The interactions between Cr(III) and calcium ion modified montmorillonite or kaolinite (CaÀ Mt or CaÀ Kaol) in the absence and presence of humic acid (HA) were investigated by batch equilibrium experiments under different pH values. A linear additive model was introduced to extrapolate the solid-liquid distribution of Cr(III) in ternary systems by using K d values obtained from binary systems among clay mineral, Cr, and HA. The different affinity of Cr(III) between HA and clay minerals had great effects on the Cr(III) adsorption in the ultimate ternary system. CaÀ Mt showed a better adsorption ability for Cr(III) due to the superior physicochemical properties compared to CaÀ Kaol. The adsorption-desorption isotherms were used to study the reversibility of Cr(III) sorption in the binary and ternary systems, and the physicochemical characterization explored the main mechanism of Cr(III) immobilization by clay minerals including cation exchange and surface complex.

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