CONICET | Buscador de Institutos y Recursos Humanos

The adsorption of tetracycline (TC) on montmorillonite was studied as a function of pH and Ca2+ concentration using a batch technique complemented with X-ray diffraction and transmission electron microscopy. In the absence of Ca2+, TC adsorption was high at low pH and decreased as the pH increased. In thepresence of Ca2+, at least two different adsorption processes took place in the studied systems, i.e., cationexchange and Ca-bridging. Cation exchange was the prevailing process at pH < 5, and thus, TC adsorptiondecreased by increasing total Ca2+ concentration. On the contrary, Ca-bridging was the prevailing processat pH > 5, and thus, TC adsorption increased by increasing Ca2+concentration. The pH 5 represents anisoadsorption pH where both adsorption processes compensate each other. TC adsorption becameindependent of Ca2+concentration at this pH. For TC adsorption on Ca2+-montmorillonite in 0.01 M NaCl experiments, the ratio adsorbed TC/retained Ca2+was close to 1 in the pH range of 59, indicating an important participation of Ca2+ 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.