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Modeling of Gold Leaching with Thiosulphate Solutions in Different Types of Reactor
Andrzej Kraslawski and Ilkka Turunen (Editors) Proceedings of the 23rd European Symposium on Computer Aided Process Engineering – ESCAPE 23, June 9-12, 2013, Lappeenranta, Finland 1045 © 2013 Elsevier B.V. All rights reserved.
Modeling of Gold Leaching with Thiosulphate Solutions in Different Types of Reactor Vladimir Zhukov, a,b Yury Sharikov, b Ilkka Turunen, a a
Department of Chemical Technology, Lappeenranta University of Technology, P. O. Box 20, 53851 Lappeenranta, Finland b Department of Automation of Technological Processes and Production, National Mineral Resources University, 21st liniya, Vasilievskiy Ostrov 2, 199106, SaintPetersburg, Russia
Abstract Gold leaching process with thiosulphate solutions is an important process of considerable significance for environmental and economic aspects of sustainability. Thiosulphate leaching helps reduce risks of environmental pollution in comparison with cyanidation, thus limiting negative societal effects, but complexity of the process chemistry still requires investigation and modeling. The objective of this work is to create models of gold leaching in various types of rectors. The results show that batch reactor model fits to experimental data, continuous reactor model allows utilizing it in scheme of series of apparatuses and cascade reactor model makes it possible to evaluate optimal number of reactors in series. Keywords: modeling, thiosulphate, gold, leaching.
1. Introduction This study is carrying out within the bounds of progress of international co-operation between National Mineral Resources University and Lappeenranta University of Technology and is a part of “Green Mining” Programme which is supported by Tekes (LUT, 2012; Tekes, 2012). Thiosulphate gold leaching as a technology has number of potential advantages as proved by numerous scientific articles (Aylmore and Muir, 2001; Breuer and Jeffrey, 2003; Feng and van Deventer, 2002; Grosse et al., 2003). This technology might finally replace the cyanidation completely, when environmental legistlation will be tightened. The technology has been implemented in industrial scale in Kazakhstan at gold beneficiation complex at the Kumystinskoe Pole (Begalinov, 2008). A disadvantage of the thiosulphate process is high reagent consumption which weakens the economy of process. Therefore optimization of reactor conditions is important, and a detailed model is a powerful tool for that.
2. Process description Thiosulphate gold leaching runs in the reactors at the thiosulphate solutions with addition ions of ammonia and copper (II) and aeration. Gold generates stable anionic complex with thiosulphate by following reaction (Hilson and Monhemius, 2006): 1 3 (1) 2 Au O2 4S 2 O3 H 2 O 2 Au ( S 2 O3)32 2OH 2
1046
V. Zhukov et al.
According numerous publications of scientific reports thiosulphate gold leaching represents electrochemical reaction of gold oxidation with formation of anionic on the one hand and reduction of bivalent copper Cu(NH3)42+ to Cu(S2O3)35- univalent copper on the other hand (Aylmore and Muir, 2001). General scheme of process can be described by reactions given below (Aylmore and Muir, 2001): ° Au Au e (2) ® 2 3 Au S 2 O3 2 °¯ Au 2S 2 O3 2 °Cu NH 3 4 e Cu NH 3 2 2 NH 3 (3) ® 2 5 Cu NH 3 S O Cu S O 2 NH ° 3 2 2 3 2 3 3 3 ¯ 2 2 5 2 (4) 2Cu NH 3 4 8S 2 O3 2Cu S 2 O3 3 S 4 O6 8NH 3
3. Material description An industrial concentrate which has been oxidized to sulphur removal was taken for investigation of kinetics. Particular elemental composition determined is presented in the table below: Table 1. Elemental composition of concentrate. Element
Content
Element
g/t
% (mass)
Ag
12.01
0.0045
As
50030.00
Au
Content g/t
% (mass)
Mn
105.20
0.0396
18.8227
Mo
3.28
0.0012
32.24
0.0121
Ni
67.40
0.0254
Cd
1.92
0.0007
Pb
83.82
0.0315
Co
30.30
0.0114
S
56130.00
21.1177
Cr
69.34
0.0261
Sb
590.30
0.2221
Cu
138.20
0.0520
Zn
102.30
0.0385
Fe
158400.00
59.5945
