Influence of oxygen reduction and hydrogen evolution in the gold and silver direct electrodeposition process from thiourea solutions in a filter press type reactor

Acidic thiourea solutions have been considered an alternative to cyanide for precious metal extraction due to their fast kinetics and low toxicity. Recovery of the metallic values has centered on the use of adsorption and cementation processes, although these represent additional costs. In the present work, gold and silver direct electrodeposition from thiourea solutions is studied in a filter press-type electrochemical reactor, using a stainless steel 316 plate as the cathode. The strong influence that the parasitic reactions (hydrogen evolution and oxygen reduction on the cathode) have on the gold and silver electrodeposition process was evaluated. Additionally, through manipulation of the reduction potential and the flow velocity, hydrogen evolution was minimized. This result is of great value, principally in the scale-up of the electrodeposition process.

►Au-Ag deposition from thiourea solutions was made in a filter press type reactor. ► The influence of deposit potential, and parasite reactions were evaluated. ► The hydrogen evolution is the most important parasite reaction. ► Oxygen presence hinder the proton reduction reaction, increasing current efficiency.