Simultaneous Removal Of Coexisting Arsenate And Fluoride In Aqueous Solutions By Modified Layered Double Hydroxides

Water environment is a primary condition for human existence. With the development of modern society and the rapid expansion of population, water environmental pollution is increasing quickly, which directly affect the quality of people’s lives. This situation has become a key factor affecting the sustainable development of our country, especially to the industry, agriculture and fisheries, and caused huge potential security problems to the health of people. The problem of water resource pollution attracts more and more attention.Technologies of removing arsenic and fluorine at home and abroad include filtration, adsorption, precipitation, ion exchange, electrodialysis method and so on. We choose the adsorption process to remove arsenic and fluorine because it has advantages of convenience for preparation, low cost, high efficiency, convenient to operate, and would not cause secondary pollution. Mg/Al(3:1) LDHs and Mg/Al/La(3:1:0.05,3:1:0.1,3:1:0.2) LDHs were prepared by co-precipitation method with Mg(NO3)2.6H2O, A1(NO3)3.9H2O, La(NO3)3.nH2O, NaOH, Na2CO3. The calcined hydrotalcite(LDOs) were abtained by calcination at temperature450℃The Microscopic morphology and phase composition of products were studied with modern instruments and different analysis methods. The particle size and morphological structure were characterized by perspective electron microscopy scanning. The surface group and interlayer anions of materials were characterized by infrared spectroscopy measurements, and X-ray diffraction(XRD) scanned special samdwich and Material composition of materials. The ability of LDOs to remove coexisting arsenic and fluoride from aqueous solution was investigated at different initial concentration of adsorbate, pH, reaction time and coexisting anions.The results showed that LDHs’layered structure is obvious. FTIR presented a typical infrared spectrogram of materials, most of H2O, OH-and CO32-of LDOs had disappeared; XRD analysis indicated that the sample has good crystalline, La was doped into the hydrotalcite successfully.Through the contrast of materials, we choose Mg/Al3:1LDOs and Mg/Al/La3:1:0.1LDOs to remove arsenic and fluorine. Mg/Al/La3:1:0:1LDOs has a better absorbing effect than Mg/Al3:1LDOs. The adsorption capacity for arsenic and fluorine could be kept highly at pH6.0. The adsorption process of Mg/Al/La LDOs followed the pseudo-second-order model for both arsenic and fluoride. The adsorption equilibrium data of arsenic and fluorine on Mg/Al/La LDOs agreed well with the Langmuir mode. Langmuir equation of arsenic is: qe=87.30×0.92Ce/(1+Ce); Langmuir equation of fluorine is:qe=102.33×0.03Ce/(1+Ce). The maximum adsorption values of arsenic and fluorine by Mg/Al/La LDOs are87.30mg/g and102.33mg/g respectively. The efficiency of different anions on the adsorption of arsenic and fluorine by LDH was compared, for arsenic:HPO42->CO32->NO3->Cl-SO42-, and for fluorine:CO32>HPO42>SO42> Cl> NO3-. Mg/Al/La LDOs can be recycled repeatedly.