The mean diameter of particles is 10 microns. It was sized up by granulometric analysis at the Lappeenranta University of Technology by particle size analyzer LS™ 13 320 MW of Beckman Coulter. The detailed results are shown in the table below:
Modeling of Gold Leaching with Thiosulphate Solutions in Different Types of Reactor
1047
Table 2. Granulometric composition of concentrate. Distribution
Particle size, μm
< 10 %
1.152
< 25 %
2.449
< 50 %
5.285
< 75 %
9.605
< 90 %
16.393
4. Experimental part Thiosulphate gold leaching was carried out in 1 L laboratory batch reactor with mechanical mixing device at the atmospheric pressure. Design of reactor makes it possible to feed air or nitrogen from the bottom. Following sensors were installed at the cover plate: 1 – sensor of pulp temperature in the reactor, 2 – pH and oxidationreduction potential sensors, 3 – dissolved oxygen sensor. The bottom of reactor is equipped by sampling device for interim analysis of pulp samples during leaching process. A schematic picture of the experimental system is shown below: 1 2
3
4
6
7
8
5
Figure 1. Scheme of the experimental setup. 1 – mixing device with a drive, 2 – temperature control and indication system, 3 – pH or oxidation-reduction potential sensor, 4 – dissolved oxygen sensor, 5 – sampling device, 6 – gas feed control and indication system, 7 and 8 – gas vessels air and nitrogen correspondingly.
Laboratory experiments were carried out at different conditions. Concentrations of components in the system, volumetric flow rate of feed gas, mixing speed of pulp in the reactor were defined as scaleable factors. Other process parameters also have been specified. pH in a range from 9 to 10, mean diameter of the particles 10 μm, density of suspension 40 w.% and initial volume of reactor loading 0.85 L were constant factors.
5. Analysis The analysis and treatment of the samples was done right after they were obtained from the reactor. Suspension sample from the reactor was filtrated in vacuum. 120·10-6 L of filtrate was diluted to 100 mL by distilled water for analysis of copper concentration and 5·10-3 L for analysis of gold and silver concentration by atomic absorption spectrometer
1048
V. Zhukov et al.
(AAS) iCE 3300 AA of Thermo Scientific. Right after filtration solid particles were washed by distilled water and dried in the oven at 70 ºC for following analysis and storage. Other part of filtrate in the amount of 120·10-6 L has been diluted to 100 mL by distilled water for analysis of sulphate and thiosulphate ions by liquid ion chromatography in the module system Advanced IC of Metrohm AG. According to previous experiments with the same concentrate, residence time of 3 hours is sufficient for leaching (Sharikov et al., 2012). Experimental data confirm the conclusion of Sharikov et al. (2012) that process can be divided into two stages: “fast” and “slow”: about 40 % of gold have already leached for the initial 20 – 25 minutes after beginning the process. Further process is going with considerably slow speed. It can be noted that the results of process behavior show necessity of frequent sampling: ones in 15-25 minutes, especially during the first hour of leaching. It can clarify system character at the initial stage of extraction.
6. Modeling In ReactOp Cascade 3.20 software there is Estimation subprogram which allows the determination of vector of kinetic parameters based on experimental data according to necessary conditions in minimal miscoordination of experimental and calculated data. These data were taken from solution of kinetic equation system by numerical integration of kinetic differential equations. In the capacity of integration method has been utilized LSODA – method of numerical calculation which is allowed to solve system of ordinary differential equations with automatic method switching for stiff and nonstiff problems that corresponds to different reaction rates simultaneously occurs reactions. For the determination of minimal miscoordination point quickest descent method has been utilized. Comparison of experimental and calculated data is shown in Fig.2. 100
80
Conversion, %
60
40
20
0
0
50
100 Time, min
150
200
Figure 2. An example of comparison experimental and calculated data (experiment 7).
