Carbon Dioxide as a Sustainable Reagent in Circular Hydrometallurgy.

This review highlights the use of CO as a reagent in hydrometallurgy, with emphasis on the new concept of circular hydrometallurgy. It is shown how waste CO can be utilised in hydrometallurgical operations for pH control or regeneration of acids for leaching. Metal-rich raffinate solutions generated after removal of the valuable metals can serve as feedstocks for mineral carbonation, providing alternative avenues for CO sequestration. Furthermore, CO can also be used as a renewable feedstock for the production of chemical reagents that can find applications in hydrometallurgy as lixiviant, as precipitation reagent or for pH control. Mineral carbonation can be combined with chemical reactions involving metal complexation reagents, as well as with solvent extraction processes for the concurrent precipitation of metal carbonates and acid regeneration. An outlook for future research in the area is also presented.