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The separation and electrowinning of bismuth from a bismuth glance concentrate using a membrane cell
Hydrometallurgy 100 (2009) 5–9
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Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / h yd r o m e t
The separation and electrowinning of bismuth from a bismuth glance concentrate using a membrane cell Jian-guang Yang a,b,⁎, Chao-bo Tang a, Sheng-hai Yang a, Jing He a, Mo-tang Tang a a b
Department of Metallurgical Science and Engineering, Central South University, 410083, China Institute of Powder Metallurgy Research, Central South University, 410083, China
a r t i c l e
i n f o
Article history: Received 14 July 2009 Received in revised form 9 September 2009 Accepted 10 September 2009 Available online 18 September 2009 Keywords: Bismuth sulfide Chloride leaching Electrowinning Membrane cell Bismuth
a b s t r a c t The main aim of this study was to separate and recover bismuth from a bismuth glance concentrate through leaching, purification and electrowinning from chloride solution. This paper reports on optimization of the process parameters for hydrochloric acid leaching and electrowinning in a membrane cell. Parameters such as bismuth and sodium chloride concentration in catholyte, temperature, current density etc. were examined for their effect on the voltage requirement and current efficiency of bismuth electro-deposition. A maximum current efficiency of > 97% was attained with an catholyte composition of 70 g/L Bi, 25 g/L NaCl, 4.5 mol/L HCl and an anolyte composition of 20 g/L NaOH at 55 °C and a cathode current density of 200 A/m2. Under these optimized conditions, the cathode bismuth purity was 99.98%. An XRD analysis of the condensed salt obtained from the anolyte identified pure sodium chlorate, which can be recycled to the leaching stage. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Very little bismuth comes from the primary processing of bismuth minerals. Most bismuth is obtained as a by-product in other metallurgical processes for copper, silver, tin, lead and gold where it is usually present in sludges or in acidic liquors. During the processing of these bismuth minerals, leaching with H2SO4 or HCl or H2SiF6 is usually involved, and highly acidic solutions containing base metals and bismuth are obtained. Generally, bismuth can be recovered from these spent solutions by hydrolysis and few authors have reported the separation of bismuth from leach solutions by electrowinning. Zertoubi et al. (1993) concluded that the niobium electrode appeared to be suitable for bismuth recovery in acidic media, but the electrochemical re-dissolution of deposited bismuth did not achieve a recovery of more than 50% even in the case of an oxide-free niobium electrode. ReyesAguilera et al. (2008) have noted a number of other methods for bismuth recovery. Fisher et al. (1975); Szymanowski (1996, 1998); Kim et al. (1998); Dreisinger et al. (1993a,b) and Wang et al. (2002) have proposed the separation of bismuth from copper through ion exchange and solvent extraction, using the Acorga SBX-50 extractant in chloride media and organo-phosphorus extractants, respectively. According to Wang et al. (2002), the extraction of As, Bi and Sb has been studied with LIX 1104, Cyanex 923 and Acorga SBX-50, from H2SO4 solutions in the presence of chlorides, and the best results were obtained using Cyanex
⁎ Corresponding author. Department of Metallurgical Science and Engineering, Central South University, 410083, China. Tel.: +86 731 88830470. E-mail address: [email protected] (J. Yang). 0304-386X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2009.09.004
923 as extractant. Other authors (Cox et al., 2002; Iyer and Dhadke, 2003; Ali and Vanjara, 2001; Moriya et al., 2001) have proposed the extraction of Bi(III) from acid or highly acidic solutions of HCl, HBr, HNO3 and/or H2SO4 using Cyanex 925, Cyanex 921, 2-bromo-alkanoic acid and Cyanex 302 as extractant. Whilst Reyes-Aguilera et al. (2008) proposed using supported liquid membranes (SLM) for the recovery of bismuth from aqueous solutions. In our previous study (Jian-guang et al., 2009), a process was proposed for the separation and recovery of bismuth from a low grade bismuth glance flotation concentrate by solvent extraction using N235 as extractant. Under the optimized conditions, the ultimate recovery of bismuth reached >99%. In this study, another process is proposed for the separation and recovery of bismuth from bismuth glance (sulfide) concentrate by leaching and electrowinning. The aim of this paper is to demonstrate that the recovery of bismuth from bismuth glance concentrate from chloride solution is not only feasible but also efficient by electrowinning. 2. Experimental 2.1. Materials The bismuth concentrate obtained from ShiZhuYuan Rare Metal Co., China, was characterized physically, chemically and mineralogically. The dry screen analysis was around 100 mesh (147 μm) and all samples were leached without further grinding. Chemical analysis of the bismuth glance concentrate was carried out by AAS, except SiO2 which was determined by gravimetric analysis, and the results are given in Table 1. X-ray diffraction analysis indicated that bismuth was present mainly as
6
J. Yang et al. / Hydrometallurgy 100 (2009) 5–9
was calculated from analysis of Fe3+ and Cu2+ concentrations by spectrophotometry and AAS.
