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Promotion of copper electrolyte self-purification with antimonic oxides
Hydrometallurgy 175 (2018) 28–34
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Promotion of copper electrolyte self-purification with antimonic oxides a
a,⁎
a
a
Xingming Wang , Xuewen Wang , Biao Liu , Mingyu Wang , Huaguang Wang Shengfan Zhoua a b
a,b
MARK a
, Xuehui Liu ,
School of Metallurgy and Environment, Central South University, Changsha 410083, China Department of Materials Science and Engineering, Michigan Technological University, Houghton, MI 49931, USA
A R T I C L E I N F O
A B S T R A C T
Keywords: Copper electrolyte Self-purification Promotion Antimonic oxides Reuse
The promotion of copper electrolyte self-purification with antimonic oxides was studied. It was found that the mixed oxides of Sb(III) and Sb(V) can be used to promote copper electrolyte self-purification. The mixture of Sb2O3·xH2O and Sb2O5·xH2O with Sb(V)/Sb(III) molar ratio 0.05 was used to promote the self- purification of copper electrolyte containing 353.21 g/L H2SO4, 19.38 g/L Cu, 20.88 g/L As, 2.29 g/L Sb and 1.51 g/L Bi. Experimental results show that the removal of impurities As, Sb and Bi from copper electrolyte mainly depends on the ratio of the molar number of arsenic in the electrolyte to the molar number of antimony in the promoter, namely the As/Sb mole ratio. When the promoter was added into the electrolyte with the As/Sb mole ratio 1:0.7 at 60 °C stirring for 0.5 h, the removal efficiencies of As, Sb and Bi are 62.0%, 93.0% and 95.0% respectively. Then the As and Bi were separated from the used promoter by adding it into 2 mol/L Na2CO3 stirring for 0.5 h at above 60 °C in pH 8–9. After filtration, the regenerated promoter was obtained by washing the filter cake with diluted sulfuric acid, and the As and Bi were separated from the regenerated solution by crystallizing Na3AsO4·12H2O at room temperature, and by precipitating Bi2O3·xH2O under the pH above 12, respectively.
1. Introduction As long as copper electrorefining has been commercially applied, the purification of copper electrolyte has received much attention since the impurities As, Sb and Bi are dissolved with Cu from the anode into the electrolyte during electrorefining due to the similarity of their standard reduction potentials to that of Cu (Zhao, 1981). The traditional method used to remove As, Sb and Bi from copper electrolyte is to electrodeposit them with copper (Navarro et al., 1999; Wan, 2010; Peng et al., 2012b). But the method has a number of drawbacks, e.g., high energy consumption and evolution of toxic arsine gas. Therefore, many other methods have been proposed to remove the impurities from copper electrolyte, such as adsorption of Sb and As using ion exchange (Cunnigham et al., 1997; Mckevitt and Dreisinger, 2009; Riveros, 2010; Salari et al., 2017), removal of Sb and Bi by solvent extraction (Navarro et al., 1999), co-precipitation of Bi and Sb by adding a carbonate of barium, strontium, or lead (Hyvarinen, 1979), and reduction and crystallization of As with SO2 (Zheng et al., 2012). However, these methods can only be used as auxiliary measures for the purification of copper electrolyte, and they cannot completely replace the electrodeposition method (Wang, 2003). It is well known that during copper electrorefining, a portion of As, Sb and Bi dissolved from the anode can spontaneously precipitate from ⁎
the electrolyte into the anode slime (Wang et al., 2011a; Wang et al., 2011b). What is more, the amounts of them deposited into the anode slime depend on their content in the anode, their concentrations in the electrolyte and the electrorefining conditions (Eichrodt and Schloen, 1954; Braun et al., 1976). This indicates that As, Sb and Bi in copper electrolyte have a certain self-purification ability. It has been found that copper electrolyte self-purification can be significantly improved by adjusting the relative content of Sb in the anode and increasing the concentration of As in the electrolyte (Wang, 2003; Wang et al., 2008). It has been found that the increase in copper electrolyte self-purification is limited, since during commercial operation, it is difficult to change the relative content of Sb in the anode at will, and the concentration of As in the electrolyte cannot be increased without restraint. But the self-purification of As, Sb and Bi in copper electrolyte can be promoted with some compounds containing antimony or arsenic and bismuth (Wang et al., 2003; Zheng et al., 2008; Xiao et al., 2011). This indicates that the self-purification of copper electrolyte can be divided into direct self-purification and indirect self-purification. Direct selfpurification is the spontaneous precipitation of As, Sb and Bi in the electrolyte during copper electrorefining, (Wang et al., 2008), while indirect self-purification is to promote their precipitation with compounds containing antimony or arsenic and bismuth (Wang et al., 2014).
Corresponding author. E-mail address: [email protected] (X. Wang).
http://dx.doi.org/10.1016/j.hydromet.2017.10.028 Received 10 April 2017; Received in revised form 25 October 2017; Accepted 25 October 2017 Available online 27 October 2017 0304-386X/ © 2017 Elsevier B.V. All rights reserved.
Hydrometallurgy 175 (2018) 28–34
X. Wang et al.
self-purification. For each experimental run, 250 mL of the electrolyte was mixed with the promoter under stirring in a 500 mL beaker. The beaker was placed in a water bath at about 60 °C to promote electrolyte self-purification. At the end of the self-purification process, the suspension was separated by filtration, and the filtrate and the used promoter were sampled for analysis. The used promoter (15 g) was mixed with water under stirring in a 250 mL beaker with the desired liquid-solid (L/S) ratio (from 2:1 mL/g to 6:1 mL/g). The beaker was placed in a water bath at the desired temperature (≥60 °C) to regenerate the promoter. During the regeneration, the solution pH was adjusted with NaOH and/or Na2CO3. After the pH was adjusted to the desired value (8–9), the solution was stirred for scheduled time (0.5–1.5 h), the regeneration was ended. By filtration and washing with 0.5 mol/L H2SO4, the regenerated promoter was obtained. The As was removed from the regenerated solution by cooling to crystallize Na3AsO4·12H2O at room temperature. After the crystal was separated, NaOH and/or Na2CO3 were added into the solution to adjust the pH to precipitate the Bi. After filtration, the solution after Bi removal can be returned to the regeneration process.
Table 1 Composition of the copper electrolyte used in the experiments, g/L. As
Sb
Bi
Na
Cu
H2SO4
20.88
2.29
1.51
0.40
19.38
353.21
The motivation of this study was the need to promote the self-purification of As, Sb and Bi in copper electrolyte. The effects of the promoter addition, reaction temperature and contact time on the removal of As, Sb and Bi from copper electrolyte, as well as the reuse of the promoter were investigated in the present work. 2. Experimental 2.1. Materials and analysis The solution used in the experiments was the copper electrolyte from which a portion of water had been evaporated and CuSO4 ∙ 5H2O had been crystallized, and was supplied by Guixi Smelter, Jiangxi Copper Industry Co. The composition of the electrolyte is listed in Table 1. To study the promotion of copper electrolyte self-purification, Sb2O3·xH2O, Bi2O3·xH2O, Sb2O5·xH2O, H2SO4, NaOH and Na2CO3 were used and they were of analytical grade. The compositions of experimental samples were determined by chemical methods and inductively coupled plasma emission spectroscopy (ICP-AES) with a PS-6 PLASMA SPECTROVAC, BAIRD (USA). The valencies of the elements were determined by standard chemical methods (Peng et al., 2012a). The X-ray diffraction (XRD) patterns were recorded on a Rigaku Miniflex diffractometer with Cu Kα X–ray radiation at 35 kV and 20 mA.
3. Results and discussion 3.1. Selection of the promoter It has been found that the As, Sb and Bi in copper electrolyte can combine with each other to form the precipitate of arsenato antimonates (Wang, 2003; Wang et al., 2006), and the compounds containing antimony or bismuth can be used to remove the impurities As, Sb and Bi from copper electrolyte (He and He, 1996; Xiao et al., 2008). This indicates that the oxides of antimony or bismuth may be used to promote copper electrolyte self-purification. But in copper electrolyte, the dissolution of Sb2O3, Bi2O3 and Sb2O5 are all very difficult. Hence, their hydrous oxides were used as the optional promoter. The promoter was added into the copper electrolyte with As/(Sb + Bi) mole ratio 1:1, in which the As is the mole number of arsenic in the electrolyte, and the (Sb + Bi) is the total mole number of antimony and bismuth in the
2.2. Experimental procedure The experiment was performed according to the flow sheet as shown in Fig. 1. The mixture of Sb2O3·xH2O and Sb2O5·xH2O with Sb(V)/Sb (III) molar ratio 0.05 was used as the promoter of copper electrolyte
Fig. 1. Flowsheet of copper electrolyte indirect self-purification process.
