Preparation Of Red Mud-based Modified Material And Its Application In Dye Wastewater Treatment

Red mud（RM）is an industrial solid waste discharged during the production of alumina,and the proper disposal of RM is the key to achieving sustainable development of the alumina industry.RM contains a large amount of metal oxides（Al₂O₃,Fe₂O₃,Ti O₂,etc.）,which can be used to prepare catalysts and catalyst carriers for various heterogeneous catalytic reaction systems.This study investigated the modification of RM and its use as a catalyst for advanced oxidation technology to treat dye wastewater.The paper focused on the following work:A zero-valent iron-based composite catalyst（Fe@RM）was synthesized by carbothermal reduction of RM using carbon black obtained from waste tire cracking as the reducing agent,and the catalytic performance of the catalyst was evaluated for the activation of H₂O₂ to degrade methylene blue（MB）in aqueous solution.The characterization results showed that the hematite in the RM was gradually transformed to Fe₃O₄ and Fe O and finally reduced to Fe⁰ with the increase of the carbon thermal reduction temperature.Under the condition that the initial mass concentration of MB was 20 mg/L,the catalyst dosage was 0.02 g/L,the concentration of H₂O₂ was 0.14 m M,the initial p H was 3,and the reaction temperature was 30 ^oC,the degradation rate of MB was as high as 90.4%at 30 min.Chemical quenching experiments proved that hydroxyl radicals（·OH）,superoxide radicals(O₂^·-)and singlet oxygen（¹O₂）played important roles in Fe@RM/H₂O₂ system.The response surface methodology of the central composite design was used to analyze the effects of the factors in the model on the response values,and the validity of the established model was verified to determine the optimal degradation conditions.The optimum degradation conditions were obtained as follows:catalyst dosage of 0.025 g/L,H₂O₂ concentration of 0.197 m M,initial mass concentration of MB of 20.3 mg/L,initial p H of 2.9,and reaction temperature of 39.8 ^oC.Under the optimal degradation conditions,the actual MB degradation rate was 92.4%and the predicted MB degradation rate was95.4%at 10 min of reaction.Preparation of red mud-biochar（BC）composited（RMBC）by pyrolysis at high temperature using waste coffee grounds and red mud as raw materials.The loaded cobalt oxide catalyst（Co₃O₄/RMBC）was prepared by isovolumetric impregnation using RMBC as the carrier,and the catalytic performance of this catalyst was evaluated for the activation of peroxymonosulfate（PMS）for the degradation of Rhodamine B（Rh B）in aqueous solution.Under the condition that the initial mass concentration of Rh B was 10mg/L,the catalyst dosage was 0.1 g/L,the concentration of PMS was 0.09 m M,the initial p H was 4.9,and the reaction temperature was 30 ^oC,the degradation rate of Rh B was as high as 96.6%at 30 min,and the degradation rate of Rh B was still as high as89.6%after four cycles.Co₃O₄/RMBC had low Co content and low leaching rate,which reduced the secondary pollution of Co to the environment.The excellent catalytic activity of Co₃O₄/RMBC was ascribed to the high dispersion of metals and the synergistic effects of Co³⁺/Co²⁺and Fe³⁺/Fe²⁺redox cycles.Chemical quenching experiments proved that sulfate radicals(SO₄^·-),·OH and ¹O₂ played important roles in Co₃O₄/RMBC/PMS system.The results of the paper provide a useful reference for the preparation of non-homogeneous catalysts using red mud for advanced oxidation of dyestuff organics and the realization of"waste to waste".