CHROMIUM STABILIZATION CHEMISTRY OF PAINT REMOVAL WASTES IN PORTLAND-CEMENT AND BLAST-FURNACE SLAG

The use of cement based systems for solidification and stabilization o f hazardous wastes has been proposed. The stabilization of Cr contamin ated paint removal wastes in ordinary Portland cement and in a Portlan d cement and blast furnace slag matrix was investigated. A loading by volume of 75% waste and 25% cement (or cement + slag) was used. The ex pression of pore solution was utilized to determine the chemical envir onment encountered by the waste species in the cement matrix. The high ly alkaline conditions of ordinary Portland cement determined the stab ility of the metal species, with Cr being highly soluble. The replacem ent of 25% of the Portland cement by blast furnace slag was found to d ecrease the [OH-] of the pore solution resulting in a decrease of the Cr concentration. For cement wastes forms hydrated for 28 days, the Cr concentration decreased in the expressed pore solution. During the TC LP tests the cement waste form and extraction solution were found to r eact, changing the chemistry of the extraction solution. The expressio n of pore solution was found to give a direct measure of the chemistry of the waste species in the cement matrix. This avoids the reaction o f the TCLP extraction solution with the cement matrix which changes th e solubility of the hazardous metals.