Physico-Chemical Properties of Molten NaCl–KCl–Na₂S System for Sulfide Electrolytic Desulfurization

Sulfide electrolysis in molten salt, a critical desulfurization and metal extraction pathway, represents a clean, low-carbon process with zero SO₂ emissions. In industrial applications, understanding properties of molten salt is vital for process stability and efficient product separation. This study analyzed the thermal absorption curve, microscopic morphology, physical phase structure, and volatility of the NaCl–KCl–Na₂S system suitable for sulfide molten salt electrolysis. Furthermore, the influence of viscosity, surface tension and conductivity on composition in the range of 700 °C to 950 °C was investigated by using molten salt electrolysis of antimony sulfide concentrate as an example. The results show that the greater the degree of superheat of the molten salt, the greater the volatilization loss, but the structure of the molten salt is stable. Increasing temperature can change the melt’s physical properties in a direction more favorable for the separation of products. The viscosity and surface tension decrease with increasing temperature, while the conductivity increases with temperature. When the impurity content in the mixed molten salt increased from 4.28 to 12.96 pct, the viscosity increased by 132 pct, and the conductivity decreased by 19.86 pct at 900 °C.