Table 1 Chemical composition of ShiZhuYuan bismuth glance concentrate (%). Bi
Pb
Fe
Cu
S
SiO2
14.71
0.82
26.30
1.23
32.50
13.10
3FeCl3 þ Bi ¼ 3FeCl2 þ BiCl3 3CuCl2 þ 2Bi ¼ 2BiCl3 þ 3Cu
bismuth sulfide (Bi2S3) (>95%) and a small quantity of bismuth oxide (Bi2O3) (<5%). Optical mineralogical analysis identified the presence of small amounts of quartz (SiO2), chalcocite (Cu2S) and some quantity of pyrite (FeS2), limonite (2Fe2O3·3H2O), and wustite (FeO). Pyrite (FeS2) was the predominant iron mineral present. 2.2. Method The schematic procedure for leaching, purification and recovery of bismuth from this bismuth glance concentrate by electrowinning is presented in Fig. 1. Leaching was carried out in 250 mL glass flasks by adding a weighed amount of bismuth concentrate, sodium chlorate, sodium chloride and surfactant to diluted HCl solution at the desired temperature with magnetic stirring at 250 rpm. The temperature of the system was controlled within 2 °C on a hot plate. A condenser was attached to the flask to prevent vaporization losses. At the end of each experiment, the insoluble leach residue was filtered and washed with 1 M HCl and then distilled water. Surfactant was added to selectively disperse the sulfide minerals and to realize selective leaching of bismuth sulfide from the pyrite (Jian-guang et al., 2009). The recovery of bismuth was calculated by mass balance using the analysis of the concentrate and the leach residue. The leach solution was recycled to leach fresh concentrate until the bismuth concentration in solution was enriched to more than 70 g/L. Bi2 S3 þ NaClO3 þ 6HCl ¼ 2BiCl3 þ NaCl þ 3H2 O þ 3S The oxidation of sulfur to sulfate ion was not significant under the conditions and duration of these tests. In the purification procedure, a weighed amount of active bismuth powder was added to the stirred solution to reduce Fe(III) and displace Cu(II) and then a quantity of ammonium sulfide was added dropwise to precipitate remaining copper. After filtration, the degree of purification
2þ
Cu
2−
þS
¼ Cu2 S
In the electrowinning tests, a two-compartment acrylic cell (dimensions 85 × 75 × 150 mm) was used, as shown in Fig. 2, which was separated by a widely used commercial anion exchange membrane (HF-201, Beijing Enling Technology Co., Ltd. China). The membrane was fitted between 2 mm thick rubber seals in a 50 mm × 40 mm acrylic window between the compartments and the distance from the anode and cathode to the membrane was 2.0 cm and 2.5 cm respectively. The cathode was made of 99.99% titanium plate with a nominal surface area of 12.00 cm2 and the anode was a graphite plate with the same surface area. The composition of the catholyte was 70 g/L Bi3+ (as bismuth chloride), 25 g/L NaCl, and 4.5 mol/L HCl. The composition of the anolyte was initially 20 g/L sodium hydroxide, but a small leakage of chloride ion from the catholyte built up over time which was oxidised to chlorate at the anode. Both electrolytes were recirculated to separate tanks by means of two peristaltic pumps at a high flow rate of 600 cm3/min to ensure good mixing of electrolyte in the cell compartments. At the cathode, the electrode reactions are: 3þ
Bi
þ 3e ¼ Bi ðmain reactionÞ
þ
2H þ 2e ¼ H2 ðsecondary reactionÞ At the anode, the following reactions are possible, but no oxygen or chlorine was detected under the conditions used: Cl− þ 6OH− − 6e ¼ ClO− 3 þ 3H2 O ðmain reactionÞ 4OH− −4e ¼ 2H2 O þ O2 ðsecondary reactionÞ 2Cl− −2e ¼ Cl2 ðsecondary reactionÞ
Fig. 1. Schematic representation of the experimental procedure.
J. Yang et al. / Hydrometallurgy 100 (2009) 5–9
7
Fig. 2. Schematic representation of the bismuth membrane electrowinning cell.
3. Results and discussions
main cell performance parameters such as cathodic current efficiency (CE) and cell voltage. The resultant sodium chlorate concentration in anolyte and the mass of deposited bismuth on the cathode were also determined.
3.1. Leaching results During preliminary experiments, various leaching conditions were examined and the most suitable conditions for bismuth extraction was obtained in the temperature range 60 to 85°C over two hours with 150 g/L HCl using a solid–liquid ratio of 1:4. As shown in Table 2, the recovery of bismuth in the leach solution was substantially higher than the other metals. Through calculations and analysis of Bi3+, Fe2+, Fe3+, and Cu2+ in the leach solutions and in the leach residue, it was found that >99.5% Bi was leached from the bismuth glance concentrate while leaching hardly any other metals. This procedure yielded a bismuthenriched solution consisting of 73.5 g/L Bi3+ contaminated with about 3 g/L iron and <1 g/L copper and lead. 3.2. Purification results and discussions The major aim of purification was to produce a pure electrolyte for electrowinning. The most suitable purification conditions were obtained in the temperature range 30 to 45°C with the addition of 1.4 times of the stoichiometric quantity of bismuth powder and stirring for a period of two hours; followed by 1.2 times of the stoichiometric quantity of ammonium sulfide for sulfide precipitation over 30min. Under these conditions, the bismuth concentration increased slightly whilst iron(III), copper and lead were substantially lower as shown in Table 2. The reduction of copper and lead was >99.8% with little loss of bismuth. 3.3. Electrowinning of bismuth The two-compartment electrowinning experiments were carried out in order to establish optimum electro-deposition parameters such as the effect of bismuth and sodium chloride concentration in catholyte, temperature, cathode current density and electrode distance on the
