Membrane Processes during the Regeneration of Galvanic Solution

Abstract

The process of Сd 2+ and Zn 2+ 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 Сd 2+ and Zn 2+ 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.

Regeneration of chromate galvanic solutions in membrane electrochemical devices

“…The technological solution ecological hazard (EH) is the ratio of the pollutant concentration in the solution (C0) to the maximum permissible concentration (MPC) [10]. Thus, before working industrial membrane electrochemical devices in cadmium and zinc passivation baths, the Cr +6 ions concentration fluctuated between 100-200 g/l, which averaged about 150 g/l.…”

“…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.…”

“…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].…”

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

“…In order to prevent the formation of insoluble hydroxides of cadmium and zinc at a cathode region, the pH of the cathode was maintained within 1-2 (Serdiuk et al 2018). A cathode deposit was identified with electron microscopy with X-ray phase analysis at an X-ray diffractometer DRON -1 -UM and cadmium and zinc were confirmed in the deposits (Bolshanina et al 2016b, Serdiuk et al 2018.…”