Effects of pH and Dissolved Humic Acid on Norfloxacin Sorption to Kaolin

Studying the effects of environmental factors on norfloxacin sorption to kaolin is helpful for understanding sorption and transport of norfloxacin in soils. The static sorption experiment results showed that the sorption process of norfloxacin follows a pseudo-second-order kinetic equation( R2 0. 999),regardless of the existence of dissolved humic acid( DHA). The existence of DHA reduced the sorption rate of norfloxacin,which prolonged the adsorption equilibrium time from 24 to 48 hours. The isotherms of norfloxacin sorption to kaolin were well described by the Langmuir equation. The maximum sorption of norfloxacin to kaolin can be obtained,when the solution pH values were around pKa1 and pKa2of norfloxacin. The modeling sorption results indicated that the zwitterionic form of norfloxacin( NOR±)contributes most to the overall sorption in the experimental pH range. Co-sorption and cumulative sorption resulted from DHA can promote norfloxacin sorption to kaolin. Solubility enhancement of norfloxacin caused by DHA can inhibit sorption of norfloxacin. The promotion and inhibition of sorption resulted from DHA are related to the solution pH and concentrations of DHA and norfloxacin.