Removal of chromium from Hanford tank sludges

Recent studies suggest that the chromium content in sludge wastes stored at the U.S. Department of Energy's Hanford Site will determine the amount of high-level borosilicate glass produced in immobilizing those wastes for dis posal. Removing chromium from the sludge solids would reduce the mass of hi gh-level borosilicate glass, which would likely result in a significant cos t savings. We have been investigating oxidative leaching methods for removi ng chromium from Hanford wastes for a number of years. In these methods, ch romium(III), which is insoluble under alkaline conditions, is converted to the soluble chromate ion. We have removed chromium on a laboratory scale fr om several different Hanford tank sludges. The most effective leaching agen ts investigated to date are permanganate and ozone, which readily oxidize c hromium(III) to chromium(VI) under alkaline conditions.