Membrane Processes during the Regeneration of Galvanic Solution

Abstract

The process of Сd2+ and Zn2+ cations transfer through the cation exchange membrane RALEX®CM-PES 11-66 in double-chamber electrolyzer was investigated. Anodic chamber electrolyte (analyte) contained model solutions which imitates galvanic baths composition for passivation processes. The analyte contained 50 g/l sodium dichromate and 10 g/l sulfuric acid as main substances and impurities of Сd2+ and Zn2+ cations in amount of 2.5 g/l of each. The electrolyte of cathode chamber is catholyte, contained 1 % solution of sulfuric acid. The titanium grade BT-0 and lead grade C-0 were used as cathode and anode respectively. Cathode processes connected with processes of ion migration through the membrane and metal release on cathode were studied. The creation of volt-ampere curves in galvanodynamic mode was supplied by impulse potentiometer, tool for combined measurements and silver chloride reference electrode. An increase of cathode overvoltage in the presence of cadmium ions and decrease of cathode potential with the increase of temperature were proved. The pH range for intensive reduction of metals was determined during investigations. Scanning electron microscopy with X-ray analysis was used for estimation of cathode deposits elemental composition. It was established that metal atoms of cadmium and zinc were presented in cathode deposits. Transference numbers of ions through cationic membrane were calculated for cadmium and mixture of cations proved the effectiveness of chromium and zinc ions extraction from chromium containing solutions. This process provides regeneration of galvanic solutions and maintains stable composition of passivation bath.

Використано метод побудови вольтамперних кривих у гальванодинамісному режимі за допомогою імпульсного потенціостату, приладів комбінованих вимірювань і хлор-срібного електроду порівняння. Доведено зростання перенапруги на катоді у присутності йонів кадмію та зниження потенціалу катода при підвищенні температури.