Lv Liang, Wang Yulin, Wei Min, Cheng Jianjun
West Branch of Zhejiang University of Technology, Zhejiang 324006, China.
J Hazard Mater. 2008 Apr 15;152(3):1130-7. doi: 10.1016/j.jhazmat.2007.07.117. Epub 2007 Aug 8.
A fundamental investigation on the uptake of bromide ion from contaminated water by calcined and uncalcined MgAl-CO3 layered double hydroxides (LDHs) were conducted in batch mode. The uptake capacity of calcined LDHs (CLDH) is higher than that of uncalcined LDHs, due to their different mechanisms which are confirmed by powder X-ray diffraction, FT-IR spectroscopy and TG-MS measurements. The former mechanism is based on the reconstruction of CLDH to Br-LDHs, whilst the latter is related to the surface adsorption. It has been found that the LDHs calcined at 500 degrees C with Mg/Al molar ratio of 4 represents the highest capacity to remove bromide ion from aqueous solution. The equilibrium isotherms of uptake of bromide by CLDH were well fitted by the Langmuir equation, and thermodynamic parameters such as Delta G0, Delta H0 and Delta S0 were calculated from Langmuir constants. The negative value of Delta H0 confirms the exothermic nature of adsorption. Three kinetics models were used to fit the kinetics experimental data, and it was found that the pseudo-second order kinetics model could be used to describe the uptake process appropriately. The value of Ea was calculated to be 79.9 kJ/mol, which suggests that the process of uptake bromide is controlled by the reaction rate of bromide with the CLDH rather than diffusion.
采用分批模式对煅烧和未煅烧的MgAl-CO₃层状双氢氧化物（LDHs）从污染水中摄取溴离子进行了基础研究。煅烧后的LDHs（CLDH）的摄取能力高于未煅烧的LDHs，这是由于它们不同的机制，粉末X射线衍射、傅里叶变换红外光谱和热重-质谱测量证实了这一点。前者的机制基于CLDH重构为Br-LDHs，而后者与表面吸附有关。已发现，在500℃下煅烧且Mg/Al摩尔比为4的LDHs表现出从水溶液中去除溴离子的最高能力。CLDH摄取溴的平衡等温线能很好地用朗缪尔方程拟合，并根据朗缪尔常数计算了诸如ΔG⁰、ΔH⁰和ΔS⁰等热力学参数。ΔH⁰的负值证实了吸附的放热性质。使用三种动力学模型拟合动力学实验数据，发现准二级动力学模型可以适当地描述摄取过程。计算出的Ea值为79.9 kJ/mol，这表明摄取溴的过程受溴与CLDH的反应速率控制而非扩散控制。
