PURPOSE:To obrain a chromium sulfate soln. fit for tanning by adding alkali to chromic acid waste liquor contg. heavy metals to remove the metals and reducing the hexavalent chromium. CONSTITUTION:Waste liquor contg. chromic acid and =20g/l heavy metals such as iron and copper and discharged from a chromium plating plant or a plated synthetic resin etching plant is adjusted to 4-7pH with soda ash or NaOH to precipitate the heavy metals as hydroxides, which are then separated by filtration. The transparent filtrate is adjusted to 0.5-1.0pH by introducing SO2 gas or adding sulfuric acid, and the hexavalent chromium is reduced with glucose added. After pH adjustment to 2-3 a chromium sulfate soln. fit for tanning is obtd.
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