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.