[Isothermal studies on liquid-phase adsorption of bisphenol A and dibutyl phthalate by paper]

Adsorption behavior of bisphenol A (BPA) and dibutyl phthalate (DnBP) from aqueous solution onto newsprint was investigated through batch adsorption experiments. Adsorption isothermal data was interpreted by the Freundlich, Langmuir, Dubinin-Radushkevich (D-R), Flory-Huggins (F-H), BET and Temkin equations. In order to determine the best fit isotherm, three error analysis methods were used to evaluate the data: correlation coefficient (R2), residual root mean square error (RMSE) and chi-square test (chi2 test). The results show that the Freundlich and Temkin equations provide the best models for BPA and DnBP biosorption with high R2 (R2 > 0.95, p < 0.01) and low values of RMSE and chi2 (RMSE < 0.05, chi2 < 0.02). The adsorption capacity increases with the hydrophobicity of adsorbate. The mean free energy of adsorption process is calculated by D-R isotherm as 1.484 and 1.609 kJ/mol while the Gibbs free energy calculated by F-H isotherm is -6.559 and -7.021 kJ/mol for BPA and DnBP, respectively. From D-R and F-H models, it is inferred that biosorption of BPA and DnBP by newsprint might be physical adsorption and a spontaneous process. As a comparison, it is indicated these Kf values in Freundlich equation (0.147 and 0.502 mg(1-n) x L(n) x g(-1) for BPA and DnBP, respectively), considered as a measure of the adsorption capacity, are higher than those obtained in the adsorption of same adsorbate by natural organic adsorbents, such as sediment. This suggests the presence of paper will retard BPA and DnBP transport and bioavalability in landfills.