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
2009
Thulane Phiri
South Deep Gold Mine
Metallurgical Plant
2009
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
5
HCl
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
&Sump
Tailings
CarbonMake-up
Tank
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/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
● TK4 Cyanide addition Set Point 90ppm
TAC 2000
● Leach TK 1
● TK1 Cyanide addition Set Point 200ppm
● TK4 Cyanide addition Set Point 90ppm
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
TK 2
● 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
TK 2
DO levels in each tank
0.00
2.00
4.00
6.00
8.00
10.00
12.00
0 1 2 3 4 5 6 7
Tank
DO
(ppm
)
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
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0 1 2 3 4 5 6 7
Tanks
DO
(ppm
)
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
days
cons
umpt
ion
(kg/
t)
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
days
cons
umpt
ion
(kg/
t)
Cyanide consumed (kg/t ) Linear (Cyanide consumed (kg/t ))
NaCN (kg/t)
0.000
0.100
0.200
0.300
0.400
0.500
0.600
12-May-08 17-May-08 22-May-08 27-May-08 01-Jun-08 06-Jun-08C
onsu
mpt
ion
(kg/
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
● Cyanide consumption during P1 was 0.366kg/t and was 0.270kg/t during P2
Solution profile
91.5
92
92.5
93
93.5
94
94.5
95
95.5
0 1 2 3 4 5 6 7Tanks
Sol
utio
n Au
(%)
Solution Profile After Oxygen addition
Solution profile
91.5
92
92.5
93
93.5
94
94.5
95
95.5
0 1 2 3 4 5 6 7Tanks
Sol
utio
n Au
(%)
Solution Profile After Oxygen addition
Solution profile
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0 1 2 3 4 5 6
Tanks
Solu
ition
Rec
over
y (%
)
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
● During P1 and P2 there was a rapid increase in dissolution of gold within the first three tanks which resulted in increased leach kinetics
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
13-Mar 23-Mar 02-Apr 12-Apr 22-Apr 02-May 12-May 22-May 01-Jun 11-Jun 21-Jun 01-Jul
Days
Gra
de (g
/t)
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
10
20
30
40
50
60
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
H2O
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
500
1000
1500
2000
2500
3000
3500
4000
0 20 40 60 80 100 120
Pow
er (W
)
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
● 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
0 20 40 60 80 100 120 140
%W
AD C
N
Retention Time (minutes)
% WAD CN in Tailing Sample
20% 40% 60% 80% 100%
0
20
40
60
80
100
120
0 20 40 60 80 100 120 140
%W
AD C
N
Retention Time (minutes)
Average Ultracept Underflow % WAD CN
20% 40% 60% 80% 100%
● Ultracep underflow WAD cyanide was reduced by 94.6% at 60% power consumption
● 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
● Ultracep overflow WAD cyanide was reduced by 94.7% at 20% power consumption
0
20
40
60
80
100
120
0 20 40 60 80 100 120 140
%W
AD C
N
Retention Time (minutes)
Average Ultracep Overflow Material WAD CN %
20% 40% 60% 80% 100%
0
20
40
60
80
100
120
0 20 40 60 80 100 120 140
%W
AD C
N
Retention Time (minutes)
Average Underground Material WAD CN %
20% 40% 60% 80% 100%
● Backfill to underground WAD cyanide was reduced by 94.5% at 60% power consumption
● Backfill to underground WAD cyanide was reduced by 94.5% at 60% power consumption
0
20
40
60
80
100
120
0 20 40 60 80 100 120 140
%W
AD C
N
Retention Time (minutes)
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
Cost
● Operating cost associated with ozone to be further investigated
Advantages of the ozone includes
● Rapid WAD cyanide destruction
● No formation of harmful off gases
Cost
● 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?
