钙预处理对磁性锆铁改性膨润土吸附水中磷酸盐的影响

Influence of Calcium Ion Pre-treatment on Phosphate Adsorption onto Magnetic Zirconium/Iron-modified Bentonite

研究制备了2种不同Ca^(2+)含量的磁性锆铁改性膨润土(ZrFeBTs),即磁性锆铁改性原始膨润土(Zr FeRBT)和磁性锆铁改性钙预处理膨润土(ZrFeCaBT),并通过吸附实验考察了Zr FeRBT和ZrFeCaBT对水中磷酸盐的吸附特征,以确定Ca^(2+)预处理对ZrFeBTs吸附水中磷酸盐的影响.结果发现,本研究所制备的ZrFeBTs包含Fe_3O_4和Zr,并且ZrFeCaBT中可交换Ca^(2+)的含量明显高于Zr FeRBT. ZrFeBTs对水中磷酸盐吸附平衡实验数据可以很好地采用Langmuir等温吸附模型加以描述,动力学实验数据可以很好地采用准二级动力学模型和颗粒内扩散模型进行描述.根据Langmuir模型确定的Zr FeRBT和ZrFeCaBT对水中磷酸盐的最大单位吸附量(以磷计)分别为8. 70 mg·g-1和11. 5 mg·g-1. ZrFeBTs吸附水中磷酸盐的过程属于化学吸附.随着p H值的增加,ZrFeBTs对水中磷酸盐的吸附效果逐渐降低.当溶液共存Cl^-、HCO_3^-、SO_4^(2-)、NO_3^-、Na^+、K^+、Mg^(2+)和Ca^(2+)等阴阳离子时,ZrFeBTs对水中磷酸盐的吸附具有很好的选择性,并且溶液共存的Ca^(2+)会极大地促进ZrFeBTs对水中磷酸盐的吸附.采用Ca^(2+)对膨润土进行预处理,极大地提高了ZrFeBTs对水中磷酸盐的吸附能力.

Two kinds of magnetic zirconium/iron-modified bentonites( ZrFeBTs),including magnetic zirconium/iron modified raw bentonite( Zr FeRBT) and magnetic zirconium/iron-modified Ca2+-pretreated bentonite,( ZrFeCaBT) were prepared and characterized. Their phosphate adsorption characteristics were compared to determine the effect of the Ca2+pre-treatment on the adsorption of phosphate onto ZrFeBTs. The results showed that the as-prepared ZrFeBTs contained Fe3O4 and Zr,and the content of exchangeable Ca2+in ZrFeCaBT was much higher than that in Zr FeRBT. The adsorption isotherm data exhibited good agreement with the Langmuir isotherm model,with maximum monolayer phosphate adsorption capacities of 8. 70 mg·g-1 and 11. 5 mg·g-1 for Zr FeRBT and ZrFeCaBT,respectively. The isotherm and kinetics studies showed that the adsorption of phosphate on ZrFeBTs was a chemisorption process. The phosphate adsorption capacities for ZrFeBTs decreased with increasing solution p H. The ZrFeBTs exhibited a high selective adsorption for phosphate in the presence of anions and cations,including Cl-,HCO3-,SO42-,NO3-,Na+,K+,Mg2+,and Ca2+. Furthermore,coexisting Ca2+greatly enhanced the adsorption of phosphate onto ZrFeBTs. The pre-treatment of raw bentonite with Ca2+significantly improved the adsorption of phosphate onto ZrFeBTs.