Removal of sulfadiazine and ciprofloxacin by clays and manganese oxides: Coupled sorption-oxidation kinetic model.

Sorption onto clays (montmorillonite and kaolinite), oxidation and sorption by manganese oxides (synthesized MnO and natural MnO), and coupled sorption-oxidation experiments were conducted for the removal of antibiotics sulfadiazine (SDZ) and ciprofloxacin (CIP) at pH 5 and 8. Individual sorption and oxidation modelling were carried out using the first-order kinetic model. A coupled sorption-oxidation kinetic model was developed to predict the simultaneous sorption and oxidation process. The coupled sorption-oxidation enhanced the antibiotic sorption, with the first-order sorption rate constants in the simultaneous presence of clays and manganese oxides (ksorp) being higher than those with clays only (ksorp0). In contrast, a depression was observed; the first-order oxidation and sorption combination rate constants in the simultaneous presence of manganese oxides and clays (kMnO) were lower than those with manganese oxides only (kMnO0). In the coupled sorption-oxidation reaction, 13.5-62.5% of SDZ and CIP removal was attributed to the sorption. The SDZ and CIP species distributions at pH 5 affected the coupled sorption and oxidation systems more than those at pH 8. The best removal efficiency was achieved by the montmorillonite-synthesized MnO combination, mainly due to the higher surface area (ABET) and pore size of montmorillonite and synthesized MnO combination compared to other clays and manganese oxides combinations.