Adsorption and photooxidation of pharmaceuticals and personal care products on clay minerals

The adsorption and photodegradation behavior of tetracycline (TC), chloramphenicol (CAP) and sulfamethoxazole (SMX) in clay mineral dispersion was investigated in this work. Only TC showed significant adsorption to natural montmorillonite and rectorite, whereas CAP and SMX adsorbed to natural montmorillonite, kaolinite and rectorite to a much lower extent. The adsorption equilibrium constants (L/kg) of TC to natural montmorillonite were 332 and 108 at pH 3.0 and 7.0, respectively. The kinetic rate constant kapp (min−1) for the removal of CAP in the presence of different clay minerals follows the sequence: montmorillonite KSF (1.6 × 10−2) > rectorite (4.6 × 10−3) > natural montmorillonite (3.8 × 10−3) > kaolinite (2.8 × 10−3). Removal of SMX follows the same sequence. Oxalate significantly promotes the removal of CAP and SMX in montmorillonite KSF dispersion, while penicillamine (PEN) and β-cyclodextrin retard the diminution. After 3 h of irradiation in 5 g/L KSF dispersion, the total organic carbon was reduced by 72 and 39% for CAP and SMX, respectively.