Effects Of Low-Molecular-Weight Organic Acids And Solution Chemistry On Sorption Characteristics Of Lomefloxacin To Kaolinite

The widespread use of fluoroquinolones antibiotics has resulted in their higher detection frequency in soil and groundwater environment.Their valence changes with pH,which makes their adsorption behavior complicated.In this study,lomefloxacin?LOM?was selected as the target pollutant.Batch experiments were carried out to investigate the effects of solution chemistry and small molecular organic acids on the adsorption behavior of cation LOM?+?,zwitterion LOM?±?and anion LOM?–?on kaolinite.The research results can provide a basis for evaluating the environmental risks of such pollutants.The main conclusions are as follows:?1?The solution pH had a significant effect on the sorption of LOM.As solution pH increased,the sorbed amount of LOM increased first and then decreased.The maximum sorption amount reached in the pH range between p K_a1 and pK_a2 of LOM.Sorption capacity of different forms of LOM to kaolinite followed as:LOM?±?>LOM?+?>LOM?–?.The sorption mechanisms of LOM?+?on kaolinite are mainly inner-sphere complexation and cation exchange,and those of LOM?±?are mainly cation exchange,hydrogen bonding and electrostatic attraction.LOM?–?had a large electrostatic repulsion with the surface of kaolinite,resulting in a little amount of sorption,which may be caused by out-sphere surface complexation.?2?The ionic strength of solution and inorganic cations had little effect on the sorption of LOM?+?to kaolinite,but both factors significantly affect the sorption of LOM?±?and LOM?–?.The sorption capacity of LOM?±?and LOM?–?decreased with increasing ionic strength,and the order of inhibition of different inorganic cations was:Mg²⁺>Ca²⁺>K⁺>Na⁺.When the ionic strength of the solution was low,the LOM desorption was slightly inhibited,and when it was higher,the desorption was promoted,and the effects on the three forms of LOM showed the same characteristics.In addition,the desorption of LOM was slightly inhibited by Na⁺and K⁺in the solution,respectively;divalent cations promoted LOM desorption,and Mg²⁺promoted it the most.?3?The effects of citric acid?CA?,oxalic acid?OA?,and alanine?AA?on the sorption of LOM?+?on kaolinite were very weak.For LOM?±?,CA and OA inhibit its sorption by binding to LOM?±?in solution and occupying the sorption sites,and AA could sorb on kaolinite and promote the sorption of LOM?±?by cumulative sorption.Low-molecular-weight-organic acids inhibited the sorption of LOM?–?to a similar extent.?4?The effect of low-molecular-weight organic acid species on the sorption and desorption of LOM on kaolinite was different.CA?a tribasic acid?and OA?a dibasic acid?could form monodentate or bidentate complexes with mineral surfaces.The carboxylic groups in them could inhibit LOM adsorption,but the number of the carboxylic groups was not the main factor affecting LOM adsorption.The same kind of low-molecular-weight-organic acids had different effects on LOM desorption of different forms.The desorption rate of LOM?+?in different solutions followed as:CA?OA<AA;and the desorption rates of LOM?±?and LOM?-?followed as:CA?OA>AA.