酸碱复合改性海泡石亚结构特征及其对Cd(Ⅱ)吸附性能

为强化海泡石(Sep)对溶液中Cd~(2+)的吸附性能,采用酸碱复合改性处理获得改性海泡石(ABsep),借助氮气吸脱附等温线、SEM-EDS、TEM、FTIR和XRD等技术分析了改性前后海泡石的结构特征,采用静态吸附实验研究了时间、ABsep/Cd~(2+)质量比、温度、吸附剂用量、pH及共存离子等因素对ABsep吸附Cd~(2+)的影响.结果表明,ABsep孔隙结构发达,比表面积、平均孔径和孔容分别较改性前增加66.1%、15.7%和34.8%,可交换性离子含量有所增加,主要成分为SiO_2和Mg(OH)_2.改性前后海泡石对Cd~(2+)吸附过程能较好地以准二级动力学方程和Langmuir模型进行拟合,且均为自发吸热反应,以化学吸附为主并伴有物理性吸附;最佳ABsep/Cd~(2+)质量比为3:1;298 K时Sips拟合ABsep对Cd~(2+)最大饱和吸附量为142.43 mg·g~(-1),为改性前海泡石的3.55倍;随着吸附剂投加量的增加,Cd~(2+)吸附量表现为先增大后减小,最佳用量为0.3 g·L~(-1);ABsep对Cd~(2+)的吸附量随溶液初始pH的升高而增加最佳pH为7;不同浓度K~+、Na~+、Mg~(2+)和Ca~(2+)的存在均会对Cd~(2+)的吸附产生一定的抑制作用其中Mg~(2+)的抑制作用最强.

Substructure Characteristics of Combined Acid-Base Modified Sepiolite and Its Adsorption for Cd(Ⅱ)

To enhance the adsorption capacity of sepiolite (Sep) on Cd²⁺ in solution, an acid-base Sep (ABsep) was obtained using the method of combined acid-base modification. The structural properties of Sep and ABsep were analyzed by adsorption-desorption isotherms of N₂, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). Static adsorption experiments were carried out to evaluate the effects of time, mass ratio of ABsep/Cd²⁺, temperature, adsorbent dose, pH, and co-existing ions on the adsorption of Cd²⁺ by ABsep. The results showed that the pore structure of the ABsep was more developed than that of Sep. In comparison to Sep, the specific surface area, average pore diameter, and pore volume of ABsep increased by 66.1%, 15.7%, and 34.8%, respectively, and the exchangeable ion contents also increased. The main components of the ABsep were SiO₂ and Mg(OH)₂. The adsorption process of Cd²⁺ by Sep and ABsep could be well fitted with a pseudo-second-order kinetic equation and Langmuir isotherm, and both were spontaneous endothermic reactions, which were mainly chemical adsorption along with physical adsorption. The best mass ratio of ABsep:Cd²⁺ was 3:1, and the maximum saturated adsorption capacity fitted by the Sips model of the ABsep on Cd²⁺ at 298 K was 142.43 mg·g^-1, which was 3.55 times that of Sep. As the adsorbent dose increased, the adsorption amounts of Cd²⁺ first increased and then decreased, with the optimum dose being 0.3 g·L^-1. The amount of Cd²⁺ adsorption by the ABsep increased with the initial pH of the solution, whereby the best pH was 7. We also found that the presence of K⁺, Na⁺, Mg²⁺, and Ca²⁺ at different concentrations could inhibit the adsorption of Cd²⁺, whereby the inhibition of Mg²⁺ was the highest.