Chromium leaching vs. oxidation state for a contaminated solidified/stabilized soil

Abstract

The toxicity, solubility, and mobility of chromium in soil are strongly dependent upon its oxidation state. Solidification/stabilization ( S S ) is a potential method for preventing Cr leaching from contaminated soil. We evaluated the leaching behavior of untreated and solidified/stabilized chromium contaminated soil samples obtained from two locations at a military facility in Louisiana. The leaching of chromium, as measured by the Toxicity Characteristic Leaching Procedure (TCLP), was expected to be dependent upon the chromium oxidation state. The pH, cation exchange capacity and particle size distribution were obtained for each sample and portions of each sample were solidified with Type I Portland cement. The oxidation state of chromium was determined by X-ray absorption spectroscopy (XAS). The sample from Site 1 contained 478 mg kg −1 total chromium while the sample from Site 2 contained 1272 mg kg −1 total Cr. The TCLP chromium concentration for Site 1 untreated soil was 3.4 mg L −1 and 2.0 mg L −1 for the S S treated sample. The sample from Site 2 had TCLP chromium concentrations below the analytical detection limit (< 1.0 mg L −1) for both untreated and S S samples. The XAS data showed the presence of the more mobile and soluble Cr +6 at Site 1 but not at Site 2. The use of Portland cement alone was not effective in reducing the Cr +6 to the less soluble and less mobile Cr +3, or in physically preventing leaching of Cr +6.