Modeling of Gold Leaching with Thiosulphate Solutions in Different Types of Reactor
1049
It can be shown from Fig. 2 that miscoordination of experimental and expected data stands in the accuracy of experimental data. Model adequacy with estimated constants has been acknowledged by statistical analysis. Therefore, kinetic model can be utilized for scale investigation of the process in industrial conditions. Mathematical model of thiosulphate gold leaching has been developed by using model of ideal mixing for description of flow structure in the apparatus with industrial size: dC j v Cf j C j R j ° (5) V ® dt °¯T T t Solution of combined equations system (5) has been performed by utilization of stationary phase method. For that goal dynamic model of transient process has been solved by numerical integration in ReactOp Cascade 3.20 software. Figure 3 presents curves of transient process in the flow reactor calculated in ReactOp Cascade 3.20 software: 100
80
Conversion, %
60
40
20
0 0
500
1e3
1,5e3
Time, min
Figure 3. Transient process in the flow reactor.
Cascade reactor model has been created by utilizing model of CSTR derived in ReactOp Cascade 3.20 software. Influence of reactor volume sectionalization to finite conversion of the process has been investigated. Results of that investigation is presented in the table below:
1050
V. Zhukov et al.
Table 4. Influence of reactor volume sectionalization to finite conversion of the process. Number of reactors
Volume of each reactor, m3
1
1
93,16
2
0,5
91,33
98,15
3
0,33
89,63
97,76
99,37
4
0,25
88,03
97,27
99,27
99,77
5
0,2
86,51
96,73
99,12
99,74
Max conversion, %
99,92
Results from table 4 show that reactor volume sectionalization has beneficial effect of finite conversion. Optimal number of reactors is from 3 to 5 because further increasing of apparatus number is unreasonably and is not get essential results according to gold conversion.
7. Conclusions The model of batch reactor based on the obtained laboratory data was created. It seems to represent successfully gold leaching with thiosulphate solutions. Scaled model of the continuous reactor was developed to describe the industrial mode. Cascade model was designed based on the continuous reactor model and can be utilized for estimation of process efficiency. The presented models for batch, continuous and cascade of reactors give possibility to create a control system of gold leaching with thiosulphate solutions.
References Aylmore, M.G. and Muir, D.M., 2001, Thiosulphate leaching of gold – a review, Minerals Engineering – 14, 2, 135-174. Begalinov, A.B., Medeuov Ch.K. and Abdullaev O.T., 2008, Thiosulphate leaching of gold (industrial experience), Gorny Journal 3, 50-52. Breuer, P. and Jeffrey, M., 2003, A Review of the Chemistry, Electrochemistry and Kinetics of the Gold Thiosulfate Leaching Process, Proc. 5th Int. Conf. : Hydrometallurgy 2003. —TMS, Vancouver (Canada), 1, 139–154. Feng, D. and van Deventer, J.S.J., 2002, Leaching Behaviour of Sulphides in Ammoniacal Thiosulphate Systems, Hydrometallurgy, 63(2), 189-200. Grosse A., Dicinoski G., Shaw M. and Haddad P., 2003, Leaching and Recovery of Gold Using Ammoniacal Thiosulfate Leach Liquors (a review), Hydrometallurgy, 69, 1–21. Hilson, G. and Monhemius A.J., 2006, Alternatives to cyanide in the gold mining industry: what prospects for the future?, Journal of Cleaner Production, 14, 1158 – 1167. LUT, Cooperation with Russia in the Green Mining Programme [e-document] [retrieved 15.01.2013], From: http://www.lut.fi/en/lut/news/2012/pages/cooperation-with-russia-in-thegreen-mining-programme.aspx Sharikov, F.Y., Zhukov, V.V. and Lampinen, M., 2012, Investigation of Gold Oxidized Leaching Process from Concentrate of Base Ore by utilization Calve Calorimetry. Problem Definition and First Results, Material Investigation by Utilization Methods of Thermal Analysis, Calorimetry and Gas Trapping, International Conference Reports, Saint-Petersburg: - Poltorak, 59-61. Tekes, Green Mining – Projects [e-document] [retrieved 15.01.2013], From: http://www.tekes.fi/programmes/GreenMining/Projects?id=10673726
