 107
Concluding Remarks 110
Acknowledgments 112
References 112
Process flowsheet selection 122
Introduction 122
Comminution Process Options 123
Overview 123
Ore characteristics 125
Throughput 125
Downstream process requirements 126
Operating cost 126
Free-Milling Ore Process Options 126
Overview 126
Site-specific issues 127
Gravity-recoverable gold 127
Treatment of high-silver ores 127
Complex Ore Process Options 128
Overview 128
Treatment of high-copper ores 128
Preg-robbing ores 130
Oxygen-consuming ores 130
Issues associated with mercury 131
Refractory Ore Process Options 132
Refractory Process Selection 132
Factors for consideration in Refractory Process Selection 134
Gold mineralogy 134
Arsenic content 135
Sulfide content 136
Gangue mineralogy 136
Ore variability 137
Project scale 138
Incremental gold recovery 138
Flotation performance 139
Site-specific environmental considerations 139
Project location and infrastructure 140
Water quality and availability 140
Power costs 140
Availability of neutralization reagents 141
Cyanide consumption and costs 141
Project life 141
Ability to pilot 142
Discussion 142
References 143
Metallurgical testwork: Gold processing options, physical ore properties and cyanide management 146
Background 146
Ore Preparation and Assessment 147
Mineralogical analysis 147
Physical analysis 149
Gravity concentration 149
Conventional jigs 150
Centrifugal jigs 150
Spirals 150
Mozley gravity separator (MGS) 150
Falcon and Knelson concentrators 150
Shaking tables 151
Super-panners 151
Cyanide leaching 151
Heap leaching 152
Recovery from solution 152
Cyanide speciation 153
Flotation 153
Filtration and settling 154
Cyanide detoxification 154
Refractory gold ores 154
References 155
Process simulation and modelling 158
Introduction 158
Benefits of Simulation 159
Alternatives to Computer Simulation 161
Experiment with the real plant operation 161
Build a physical model 161
Classification of Simulation Models 161
Steady-State Continuous Simulation 162
Comminution and size separation 163
Recovery of gold from ore 165
Dynamic Continuous Simulation 166
Dynamic Discrete Simulation 168
Computational Fluid Dynamics 168
The Future of Process Simulation 169
Feasibility study plant design 172
Introduction 172
General Site Issues 172
Crushing and Ore Storage 174
Crushing plant throughput 174
Operating schedule 174
Ore competence 176
Ore material handling properties 177
ROM and product size required 177
Requirements for blending and surge capacity 177
Environment 178
Grinding 179
Single or twin-stage 179
Feed and product size 180
Ore material handling properties 180
Pebble management 181
Power balancing 181
Slurry density, viscosity and specific gravity 182
Ball charging 182
Presence of gravity circuit 183
Spillage handling 183
Gravity Concentration 183
Gravity device location 184
Product destination 184
Water demand (Quality, volume and pressure) 185
Impact on water balance 185
Security 185
Leaching and Adsorption 186
Particle size 186
Slurry density and viscosity 186
Requirement for leach feed thickener 187
CIP or CIL 188
Number of stages 189
Aeration requirements 189
Bypassing requirements 189
Carbon movement 189
Bunding requirements 190
Barren carbon return 190
Leach tails thickener 190
Cyanide Detoxification and Tailings Disposal 190
Residence time 191
Number of stages in the process 191
Aeration and agitation requirements 191
Materials of construction 191
Tailings pumping 191
Elution and Gold Room 192
Type of elution circuit 192
One or two columns 193
Column location 193
Degree of automation 194
Gold room 194
Location of gold room 194
Complexity of gold room operations 194
Security 195
Flotation 195
Flotation slurry density 195
Residence time 195
Circuit configuration 196
Product destination 196
Wear and corrosion 196
