Investigation and optimization of tin electrorefining in hydrochloric acid solutions

Abstract

High-tin containing soldering waste material could be recycled close to its origin on a flexible scale by electrolytic refining in pure hydrochloric acid–tin-chloride solutions. This method, offering potentially low costs, may become feasible by overcoming the difficulties of solution stability, electrolytic efficiency and deposit morphology. The tendency of the Sn(II) oxidation and precipitation can be overcome by properly controlling the concentration of the main components and the ratio of Sn(IV)/Sn(II) in the electrolyte solution. The virtual cathodic current efficiency can be increased above 90 % by assuring the dominance of Sn(II) species and optimising the composition of the electrolyte solution, the applied apparent current density and the parameters of the periodical current reversal. In the selected medium, the formation of chloro-complex ionic species may offer a beneficial level of natural inhibition. Organic additives exert no beneficial effect on any of the electrolysis characteristics. Applying a short cycle periodic current reversal technology is efficient in improving the morphology of the cathodic deposit. The loose structure of deposited metal requires special cell arrangement and care during operation. Electrolyte circulation does not affect current efficiency significantly. It should be applied in practice for the control of composition. The attainable purity is close to 99.99 %, which greatly surpasses the technical standards.