Application of HCl solutions for recovering the high purity metal from tin scrap by electrorefining

Abstract

Soldering scrap, generated in large quantities by modern electronic industry, is basically lead-free but contains significant concentrations of copper and silver. This is a valuable raw material, and high purity tin can be obtained by electrolytic refining. There are a number of advantages in applying pure hydrochloric acid–tin chloride media, if the difficulties of solution stability, electrolytic efficiency and deposit morphology can be overcome. An aqueous procedure was developed on the basis of potentiodynamic studies and long-term electrorefining experiments. It can be used for an efficient purification of the valuable waste material in a single operational step. The formation of chloro-complex ionic species may offer a beneficial level of natural inhibition, therefore the inefficient and in some respects harmful organic additives should be omitted. The tendency of Sn(II) oxidation and precipitation can be overcome by properly controlling the concentration of the main components in the electrolyte solution. The virtual cathodic current efficiency can be increased close to the theoretical value by optimizing the composition of the electrolyte solution, the applied apparent current density and the technological parameters of the PCR (periodical current reversal) electric supply. The loose structure of a deposited metal may satisfy the technical requirements but it requires special cell arrangement and care during operation. Electrolyte circulation should only be applied for the control of composition. The attainable purity – of close to 99.99% – surpasses the standard technical requirements.