Leaching behavior and efficiency of cadmium in alkaline soil by adding two novel immobilization materials

The seriousness and harmfulness of cadmium (Cd) pollution have been gradually attracting wide attention. Remediation materials currently play a critical role in the remediation of Cd-polluted soils. However, the amendments that can efficiently remediate Cd-polluted alkaline soils are relatively few. In this study, a column leaching experiment was conducted to determine the effects of mercapto-palygorskite (MPAL) and mercapto-sepiolite (MSEP) on the leaching behavior and chemical fraction distribution of heavy metals, and to explore the remediation efficiency of two novel materials in alkaline soils through aging experiments. The results showed that, under DTPA-assisted leaching, the maximum concentration of leachate Cd in MPAL and MSEP was below 1/30 (0.1 mg·kg^-1) of the total Cd concentration among leaching and significantly lower than that in CK, palygorskite (PAL), and sepiolite (SEP) treatments. Meanwhile, MPAL and MSEP decreased the leaching efficiency of Cd stability, had negligible effects on the essential micronutrients Cu and Zn, and did not influence the pH and electrical conductivity (EC) values of leachate. After leaching, the Fe/Mn oxide-bound Cd increased in MPAL and MSEP, whereas the exchange fraction Cd and carbonate-bound Cd decreased. Aging results showed that MPAL and MSEP effectively reduced 62.39% and 44.89% of DTPA-Cd after 1 day of aging, while at same dosage (0.3%) PAL and SEP reduced 7.79% and 6.75% of DTPA-Cd after 30 days of aging and showed no obvious efficiency. It was thus concluded that MPAL and MSEP can be considered as two novel and efficient soil remediation materials for Cd-polluted alkaline soils.