17.1 Mineral Processing by Aqueous Solutions

The present annual world production of iron/steel, aluminium, copper, zinc, lead, nickel, and magnesium is close to 1 billion tonnes. Most metals and their alloys are synthesized from oxide, sulfide, and halide sources. Hydrometallurgy is a specialized branch of extractive metallurgy dealing with metal recovery from ores, concentrates, and other metallurgical intermediate products by aqueous processes. These processes are usually very dependent on solubility of the reactants. In hydrometallurgical leaching the desired metal is obtained from the ore or its concentrate, and the residue, after washing, is rejected. The leach liquor, containing one or more metal ions in solution is then processed to solid metals. Hydro processes operate at lower temperature than pyro processes, usually 50 250 C.

The production of zinc is an important hydrometallurgical process and almost all the world s zinc production is derived from the treatment of sulfide concentrates in which sphalerite, (Zn,Fe)S, is the dominant zinc mineral. The concentrate, together with the slurry from the conversion process and acid from the electrolysis, is fed to the reactors where the leaching takes place by injecting oxygen into the slurry. The availability of dissolved oxygen for reactions has an important effect on the kinetics of the whole process as the oxidation of Fe ²⁺ into Fe ³⁺ controls the overall rate of leaching during the early stages of the process. The overall leaching reaction rate is controlled by gas diffusion...