Sorption and desorption of tetracycline on layered manganese dioxide birnessite

Birnessite is one of the most common manganese oxides in the clay-sized fraction (<2 µm) of soils and has high cation exchange capacity and larger surface area. Birnessite was previously studied for decomposition of selected antibiotics from water. In this study, the removal of tetracycline (TC) by birnessite from aqueous solution was investigated as a function of initial tetracycline concentration, solution pH, temperature, and equilibrium time. Changes in solid phase after TC adsorption and desorption were characterized by X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and Fourier transform infrared analyses. Desorption of exchangeable cations accompanying TC removal and partial desorption of TC from birnessite by AlCl₃ confirmed that cation exchange was responsible for TC removal at low initial concentrations. Both the external and internal surface areas were readily available for TC uptake by birnessite. The intercalated TC formed a horizontal monolayer configuration in the interlayer of birnessite as deduced from XRD analyses.