Electrochemical reduction mechanism of Zn2+ in molten NaCl−KCl eutectic

Abstract

A process comprising selective chlorination and molten salt electrolysis was proposed to develop an efficient and environmental-friendly technology for zinc recovery from metallurgical dusts. The theoretical feasibility of this technology was firstly estimated based on thermodynamic fundamentals. Subsequently, the electrochemical behavior of Zn2+ on tungsten electrode was investigated in molten NaCl−KCl eutectic at 973 K by many electrochemical transient methods. The results showed that the reduction of Zn2+ on tungsten electrode was found to be a one-step process exchanging two electrons with the initial reduction potential of −0.74 V (vs Ag/AgCl), and the electrode process was considered as quasi-reversible and controlled by diffusion. The diffusion coefficient of Zn2+ ions in the melts was determined in the order of 10−5 cm2/s. Finally, the electrolytic preparation of zinc was carried out by potentiostatic electrolysis in molten NaCl−KCl−ZnCl2 eutectic at −1.6 V (vs Ag/AgCl). Spheroidic granular metal with silver-white luster was attained after electrolysis for 9.5 h, and identified as pure Zn. The present study confirms that it is practically feasible to extract pure zinc metal by direct electrolysis of ZnCl2 in molten NaCl−KCl eutectic, and provides a valuable theoretical reference for the efficient recovery of zinc from metallurgical dusts.