The Immobilization Effect of Natural Mineral Materials on Cr(VI) Remediation in Water and Soil

The effects of sepiolite, montmorillonite, and attapulgite on the removal and immobilization of Cr(VI) in water and soil were studied. X-ray diffraction (XRD) characterizations showed that the purities of these three mineral materials decreased in the following order: montmorillonite > attapulgite > sepiolite, and that their surface molecular bond types were similar. The adsorption potential of Cr(VI) in aqueous solutions of the three mineral materials was in the following order: sepiolite > attapulgite > montmorillonite. The adsorption mechanism for attapulgite was consistent with the Freundlich isotherm adsorption model, whereas that for montmorillonite was more consistent with the Langmuir model. Sepiolite had a good fitting effect for both isothermal adsorption models. For montmorillonite and attapulgite, a lower pH corresponded to a higher removal of Cr(VI). For sepiolite, however, the removal efficiency of Cr(VI) from an aqueous solution was the lowest at a pH of approximately 5.0. The results of the soil toxicity characteristic leaching procedure showed that, following the addition of 15% sepiolite, attapulgite, or montmorillonite to the contaminated soil, Cr(VI) concentrations in the leachates decreased by 16.8%, 18.9%, and 15.9%, respectively, and the total Cr concentrations in the leachates were reduced by 21.2%, 29.2%, and 17.6%. Of the three mineral materials, attapulgite demonstrated the highest Cr(VI) immobilization efficiency in soil. This study emphasizes the effect of attapulgite on the immobilization of Cr(VI) in soil and aqueous solutions, thus providing a theoretical basis for the potential application of natural mineral material remediation of Cr(VI)-contaminated aqueous solutions and soils.