How does zinc dust remove copper, nickel, cadmium, cobalt, and germanium from zinc sulfate solution?

In the context of zinc processing, zinc dust removes impurities such as copper, nickel, cadmium, cobalt, and germanium from a zinc sulfate solution through a process known as cementation.1

Cementation is a form of chemical precipitation that relies on a displacement reaction. In this process, the zinc dust acts as a reducing agent. Because zinc is a more active metal than the impurities present in the solution, it displaces the less active metal ions. As the zinc dust dissolves into the solution, the metallic impurities are forced out of the solution and precipitate as solid particles.23

This purification stage is essential because the presence of these metallic impurities, even at very low concentrations, can interfere with the electrolysis process. Specifically, these impurities lower the hydrogen overvoltage, which would otherwise lead to the production of hydrogen gas at the cathode instead of the desired deposition of high-purity zinc.1