Influence of Ca2+ on tetracycline adsorption on montmorillonite

► The adsorption of TC on montmorillonite was studied as a function of pH and Ca2+. ► In the presence of Ca2+, two different TC adsorption processes took place. ► TC adsorption became independent of Ca2+ concentration only at pH 5. ► XRD and TEM indicate that TC was intercalated in the interlayer space.