Immobilization remediation of Cr-contaminated soils by hydrocalumite and the relevant risk assessment

Five typical Chinese soils, including brown soil, red soil, yellow soil, black soil and cinnamon soil, were collected and artificially contaminated with Cr(VI) to a concentration of 80mg/kg. Hydrocalumite, a promising layered double hydroxide, was applied as a first attempt to immobilize the Cr-contaminated soils. The remediation effects were comprehensively evaluated on soil basic physicochemical properties, and fractionation, ecological risk and health risk of soil Cr. The relevant mechanisms and cost were discussed. Results showed that hydrocalumite significantly increased soil pH, and effectively reduced the Cr activity (59.09%~79.22%), ecological risk (14.17%~57.66%) and health (carcinogenic) risk (13.04%~63.04% in gastric phase and 22.73%~56.60% in small intestinal phase) of soil Cr. In addition to active Cr fraction, inactive Cr fraction also contributed to its ecological and health risks before and after remediation. Hydrocalumite could not only transform active Cr fraction into inactive precipitated fraction for a partial reduction or a complete elimination of its ecological risk or health risk, but also further suppress the dissolution of other inactive Cr fraction in certain soils in the TCLP or in vitro test. Regarding the reagent cost, a reasonable 6.4CNY could cover the remediation of 1m3 of actual construction land with a Cr(VI) concentration of 80mg/kg, under the relatively optimum dosage (mCr: mhydrocalumite = 1: 20). As a new-type immobilizing agent for Cr-contaminated soils, hydrocalumite is highly expected to make contributions to the improvement of soil quality and public health. © 2021, Editorial Board of China Environmental Science. All right reserved.