Table 2 Leaching and purification analyses under optimized conditions. Elements in lixivium
Bi3+
Pb2+
Fe2+
Fe3+
Cu2+
Leach (g/L) Purification (g/L)
73.54 74.67
0.33 0.01
2.43 2.92
0.52 trace
0.47 0.02
3.3.1. Effect of bismuth concentration Electrowinning was first conducted by varying the bismuth concentration in the catholyte from 25 g/L to 75 g/L in the presence of 20 g/L NaCl and 4.5 M HCl at a temperature of 50°C and a current density of 200 A/m2. The optimum operation conditions for the membrane cell runs are summarized in Table 3 and the results are shown in Table 4. Clearly, the current efficiency increases with increasing bismuth concentration, but at low bismuth concentrations spongy deposits were observed, which get easily detached from the cathode during electrolysis. At lower bismuth concentrations, there was higher hydrogen evolution which not only results in lower current efficiencies, but also incorporates hydrogen into the deposit to give brittle bismuth plates and sponge. Since no notable additional benefit was derived in going beyond a bismuth concentration of 70 g/L, this value was chosen as the optimum. 3.3.2. Effect of sodium chloride concentration in catholyte The concentration of sodium chloride in the catholyte was varied from 5 g/L to 30 g/L in the presence of 70 g/L Bi under the same operating conditions shown in Table 3. The aim of incorporation of sodium chloride into the electrolyte was to enhance the formation of BiCl− 4 species and the conductivity of the solution during bismuth electrowinning. The effect of sodium chloride concentration on the current efficiency and cell voltage is summarized in Table 5. The current efficiency increases and the cell voltage decreases with NaCl addition
Table 3 Optimum operating conditions for the electrowinning cell. Electrode distance (cm) Current density (A/m2) Temperature (°C) Additive Concentration (mg/L) Electrowinning duration (h) Agitation mode HCl concentration (mol/L) NaCl (g/L)
5 200 50 25 15 Electromagnetic 4.5 20
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J. Yang et al. / Hydrometallurgy 100 (2009) 5–9
Table 4 Effect of bismuth concentration on the current efficiency.
Table 6 Effect of temperature on current efficiency and cell voltage.
Bismuth concentration (g/L)
Cathode bismuth yield (g)
Current efficiency (%)
Temperature (°C)
Current efficiency (%)
Cell voltage (V)
25 35 45 55 65 70 75
8.23 9.38 10.08 12.65 13.00 13.45 13.49
58.0 66.1 71.1 89.2 91.7 96.4 96.4
25 35 45 55 65
86.2 91.3 95.7 97.2 97.3
3.5 3.3 2.6 2.5 2.5
up to 25 g/L, beyond which there is no benefit. This may be explained by increasing BiCl− 4 species and lower cathodic overpotential required to obtain the desired current density. The decreased overpotential results in lower H2 evolution and higher efficiency for bismuth deposition. Therefore 20–25 g/L NaCl was chosen as the optimum sodium chloride concentration in the catholyte. 3.3.3. Effect of electrowinning temperature Table 6 shows the effect of temperature on the current efficiency and cell voltage at a current density of 200 A/m2, using a catholyte composition of 70 g/L Bi and 25 g/L NaCl. When the temperature increased from 25 to 65 °C, the current efficiency increased and the cell voltage decreased. Furthermore, the bismuth deposit formed at temperatures below 45 °C was non-uniform and non-adherent, whilst higher temperatures improved both the quality and adherence. The higher current efficiency and deposit quality is obviously due to increased bismuth ion mobilities at higher temperatures and less H2 production. However, the increased temperature also results in water and HCl volatilization, Hence a temperature of 55 °C was selected for obtaining bismuth plates of good morphology. 3.3.4. Effect of cathode current density The effect of cathode current density on the current efficiency, cell voltage and resultant sodium chlorate concentration in anolyte was conducted by varying the cathode current density from 100 A/m2 to 300 A/m2 in the presence of 70 g/L Bi and 4.5 M HCl at 50°C and electrowinning for 9 h. Table 7 shows that the current efficiency remained constant around 96.4% to 97.8%, while cell voltage increased steadily with cathode current density. At the same time, the quality of the deposit also changed. The deposit was loose and non-adherent at low cathode current density, but as the current density increased from 100 A/m2 to 250 A/m2, the bismuth coverage of the cathode increased and the deposit was more adherent. However, the higher current density required an increase in the cathodic voltage, which resulted in more H2 evolution. This made the deposit at the edges become increasingly powdery and dendritic. Considering all these factors, 200 A/m2 was chosen as the optimum cathode current density at 50°C. The effect of cathode current density on the sodium chlorate concentration in the anolyte is also shown in Table 7. As the cathode current density increased, the electro-synthesized sodium chlorate concentration increased smoothly. It appears that the steady increase of cathode current density causes a greater rate of penetration of chloride
Table 5 Effect of NaCl concentration on the current efficiency and cell voltage. NaCl concentration (g/L)
Current efficiency (%)
Cell voltage (V)
5 10 15 20 25 30
88.3 92.2 95.0 97.3 97.4 97.3
3.4 3.1 2.7 2.5 2.4 2.4
Table 7 Effect of cathode current density on current efficiency, cell voltage and sodium chlorate concentration in anolyte. Cathode current density (A/m2)
