Recycling sulfidic spent caustic streams using a sulfide/air fuel cell

It is urgent to develop a green and cost-efficient process to recycle the resources and energy from spent caustic streams. We develop an energy-free strategy to recover sulfur, caustic, and energy from spent caustic streams in the meantime. Two-electron route sulfide oxidation reaction and four-electron route oxygen reduction reaction are combined to run as an abiotic sulfide/air fuel cell. The feasibility of the sulfide/air fuel cell is proven. The lab-scale prototype can self-driven run at >6.5 mA cm−2 for 10 h, with a current efficiency of about 14 %. A sulfidic spent caustic stream is adopted to evaluate the real stream treatment performances. The cell can discharge at >2 mA cm−2 for 60 h, where the sulfide concentration of the sulfidic spent caustic stream is continuously decreased from 0.56 mol/L to 0.31 mol/L. Cost-efficient carbon-supported silver catalysts are synthesized as the cathode catalysts, which can be prepared from silver electroplating effluent.