Abstract: We carried out batch experiments to investigate the sorption characteristics of different forms of lomefloxacin (LOM) on kaolinite. Sorption kinetics were pseudo-second-order, and all equilibrium data could be well described by the Langmuir equation. As solution pH increased, the amount of LOM sorption increased first and then decreased. Maximum sorption was achieved at pH values between pKa1 and pKa2 of LOM. The sorption capacity of different forms of LOM on kaolinite ranked as LOM±>LOM+>LOM-. The ionic strength of LOM solution and inorganic cations had little effect on LOM+ sorption, but both factors significantly inhibited LOM± sorption. The sorption capacity of LOM± decreased with increasing ionic strength, and the inhibition potency of different inorganic cations was in the order of Mg2+>Ca2+>K+>Na+. The sorption mechanisms were mainly inner-sphere complexation and cation exchange for LOM+ or cation exchange, hydrogen bonding and electrostatic attraction for LOM± on kaolinite. LOM- sorption on kaolinite is very small due to strong repulsive electrostatic effect; the small sorption may resulted from outer-sphere surface complexation.

Key words: lomefloxacin, kaolinite, sorption, different forms