Sorption Equilibrium Of Perfluorooctanoic Acid On Soils And Its Compositions

Perfluorinated compounds have been extensively used for over 50 years worldwide.Applications involving daily necessities,pharmaceuticals and aviation industries,and perfluorinated compounds were included in the Stockholm Convention in 2009 as prohibited substances for use as persistent organic substances.After entering the environment,it will react with the environmental media in a complex physical and chemical reactions,thus affecting its migration in the environment.The perfluorinated compounds entering the environment will pose a hazard to ecosystems and human health.Domestic and foreign scholars have done some research on the migration and transformation of perfluorinated compounds in the environment,but the characteristics and mechanism of the perfluorinated compounds in different soil and soil media are not clear.Therefore,perfluorooctanoic acid(PFOA)was used as the sorbate to study the adsorption characteristics and mechanism of PFOA on ten different soils,goethite,montmorillonite and humic acid,respectively.The main conclusions are as follows:1.Sorption of PFOA on ten different soils was systematically measured.The results showed that the sorption of PFOA on S01-S10 could attain equilibrium within 24hrs.The pseudo-second-order model can fit well with the kinetics data of adsorption PFOA on ten different soils,and the correlation coefficient was more than 0.9.Sorption-desorption isotherm indicates that the adsorption of PFOA on the soil has obvious linear distribution.The Sorption-desorption isotherm can be fitted with Freundlich and liner model.Sorption capacity of PFOA on S01-S10 and soil mineral composition,content and organic matter content is closely related.Hydrophobicity may be the main mechanism for the sorption of PFOA on soil.2.Sorption of PFOA on goethite and montmorillonite could attain equilibrium within 24hrs and 24hrs.The kinetics data of the sorption of PFOA on goethite and montmorillonite can fit well with pseudo-second-order model,the correlation coefficient was 0.999.The sorption of PFOA on goethite and montmorillonite were fitted well by Linear and Langmuir models,respectively.Compared the difference FTIR and XRD before and after sorption,it could concluded that the main factors for sorption of PFOA on goethite were electrostatic interaction and hydrogen bonding,and the sorption mechanism of PFOA on montmorillonite might be dominated by hydrogen bonding between montmorillonite layers.3.Sorption of PFOA on humic acid(HA)could attain equilibrium within 24hrs.The kinetics data of the sorption of PFOA on HA can fit well with pseudo-second-order model.And the sorption of PFOA on HA were fitted well by Linear,Freundlich and Langmuir models,the correlation coefficient were more than 0.95.N>1 indicated that the sorption of PFOA on HA is mainly through the active adsorption sites on the HA surface.Therefore,hydrophobic distribution may be the main mechanism for the sorption of PFOA on HA.