CATHODIC BEHAVIOR OF ANTIMONY (III) SPECIES IN CHLORIDE SOLUTIONS

Cathodic copper is easily contaminated by antimony in copper electrowi nning from chloride solutions even when the antimony concentration in the electrolyte is as low as 2 p.p.m. Reduction potential measurements of copper and antimony species indicate that electrodeposition of ant imony is unlikely unless copper concentration polarization exists near the cathode surface. A.c. impedance measurements and the effect of th e rotation speed of the disc electrode indicate that the cathodic proc ess mechanism for antimony is complicated. Both diffusion and chemical reactions occurring on the cathode surface supply the electrochemical active antimony species for the cathodic process. Reaction orders of the cathodic process with respect to antimony chloride, hydrogen and c hloride ion concentrations are 2, -1 and -1, respectively. A proposed reaction mechanism for the process explains the experimental findings satisfactorily.