Competitive Sorption Machanism Of Tylosin And Enrofloxacin In Lou Soil

Tylosin（TYL）and Enrofloxacin（ENR）are widely used as veterinary antibiotics,and it can potentially harm the environment by entering the environment through various means such as animal manure,wastewater irrigation and medical wastewater.In order to better understand the interaction and behavior between these emerging pollutants and soil,batch equilibrium experiment was used to investigate the adsorption/desorption characteristics of ENR and TYL in a single adsorption system on Lou soil as well as the adsorption behavior of two antibiotics co-existing,and to explore the effects of different influencing factors（p H value,ion type and strength）on the adsorption behavior.Moreover,the structural characteristics of Lou soil before and after adsorption were characterized by infrared spectrum,and then the adsorption mechanism of TYL and ENR on Lou soil was concluded.The main results are as follows:1.The adsorption and desorption characteristics of TYL on Lou soil,as well as the effects of solution p H value,ion type and strength were studied.The adsorption kinetics of TYL conforms to the pseudo-second-order kinetic equation,and the adsorption process involves chemisorption with multiple rate control steps.The adsorption capacity of TYL increased with the increase of the initial concentration.The isothermal adsorption process of TYL was best described by Langmuir equation,which belonged to monolayer adsorption.Thermodynamic analysis showed that the adsorption of TYL in Lou soil was a spontaneous exothermic reaction,which was physical in the desorption process,there was a desorption hysteresis under low concentration,while the hysteresis was not obvious under high concentration（HI≈0.7）,which was related to the large molecular weight and polarity of TYL.The saturated adsorption capacity of TYL decreased with the increase of p H value of the solution,and the acidic condition was conducive to the adsorption of TYL,which was dominated by cation exchange and hydrophobic distribution.The presence of different cations would promote the adsorption of TYL,and with the increase of ionic strength and charge,the promotion effect became smaller.The greater the concentration of NH₄⁺,the greater the promoting effect on the adsorption of TYL,which may be related to the acid of TYL hydrolysis.Mg²⁺has an inhibitory effect on TYL adsorption,which is related to its ionic radius and electronegativity.2.The adsorption/desorption of ENR on Lou soil was studied,and the effects of different solution p H,ion type and strength were discussed.The adsorption kinetics and isotherm process of ENR on Lou soil accord with the pseudo-second-order kinetic equation and Freundlich equation,respectively.It is a spontaneous exothermic reaction and the systematic order increases.The adsorption process is physical.The adsorption capacity of ENR is much larger than the desorption capacity,indicating the existence of obvious desorption hysteresis.The carboxyl group and piperazine group in ENR will ionize with different p H values,so ENR is more conducive to adsorption under acidic conditions.In the presence of different cations,the adsorption capacity of ENR decreased gradually as the ionic strength increased from 0.01M to0.1M,but the overall effect was promoting,and the high concentration of Ca²⁺and Mg²⁺showed inhibitory effect.The study showed that the adsorption of ENR in Lou soil was mainly influenced by cation exchange,electrostatic interaction,hydrogen bonding and hydrophobic mechanism.3.The adsorption of TYL and ENR on Lou soil was investigated when the two antibiotics co-existed.It was found that TYL promoted the adsorption of ENR when the two antibiotics co-existed,showing synergic adsorption,which was attributed to TYL playing a role similar to"organic matter".With the increase of TYL concentration,the promotion amount decreased,which was due to the higher concentration of TYL,the higher the concentration of TYL-ENR compounds in the system,the ability of TYL and TYL to jointly seize the adsorption site of ENR on the soil surface will be stronger,and the formed macromolecular compounds will produce strong steric hindrance.The kinetics and isotherm processes were described better by the pseudo-second-order kinetic model and Freundlich model.The adsorption performance of p H value,ion type and strength were consistent with that of single system for ENR adsorption,only the adsorption capacity increased overall.4.When the two antibiotics co-existed,ENR could significantly enhance the adsorption of TYL in Lou soil.With the addition of ENR concentration（2,10,and 18mg/L）,the adsorption capacity of TYL increased by 88%,68%,and 45%,respectively.In the presence of ENR,the adsorption capacity of TYL reached its maximum at 25℃,which was different from that of a single TYL adsorption system.The change of p H value had a great influence on the adsorption of TYL（in the coexistence system of TYL and ENR）.With the increase of pH value,the adsorption amount increased first and then decreased,but the overall performance was that alkaline conditions were favorable for adsorption,and surface complexation may be the dominant effect mechanism.When Ca²⁺concentration increased from 0.01M to 0.1M,the adsorption capacity of TYL（in coexistence system）increased first and then decreased.The adsorption capacity of TYL（in coexistence system）by different types of ions was NH₄⁺>K⁺>Ca²⁺>control>Mg²⁺.When TYL and ENR were co-existed,the adsorption was mainly controlled by hydrogen bonding,surface complexation,hydrophobic and chemical reactions.In this study,ENR and TYL with low concentration will stay in the soil for a long time due to desorption hysteresis,which will bring potential risks to the soil environment.However,the desorption hysteresis of TYL with high concentration was not obvious,and only a small amount remained in the soil.Through leaching,Ty L entered the surface water and groundwater,thus causing pollution to the water environment.The co-existence of two antibiotics can promote the adsorption of soil,which may make them less mobile and reduce the risk of contaminating groundwater.