Modeling of Gold Leaching with Thiosulphate Solutions in Different Types of Reactor Vladimir Zhukov, a,b Yury Sharikov, b Ilkka Turunen, a a
Department of Chemical Technology, Lappeenranta University of Technology, P. O. Box 20, 53851 Lappeenranta, Finland b Department of Automation of Technological Processes and Production, National Mineral Resources University, 21st liniya, Vasilievskiy Ostrov 2, 199106, SaintPetersburg, Russia
Abstract Gold leaching process with thiosulphate solutions is an important process of considerable significance for environmental and economic aspects of sustainability. Thiosulphate leaching helps reduce risks of environmental pollution in comparison with cyanidation, thus limiting negative societal effects, but complexity of the process chemistry still requires investigation and modeling. The objective of this work is to create models of gold leaching in various types of rectors. The results show that batch reactor model fits to experimental data, continuous reactor model allows utilizing it in scheme of series of apparatuses and cascade reactor model makes it possible to evaluate optimal number of reactors in series. Keywords: modeling, thiosulphate, gold, leaching.
1. Introduction This study is carrying out within the bounds of progress of international co-operation between National Mineral Resources University and Lappeenranta University of Technology and is a part of “Green Mining” Programme which is supported by Tekes (LUT, 2012; Tekes, 2012). Thiosulphate gold leaching as a technology has number of potential advantages as proved by numerous scientific articles (Aylmore and Muir, 2001; Breuer and Jeffrey, 2003; Feng and van Deventer, 2002; Grosse et al., 2003). This technology might finally replace the cyanidation completely, when environmental legistlation will be tightened. The technology has been implemented in industrial scale in Kazakhstan at gold beneficiation complex at the Kumystinskoe Pole (Begalinov, 2008). A disadvantage of the thiosulphate process is high reagent consumption which weakens the economy of process. Therefore optimization of reactor conditions is important, and a detailed model is a powerful tool for that.
2. Process description Thiosulphate gold leaching runs in the reactors at the thiosulphate solutions with addition ions of ammonia and copper (II) and aeration. Gold generates stable anionic complex with thiosulphate by following reaction (Hilson and Monhemius, 2006): 1 3 (1) 2 Au O2 4S 2 O3 H 2 O 2 Au ( S 2 O3)32 2OH 2
1046
V. Zhukov et al.
According numerous publications of scientific reports thiosulphate gold leaching represents electrochemical reaction of gold oxidation with formation of anionic on the one hand and reduction of bivalent copper Cu(NH3)42+ to Cu(S2O3)35- univalent copper on the other hand (Aylmore and Muir, 2001). General scheme of process can be described by reactions given below (Aylmore and Muir, 2001): ° Au Au e (2) ® 2 3 Au S 2 O3 2 °¯ Au 2S 2 O3 2 °Cu NH 3 4 e Cu NH 3 2 2 NH 3 (3) ® 2 5 Cu NH 3 S O Cu S O 2 NH ° 3 2 2 3 2 3 3 3 ¯ 2 2 5 2 (4) 2Cu NH 3 4 8S 2 O3 2Cu S 2 O3 3 S 4 O6 8NH 3
3. Material description An industrial concentrate which has been oxidized to sulphur removal was taken for investigation of kinetics. Particular elemental composition determined is presented in the table below: Table 1. Elemental composition of concentrate. Element
Content
Element
g/t
% (mass)
Ag
12.01
0.0045
As
50030.00
Au
Content g/t
% (mass)
Mn
105.20
0.0396
18.8227
Mo
3.28
0.0012
32.24
0.0121
Ni
67.40
0.0254
Cd
1.92
0.0007
Pb
83.82
0.0315
Co
30.30
0.0114
S
56130.00
21.1177
Cr
69.34
0.0261
Sb
590.30
0.2221
Cu
138.20
0.0520
Zn
102.30
0.0385
Fe
158400.00
59.5945
The mean diameter of particles is 10 microns. It was sized up by granulometric analysis at the Lappeenranta University of Technology by particle size analyzer LS™ 13 320 MW of Beckman Coulter. The detailed results are shown in the table below:
