Oxidative removal of sulfadiazine using synthetic and natural manganese dioxides

Studies on oxidation kinetics of sulfadiazine (SDZ) using δ−MnO₂ (birnessite) and natural MnO₂ are limited. Reaction order at different SDZ speciation was determined based on the effects of initial H⁺, MnO₂ and SDZ concentrations using initial rate method, which would be useful to determine the optimum pH and MnO₂ concentration. Birnessite and natural MnO₂ with different physico-chemical properties such as BET surface area, pH_PZC, d-spacing, and crystal size similarly showed good efficiencies in oxidizing neutral SDZ (pH 5) and anionic SDZ (pH 8). Activation energy (E_a) and thermodynamic parameters indicated the similar oxidation efficiencies in the temperature range of 10–40°C. The ${SO}_4^{2-}$ was produced from the SDZ oxidation coupled to the reduction of MnO₂ to Mn²⁺. The effect of co-solute ciprofloxacin (CIP) on the oxidation kinetics of SDZ was also studied. The rates of SDZ oxidation by both birnessite and natural MnO₂ were reduced by the presence of CIP due to competition in oxidation between SDZ and CIP. The SDZ was more rapidly oxidized than CIP in both single- and bi-solute systems, as indicated by the presence of CIP intermediate, whereas the intermediate of SDZ was not detected.