Products formed during cobalt cementation on zinc in zinc sulfate electrolytes

Abstract The observed removal of Co 2+ during cementation on zinc is due to two reactions. 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 local high pH at the zinc surface and the concentration of Zn 2+ . The high local 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 particle is consumed, and basic cobalt salts in the particle may redissolve. Basic cobalt salts redissolve more easily than Co alloys and is the major reason for cobalt redissolution during the technical purification of the zinc sulfate electrolyte before zinc electrolysis.