Effect of ions on sorption of tylosin on clay minerals

A widely used veterinary antibiotic tylosin is associated with a fast increase in the prevalence of genes for macrolide resistance. Therefore, there are growing concerns of its potentially adverse effects on natural ecosystems, and a study on the sorption of tylosin is an important step in this direction. As a weak base, prior studies pointed out that cation exchange was the main sorption mechanism for tylosin in soil, and minerals were important factors in influencing the sorption. However, the ionic effect on the tylosin sorption process on minerals has not been systematically conducted. In this study, the sorption of tylosin on pure clay minerals was investigated in different ionic strength solutions. Moreover, the interlayer interaction of tylosin on different types of montmorillonite was preliminarily studied. All of the sorption data were fitted with the Langmuir-Freundlich-Hill sorption model. The results showed that the variation tendency of tylosin sorption capacity on montmorillonite and kaolinite were nearly the same. The sorption capacity of tylosin at different ionic strengths decreased with the order: 0.008 M > 0.051 M > 0.108 M > 0.508 M. In different ion solutions, the sorption capacity of tylosin decreased in the following order: K + > Na + > Ca 2+ Mg 2+ . However, the sorption of tylosin on montmorillonite at low initial concentration of tylosin displayed a different tendency. When the initial concentration of tylosin was low, its sorption capacities on montmorillonite at different ionic strengths decreased with the order: 0.051 M 0.108 M > 0.008 M > 0.508 M. For different ionic solutions, the sorption of tylosin decreased in the order of Mg 2+ Ca 2+ > K + > Na + . The cation effect on tylosin sorption in the interlayers of montmorillonite was also investigated. The sorption of tylosin on different montmorillonites decreased in the order of Ca-montmorillonite > Na-montmorillonite > K-montmorillonite. These indicated that the hydration of inorganic ions influenced the sorption of tylosin. The results provide a more comprehensive understanding about the sorption of tylosin on minerals. Tylosin sorption on three ion-exchanged montmorillonites indicated that hydrogen bond interactions were more important than cation exchange in the montmorillonite interlayer.