Regeneration of waste chromate solns. by pptn. and electrolysis - to recover chromic acid and barium-contg. precipitant

摘要

A process is disclosed for the regeneration of chromate solns., esp. from chromate-contg. effluents and/or process solns. The process firstly comprises chemical precipitation, followed by solid/liq sepn. and electrolysis in a diaphragm cell, wherein the effluent or process soln. is converted to chromic acid. The liquor is treated with barium ions; the pptd. purified barium chromate is removed from the system during the solid/liq sepn.; the precipitating agent and the chromic acid are formed from the barium chromate thus produced, and its sludge; and the recovered precipitating agent is recycled to the pptn. stage. A process is also claimed for the dissolution of insoluble barium chromate from chromate solns., by precipitating it as above, followed by the addn of sulphuric acid to give chromic acid and barium sulphate. USE/ADVANTAGE - The invention can be used in the chromium-plating industry, in the chromate-passivation of metals prior to painting, and in the extraction of Cr from its ores, to reduce pollution and improve materials utilisation. It overcomes some of the disadvantages (complexity, cost) of previous methods of chromium ion recovery.