Froth tenacity 197
Presence of an on-stream analyser (OSA) system 197
Refractory Ore Processing 197
Bio-oxidation 197
Pressure oxidation 198
Roasting 199
Services and utilities 199
Reagents 199
Power 200
Water 200
Air/oxygen 201
Fuel/diesel/gas 201
Special Issues for Large Facilities 201
Constructability 202
Pitfalls in Feasibility Design 202
I.2 Commissioning 206
Commissioning 207
Introduction 207
An Overview 208
Impact of Project Size, Contracting Strategy and Process Complexity 209
Contracting strategy 209
Lump sum turn key projects 210
EPC contracts 210
EPCM contracts 211
Project complexity 211
Project size 212
Commissioning Planning 212
When does commissioning start? 212
The planning process 212
Roles and responsibilities in plant commissioning 213
Packaging the commissioning process 217
Input from vendors 217
Safety considerations 217
Pre-Commissioning 218
Personnel 219
Testing sequence 219
Installation testing 220
No-load testing 220
Systems checks 220
Process Commissioning 221
Who commissions the plant? 221
Personnel selection 221
Water commissioning 222
Ore commissioning 223
Operations and maintenance training 223
What happens when things go wrong 224
Principal causes of poor commissioning outcomes 224
Performance Testing 224
Contractor warranties 224
Owner warranties 225
Process test completion 225
Post-Commissioning Optimization 226
Definitions 227
Acknowledgements 228
References 228
I.3 Safety, Process Control and Environmental Management 230
International cyanide management code 231
Background to the Code 231
Code Development and Administration 232
Code Content 234
Case Study – Operating Site Compliance Strategy 234
Verification and Certification 244
Practical Advice for Audit Teams 245
Practical Advice for Operating Sites Preparing for Audits 247
References 247
Process control 250
Measurements 251
Solids flow on a conveyor belt 251
Water flowrate 251
Slurry flowrate 251
Density of slurry in a pipe 252
Mill power 252
Slurry levels 252
Angle of hydrocyclone underflow spray 252
Particle size of milled product 252
Grade 253
Cyanide concentration 253
The Basics of Process Control 253
Actuators 253
Noise and signal conditioning 254
Proportional-integral control 254
Hierarchy 254
Simulation 255
Advanced Control and Optimization 255
Solids feed control 256
Crusher plant control 256
Mill circuit control 257
Thickener control 258
Carbon-in-pulp and carbon-in-leach control 258
Flotation 258
References 261
I.4 Closure and Rehabilitation 262
Closure and rehabilitation of gold-processing plants 263
Process Closure and Clean-Up 263
Relocation and Sale – Owner’s Perspectives 264
Relocation and Sale – The Marketing Manager’s Perspectives 267
Scrap, Recycle and Re-Use 268
Consideration of Heritage Values Prior to Closure and Decommissioning 268
Infrastructure Removal and Site Decommissioning 270
Closure Plant Sites – Contamination and Risk 274
Final Land Use and Rehabilitation – Plant Sites 276
Relinquishment 277
References 277
Closure and rehabilitation tailings storage facilities 282
Standards and Closure Criteria 282
Closure Preparation, Provisioning and Planning 284
Stakeholder Engagement and Acceptance of Plans 287
Decommission Planning, Rehabilitation, and Closure 289
Principal properties and difficulties 291
Erosion 291
Water management 291
Options in closure and rehabilitation strategies 292
Physical stabilization 292
Vegetative stabilization 292
Chemical amendments 293
Chemical stabilization 293
Combinations 293
Variability 293
Post-Closure Management, Monitoring and Relinquishment 294
Conclusions 297
References 298
Part II. Unit Operations 300
II.1 Comminution 301
Comminution circuits for gold ore processing 302
Introduction 302
Circuit Design Issues 303
Drilling and Blasting 305
