Methanesulfonic Acid Medium Electrolytic Refining Rough Solder

Methanesulphonic acid（MSA）has a range of advantages such as high conductivity,strong tin/lead solubility,low toxicity,the ability to work at high current densities and the ease of harmless disposal of waste liquids.In this paper,MSA is used as the main solution to electrolyse tin in order to avoid the problems of high environmental pollution and energy consumption associated with conventional electrolysis of coarse solder.The following useful results were obtained through systematic research.（1）The results of CV tests show that the reduction of Sn²⁺at the stainless steel electrode is mainly controlled by diffusion,and is an irreversible process;where the diffusion coefficient increases with increasing temperature and free MSA concentration.The results of LSV showed that the reduction precipitation rate of the cathode and the oxidation dissolution rate of the anode increased with increasing temperature,free MSA concentration and Sn²⁺concentration.The results of Tafel tests show that the exchange current density gradually increases with increasing electrolyte temperature and Sn²⁺concentration;the exchange current density first increases and then decreases with increasing MSA concentration.（2）In the MSA medium,increasing the free MSA concentration and the temperature both increased the conductivity of the solution;when the Sn²⁺concentration increased,the conductivity instead decreased.And a linear relationship between the four was established.δ=-209.38+0.733T-0.136[Sn²⁺]+0.076[MSA]（3）Fine solder was prepared by electrolysis in MSA medium with crude solder as the anode and stainless steel as the cathode.The results show that at a current density of 207 A/m2,free MSA 130 g/L,Sn²⁺130 g/L,pole spacing of 4.0 cm,C10H8O 0.32 g/L,C20H₂4Na2O10S2 0.6 g/L,bone gum 2.0 g/L and temperature of 305.15 K,the cathode was dense and glossy,the bath voltage was 0.2142 V and the current efficiency was:99.31%.（4）Fine tin was prepared by electrolysis in MSA-H₂SO4 medium with crude solder as the anode and stainless steel as the cathode.It was found that the best electrolysis results were obtained at a current density of 175 A/m2,free MSA 120 g/L,Sn²⁺150 g/L,pole spacing of 2.0 cm,C10H8O 0.32 g/L,C20H₂4Na2O10S2 0.6 g/L,bone gum 2.0 g/L,temperature of 318.15 K,H₂SO4 concentration added 8.5 times the actual amount added,tank voltage 0.3437 V,current efficiency:99.49%,dense and glossy cathode,99.98%tin content and 0.0014%lead content.