Adsorption and desorption of Thallium(I) in soils: The predominant contribution by clay minerals

Thallium (Tl) is a highly toxic environmental contaminant. To understand the mechanism controlling the mobility and availability of Tl in soil, the adsorption and desorption of Tl(I) were evaluated for six soils. The maximum Tl adsorption capacities of the soils ranged from 6.9 to 244.5 mmol kg?1. The corresponding Tl LIII-edge X-ray absorption near-edge structure (XANES) data revealed that illite, vermiculite, and smectite are the preferential soil constituents for adsorbing Tl(I). Tl(I) adsorption by the soils was reversible in the low Tl adsorption regime and exhibited various degrees of hysteresis as the amount of absorbed Tl increased. The Tl(I) adsorption and extent of adsorption reversibility were mainly dependent on the type and content of clay minerals and exchangeable cations in different soils. Despite high Tl(I) adsorption by the soils, the reversibility of Tl(I) adsorption may result in relatively high mobility and availability of Tl(I) in soils, leading to high environmental risk. Ignoring the reversibility of Tl adsorption could lead to an erroneous prediction of the mobility and availability of Tl in soils and a significant underestimation of the environmental risk posed by Tl in the environment. ? 2021 Elsevier B.V.