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

Abstract

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.