| In this paper, three Mg-based layered doubled hydroxides (LDH), noted as Mg/Al-LDH, Mg/Al/Fe-LDH, and Mg/Fe-LDH, were prepared via hydrothermal process. FTIR, SEM, TG-DTA, XRD and ICAP were used to characterize these compounds. A series of batch experiments were performed with many operation parameters, and the optimum parameters for the three compounds were determined. On this base, Mg/Al-LDH/PES, Mg/Al/Fe-LDH/PES and Mg/Fe-LDH/PES hybrid membranes were prepared with different weight ratio of LDH/PES via a blending method. The hybrid membranes were characterized by SEM and FTIR, and then, the fluoride capacity of the membranes from solutions were measured. The main research contents and results are as follows:(1) The results of the characterization showed that three Mg-based LDH with NO3- -as the interlayer anion were successfully prepared via hydrothermal process. The thermal stability of the three compounds was proved to be in a good state. The pHzpc of Mg/Al-LDH, Mg/Al/Fe-LDH and Mg/Fe-LDHO was 9.5,9.8, and 10.4, respectively.(2) Three hybrid membranes with different weight ratio of LDH/PES were prepared via a blending method, and adsorption experiments were carried out to determine the optimum proportion. The suitable proportion determined by adsorption experiments was showed as following:3:2 for hybrid membrane of Mg/Al-LDH; 3:2 for hybrid membrane of Mg/Al/Fe-LDH; 2:1 for hybrid membrane of Mg/Fe-LDH. The results of SEM and FTIR showed that Mg-based LDH evenly distributed and stably fixed in the hybrid membranes.(3) The adsorption capacity of fluoride onto Mg-based LDH was respectively measured. A series of batch experiments were performed to investigate the effects of various experimental parameters, such as calcination temperature, adsorbent dosage, fluoride concentration, initial pH, contact time, adsorption temperature and co-existing anions. With the increase of adsorbent dosage, fluoride concentration and contact time, the adsorption capacity of these three Mg-based LDH clearly increased. The effect of initial pH on the three Mg-based LDH was almost in a consistent trend. The defluoridation performance exhibited negative trends in the presence of co-existing anions. In laboratory conditions, the fluoride capacity of Mg/Al-LDH, Mg/Al/Fe-LDH and Mg/Fe-LDH was 25.39mg/g,15.66mg/g and 15.65mg/g, respectively. The Langmuir isotherm model and pseudo-second-order kinetic model could be well used to fit the adsorption process.(4) The adsorption capacity of fluoride onto hybrid membranes was respectively measured. A series of batch experiments were performed to investigate the effects of various experimental parameters, such as initial pH, contact time, adsorption temperature and co-existing anions. There was a difference of adsorption equilibrium time among the three hybrid membranes. The defluoridation performance exhibited negative trends in the presence of co-existing anions. In laboratory conditions, the fluoride capacity of Mg/Al-LDH/PES hybrid membrane, Mg/Al/Fe-LDH/PES hybrid membrane and Mg/Fe-LDH/PES hybrid membrane was 6.17mg/g,3.72mg/g and 4.9mg/g, respectively. The experiment dates of the three hybrid membranes could be well described by pseudo-second-order kinetic model. The Langmuir isotherm model was fit for the adsorption process of Mg/Al-LDH/PES hybrid membrane and Mg/Fe-LDH/PES hybrid membrane with 50 ℃. However, the experiment dates obtained from Mg/Al/Fe-LDH hybrid membrane and Mg/Fe-LDH/PES hybrid membrane with 25 ℃ was more suitable for Freundlich model.The results of this research showed that, the Mg-based LDH and the hybrid membranes, prepared via hydrothermal process and blending method respectively, played a good performance in fluoride adsorption from solutions. In general, the research on using magnesium salts to synthesize Mg-based LDH and shaping it into membrane with PES will provide a new way for the utilization of magnesium salts from brine and the widely utilized of powder adsorbent. |
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