Hydrometallurgy

Hydrometallurgy is the branch of extractive metallurgy that uses aqueous chemistry to extract metals from ores, concentrates, and residues. In hydrometallurgical processing, metal values are dissolved into an aqueous solution and subsequently recovered in purified form. It is often contrasted with pyrometallurgy, which relies on high-temperature smelting and refining. Hydrometallurgical methods are widely used for copper, nickel, zinc, cobalt, and gold, as well as many specialty metals.

Key processes include leaching, solution purification, and metal recovery. Leaching uses acids, bases, or biological agents to dissolve metals, producing a pregnant leach solution. Purification concentrates the metal by solvent extraction, ion exchange, or precipitation. Recovery converts the metal back to a solid or electrodeposited form, commonly by precipitation, cementation, or electro-winning. In situ and heap leaching are economical options for select ore types.

Common applications include copper from oxides and secondary sulfides via acid leaching followed by solvent extraction and electro-winning (SX-EW), and gold recovery by cyanide leaching. Hydrometallurgy is also used for nickel, cobalt, zinc, and various base and precious metals, as well as recycling of electronic waste and spent catalysts. It enables processing of low-grade or complex ores not suitable for smelting.

Advantages include lower energy consumption relative to smelting, the ability to treat oxidized or marginal ores, and the potential for selective metal recovery. Limitations involve chemical consumption, wastewater management, slower kinetics, and sensitivity to ore mineralogy and solution chemistry. Environmental and safety considerations demand controls on reagents, containment, and effluent treatment.

Historically developed in the 19th and 20th centuries, hydrometallurgy expanded with solvent extraction and electro-winning technologies, enabling large-scale copper production from low-grade ores and heap leaching. Ongoing research aims to improve leaching rates, reduce chemical use, and enable sustainable recycling and processing of critical metals.