Bleed electrolyte from tank house Evaporation and crystallization Promoter
CuSO4· 5H2O
Self-purification Filtration
Used promoter
Filtrate
Regeneration
Evaporation and crystallization
NaOH/Na2CO3
Raw NiSO4· xH2O
Filtration, washing Regenerated solution
Regenerated promoter
Acidic solution to be recycled
Crystallization, filtration Na3AsO4· 12H2O NaOH/Na2CO3
Bi2O3·xH 2O
Dearsenization solution pH adjustion, filtration
Solution after Bi removal
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Table 2 Experimental results of the copper electrolyte indirect self-purification with different promoters under As/(Sb + Bi) mole ratio 1:1 at 60 °C stirring for 1 h.
Bi(III) Bi(III)/Sb(III) molar ratio 0.8 Bi(III)/Sb(III) molar ratio 0.4 Bi(III)/Sb(III) molar ratio 0.2 Sb(V) Sb(V)/Sb(III) molar ratio 0.75 Sb(V)/Sb(III) molar ratio 0.05 Sb(III)
Removal efficiency, %
Promoter
100
Indirect self-purified copper electrolyte, g/L As
Sb
Bi
17.59 9.39 6.86 4.04 17.23 14.95 3.82 5.16
0.12 0.21 0.16 0.16 4.19 0.32 0.13 0.97
8.43 10.71 9.03 3.97 0.16 0.25 0.15 0.23
80 60 40
As Sb Bi
20 0
promoter. After stirring for 1 h at 60 °C, filtration was carried out, and then the removal efficiencies of As, Sb and Bi were determined by measuring the content of As, Sb and Bi in the electrolyte before and after indirect self-purification. The experimental results are shown in Table 2. Table 2 shows that as long as there is Bi2O3·xH2O in the promoter, the concentration of Bi will be increased in the self-purified electrolyte. Bi2O3·xH2O is unsuitable for use as the promoter. When Sb2O5·xH2O was added into the copper electrolyte, not only did the concentration of As not decrease, but that of Sb increased significantly, which indicates that Sb2O5·xH2O cannot be used alone as the promoter. After Sb2O3·xH2O was added into the copper electrolyte, though the concentrations of both As and Bi significantly decreased, the decrease in Sb was not obvious, which was not desirable. So Sb2O3·xH2O also cannot be used alone as the promoter. However, when Sb2O3·xH2O and Sb2O5·xH2O were mixed and used as the promoter, the concentrations of As, Sb and Bi all decreased in the self-purified electrolyte, along with a decrease with the decrease in Sb(V)/Sb(III) molar ratio in the promoter. Thus, the mixture of Sb2O3·xH2O and Sb2O5·xH2O with Sb(V)/Sb (III) molar ratio 0.05 is selected as the promoter in the following experiments, and the As/(Sb + Bi) mole ratio is turned into As/Sb mole ratio. In copper electrolyte, As(V) can combine with Sb(V) to form the arsenato antimonic acid of AAAc(1:1), which has the structure of (HO)3As-O-Sb(OH)4-O– Sb(OH)4-O-As(OH)3 and has good solubility (Wang, 2003; Wang et al., 2005). However, if there are Sb(III), As(III) and Bi(III) in the electrolyte, AAAc(1:1) can combine with them to form the precipitate of arsenato antimonates (Wang et al., 2006), which makes the concentrations of As, Sb and Bi decrease obviously. The formation of AAAc(1:1) and arsenato antimonates can be expressed by the following equations (Wang et al., 2005; Wang et al., 2006; Wang et al., 2011a): (1)
H3 AsO4 + HSb(OH)5 = H[H2 AsO3 − O − Sb(OH)5] + H2 O
(2)
50
60
70
80
90
100
Fig. 2. Effect of temperature on copper electrolyte indirect self-purification with As/Sb mole ratio 1:0.4 stirring for 1 h.
the promoter into the electrolyte with the As/Sb mole ratio 1:0.4 at the temperature from 25 °C to 90 °Cstirring for 1 h. As can be seen, the removal efficiencies of As, Sb and Bi all increase with the increase in temperature, and their removal efficiencies increase sharply from room temperature to about 60 °C and then increase slowly. At 60 °C, the removal efficiencies of As, Sb and Bi are 38.7%, 88.7% and 92.1% respectively. During copper electrorefining, the electrolyte temperature is 60–65 °C. Without heating, the self-purification process is energy saving. Therefore, it is reasonable to carry out the self-purification with a temperature at about 60 °C. Fig. 3 shows the XRD patterns of the used promoter obtained at 60 °C. From Fig. 3 it can be seen that there is an amorphous portion in the used promoter except for the crystals of SbAsO4, AsSbO4, BiAsO4 and Bi3SbO7. The arsenato antimonates formed in copper electrolyte are amorphous (Wang et al., 2006). This indicates that during selfpurification, the impurities As, Sb and Bi in the electrolyte were turned into SbAsO4, AsSbO4, BiAsO4, Bi3SbO7 and arsenato antimonates. The solubility of Sb2O3·xH2O in copper electrolyte increases with the increase in temperature, which accelerated the formation of SbAsO4, AsSbO4, BiAsO4, Bi3SbO7 and arsenato antimonates. The formation of SbAsO4, AsSbO4, BiAsO4 and Bi3SbO7 in copper electrolyte can be expressed by the following equations:
SbAsO4
(3)
aH3 AsO4 + bH[Sb(OH)6] + c MeO+ → Mec Asa Sbb O(3a + 5b + c /2 + 1) H(a + 5b –2c + 2) ·x H2 O ↓ + c H+ + (a + b + c /2–1–x )H2 O, where Me = As(III), Bi(III) and Sb(III); a ≥ 1, b ≥ 1, c ≤ ( 3a + b)
40
Temperature,
2H[H2 AsO3 − O − Sb(OH)5] = (HO)3 As − O − Sb(OH)4 − O − Sb(OH)4 − O − As(OH)3 + H2 O
30
BiAsO4
Intensity (Counts)
H3 AsO4 + SbO+ + 3H2 O ⇄ HSb(OH)6 + HAsO2 + H+
20
AsSbO4 Bi3SbO7
(4)
3.2. Indirect self-purification
10
20
30
40
50
60
2-Theta(°)
3.2.1. Effect of temperature Fig. 2 shows the experimental results of the effect of temperature on the removal of impurities As, Sb and Bi, which were obtained by adding
Fig. 3. XRD patterns of the used promoter.
30
70
80
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X. Wang et al.
100
Removal efficiency, %
Removal efficiency, %
100 80 60
As Sb Bi
40 20
80
60
As Sb Bi
40
20 0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1:0.3
1:0.5
Time, h
H3 AsO4 + SbO+ = SbAsO4 ↓ + H+ + H2 O
(5)
HSb(OH)6 + HAsO2 = AsSbO4 ↓ + 4H2 O
(6)
H3 AsO4 +
= BiAsO4 ↓ +
3H+
HSb(OH)6 + 3Bi3 + + H2 O = Bi3SbO7 ↓ + 9H+
1:1
1:1.7
1:2
1:3
As/Sb mole ratio
Fig. 4. Effect of contact time on copper electrolyte indirect self-purification with As/Sb mole ratio 1:0.7 at 60 °C.
Bi3 +
1:0.7
Fig. 5. Effect of promoter addition on copper electrolyte indirect self-purification at 60 °C stirring for 1 h.
respectively with the As/Sb mole ratio 1:0.7. During copper electrorefining, Sb and Bi are the most harmful impurities in the electrolyte. Therefore, the suitable range of the As/Sb mole ratio is from 1:0.7 to 1:1. The composition of the self-purified electrolyte is listed in Table 3. It was obtained by adding the promoter into the electrolyte with the As/ Sb mole ratio 1:0.7 at 60 °C and stirring for 1 h. As can be seen, the selfpurified electrolyte can be returned to the circulating system of copper electrolyte after Ni is removed, see Fig. 1.
(7) (8)
Once the promoter is added into the electrolyte, SbAsO4, AsSbO4, BiAsO4 and Bi3SbO7 all can be formed. It has been found that in copper electrolyte, SbAsO4 can be dissolved (Braun et al., 1976), while BiAsO4 cannot (Wang et al., 2017). If there are no arsenato antimonates, AsSbO4 and Bi3SbO7 formed in the electrolyte, then formed SbAsO4 will be redissolved. The dissolution of SbAsO4 is retarded by the arsenato antimonates, AsSbO4 and Bi3SbO7 as they are all insoluble in copper electrolyte (Wang et al., 2006; Wang et al., 2011a).
