The effect of accumulation of cathodic decomposition on the anodic conversion of sulfide ions to sulfur in a continuous extractive electrochemical reactor

The continuous and direct conversion of sulfide ions to sulfur using an extractive electrochemical method was studied. A concentrated sulfide ion solution was continuously supplied into a semi‐batch reactor to keep the reaction rate stable. The overall efficiency (η o) was used as an index for this conversion. Theoretical analysis indicates that the decay of the overall efficiency (η o) is inevitable due to the chemical dissolution of the adherent sulfur by the unremovable hydroxide ions and polysulfide ions in the alkaline electrolysis solution under long‐term operation. The concentration of hydroxide ions increases as a result of the cathodic decomposition of water. The polysulfide ions are produced from the combination of adherent sulfur and hydroxide ions. However, the decaying rate of the overall efficiency (ηo ) was improved experimentally to be more than 15% by carefully regulating the electrolyte concentration under long‐term operation. This paper reports on two key factors in controlling the decaying rate such that it is within an acceptable range for industrial operation: feeding interval (?t) and feeding concentration (?C).