The adsorption of tetracycline (TC) from aqueous solution by different types of montmorillonite (MMT) was studied under varying pH, temperature, and ionic strength conditions. The adsorption data obeyed the Langmuir isotherm with maximum TC adsorption at 468, 404, and 243 mg/g on SAz-1, SWy-2, and SYn-1 at pH 1.5, and at 375 mg/g on SHCa-1 at pH 8.7, corresponding to 0.86, 1.07, 0.78, and 1.28 of their cation exchange capacities, respectively. The kinetics of TC adsorption was very fast and reached equilibrium in almost 2 h and the results followed the pseudo-second-order kinetic model. In general, lower solution pH facilitated TC adsorption except for SHCa-1. Ionic strength had minimal influences on TC adsorption. The adsorption of TC on MMTs was endothermic, suggesting a strong physical adsorption. Under a weak alkaline condition, the TC adsorption resulted in extensive MMT delamination or exfoliation. Because of its high TC adsorption capacity, the results suggested that MMT could be a very good candidate to remove TC from wastewater containing high amounts of TC.
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