3.3. Promoter regeneration For indirect self-purification of copper electrolyte, the regeneration of used promoter is very important. The promoters used under different conditions were collected and mixed uniformly. The composition of the mixed promoter is listed in Table 4. The effects of temperature, L/S ratio, contact time and solution pH on the regeneration were studied.
3.2.2. Effect of contact time Fig. 4 shows the experimental results of the effect of contact time on the removal of impurities As, Sb and Bi, which were obtained by adding the promoter into the electrolyte with the As/Sb mole ratio 1:0.7 and stirring for different time at 60 °C. As can be seen, the indirect selfpurification of impurities As, Sb and Bi in copper electrolyte is very fast. After the promoter was added into the electrolyte and stirred for half an hour, the formations of SbAsO4, AsSbO4, BiAsO4, Bi3SbO7 and arsenato antimonates have reached their ends. Therefore, for indirect self-purification, when the promoter is added, stirring for 0.5 h is enough.
3.3.1. Effect of L/S ratio The experimental results of the effect of liquid-solid ratio (L/S ratio mL/g) on the removal of As, Sb and Bi from the used promoter are shown in Fig. 6. These results were obtained by adding the used promoter into 2 mol/L Na2CO3 with different L/S ratio under stirring at room temperature, and then adjusting the pH to 8–9 with NaOH and/or Na2CO3. After the pH was stabilized at about 8.5 for 1.5 h, filtration was carried out. It can be seen from Fig. 6 that the removal efficiencies of As and Bi increase with the increase in L/S ratio, while that of Sb is a constant at about 1%. This indicates that SbAsO4, AsSbO4, BiAsO4 and Bi3SbO7 can all be decomposed under the pH 8–9. Their decomposition can be expressed by the following equations:
3.2.3. Effect of promoter addition Fig. 5 shows the experimental results of the effect of promoter addition on the removal of impurities As, Sb and Bi, which were obtained by adding the promoter into the electrolyte with different As/Sb mole ratios at 60 °C stirring for 1 h. As seen, the removal efficiencies of As and Bi increase with the increase in the As/Sb mole ratio, while that of Sb decreases. With the increase in the As/Sb mole ratio from 1:0.3 to 1:1, the removal efficiency of As increases from 27.4% to 80.8%, and that of Bi increases from 86.1% to 97.9%, while that of Sb decreases from 94.7% to 83.4%. With the further increase in the As/Sb mole ratio, the removal efficiencies of As and Bi both increase slowly, while that of Sb declines sharply. With the increase in promoter addition, the As/Sb mole ratio decreases, and the content of SbAsO4 in the used promoter increases. If the formed SbAsO4 cannot be effectively wrapped up by the AsSbO4, Bi3SbO7 and arsenato antimonates, it will be redissolved, which makes the concentration of Sb(III) increase in the self-purified electrolyte. The removal efficiencies of As, Sb and Bi are 62.0%, 93.0% and 95.0%
2SbAsO4 + 6OH− + (x − 3)H2 O = 2AsO43 − + Sb2 O3 ·x H2 O
(9)
2BiAsO4 + 6OH− + (x − 3)H2 O = 2AsO43 − + Bi2 O3 ·x H2 O
(10)
2AsSbO4 + 2OH− + (x − 1)H2 O = 2AsO2− + Sb2 O5 ·x H2 O
(11)
2 Bi3SbO7 + (x + 9)H2 O = 6Bi(OH)3 + Sb2 O5 ·x H2 O
(12)
Table 3 Composition of the copper electrolyte after indirect self-purification with the As/Sb mole ratio 1:0.7 at 60 °C stirring for 1 h, g/L.
31
As
Sb
Bi
Na
Cu
H2SO4
8.15
0.15
0.04
0.43
18.79
321.64
Hydrometallurgy 175 (2018) 28–34
X. Wang et al.
100
Before After
As
Sb
Bi
Cu
Fe
16.37 2.56
31.68 58.47
1.89 1.21
0.15 0.03
0.07 0.05
Removal efficiency, %
Table 4 Composition of the used promoter before and after regeneration in 2 mol/L Na2CO3 with L/S ratio 4:1 mL/g under pH 9 stirring for 0.5 h at room temperature, wt%.
Removal efficiency, %
100 80
60 40
As Sb Bi
20 1.6 0.8
60
0.0
As Sb Bi
40 20
30
40
50
60
70
80
Temperature, Fig. 8. Effect of temperature on the removal of As, Sb and Bi from the used promoter in 2 mol/L Na2CO3 with L/S ratio 3:1 mL/g under pH 9.5 contact for 0.5 h.
3000
0 3:1
4:1
5:1
6:1
8:1
10:1
12:1
2500
Intensity (Counts)
2:1
Liquid-solid ratio, mL/g Fig. 6. Effect of L/S ratio on the removal of As, Sb and Bi from the used promoter in 2 mol/L Na2CO3 at room temperature under pH 8.5 contact for 1.5 h.
100 80
Na3 AsO4· 12H2O
2000 1500 1000 500 0
60 10
40 20
20
30
40
50
60
70
80
2-Theta(°)
As Sb Bi
Fig. 9. XRD patterns of the crystal formed in the regeneration solution.
100
0 0.0
0.5
1.0
1.5
2.0
Removal efficiency, %
Removal efficiency, %
80
2.5
Time, h Fig. 7. Effect of contact time on the removal of As, Sb and Bi from the used promoter in 2 mol/L Na2CO3 with L/S ratio 4:1 mL/g under pH 9.5 at room temperature.
Fig. 6 shows that with the increase in L/S ratio from 2:1 mL/g to 6:1 mL/g, the removal efficiencies of As and Bi increase from 62.9% and 11.2% to 95.4% and 61.7% respectively, and then their removal efficiencies do not significantly increase with the further increase in L/S ratio. This may be because with the decomposition of SbAsO4 and BiAsO4, the concentration of As(V) increases in the solution, which makes the dissolution of Bi(III) increase as shown in reactions (13) and (14). Considering the disposal of arsenic contained in the waste water, the L/S ratio should be controlled at 2:1 mL/g to 6:1 mL/g.
Bi(OH)3 ⇄ Bi3 + + 3OH−
(13)
x AsO43 − + y Bi3 + ⇄ [Biy (AsO4 )x ]3(x − y) −
(14)
80
As Sb Bi
60 40 20 0 7
8
9
10
11
12
13
14
pH Fig. 10. Effect of solution pH on the removal of As, Sb and Bi from the used promoter in 2 mol/L Na2CO3 with L/S ratio 4:1 mL/g at room temperature contact for 0.5 h.
32
Hydrometallurgy 175 (2018) 28–34
X. Wang et al.
for 1 h. After filtration, the used promoter was regenerated by adding into 2 mol/L Na2CO3 with L/S ratio 3:1 mL/g and stirring for 1 h at 60 °C, filtrating immediately and washing with 0.5 mol/L H2SO4. During stirring, the pH was adjusted to about 9 with NaOH and/or Na2CO3. The regenerated promoter was reused in the experiments, as shown in Fig. 1. The regenerated solution was reused in the experiments after the As and Bi were separated. It can be seen from Table 5 that after reused 3 times, the promoter function did not decay, and its composition did not change obviously. This indicates that the promoter containing Sb(III) and Sb(V) can be reused throughout, and the amount of promoter will gradually increase with the increase in the reuse times.
Table 5 Experimental results of the promoter reused in the indirect self-purification with As/Sb mole ratio 1:0.7 at 60 °C stirring for 1 h, and the regeneration of the used promoter in 2 mol/L Na2CO3 with L/S ratio 3:1 mL/g stirring for 1 h at 60 °C. Cycle times
1 2 3
Self-purified solution, g/L
Regenerated promoter, %
As
Sb
Bi
As
Sb
Bi
8.12 8.07 8.21
0.16 0.13 0.15
0.05 0.07 0.06
2.56 2.61 2.54
58.47 59.01 59.11
1.21 1.37 1.35
3.3.2. Effect of contact time The experimental results of the effect of contact time on the removal of As, Sb and Bi from the used promoter are shown in Fig. 7. These results were obtained by adding the used promoter into 2 mol/L Na2CO3 with L/S ratio 4:1 mL/g and then maintaining the pH at about 9.5 stirring for predetermined time at room temperature. As seen, the separation of As and Bi from the used promoter is very fast. After stirring for 0.5 h, the reactions (9)–(14) have reached their end points. This indicates that when the used promoter is added into the Na2CO3 solution, stirring for 0.5 h is enough.
