A One-step Method for Recycling Waste Chromic Acid-sulfuric Acid Etching Solutions.
Soboroff DM; Troyer JD; Cochran AA
33D Ann Ind Waste Conf Purdue Univ 5/9-11/78 Ann Arbor Sci Pub inc 1/79 PP 758-763 :758-763
Two missions of the federal Bureau of Mines are to conserve scarce, costly metals and to effect pollution abatement. In accordance with these missions, the objective of this investigation was to develop a method of recycling spent chromium etching solutions that are now discarded as wastes. Solutions containing hexavalent chromium (as chromic acid or sodium dichromate) and sulfuric acid are used in brass finishing, printed circuit board etching, preparation and plastic for plating, anodizing, and various other surface treatments. As the solutions are used, cr+6 is reduced to cr+3, the dissolved solids content increases, and the effective acid concentration is reduced. The solutions are discarded when the etching rate is below what is required for a given operation. Technology for ultimate disposal of chromium wastes usually involves the reduction of the remaining cr+6 to cr+3, followed by base addition to precipitate chromium and other metallic hydroxides. The resulting sludge is then used for landfill. See ri 8377.
33D Ann. Ind. Waste Conf., Purdue Univ., 5/9-11/78; Ann Arbor Sci. Pub., Inc., 1/79, PP. 758-763