Current efficiency Cell voltage (%) (V)
NaClO3 in anolyte (g/L)
100 150 200 250 300
96.8 97.0 97.9 96.4 96.8
17.4 17.9 19.6 19.9 20.2
1.6 1.9 2.4 3.1 3.5
ions through the membrane into the anode compartment and causes the following anodic reaction. −
−
−
Cl þ 6OH −6e ¼ ClO3 þ 3H2 O 3.4. Confirmation experiment Based on the above studies, the optimum conditions for the electro-deposition of bismuth from a chloride solution in a membrane cell were as follows: Bi 70 g/L, NaCl 25 g/L, temperature 55 °C, HCl 4.5 M in catholyte, electrode distance = 5 cm, cathode current density = 200 A/m2. These conditions were then applied in a confirmation experiment to prepare bismuth metal sheets directly from the bismuth concentrate without leach recycling. The bismuth concentrate leach solution was first purified according to the described optimized conditions and then subjected to electrowinning without further upgrading of the bismuth concentration carried out with the synthetic solutions. In each case, a good quality bismuth plate and eligible anolyte for recycling was obtained. Table 8 and Fig. 3 give the typical analysis of the bismuth plate and the XRD pattern of evaporated salt obtained from the resulting anolyte. It can be seen from Fig. 3 that all the peaks readily indexed to pure sodium chlorate (JCPDS file No. 70-0575). Therefore, the anolyte can be recirculated to the leaching tank as the oxidising agent. 4. Conclusions A comprehensive procedure was developed for the separation and recovery of bismuth from bismuth sulfide concentrate containing mainly pyrite and minor quantities of copper, lead and silica. All the process conditions, including HCl leaching; purification and electrowinning of bismuth, were optimized. Selective leaching of bismuth from pyrite was achieved using chlorate ion as oxidant and copper and lead impurities were removed by cementation and sulfide precipitation. By using an electrolytic cell fitted with an anion exchange membrane separator, pure bismuth plate (99.98%) was obtained from the purified leach liquor catholyte with >97% current efficiency. Some chloride ion migrated
Table 8 Chemical analysis of electrodeposited bismuth plate. Element
Bi
Pb
Fe
Mg
Cu
Others
Content (%)
99.98
0.001
0.003
0.002
0.005
< 0.008
J. Yang et al. / Hydrometallurgy 100 (2009) 5–9
9
References
Fig. 3. X-ray diffraction pattern of salt evaporated from resultant anolyte.
through the membrane into the anolyte containing 20 g/L NaOH and was oxidised to chlorate ion which can be recycled to the leach. Acknowledgment Project (50804056) was supported by the National Nature Science Foundation of China; Project (20080431028) was supported by the China Postdoctoral Science Foundation; Project (2006BAB02B05-0401/02) was supported by the Department of Science and Technology of China.
Ali, K.A., Vanjara, A.K., 2001. Solvent extraction and separation of Bi(III) and Sb(III) from HCl and HBr media using tri-n-octyl phosphine oxide (TOPO). Ind. J. Chem. Technol. 8, 239–243. Cox, M., Flett, D.S., Velea, T., Vasiliu, C., 2002. Impurity removal from copper tankhouse liquors by solvent extraction. International Solvent Extraction Conference. Springer, Cape Town, pp. 995–1000. Dreisinger, D.B., Leong, B.J.Y., Saito, B.R., West-Sells, P.J., 1993a. Hydrometallurgy fundamentals. In: Hiskey, J.B., Warren, G.W. (Eds.), Technology and Innovation. SME, Littleton, Colorado, pp. 801–815. Dreisinger, D.B., Leong, B.J.Y., Bailint, B.J., Beyad, M.H., 1993b. The solvent extraction of As, Sb and Bi from copper refining electrolytes using organo-phosphorus reagents. Proceedings of International Solvent Extraction Conference. Elsevier Applied Science, London, pp. 1271–1278. Fisher, B.M., Hills, R.C., Touro, F.J., 1975. Process for the manufacture of electrolytic copper. US Patent 3,917,519. Gupta, C.K., 1992. Extractive Metallurgy of Molybdenum. CRC Press, Boca Raton, USA. Iyer, J.N., Dhadke, P.M., 2003. Solvent extraction and separation studies of antimony (III) and bismuth(III) by using Cyanex-925. Ind. J. Chem. Technol. 10, 665–669. Jian-guang, Y., Jian-ying, Y., Mo-tang, T., Chao-bo, T., Wei, L., 2009. The solvent extraction separation of bismuth and molybdenum from a low grade bismuth glance flotation concentrate. Hydrometallurgy 96, 342–348. Kim, D.K., Leese, T.A., Neild, M.N., Saito, B.R., Young, S.K., Weidner, C.J., 1998. Use of solvent extraction to remove bismuth and antimony from copper electrolyte at the San Manuel refinery; EPD Congress 1998. Proc. TMS Annual Meeting, San Antonio, TMS, Warrendale, pp. 301–315. Moriya, Y., Sugai, M., Nakata, S., Ogawa, N., 2001. Extraction of bismuth (III) with 2bromoalkanoic acid non-donating solvent from highly acidic aqueous solution. Anal. Sci. 17, 297–300. Reyes-Aguilera, J.A., Gonzalez, M.P., Navarro, R., Saucedo, T.I., Avila-Rodriguez, M., 2008. Supported liquid membranes (SLM) for recovery of bismuth from aqueous solutions. J. Membr. Sci. 310, 13–19. Szymanowski, J., 1996. Industrial processes for copper extraction. Part II Removal of arsenic, antimony and bismuth from technological sulfuric acid solutions. Pol. J. Appl. Chem. 40, 3–15. Szymanowski, J., 1998. Removal of toxic elements from copper electrolyte by solvent extraction. Miner. Process. Extr. Metall. Rev. 18, 389–418. Wang, C., Jiang, K., Liu, D.,Wang, H., 2002. Purification of copper electrolyte with Cyanex 923. International Solvent Extraction Conference, Cape Town, publisher? pp. 1039–1044. Zertoubi, M., Chatelut, M., Vittori, O., 1993. Electrochemical recovery of bismuth in acidic media using a niobium electrode. Hydrometallurgy 34, 109–118.
