Scrubbing
also known as wash stage
Scrubbing contacts loaded organic with a small aqueous stream, usually a dilute solution of the target metal or a controlled-pH solution, to displace co-extracted impurities such as iron or entrained aqueous droplets. It sits between extraction and stripping. The scrub stream is normally recycled back into the feed so no target metal is lost.
Why it matters in practice
Scrubbing is the cheapest purity lever in an SX circuit. Without it, co-extracted impurities report to the strip liquor and follow the metal all the way into final product, where removing them costs far more than one extra contactor stage would have.
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Equipment referenced in this entry
Related terms
Reference entry GL-SCRUBBING. Definitions on this page describe engineering practice in hydrometallurgical process design; they are not a substitute for test work on your own material.