五氯苯酚在矿物表面吸附——实验、表面反应模式及其环境意义

Sorption of pentachlorophenol on minerals: experiments, surface reaction model and environmental implications

利用批量平衡技术研究了石英、高岭石、伊利石、蒙脱石和铁氧化物对五氯苯酚(PCP)吸附的pH关系等温线和浓度关系等温线,发现所有矿物的pH关系等温线都表现出典型的峰形曲线特征,峰位在pH=5～6之间,依矿物不同而不同。基于矿物表面羟基位化合态和PCP的化合态考虑,提出一种包含表面络合反应和表面静电吸附反应的模式,对pH关系等温线计算拟合发现有很好的相关性。模式计算还表明,石英和层状硅酸盐矿物对PCP吸附以表面络合反应为主,而氧化铁矿物则包含表面络合反应和表面静电吸附反应,但以后者占主导,其反应平衡常数比前者大1～3个数量级。高岭石和氧化铁矿物的浓度吸附等温线可用Langmuir方程很好拟合,最大吸附量的大小顺序是赤铁矿>纤铁矿>针铁矿>高岭石>石英>蒙脱石≈伊利石,并可以用矿物表面羟基位浓度和反应机制加以解释。PCP在矿物表面可观的吸附量说明矿物表面吸附对憎水性可离解有机化合物(HIOCs)在天然水相体系和沉积中的迁移转化过程起着相当重要的作用。

The adsorption of pentachlorophenol （PCP） on quartz, kaolinite, illite, montmorillonite and iron oxides were investigated by batch equilibrium techniques. The pH-dependence isotherms are curves with a peak value, whose position is at about pH = 5- 6 depending on the mineral species. Based on the distribution of both speciation of surface hydroxyls on minerals and PCP in solution, the authors put forward a surface reaction model involving surface complexation and surface electrostatic attraction to fit the pH-dependence isotherms, and calculated both reaction constants. The results show that on quartz and phyllosilicate minerals the predominant adsorption reaction is surface complexation, whereas both surface electrostatic attraction and surface complexation are involved in the iron oxide minerals. The reaction constants of surface electrostatic adsorption are usually one to three orders of magnitude larger than that of surface complexation. The concentration-dependence isotherms can be well fitted by Langmuir equation with correlation coefficient R〉0.93 for kaolinite and iron oxides. The maximum adsorption has been found in order of hematite 〉 lepidocrocite〉 goethite〉 kaolinite 〉quartz〉montmorillonite≈illite, which can be interpreted by consideration of both reaction mechanism and surface hydroxyl density. The significant adsorption of PCP on mineral surfaces suggests that clay and iron oxide minerals can play an important role as HIOCs adsorption in laterite or latertoid soil, which is widely spread in south China.