Zero-waste regeneration of zinc passivating solutions by electromembrane process

Issue 24(1) 2019
Pages 56-63

S.S. Kruglikov1, N.E. Nekrasova1, V.V. Kuznetsov1, E.A. Filatova1, A.V. Telezhkina1, N.G. Novikova2

1Dmitry Mendeleev University of Chemical Technology, Moscow
2Research Institute of Comprehensive Exploitation of Mineral Resources of Russian Academy of Sciences, Moscow

Keywords: zinc, regeneration, passivation solution, electromembrane process

Conventional electromembrane process of the regeneration of chromate-based zinc passivating solutions produces liquid waste containing chromium and zinc compounds. As a result the consumption of chromate increases. An improved process has been developed which consists of two stages: (1) anodic oxidation of the major part of chromium(III) accompanied by electrolytic transport of zinc and some part of chromium(III) ions into the catholyte, and (2) electrodeposition of zinc at the cathode in a compact form. In the first stage the catholyte pH is low – about 0 to 1 and zinc is not deposited in a dendritic form. In the second stage at pH 3…4 zinc is deposited at the cathode in a compact form because of much higher concentration of its ions in the catholyte. Finally, alkali is added to the catholyte  and chromium hydroxide formed is returned to the anolyte.