高岭石和蒙脱石吸附胡敏酸的对比研究

A comparative study of the humic acid adsorption capability between kaolinite and montmorillonite

高岭石和蒙脱石分别是暖湿和冷干气候带内典型土壤的代表性矿物,对二者吸附胡敏酸特点的对比研究可以为探索不同地带土壤中重金属的环境行为提供重要的依据。笔者通过一系列实验研究了pH值、离子强度和胡敏酸初始浓度对胡敏酸在高岭石和蒙脱石上吸附量的影响,重点剖析了引起高岭石和蒙脱石在吸附胡敏酸方面表现出的共性和差异的原因。研究结果表明:1)在pH=5条件下,胡敏酸在高岭石和蒙脱石上的吸附量均随着胡敏酸初始浓度和离子强度的升高而逐渐增加;2)胡敏酸在高岭石和蒙脱石上的吸附量均随着pH值的升高而降低;3)pH<6时,高岭石吸附的胡敏酸量多于蒙脱石,pH>6时则相反。这是由高岭石和蒙脱石在不同pH条件下吸附胡敏酸的机制不同造成的。在pH<6时,高岭石与胡敏酸之间的静电引力起主导作用,其次是配位交换作用和氢键作用。此时,蒙脱石以氢键作用为主要吸附机制。在pH>6时,高岭石和蒙脱石的主要吸附机制分别是疏水性作用和阳离子键桥。

Kaolinite and montmorillonite are representative minerals of the warm-humid and cold-arid climate, respectively. A comparative study of the hurnic acid adsorption capability between kaolinite and montmorillonite might provide important evidence for the environmental behaviors of heavy metals in soils which are developed in different climate zones. In this study, batch adsorption experiments for humic acid were carried out with two species of clay minerals （kaolinite and montmorillonite） under different solution conditions of pH values, ionic strengths and initial concentrations of the humic acid. The aim of this study was to explore the causes responsible for the generality and diversity between kaolinite and montmorillonite in the adsorption of humic acid. Some conclusions have been reached： 1） humic acid adsorbed on both kaolinite and montorillonite gradually increases with increasing initial concentrations of humic acid and ionic strength under the condition pH--5; 2） the adsorption amount of humic acid on kaolinite and montorillonite decreases with the increasing pH value; 3） the humic acid adsorbed on kaolinite is higher than that adsorbed on montorillonite under the condition pH〈6, and things are just the opposite under the condition pH〉6, which may be related to different adsorption mechanisms of kaolinite and montmorillonite for hurnic acid. When pH 〈6, electrostatic interaction between kaolinite and humic acid dominantes, and the ligand exchange and hydrogen bonds seem to play a minor role, while hydrogen bonds are the main adsorption mechanism for montmorillonite. When pH〉6, the main adsorption mechanisms of kaolinite and montmorillonite are hydrophobic interaction and cationic bridge, respectively.