Why Dimensionally Stable Anodes(DSAs) Are Used for Zinc Electrowinning?

Sep 05, 2022

Why Dimensionally Stable Anodes(DSAs) Are Used for Zinc Electrowinning?

Zinc electrowinning is one of the basic processes of the electrochemical industry. Lead-silver anodes have been used in zinc production for years. Although these electrodes have the lowest current efficiency for zinc deposition and higher electrical energy consumption when compared to pure lead anodes, they are widely used because of their high corrosion stability in acid (H2SO4) solution and because of the higher purity of the zinc cathodic deposits.

In searching for an alloying element for Pb, various other metals were investigated such as: Ca, Th, Sn, Co, Sb, Tl, Sr, or the anodic oxides formed on Pb under di€erent potentials and pH, the massive manganese oxide electrode or the Mn-oxide electrodes prepared by thermal decomposition of manganese(II) nitrate on the Ti and Pt substrate, and finally the lead-dioxide-titanium electrodes or the titanium anodes coated with a layer of RuO2 and TiO2.

Lead or lead-rich alloy anodes which are insoluble in chromic acid are generally used in electroplating and electrowinning of chromium from the chromic acid electrolyte. Because of the strong passivating properties of the bath, it is generally believed that these materials are immune to acid attacks. Practical experience shows, however, that this is not the case. Depending on the type of alloy and the operating conditions, the life of lead anodes is between 2 and 5 years.

The development of activated titanium anodes for oxygen evolution based on dimensionally stable anodes(DSAs), widely used in Chlor-alkali electrolysis, can optimize all the requirements in hydrometallurgical processes for pure metals production (Cu, Zn, Co, Cd, etc.). Such an anodic material would allow operation with a small and constant gap between electrodes and without contamination of the electrolyte and the metal deposit by lead dissolved from the anodes. In addition, decreased electrical energy consumption and increased cell productivity would be achieved. Therefore, these dimensionally stable anodes(DSAs) are widely used in zinc electrowinning plants.

One of the basic aims of electrolytic zinc production is to get a high-quality anodic material with high corrosion stability and high cathodic activity. Detailed as below:
(a) production of high purity metal deposits (elimination of lead contamination of the electrolyte and the metal product, originating from lead anodes),
(b) increasing the current efficiency,
(c) increasing the capacity of the existing electrolytic plants, and
(d) improved morphology of the cathodic metal deposit.

All these purposes can be achieved by using DSA anodes with proper appropriate electrocatalyst.