Electrochemical sulfur removal from chalcopyrite in molten NaCl-KCl

Abstract Electrolysis of solid chalcopyrite (CuFeS 2 ) against a graphite inert anode has been studied in equimolar NaCl-KCl melt at 700 °C. During electrolysis, S 2− ions are released from the solid CuFeS 2 cathode, transfer to the graphite anode and discharge to S 2 gas. The reduction mechanism of CuFeS 2 was investigated by cyclic voltammetry, potentiostatic and constant voltage electrolysis together with spectroscopic and scanning electron microscopic analyses. The reduction contains mainly three stages: the insertion of Na + or K + into CuFeS 2 , forming L x CuFeS 2 (L = Na or K, x ≤ 1); the partial reduction of L x CuFeS 2 to L x-w CuFe 1-y S 2-z and Fe; the complete reduction to a mixture of Cu and Fe, which can be magnetically separated. After the separation, pure Cu can be obtained by leaching out the residual Fe with acid. Electrolysis at a cell voltage of 2.4 V has led to a rapid reduction of CuFeS 2 . The current efficiency and energy consumption were 85% and 1.68 kWh/kg-CuFeS 2 , respectively.