Prevention of Hydrosphere Contamination with Electroplating Solutions through Electromembrane Processes of Regeneration

Abstract

The work studies the process of Сd 2+ and Zn 2+ cations transfer through a RALEX®CM-PES 11-66 cation-exchange membrane and the cations reduction as metals on the cathodes at the cathode chambers of the electrochemical units with a view to prevent the hydrosphere contamination with the electroplating solutions. Electrolysis of the solutions that imitated the possible composition of the passivating baths contained 50 g/l sodium dichromate, 10 g/l sulfuric acid and impurity ions of Сd 2+ and Zn 2+ in various concentrations. The designed passivation solutions with certain amount of impurity ions in the colour solution were forcibly mixed. The impact of the impurity ions concentration in the colour solution and of a forced mixing on the metal reduction was studied. Regularity in the increased metal reduction dependent on the metal concentration was found and the conditions favouring the ion migration through the cation-exchange membrane due to forced mixing were defined.

Regeneration of chromate galvanic solutions in membrane electrochemical devices

“…A feature of lead anodes is the ability to oxidize Cr 3+ ions into CrO4 2ions [6][7][8]. Cr 3+ ions are formed in passivation baths due to the interaction of cadmium or zinc coating in the formation processes of protective conversion films on them.…”

“…The rate of Cr 3+ ions oxidation to CrO4 2ions at the anode depends on the concentration of Cr 3+ ions in the solution, temperature, and current density at the anode [9]. Thus, to maintain the concentration at approximately 1 % in electrochemical chromium plating electrolytes, it is necessary to have a ratio between the cathode areas and anodes in the bath of 1:2 [8]. The lack of proportionality between the reaction rate and the anode current density indicates that the Cr 3+ ion's oxidation to CrO4 2ions at the anode is not a purely electrochemical reaction [9,10].…”