焙烧层状氢氧化镁铝对水溶液中As(Ⅲ)和As(Ⅴ)的吸附性能比较

Comparison of the Adsorption of Arsenite and Arsenate Anions from Aqueous Solution by Calcined Mg-Al Layered Double Hydroxides

通过静态吸附实验,对比研究了焙烧层状氢氧化镁铝（Mg-Al CLDH）对水溶液中As（Ⅲ）和As（Ⅴ）阴离子的吸附特性,并用粉末X射线衍射对Mg-Al CLDH吸附前后的结构进行了表征.结果表明,Mg-Al CLDH对As（Ⅲ）和As（Ⅴ）的吸附是通过“结构记忆”效应实现的.Mg-Al CLDH可有效脱除溶液中的含砷阴离子,其吸附量明显高于现有文献的报道.当As（Ⅲ）和As（Ⅴ）初始浓度（以As计）分别高达10 mg.L-1和40 mg.L-1时,吸附后溶液中残余As浓度〈10μg.L-1.在本研究的初始浓度4～500mg.L-1范围内,在298～323 K下,As（Ⅲ）和As（Ⅴ）在Mg-Al CLDH上的最大吸附量（以As计）分别为150.46～224.03 mg.g-1和149.62～224.76 mg.g-1,且吸附量仍呈直线上升趋势.吸附量随温度升高而增大,表现为吸热吸附.As（Ⅲ）和As（Ⅴ）阴离子在Mg-Al CLDH上的吸附等温线分别属于L型和H型.在低浓度区域,As（Ⅲ）在Mg-Al CLDH上的吸附可用Freundlich等温方程式来描述,As（Ⅴ）更符合Langmuir等温方程式;在高浓度范围内,均可用Freundlich等温方程式来描述.在相同初始浓度和温度下,Mg-Al CLDH对As（Ⅴ）的吸附速率和脱除率远远大于As（Ⅲ）,吸附速率和脱除率随溶液初始浓度的降低和温度的升高而增大,伪二级动力学方程可较好地描述二者在Mg-Al CLDH上的吸附动力学过程.吸附基本不受溶液初始pH值（3.0～10.0）和离子强度的影响.当溶液中As（Ⅴ）和As（Ⅲ）同时存在时,Mg-Al CLDH优先吸附As（Ⅴ）.

The comparison of calcined Mg-Al layered double hydroxides （Mg-Al CLDH） for adsorption of arsenite and arsenate anions from aqueous solution was investigated by batch method. The results show that Mg-Al CLDH is an effective adsorbent for the removal of arsenite and arsenate anions. The adsorption processes are followed ＇memory effect＇. When the initial concentration of arsenic is lower than 10 mg· L-1 for arsenite and 40 mg· L-1 for arsenate, the equilibrium concentration of arsenic is lower than 10 μg·L-1 . In the range of 4-500 mg· L-1 for initial arsenic concentration, the maximum adsorption capacity of arsenite and arsenate on Mg-Al CLDH from 298 to 323 K is 150.46-224.03 mg· L-1 and 149.62-224.76mg· L-1 , respectively, which are much larger than other adsorbents. But the adsorption capacity is not reached saturation, it is continued to increase significantly. L and H model can be used to describe the adsorption isotherm of arsenite and arsenate, respectively. The adsorption data are corresponded to the Freundlich model for arsenite and Langmuir model for arsenate at lower equilibrium concentration, but corresponded to Freundlich model for arsenite and arsenate at higher equilibrium concentration. Under the same temperature and initial concentration, the adsorption rate and removal rate of arsenate are higher than those of arsenite. And they are increased with temperate but decreased with increase in initial concentration. Adsorption processes follow the pseudo-second-order kinetic model for both arsenite and arsenate. The removal rate is not influenced by the initial pH （3.0-10.0）. The adsorption capacity is influenced insignificantly by ionic strength. Arsenate anions are adsorbed firstly from arsenite and arsenate solution on Mg-Al CLDH.