TiO2/膨润土复合材料对Hg2+的吸附性能研究

利用纳米TiO_2对膨润土进行复合改性,制备TiO_2/膨润土复合材料.采用电镜扫描、X-射线衍射表征改性前后膨润土的结构和形貌.通过室内模拟实验,以膨润土为对照,研究不同添加量、pH、吸附时间及初始Hg~(2+)浓度等条件下,TiO_2/膨润土复合材料对Hg~(2+)的吸附特性与性能,同时通过正交试验,探究TiO_2/膨润土复合材料吸附Hg~(2+)的最优条件.结果表明,改性后的膨润土颗粒明显变小,且颗粒疏松多空孔,层间距增大.相比于膨润土,TiO_2/膨润土复合材料吸附性能得到极大提高.TiO_2/膨润土复合材料对Hg~(2+)的吸附率均随着添加量、pH、吸附时间的增大而增大,添加量为1.5 g·L~(-1)、pH为7.0、吸附时间为120 min时,吸附率达98.0%以上.但TiO_2/膨润土复合材料对Hg~(2+)的吸附率随着初始Hg~(2+)浓度的增大而减小.通过4种动力学模型拟合发现,吸附过程符合假二级动力学方程,吸附以化学吸附为主.吸附等温线更符合Langmuir等温方程,属于典型的单分子层吸附,最大吸附量为20.66 mg·g-1.吸附Hg~(2+)的最优实验条件:添加量为2.0 g·L~(-1),pH为8.0,初始Hg~(2+)浓度为45 mg·L~(-1),吸附时间为16 h,此时吸附率99.9%,平衡浓度为0.034 mg·L~(-1).

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