4. Conclusion Experiments confirmed that the self-purification of impurities As, Sb and Bi in copper electrolyte can be promoted with antimonic oxides. Using the mixture of Sb2O3·xH2O and Sb2O5·xH2O with Sb(V)/Sb(III) molar ratio 0.05 as the promoter, the removal efficiencies of As and Bi increase with the increase in the As/Sb mole ratio from 1:0.5 to 1:3, while that of Sb decreases. The removal efficiencies of As, Sb and Bi are 61.0%, 93.5% and 97.4% respectively when adding the promoter into the electrolyte with the As/Sb mole ratio 1:0.7 at 60 °C and stirring for 1 h. The used promoter can be regenerated in Na2CO3 solution at the pH 8–9 under stirring at a temperature above 40 °C, and the As and Bi can be separated from the regenerated solution by crystallization and precipitation, respectively. The promoter can be reused throughout as after repeated use, its function and composition did not change significantly.
3.3.3. Effect of temperature The experimental results of the effect of temperature on the removal of As, Sb and Bi from the used promoter are shown in Fig. 8. These results were obtained by adding the used promoter into 2 mol/L Na2CO3 with L/S ratio 3:1 mL/g at a predetermined temperature, and then maintaining the pH at about 9.5 and stirring for 0.5 h. As can be seen, the removal efficiencies of As and Bi increase with the increase in temperature from room temperature to 60 °C, while that of Sb decreases slightly. At 60 °C, the removal efficiencies of As, Sb and Bi are 94.7%, 1.2% and 57.9% respectively. Then the removal efficiencies of As, Sb and Bi have no obvious change with the further increase in temperature. It was found that the crystal of Na3AsO4·12H2O can be obtained by cooling the regenerated solution from above 40 °C to room temperature. Therefore, the regeneration should be carried out at ≥ 60 °C. The XRD patterns of the crystal Na3AsO4·12H2O are shown in Fig. 9.
References Braun, T.B., Rawling, J.R., Richards, K.J., 1976. Factors affecting the quality of electrorefining cathode copper. In: Agarwal, J.C. (Ed.), Yannopoulos. Extractive Metallurgy of Copper vol. I. Metallurgical Society Inc., New York, pp. 511–524. Cunnigham, R.M., Calara, J.V., King, M.G., 1997. In: Mishra, B. (Ed.), EPD Congress. TMS, Warrendale, PA, USA, pp. 453–460. Eichrodt, C.W., Schloen, J.H., 1954. In: Butts (Ed.), Copper-the Science and Technology of the Metal, Its Alloys, and Compounds. Reinhold, New York, pp. 171–173. He, W.N., He, S.J., 1996. Methods for purifying impurities in copper electrolyte. Jiangxi Nonferrous Metals 10 (01), 38–40. Hyvarinen, O.V.J., 1979. U. S. Patent No. 4, 157,946. McKevitt, B., Dreisinger, D., 2009. A comparison of various ion exchange resins for the removal of ferric ions from copper electrowinning electrolyte solutions part II: electrolytes containing antimony and bismuth. Hydrometallurgy 98, 122–127. Navarro, P., Simpson, J., Alguacil, F.J., 1999. Removal of antimony(III) from copper in sulphuric acid solutions by solvent extraction with LIX 1104SM. Hydrometallurgy 53, 121–131. Peng, Y.L., Zheng, Y.J., Chen, W.M., 2012a. The oxidation of arsenic from As(III) to As(V) during copper electrorefining. Hydrometallurgy 129-130, 156–160. Peng, Y.L., Zheng, Y.J., Zhou, W.K., 2012b. The separation of copper and arsenic in copper electrolyte purification and recycling. Trans. Nonferrous Metals Soc. China 22 (9), 2268–2273. Riveros, P.A., 2010. The removal of antimony from copper electrolytes using aminophosphonic resins: improving the elution of pentavalent antimony. Hydrometallurgy 105, 110–114. Salari, K., Hashemian, S., Baei, M.T., 2017. Sb(V) removal from copper electrorefining electrolyte: comparative study by different sorbents. Trans. Nonferrous Metals Soc. China 27, 440 − 449. Wan, L.M., 2010. Chemical Purification of Copper Electrolyte Technology Research. Master's Thesis. Central South University, Changsha. Wang, X.W., 2003. Study on the Mechanism of the Formation and Action of Arsenato Antimonic Acid in Copper Electrorefining. Ph.D. Dissertation. Central South University, Changsha. Wang, X.W., Chen, Q.Y., Yin, Z.L., Zhang, P.M., Long, Z.P., Su, Z.F., 2003. Removal of impurities from copper electrolyte with adsorbent containing antimony. Hydrometallurgy 69, 39–44. Wang, X.W., Chen, Q.Y., Yin, Z.L., Zhang, P.M., Wang, Y.W., 2005. Synthesis and characterization of arsenato antimonic acid AAAc(1:1). J. Cent. South Univ. Technol. 12 (Suppl. 1), 76–81. Wang, X.W., Chen, Q.Y., Yin, Z.L., Xiao, L.S., 2006. Identification of arsenato antimonates in copper anode slimes. Hydrometallurgy 84, 211–217. Wang, X.W., Chen, Q.Y., Xiao, L.S., Yin, Z.L., Zhang, Q.X., Zhang, P.M., 2008. A techniques for the purification of copper electrolyte. Chinese Patent No. CN101260539A. Wang, X.W., Chen, Q.Y., Yin, Z.L., Wang, M.Y., Tang, F., 2011a. The role of arsenic in the homogeneous precipitation of As, Sb and Bi impurities in copper electrolyte. Hydrometallurgy 108 (3–4), 199–204.
3.3.4. Effect of solution pH The experimental results of solution pH effect on the removal of As, Sb and Bi from the used promoter are shown in Fig. 10. These results were obtained by adding the used promoter into 2 mol/L Na2CO3 with L/S ratio 4:1 mL/g at room temperature after the solution pH was adjusted to the predetermined value and continued stirring for 0.5 h. As seen, the removal efficiency of Sb is a constant at about 1% with the increase in pH from 7 to 12, but that of As and Bi increase rapidly with the increase in pH from 7 to 8, and their removal efficiencies reach the top at pH 9. Then the removal efficiency of Bi decreases significantly with the increase in pH from 9 to 12, while that of As initially decreases and then rises in this pH range. This indicates that reactions (9)–(14) are accelerated with the increase in pH from 7 to 9, and they reach their ends at pH 9. However, when the pH increases from 9 to 12, the inverse reactions (13)–(14) occur, which reforms the precipitate of Bi2O3·xH2O. Therefore, the regeneration should be carried out at pH between 8 and 9, and the As and Bi can be separated from the regenerated solution by crystallization and precipitation, as shown by Fig. 1. After filtration and washing with 0.5 mol/L H2SO4, the regenerated promoter was obtained. The composition of the regenerated promoter obtained at pH 9 is listed in Table 4 as well. 3.4. Promoter reuse Table 5 shows the experimental results of the promoter reused in the experiments, which were obtained by adding the promoter into the copper electrolyte with the As/Sb mole ratio 1:0.7 at 60 °C and stirring 33
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Xiao, F.X., Mao, J.W., Cao, D., Shen, X.N., Yang, D.X., 2011. Research progress on selfpurification of copper electrolyte. China Nonferrous Metallurgy 06, 73–79. Zhao, T.C., 1981. Metallurgy of Heavy Metals (Part I). Metallurgical Industry Press, Beijing (in Chinese). Zheng, Y.J., Xiao, F.X., Wang, Y., Li, C.H., Xu, W., Jian, H.S., Ma, Y.T., 2008. Industrial experiment of copper electrolyte purification by copper arsenite. J. Cent. South Univ. Technol. 15, 204– −208. Zheng, Y.J., Cui, T., Peng, Y.L., 2012. New process of arsenic removal from second stage decopperizing electrolyte by reduction and crystallization. Chin. J. Nonferrous Metals 22 (7), 2103–2110.
Wang, X.W., Chen, Q.Y., Yin, Z.L., Wang, M.Y., Xiao, B.R., Zhang, F., 2011b. Homogeneous precipitation of As, Sb and Bi impurities in copper electrolyte during electrorefining. Hydrometallurgy 105, 355–358. Wang, X W., Wang, X.M., Wang, M.Y., 2014. A techniques for the removal of impurities from copper electrolyte. Chinese Patent No. ZL 201410333413.1. Wang, X.W., Wang, X.M., Wang, M.Y., 2017. Characteristics of BiAsO4 precipitate formation in copper electrolyte. Hydrometallurgy 171, 95–98. Xiao, F.X., Zheng, Y.J., Wang, Y., Jian, H.S., Huang, X.Y., Ma, Y.T., 2008. Purification mechanism of copper electrolyte by As(III). Trans. Nonferrous Metals Soc. China 18, 1275–1278.
