Selective Precipitation of Impurities during Cementation Purification of Zinc Solutions.

It is shown that selective cementation purification of zinc solutions to obtain Cu-Cd cake in the first stage and cemented cobalt cake in the second stage can be carried out rationally only at low concentrations of Ni ( less than 3. 0-3. 5 mg/dm**3) and Co( less than 6. 0 mg/dm**3) in the solution, since, in spite of the poor selection of Ni from Cd, very little Ni ends up in the Cu-Cd cake, while Co will not precipitate. Selective cementation gives much richer Cu-Cd cakes than collective cementation. During selective cementation the Zn/Cd ratio in the cake is much lower than during collective cementation.