Primary Crushing and Stockpile Management 308
SAG Mill Configuration and Operation 309
Lifter development 310
Pulp discharge 311
Grinding media size 313
Mill relines 314
SAG mill discharge classification 315
Pebble crushing 315
Ball-Mill Circuit Operation 319
Gold Recovery in Comminution Circuits 320
Process Control 322
Alternate Grinding Technologies 323
Ore Sorting 324
Acknowledgments 324
References 324
II.2 Concentration 328
Advances in gravity gold technology 329
Introduction 329
Economics 331
Non-Centrifuge Continuous Concentrators 333
Existing practice 333
Optimum yield and recovery 334
Testwork 335
Plant examples 336
Beaconsfield gold mine 336
St. Ives gold mine 337
Centrifuge Units 338
Existing practice 338
Testwork 341
Unit and flowsheet selection based on test results 342
Modelling for unit selection, circuit design and optimization 343
Gold Rooms: Tabling and Intensive Cyanidation 345
Table-based recovery 345
Intensive cyanidation 348
The batch inline leach reactor 349
Acacia reactor 350
Continuous inline leach reactor 351
Measuring Metallurgical Performance 352
Conclusions and Future Trends 354
References 354
Flotation of gold and gold-bearing ores 358
Background 358
Mineralogy 359
General aspects of gold flotation 359
Surface characteristics of pure gold 360
Collectorless Flotation of Naturally Occurring Gold 361
Collectors in Gold Flotation 361
Collector flotation of naturally occurring, placer and liberated gold 361
Flotation collectors for gold and gold carriers 361
Frothers in Gold Flotation 364
Activators in Gold Flotation 365
Metal salts 365
Sulfidization 367
Depression of Gold in Flotation 368
Selective depression of sulfide minerals 368
Depression of sulfide minerals with cyanide 369
Flotation of Gold and Gold-Bearing Minerals 370
Differential flotation of natural and liberated gold 370
Flotation of telluride minerals 370
Flotation of gold-carrying iron sulfides 371
Flotation of aurostibite, stibnite, and maldonite 371
Flotation of copper-gold ores 372
Influence of Conditions on Gold Flotation 372
Eh of the flotation pulp 372
Flotation gases and the impact of oxidation on flotation 374
Modification of pH for flotation 375
Particle size and shape in flotation 376
Flotation kinetics 376
Electrical double layer 377
Slime coatings and floatable non-sulfide gangue 377
Natural metal and organic coatings on gold 379
Flotation circuits 380
Flotation Practice 380
Refractory gold ores 381
Arsenopyrite, pyrrhotite and pyrite ores 381
Gold ores containing telluride minerals 382
Pyritic gold ores 383
Copper-gold ores 384
References 384
II.3 Oxidation of Sulfide Concentrates 394
Pressure oxidation overview 395
Introduction 396
Thermodynamic considerations 396
Kinetic considerations 398
Partial pressure and agitation 400
Environmental considerations 400
Pressure hydrometallurgy history 401
Gold Pressure Oxidation 404
Acidic Pressure Oxidation – Whole Ore 405
Geology and mining 405
Autoclave circuit 406
Alkaline Pressure Oxidation – Whole Ore 408
Geology and mining 408
Acid and Alkaline Autoclave – Comparison 410
Chemistry 410
Acid chemistry 410
Alkaline chemistry 411
Materials of construction 412
Operating cost 412
Acidic Pressure Oxidation – Concentrate 413
Pressure-Oxidation Summary 417
References 417
Bacterial oxidation of refractory gold concentrates 420
Introduction and Background 421
Current Bacterial-Oxidation Plant Design and Practice 424
Agitation, aeration and reactors 427
Bacterial-oxidation reagent consumption 429
Cyanide consumption of bacterially-oxidized residue 429
Reasons for high cyanide consumption 431
Process concepts to reduce cyanide consumption 433
Prevention and cure of polysulfide formation 433
Polysulfide process prevention – influence of bacterial-oxidation residence time 434
