Layered Double Hydroxides(LDH) Preparation And Application On Simultaneously Removal Of Coexisting Arsenate And Fluoride

Mg (NO3)2.6H2O,Al(NO3)3.9H2O,NaOH,Na2CO3being raw maerial, Three different proportions of nanoscale adsorbent called Layered Double Hydroxides (LDH)(Mg:Al=1:1,2:1,3:1) was prepared by co-precipitation method, and product of roasted LDH were abtained by calcination in the muffle furnace at temperature450℃for8h.All the absorent was characterized by all kinds of chemical analysis method and the modern techniques. The structure,surface functional groups and morphology of the three different proportions LDH (Mg:Al=1:1,2:1,3:1) was studied by infrared spectroscopy measurements, perspective electron microscopy scanning,X-ray diffraction(XRD),etc.The ability of LDH which was calcined or uncalcined to remove arsenic and fluoride from aqueous solution was investigated contrastively,All the adsorption experiments were carried out at differnt initial concentration of adsorb-ate, pH, fuction time,etc.Their adsorption of coexisting arsenate and fluoride was further investigated,at the same time,the effects of CI-、CO32-、HPO42-、SO42-、N03-on the adsorption of coexisting arsenate and fluoride was investigated absolutly.This paper main research conclusions were as follows:(1) The samples prepared is hexagonal multilayer in structure, which is similar with the structure of hydrotalcite crystal.The samples prepared contains a lot of OH" on the surface and there are CO32-anion at the interlayer of it.Relative to the uncalcined LDH,there are not CO32-at590cm-1on the calcined LDH.(2) The adsorption of arsenic and fluorine on the LDH which have been calcined on450℃,is better than the uncalcined one.the adsorption mode of arsenic and fluorine on the LDH fitted well into Langmuir equation.and it shows that the LDH (Mg:Al=2:1) is the best one, the adsorption of arsenic qmax=84.7458mg/g, the adsorption of fluourine qmax=81.3008mg/g.(3) In the research about the adsorption of coexisting arsenate and fluoride, the calcined LDH (Mg:Al=2:1) was chosen as the absorsent. It was found that Langmuir equation of arsenic is: qe=51.02×0.66Ce/(1+Ce),Freundlich equation of fluorine is: Log(qe)=0.75×logCe+log1.77.In the dynamic experiment,the maximum adsorption of LDH (Mg:Al=2:1) for arsenic takes place within6h, for fluorine within10h,the adsorption follows pseudo-second order kinetics,and the results of R2is0.9999,0.9589respectively.the adsorption efficiency for arsenic could be kept well at pH=4-10, for fluorine at pH=6-8.(4) The effects of Cl-、CO32-、HPO42-、SO42-、NO3-on the uptakes of asenic and fluorine on LDH. The effects for arsenic:HPO42->CO32->NO3->Cl->SO42-.The effects for fluorine:CO32->HPO42->SO42->CI->NO3.To analyze and discuss in theory and to test and verify by experiments, the results prove that based on the way of adsorption of coexisting arsenate and fluoride by LDH is an effectine arsenic and fluorine removal method,and it is economical and practical technology valuable to popularize in water area.