CYANIDE OPTIMIZATION AND THE USE OF OZONE FOR WAD CYANIDE ... Documentation... · CYANIDE...

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CYANIDE OPTIMIZATION AND THE CYANIDE OPTIMIZATION AND THE USE OF OZONE FOR WAD CYANIDE USE OF OZONE FOR WAD CYANIDE

DESTRUCTIONDESTRUCTION

South Deep Gold Mine

Metallurgical Plant

Thulane Phiri

South Deep Gold Mine

Metallurgical Plant

Thulane Phiri

AGENDAAGENDA

1. Introduction2. Metallurgical Plant3. ICMI Code and Implications4. Initiatives

4.1. Cyanide Reduction4.1.1. Oxidation Trial4.1.2. Two Stage cyanide control

4.2. WAD Cyanide Destruction4.2.1. Hydrogen Peroxide (H2O2) Trial4.2.2. Ozone Trial

5. Conclusion

1. Introduction2. Metallurgical Plant3. ICMI Code and Implications4. Initiatives

4.1. Cyanide Reduction4.1.1. Oxidation Trial4.1.2. Two Stage cyanide control

4.2. WAD Cyanide Destruction4.2.1. Hydrogen Peroxide (H2O2) Trial4.2.2. Ozone Trial

5. Conclusion

1. INTRODUCTION 1. INTRODUCTION

● Gold Fields South Deep is Located in the South West Rand

● New gold plant was commissioned in 2002

● Design capacity of 220 000 t/month

● The mining method by Trackless mining

● Gold recovery achieved by Milling, Classification (cyclones),Gravity gold, Thickening, Leaching, CIP, Elution, Electro-wining and Smelting

● Gold Fields South Deep is Located in the South West Rand

● New gold plant was commissioned in 2002

● Design capacity of 220 000 t/month

● The mining method by Trackless mining

● Gold recovery achieved by Milling, Classification (cyclones),Gravity gold, Thickening, Leaching, CIP, Elution, Electro-wining and Smelting

2. METALLURGICAL PLANT2. METALLURGICAL PLANT

Stockpile

SAG Mill Feed Belt

SAG Mill

WoodchipDe-watering

Screen

WoodchipRemoval Screens

Floc Plant HR Thickener &

Underflow Pumps

Leach Tanks

Cyanide Tanks

Water Storage Tanks & Pumps

Lime DosageTank

CIPPumpCellPlant

LoadedCarbon Screen

TailingsScreen

Tailings

CarbonMake-up

CarbonSizingScreen

Sized Carbon Transfer Vessel

Rotary Kiln

Regenerated CarbonTransfer Vessel

ElutionColumn

EluateStorage Tanks

Cyclone Cluster

Knelson Feed Screen

Ball Mill

SAG MillDischarge Screens & Sump

Water Tanks

NaOHNaCN

Pebble Hopper

SludgeReactors

Plate & Frame Filters

SludgeTanks

KnelsonConcentrators

Calciners

InductionFurnace

GeminiTable

NewCarbon

BULLION

SOUTH DEEP GOLD PLANT PROCESS FLOW

Reject Pebbles

Pebble RejectConveyer

Thickener Overflow

Eluted CarbonScreen

● In the year 2000 the ICMI (International Cyanide Management Institute) Code was developed after an accidents in Baia Mare

● Mines that are compliant with the ICMI code they have to implement the Principles and Standard of practice

- Production- Transportation- Handling and storage- Operation- Decommissioning- Workers safety- Emergency response- Training- Dialogue

● In the year 2000 the ICMI (International Cyanide Management Institute) Code was developed after an accidents in Baia Mare

● Mines that are compliant with the ICMI code they have to implement the Principles and Standard of practice

- Production- Transportation- Handling and storage- Operation- Decommissioning- Workers safety- Emergency response- Training- Dialogue

3. ICMI CODE3. ICMI CODE AND IMPLICATIONSAND IMPLICATIONS

● Gold Fields South Deep Gold Mine has been certified as fully compliant with the ICMI Code as from the 1 April 2009

● The Metallurgical Plant had to demonstrate that it has implement programs, procedures and practises as required by ICMI

● Principle 4: Standard of Practice 4.2 of the code “Has the operation introduced management and operating systems to minimize cyanide use, thereby limiting concentrations of cyanide in mill tailings”

● Standard of Practice 4.6.3 “Has the potential impacts to workers health and the beneficial uses of ground water been evaluated and have been measures been implemented as necessary to address them?”

