Immobilization of Cr(VI) contaminated soil using green-tea impregnated attapulgite

Abstract

Soil contaminated by hexavalent chromium (Cr(VI)) requires special attention not only because of the carcinogenicity and high toxicity of Cr(VI) but also the distinct nature (e.g., changed valency, anionic forms across various pH). Combining the natural clay mineral attapulgite and natural antioxidant tea polyphenols could offer a cost-effective, environmental-friendly, and efficient solution in remediating the Cr(VI) contaminated soils. In this study, attapulgite and green tea extract were used to prepare a green-tea impregnated attapulgite (GATP). The as-formed material was used to remediate a Cr(VI) contaminated soil, and the remediation effects and mechanism were studied. The results of the incubation test showed that the Cr(VI) content in the soil of the 10% GATP group decreased from 450.6 mg/kg to 165.5 mg/kg, and 62.98% of Cr(VI) was converted to Cr(III). Meanwhile, the total extractable Cr contents in the simple bioaccessibility extraction test (SBET), physiologically based extraction test (PBET), simple gastrointestinal extraction test (SGET) and synthetic precipitation leaching procedure (SPLP) experiments decreased by 48.1%, 39.1%, 71.8%, and 53.8% in the 10% GATP treatment, respectively. The results of the sequential extraction program (SEP) experiment and X-ray photoelectron spectroscopy (XPS) analysis showed that GATP promoted the conversion of weak acid extractable Cr to the residual state, and produced stable Cr(III) and chromium-silicon oxide. Besides, soil enzyme activities of the GATP amended soils were significantly improved. Therefore, GATP had advantages of having a simple preparation process and lower prices and improved soil physicochemical and environmental conditions.