Extractionelectrodeposition

Extractionelectrodeposition, commonly referred to in industry as solvent extraction followed by electrowinning (SX-EW), is a hydrometallurgical process that combines solvent extraction with electrochemical metal recovery. The method uses a two-stage sequence: first transfer of metal ions from an aqueous feed solution into an organic extractant phase, and then electrochemical deposition of the metal from an electrolyte onto a cathode.

In the extraction stage, the target metal ions are selectively moved from an aqueous solution, such as a leachate or process stream, into an immiscible organic phase containing an appropriate extractant. The distribution depends on chemical speciation, pH, and complexation. The raffinate leaves behind impurities. After stripping, the metal is recovered from the organic phase into an aqueous electrolyte, typically by contacting with a strong acid to reform a metal-rich stripping solution suitable for electro-winning.

In the electrodeposition stage, the metal ions in the electrolyte are reduced and deposited onto cathodes as metallic metal, with the anode undergoing concurrent oxidation reactions. This stage can be arranged in continuous or batch configurations and is often operated in electro-winning cells with multiple passes.

Copper is the most common example of SX-EW application, but the approach is also used for other metals such as nickel, cobalt, zinc, and, in research settings, some rare earths. Advantages include the production of high-purity metal, adaptability to low-grade ores, and reduced energy and emissions compared with smelting. Limitations involve solvent management, potential third-phase formation, impurity buildup, and the need for careful process control and infrastructure.