Study On Adsorption Of Oxytetracycline Onto Goethite And Hematite

The use of antibiotics has cause serious contamination in the environment.The antibiotics could not only inhibit the growth of microorganisms,but also induce the production of resistance genes.Antibiotics have different charge formation in different environmental conditions,resulting in different adsorption behaviors on minerals?such as electrostatic adsorption,complex adsorption?,which affects the bioavailability of antibiotics.Belong all the trivalent iron?hydro?oxides in the environment,goethite and hematite are the most common types,and they could adsorb the antibiotics.However,due to differences in their physicochemical properties,the adsorption behaviors are different.Therefore,comparing the differences in the adsorption behavior of these two minerals for antibiotics is of great significance for understanding the occurrence and geochemical behavior of antibiotics.In this study,we investigated the adsorption behavior of oxygen tetracycline?OTC?on goethite and hematite.The effects of environmental factors?such as pH value,coexisting ions,etc.?on the adsorption,and the adsorption mechanism have been discussed.The main results are as follows:?1?The adsorption capacity of hematite is stronger than goethite,which is related to the pore structure of goethite and hematite.The average pore size of hematite is larger than goethite,and hematite has more mesoporous structure?2-50nm?which is more conducive to OTC adsorption;the Al³⁺which dissolved from hematite also increased the adsorption capacity of hematite.?2?Al³⁺and Cu²⁺could promote the adsorption of goethite and hematite in the all pH conditions.However,Pb²⁺could promoted adsorption under medium-acidic conditions,but slightly inhibited under alkaline conditions.Besides,Cd²⁺has no significant effect on the adsorption;the order of the promotion effect by metal ions on the adsorption of goethite has a similar sequence with the affinity order of OTC,that is,Al³⁺>Cu²⁺>Pb²⁺>Cd²⁺;?3?Hematite has a stronger affinity to metal ions than goethite,the adsorption of Cu²⁺is higher than Al³⁺.The competitive between the soluble Al³⁺from hematite and the exogenous Al³⁺also cause that the promotion of Al³⁺less than Cu²⁺;In addition,under the experimental conditions of this study,phosphate has no obvious effect on the adsorption of OTC by goethite and hematite.?4?The results indicated that OTC forms complexes with iron oxides by replacing the hydroxyl groups on the surface of goethite and hematite.Electrostatic interactions control the adsorption of OTC by goethite and hematite;However,the adsorption mechanism of OTC onto hematite may be more complicated which the pore adsorption also control the adsorption of OTC.Besides,the system of hematite and OTC may also include dissolution and mineralization effects.