凹凸棒黏土对水体和底泥中Cr(Ⅵ)的吸附

Adsorption of Attapulgite on Cr(Ⅵ) in Water and Sediment

为考察凹凸棒黏土对水体和底泥中Cr(Ⅵ)污染治理与修复效果,通过实验室模拟试验,运用Langmuir和Frundlich等温吸附模型及准一级和准二级动力学模型,研究了天然凹凸棒黏土对水体中Cr(Ⅵ)的吸附特性,并研究了pH对吸附过程的影响及凹凸棒黏土对底泥中Cr(Ⅵ)金属形态的影响,通过XRF(X-射线荧光光谱仪)和SEM(扫描电镜)确定凹凸棒黏土的化学组成和微观形貌结构.结果表明:天然凹凸棒黏土内部呈纤维状且多孔隙,成分中含有铁、铝、钙等元素,吸附后的材料中发现了Cr元素;Langmuir-Frundlich吸附等温模型(R^2=0.996)和准一级动力学模型(R^2=0.993)较好地拟合了凹凸棒黏土对Cr(Ⅵ)的吸附热力学与动力学过程,动力学模拟的Cr(Ⅳ)平衡吸附量及实测值分别为1.38和1.37 mg/g.溶液pH对Cr(Ⅵ)的吸附具有影响,其最佳pH为3,此时吸附率最高,为85.80%.研究显示,向底泥中添加凹凸棒黏土能促使Cr形态由不稳定态(酸溶态和铁铝还原态之和)向稳定态(可氧化态和残渣态之和)转化,从而达到修复底泥中Cr(Ⅵ)污染的目的.

The adsorption properties of Cr（ Ⅵ） in water and the effects of attapulgite on metal fractions of Cr in sediment by using natural attapulgite clay were investigated by classic models,and the basic properties of attapulgite and changes of internal structure and composition before and after adsorption were analyzed by X-ray fluorescence spectrometer（ XRF） and Scanning Electron Microscope（ SEM）. The results indicated that the internal structure of attpulgite was observed with fibrous structure and porosity. Aluminum,calcium and other elements and Cr element were increased after adsorption. The adsorption kinetics and isotherms couldbe best fitted with the pseudo-first order kinetics（ R^2= 0. 993） model and the Langmuir-Freundlich（ R^2= 0. 996） model,respectively. The simulated amount and measured value of kinetic were 1. 38 and 1. 37 mg/g,respectively. The initial pH value had an influence on Cr（ Ⅵ）adsorption. The optimal pH value for adsorption was 3. 0,and the highest adsorption rate was 85. 80%. The addition of attapulgite to the sediment may lead to the transformation of Cr fractions from the unstable fraction（ acid exchangeable fraction and reducible fraction） to the stable fraction（ oxidizable fraction and residual fraction）.