Microwaves in extractive metallurgy: Part 2 – A review of applications

In metal extraction processes, such as reduction or smelting, a source of energy is required for the endothermic reactions. This energy is often supplied by the combustion of carbonaceous materials or hydrocarbons or by inputting some electrical energy. Typically, large-scale reactors are used and the energy is transported to the reacting materials from the heat source via convective, conductive and radiative processes. Additionally, considerable heat is transferred to the containment vessel, the surroundings and the off-gases and this energy is difficult to recover. On the other hand, microwave heating systems can be designed such that only the material to be processed absorbs the microwaves, since microwave radiation is deposited directly in the material to be heated. Other potential advantages of microwave processing include; high energy densities, selective heating, improved control, environmental benefits and minimal off-gas generation. In the present research, the utilization of microwaves as an energy source in metal extraction and, in particular the pyrometallurgical processing of oxide ores, is reviewed.