Sustainable Electrochemical Valorization of Sulfite in Industrial Wastewater Into Sulfonate-Based Molecules

Sulfite (SO₃ ^2-), abundant in industrial wastewater, poses environmental challenges due to its instability, oxygen scavenging, and microbial toxicity. However, current sulfite treatment methods primarily focus on oxidation to inert sulfate or biological reduction, both of which suffer from low efficiency, secondary emissions, or loss of sulfur value. In this study, we present a sustainable electrocatalytic strategy for upgrading sulfite-laden wastewater by directly converting SO₃ ^2- into value-added sulfonates under ambient conditions. Using commercial Ni catalysts and methanol as a representative feedstock, the system achieves a sulfite-to-sulfonate conversion ratio exceeding 90% after 3 h of continuous electrolysis, with a maximum sulfonate production rate of 7870 µmol cm^-2 h^-1 at 1000 mA cm^-2, highlighting efficient upgrading of sulfite-laden wastewater into organosulfur products. To enable continuous system operation, Ni nanoparticles were incorporated into a carbon nanotube (CNT)-based electrochemical membrane, which shows a sulfite removal ratio above 93% and a sulfite-to-sulfonate conversion ratio above 90%, demonstrating suitability for scalable wastewater treatment and sulfur valorization. Moreover, techno-economic analysis reveals a minimum levelized production cost of $300.84 per ton at 400 mA, corresponding to an 79.85% reduction compared with conventional routes. This integrated electrocatalytic membrane system offers a promising route for coupling sulfite removal with organosulfur synthesis.