Preparation And Application Of Modified Red Mud Catalysts For Degradation Of Organical Pollutants In Wastewater

Red mud is a strong alkaline solid waste discharged from the aluminum industry.Nowadays,red mud is mainly treated in storage,which causes serious damage to the ecological environment.Red mud contains a large number of metal oxides such as iron and aluminum,which are commonly used as the active components and supports of catalysts.Therefore,this study focuses on the utilization of red mud for preparing heterogeneous catalysts with two methods.The prepared catalysts were used for the treatment of organic pollutants in wastewater.A Co-based catalyst（Co₃O₄/ARM）was prepared by treating the red mud with hydrochloric acid and then anchoring cobalt oxides on its surface with an impregnation method.Additionally,a Fe-based catalyst（Fe₃O₄/MRM）was prepared by direct calcining the mixture of raw red mud and carbon black at high temperature.Rhodamine B（Rh B）and orange II were used as target pollutants to investigate the catalytic performance of these two catalysts.The kinetic laws and reaction mechanisms were also investigated.The experimental results of the degradation of Rh B via peroxymonosulfate（PMS）activation on Co₃O₄/ARM showed that the removal of Rh B could reach 95.9%under the conditions of a catalyst dosage of 0.05 g/L,PMS concentration of 0.1 mmol/L,initial p H of 4.8,the temperature of 65℃,Rh B concentration of 10 mg/L,and reaction time of 50 min.The degradation of Rh B followed the quasi-first order kinetics,the reaction rate constant was 0.072 min^-1and the activation energy was 55.1 KJ/mol.The results of quenching experiments showed that the sulfate radicals,hydroxyl radicals and singlet oxygen are generated in the reaction system.Singlet oxygen plays a major role in the oxidation of Rh B.The results showed that the removal efficiency of Rh B remained above 80.0%after four reaction cycles.A series of Fe-based catalysts were prepared with different calcination temperatures and times,and their catalytic performances for activating PMS to degrade orange II were evaluated.The optimal preparation conditions of Fe₃O₄/MRM were determined as follows:the calcination temperature was 600℃,the calcination time was 90 min.XRD analyses show that the inert hematite in red mud can be reduced to magnetite with higher catalytic activity after calcination under high temperature.The experimental results of the degradation of Orange II via PMS activation on Fe₃O₄/MRM showed that Orange II could reach 96.0%under the conditions of a catalyst dosage of 0.20 g/L,PMS concentration of 0.5 mmol/L,initial p H of 5.85,the temperature of 60℃,Orange II concentration of 30 mg/L,and reaction time of 90 min.The degradation of Orange II followed the quasi-first order kinetics,the reaction rate constant was 0.036 min^-1and the activation energy of degradation reaction was 39.8KJ/mol.The results of quenching experiments showed that the sulfate radicals,hydroxyl radicals and singlet oxygen are present in the reaction system.the sulfate radicals and singlet oxygen play a major role in the oxidation of Orange II.The results showed that the removal efficiency of Orange II remained 78.5%after four reaction cycles.