Polysulfide process prevention – influence of feed particle size 437
Polysulfide process prevention – bacterial-oxidation intermediate liquor removal 438
Polysulfide process prevention – effect of solid/liquid separation after bacterial oxidation 440
Polysulfide process cure – post-treatment of bacterial oxidation-residues to remove polysulfides prior to cyanidation 443
Brief Comparison of Bacterial Oxidation with Process Alternatives 443
Conclusions 445
Recommendations for Future Areas of Investigation 446
Ultra-fine grinding 447
Post-treatment techniques 447
Liquor stripping to enable operation at a higher pulp density 447
References 448
Roasting developments – especially oxygenated roasting 452
Rabble Roasters 454
Fluidized-Bed Roasters 455
Circulating Fluidized-Bed (CFB) Roasters 457
Oxygenated Roasters 459
Oxygenated Roasting 460
Introduction 460
Ore mineralogy 462
Roaster chemistry 462
Dry grinding 465
Roaster operation 466
Process design basis – roaster 469
Process design basis – roaster off-gas cleaning 474
References 479
Roasting of gold ore in the circulating fluidized-bed technology 482
History of Gold-Ore Circulating Fluid-Bed Roasting Technology 482
Theoretical Background of Roasting 483
Categories of fluidization reaction systems 484
The ’Classical’ bubbling fluidized bed or stationary fluidized bed 484
The ’expanded’ fluidized bed 484
The ’circulating’ fluidized bed 485
The flash reactor 485
Testing and plant design 485
Scale-up approach for circulating fluidized-bed systems 486
Some Advanced Metallurgical and Mineral Applications 487
Non-Gold roasting applications 487
Alumina calcination 487
Pre-heating, pre-reduction and direct reduction (DR) of iron-ore fines 488
Charring of high volatile-matter (VM)-containing coals with pre-reduction 488
Oxidation and pre-treatment of Ilmenite 489
Oxidation and reduction of laterite Nickel ores 489
Roasting of refractory gold - ores 489
Performance of Existing CFB Gold Roasters 492
Kalgoorlie Consolidated Gold mines – Gidji, Western Australia 492
Slurry-feed system 493
Roasting 494
Placer Dome – Cortez, Nevada 494
Roasting 494
Gas cleaning operation 495
Newmont Gold Company – Nevada 496
Ore pre-heating operation 496
Roasting operation 497
Gas-cleaning operation 498
Sulfuric acid plant 499
Newmont Gold Company – Minahasa, Indonesia 499
Roasting operation 499
Conclusions 501
Further Reading 501
II.4 Leaching 504
Heap leaching of gold and silver ores* 505
Introduction 505
What is heap leaching? 507
Why select heap leaching as the processing method? 507
Capital risk 508
Capital is very difficult or expensive to raise 508
Lack of sufficient reserves 508
Equal or better percent recovery 509
Differential recovery is not sufficient to justify added investment 509
Chemistry of gold and silver heap leaching 509
Factors Influencing Heap-Leach Efficiency 509
Type of ore 509
Carlin-type sedimentary ores 510
Low-sulfide acid volcanics or intrusives 510
Oxidized massive sulfides 510
Saprolites/laterites 510
Clay-rich deposits 511
Silver-rich deposits 511
Climate extremes 511
Heap permeability and flow efficiency 512
Recovery delay in multiple lift heaps 512
Solution application rate, cyanide strength and leach time 513
Design for Ambient Weather Conditions 513
Laboratory testing and control 513
Design for temperature extremes 514
Water balance 515
Solution application equipment 516
Leach pads and ponds 517
Valley fill heap leach 517
Pad construction cost 518
Mining, ore preparation and stacking 518
Agglomeration 520
Truck stacking 520
Conveyor stacking 521
Recovery of gold and silver from heap-leach solutions 521
Design considerations for reclamation and closure 523
Capital cost 524
Operating cost 524
Conclusions 524
Acknowledgements 525
References 526
Further Reading 526
Advances in the cyanidation of gold 528
