Cosorption Mechanism of Zn and Tetracycline on Al2O3 and Montmorillonite: Insights from EXAFS, ATR-FTIR, XRD Analyses.

 A long-term application of manures containing heavy metals and antibiotics on land results in their accumulation in soils; however, the interaction between heavy metals and antibiotics on soil mineral surfaces is not well understood. In this study, tetracycline (TC) and Zn(II) co-sorption on γ-Al₂O₃ and montmorillonite at pH 5.5 and 8.0 was studied using a combination of batch sorption experiments, XRD, and ATR-FTIR and EXAFS spectroscopy. Results show that at pH 5.5, TC decreased Zn sorption on γ-Al₂O₃ and enhanced its sorption on montmorillonite while it decreased Zn sorption on both adsorbents at pH 8.0. At pH 8.0, Zn formed Zn-Al layered double hydroxide (Zn-Al LDH) on γ-Al₂O₃ and montmorillonite, but the presence of TC inhibited its formation, decreasing Zn sorption. At pH 5.5, Zn formed outer-sphere and inner-sphere complexes on montmorillonite and γ-Al₂O₃, respectively, in the absence of TC; in the presence of TC, a ternary surface complex adsorbent-TC-Zn was formed on γ-Al₂O₃ whereas the intercalation of TC-Zn complexes into the interlayer occurred mainly on montmorillonite. However, TC-promoted dissolution of γ-Al₂O₃ reduced Zn sorption on γ-Al₂O_3. These findings improve our understanding of the fate of co-existing heavy metals and antibiotics in soils amended with biosolids.