Recovery of chromate from electroplating sludge

Recycling chromium from electroplating waste sludge is attractive both economically and environmentally. Oxidizing chromium(III)-containing electroplating waste with aqueous oxidants in alkaline suspensions did not allow complete recovery of the chromium. Hypochlorite was potentially a suitable oxidant as it could completely oxidize a suspension of chromium(III) hydroxide to chromate at basic pH. From sludge, however, only up to 85% of the chromium was recovered; complete recovery was not achieved despite different experimental conditions and procedures. The unrecovered chromium was found by X-ray photoelectron spectroscopy to have been oxidized and is most likely present as insoluble metal chromates trapped in the sludge. Roasting the sludge followed by aqueous leaching, however, enabled complete recovery of the chromium.