INFLUENCE OF THIOUREA AND THIOUREA AGING ON THE ELECTRODEPOSITION OF COPPER FROM ACID SULFATE-SOLUTIONS STUDIED BY THE RING-DISC TECHNIQUE

The influence of the additive thiourea in freshly made and aged soluti ons on copper deposition from acid sulfate solutions was studied using a Pt/Pt rotating ring-disc electrode. In fresh thiourea solutions cop per deposition is retarded, but the most distinct effect of thiourea i s seen during dissolution of the deposits. The intermediate in copper dissolution, Cu+, is partly complexed with adsorbed thiourea. Thus Cu is adsorbed at the electrode surface and the current peak at the ring due to dissolving Cu+ becomes very small. The small peak indicates th at active additive is present in the deposit. Thiourea containing solu tions aged for only a few days have a distinct effect on the electrode reactions. At low concentrations of thiourea (1 mg dm(-3)) a correlat ion between ageing and growth of the Cu+ peak at the ring is clearly s een. At high thiourea concentrations (100 mg dm(-3)) a small growth of the Cu+ peak is seen during the first few days but upon further agein g of the thiourea solution copper deposition becomes strongly inhibite d. The ring current can be used as a qualitative diagnostic criterion for the concentration and state of thiourea in copper sulfate solution s.