Study On Preparation And Adsorption Behavior Of Layer Double Hydroxide And Layer Double Oxide

Nano-Mg/Al Layer double hydroxides (LDHs) with differrent Mg/Al mol rations were prepared by co-precipitation method and different Mg/Al Layer double oxides were obtained by calcination of corresponding LDHs. Both LDHs and LDOs were characterized by XRD, TG-DTA-DSC, FTIR, TEM and BET surface area. The ability of Mg/Al oxides to remove F~- from aqueous solution was investigated. All the adsorption experiments were carried out as a function of time, pH, concentration of adsorbate, adsorbent dose etc. It was found that:(1)The adsorption ability of the calcined products (LDOs) were found to increase with the increase of calcination temperature untill 500℃,while LDHs appearred little adsoption ability for Fluoride.The LDO obtained from LDH with Mg/Al mol ratio 3 calcined at 500℃ for 4h was showed to have the stongest adsorption ability. Zeta potential measurements indicated that the LDO3 have surface residual positive charge,and its pHpzc was found to be 11.8.(2)The maximum adsorption takes place within 3h at pH 6.0. The percentage of adsorption increases with increase in the adsorbent dose,but decreases with increase in the adsorbate concentration. The percentage of adsorption of LDO3 was little affected by pH within the range pH4~ 11, and decreased with the further increase of pH at fluoride concentration 10mg/L, LDO3 dose 1g/L.(3) The removal of fluoride obtained perhaps through surface adsorption and structural recovery was not in direct ratio to the surface area, so the dominant place of structural recovery was concluded.(4)Different distribution coefficient calculated at differrnt LDO3 dose indicated the surface site of LDO3 is heterogeneous.(5)The batch adsorption kinetics has been described by the Lagergren equation which is a first-orderrate expression.(6)The adsorption data fitted well into the linearly transformed Langmuir equation.(7)Only part of LDO recoverred LDH Layer structure after adsorption of fluoride, and recoverring degree decreased with the increase of calcination temperature, the experimental maximum removal of fluoride is only 58.1 percentage of theoretic one.