Characteristics of norfloxacin sorption on goethite

The kinetics characteristics and sorption amount under different pH conditions(i.e.pH=3.5,5.0,5.6 and 6.2) and the thermodynamics characteristics of norfloxacin(NOR) sorption on goethite(α-FeOOH) were determined by batch equilibrium experiments according to OECD Guideline 106 in this study.The sorption mechanisms were also found out.Results showed that the sorption of NOR on α-FeOOH began from a rapid stage with continuing for approximately 6 h,and then followed with a slow stage until a 48 h of sorption equilibrium time.Sorption kinetic curves fit a pseudo second-order kinetic model well at different pH.The sorption amount of different pH corresponded to the decreasing order of 5.6 5.0 6.2 3.5,which depended on the sum of the products concentrations obtained from different species of α-FeOOH and NOR at respective pH value.This result also indicated that the order of sorption amount was mostly attributed to the sorption of NORH2± on the surface of α-FeOOH.The Freundlich model could compatibly describe sorption isotherm of NOR on α-FeOOH.The 1/n of the isotherm fitted by the Freundlich model increased from 0.43 to 0.61 with increasing temperature from 15 ℃ to 35 ℃,which indicated that an increase in temperature could reduce the nonlinear sorption of NOR on α-FeOOH.Results with-39.45 kJ/mol of ΔH0 and less than 0 of ΔG0 revealed that the sorption of NOR on α-FeOOH was a spontaneously exothermic process.The exchange of ion was a dominant sorption mechanism for NOR sorption on α-FeOOH,while the H-bonding and dipole force were other possible sorption mechanisms.Less than 0 of ΔS0 indicated an entropy decrease during the sorption process.