Introduction 528
Mechanism of Cyanidation 529
Chemistry and electrochemistry 529
Reaction with sulfide minerals 531
Control Strategy for Cyanide, Oxygen and Lead Nitrate 535
Control of cyanide 535
Oxygen 537
Lead nitrate 539
Applications 541
Low-sulfide ore 541
Gold ore with pyrite and arsenopyrite 543
Gold ore with pyrrhotite 545
Conclusions 546
References 546
Alternative lixiviants to cyanide for leaching gold ores 550
Introduction 550
Stability of alternative lixiviants and gold complexes 552
Thiosulfate Leaching 553
Thiosulfate – process conditions 554
Thiosulfate – optimum conditions for leaching 554
Thiourea Leaching 555
Thiourea – process conditions 555
Thiourea – stabilizers 556
Thiourea – applications 557
Thiourea – current status 558
Halide Leaching 558
Halides – process conditions 559
Chlorine 560
Bromine 560
Iodine 561
Halides – applications 562
Halides – current status 562
Other halide processes 563
The MinataurTM process 563
Intec gold process 563
Oxidative Chloride Leach Processes 563
Oxidative chloride leach – process conditions 564
Platsolreg process 565
Oxidative chloride leach – current status 565
Sulfide/Bisulfide/Sulfite Leaching 566
Sulfide/bisulfide/sulfite leaching – process conditions 566
Nitrogen species catalysed pressure leaching process 568
Sulfide/bisulfide/sulfite leaching – applications 569
Sulfide/bisulfide/sulfite leaching – current status 569
Ammonia Leaching 570
Ammonia – process conditions 570
Ammonia – applications 571
Ammonia – current status 571
Bacterial and Natural Acid Leaching 571
Bacterial and natural acid – conditions 571
Bacterial and natural acid – current status 573
Thiocyanate Leaching 573
Thiocyanate – conditions 573
Thiocyanate – applications 574
Thiocyanate – current status 574
Recovery Processes 575
Economic Evaluation 575
Environmental Concerns 578
Conclusions 580
Acknowledgments 581
References 582
Thiosulfate as an alternative lixiviant to cyanide for gold ores 590
Introduction 590
Thiosulfate Chemistry 592
Mechanism of gold leaching 592
Kinetics of gold leaching 595
Decomposition of thiosulfate and polythionates 596
Passivation of gold 599
Leaching Studies with Ammoniacal Thiosulfate 599
Background and recent studies 599
Factors affecting gold recovery and optimum reagent composition 601
Environmental issues 602
Alternative thiosulfate systems 602
Summary and Conclusions 603
References 605
II.5 Gold Recovery 610
Carbon-in-pulp 611
Introduction 611
Early history of carbon use in gold recovery 611
The modern era of CIP 612
Activated Carbon 613
Carbon assessment methods 613
Kinetic activity 613
Gold-loading capacity 616
Attrition resistance (hardness) 616
Ball-pan hardness 616
Wet-attrition resistance 616
Particle-size distribution 617
Apparent density 617
Surface-area determination 617
BET technique 617
Iodine number 617
Carbon-tetrachloride activity 617
Ash content 617
Moisture content 617
Platelet content 618
Modelling Carbon-in-Pulp Circuits 618
Nicol and Fleming model 619
Stange model 619
Liebenberg and van Deventer 620
Circuit Design and Carbon Management Considerations 620
Number of adsorption stages 620
Pump cells and carousel circuits 622
Carbon residence time 624
Effect of carbon activity on soluble gold loss and carbon inventory 625
Effect of carbon distribution on soluble gold loss 626
Effect of barren-carbon grade on soluble gold loss 627
Carbon usage rate 627
Target gold loading on carbon 629
Gold-loading distribution 630
Carbon transfer 631
Conclusions 632
Acknowledgments 632
References 632
Zinc cementation 638
Introduction 638
Chemistry 638
History 640
Application 641
High silver/gold ratio 641
High mercury content 641
Other applications 642
Basic flowsheet 642
Equipment 644
Clarification 644
De-aeration 644
Zinc cementation 645
Precipitate filtration 645
