Products formed during cobalt cementation on zinc in zinc sulfate electrolytes

The observed removal of Co2+ during cementation on zinc is due to two react ions. One reaction is formation of a Co alloy or Co in solid solutions. The second reaction is formation of basic cobalt salts, and is a function of l ocal high pH at the zinc surface and the concentration of Zn2+. The high lo cal pH close to the zinc surface is created by evolution of hydrogen. This hydrogen evolution stops when the core of metallic zinc in the cemented par ticle is consumed, and basic cobalt salts in the particle may redissolve. B asic cobalt salts redissolve more easily than Co alloys and is the major re ason for cobalt redissolution during the technical purification of the zinc sulfate electrolyte before zinc electrolysis. (C) 2000 Elsevier Science B. V. All rights reserved.