By reviewing relevant domestic and international data, it was found that the main process of tin refining carried out by enterprises at present was the acidic sulfate tin electrolytic system. However, cresol sulfonic acid was irritating and toxic to human body and deteriorated the operating environment, so it was urgent to find a green, non-toxic and efficient additive to replace cresol sulfonic acid. In this paper, the cathodic polarization curves and Tafel curves of electrolytes containing different additives were comparatively studied to analyze the effects of various additives on the reduction deposition behavior of cathodic tin during electrolysis. Then, a comparative study of the effects of different additives on electrolyte stability, current efficiency and cathodic tin morphology, and the tin electrolysis process conditions were optimized. The effects of sulfuric acid concentration, stannous sulfate concentration, temperature and current density on the tin electrolytic refining process were investigated under the conditions of the optimum additive package, and then the optimum tin electrolytic process conditions were obtained. The current efficiency was determined by the weight method and it was found that all the additives were able to improve the current efficiency of cathodic tin deposition to some extent. Among them, resveratrol had the best effect, with a current efficiency of 99.06%. Sodium benzene sulfonate had the worst effect on the improvement of current efficiency, with a current efficiency of 96.87%. Through electrolysis experiments, cathodic polarization curves and Tafel curves, it was found that cresylic acid and sodium benzenesulfonate had strong dispersing ability for tin ions in the electrolyte. Because of their ability to adsorb on the cathodic tin surface to form a dense adsorption film, stalling the deposition rate of Sn2+ and improving the leveling and denseness of the cathodic tin surface; resveratrol did not have an improving effect on the leveling and denseness of the cathodic deposited tin. As to sodium benzene sulfonate, it had good leveling property but low current efficiency. And resveratrol as an additive had higher current efficiency but poor leveling property. A composite additive, namely resveratrol/sodium benzenesulfonate, was combined by screening. Through the study of two composite additives by electrolysis experiment, cathodic polarization curve and Tafel curve, it was found that the resveratrol/sodium benzene sulfonate composite additive could improve the stability of tin ions in electrolyte. In addition, the use of resveratrol/sodium benzene sulfonate additive package could reduce the acidity of electrolyte. It was promising to replace cresol sulfonic acid as an additive in tin electrolytic refining electrolyte. The optimal concentration of the combination additive was 8 g·L-1 sodium benzenesulfonate of -30 mg·L-1 resveratrol. Starting from the molecular structure of cresol sulfonic acid, a green non-toxic resveratrol with three phenolic hydroxyl groups and a green non-toxic sodium benzene sulfonate with one sulfonic acid group were screened, and the current efficiency was determined by the weight method, and it was found that all the additives were able to improve the current efficiency of cathodic tin deposition to some extent. Among them, resveratrol was the most effective, with a current efficiency of 99.06%. Sodium benzenesulfonate was the least effective in improving the current efficiency, with a current efficiency of 96.87%. It was found by electrolysis experiment, cathodic polarization curve and Tafel curve that cresolsulfonic acid and sodium benzenesulfonic acid had strong dispersing ability to electrolyte, which could adsorb on the cathodic tin surface, hinder the deposition rate of Sn2+ and improve the leveling of the cathodic deposited tin surface; while resveratrol had poor leveling property. The optimal process conditions for using Res/SB as a complex additive in tin electrolytic refining were: sulfuric acid 60 g·L-1, stannous sulfate 24 g·L-1, SB 8 g·L-1, Res 30 mg·L-1, β-naphthol 0.2 g·L-1, gelatin 1.0 g·L-1, pole distance 5 cm, temperature 35 ℃, and current density 100 A·m-2. Under the optimal process conditions, the current efficiency of tin electrolytic refining in the electrolyte could reach 98.65%, the purity of tin could reach 99.96%, and the flatness of the cathode tin surface was good, indicating that the additive complex Res/SB could replace CSA as the tin electrolytic additive. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.