Modeling of Gold Leaching with Thiosulphate Solutions in Different Types of Reactor
1047
Table 2. Granulometric composition of concentrate. Distribution
Particle size, μm
< 10 %
1.152
< 25 %
2.449
< 50 %
5.285
< 75 %
9.605
< 90 %
16.393
4. Experimental part Thiosulphate gold leaching was carried out in 1 L laboratory batch reactor with mechanical mixing device at the atmospheric pressure. Design of reactor makes it possible to feed air or nitrogen from the bottom. Following sensors were installed at the cover plate: 1 – sensor of pulp temperature in the reactor, 2 – pH and oxidationreduction potential sensors, 3 – dissolved oxygen sensor. The bottom of reactor is equipped by sampling device for interim analysis of pulp samples during leaching process. A schematic picture of the experimental system is shown below: 1 2
3
4
6
7
8
5
Figure 1. Scheme of the experimental setup. 1 – mixing device with a drive, 2 – temperature control and indication system, 3 – pH or oxidation-reduction potential sensor, 4 – dissolved oxygen sensor, 5 – sampling device, 6 – gas feed control and indication system, 7 and 8 – gas vessels air and nitrogen correspondingly.
Laboratory experiments were carried out at different conditions. Concentrations of components in the system, volumetric flow rate of feed gas, mixing speed of pulp in the reactor were defined as scaleable factors. Other process parameters also have been specified. pH in a range from 9 to 10, mean diameter of the particles 10 μm, density of suspension 40 w.% and initial volume of reactor loading 0.85 L were constant factors.
5. Analysis The analysis and treatment of the samples was done right after they were obtained from the reactor. Suspension sample from the reactor was filtrated in vacuum. 120·10-6 L of filtrate was diluted to 100 mL by distilled water for analysis of copper concentration and 5·10-3 L for analysis of gold and silver concentration by atomic absorption spectrometer
1048
V. Zhukov et al.
(AAS) iCE 3300 AA of Thermo Scientific. Right after filtration solid particles were washed by distilled water and dried in the oven at 70 ºC for following analysis and storage. Other part of filtrate in the amount of 120·10-6 L has been diluted to 100 mL by distilled water for analysis of sulphate and thiosulphate ions by liquid ion chromatography in the module system Advanced IC of Metrohm AG. According to previous experiments with the same concentrate, residence time of 3 hours is sufficient for leaching (Sharikov et al., 2012). Experimental data confirm the conclusion of Sharikov et al. (2012) that process can be divided into two stages: “fast” and “slow”: about 40 % of gold have already leached for the initial 20 – 25 minutes after beginning the process. Further process is going with considerably slow speed. It can be noted that the results of process behavior show necessity of frequent sampling: ones in 15-25 minutes, especially during the first hour of leaching. It can clarify system character at the initial stage of extraction.
6. Modeling In ReactOp Cascade 3.20 software there is Estimation subprogram which allows the determination of vector of kinetic parameters based on experimental data according to necessary conditions in minimal miscoordination of experimental and calculated data. These data were taken from solution of kinetic equation system by numerical integration of kinetic differential equations. In the capacity of integration method has been utilized LSODA – method of numerical calculation which is allowed to solve system of ordinary differential equations with automatic method switching for stiff and nonstiff problems that corresponds to different reaction rates simultaneously occurs reactions. For the determination of minimal miscoordination point quickest descent method has been utilized. Comparison of experimental and calculated data is shown in Fig.2. 100
80
Conversion, %
60
40
20
0
0
50
100 Time, min
150
200
Figure 2. An example of comparison experimental and calculated data (experiment 7).