● Gold Fields South Deep Gold Mine has been certified as fully compliant with the ICMI Code as from the 1 April 2009

● The Metallurgical Plant had to demonstrate that it has implement programs, procedures and practises as required by ICMI

● Principle 4: Standard of Practice 4.2 of the code “Has the operation introduced management and operating systems to minimize cyanide use, thereby limiting concentrations of cyanide in mill tailings”

● Standard of Practice 4.6.3 “Has the potential impacts to workers health and the beneficial uses of ground water been evaluated and have been measures been implemented as necessary to address them?”

Cyanide AdditionCyanide Addition and Monitoringand Monitoring

Leach Tanks

Cyanide Tanks

Tailings Screen & Sump

Make up Tank

Shaft Backfill Storage Tank

TK 21 TK 22

Ultracepts

Spillage Tank

Backfill Tailings Tank

Slimes DamTSF

Make up Water Tank

O/F O/F

U/FCyclone Cluster

Lime Dosage Tank

Areas of concern (UndergroundAreas of concern (Undergroundand Slimes dam)and Slimes dam)

● Possibility of HCN gassing● No CN monitors● “Cyanide tracking underground as a function of backfill seepage”

P. W. Lotz

● Possibility of HCN gassing● No CN monitors● “Cyanide tracking underground as a function of backfill seepage”

P. W. Lotz

Cyanide Addition Cyanide Addition

TAC 2000

● Leach TK 1

● TK1 Cyanide addition Set Point 200ppm

TAC 2000

● Leach TK 1

WAD 1000 (Plant and Backfill)

● Pump● Probe at Tailings Sump

● Analyser for Analysis and Data collection

WAD 1000 (Plant and Backfill)

● Pump● Probe at Tailings Sump

● Analyser for Analysis and Data collection

WAD Cyanide MonitoringWAD Cyanide Monitoring

4. INITIATIVES 4. INITIATIVES 4.1. CYANIDE REDUCTION4.1. CYANIDE REDUCTION

4.1.1.O4.1.1.Oxidation Trial xidation Trial

● Oxygen from Air Products was used to improve

- Recoveries- Leach kinetics- Dissolved oxygen levels- Lower cyanide consumption

● First phase of the trial- Oxygen added in TK 1 together with cyanide and lime

● Second phase- Pre-Oxidation in TK 1 leach tank prior to adding cyanide and Lime in

● Oxygen from Air Products was used to improve

- Recoveries- Leach kinetics- Dissolved oxygen levels- Lower cyanide consumption

● First phase of the trial- Oxygen added in TK 1 together with cyanide and lime

● Second phase- Pre-Oxidation in TK 1 leach tank prior to adding cyanide and Lime in

DO levels in each tank

0 1 2 3 4 5 6 7

Average DO levels

4 Au + 8 CN- + O2 + 2 H2O = 4 Au(CN)-2 + 4 OH-

● The DO level during P1 was <4.2ppm and during P2 the DO levels increased in TK 1 and TK 2 to 10.02ppm and 7.16ppm

4 Au + 8 CN- + O2 + 2 H2O = 4 Au(CN)-2 + 4 OH-

● The DO level during P1 was <4.2ppm and during P2 the DO levels increased in TK 1 and TK 2 to 10.02ppm and 7.16ppm

DO levels in each tank

0 1 2 3 4 5 6 7

Average DO levels

NaCN (kg/t)

0.0000

0.1000

0.2000

0.3000

0.4000

0.5000

0.6000

15-Sep-07

20-Sep-07

25-Sep-07

30-Sep-07

05-Oct-07

10-Oct-07

15-Oct-07

20-Oct-07

25-Oct-07

30-Oct-07

04-Nov-07

Cyanide consumed (kg/t ) Linear (Cyanide consumed (kg/t ))

NaCN (kg/t)

0.0000

0.1000

0.2000

0.3000

0.4000

0.5000

0.6000

15-Sep-07

20-Sep-07

25-Sep-07

30-Sep-07

05-Oct-07

10-Oct-07

15-Oct-07

20-Oct-07

25-Oct-07

30-Oct-07

04-Nov-07

Cyanide consumed (kg/t ) Linear (Cyanide consumed (kg/t ))

