Tetracycline adsorption on montmorillonite: pH and ionic strength effects

Abstract The adsorption of tetracycline (TC) on a Patagonian montmorillonite is studied as a function of pH, ionic strength and TC concentration by using X-ray diffraction, UV–Visible spectroscopy, ATR-FTIR spectroscopy, batch experiments and adsorption modeling. X-ray diffraction reveals that TC species can intercalate into the interlayer space of montmorillonite as deduced from the change in the basal spacing from 12.6 A to 19.5 A, in the absence or presence of TC respectively. UV–Visible and ATR-FTIR spectroscopies show that the corresponding spectra of TC change upon adsorption, suggesting important montmorillonite–TC interactions in the adsorbed state. Batch experiments, on the other hand, reveal that there is an important adsorption of TC in a wide range of pH. Since at low pH (pH