Modeling of Gold Leaching with Thiosulphate Solutions in Different Types of Reactor
1049
It can be shown from Fig. 2 that miscoordination of experimental and expected data stands in the accuracy of experimental data. Model adequacy with estimated constants has been acknowledged by statistical analysis. Therefore, kinetic model can be utilized for scale investigation of the process in industrial conditions. Mathematical model of thiosulphate gold leaching has been developed by using model of ideal mixing for description of flow structure in the apparatus with industrial size: dC j v Cf j C j R j ° (5) V ® dt °¯T T t Solution of combined equations system (5) has been performed by utilization of stationary phase method. For that goal dynamic model of transient process has been solved by numerical integration in ReactOp Cascade 3.20 software. Figure 3 presents curves of transient process in the flow reactor calculated in ReactOp Cascade 3.20 software: 100
80
Conversion, %
60
40
20
0 0
500
1e3
1,5e3
Time, min
Figure 3. Transient process in the flow reactor.
Cascade reactor model has been created by utilizing model of CSTR derived in ReactOp Cascade 3.20 software. Influence of reactor volume sectionalization to finite conversion of the process has been investigated. Results of that investigation is presented in the table below:
1050
V. Zhukov et al.
Table 4. Influence of reactor volume sectionalization to finite conversion of the process. Number of reactors
Volume of each reactor, m3
1
1
93,16
2
0,5
91,33
98,15
3
0,33
89,63
97,76
99,37
4
0,25
88,03
97,27
99,27
99,77
5
0,2
86,51
96,73
99,12
99,74
Max conversion, %
99,92
Results from table 4 show that reactor volume sectionalization has beneficial effect of finite conversion. Optimal number of reactors is from 3 to 5 because further increasing of apparatus number is unreasonably and is not get essential results according to gold conversion.
7. Conclusions The model of batch reactor based on the obtained laboratory data was created. It seems to represent successfully gold leaching with thiosulphate solutions. Scaled model of the continuous reactor was developed to describe the industrial mode. Cascade model was designed based on the continuous reactor model and can be utilized for estimation of process efficiency. The presented models for batch, continuous and cascade of reactors give possibility to create a control system of gold leaching with thiosulphate solutions.
References Aylmore, M.G. and Muir, D.M., 2001, Thiosulphate leaching of gold – a review, Minerals Engineering – 14, 2, 135-174. Begalinov, A.B., Medeuov Ch.K. and Abdullaev O.T., 2008, Thiosulphate leaching of gold (industrial experience), Gorny Journal 3, 50-52. Breuer, P. and Jeffrey, M., 2003, A Review of the Chemistry, Electrochemistry and Kinetics of the Gold Thiosulfate Leaching Process, Proc. 5th Int. Conf. : Hydrometallurgy 2003. —TMS, Vancouver (Canada), 1, 139–154. Feng, D. and van Deventer, J.S.J., 2002, Leaching Behaviour of Sulphides in Ammoniacal Thiosulphate Systems, Hydrometallurgy, 63(2), 189-200. Grosse A., Dicinoski G., Shaw M. and Haddad P., 2003, Leaching and Recovery of Gold Using Ammoniacal Thiosulfate Leach Liquors (a review), Hydrometallurgy, 69, 1–21. Hilson, G. and Monhemius A.J., 2006, Alternatives to cyanide in the gold mining industry: what prospects for the future?, Journal of Cleaner Production, 14, 1158 – 1167. LUT, Cooperation with Russia in the Green Mining Programme [e-document] [retrieved 15.01.2013], From: http://www.lut.fi/en/lut/news/2012/pages/cooperation-with-russia-in-thegreen-mining-programme.aspx Sharikov, F.Y., Zhukov, V.V. and Lampinen, M., 2012, Investigation of Gold Oxidized Leaching Process from Concentrate of Base Ore by utilization Calve Calorimetry. Problem Definition and First Results, Material Investigation by Utilization Methods of Thermal Analysis, Calorimetry and Gas Trapping, International Conference Reports, Saint-Petersburg: - Poltorak, 59-61. Tekes, Green Mining – Projects [e-document] [retrieved 15.01.2013], From: http://www.tekes.fi/programmes/GreenMining/Projects?id=10673726