Contents lists available at ScienceDirect
Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / h yd r o m e t
The separation and electrowinning of bismuth from a bismuth glance concentrate using a membrane cell Jian-guang Yang a,b,⁎, Chao-bo Tang a, Sheng-hai Yang a, Jing He a, Mo-tang Tang a a b
Department of Metallurgical Science and Engineering, Central South University, 410083, China Institute of Powder Metallurgy Research, Central South University, 410083, China
a r t i c l e
i n f o
Article history: Received 14 July 2009 Received in revised form 9 September 2009 Accepted 10 September 2009 Available online 18 September 2009 Keywords: Bismuth sulfide Chloride leaching Electrowinning Membrane cell Bismuth
a b s t r a c t The main aim of this study was to separate and recover bismuth from a bismuth glance concentrate through leaching, purification and electrowinning from chloride solution. This paper reports on optimization of the process parameters for hydrochloric acid leaching and electrowinning in a membrane cell. Parameters such as bismuth and sodium chloride concentration in catholyte, temperature, current density etc. were examined for their effect on the voltage requirement and current efficiency of bismuth electro-deposition. A maximum current efficiency of > 97% was attained with an catholyte composition of 70 g/L Bi, 25 g/L NaCl, 4.5 mol/L HCl and an anolyte composition of 20 g/L NaOH at 55 °C and a cathode current density of 200 A/m2. Under these optimized conditions, the cathode bismuth purity was 99.98%. An XRD analysis of the condensed salt obtained from the anolyte identified pure sodium chlorate, which can be recycled to the leaching stage. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Very little bismuth comes from the primary processing of bismuth minerals. Most bismuth is obtained as a by-product in other metallurgical processes for copper, silver, tin, lead and gold where it is usually present in sludges or in acidic liquors. During the processing of these bismuth minerals, leaching with H2SO4 or HCl or H2SiF6 is usually involved, and highly acidic solutions containing base metals and bismuth are obtained. Generally, bismuth can be recovered from these spent solutions by hydrolysis and few authors have reported the separation of bismuth from leach solutions by electrowinning. Zertoubi et al. (1993) concluded that the niobium electrode appeared to be suitable for bismuth recovery in acidic media, but the electrochemical re-dissolution of deposited bismuth did not achieve a recovery of more than 50% even in the case of an oxide-free niobium electrode. ReyesAguilera et al. (2008) have noted a number of other methods for bismuth recovery. Fisher et al. (1975); Szymanowski (1996, 1998); Kim et al. (1998); Dreisinger et al. (1993a,b) and Wang et al. (2002) have proposed the separation of bismuth from copper through ion exchange and solvent extraction, using the Acorga SBX-50 extractant in chloride media and organo-phosphorus extractants, respectively. According to Wang et al. (2002), the extraction of As, Bi and Sb has been studied with LIX 1104, Cyanex 923 and Acorga SBX-50, from H2SO4 solutions in the presence of chlorides, and the best results were obtained using Cyanex
⁎ Corresponding author. Department of Metallurgical Science and Engineering, Central South University, 410083, China. Tel.: +86 731 88830470. E-mail address: [email protected] (J. Yang). 0304-386X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2009.09.004
923 as extractant. Other authors (Cox et al., 2002; Iyer and Dhadke, 2003; Ali and Vanjara, 2001; Moriya et al., 2001) have proposed the extraction of Bi(III) from acid or highly acidic solutions of HCl, HBr, HNO3 and/or H2SO4 using Cyanex 925, Cyanex 921, 2-bromo-alkanoic acid and Cyanex 302 as extractant. Whilst Reyes-Aguilera et al. (2008) proposed using supported liquid membranes (SLM) for the recovery of bismuth from aqueous solutions. In our previous study (Jian-guang et al., 2009), a process was proposed for the separation and recovery of bismuth from a low grade bismuth glance flotation concentrate by solvent extraction using N235 as extractant. Under the optimized conditions, the ultimate recovery of bismuth reached >99%. In this study, another process is proposed for the separation and recovery of bismuth from bismuth glance (sulfide) concentrate by leaching and electrowinning. The aim of this paper is to demonstrate that the recovery of bismuth from bismuth glance concentrate from chloride solution is not only feasible but also efficient by electrowinning. 2. Experimental 2.1. Materials The bismuth concentrate obtained from ShiZhuYuan Rare Metal Co., China, was characterized physically, chemically and mineralogically. The dry screen analysis was around 100 mesh (147 μm) and all samples were leached without further grinding. Chemical analysis of the bismuth glance concentrate was carried out by AAS, except SiO2 which was determined by gravimetric analysis, and the results are given in Table 1. X-ray diffraction analysis indicated that bismuth was present mainly as
6
J. Yang et al. / Hydrometallurgy 100 (2009) 5–9
was calculated from analysis of Fe3+ and Cu2+ concentrations by spectrophotometry and AAS.
