Sorption mechanism of cadmium on soils: A combination of batch experiment, path analysis, and EXAFS techniques

Abstract

• The sorption mechanism of Cd(II) in 49 soils was fully explored. • Cd(II) sorption capacities were closely related to soil physicochemical properties. • Cd in soils was mainly bound to metal (hydro)oxides or existed as CdCO 3 . Soil cadmium (Cd) contamination has emerged as an alarming environmental issue worldwide. Chemical reactivity and bioavailability of Cd in soils are highly dependent on soil properties. However, the sorption mechanism of Cd(II) on soils is not yet fully explored. For this purpose, batch sorption experiments, statistical analysis, and extended X-ray absorption fine structure (EXAFS) spectroscopy were integrated to elucidate the Cd(II) sorption mechanism by investigating the Cd(II) sorption behaviors in 49 soils with contrasting physicochemical characteristics and to figure out the influence of soil properties on Cd(II) sorption in soils. The outcomes of this study revealed that the soils from different areas had large differences in their abilities to adsorb Cd(II), while the differences were closely related to the physicochemical properties of soils. Cd(II) sorption capacities were controlled together by pH, metal (hydro)oxides, organic matter, and cation exchange capacity. The soil pH was the most critical factor in connecting Q max with soil properties. EXAFS results indicated that Cd(II) adsorbed on soils was mainly bound with metal (hydro)oxides or existed as CdCO 3 precipitate. The findings of this study provide a theoretical basis for predicting the risk of soil Cd contamination.