| Sorption-desorption are the two important processes governing the fate of phenolic endocrine disrupting chemicals in soil system. Sorption-desorption on soils is shown to control the transport, degradation and biological processes of phenolic endocrine disrupting chemicals in the subsurface. It is meaningful to investigate the sorptiondesorption of phenolic endocrine disrupting chemicals and to establish a fast forecasting model of the absorption behavior of the phenolic endocrine disrupting chemicals on different soils for evaluating the potential effects on soil and groundwater and developing the soil remediation. Batch adsorption-desorption experiments of bisphenol A(BPA) were performed using twelve typical soil samples(seven kinds of zonal soils and five kinds of non-zonal soils). A series of kinetic, isotherm and thermodynamic sorption experiments were mainly investigated, and the influence of environmental factors, such as(p H, temperature, ionic strength) were also studied. Combined with SPSS statistical analysis software to study the influence between soil adsorption coefficient and different physicochemical of soils, and to identify the degree of the variation proportion in BPA sorption caused by the selected soil parameters. And the adsorption prediction model of BPA was established by multiple stepwise regression analysis. The Fourier transform infrared spectra(FTIR) was used to clarify the change of functional groups before and after the adsorption of BPA on soil. The adsorption mechanism of BPA on soil was discussed preliminary. The investigation would help to evaluate the behaviors and fate of BPA in the ecosystem. The main conclusions are as follows.1. The kinetic mechanism of BPA adsorption on the surface of soil was manifested. The results showed that adsorption amount of BPA on soils increased with time and finally tended to be stable. The adsorption process was divided into a fast adsorption and a slow adsorption and the adsorption equilibrium was approached within 24 h. Pesudosecond-order, Elovich equation and parabolic diffusion equation fitting were used to fit the adsorption kinetic data. And Pesudo-second-order was the optimum model for their adsorption kenitics, of which the coefficients(R2)>0.92, indicating that the adsorption process was complicated, and chemical adsorption was rate control steps.2. Chemical adsorption-desorption and Fourier transform infrared spectra(FTIR) were used to study the adsorption-desorption characteristics of BPA on soils. The results showed that both linear and Freundlich isotherms were fit to the experimental data. Among all the soils, the maximum sorption capacity of BPA was the Paddy soil, while the soil planting peach was the least. The largest distribution coefficient was 3.03 times as that of the smallest. The adsorption ratios of BPA by electrostatic interactions and by ligand exchange were got using a continuous desorption process with Ca Cl2 solution and phosphate buffer solution. For all the soils, the proportion of electrostatic interactions was 3.4%-11.8%, and of ligand exchange was 2.9%-13.2%. The proportion of the both was 10.1% to 21.9%. It was illustrated that electrostatic interactions and ligand exchange were not the main force of the adsorption. The FTIR results indicated that the hydrogen bonding interaction was also involved in the adsorption of BPA on soil.3. The environmental factor experiments indicted that all the soils except the red soil and the soil of tea garden in huazhong agricultural university, had a great adsorption amount under acid condition(p H 3-5), and the adsorption capacity gradually reduced with the increase of p H. When p H was around 6-8, the adsorption capacity reached the balance. And with further increases in p H, adsorption capacity fell down sharply. This was because of the surface charge on soil and the degree of dissociation of BPA in different p H conditions. With the increase of Ca Cl2 concentration, the BPA sorption on all the soils showed a slight increase, indicating the presence of Ca2+ promoted the adsorption of BPA. Compared the original soil with the organic matter remover soil, the adsorption amount of the latter was decreased obviously, suggesting that organic matter content was an important factor that affected the adsorption. Expect the yellow brown soil in hubei wuhan, the adsorption amount of the rest soils were all decreased with the increase of temperature, showing that the temperature was not conducive to the adsorption reaction.4. Adsorption thermodynamics showed the free energy of adsorption(△G) on soil surface was negative indicating the adsorption was spontaneous. And the absolute value of △G was less than 40 k J/mol showing it was mainly a physical adsorption.The adsorption enthalpy change △H(except the yellow brown soil in hubei wuhan) was also less than zero, showing that adsorption was an exothermic reaction, and this was consistent with the influence by the temperature change on the adsorption. The change of entropy value(△S) was all negative explaining the adsorption was a process of entropy decreasing. The adsorption of BPA was mainly a spontaneous, exothermic, entropy decreasing physical adsorption process.5. Using the SPSS statistical analysis software to study the degree of the variation proportion in BPA sorption caused by the selected soil parameters. For simple correlation analysis, the adsorption of BPA was highly relevant to organic matter content of the soil, was moderately related to CEC, was associated with p H and clay content, weakly, and had almost irrelevant to EC and SSA. For partial regression analysis, the organic matter was the main factors influencing the adsorption, consistently with the simple correlation analysis. Multiple stepwise regression showed that the organic matter content was the dominant factors influencing soil adsorption. And with the increase of organic matter content, the adsorption amount was enhanced. And the adsorption prediction model of BPA was established by multiple stepwise regression analysis, revealing the quantitative relationships between SOM and the soil adsorption coefficient, which had strong theoretical guiding significance. |
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