Removal of hexavalent chromium from waste material

• Main Author: PILZNIENSKI; JOHN F
• Format: Patent
• Language: English
• Published: 06.04.1993
• Subjects: CHEMISTRY; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; METALLURGY; TECHNICAL SUBJECTS COVERED BY FORMER USPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ARTCOLLECTIONS [XRACs] AND DIGESTS; TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE

A method of removing Cr+6 from a solution is provided. In removing the Cr+6, an effective amount of an alkali metal dithionite is added to the solution to reduce substantially all of the Cr+6 to Cr+3. A soluble material is provided in the solution which will form a precipitate. Further, the soluble material is selected such that it will coprecipitate and tie up any dissolved or colloidal Cr+3 formed as a result of the reduction of the Cr+6. In one embodiment, the solution is alkaline and preferably, the pH of the solution is reduced sufficiently such that the soluble material will quickly precipitate and form the coprecipitate material with the Cr+3. Thereafter, the solution is filtered to remove the coprecipitated material from the solution and thereby form a supernatant solution suitable for waste discharge which has substantially lowered chromium values. The precipitate has the Cr+3 tied up in an insoluble non-leachable form.