聚合羟基铁铝蒙脱石复合体对磷的吸附行为及其动力学

BEHAVIOR AND KINETICS OF PHOSPHATE ADSORPTION ON HYDROXYALUMINUM/HYDROXYIRON-MONTMORILLONITE COMPLEXES

在一定条件下利用钠基化蒙脱石合成了聚合羟基铝-蒙脱石复合体(HyA1-Mt)、2个不同铁含量的聚合羟基铁-蒙脱石复合体(HyFe-Mt)和3个不同Fe:Al摩尔比的聚合羟基铁铝-蒙脱石复合体(HyFeAl-Mt),研究了酸性和弱酸性条件下(pH=3.0～6.5)以上蒙脱石复合体对磷的吸附行为和动力学特征。结果表明,HyFeAl-Mt对磷的吸附容量大于HyA1-Mt和HyFe-Mt复合体,且随着Fe:Al摩尔比的增大,对磷的吸附容量依次增加。随pH升高,蒙脱石复合体对磷的吸附量容量变小。但随Fe:Al摩尔比增大,HyFeAl-Mt复合体零电荷点(pHZPC)升高,pH对磷的吸附的影响越来越小,HyFe-Mt对磷的吸附几乎不受pH的影响。随Fe:A1摩尔比的增大,HyFeAl-Mt对磷的吸附能力增强,铁含量是磷吸附量的重要控制因素。磷在各蒙脱石复合体上的吸附实验数据可很好地用Langmuir吸附等温方程拟合。磷在各蒙脱石复合体上的吸附动力学过程可分为快速和慢速两个过程,快速过程中的动力学受铁含量影响明显。动力学数据可同时用准二级动力学方程和Elovich方程拟合。

One hydroxyaluminum-montmorillonite complex （HyAl-Mt）, two hydroxyiron-montmorillonite complexes （HyFe-Mt） with different iron contents, and three hydroxyiron/aluminmum-montmorillonite complexes （HyFeAl-Mt） with different Fe： Al molar ratios were synthesized. The behavior and kinetics of phosphate sorption on the Mt-complexes mentioned above were investigated under weakly to strongly acidified conditions. The results indicated that the sorption capacities of HyFeAl-Mt for phosphate are higher than those of HyAl-Mt and HyFe-Mt. For HyFeAl-Mt, the sorption capacity increases with increasing Fe： Al molar ratio. The amount of phosphate sorption increases with a decrease in pH in the pH range （3.0 -6. 5）. However, the effects of pH become weaker with increasing Fe： Al molar ratio due to increasing pHzpc of Mt-complexes. For HyFe-Mt, the effect of pH on phosphate adsorption is slight. The phosphate adsorption data can be well fit to the Langmuir isotherm. The kinetics of phosphate adsorption is characterized by the initial fast step and later slow one, with the fast step being very sensitive to iron contents in Mr-complexes. The kinetic data of phosphate adsorption can be well described by both the pseudo second-order rate equation and Elovich equation.