Mechanisms of removal of three widespread pharmaceuticals by two clay materials

•LECA efficiently removes gemfibrozil, mefenamic acid and naproxen from water.•Vermiculite has faster adsorption kinetics than LECA (non-stirring conditions).•Gemfibrozil and mefenamic acid attain a partition equilibrium onto vermiculite.•Adsorption of naproxen onto vermiculite follows a Langmuir isotherm.•The three drugs all bind to vermiculite in a similar way through the surface’s Mg2+. Pharmaceutical residues presence in the environment is among nowadays top emergent environmental issues. For removal of such pollutants, adsorption is a generally efficient process that can be complementary to conventional treatment. Research of cheap, widely available adsorbents may make this process economically attractive. The aim of the present work was to evaluate the capacity of two clay materials (exfoliated vermiculite, LECA) to adsorb gemfibrozil, mefenamic acid and naproxen in lab-scale batch assays. Results show that both adsorbents are able to remove the pharmaceuticals from aqueous medium. Although vermiculite exhibited higher adsorption capacities per unit mass of adsorbent, LECA yielded higher absolute removals of the pharmaceuticals due to the larger mass of adsorbent. Quantum chemistry calculations predicted that the forms of binding of the three molecules to the vermiculite surface are essentially identical, but the adsorption isotherm of naproxen differs substantially from the other two's. The linear forms of the latter impose limits at lower concentrations to the removal efficiencies of these pharmaceuticals by vermiculite, thereby electing LECA as more efficient. Notwithstanding, vermiculite's high specific adsorption capacity and also its much faster adsorption kinetics suggest that there may be some benefits in combining both materials as a composite adsorbent solution.