Lv Liang, He Jing, Wei Min, Evans D G, Duan Xue
Key Laboratory of Science and Technology of Controllable Chemical Reactions, Ministry of Education, Beijing University of Chemical Technology, Chao Yang District, China.
J Hazard Mater. 2006 May 20;133(1-3):119-28. doi: 10.1016/j.jhazmat.2005.10.012. Epub 2005 Dec 15.
Layered double hydroxides (LDH) calcined at different temperatures (denoted as CLDH) have been demonstrated to recover their original layered structure in the presence of appropriate anions. In the light of this so-called "memory effect", a study of removal of fluoride from aqueous solution by calcined Mg-Al-CO(3)-LDH has been carried out. The LDH calcined at 500 degrees C had the highest capacity of removal of fluoride ion, because of retention of its intrinsic structure. The CLDH with an Mg/Al ratio of 2 has a remarkable ability to adsorb anions. The adsorption loading is higher for the calcined Mg-Al-LDH than for calcined Zn-Al and Ni-Al-LDH. The influence of varying the conditions for removal of fluoride, such as the pH of aqueous solution, the initial fluoride concentration, the dosage of adsorbent, and temperature on removal of fluoride have been investigated. The influence of co-existing anions in fluoride aqueous solution indicates that the percentage of removal of fluoride increased in order PO(4)(3-) < Cl(-) approximately SO(4)(2-) < Br(-) << NO(3)(-). It was found that maximum removal of fluoride from aqueous solutions was obtained in 6h at pH 6.0 with an initial concentration of 50 mg/L, and that the retention of fluoride ions by the CLDH material was 98% or higher. The residual fluoride concentration was found to be 0.4 mg/L with an initial concentration of 20 mg/L, which meets the national standard for drinking water quality. The Freundlich isotherm and Langmuir isotherm were used to fit the data of equilibrium experiments. The results of X-ray diffraction, FT-IR and TG-MS demonstrate that the adsorption phenomenon is accompanied by rehydration with concomitant uptake of fluoride ions to rebuild the initial layered structure.
在不同温度下煅烧的层状双氢氧化物（LDH，记为CLDH）已被证明在存在适当阴离子的情况下可恢复其原始层状结构。鉴于这种所谓的“记忆效应”，开展了一项关于煅烧的Mg-Al-CO(3)-LDH从水溶液中去除氟化物的研究。在500℃煅烧的LDH具有最高的氟离子去除能力，这归因于其固有结构的保留。Mg/Al比为2的CLDH具有显著的阴离子吸附能力。煅烧的Mg-Al-LDH的吸附负载量高于煅烧的Zn-Al-LDH和Ni-Al-LDH。研究了改变去除氟化物的条件，如水溶液的pH值、初始氟化物浓度、吸附剂用量和温度对氟化物去除的影响。氟化物水溶液中共存阴离子的影响表明，氟化物的去除百分比按PO(4)(3-) < Cl(-) ≈ SO(4)(2-) < Br(-) << NO(3)(-)的顺序增加。结果发现，在pH 6.0、初始浓度为50 mg/L的条件下，6小时内可从水溶液中最大程度地去除氟化物，且CLDH材料对氟离子的保留率达到98%或更高。当初始浓度为20 mg/L时，残余氟化物浓度为0.4 mg/L，符合国家饮用水水质标准。采用Freundlich等温线和Langmuir等温线对平衡实验数据进行拟合。X射线衍射、傅里叶变换红外光谱和热重-质谱的结果表明，吸附现象伴随着再水化以及氟离子的吸收，从而重建初始层状结构。
