Direct electrochemical reduction of copper sulfide in molten borax

Abstract

In this study, for the first time, direct copper production from copper sulfide was carried out via direct electrochemical reduction method using inexpensive and stable molten borax electrolyte. The effects of current density (100–800 mA/cm²) and electrolysis time (15–90 min) on both the cathodic current efficiency and copper yield were systematically investigated in consideration of possible electrochemical/chemical reactions at 1200°C. The copper production yield reached 98.09% after 90 min of electrolysis at a current density of 600 mA/cm². Direct metal production was shown to be possible with 6 kWh/kg energy consumption at a 600 mA/cm² current density, at which the highest current efficiency (41%) was obtained. The suggested method can also be applied to metal/alloy production from single- and mixed-metal sulfides coming from primary production and precipitated sulfides, which are produced in the mining and metallurgical industries during treatment of process solutions or wastewaters.

Keywords

molten salt electrolysis / electro-reduction / copper extraction / copper sulfide / borax

References

[1] Habashi F. Handbook of Extractive Metallurg, 1998, Weinheim, Wiley-VCH 491.

[2] Habashi F. Pollution problems in the metallurgical industry: A review. J. Min. Environ., 2011, 2(1): 17.

[3] Li GM, Wang DH, Jin XB, Chen GZ. Electrolysis of solid MoS₂ in molten CaCl₂ for Mo extraction without CO₂ emission. Electrochem. Commun., 2007, 9(8): 1951.

[4] Vignes A. Extractive Metallurgy 3: Processing Operations and Routes, 2013, New Jersey, John Wiley & Sons Inc. 265.

[5] Vignes A. Extractive Metallurgy 2: Metallurgical Reaction Processe, 2013, New Jersey, John Wiley & Sons Inc. 87.

[6] Chen GZ, Fray DJ, Farthing TW. Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride. Nature, 2000, 407(6802): 361.

[7] Wang SL, Wang W, Li SC, Cao SH. Cathodic behavior of molten CaCl₂-CaO and CaCl₂-NaCl-CaO. Int. J. Miner. Metall. Mater., 2010, 17(6): 791.

[8] Li ZQ, Ru LY, Bai CG, Zhang N, Wang HH. Effect of sintering temperature on the electrolysis of TiO₂. Int. J. Miner. Metall. Mater., 2012, 19(7): 636.

[9] Liu Y, Zhang YA, Wang W, Li DS, Ma JY. Microstructure and electrolysis behavior of self-healing Cu-Ni-Fe composite inert anodes for aluminum electrowinning. Int. J. Miner. Metall. Mater., 2018, 25(10): 1208.

[10] Gao HP, Tan MS, Rong LB, Wang ZY, Peng JJ, Jin XB, Chen GZ. Preparation of Mo nanopowders through electroreduction of solid MoS₂ in molten KCl-NaCl. Phys. Chem. Chem. Phys., 2014, 16(36): 19514.

[11] Xiao Y, van der Plas DW, Bohte J, Lans SC, van Sandwijk A, Reuter MA. Electrowinning Al from Al₂S₃ in molten salt. J. Electrochem. Soc., 2007, 154(6): 334.

[12] Wang T, Gao HP, Jin XB, Chen HL, Peng JJ, Chen GZ. Electrolysis of solid metal sulfide to metal and sulfur in molten NaCl-KCl. Electrochem. Commun., 2011, 13(12): 1492.

[13] Suzuki N, Tanaka M, Noguchi H, Natsui S, Kikuchi T, Suzuki RO. Reduction of TiS₂ by OS process in CaCl₂ melt. ECS Trans., 2016, 75(15): 507.

[14] Matsuzaki T, Natsui S, Kikuchi T, Suzuki RO. Electrolytic reduction of V3S4 in molten CaCl2. Mater. Trans., 2017, 58(3): 371.

[15] H.Y. Yin, B. Chung, and D.R. Sadoway, Electrolysis of a molten semiconductor, Nat. Commun., 7(2016), art. No. 12584.

[16] Ge XL, Wang XD, Seetharaman S. Copper extraction from copper ore by electro-reduction in molten CaCl2-NaCl. Electrochim. Acta, 2009, 54(18): 4397.

[17] Ge XL, Seetharaman S. The salt extraction process — a novel route for metal extraction Part 2 — Cu/Fe extraction from copper oxide and sulphides. Miner. Process. Extr. Metall., 2010, 119(2): 93.

[18] Sokhanvaran S, Lee SK, Lambotte G, Allanore A. Electrochemistry of molten sulfides: copper extraction from BaS-Cu₂S. J. Electrochem. Soc., 2016, 163(3): 115.

[19] Sahu SK, Chmielowiec B, Allanore A. Electrolytic extraction of copper, molybdenum and rhenium from molten sulfide electrolyte. Electrochim. Acta, 2017, 243, 382.

[20] Tan MS, He R, Yuan YT, Wang ZY, Jin XB. Electrochemical sulfur removal from chalcopyrite in molten NaCl-KCl. Electrochim. Acta, 2016, 213, 148.

[21] Mohandas KS, Fray DJ. Electrochemical deoxidation of solid zirconium dioxide in molten calcium chloride. Metall. Mater. Trans. B, 2009, 40(5): 685.

[22] Wang SL, Li SC, Wan LF, Wang CH. Electro-deoxidation of V₂O₃ in molten CaCl₂-NaCl-CaO. Int. J. Miner. Metall. Mater., 2012, 19(3): 212.