Development And Application Of Novel Electrolyte Additives For Tin Electrorefining

Traditional electrolyte for tin electrorefining contains H₂SO₄,SnSO₄,and Cresol Sulfonic Acid（CSA）.Among which CSA increases cathodic polarization and inhibits the electrodeposition of Sn²⁺,consequently,CSA is beneficial to obtain cathodic tin with high flatness and compactness.However,CSA is poisonous and harmful to environment and human body.In order to search for an environmental friendly additive to replace CSA,effects of several common additives used in electrolysis on tin electrorefining process were investigated.Based on the molecular structure of CSA,effect of gallic acid（GA）and SL on tin cathodic electrodeposition behavior were investigated due to the presence of phenol hydroxyl on GA and sulfonic group on SL.Results showed that SL addition was beneficial to improve the cathodic morphology,GA addition was beneficial to stability of electrolyte and current efficiency.But due to the small solubility of GA,SS was selected as a stabilizer.Results revealed that SS has a good result in stabilizing electrolyte and improving current efficiency.The effects of GA and SS on current efficiency,electrolyte stability and the cathodic morphology were investigated.Results showed that addition of 2 g·L^-1 SL and 4 g·L^-1 SS could obtain comparable cathodic morphology,current efficiency and electrolyte stability with that in traditional electrolyte contained CSA.In order to optimize the electrolysis process parameters of mixed additives,electrorefining parameters（current density、initial acidity、initial concentration of SnSO₄ and temperature）were further studied in electrolyte contained SL and SS.Optimal electrorefining parameters was obtained as follows:current density of 100A·m^-2,initial SnSO₄ concentration of 22.11 g·L^-1,initial H₂SO₄ concentration of 90g·L^-1,temperature of 35℃.Under the optimal conditions,the current efficiency reached 99.47%,and the cathodic tin presented flat and compact surface.The applicability of the selected additive in the actual electrolyte was studied.Results showed that SS and SL were beneficial to keep stability of Sn（II）and H⁺by industrial experiments,respectively.The content of cathode tin accords with national standard,but the obtained composition of cathode exists disadvantage with elevated Pb and Sb levels when the two additives were added to the electrolyte,respectively.Based on the above results,it was concluded that SL-SS could be used as an environmental friendly mixed additive to replace CSA.Compared with electrolytes with CSA,the addition of SL-SS was beneficial to keep current efficiency,electrolyte stability and cathode morphology to a comparable level.