Precipitate handling and treatment 646
Design criteria 646
Operations 648
South Africa 648
Canada 648
USA 648
Mexico 648
South America 648
Other 649
Advances 649
References 650
Resin-in-pulp and resin-in-solution 652
Introduction 652
Solution Chemistry of Cyanided Gold Pulps 653
Development of Gold-Selective Resins 654
Strong-base resins 655
Medium-base resins 656
Weak-base resins 656
Other resin types 657
Elution of Different Resin Types 657
Elution of minix strong-base resin 657
Elution of AM-2B resin 658
Elution of AuRIXreg resin 659
Elution of conventional strong-base resins (A161 L, A161RIP, Vitrokele 912) 660
Resin Evaluation Techniques 662
Mini-column loading tests 662
Counter-current ion-exchange tests 663
Equilibrium isotherm 663
Kinetics 665
Simulation of an adsorption circuit 667
Resin strength and durability 668
Relative Cost Comparison of RIP vs. CIP 671
Recovery of Gold from Preg-Robbing Ores 673
Resin-in-Solution 675
Minix 675
AuRIXreg 676
RIP Plants 678
Golden Jubilee Mine, South Africa 678
Penjom Gold Mine, Malaysia 678
Muruntau, Uzbekistan 680
Barbrook Gold Mine, South Africa 680
Conclusions 681
References 681
Electrowinning 686
Background 686
Historical Developments 688
Electrowinning Cell Design 689
Early designs 689
Cell types in use in Australia 689
Cells for pressurized elution circuits 690
Cathode design 691
Multiple-cathode parallel-plate electrowinning cells 691
Wound single-layer wrapped cathodes 691
Woven stainless-steel cathodes - plate and replate cells 692
Pressure-cleaned systems for stainless-steel cathodes 693
Pressure-jetting bullion-sludge removal 693
Gangued cathode and anode arrays 694
Ultrasonic bullion removal 694
Pressurized electrowinning cells 694
Rotating-cathode electrowinning cells with in-cell pressure bullion removal 695
Special Applications 695
Electrowinning from gravity concentrates 695
Direct electrowinning from biologically oxidized filtered leach solutions 695
Key Aspects of Electrowinning Cell Design and Operation 696
Gold to steel-wool loading ratio 696
Limiting linear velocity 696
Cell flowrate and required cross-sectional area 696
Current requirements 696
Current-density limitations 697
Impact of type of elution system 697
Number of cathodes required 697
Solution by-pass 698
Plate attachment and the role of silver and copper 698
Electrical connections (resistivity, material selection and fire) 698
Automatic current-control rectifiers 699
Health hazards 700
Acknowledgments 700
References 700
Recent advances in gold refining technology at Rand Refinery 702
Introduction 702
Evaluation 705
The High-Speed Silver-Electrolysis Plant Operation 707
Gold Electrolysis 710
Rand Refinery Smelter Operations 715
Small-Bar Plant 717
Certification and Accreditation 718
References 718
II.6 Disposal of Residues and Effluents 720
Cyanide treatment: Physical, chemical and biological processes 721
Introduction 721
Cyanide Management Plan 722
Analysis of Cyanide 723
Biological Cyanide Destruction Processes 724
Chemical Treatment Processes 729
Alkaline chlorination process 729
Sulfur dioxide and air process 731
Copper-catalysed hydrogen peroxide process 732
Caro’s acid process 733
Iron-cyanide precipitation 734
Activated carbon polishing 736
Other cyanide-treatment processes 737
Natural Cyanide Attenuation 738
Treatment of Cyanide-Related Compounds 740
Thiocyanate treatment 740
Cyanate treatment 741
Ammonia treatment 742
Nitrate treatment 744
Effluent Standards 745
Summary 747
References 748
Cyanide recovery 752
Introduction 753
Theoretical Background 754
Practical Considerations 756
Process Alternatives 758
Direct recovery without preconcentration, by tailings-solution recycling 758
Direct recovery by the SART process 758
Direct recovery by the AVR process 761
