Water and Wastewater Terms Beginning H

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hexavalent chromium

Wastewaters bearing hexavalent chromium (Cr⁶⁺) are produced in chromium electroplating, chromium conversion coatings, etching with chromic acid, and in metal finishing operations carried out on chromium as a basis metal. Hexavalent chromium must be reduced to trivalent chromium (Cr³⁺) before chromium can be removed from metal wastestreams by hydroxide precipitation. Hexavalent chromium is highly toxic in comparison with trivalent chromium. Also see chrome plate, chromium, and trivalent chromium.