Cotransport of Tl(I) and kaolinite colloids in water-saturated porous media: Two systems with different components

Media components and colloid particles may affect Tl(I) transport in water-saturated porous media. It is sig-nificant to study the cotransport of Tl(I) and kaolinite in two systems with different components under different ISs, pH and kaolinite concentrations. The results of experiments conducted in quartz sand columns indicated that Tl(I) transport was promoted under low pH and high IS, due to competition between Tl(I) and cations (Na+ and H+) for adsorption sites. The effect of kaolinite on Tl(I) transport changed from inhibition to promotion with increasing kaolinite concentration and decreasing pH, because colloidal particles and H+ occupy more adsorp-tion sites and competed with Tl(I). In the mica-quartz sand column, Tl(I) transport was promoted at low pH, which was consistent with the results of the quartz sand column experiments. However, Tl(I) transport was inhibited under high IS, due to the adsorption of heavy metals caused by the unique structure of mica. Tl(I) transport was promoted when kaolinite was present, which occurred mainly because of the adsorption of Tl(I) by kaolinite colloids and competitive adsorption between Tl(I) and colloids. The transport curves were fitted by two -site nonequilibrium sorption model, two-site kinetic attachment/detachment model, and colloid-facilitated so-lute transport model, respectively. In this study, the transport process of Tl(I) and kaolinite in porous media with different components was explored in depth, and the role of media in Tl(I) transport was investigated using novel approaches. The results facilitate the predicting of Tl(I) transport in underground environments and support remediation efforts for Tl contaminated soil and groundwater.