Indirect recovery with preconcentration by ion-exchange resins 763
Cyanide recovery by RIP using zinc complexation (zinc cyanide process) 764
Cyanide recovery by RIP extraction of copper cyanide 768
The AuGMENT process 768
The Hannah process 771
Environmental, Social, Health and Safety Benefits of Cyanide Recycling 772
Conclusions 774
References 774
Tailings storage facilities 778
Evolution of Tailings Management 778
Past Failures 780
Constraints and Drivers 780
Public perceptions and politics 780
Legislation 781
Tailings Characterization 781
Physical characterization 782
Particle size distribution 782
Atterberg limits 783
Settling and drying properties 783
Permeability 783
Consolidation behaviour 784
Shear strength 784
Beach evaporation 785
Rheology 785
Piezocone investigations 785
Geochemical characterization 786
Static testing 786
Kinetic testing 786
Risk-Based Design 787
Recent Major Advances 789
Water reduction 790
’Dry’ tailings 791
Centrally thickened discharge 791
Backfill 791
In-pit storage 792
Lining of tailings storage facilities 792
Management of acid mine drainage 793
TSF Completion or Closure 794
Safety 794
Stability 795
Aesthetic acceptability 795
Future Possibilities 796
Paste 796
Co-disposal of mine wastes 797
Geotubes 798
High-sulfur management 798
References 799
Retreatment of gold residues 802
Introduction 802
Evaluation Phases 803
Scouting 803
Pre-feasibility study 804
Sampling and Metallurgical Testwork 804
Sample preparation 805
Assaying 806
Metallurgical testwork 806
Evaluation 807
Flowsheet development 807
Tonnage and grade calculation 808
Size distribution 809
General observations 809
Financial evaluation 810
Infrastructure requirements 810
Environmental costs 811
Operating costs 811
Operational Phase 812
Reclamation methods overview 812
Slime reclamation by hydraulic re-mining 813
Starting a reclamation operation 815
Reclamation technique 815
Monitor guns 817
Screening 818
Pump stations 819
Pipelines 820
Water balance 821
Reclamation guidelines 822
Sand reclamation and milling 823
Hydraulic reclamation 823
Mechanical reclamation of sand 823
Milling of sand 824
Metallurgical Treatment 824
Slime treatment with no pyrite recovery 824
Slime treatment with pyrite recovery 827
Sand treatment 829
Environmental Rehabilitation 829
Process Flowsheets 830
Acknowledgments 832
Further Reading 832
Part III. Case Study Flowsheets 836
III.1 Polymetallic Ores 837
Gold-copper ores 838
Chemistry of Copper Cyanides 838
Copper– cyanide complexes 840
Solubility of copper minerals in cyanide solutions 842
Reactions of copper minerals in cyanide solutions 843
Dissolution of gold and copper in cyanide solutions 844
Preg-robbing of gold onto copper and copper minerals 844
Effect of copper– cyanide complexes on the gold cyanidation process 845
Effect of sulfides with copper on the gold cyanidation process 846
Gold Recovery 847
Merrill– Crowe process 849
Carbon-in-pulp and Carbon-in-leach process 849
Processes for Treating High-Copper Gold Ores 850
Use of ammonia for minimization of the effect of copper 851
Plant experience using ammonia 854
Copper and Cyanide Recovery Processes 857
Sulfide-precipitation processes 857
MNR process 858
Sulfidization– acidification– recycling– thickening process 858
Cutech process 858
Sceresini process 859
CyanoMet R process 861
CyanisorbTM process 861
Ion-exchange technologies –- Resins 862
Oretek CPC process 862
VitrokeleTM 862
Elutech process 863
Augment process 863
Hannah process 864
Ion-exchange technologies –- solvents 864
Electrowinning 867
Alternative Lixiviants 868
Thiosulfate leaching 868
References 869
Case study flowsheets: copper–gold concentrate treatment 874
Introduction 874
Background – Sulfide Leaching 878
Copper–Gold Concentrate Treatment Processes 881
Total pressure-oxidation process 883
