Sorption Of Gemfibrozil To Montmorillonite And Kaolinite And Its Influencing Factors

Pharmaceuticals and personal care products(PPCPs) in reclaimed water may cause the groundwater pollution risk in the reclaimed water recharging process.To study the sorptioncharacteristics of PPCPs in soil can provide important information forevaluatingthe groundwater pollution risk. In this study, gemfibrozil, a hypolipidemic agent frequently detected in aquatic environment,was chosen as arepresentative of PPCPs.Its sorption to montmorillonite and kaolinite was investigatedby means ofbatch experiments,X-ray diffraction and Fourier transform infrared spectroscopy analysis.The main conclusionsare as follows.(1) Sorption of gemfibrozil to montmorillonite and kaoliniteboth decreased with increasinginitialsolution p H(3~11), the highest sorption capacity was observed at p H 3 for montmorillonite(0.111 mg/g) and kaolinite(0.263 mg/g), respectively. Since different p H posed great influence on the speciation of gemfibrozil andsurface chargecharacteristics of clay minerals, there was a stronger electrostatic repulsion betweenthe clay mineralsand gemfibrozilunder higher p Hconditions(4~11), which inhibitedthe sorption.(2)The influence of inorganic ion on the sorption of gemfibrozil toclay mineralswas related to both ion species and ionicstrength, including promoting and inhibiting effect. This is due to the weakenedelectrostatic repulsion between the clay minerals and gemfibrozil caused by theintroduction of ion in solution and salting out effect.It is alsobecause Ca2+is stronger than Na+ in competingwith gemfibrozil for the sorption siteson montmorilloniteunderhigher ionic strength(0.05 M~1 M). Besides, it can promote the gemfibrozilsorption better with Ca Cl2 as background solution than thatwith Na Cl, indicatingthe cation bridgehas a great influence on gemfibrozilsorption.(3)The influence of dissolved organic matter(DOM) on gemfibrozil sorption was related to the concentration of DOM and types of clay minerals.As DOM had astronger affinity to kaoliniteand could compete more with gemfibrozil for the sorption sites, it hada smaller influence on gemfibrozil sorption to kaolinite than that to montmorillonite. The experimental results, X-ray diffraction and Fourier transform infrared spectroscopy analysisresultsindicated thatwith the introduction of DOM, cosorptionisthe main promoting mechanisminthe clay minerals-DOM-gemfibrozil sorption system.(4)Thesorption characteristics of montmorillonite and kaolinite were different. The sorbed amount of gemfibrozil to kaolinite was higher than that to montmorillonite under the same conditions. The reason is thatkaolinite had a smaller surface charge density and there was a stronger electrostatic repulsion between gemfibrozil and montmorillonite than that between gemfibrozil and kaolinite. As a result, kaolinite had a stronger effect on controlling the transport of gemfibrozil in subsurface environment and reducing the groundwater pollution risk than montmorillonite.