Removal of Cr(VI) from Chromium Contaminated Sites by Washing with Hot Water

Abstract

Extraction of chromium from a mixture of ore processing residue and soil (slag) is studied by hot water and dilute alkali (0.01M NaOH) washing. We report that hexavalent chromium, which is the most dangerous and mobile form of chromium, can be effectively removed (95-99%) from the slag by washing with these extraction solutions. The extract can be reused after removing the Cr(VI). ions by ionexchange technologies. Trivalent chromium is strongly adsorbed by clay minerals and remains in the residue after this mild extraction. The hot water or mild hot alkali washing is recommended as a rapid and inexpensive treatment for chromium contaminated sites to prevent chromium(VI) migration through soils into groundwater or dispersion as a dust into the atmosphere. Cr(III) remaining in the residue may then be left on site preferably with the addition of a reducing agent, to prevent conversion to Cr(VI) until further clean up is mandated. Cr(III) could be also separately extracted by use of hot concentrated acid solution. The observed facile removal with these mild solutions between 25 and 100°C indicates that Cr(VI) may be able to migrate through soils relatively easily.