Table 1 Chemical composition of ShiZhuYuan bismuth glance concentrate (%). Bi
Pb
Fe
Cu
S
SiO2
14.71
0.82
26.30
1.23
32.50
13.10
3FeCl3 þ Bi ¼ 3FeCl2 þ BiCl3 3CuCl2 þ 2Bi ¼ 2BiCl3 þ 3Cu
bismuth sulfide (Bi2S3) (>95%) and a small quantity of bismuth oxide (Bi2O3) (<5%). Optical mineralogical analysis identified the presence of small amounts of quartz (SiO2), chalcocite (Cu2S) and some quantity of pyrite (FeS2), limonite (2Fe2O3·3H2O), and wustite (FeO). Pyrite (FeS2) was the predominant iron mineral present. 2.2. Method The schematic procedure for leaching, purification and recovery of bismuth from this bismuth glance concentrate by electrowinning is presented in Fig. 1. Leaching was carried out in 250 mL glass flasks by adding a weighed amount of bismuth concentrate, sodium chlorate, sodium chloride and surfactant to diluted HCl solution at the desired temperature with magnetic stirring at 250 rpm. The temperature of the system was controlled within 2 °C on a hot plate. A condenser was attached to the flask to prevent vaporization losses. At the end of each experiment, the insoluble leach residue was filtered and washed with 1 M HCl and then distilled water. Surfactant was added to selectively disperse the sulfide minerals and to realize selective leaching of bismuth sulfide from the pyrite (Jian-guang et al., 2009). The recovery of bismuth was calculated by mass balance using the analysis of the concentrate and the leach residue. The leach solution was recycled to leach fresh concentrate until the bismuth concentration in solution was enriched to more than 70 g/L. Bi2 S3 þ NaClO3 þ 6HCl ¼ 2BiCl3 þ NaCl þ 3H2 O þ 3S The oxidation of sulfur to sulfate ion was not significant under the conditions and duration of these tests. In the purification procedure, a weighed amount of active bismuth powder was added to the stirred solution to reduce Fe(III) and displace Cu(II) and then a quantity of ammonium sulfide was added dropwise to precipitate remaining copper. After filtration, the degree of purification
2þ
Cu
2−
þS
¼ Cu2 S
In the electrowinning tests, a two-compartment acrylic cell (dimensions 85 × 75 × 150 mm) was used, as shown in Fig. 2, which was separated by a widely used commercial anion exchange membrane (HF-201, Beijing Enling Technology Co., Ltd. China). The membrane was fitted between 2 mm thick rubber seals in a 50 mm × 40 mm acrylic window between the compartments and the distance from the anode and cathode to the membrane was 2.0 cm and 2.5 cm respectively. The cathode was made of 99.99% titanium plate with a nominal surface area of 12.00 cm2 and the anode was a graphite plate with the same surface area. The composition of the catholyte was 70 g/L Bi3+ (as bismuth chloride), 25 g/L NaCl, and 4.5 mol/L HCl. The composition of the anolyte was initially 20 g/L sodium hydroxide, but a small leakage of chloride ion from the catholyte built up over time which was oxidised to chlorate at the anode. Both electrolytes were recirculated to separate tanks by means of two peristaltic pumps at a high flow rate of 600 cm3/min to ensure good mixing of electrolyte in the cell compartments. At the cathode, the electrode reactions are: 3þ
Bi
þ 3e ¼ Bi ðmain reactionÞ
þ
2H þ 2e ¼ H2 ðsecondary reactionÞ At the anode, the following reactions are possible, but no oxygen or chlorine was detected under the conditions used: Cl− þ 6OH− − 6e ¼ ClO− 3 þ 3H2 O ðmain reactionÞ 4OH− −4e ¼ 2H2 O þ O2 ðsecondary reactionÞ 2Cl− −2e ¼ Cl2 ðsecondary reactionÞ
Fig. 1. Schematic representation of the experimental procedure.
J. Yang et al. / Hydrometallurgy 100 (2009) 5–9
7
Fig. 2. Schematic representation of the bismuth membrane electrowinning cell.
3. Results and discussions
main cell performance parameters such as cathodic current efficiency (CE) and cell voltage. The resultant sodium chlorate concentration in anolyte and the mass of deposited bismuth on the cathode were also determined.
3.1. Leaching results During preliminary experiments, various leaching conditions were examined and the most suitable conditions for bismuth extraction was obtained in the temperature range 60 to 85°C over two hours with 150 g/L HCl using a solid–liquid ratio of 1:4. As shown in Table 2, the recovery of bismuth in the leach solution was substantially higher than the other metals. Through calculations and analysis of Bi3+, Fe2+, Fe3+, and Cu2+ in the leach solutions and in the leach residue, it was found that >99.5% Bi was leached from the bismuth glance concentrate while leaching hardly any other metals. This procedure yielded a bismuthenriched solution consisting of 73.5 g/L Bi3+ contaminated with about 3 g/L iron and <1 g/L copper and lead. 3.2. Purification results and discussions The major aim of purification was to produce a pure electrolyte for electrowinning. The most suitable purification conditions were obtained in the temperature range 30 to 45°C with the addition of 1.4 times of the stoichiometric quantity of bismuth powder and stirring for a period of two hours; followed by 1.2 times of the stoichiometric quantity of ammonium sulfide for sulfide precipitation over 30min. Under these conditions, the bismuth concentration increased slightly whilst iron(III), copper and lead were substantially lower as shown in Table 2. The reduction of copper and lead was >99.8% with little loss of bismuth. 3.3. Electrowinning of bismuth The two-compartment electrowinning experiments were carried out in order to establish optimum electro-deposition parameters such as the effect of bismuth and sodium chloride concentration in catholyte, temperature, cathode current density and electrode distance on the
