PRODUCTION OF HIGH PURITY CHROMIUM (VI) OXIDE SOLUTION FROM COMPOSITION CONTAINING TRIVALENT CHROMIUM AND/OR HEXAVALENT CHROMIUM

PURPOSE:To obtain a Cr (VI) oxide soln. from a waste soln. contg. Cr (II) and Cr (VI) salts by adding peroxide to a soln. of a Cr (III) complex contg. an org. carboxylic acid anion as a ligand and carrying out oxidation. CONSTITUTION:Floating impurities in a soln. to be treated are filtered off and org. carboxylic acid (salt) such as oxalic acid and a reducing agent such as a mixed soln. contg. dithionite and hydrogensulfite are added to the soln. to be treated under stirring while keeping pH 3-4. The amt. of the carboxylic acid added is 1-2 times (mol) as large as the total amt. of Cr in the soln. or >=2 times if necessary. The reducing agent is added by an amt. enough to reduce Cr (VI) oxide or Cr (VI) salt in the soln. to Cr (III). The resulting soln. is allowed to stand for 1-6hr and adjusted to pH>=11 with an aq. NaOH soln. Peroxide such as an aq. hydrogen peroxide soln. is then added to the soln. of pH>=11 by 1.5-5mol per 1mol Cr (III) and this soln. is stirred, allowed to stand over night and heated to about 70 deg.C. A deposited precipitate is filtered off and a Cr (VI) oxide soln. contg. no org. carboxylic acid is obtd.