BIOCOPTM process 886
Outokumpu HydrocopperTM process 887
Anglo American Corporation/University of British Columbia copper process 889
PLATSOL® process 891
Application to copper– gold ores 892
Conclusions 892
References 894
Processing of high-silver gold ores 898
Introduction 898
Fundamentals 898
Flowsheet Selection 903
Heap leaching 903
Slurry processes 903
Leaching 904
Gold recovery on carbon 904
Gold recovery by Merrill– Crowe 906
Indicative Plant Design Criteria 907
Acknowledgments 908
References 908
Recovery of gold as by-product from the base-metals industries 910
Introduction 910
Recovery of Gold in Copper Smelters 911
Noranda CCR refinery 912
The Outokumpu Pori refinery 912
Phelps Dodge El Paso refinery 913
Recovery of Gold as a By-Product from Nickel Sulfide Ores 915
Inco 917
Falconbridge 921
Norilsk 922
Recovery of Gold in Zinc Smelters 925
Roast-leach-electrowinning 926
Sherritt Gordon zinc pressure-leaching (ZPL) 927
Smelting of the zinc leach residue 929
Recovery of Gold from Lead Concentrates 929
Smelting processes 929
Hydrometallurgy for lead concentrates 932
Recovery of Gold from Cobalt Concentrates 934
Recovery of Gold from the Recycling of Electronic Scrap 935
Direct Leaching of Gold and PGMs from Ores or Concentrates 935
The BHP TML process 937
The North American palladium process 937
The PLATSOLTM process 938
Conclusions 940
References 940
Extraction of gold from platinum group metal (PGM) ores 946
1. Primary Extraction Circuits 946
2. Gold Extraction from Secondary Sources 948
Processing high-grade gold alloys 950
Refining gold–PGM alloys 950
Gold– copper alloys 950
Low-grade Cu– Au–PGM 951
Low-grade sweeps 952
Traditional methods 952
Modern low-grade circuits 953
Hydrometallurgical Gold Processes in Precious Metal Refineries 955
Dissolution of concentrates and alloys 956
Selective gold extraction and recovery from complex PGM solutions 957
Selective reduction of gold in PGM solutions 957
Selective solvent extraction of gold from PGM solutions 959
Gold solvent extraction with dibutyl carbitol 961
Gold solvent extraction with MIBK 962
Gold solvent extraction with 2-ethyl hexanol 963
Ion exchange 963
Conclusions 964
References 964
III.2 Refractory Ores 968
Refractory sulfide ores – case studies 969
Introduction 969
Sansu Project, Ashanti Goldfields Corporation (Ghana) 970
Kanowna Belle Project (Western Australia) 975
Macraes Gold Project (New Zealand) 980
References 983
Preg-robbing gold ores 986
Introduction 986
Carbonaceous Matter and Gold Adsorption 991
Chemical characteristics 991
Adsorption phenomena 993
Treatment of Carbonaceous Ore 998
Activated carbon-in-leach (CIL) and resin-in-leach (RIL) 999
Blinding or blanking 1000
Roasting 1001
Chlorination 1002
Pressure oxidation 1003
Nitric acid treatment 1004
Microbial deactivation 1005
Thiosulfate leaching 1005
Non-Carbonaceous Preg-Robbing 1007
Examples of Plant Practice 1008
Practical Ore Characterization 1010
References 1012
Treatment of gold-telluride ores 1022
Introduction 1022
Tellurium-bearing ores and materials 1022
Toxicity 1023
Assaying 1023
Historical Treatment Methods 1024
Cripple Creek 1024
Kalgoorlie 1025
Kirkland Lake 1026
Fiji 1027
Recent Research 1028
Milling 1028
Flotation 1028
Cyanide leaching – testwork results 1028
Cyanide leaching – theoretical considerations 1030
Other oxidative processes 1031
References 1032
Treatment of antimonial gold ores 1034
Introduction 1034
Fundamentals 1034
Commercial Operations 1036
Hillgrove 1037
Consolidated Murchison 1037
New Plant Design 1038
References 1039
III.3 Summary of Gold Plants and Processes 1042
Summary of gold plants and processes 1043
Introduction 1043
Summary of Gold Plants and Processes 1043
Conclusions 1044
Subject Index 1064
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