Table 2 Leaching and purification analyses under optimized conditions. Elements in lixivium
Bi3+
Pb2+
Fe2+
Fe3+
Cu2+
Leach (g/L) Purification (g/L)
73.54 74.67
0.33 0.01
2.43 2.92
0.52 trace
0.47 0.02
3.3.1. Effect of bismuth concentration Electrowinning was first conducted by varying the bismuth concentration in the catholyte from 25 g/L to 75 g/L in the presence of 20 g/L NaCl and 4.5 M HCl at a temperature of 50°C and a current density of 200 A/m2. The optimum operation conditions for the membrane cell runs are summarized in Table 3 and the results are shown in Table 4. Clearly, the current efficiency increases with increasing bismuth concentration, but at low bismuth concentrations spongy deposits were observed, which get easily detached from the cathode during electrolysis. At lower bismuth concentrations, there was higher hydrogen evolution which not only results in lower current efficiencies, but also incorporates hydrogen into the deposit to give brittle bismuth plates and sponge. Since no notable additional benefit was derived in going beyond a bismuth concentration of 70 g/L, this value was chosen as the optimum. 3.3.2. Effect of sodium chloride concentration in catholyte The concentration of sodium chloride in the catholyte was varied from 5 g/L to 30 g/L in the presence of 70 g/L Bi under the same operating conditions shown in Table 3. The aim of incorporation of sodium chloride into the electrolyte was to enhance the formation of BiCl− 4 species and the conductivity of the solution during bismuth electrowinning. The effect of sodium chloride concentration on the current efficiency and cell voltage is summarized in Table 5. The current efficiency increases and the cell voltage decreases with NaCl addition
Table 3 Optimum operating conditions for the electrowinning cell. Electrode distance (cm) Current density (A/m2) Temperature (°C) Additive Concentration (mg/L) Electrowinning duration (h) Agitation mode HCl concentration (mol/L) NaCl (g/L)
5 200 50 25 15 Electromagnetic 4.5 20
8
J. Yang et al. / Hydrometallurgy 100 (2009) 5–9
Table 4 Effect of bismuth concentration on the current efficiency.
Table 6 Effect of temperature on current efficiency and cell voltage.
Bismuth concentration (g/L)
Cathode bismuth yield (g)
Current efficiency (%)
Temperature (°C)
Current efficiency (%)
Cell voltage (V)
25 35 45 55 65 70 75
8.23 9.38 10.08 12.65 13.00 13.45 13.49
58.0 66.1 71.1 89.2 91.7 96.4 96.4
25 35 45 55 65
86.2 91.3 95.7 97.2 97.3
3.5 3.3 2.6 2.5 2.5
up to 25 g/L, beyond which there is no benefit. This may be explained by increasing BiCl− 4 species and lower cathodic overpotential required to obtain the desired current density. The decreased overpotential results in lower H2 evolution and higher efficiency for bismuth deposition. Therefore 20–25 g/L NaCl was chosen as the optimum sodium chloride concentration in the catholyte. 3.3.3. Effect of electrowinning temperature Table 6 shows the effect of temperature on the current efficiency and cell voltage at a current density of 200 A/m2, using a catholyte composition of 70 g/L Bi and 25 g/L NaCl. When the temperature increased from 25 to 65 °C, the current efficiency increased and the cell voltage decreased. Furthermore, the bismuth deposit formed at temperatures below 45 °C was non-uniform and non-adherent, whilst higher temperatures improved both the quality and adherence. The higher current efficiency and deposit quality is obviously due to increased bismuth ion mobilities at higher temperatures and less H2 production. However, the increased temperature also results in water and HCl volatilization, Hence a temperature of 55 °C was selected for obtaining bismuth plates of good morphology. 3.3.4. Effect of cathode current density The effect of cathode current density on the current efficiency, cell voltage and resultant sodium chlorate concentration in anolyte was conducted by varying the cathode current density from 100 A/m2 to 300 A/m2 in the presence of 70 g/L Bi and 4.5 M HCl at 50°C and electrowinning for 9 h. Table 7 shows that the current efficiency remained constant around 96.4% to 97.8%, while cell voltage increased steadily with cathode current density. At the same time, the quality of the deposit also changed. The deposit was loose and non-adherent at low cathode current density, but as the current density increased from 100 A/m2 to 250 A/m2, the bismuth coverage of the cathode increased and the deposit was more adherent. However, the higher current density required an increase in the cathodic voltage, which resulted in more H2 evolution. This made the deposit at the edges become increasingly powdery and dendritic. Considering all these factors, 200 A/m2 was chosen as the optimum cathode current density at 50°C. The effect of cathode current density on the sodium chlorate concentration in the anolyte is also shown in Table 7. As the cathode current density increased, the electro-synthesized sodium chlorate concentration increased smoothly. It appears that the steady increase of cathode current density causes a greater rate of penetration of chloride
Table 5 Effect of NaCl concentration on the current efficiency and cell voltage. NaCl concentration (g/L)
Current efficiency (%)
Cell voltage (V)
5 10 15 20 25 30
88.3 92.2 95.0 97.3 97.4 97.3
3.4 3.1 2.7 2.5 2.4 2.4
Table 7 Effect of cathode current density on current efficiency, cell voltage and sodium chlorate concentration in anolyte. Cathode current density (A/m2)
Current efficiency Cell voltage (%) (V)
NaClO3 in anolyte (g/L)
