Dissolution Characteristics and Behavior of Antimony, Sulfur, and Antimony Sulfide in Molten NaCl–KCl

Molten salt electrolysis of antimony sulfide presents a sustainable process for antimony extraction. This study investigates the solubility and reaction behaviors of Sb₂S₃ and its electrolysis products (Sb and S) in NaCl–KCl molten salt at temperatures ranging from 700 to 900 °C and with varying molten salt compositions. The results indicate that the solubility of Sb and Sb₂S₃ in the molten salt increases with rising temperature, whereas the concentration of S in the molten salt initially increases and then decreases, reaching maximum solubilities of 0.326, 0.84, and 0.016%, respectively. Changes in molten salt composition also affect the solubility of each substance. The highest solubility of Sb, 0.35%, was observed in NaCl_37.5%-KCl_62.5% molten salts. In contrast, at NaCl_57.1%–KCl_42.9% and NaCl_62.5%–KCl_37.5%, the solubilities of S and Sb₂S₃ reached their lowest values, at 0.0047 and 0.44%, respectively. The chemical reaction between Sb and S is the primary cause of the secondary loss of Sb. In addition, changes in material spacing, molten salt structure, and melt temperature can influence the loss rate. Therefore, minimizing the residence time and diffusion of S in molten salt, as well as limiting the solubility of Sb during molten salt electrolysis, are crucial for improving current efficiency.