富里酸和胡敏酸在蒙脱石上的吸附特性

为进一步揭示有机污染物在黏土矿物上的迁移转化规律,运用1H核磁共振光谱、高效体积排阻色谱、扫描电镜、比表面分析以及傅里叶变换红外光谱等多种分析技术综合分析了富里酸和胡敏酸在蒙脱石上的吸附行为. 结果表明,由于不同官能团与蒙脱石的亲和性不同,富里酸和胡敏酸在吸附过程中均产生组分分级,大分子被优先吸附在蒙脱石表面. 由于疏水性作用,蒙脱石对疏水性更强的胡敏酸的吸附量更大. 蒙脱石吸附富里酸后比表面积和孔容分别下降3.67m2/g和0.005cm3/g,而吸附胡敏酸后则均略微增大,说明具有较大颗粒尺寸的胡敏酸更多地堆积在蒙脱石外表面,而富里酸则更易进入蒙脱石孔隙. 蒙脱石吸附富里酸和胡敏酸后溶液pH分别升高了0.44和0.41,说明发生了配体交换反应. 蒙脱石对富里酸和胡敏酸的吸附量随pH增大和离子强度的降低而减少,表明羟基能够抑制富里酸/胡敏酸负电基团与蒙脱石表面羟基的配体交换反应,而盐离子则能降低蒙脱石和腐殖质间的静电斥力. 

Studies on the Adsorption Mechanisms of Fulvic Acid and Humic Acid on Smectite

In order to explore adsorption mechanisms of organic contaminants on clay minerals, adsorption behaviors of humic substances on smectite were studied by using several analytical techniques including liquid-state 1H nuclear magnetic resonance spectroscopy, high performance size exclusion chromatography, scanning electron microscope, surface area analysis and Fourier transform infrared spectroscopy. The results showed that both fulvic acid (FA) and humic acid (HA) underwent fractionation during the adsorption process due to the different affinity for the functional moieties of humic substances on smectite. FA/HA molecules with large molecular size and weight were preferentially adsorbed on the mineral surfaces. The amount of HA was higher than that of FA was adsorbed on smectite via hydrophobic partitioning. After FA adsorption, specific surface areas and pore volumes of smectite decreased by 3.67m2/g and 0.005cm3/g, respectively, while a slight increase was observed after HA adsorption. The results indicated that HA with larger particle size was preferred to accumulate on the external surfaces of smectite, while FA was prone to block the pores of smectite. The increase in pH (0.44and 0.41) in smectite suspensions after FA and HA adsorption suggested that ligand exchange occurred and FA/HA-smectite complexes were formed. The increase in the equilibrium pH or the decrease in the ionic strength led to the reduction of FA/HA adsorption on smectite, which implied that hydroxyl ions in the aqueous solutions were likely to suppress ligand exchange between negatively charged FA/HA groups and the surface hydroxyl groups of smectite. The results also implied that electrolytes could reduce the electrostatic repulsion between smectite and FA/HA.