Extractive metallurgy - Hydrometallurgy

Extractive metallurgy processes rely on an initial mineral processing stage designed to concentrate the metals contained in the resources to be processed (primary resources from mines, secondary resources from mining or recycling activities) in order to facilitate downstream stages and reduce the volume of material to be processed, thereby reducing the size of industrial facilities and, consequently, processing costs (CAPEX and OPEX). The stages following the mineral processing stage may involve either a pyrometallurgical or a hydrometallurgical route.

Pyrometallurgy was the first method used to extract metals from primary resources, dating back to ancient times. Hydrometallurgy, on the other hand, did not emerge until the late 19th century. Examples include the gold cyanidation process, developed in 1887, and the silver cyanidation process, developed in 1900, as well as zinc electrolysis, which was first carried out industrially in 1916. Hydrometallurgy has developed significantly since the early 20th century and continues to replace pyrometallurgical processes for the production of many metals found in primary resources (Zn, Ni, Cu, rare earths), but also more recently for recycling (recovery of rare earths from permanent magnets, recycling of waste electrical and electronic equipment, including lithium-ion batteries, etc.).

Compared to pyrometallurgy, hydrometallurgy is more energy-efficient because the processes are carried out at much lower temperatures. Scale is also a factor to consider, as smaller units can be designed at lower costs. It also allows for the processing of lower-grade ores while improving refining and extraction efficiency.

In this article, we will examine, in turn, the various stages of hydrometallurgical processing, design considerations, and examples of ore and waste treatment.