34
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Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Promotion of copper electrolyte self-purification with antimonic oxides a
a,⁎
a
a
Xingming Wang , Xuewen Wang , Biao Liu , Mingyu Wang , Huaguang Wang Shengfan Zhoua a b
a,b
MARK a
, Xuehui Liu ,
School of Metallurgy and Environment, Central South University, Changsha 410083, China Department of Materials Science and Engineering, Michigan Technological University, Houghton, MI 49931, USA
A R T I C L E I N F O
A B S T R A C T
Keywords: Copper electrolyte Self-purification Promotion Antimonic oxides Reuse
The promotion of copper electrolyte self-purification with antimonic oxides was studied. It was found that the mixed oxides of Sb(III) and Sb(V) can be used to promote copper electrolyte self-purification. The mixture of Sb2O3·xH2O and Sb2O5·xH2O with Sb(V)/Sb(III) molar ratio 0.05 was used to promote the self- purification of copper electrolyte containing 353.21 g/L H2SO4, 19.38 g/L Cu, 20.88 g/L As, 2.29 g/L Sb and 1.51 g/L Bi. Experimental results show that the removal of impurities As, Sb and Bi from copper electrolyte mainly depends on the ratio of the molar number of arsenic in the electrolyte to the molar number of antimony in the promoter, namely the As/Sb mole ratio. When the promoter was added into the electrolyte with the As/Sb mole ratio 1:0.7 at 60 °C stirring for 0.5 h, the removal efficiencies of As, Sb and Bi are 62.0%, 93.0% and 95.0% respectively. Then the As and Bi were separated from the used promoter by adding it into 2 mol/L Na2CO3 stirring for 0.5 h at above 60 °C in pH 8–9. After filtration, the regenerated promoter was obtained by washing the filter cake with diluted sulfuric acid, and the As and Bi were separated from the regenerated solution by crystallizing Na3AsO4·12H2O at room temperature, and by precipitating Bi2O3·xH2O under the pH above 12, respectively.
1. Introduction As long as copper electrorefining has been commercially applied, the purification of copper electrolyte has received much attention since the impurities As, Sb and Bi are dissolved with Cu from the anode into the electrolyte during electrorefining due to the similarity of their standard reduction potentials to that of Cu (Zhao, 1981). The traditional method used to remove As, Sb and Bi from copper electrolyte is to electrodeposit them with copper (Navarro et al., 1999; Wan, 2010; Peng et al., 2012b). But the method has a number of drawbacks, e.g., high energy consumption and evolution of toxic arsine gas. Therefore, many other methods have been proposed to remove the impurities from copper electrolyte, such as adsorption of Sb and As using ion exchange (Cunnigham et al., 1997; Mckevitt and Dreisinger, 2009; Riveros, 2010; Salari et al., 2017), removal of Sb and Bi by solvent extraction (Navarro et al., 1999), co-precipitation of Bi and Sb by adding a carbonate of barium, strontium, or lead (Hyvarinen, 1979), and reduction and crystallization of As with SO2 (Zheng et al., 2012). However, these methods can only be used as auxiliary measures for the purification of copper electrolyte, and they cannot completely replace the electrodeposition method (Wang, 2003). It is well known that during copper electrorefining, a portion of As, Sb and Bi dissolved from the anode can spontaneously precipitate from ⁎
the electrolyte into the anode slime (Wang et al., 2011a; Wang et al., 2011b). What is more, the amounts of them deposited into the anode slime depend on their content in the anode, their concentrations in the electrolyte and the electrorefining conditions (Eichrodt and Schloen, 1954; Braun et al., 1976). This indicates that As, Sb and Bi in copper electrolyte have a certain self-purification ability. It has been found that copper electrolyte self-purification can be significantly improved by adjusting the relative content of Sb in the anode and increasing the concentration of As in the electrolyte (Wang, 2003; Wang et al., 2008). It has been found that the increase in copper electrolyte self-purification is limited, since during commercial operation, it is difficult to change the relative content of Sb in the anode at will, and the concentration of As in the electrolyte cannot be increased without restraint. But the self-purification of As, Sb and Bi in copper electrolyte can be promoted with some compounds containing antimony or arsenic and bismuth (Wang et al., 2003; Zheng et al., 2008; Xiao et al., 2011). This indicates that the self-purification of copper electrolyte can be divided into direct self-purification and indirect self-purification. Direct selfpurification is the spontaneous precipitation of As, Sb and Bi in the electrolyte during copper electrorefining, (Wang et al., 2008), while indirect self-purification is to promote their precipitation with compounds containing antimony or arsenic and bismuth (Wang et al., 2014).
Corresponding author. E-mail address: [email protected] (X. Wang).
http://dx.doi.org/10.1016/j.hydromet.2017.10.028 Received 10 April 2017; Received in revised form 25 October 2017; Accepted 25 October 2017 Available online 27 October 2017 0304-386X/ © 2017 Elsevier B.V. All rights reserved.
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self-purification. For each experimental run, 250 mL of the electrolyte was mixed with the promoter under stirring in a 500 mL beaker. The beaker was placed in a water bath at about 60 °C to promote electrolyte self-purification. At the end of the self-purification process, the suspension was separated by filtration, and the filtrate and the used promoter were sampled for analysis. The used promoter (15 g) was mixed with water under stirring in a 250 mL beaker with the desired liquid-solid (L/S) ratio (from 2:1 mL/g to 6:1 mL/g). The beaker was placed in a water bath at the desired temperature (≥60 °C) to regenerate the promoter. During the regeneration, the solution pH was adjusted with NaOH and/or Na2CO3. After the pH was adjusted to the desired value (8–9), the solution was stirred for scheduled time (0.5–1.5 h), the regeneration was ended. By filtration and washing with 0.5 mol/L H2SO4, the regenerated promoter was obtained. The As was removed from the regenerated solution by cooling to crystallize Na3AsO4·12H2O at room temperature. After the crystal was separated, NaOH and/or Na2CO3 were added into the solution to adjust the pH to precipitate the Bi. After filtration, the solution after Bi removal can be returned to the regeneration process.
Table 1 Composition of the copper electrolyte used in the experiments, g/L. As
Sb
Bi
Na
Cu
H2SO4
20.88
2.29
1.51
0.40
19.38
353.21
The motivation of this study was the need to promote the self-purification of As, Sb and Bi in copper electrolyte. The effects of the promoter addition, reaction temperature and contact time on the removal of As, Sb and Bi from copper electrolyte, as well as the reuse of the promoter were investigated in the present work. 2. Experimental 2.1. Materials and analysis The solution used in the experiments was the copper electrolyte from which a portion of water had been evaporated and CuSO4 ∙ 5H2O had been crystallized, and was supplied by Guixi Smelter, Jiangxi Copper Industry Co. The composition of the electrolyte is listed in Table 1. To study the promotion of copper electrolyte self-purification, Sb2O3·xH2O, Bi2O3·xH2O, Sb2O5·xH2O, H2SO4, NaOH and Na2CO3 were used and they were of analytical grade. The compositions of experimental samples were determined by chemical methods and inductively coupled plasma emission spectroscopy (ICP-AES) with a PS-6 PLASMA SPECTROVAC, BAIRD (USA). The valencies of the elements were determined by standard chemical methods (Peng et al., 2012a). The X-ray diffraction (XRD) patterns were recorded on a Rigaku Miniflex diffractometer with Cu Kα X–ray radiation at 35 kV and 20 mA.
3. Results and discussion 3.1. Selection of the promoter It has been found that the As, Sb and Bi in copper electrolyte can combine with each other to form the precipitate of arsenato antimonates (Wang, 2003; Wang et al., 2006), and the compounds containing antimony or bismuth can be used to remove the impurities As, Sb and Bi from copper electrolyte (He and He, 1996; Xiao et al., 2008). This indicates that the oxides of antimony or bismuth may be used to promote copper electrolyte self-purification. But in copper electrolyte, the dissolution of Sb2O3, Bi2O3 and Sb2O5 are all very difficult. Hence, their hydrous oxides were used as the optional promoter. The promoter was added into the copper electrolyte with As/(Sb + Bi) mole ratio 1:1, in which the As is the mole number of arsenic in the electrolyte, and the (Sb + Bi) is the total mole number of antimony and bismuth in the
2.2. Experimental procedure The experiment was performed according to the flow sheet as shown in Fig. 1. The mixture of Sb2O3·xH2O and Sb2O5·xH2O with Sb(V)/Sb (III) molar ratio 0.05 was used as the promoter of copper electrolyte
Fig. 1. Flowsheet of copper electrolyte indirect self-purification process.
