title: Influence of Ca2+ on tetracycline adsorption on montmorillonite.
abstract: The adsorption of tetracycline (TC) on montmorillonite was studied as a function of pH and Ca(2+) concentration using a batch technique complemented with X-ray diffraction and transmission electron microscopy. In the absence of Ca(2+), TC adsorption was high at low pH and decreased as the pH increased. In the presence of Ca(2+), at least two different adsorption processes took place in the studied systems, i.e., cation exchange and Ca-bridging. Cation exchange was the prevailing process at pH<5, and thus, TC adsorption decreased by increasing total Ca(2+) concentration. On the contrary, Ca-bridging was the prevailing process at pH>5, and thus, TC adsorption increased by increasing Ca(2+) concentration. The pH 5 represents an isoadsorption pH where both adsorption processes compensate each other. TC adsorption became independent of Ca(2+) concentration at this pH. For TC adsorption on Ca(2+)-montmorillonite in 0.01 M NaCl experiments, the ratio adsorbed TC/retained Ca(2+) was close to 1 in the pH range of 5-9, indicating an important participation of Ca(2+) in the binding of TC to montmorillonite. X-ray diffraction and transmission electron microscopy showed that TC adsorption induced intercalation between montmorillonite layers forming a multiphase system with stacking of layers with and without intercalated TC.
authors.affiliation: Facultad de Ingeniería, Universidad Nacional del Comahue, Neuquén 8300, Argentina. maria.parolo@fain.uncoma.edu.ar
authors.forename: M Eugenia
authors.initials: ME
authors.lastname: Parolo
authors.forename: Marcelo J
authors.initials: MJ
authors.lastname: Avena
authors.forename: Gisela R
authors.initials: GR
authors.lastname: Pettinari
authors.forename: Miria T
authors.initials: MT
authors.lastname: Baschini
mesh_terms: D000327:Adsorption; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000378:metabolism; D001546:Bentonite / Q000737:chemistry* / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D046529:Microscopy, Electron, Transmission; D013752:Tetracycline / Q000737:chemistry* / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D000900:Anti-Bacterial Agents; D001546:Bentonite; D013752:Tetracycline; D002118:Calcium