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Water Treatment
Water Treatment > Quality Water Solutions > Treatment of Chromium Wastes Introduction
Increased ecological concerns and stringent regulations governing waste discharges have given a high priority to the effective treatment of effluents containing chromium. Treatment of chromium wastes consists of reduction of Cr+6 to Cr+3 at pH < 4.5 and the subsequent precipitation of Cr+3 by raising the pH to about 8.5 with the addition of an alkali. Precipitated Cr+3 is then removed by filtration and disposed of in accordance with existing governmental regulations. General Chemical produces the following agents: sodium metabisulfite, sodium bisulfite solution and sodium sulfite. Chemicals Used
Quantities of Chemicals
As already noted, sodium metabisulfite, sodium sulfite and sulfuric acid are required in somewhat greater amounts than theory would suggest. The rate of reduction of the hexavalent chromium is pH dependent. At pH of 2.0 or below, the reaction is complete in about five minutes, while at pH 2.5 to 3.0, thirty minutes may be required. In the case of chromic acid, the theoretical chemical requirements are given in the following table: Parts of Reactants per part of chromic acid using:
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