Closed-loop recycling of spent nitric acid-based tin stripping solution via electrochemical selective separation of copper and tin

One-step electrolysis realizes closed-loop recycling of spent stripping solution. • Cathodic reduction and hydrolysis enable the selective separation of Cu and Sn. • Cu recovery of 98.64% and Sn removal of 96.17% are achieved. • The treated spent solution can be directly reused for tin tripping in PCB process. The sustained growth of the printed circuit board (PCB) industry has made the disposal and resource reclamation of spent nitric acid-based tin stripping solution an increasingly urgent concern. Herein, a one-step electrolysis strategy based on the intrinsic differences between Cu 2+ and Sn 4+ in electrochemical reduction potentials and hydrolysis behaviors is proposed to enable their simultaneous and differentiated separation. The electrochemical behavior of Cu 2+ was systematically investigated in HNO 3 -Cu(NO 3 ) 2 system, revealing that its reduction is a diffusion-controlled irreversible process, with copper electrocrystallization following an instantaneous nucleation mechanism. Key kinetic parameters, including diffusion coefficient, charge-transfer resistance, and activation energy, were obtained. Furthermore, the effects of Fe 3+ and Sn 2+ on Cu 2+ reduction were examined, elucidating the promotion and competitive adsorption patterns of coexisting ions. Electrolysis of actual industrial spent tin stripping solution was then carried out. Under optimized conditions, Cu 2+ was reduced to copper metal at the cathode with a removal efficiency of 98.64%, while Sn 4+ was precipitated as SnO 2 · n H 2 O with a removal efficiency of 96.17%. The post-electrolysis solution can be directly reused in the PCB tin-stripping process. This study opens an alternative technological pathway for green, short-process closed-loop utilization of spent tin stripping solution and provides a theoretical reference for electrochemical recovery of complex acidic waste liquids.