Modification And Granulation Of Mg/Al Layered Double Hydroxides And Adsorption Of Halide Anions

MG Mg-Al·LDH was prepared by Mg-Al·LDH, magnesium acetate, starch, and sodium silicate. The effect of calcination temperature on the adsorption capability has been investigated. The materials are characterized by BET, X-ray diffraction (XRD), FT-IR spectrometers and thermogravimetry. The static and dynamic adsorption capacities of Mg-Al·CLDH and MG Mg-Al·CLDH were evaluated by adsorbing halide anions (F-,Cl-, Br- and I-) from aqueous solution.The optimum conditions for preparing MG Mg-Al·LDH were determined by exploring the effect of calcination temperature on the adsorption properties of these materials. The optimum conditions were:mass ratio of Mg-Al·LDH, Mg(Ac)2 and Na2SiO3·9H2O was 47.5:50:2.5, the pH was 10, reaction time was 60min, solid-liquid ratio was 1:10, the calcinations temperature was 500℃and the calcinations time was 3h. The BET results showed that the surface area and microspore volume of MG Mg-Al·LDH were larger than those of Mg-Al·CLDH. MG Mg-Al·CLDH maintains the original peak shape of Mg-Al·CLDH in infrared spectrum, with the peak wave number shifting a little. According to the XRD results, after modification, the layer spacing change of Mg-Al·LDH was very small, which indicated that the group of Ac-was inserted from the outside of the shelves. FT-IR spectrometers results indicated that Mg2+ was not formed by Mg(OH)2. The TG-DSC analysis showed that the thermal decomposition of magnesium acetate resulted in weight loss phase shift to the low temperature significantly. MG Mg-Al'LDH weight loss rate increased.The static adsorption of Mg-Al·CLDH and MG Mg-Al'CLDH for halide anions (F-, Cl-, Br- and I-) in aqueous solution was studied. The results showed that the adsorption capacity of MG Mg-Al·CLDH for halide anions was greater than that of Mg-Al·CLDH. The maximum adsorption capacities of Mg-Al·CLDH for F-, Cl-, Br-and I- were 128.55,106.82,153.85 and 181.81 mg·g-1, while those of MG Mg-Al·CLDH reached 256.0,216.01,270.27 and 303.03 mg·g-1. Under the same condition, the maximum adsorption capacity of MG Mg-Al·CLDH for halide anion is 2 times of that of Mg-Al·CLDH. The adsorption of Mg-Al·CLDH and MG Mg-Al·CLDH for halide anion followed Langmuir adsorption isotherm model. Studies showed that the adsorption of Mg-Al·CLDH for F-, Br- and I- and the adsorption of MG Mg-Al·CLDH for I- followed the pseudo-first order model, while the adsorption of Mg-Al·CLDH for Cl- and the adsorption of MG Mg-Al·CLDH for F-, Cl- and I- followed the pseudo-second order model.The dynamic adsorption of MG Mg-Al·CLDH for halide anions (F-, Cl-, Br- and I-) in aqueous solution was studied. The effects of initial concentration, the pH value, the flow rate and the height of the fix-bed on the adsorption of MG Mg-Al·CLDH have been investigated. The results showed that the breakthrough adsorption quantity increased frist and decreased later when increasing the initial concentration and it decreased with the flow rate. There is little change when the height of the fix-bed increased. MG Mg-Al·CLDH has a good adsorption capacity for halide anion in a wide range of pH values. Particle diffusion and mass transfer are the limiting steps of adsorption process. The material of MG Mg-Al·CLDH had an ability of removal of halide anion in aqueous solution.MG Mg-Al·LDH was prepared from Mg-Al·LDH, magnesium acetate, starch and sodium silicate. MG Mg-Al·CLDH shows good adsorption properties and it may provide a new way for the utilization of magnesium salts.