Solvent Extraction-Electrowinning, commonly referred to as SX-EW, is a two-stage hydrometallurgical process used to recover high-purity metals—most notably copper and cobalt—from low-grade ores, tailings, and waste materials (Godirilwe et al., 2021; Tinkler & Sole, 2023). This technology has become a cornerstone of modern metallurgy because it allows for the cost-effective production of high-grade metal cathodes while minimizing the environmental impact associated with traditional smelting (Godirilwe et al., 2021).
The solvent extraction (SX) stage
The process begins with a “pregnant leach solution” (PLS), which is an acidic or alkaline liquid containing dissolved metal ions alongside various impurities (Tinkler & Sole, 2023). During the Solvent Extraction phase, this aqueous solution is mixed with an organic phase consisting of a selective extractant—often phenolic oximes for copper—dissolved in a hydrocarbon diluent (Tinkler & Sole, 2023). The extractant selectively chelates the target metal ions, transferring them from the impure aqueous phase into the organic phase (Li et al., 2021). After the phases separate, the “loaded” organic phase is contacted with a strong acid solution (strip liquor), which reverses the chemical reaction and “strips” the concentrated metal back into a clean aqueous electrolyte (Godirilwe et al., 2021; Tinkler & Sole, 2023).
The electrowinning (EW) stage
In the final Electrowinning stage, the purified and concentrated electrolyte is passed through electrolytic cells. An electrical current is applied between anodes and cathodes, causing the metal ions (M2+) to reduce and deposit as solid metal ($M^0$) on the cathode surface (Cesiulis & Tsyntsaru, 2023). This electrochemical process typically produces metal cathodes with a purity exceeding 99.99% (Tinkler & Sole, 2023). A significant advantage of SX-EW is its circularity; the acid generated during electrowinning is recycled back to the stripping or leaching stages, creating a closed-loop system that reduces reagent consumption (Godirilwe et al., 2021; Tinkler & Sole, 2023).
References
Cesiulis, H., & Tsyntsaru, N. (2023). Eco-friendly electrowinning for metals recovery from waste electrical and electronic equipment (WEEE). Coatings, 13(3), 574. https://doi.org/10.3390/coatings13030574
Godirilwe, L. L., Haga, K., Altansukh, B., Takasaki, Y., Ishiyama, D., Trifunovic, V., Avramovic, L., Jonovic, R., Stevanovic, Z., & Shibayama, A. (2021). Copper recovery and reduction of environmental loading from mine tailings by high-pressure leaching and SX-EW process. Metals, 11(9), 1335. https://doi.org/10.3390/met11091335
Li, Z., Dewulf, B., & Binnemans, K. (2021). Nonaqueous solvent extraction for enhanced metal separations: Concept, systems, and mechanisms. Industrial & Engineering Chemistry Research, 60(48), 17285–17302. https://doi.org/10.1021/acs.iecr.1c02287
Tinkler, O. S., & Sole, K. C. (2023). Copper solvent extraction on the African Copperbelt: From historic origins to world-leading status. Journal of the Southern African Institute of Mining and Metallurgy, 123(7), 349–356. https://doi.org/10.17159/2411-9717/2906/2023
