Ammonia oxidation by in-situ chloride electrolysis in etching wastewater of semiconductor manufacturing using RuSnO/Ti electrode: Effect of plating mode and metal ratio.

The indirect chloride-mediated ammonia oxidation encounters challenges in maintaining the effectiveness of metal oxide anodes when treating wastewaters with complex compositions. This study aims to develop a highly stable anode with RuO-SnO coatings for treating an etching effluent from semiconductor manufacturing, which majorly contains NH and organic compounds. The RuSnO/Ti electrode was synthesized using wet impregnation and calcination processes. The metal oxide configuration on Ti plate substrate was tuned by varying the step-dipping process in RuCl and SnCl baths. A 10-day continuous-flow electrolysis was conducted for studying the ammonia removal and chlorine yield under variable conditions, including detention, pH, current density, and initial ammonia and chloride concentrations. In the RuSnO coatings, the configuration comprising RuO nanorods as the surface layer and an intermediate layer of SnO crystallites (by plating Ru for three times to cover one Sn layer, denoted as the RuSn/Ti electrode) exhibited the best durability for acid washing, along with relatively high Faradaic efficiency and low energy consumption. To further improve the treatability of real wastewater (NH-N = 634 mg L, chemical oxygen demand (COD) = 6700 mg L, Cl = 2000 mg L, pH 11), the duel-cell electrolyzers were constructed in series under a current density of 30 mA cm and 45 min detention. Ultimately, removals of NH and COD reached 95.8% and 76.3%, respectively, with successful limitation of chloramine formation.