100 150 200 250 300
96.8 97.0 97.9 96.4 96.8
17.4 17.9 19.6 19.9 20.2
1.6 1.9 2.4 3.1 3.5
ions through the membrane into the anode compartment and causes the following anodic reaction. −
−
−
Cl þ 6OH −6e ¼ ClO3 þ 3H2 O 3.4. Confirmation experiment Based on the above studies, the optimum conditions for the electro-deposition of bismuth from a chloride solution in a membrane cell were as follows: Bi 70 g/L, NaCl 25 g/L, temperature 55 °C, HCl 4.5 M in catholyte, electrode distance = 5 cm, cathode current density = 200 A/m2. These conditions were then applied in a confirmation experiment to prepare bismuth metal sheets directly from the bismuth concentrate without leach recycling. The bismuth concentrate leach solution was first purified according to the described optimized conditions and then subjected to electrowinning without further upgrading of the bismuth concentration carried out with the synthetic solutions. In each case, a good quality bismuth plate and eligible anolyte for recycling was obtained. Table 8 and Fig. 3 give the typical analysis of the bismuth plate and the XRD pattern of evaporated salt obtained from the resulting anolyte. It can be seen from Fig. 3 that all the peaks readily indexed to pure sodium chlorate (JCPDS file No. 70-0575). Therefore, the anolyte can be recirculated to the leaching tank as the oxidising agent. 4. Conclusions A comprehensive procedure was developed for the separation and recovery of bismuth from bismuth sulfide concentrate containing mainly pyrite and minor quantities of copper, lead and silica. All the process conditions, including HCl leaching; purification and electrowinning of bismuth, were optimized. Selective leaching of bismuth from pyrite was achieved using chlorate ion as oxidant and copper and lead impurities were removed by cementation and sulfide precipitation. By using an electrolytic cell fitted with an anion exchange membrane separator, pure bismuth plate (99.98%) was obtained from the purified leach liquor catholyte with >97% current efficiency. Some chloride ion migrated
Table 8 Chemical analysis of electrodeposited bismuth plate. Element
Bi
Pb
Fe
Mg
Cu
Others
Content (%)
99.98
0.001
0.003
0.002
0.005
< 0.008
J. Yang et al. / Hydrometallurgy 100 (2009) 5–9
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References
Fig. 3. X-ray diffraction pattern of salt evaporated from resultant anolyte.
through the membrane into the anolyte containing 20 g/L NaOH and was oxidised to chlorate ion which can be recycled to the leach. Acknowledgment Project (50804056) was supported by the National Nature Science Foundation of China; Project (20080431028) was supported by the China Postdoctoral Science Foundation; Project (2006BAB02B05-0401/02) was supported by the Department of Science and Technology of China.
Ali, K.A., Vanjara, A.K., 2001. Solvent extraction and separation of Bi(III) and Sb(III) from HCl and HBr media using tri-n-octyl phosphine oxide (TOPO). Ind. J. Chem. Technol. 8, 239–243. Cox, M., Flett, D.S., Velea, T., Vasiliu, C., 2002. Impurity removal from copper tankhouse liquors by solvent extraction. International Solvent Extraction Conference. Springer, Cape Town, pp. 995–1000. Dreisinger, D.B., Leong, B.J.Y., Saito, B.R., West-Sells, P.J., 1993a. Hydrometallurgy fundamentals. In: Hiskey, J.B., Warren, G.W. (Eds.), Technology and Innovation. SME, Littleton, Colorado, pp. 801–815. Dreisinger, D.B., Leong, B.J.Y., Bailint, B.J., Beyad, M.H., 1993b. The solvent extraction of As, Sb and Bi from copper refining electrolytes using organo-phosphorus reagents. Proceedings of International Solvent Extraction Conference. Elsevier Applied Science, London, pp. 1271–1278. Fisher, B.M., Hills, R.C., Touro, F.J., 1975. Process for the manufacture of electrolytic copper. US Patent 3,917,519. Gupta, C.K., 1992. Extractive Metallurgy of Molybdenum. CRC Press, Boca Raton, USA. Iyer, J.N., Dhadke, P.M., 2003. Solvent extraction and separation studies of antimony (III) and bismuth(III) by using Cyanex-925. Ind. J. Chem. Technol. 10, 665–669. Jian-guang, Y., Jian-ying, Y., Mo-tang, T., Chao-bo, T., Wei, L., 2009. The solvent extraction separation of bismuth and molybdenum from a low grade bismuth glance flotation concentrate. Hydrometallurgy 96, 342–348. Kim, D.K., Leese, T.A., Neild, M.N., Saito, B.R., Young, S.K., Weidner, C.J., 1998. Use of solvent extraction to remove bismuth and antimony from copper electrolyte at the San Manuel refinery; EPD Congress 1998. Proc. TMS Annual Meeting, San Antonio, TMS, Warrendale, pp. 301–315. Moriya, Y., Sugai, M., Nakata, S., Ogawa, N., 2001. Extraction of bismuth (III) with 2bromoalkanoic acid non-donating solvent from highly acidic aqueous solution. Anal. Sci. 17, 297–300. Reyes-Aguilera, J.A., Gonzalez, M.P., Navarro, R., Saucedo, T.I., Avila-Rodriguez, M., 2008. Supported liquid membranes (SLM) for recovery of bismuth from aqueous solutions. J. Membr. Sci. 310, 13–19. Szymanowski, J., 1996. Industrial processes for copper extraction. Part II Removal of arsenic, antimony and bismuth from technological sulfuric acid solutions. Pol. J. Appl. Chem. 40, 3–15. Szymanowski, J., 1998. Removal of toxic elements from copper electrolyte by solvent extraction. Miner. Process. Extr. Metall. Rev. 18, 389–418. Wang, C., Jiang, K., Liu, D.,Wang, H., 2002. Purification of copper electrolyte with Cyanex 923. International Solvent Extraction Conference, Cape Town, publisher? pp. 1039–1044. Zertoubi, M., Chatelut, M., Vittori, O., 1993. Electrochemical recovery of bismuth in acidic media using a niobium electrode. Hydrometallurgy 34, 109–118.