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通过静态吸附实验,研究了Cr(Ⅵ)在Mg/Al水滑石焙烧产物层状双金属氧化物(layered double oxides,LDO)的吸附性能。考察了温度对其吸附性能的影响,探讨了吸附动力学和热力学规律。研究表明:吸附动力学符合准二级动力学模型,LDO的吸附活化能为21.42kJ/mol,表现为扩散控制过程。在293～333K温度范围内,吸附自由能(ΔG°)变小是Cr(Ⅵ)在LDO上的吸附推动力;吸附热(吸附焓变ΔH0)为5.12kJ/mol,是一自发的物理吸附过程;LDO吸附Cr(Ⅵ)为熵增过程,其熵变为49.12J/(mol·K)。结合XRD表征结果探讨了吸附机理:LDO吸附Cr(Ⅵ)无配位基交换、化学键等强的作用力,Mg/Al金属氧化物在吸附Cr(Ⅵ)后恢复为LDH层状结构,因此,LDO对Cr(VI)的强吸附能力是因为其具有较强的结构“记忆效应”。
The adsorption properties of Cr (Ⅵ) on layered double oxides (LDO) calcined by Mg / Al hydrotalcite were investigated by static adsorption experiments. The effects of temperature on the adsorption properties were investigated. The adsorption kinetics and thermodynamic laws were also discussed. The results show that the adsorption kinetics is in accordance with the quasi-second-order kinetic model. The adsorption activation energy of LDO is 21.42 kJ / mol, indicating the diffusion control process. The smaller adsorption free energy (ΔG °) is the adsorption force of Cr (Ⅵ) on LDO at the temperature range of 293 ~ 333K. The adsorption heat (adsorption enthalpy change △ H0) is 5.12kJ / mol and is a spontaneous physical adsorption The adsorption of Cr (Ⅵ) to LDO was entropy increasing process, and its entropy was 49.12 J / (mol · K). The adsorption mechanism was discussed based on the XRD results: LDO adsorbed Cr (Ⅵ) without strong ligand exchange and chemical bond, and Mg / Al metal oxide restored to LDH after adsorbing Cr (Ⅵ) The strong adsorption capacity of LDO for Cr (VI) is due to its strong structure “memory effect ”.