Solvent extraction and electrowinning

What is SX-EW?

Copper oxide ores and some sulfide ores are processed by leaching, often heap leaching with sulfuric acid. The resulting pregnant leach solution contains copper, but at low concentrations and with other dissolved metals such as iron. SX-EW turns that dilute, impure solution into copper metal without smelting.

Solvent extraction

1. Extraction. The leach solution is mixed with an organic phase, an extractant, commonly oxime-based, dissolved in a kerosene-like diluent. The extractant selectively picks up copper ions, leaving most impurities behind.
2. Separation. The two liquids separate by density, like oil and water.
3. Stripping. The copper-loaded organic is mixed with a strongly acidic electrolyte, which pulls the copper back out of the organic.

The leach solution, now depleted of copper, is returned to the heap, and the stripped organic is reused. The result is a clean electrolyte with a much higher copper concentration.

Electrowinning

The electrolyte flows into cells where an electric current passes between inert anodes and cathodes. Copper plates onto the cathodes, typically stainless steel blanks, and is harvested as sheets of high-purity copper cathode.

Why it matters

• No smelting, so the process avoids the sulfur dioxide emissions of smelting and the need to ship concentrate.
• Low-grade ores can be processed economically by combining heap leaching with SX-EW.
• High-purity product, cathode that can be sold directly.

SX-EW accounts for a significant share of world copper production.

Frequently asked questions