NaCN (kg/t)

12-May-08 17-May-08 22-May-08 27-May-08 01-Jun-08 06-Jun-08C

t)Cyanide consumed (kg/t) Linear (Cyanide consumed (kg/t))

● Cyanide consumption during P1 was 0.366kg/t and was 0.270kg/t during P2

Solution profile

0 1 2 3 4 5 6 7Tanks

Solution Profile After Oxygen addition

Solution profile

0 1 2 3 4 5 6 7Tanks

Solution Profile After Oxygen addition

Solution profile

100.00

120.00

0 1 2 3 4 5 6

Solution Au (%) Log. (Solution Au (%))

● During P1 and P2 there was a rapid increase in dissolution of gold within the first three tanks which resulted in increased leach kinetics

13-Mar 23-Mar 02-Apr 12-Apr 22-Apr 02-May 12-May 22-May 01-Jun 11-Jun 21-Jun 01-Jul

Solution Washed residue Linear (Washed residue) Linear (Solution)

● The increase in residue resulted in increase cyanide set point● During P2 residues dropped for both solution and washed solids and

that resulted in cyanide addition set points from 350ppm to 180ppm

● The increase in residue resulted in increase cyanide set point● During P2 residues dropped for both solution and washed solids and

that resulted in cyanide addition set points from 350ppm to 180ppm

● Phase 1 results- Oxygen trial improved

- Dissolved Oxygen levels

- No changes in cyanide consumption

- Leach profiles indicated faster leach kinetics

● Phase 2 results

- Pre-oxidation resulted in reduction in cyanide consumption from 0.366 kg/t to 0.270kg/t

- Increased leach kinetics

- Dissolved oxygen levels

- Leach could be operated with less tanks resulting in reduction in gold lock up and maintenance cost

- Cyanide set point was reduced from 350ppm to 180ppm

● Phase 1 results- Oxygen trial improved

- Dissolved Oxygen levels

- No changes in cyanide consumption

- Leach profiles indicated faster leach kinetics

● Phase 2 results

- Pre-oxidation resulted in reduction in cyanide consumption from 0.366 kg/t to 0.270kg/t

- Increased leach kinetics

- Dissolved oxygen levels

- Leach could be operated with less tanks resulting in reduction in gold lock up and maintenance cost

- Cyanide set point was reduced from 350ppm to 180ppm

● The aim

- Optimize the cyanide addition at the Leach circuit

- To reduce cyanide cost

- Reducing the WAD cyanide leaving the Plant to < 50ppm as required by the ICMI

● The cyanide is dosed at TK 1 using TAC 2000

- Cyanide set point in TK 1 is 200ppm and at TK 4 is 90ppm

- The WAD Cyanide leaving the Plant is currently 28ppm which is bellow ICMI requirement of 50ppm WAD

● The aim

- Optimize the cyanide addition at the Leach circuit

- To reduce cyanide cost

- Reducing the WAD cyanide leaving the Plant to < 50ppm as required by the ICMI

● The cyanide is dosed at TK 1 using TAC 2000

- Cyanide set point in TK 1 is 200ppm and at TK 4 is 90ppm

- The WAD Cyanide leaving the Plant is currently 28ppm which is bellow ICMI requirement of 50ppm WAD

4.1.2. Two Stage cyanide control 4.1.2. Two Stage cyanide control

● TK 4 has been identified as the cyanide second stage addition point● The installation of the second stage at TK 4 has been completed● The cyanide reduction should impact the WAD cyanide to levels lower than

28ppm thus reducing cyanide consumption and cost

● TK 4 has been identified as the cyanide second stage addition point● The installation of the second stage at TK 4 has been completed● The cyanide reduction should impact the WAD cyanide to levels lower than

28ppm thus reducing cyanide consumption and cost

Leach Tanks

Cyanide Tanks

Lime DosageTank

CIP Tanks

4.2. WAD CYANIDE DESTRUCTION4.2. WAD CYANIDE DESTRUCTION

4.2.1. Hydrogen Peroxide (H4.2.1. Hydrogen Peroxide (H22OO22) Trial) Trial

● The aim- Determine the effectiveness of Hydrogen peroxide (H2O2) with regard

to WAD cyanide destruction to levels <20ppm- Determine if Hydrogen peroxide could be used as an alternative to

