Kinetics on Carbosulfidation of the Mixture of Barium Sulfate and Lanthanum Oxide

Molten sulfide electrolysis, which produces metals and sulfur gas by electrolyzing sulfides, is expected to be a sustainable metal production technology due to its extremely low CO2 emissions. A mixture of BaS and La2S3 is used as the electrolyte for molten sulfide electrolysis. In this study, the kinetics of the carbosulfidation reaction of BaSO4–La2O3 mixtures were investigated to develop an electrolyte manufacturing process for molten sulfide electrolysis. Sulfidation of the mixture was performed at 1423 K in the presence of carbon under a sulfur partial pressure of 0.10 atm, confirming CO gas generation from the carbosulfidation reaction. The fraction of oxygen removal from the BaSO4–La2O3 mixture reached 99%, yielding a mixture of BaS and BaLa2S4. Under these experimental conditions, the rate-controlling step was the chemical reaction. The apparent activation energy of the reaction was estimated as 140 ± 34 kJ·mol−1 based on the experiments at 1323–1473 K. Furthermore, the analysis based on the Langmuir adsorption model indicated that the reaction rate was governed by the chemical adsorption of sulfur molecules on the adsorption site. The findings from this study are expected to contribute to the optimization and industrialization of the electrolyte manufacturing process for molten sulfide electrolysis.