Bleed electrolyte from tank house Evaporation and crystallization Promoter
CuSO4· 5H2O
Self-purification Filtration
Used promoter
Filtrate
Regeneration
Evaporation and crystallization
NaOH/Na2CO3
Raw NiSO4· xH2O
Filtration, washing Regenerated solution
Regenerated promoter
Acidic solution to be recycled
Crystallization, filtration Na3AsO4· 12H2O NaOH/Na2CO3
Bi2O3·xH 2O
Dearsenization solution pH adjustion, filtration
Solution after Bi removal
29
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Table 2 Experimental results of the copper electrolyte indirect self-purification with different promoters under As/(Sb + Bi) mole ratio 1:1 at 60 °C stirring for 1 h.
Bi(III) Bi(III)/Sb(III) molar ratio 0.8 Bi(III)/Sb(III) molar ratio 0.4 Bi(III)/Sb(III) molar ratio 0.2 Sb(V) Sb(V)/Sb(III) molar ratio 0.75 Sb(V)/Sb(III) molar ratio 0.05 Sb(III)
Removal efficiency, %
Promoter
100
Indirect self-purified copper electrolyte, g/L As
Sb
Bi
17.59 9.39 6.86 4.04 17.23 14.95 3.82 5.16
0.12 0.21 0.16 0.16 4.19 0.32 0.13 0.97
8.43 10.71 9.03 3.97 0.16 0.25 0.15 0.23
80 60 40
As Sb Bi
20 0
promoter. After stirring for 1 h at 60 °C, filtration was carried out, and then the removal efficiencies of As, Sb and Bi were determined by measuring the content of As, Sb and Bi in the electrolyte before and after indirect self-purification. The experimental results are shown in Table 2. Table 2 shows that as long as there is Bi2O3·xH2O in the promoter, the concentration of Bi will be increased in the self-purified electrolyte. Bi2O3·xH2O is unsuitable for use as the promoter. When Sb2O5·xH2O was added into the copper electrolyte, not only did the concentration of As not decrease, but that of Sb increased significantly, which indicates that Sb2O5·xH2O cannot be used alone as the promoter. After Sb2O3·xH2O was added into the copper electrolyte, though the concentrations of both As and Bi significantly decreased, the decrease in Sb was not obvious, which was not desirable. So Sb2O3·xH2O also cannot be used alone as the promoter. However, when Sb2O3·xH2O and Sb2O5·xH2O were mixed and used as the promoter, the concentrations of As, Sb and Bi all decreased in the self-purified electrolyte, along with a decrease with the decrease in Sb(V)/Sb(III) molar ratio in the promoter. Thus, the mixture of Sb2O3·xH2O and Sb2O5·xH2O with Sb(V)/Sb (III) molar ratio 0.05 is selected as the promoter in the following experiments, and the As/(Sb + Bi) mole ratio is turned into As/Sb mole ratio. In copper electrolyte, As(V) can combine with Sb(V) to form the arsenato antimonic acid of AAAc(1:1), which has the structure of (HO)3As-O-Sb(OH)4-O– Sb(OH)4-O-As(OH)3 and has good solubility (Wang, 2003; Wang et al., 2005). However, if there are Sb(III), As(III) and Bi(III) in the electrolyte, AAAc(1:1) can combine with them to form the precipitate of arsenato antimonates (Wang et al., 2006), which makes the concentrations of As, Sb and Bi decrease obviously. The formation of AAAc(1:1) and arsenato antimonates can be expressed by the following equations (Wang et al., 2005; Wang et al., 2006; Wang et al., 2011a): (1)
H3 AsO4 + HSb(OH)5 = H[H2 AsO3 − O − Sb(OH)5] + H2 O
(2)
50
60
70
80
90
100
Fig. 2. Effect of temperature on copper electrolyte indirect self-purification with As/Sb mole ratio 1:0.4 stirring for 1 h.
the promoter into the electrolyte with the As/Sb mole ratio 1:0.4 at the temperature from 25 °C to 90 °Cstirring for 1 h. As can be seen, the removal efficiencies of As, Sb and Bi all increase with the increase in temperature, and their removal efficiencies increase sharply from room temperature to about 60 °C and then increase slowly. At 60 °C, the removal efficiencies of As, Sb and Bi are 38.7%, 88.7% and 92.1% respectively. During copper electrorefining, the electrolyte temperature is 60–65 °C. Without heating, the self-purification process is energy saving. Therefore, it is reasonable to carry out the self-purification with a temperature at about 60 °C. Fig. 3 shows the XRD patterns of the used promoter obtained at 60 °C. From Fig. 3 it can be seen that there is an amorphous portion in the used promoter except for the crystals of SbAsO4, AsSbO4, BiAsO4 and Bi3SbO7. The arsenato antimonates formed in copper electrolyte are amorphous (Wang et al., 2006). This indicates that during selfpurification, the impurities As, Sb and Bi in the electrolyte were turned into SbAsO4, AsSbO4, BiAsO4, Bi3SbO7 and arsenato antimonates. The solubility of Sb2O3·xH2O in copper electrolyte increases with the increase in temperature, which accelerated the formation of SbAsO4, AsSbO4, BiAsO4, Bi3SbO7 and arsenato antimonates. The formation of SbAsO4, AsSbO4, BiAsO4 and Bi3SbO7 in copper electrolyte can be expressed by the following equations:
SbAsO4
(3)
aH3 AsO4 + bH[Sb(OH)6] + c MeO+ → Mec Asa Sbb O(3a + 5b + c /2 + 1) H(a + 5b –2c + 2) ·x H2 O ↓ + c H+ + (a + b + c /2–1–x )H2 O, where Me = As(III), Bi(III) and Sb(III); a ≥ 1, b ≥ 1, c ≤ ( 3a + b)
40
Temperature,
2H[H2 AsO3 − O − Sb(OH)5] = (HO)3 As − O − Sb(OH)4 − O − Sb(OH)4 − O − As(OH)3 + H2 O
30
BiAsO4
Intensity (Counts)
H3 AsO4 + SbO+ + 3H2 O ⇄ HSb(OH)6 + HAsO2 + H+
20
AsSbO4 Bi3SbO7
(4)
3.2. Indirect self-purification
10
20
30
40
50
60
2-Theta(°)
3.2.1. Effect of temperature Fig. 2 shows the experimental results of the effect of temperature on the removal of impurities As, Sb and Bi, which were obtained by adding
Fig. 3. XRD patterns of the used promoter.
30
70
80
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X. Wang et al.
100
Removal efficiency, %
Removal efficiency, %
100 80 60
As Sb Bi
40 20
80
60
As Sb Bi
40
20 0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1:0.3
1:0.5
Time, h
H3 AsO4 + SbO+ = SbAsO4 ↓ + H+ + H2 O
(5)
HSb(OH)6 + HAsO2 = AsSbO4 ↓ + 4H2 O
(6)
H3 AsO4 +
= BiAsO4 ↓ +
3H+
HSb(OH)6 + 3Bi3 + + H2 O = Bi3SbO7 ↓ + 9H+
1:1
1:1.7
1:2
1:3
As/Sb mole ratio
Fig. 4. Effect of contact time on copper electrolyte indirect self-purification with As/Sb mole ratio 1:0.7 at 60 °C.
Bi3 +
1:0.7
Fig. 5. Effect of promoter addition on copper electrolyte indirect self-purification at 60 °C stirring for 1 h.
respectively with the As/Sb mole ratio 1:0.7. During copper electrorefining, Sb and Bi are the most harmful impurities in the electrolyte. Therefore, the suitable range of the As/Sb mole ratio is from 1:0.7 to 1:1. The composition of the self-purified electrolyte is listed in Table 3. It was obtained by adding the promoter into the electrolyte with the As/ Sb mole ratio 1:0.7 at 60 °C and stirring for 1 h. As can be seen, the selfpurified electrolyte can be returned to the circulating system of copper electrolyte after Ni is removed, see Fig. 1.
(7) (8)
Once the promoter is added into the electrolyte, SbAsO4, AsSbO4, BiAsO4 and Bi3SbO7 all can be formed. It has been found that in copper electrolyte, SbAsO4 can be dissolved (Braun et al., 1976), while BiAsO4 cannot (Wang et al., 2017). If there are no arsenato antimonates, AsSbO4 and Bi3SbO7 formed in the electrolyte, then formed SbAsO4 will be redissolved. The dissolution of SbAsO4 is retarded by the arsenato antimonates, AsSbO4 and Bi3SbO7 as they are all insoluble in copper electrolyte (Wang et al., 2006; Wang et al., 2011a).
