[Experimental Research of Hg²⁺Removal by TiO₂/Bentonite Composite]

The TiO₂/bentonite composite was synthesized by modifying calcium-based bentonite with Nano-TiO₂. The products before and after modification were characterized via the approach of X-ray power diffraction(XRD) and scanning electron microscope(SEM).The effect of TiO₂/bentonite composite on mercury removal from aqueous solutions of HgCl₂was studied at different dosage, pH, adsorption time and the initial concentration of Hg²⁺ was investigated and compared with the bentonite by indoor simulation experiment, as well as the orthogonal experiments to determine the optimal condition of Hg²⁺ adsorption. The experimental results showed:after modified by TiO₂, TiO₂/bentonite composite particles were apparently smaller, the basal spacing was increased and with a loose and porous structure. The adsorption rates of TiO₂/bentonite composite on Hg²⁺ were increased compared with bentonite. The Hg²⁺ adsorption rates were increased with the increasing dosages, pH and adsorption time. The adsorption rates were higher than 98.0% when the dosage was 1.5 g·L^-1, pH 7.0, and the adsorption time was 120 min. The adsorption rates became smaller with increasing initial concentration of Hg²⁺. False secondary dynamic equation could describe the adsorption of TiO₂/bentonite composite on Hg²⁺, and the chemical adsorption was dominant. The adsorption isotherm of Hg²⁺ conformed to Langmuir equation, indicating that the adsorption of Hg²⁺ was typical monolayer adsorption. The optimal experimental condition was:dosage of 2.0 g·L^-1, pH 8.0, adsorption time of 16 h and the initial Hg²⁺concentration of 45 mg·L^-1. Under this condition, the adsorption rate was 99.9%, and the equilibrium concentration of Hg²⁺ was 0.034 mg·L^-1.