Study On Mechanism Of Interaction Between Tetracycline And Common Iron Oxide Minerals In Aquifer

The tetracycline antibiotic,owing to its broad spectrum of antibacterial effects and high efficiency and low cost,has become one of the most widely used and largest dosage types of antibiotics.In recent years,it has been continuously accumulated in the environment because of its abusement and the poor absorption of organisms,leading to the occurrence of drug-resistant genes and harm to organisms.The high risk of antibiotic pollution has aroused worldwide attention.Tetracycline is a representative class of tetracycline antibiotics with simpler element component.This paper focuses on the migration and transformation of tetracycline in soil and water environment.Three kinds of common iron oxide minerals,goethite,ferrihydrite and hematite are selected.The adsorption process between minerals and tetracycline was described through batch experiments.Supplemented by a variety of characterization(XRD,SEM,TEM,BET,BJH,XPS,FTIR),the differences of minerals' physicochemical properties were described and analyzed before and after the interaction,which is in order to reveal the interaction mechanism between tetracycline and different types of common iron oxide minerals.Experimental results show:(1)The adsorption equilibrium time of tetracycline on goethite and ferrihydrite is 4 d.The adsorption rate of ferrihydrite is the fastest and the equilibrium adsorption amount is larger than that of goethite because of its absolute superiority of surface area.The hematite isothermal adsorption didn't reach equilibrium in the 4 d experiment time due to its crystal defects,which lead to continuously splitting and make the kinetic curve ladder-like.And the isothermal adsorption amount of goethite and ferrihydrite increases with the initial concentration increasing until saturation,while the hematite is multi-stage adsorption and the adsorption amount is the largest compared to goethite and ferrihydrite in the 4 d experimental time.(2)The iron in selected iron minerals in the experiment is trivalent and the ferrous irons can be detected in the supernatant after the adsorption reaction,indicating that the oxidation-reduction reaction occurs during the adsorption of tetracycline.The concentration of ferrous irons is pretty low in goethite system which indicates chemical reaction is limited in goethite.The surface of minerals before and after the reaction was analyzed by infrared spectroscopy.It was found that the interface functional groups changed,proving that there was a complex phenomenon during the interaction process between the three iron minerals and tetracycline.It is presumed that ferrous iron is generated from electron transfer after tetracycline complexes to the surface of the minerals.(3)In the study of the influence of water chemical parameters on the adsorption,the adsorption amount of tetracycline on these three kinds of iron minerals was increased a little with the increasement of the concentration of ionic strength,indicating the adsorption is mainly specific adsorption.Under the influence of pH,the adsorption amount of tetracycline on iron minerals gets to the maximum at some specific pH value,which shows that there is electrostatic effect in the process of adsorption.The common cations have no significant effect on adsorption,while Cu2+ acts as a bond bridge and influences differently on the adsorption amount of tetracycline on iron minerals,suggesting that it's related with the degree of crystallization of minerals.