Leaching behavior of Cr(III) in stabilized/solidified soil

The leaching behavior of chromium was studied using batch leaching tests, surface complexation modeling and X-ray absorption near edge structure (XANES) spectroscopy. A contaminated soil sample containing 1330 mg-Cr kg^-1 and 25 600 mg-Fe kg^-1 of dry soil was stabilized/solidified (S/S) with 10% cement, 25% cement, 10% lime and a mixture of 20% flyash and 5% lime. The XANES analysis showed that Cr(III) was the only Cr species in untreated soil and S/S-treated samples. The leachate Cr concentration determined using the toxicity characteristic leaching procedure (TCLP) was reduced from 5.18 mg l^-1 for untreated soil to 0.84 mg l^-1 for the sample treated with 25% cement. The Cr leachability in untreated and treated soil samples decreased dramatically as the pH increased from 3 to 5, remained at similar levels in the pH range between 5 and 10.5, and further decreased at pH > 10.5. Modeling results indicated that the release of Cr(III) was controlled by adsorption on iron oxides at pH < 10.5, and by precipitation of Ca₂Cr₂O₅ · 6H₂O at pH > 10.5.