3.3. Promoter regeneration For indirect self-purification of copper electrolyte, the regeneration of used promoter is very important. The promoters used under different conditions were collected and mixed uniformly. The composition of the mixed promoter is listed in Table 4. The effects of temperature, L/S ratio, contact time and solution pH on the regeneration were studied.
3.2.2. Effect of contact time Fig. 4 shows the experimental results of the effect of contact time on the removal of impurities As, Sb and Bi, which were obtained by adding the promoter into the electrolyte with the As/Sb mole ratio 1:0.7 and stirring for different time at 60 °C. As can be seen, the indirect selfpurification of impurities As, Sb and Bi in copper electrolyte is very fast. After the promoter was added into the electrolyte and stirred for half an hour, the formations of SbAsO4, AsSbO4, BiAsO4, Bi3SbO7 and arsenato antimonates have reached their ends. Therefore, for indirect self-purification, when the promoter is added, stirring for 0.5 h is enough.
3.3.1. Effect of L/S ratio The experimental results of the effect of liquid-solid ratio (L/S ratio mL/g) on the removal of As, Sb and Bi from the used promoter are shown in Fig. 6. These results were obtained by adding the used promoter into 2 mol/L Na2CO3 with different L/S ratio under stirring at room temperature, and then adjusting the pH to 8–9 with NaOH and/or Na2CO3. After the pH was stabilized at about 8.5 for 1.5 h, filtration was carried out. It can be seen from Fig. 6 that the removal efficiencies of As and Bi increase with the increase in L/S ratio, while that of Sb is a constant at about 1%. This indicates that SbAsO4, AsSbO4, BiAsO4 and Bi3SbO7 can all be decomposed under the pH 8–9. Their decomposition can be expressed by the following equations:
3.2.3. Effect of promoter addition Fig. 5 shows the experimental results of the effect of promoter addition on the removal of impurities As, Sb and Bi, which were obtained by adding the promoter into the electrolyte with different As/Sb mole ratios at 60 °C stirring for 1 h. As seen, the removal efficiencies of As and Bi increase with the increase in the As/Sb mole ratio, while that of Sb decreases. With the increase in the As/Sb mole ratio from 1:0.3 to 1:1, the removal efficiency of As increases from 27.4% to 80.8%, and that of Bi increases from 86.1% to 97.9%, while that of Sb decreases from 94.7% to 83.4%. With the further increase in the As/Sb mole ratio, the removal efficiencies of As and Bi both increase slowly, while that of Sb declines sharply. With the increase in promoter addition, the As/Sb mole ratio decreases, and the content of SbAsO4 in the used promoter increases. If the formed SbAsO4 cannot be effectively wrapped up by the AsSbO4, Bi3SbO7 and arsenato antimonates, it will be redissolved, which makes the concentration of Sb(III) increase in the self-purified electrolyte. The removal efficiencies of As, Sb and Bi are 62.0%, 93.0% and 95.0%
2SbAsO4 + 6OH− + (x − 3)H2 O = 2AsO43 − + Sb2 O3 ·x H2 O
(9)
2BiAsO4 + 6OH− + (x − 3)H2 O = 2AsO43 − + Bi2 O3 ·x H2 O
(10)
2AsSbO4 + 2OH− + (x − 1)H2 O = 2AsO2− + Sb2 O5 ·x H2 O
(11)
2 Bi3SbO7 + (x + 9)H2 O = 6Bi(OH)3 + Sb2 O5 ·x H2 O
(12)
Table 3 Composition of the copper electrolyte after indirect self-purification with the As/Sb mole ratio 1:0.7 at 60 °C stirring for 1 h, g/L.
31
As
Sb
Bi
Na
Cu
H2SO4
8.15
0.15
0.04
0.43
18.79
321.64
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100
Before After
As
Sb
Bi
Cu
Fe
16.37 2.56
31.68 58.47
1.89 1.21
0.15 0.03
0.07 0.05
Removal efficiency, %
Table 4 Composition of the used promoter before and after regeneration in 2 mol/L Na2CO3 with L/S ratio 4:1 mL/g under pH 9 stirring for 0.5 h at room temperature, wt%.
Removal efficiency, %
100 80
60 40
As Sb Bi
20 1.6 0.8
60
0.0
As Sb Bi
40 20
30
40
50
60
70
80
Temperature, Fig. 8. Effect of temperature on the removal of As, Sb and Bi from the used promoter in 2 mol/L Na2CO3 with L/S ratio 3:1 mL/g under pH 9.5 contact for 0.5 h.
3000
0 3:1
4:1
5:1
6:1
8:1
10:1
12:1
2500
Intensity (Counts)
2:1
Liquid-solid ratio, mL/g Fig. 6. Effect of L/S ratio on the removal of As, Sb and Bi from the used promoter in 2 mol/L Na2CO3 at room temperature under pH 8.5 contact for 1.5 h.
100 80
Na3 AsO4· 12H2O
2000 1500 1000 500 0
60 10
40 20
20
30
40
50
60
70
80
2-Theta(°)
As Sb Bi
Fig. 9. XRD patterns of the crystal formed in the regeneration solution.
100
0 0.0
0.5
1.0
1.5
2.0
Removal efficiency, %
Removal efficiency, %
80
2.5
Time, h Fig. 7. Effect of contact time on the removal of As, Sb and Bi from the used promoter in 2 mol/L Na2CO3 with L/S ratio 4:1 mL/g under pH 9.5 at room temperature.
Fig. 6 shows that with the increase in L/S ratio from 2:1 mL/g to 6:1 mL/g, the removal efficiencies of As and Bi increase from 62.9% and 11.2% to 95.4% and 61.7% respectively, and then their removal efficiencies do not significantly increase with the further increase in L/S ratio. This may be because with the decomposition of SbAsO4 and BiAsO4, the concentration of As(V) increases in the solution, which makes the dissolution of Bi(III) increase as shown in reactions (13) and (14). Considering the disposal of arsenic contained in the waste water, the L/S ratio should be controlled at 2:1 mL/g to 6:1 mL/g.
Bi(OH)3 ⇄ Bi3 + + 3OH−
(13)
x AsO43 − + y Bi3 + ⇄ [Biy (AsO4 )x ]3(x − y) −
(14)
80
As Sb Bi
60 40 20 0 7
8
9
10
11
12
13
14
pH Fig. 10. Effect of solution pH on the removal of As, Sb and Bi from the used promoter in 2 mol/L Na2CO3 with L/S ratio 4:1 mL/g at room temperature contact for 0.5 h.
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Hydrometallurgy 175 (2018) 28–34
X. Wang et al.
for 1 h. After filtration, the used promoter was regenerated by adding into 2 mol/L Na2CO3 with L/S ratio 3:1 mL/g and stirring for 1 h at 60 °C, filtrating immediately and washing with 0.5 mol/L H2SO4. During stirring, the pH was adjusted to about 9 with NaOH and/or Na2CO3. The regenerated promoter was reused in the experiments, as shown in Fig. 1. The regenerated solution was reused in the experiments after the As and Bi were separated. It can be seen from Table 5 that after reused 3 times, the promoter function did not decay, and its composition did not change obviously. This indicates that the promoter containing Sb(III) and Sb(V) can be reused throughout, and the amount of promoter will gradually increase with the increase in the reuse times.
Table 5 Experimental results of the promoter reused in the indirect self-purification with As/Sb mole ratio 1:0.7 at 60 °C stirring for 1 h, and the regeneration of the used promoter in 2 mol/L Na2CO3 with L/S ratio 3:1 mL/g stirring for 1 h at 60 °C. Cycle times
1 2 3
Self-purified solution, g/L
Regenerated promoter, %
As
Sb
Bi
As
Sb
Bi
8.12 8.07 8.21
0.16 0.13 0.15
0.05 0.07 0.06
2.56 2.61 2.54
58.47 59.01 59.11
1.21 1.37 1.35
3.3.2. Effect of contact time The experimental results of the effect of contact time on the removal of As, Sb and Bi from the used promoter are shown in Fig. 7. These results were obtained by adding the used promoter into 2 mol/L Na2CO3 with L/S ratio 4:1 mL/g and then maintaining the pH at about 9.5 stirring for predetermined time at room temperature. As seen, the separation of As and Bi from the used promoter is very fast. After stirring for 0.5 h, the reactions (9)–(14) have reached their end points. This indicates that when the used promoter is added into the Na2CO3 solution, stirring for 0.5 h is enough.
