Sulfhydryl Grafted Palygorskite Amendment with Different Loading Rates : Preparation, Characterization and Immobilization Effects for Soil Cd

In this study, emerging amendments sulfhydryl grafted palygorskite (SGP) with different sulfhydryl loading rates were prepared and characterized in detail. Their immobilization efficiency for Cd and dose-effect relationship were investigated via sorption in solutions, soil incubation, and field-scale wheat cultivation experiments. The effects of different sulfhydryl loading rates on the structure and surface properties of SGP were confirmed by 29 Si NMR, XRD, DSC, zeta potential, and potentiometric titration analyses. The saturated sorption capacity of SGP for Cd 2+ in solutions had linear relationship with sulfhydryl content. The second-order kinetic equation and Langmuir isotherm could fit the sorption process of Cd 2+ on SGP. XPS revealed the surface complexation of sulfhydryl and Cd 2+ on SGP. Meanwhile SGP could reduce both available Cd concentration in alkaline soil and wheat grain Cd by different percentages. The relationship between the immobilization efficiency and total sulfhydryl group could be fitted by the Michaelis-Menten equation. The sulfhydryl group was the key site of SGP amendments, and its amount added to the soil determined the reduction of soil Cd bioavailability. The clarification of the dose-effect relationship will be the theoretical support for the accurate regulation in the safe utilization of heavy metal contaminated farmland