Ferrous sulphate that is currently used

Fe+2 + 6 CN- + ¼ O2 + H+ = Fe(CN)-36 + ½ H20

4 Fe+2 + 3 Fe(CN)-36 + ½ O2 + H+ = Fe4[Fe(CN)6]3 + ½ H20

● The test works were done Plant scale and Lab scale

● The aim- Determine the effectiveness of Hydrogen peroxide (H2O2) with regard

to WAD cyanide destruction to levels <20ppm- Determine if Hydrogen peroxide could be used as an alternative to

Ferrous sulphate that is currently used

Fe+2 + 6 CN- + ¼ O2 + H+ = Fe(CN)-36 + ½ H20

4 Fe+2 + 3 Fe(CN)-36 + ½ O2 + H+ = Fe4[Fe(CN)6]3 + ½ H20

● The test works were done Plant scale and Lab scale

Table 2: WAD destruction results summary using Hydrogen Peroxide Test 1 Test 2 Test 3 Test 4 Test5

Density of Slurry (kg/l) 1.82 1.6 1.75 1.751.92

Volume of Slurry (l) 215000 5 5 596000

Mass of Slurry (kg) 391300 8 8.75 8.75

184320

Density of Hydrogen peroxide (kg/l) 1.2 1.2 1.2 1.2 1.2

Volume of Hydrogen peroxide (l) 150 0.5 0.05 0.01200

Mass of Hydrogen peroxide (kg) 180 0.6 0.06 0.012240

Consumption (kg/t) 0.46 75.00 6.86 1.371.30

Duration (hr) 32 2 2 2 2

WAD first value (ppm) 52.8 19.6 23.6 21.631.5

WAD Last value (ppm) 20.1 0.1 2.7 4.33.3

Efficiency 61.9 99.5 88.6 80.189.52

Cost per ton (R/t) 3.86 629.38 57.54 11.51 10.93

0 2 4 6 8 10 12 14 16 18 20

Sample number

WAD (ppm

3.5 l/min day 1 day 2 Linear (3.5 l/min)

● The results indicates that WAD cyanide was best reduced in Test 2 followed by 3 and 4 although Hydrogen peroxide consumption was high for Test 2, 3 than 4

CN- + H2O2 = OCN- + H2O

● Hydrogen Peroxide does reduce the WAD cyanide levels to <5ppm in 2 hours

● The results indicates that WAD cyanide was best reduced in Test 2 followed by 3 and 4 although Hydrogen peroxide consumption was high for Test 2, 3 than 4

CN- + H2O2 = OCN- + H2O

● Hydrogen Peroxide does reduce the WAD cyanide levels to <5ppm in 2 hours

● It was concluded- Hydrogen Peroxide does reduce the WAD cyanide levels to even

<5ppm effectively- Hydrogen Peroxide can be used as an alternative to ferrous

sulphate

● It was recommended- Attempts be made to lower consumptions to minimize operational

cost - WAD Cyanide be destroyed at Metallurgical Plant Tailings to levels

<50ppm

● It was concluded- Hydrogen Peroxide does reduce the WAD cyanide levels to even

<5ppm effectively- Hydrogen Peroxide can be used as an alternative to ferrous

sulphate

● It was recommended- Attempts be made to lower consumptions to minimize operational

cost - WAD Cyanide be destroyed at Metallurgical Plant Tailings to levels

<50ppm

4.2.2. Ozone Trial 4.2.2. Ozone Trial

● The cyanide destruction using Ozone is done to reduce the WAD cyanide leaving the Plant to Slimes dam and Underground

● The Ozone is a powerful oxidant and highly destructive toward WAD cyanide according to Lab test results

CN- + O3 (aq) = OCN- + O2 (aq) 1

3CN- + O3 (aq) = 3 OCN- 2

OCN- + 3O3 (aq) + H2O = 2HCO3- + N2 (g) + 3O3 (aq) 3

● These are initiatives taken to protect the people and the environment

● The cyanide destruction using Ozone is done to reduce the WAD cyanide leaving the Plant to Slimes dam and Underground

● The Ozone is a powerful oxidant and highly destructive toward WAD cyanide according to Lab test results

