Influence of taurine on the tin electrorefining process

Acidic electrolyte for tin electrorefining usually contained 10-20 g/L 4-hydroxybenzenesulfonic acid (HBSA), but, HBSA was toxic and harmful. It's urgent to develop novel green additive alternative. Hence, in this work, a novel environmental-friendly additive was designed based on the functional mechanism of HBSA, furthermore, its performance was evaluated during tin electrorefining process. Firstly, the roles of phenolic hydroxyl group and sulfonic group of HBSA in electrolyte stability and cathodic tin properties were clarified through comparatively investigating the effects of HBSA and p-toluenesulfonic acid(pTSA) on dissolved oxygen concentration, mass of tin sludge, and morphology of cathodic tin. The results show that phenolic hydroxyl group and sulfonic group can inhibit the oxidation-hydrolysis of Sn(II) and further improve electrolyte stability through reduction and complexation mechanism, respectively. Additionally, phenolic hydroxyl group can also present leveling effect on cathodic tin. Based on the functional mechanism of HBSA, among sulfonic compounds with reducibility, safe and non-toxic taurine was selected as potential alternative for HBSA. Furthermore, the effects of taurine on electrolyte stability, cathodic tin properties, and current efficiency were investigated to evaluate the feasibility of taurine. The results show that taurine substantially improves electrolyte stability, which overwhelms HBSA. Additionally, taurine is beneficial to enhance current efficiency, and impose no negative effect on Sn(II) deposition behavior, morphology of cathodic tin and cathodic potential. Taurine could be a potential alternative of HBSA to improve electrolyte stability. However, due to the minimal leveling effect of taurine, it is suggested that a leveling agent should be added with taurine in the scenario where cathodic tin with high flatness is demanded. © 2020, Central South University Press. All right reserved.