4. Conclusion Experiments confirmed that the self-purification of impurities As, Sb and Bi in copper electrolyte can be promoted with antimonic oxides. Using the mixture of Sb2O3·xH2O and Sb2O5·xH2O with Sb(V)/Sb(III) molar ratio 0.05 as the promoter, the removal efficiencies of As and Bi increase with the increase in the As/Sb mole ratio from 1:0.5 to 1:3, while that of Sb decreases. The removal efficiencies of As, Sb and Bi are 61.0%, 93.5% and 97.4% respectively when adding the promoter into the electrolyte with the As/Sb mole ratio 1:0.7 at 60 °C and stirring for 1 h. The used promoter can be regenerated in Na2CO3 solution at the pH 8–9 under stirring at a temperature above 40 °C, and the As and Bi can be separated from the regenerated solution by crystallization and precipitation, respectively. The promoter can be reused throughout as after repeated use, its function and composition did not change significantly.
3.3.3. Effect of temperature The experimental results of the effect of temperature on the removal of As, Sb and Bi from the used promoter are shown in Fig. 8. These results were obtained by adding the used promoter into 2 mol/L Na2CO3 with L/S ratio 3:1 mL/g at a predetermined temperature, and then maintaining the pH at about 9.5 and stirring for 0.5 h. As can be seen, the removal efficiencies of As and Bi increase with the increase in temperature from room temperature to 60 °C, while that of Sb decreases slightly. At 60 °C, the removal efficiencies of As, Sb and Bi are 94.7%, 1.2% and 57.9% respectively. Then the removal efficiencies of As, Sb and Bi have no obvious change with the further increase in temperature. It was found that the crystal of Na3AsO4·12H2O can be obtained by cooling the regenerated solution from above 40 °C to room temperature. Therefore, the regeneration should be carried out at ≥ 60 °C. The XRD patterns of the crystal Na3AsO4·12H2O are shown in Fig. 9.
References Braun, T.B., Rawling, J.R., Richards, K.J., 1976. Factors affecting the quality of electrorefining cathode copper. In: Agarwal, J.C. (Ed.), Yannopoulos. Extractive Metallurgy of Copper vol. I. Metallurgical Society Inc., New York, pp. 511–524. Cunnigham, R.M., Calara, J.V., King, M.G., 1997. In: Mishra, B. (Ed.), EPD Congress. TMS, Warrendale, PA, USA, pp. 453–460. Eichrodt, C.W., Schloen, J.H., 1954. In: Butts (Ed.), Copper-the Science and Technology of the Metal, Its Alloys, and Compounds. Reinhold, New York, pp. 171–173. He, W.N., He, S.J., 1996. Methods for purifying impurities in copper electrolyte. Jiangxi Nonferrous Metals 10 (01), 38–40. Hyvarinen, O.V.J., 1979. U. S. Patent No. 4, 157,946. McKevitt, B., Dreisinger, D., 2009. A comparison of various ion exchange resins for the removal of ferric ions from copper electrowinning electrolyte solutions part II: electrolytes containing antimony and bismuth. Hydrometallurgy 98, 122–127. Navarro, P., Simpson, J., Alguacil, F.J., 1999. Removal of antimony(III) from copper in sulphuric acid solutions by solvent extraction with LIX 1104SM. Hydrometallurgy 53, 121–131. Peng, Y.L., Zheng, Y.J., Chen, W.M., 2012a. The oxidation of arsenic from As(III) to As(V) during copper electrorefining. Hydrometallurgy 129-130, 156–160. Peng, Y.L., Zheng, Y.J., Zhou, W.K., 2012b. The separation of copper and arsenic in copper electrolyte purification and recycling. Trans. Nonferrous Metals Soc. China 22 (9), 2268–2273. Riveros, P.A., 2010. The removal of antimony from copper electrolytes using aminophosphonic resins: improving the elution of pentavalent antimony. Hydrometallurgy 105, 110–114. Salari, K., Hashemian, S., Baei, M.T., 2017. Sb(V) removal from copper electrorefining electrolyte: comparative study by different sorbents. Trans. Nonferrous Metals Soc. China 27, 440 − 449. Wan, L.M., 2010. Chemical Purification of Copper Electrolyte Technology Research. Master's Thesis. Central South University, Changsha. Wang, X.W., 2003. Study on the Mechanism of the Formation and Action of Arsenato Antimonic Acid in Copper Electrorefining. Ph.D. Dissertation. Central South University, Changsha. Wang, X.W., Chen, Q.Y., Yin, Z.L., Zhang, P.M., Long, Z.P., Su, Z.F., 2003. Removal of impurities from copper electrolyte with adsorbent containing antimony. Hydrometallurgy 69, 39–44. Wang, X.W., Chen, Q.Y., Yin, Z.L., Zhang, P.M., Wang, Y.W., 2005. Synthesis and characterization of arsenato antimonic acid AAAc(1:1). J. Cent. South Univ. Technol. 12 (Suppl. 1), 76–81. Wang, X.W., Chen, Q.Y., Yin, Z.L., Xiao, L.S., 2006. Identification of arsenato antimonates in copper anode slimes. Hydrometallurgy 84, 211–217. Wang, X.W., Chen, Q.Y., Xiao, L.S., Yin, Z.L., Zhang, Q.X., Zhang, P.M., 2008. A techniques for the purification of copper electrolyte. Chinese Patent No. CN101260539A. Wang, X.W., Chen, Q.Y., Yin, Z.L., Wang, M.Y., Tang, F., 2011a. The role of arsenic in the homogeneous precipitation of As, Sb and Bi impurities in copper electrolyte. Hydrometallurgy 108 (3–4), 199–204.
3.3.4. Effect of solution pH The experimental results of solution pH effect on the removal of As, Sb and Bi from the used promoter are shown in Fig. 10. These results were obtained by adding the used promoter into 2 mol/L Na2CO3 with L/S ratio 4:1 mL/g at room temperature after the solution pH was adjusted to the predetermined value and continued stirring for 0.5 h. As seen, the removal efficiency of Sb is a constant at about 1% with the increase in pH from 7 to 12, but that of As and Bi increase rapidly with the increase in pH from 7 to 8, and their removal efficiencies reach the top at pH 9. Then the removal efficiency of Bi decreases significantly with the increase in pH from 9 to 12, while that of As initially decreases and then rises in this pH range. This indicates that reactions (9)–(14) are accelerated with the increase in pH from 7 to 9, and they reach their ends at pH 9. However, when the pH increases from 9 to 12, the inverse reactions (13)–(14) occur, which reforms the precipitate of Bi2O3·xH2O. Therefore, the regeneration should be carried out at pH between 8 and 9, and the As and Bi can be separated from the regenerated solution by crystallization and precipitation, as shown by Fig. 1. After filtration and washing with 0.5 mol/L H2SO4, the regenerated promoter was obtained. The composition of the regenerated promoter obtained at pH 9 is listed in Table 4 as well. 3.4. Promoter reuse Table 5 shows the experimental results of the promoter reused in the experiments, which were obtained by adding the promoter into the copper electrolyte with the As/Sb mole ratio 1:0.7 at 60 °C and stirring 33
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Xiao, F.X., Mao, J.W., Cao, D., Shen, X.N., Yang, D.X., 2011. Research progress on selfpurification of copper electrolyte. China Nonferrous Metallurgy 06, 73–79. Zhao, T.C., 1981. Metallurgy of Heavy Metals (Part I). Metallurgical Industry Press, Beijing (in Chinese). Zheng, Y.J., Xiao, F.X., Wang, Y., Li, C.H., Xu, W., Jian, H.S., Ma, Y.T., 2008. Industrial experiment of copper electrolyte purification by copper arsenite. J. Cent. South Univ. Technol. 15, 204– −208. Zheng, Y.J., Cui, T., Peng, Y.L., 2012. New process of arsenic removal from second stage decopperizing electrolyte by reduction and crystallization. Chin. J. Nonferrous Metals 22 (7), 2103–2110.
Wang, X.W., Chen, Q.Y., Yin, Z.L., Wang, M.Y., Xiao, B.R., Zhang, F., 2011b. Homogeneous precipitation of As, Sb and Bi impurities in copper electrolyte during electrorefining. Hydrometallurgy 105, 355–358. Wang, X W., Wang, X.M., Wang, M.Y., 2014. A techniques for the removal of impurities from copper electrolyte. Chinese Patent No. ZL 201410333413.1. Wang, X.W., Wang, X.M., Wang, M.Y., 2017. Characteristics of BiAsO4 precipitate formation in copper electrolyte. Hydrometallurgy 171, 95–98. Xiao, F.X., Zheng, Y.J., Wang, Y., Jian, H.S., Huang, X.Y., Ma, Y.T., 2008. Purification mechanism of copper electrolyte by As(III). Trans. Nonferrous Metals Soc. China 18, 1275–1278.
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