CN- + O3 (aq) = OCN- + O2 (aq) 1

3CN- + O3 (aq) = 3 OCN- 2

OCN- + 3O3 (aq) + H2O = 2HCO3- + N2 (g) + 3O3 (aq) 3

● These are initiatives taken to protect the people and the environment

Ozone skid/generation Ozone skid/generation

Feed Sample

Sampling Point

Discharge Point

Pressure/Vacuum Vessel O2 O2 O3

Oxygen Storage Tank

Oxygen Generator

WEDECO

Oxygen Buffer Vessel

VSA Generator WEDECO Ozone Generator

Mixing vessel

Oxygen Buffer Vessel

VSA Generator WEDECO Ozone Generator

Mixing vessel

● The Ozone Trial was planned for 3 months at following streams

Backfill Tailings to Slime dam

Backfill to underground

Ultracep underflow

Ultracep overflow

Spent sample

● WAD cyanide was analysed using WAD 1000

● The Ozone Trial was planned for 3 months at following streams

Backfill Tailings to Slime dam

Backfill to underground

Ultracep underflow

Ultracep overflow

Spent sample

● WAD cyanide was analysed using WAD 1000

Relationship between Power (W) and Power consumption % is linear Relationship between Power (W) and Power consumption % is linear

AchievementAchievement

0 20 40 60 80 100 120

Power consumption %

Relationship between Power consumption % and Ozone concentration Relationship between Power consumption % and Ozone concentration

Power consumption %

Ozone concentration (g/m3)

20 2440 4460 5980 73100 80

● WAD cyanide reduction of 98.7% for the slurry pumped from Backfill Tailings to Slimes dam at 60% power consumption

0 20 40 60 80 100 120 140

Retention Time (minutes)

% WAD CN in Tailing Sample

20% 40% 60% 80% 100%

0 20 40 60 80 100 120 140

Average Ultracept Underflow % WAD CN

20% 40% 60% 80% 100%

● Ultracep underflow WAD cyanide was reduced by 94.6% at 60% power consumption

● Ultracep overflow WAD cyanide was reduced by 94.7% at 20% power consumption

0 20 40 60 80 100 120 140

Average Ultracep Overflow Material WAD CN %

20% 40% 60% 80% 100%

0 20 40 60 80 100 120 140

Average Underground Material WAD CN %

20% 40% 60% 80% 100%

● Backfill to underground WAD cyanide was reduced by 94.5% at 60% power consumption

0 20 40 60 80 100 120 140

Spent Electrolyte %WAD CN

60% 80% 100%

•Spent sample WAD cyanide was reduced by 92% at 80% power consumption•Spent sample WAD cyanide was reduced by 92% at 80% power consumption

● Ozone trial was successful in WAD cyanide destruction for all the streamstested as >92% destruction at optimum condition

● Alternative method to destroy WAD cyanide

● WAD levels < 50ppm at all times

● Ozone trial was successful in WAD cyanide destruction for all the streamstested as >92% destruction at optimum condition

● Alternative method to destroy WAD cyanide

● WAD levels < 50ppm at all times

Advantages of the ozone includes

● Rapid WAD cyanide destruction

● No formation of harmful off gases

● Operating cost associated with ozone to be further investigated

Advantages of the ozone includes

● Rapid WAD cyanide destruction

● No formation of harmful off gases

● Operating cost associated with ozone to be further investigated

5. CONCLUSION5. CONCLUSION

● South Deep has achieved WAD <50ppm

● Compliant with the ICMI Code

● Reduced and maintained cyanide addition levels from 0.366kg/t to 0.270kg/t

● Initiatives successful in WAD cyanide destruction to lower levels

● Alternative in both cyanide reduction and WAD cyanide destruction

● Prepared for the future changes in legislation

● South Deep has achieved WAD <50ppm

● Compliant with the ICMI Code

● Reduced and maintained cyanide addition levels from 0.366kg/t to 0.270kg/t

● Initiatives successful in WAD cyanide destruction to lower levels

● Alternative in both cyanide reduction and WAD cyanide destruction

● Prepared for the future changes in legislation

QUESTIONS?QUESTIONS?

CYANIDE OPTIMIZATION AND THE USE OF OZONE FOR WAD CYANIDE ... Documentation... · CYANIDE...

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