Degradation Of Sulfamethazine By Red Mud-based Heterogeneous Fenton System

In recent years,the abuse of antibiotics has led to a greater threat to the ecological environment and human health.At present,heterogeneous Fenton oxidation technology is an advanced oxidation process with better degradation effect of antibiotics in water.Therefore,the selection of cheap and effective catalysts can effectively promote the development of heterogeneous Fenton technology.Red mud,as a by-product of alumina industry,has a huge emission while with limited utilization rate.However,red mud is rich in iron oxides,which makes it possible for red mud to be used in the field of catalysts.In the above context,as a typical sulfonamide antibiotic,Sulfamethazine（SMT）was selected as the target pollutant,and red mud was adopted as the catalyst in this study.Then the catalytic degradation of SMT in aqueous solution was conducted via heterogeneous Fenton oxidation technology.The optimization of reaction parameters,influencing factors and heterogeneous Fenton catalytic mechanism of red mud were studied.The main conclusions were demonstrated as follows:（1）The catalytic activity of red mud was related to calcination temperature.The removal efficiencies of SMT at different calcination temperatures were200℃>100℃>non calcination>300℃>400℃>500℃.Considering the removal efficiency of SMT and the cost of catalyst preparation,uncalcined red mud was chosen as catalyst for heterogeneous Fenton system.What is more,appropriate increases in the red mud dosage can effectively improve the removal efficiency of SMT.However,there was an optimum value(20 g·L^-1)for red mud dosage,beyond which the removal efficiency of SMT showed a downward trend.After three cycles of reuse,the removal efficiency of SMT can still reached 81%,which indicated that red mud was suitable for heterogeneous Fenton catalyst with excellent stability and high catalytic activity.（2）The degradation rate constants of SMT in different initial pH solutions were as follows:pH 9>pH 3>pH5>pH 7.Simultaneously,the heterogeneous Fenton system based on red mud catalysis had good pH adaptability for SMT degradation,and can achieve good removal effect even under alkaline conditions.The red mud dosage and H₂O₂concentration had significant effects on the removal efficiency of SMT.Appropriate increases in the red mud dosage can effectively improve the removal efficiency of SMT.Results also showed that the removal efficiency of SMT was enhanced with the increase of the concentration of H₂O₂ and temperature.In addition,ultraviolet radiation and red mud-based heterogeneous Fenton system showed good synergy in the degradation of SMT.（3）The iron oxides in the red mud played a key role in the degradation of SMT,in which amorphous iron oxide and crystalline iron oxide respectively contributed 37.5%and 25.2%of SMT removal.According to the results of trapping experiments and electron paramagnetic resonance（EPR）,the main active species of SMT in the process of catalytic degradation were hydroxyl free（·OH）,radical vacancies（O₂·^-）and vacancies（h⁺）.（4）Seven main intermediate products of SMT degradation were identified by HPLC/MS/MS.The degradation of SMT by heterogeneous Fenton system catalyzed by red mud mainly involved hydroxyl substitution of benzene ring-linked amino groups,sulfonamide bond[S-N]cleavage,carbon-nitrogen double bond[C=N]and carbon-nitrogen single bond[C-N]cleavage in pyrimidine ring.