Extractive metallurgy - Hydrometallurgy

Extractive metallurgy processes are based on an initial mineral processing stage, the aim of which is to concentrate the metals contained in the resources to be processed (primary resources from the mine, secondary resources from mining or recycling activities), in order to facilitate the downstream stages, and reduce the volumes of flows to be processed, and, therefore, the size of the industrial facilities, and thus the cost of processing (CAPEX and OPEX). The downstream stages of mineral processes may involve a pyrometallurgical or hydrometallurgical route.

Pyrometallurgy was the first method used to recover metals from primary resources, as far back as Antiquity. Hydrometallurgy, on the other hand, only came into being at the end of the 19 ^th  century. Examples include the cyanidation process for gold, developed in 1887, and that for silver, developed in 1900, or the electrolysis of zinc, industrially implemented from 1916. Hydrometallurgy has developed strongly since the beginning of the 20 ^th  century and continues to take precedence over pyrometallurgical processes to produce many metals contained in primary resources (Zn, Ni, Cu, rare earth elements), but also more recently for recycling (recovery of rare earth elements in permanent magnets, recycling of waste electrical and electronic equipment including lithium-ion batteries, etc.).

Compared with pyrometallurgy, hydrometallurgy is less energy-intensive, since operations are carried out at much lower temperatures. Size is also a factor, as small units can be designed at reduced cost. It also makes it possible to process poorer ore, while improving refining and extraction yields.

In this article, we’ll look in turn at the various stages of hydrometallurgical treatment, dimensioning elements and examples of ore and waste treatment.