Preparation And Application Of Red Mud-based Polyaluminum Ferric Chloride Flocculant And Magnetic NaP1 Zeolite

With the rapid development of the global economy,the consumption of mineral resources continues to increase,and a large number of pollutants,including industrial wastewater and solid waste,are generated during the mining and processing of minerals.Among them,the strong alkaline solid waste red mud produced by the conversion and utilization of bauxite is particularly prominent.At the same time,with the development of industrialization and urbanization,environmental safety issues caused by landfill leachate and organic dye wastewater have also attracted much attention.Therefore,how to use red mud as a raw material to prepare high value-added products to treat wastewater is the most significant challenge at present.Red mud is rich in aluminum,silicon and iron.Aluminum and silicon are important potential raw materials for the synthesis of NaP1zeolite,and aluminum and iron can be used to prepare polyaluminum ferric chloride flocculant（PAFC）.NaP1 zeolite can be used as an adsorbent to treat organic dye wastewater,but after the adsorption is saturated,the adsorbent will exist in a suspension state,which is not easy to recycle,and is likely to cause secondary pollution and waste of resources.Hence,the composite material Sr Fe₁₂O₁₉@NaP1（SFO@NaP1）zeolite was prepared from the magnetic matrix SFO and NaP1 zeolite in this paper,so as to realize repeated recycling.In addition,the use of PAFC to flocculate and purify landfill leachate can achieve comprehensive utilization of mineral resources.The red mud was leached with hydrochloric acid to obtain the acid leaching residue（ARM）for preparing magnetic zeolite and the acid leaching solution for preparing PAFC.Single factor experiment and orthogonal experiment were used to explore the influence of acid leaching time,liquid-solid ratio,acid leaching temperature and acid leaching concentration on the leaching rate.The results showed that the conditions for the acid leaching to obtain the maximum aluminum-silica content,the acid leaching time was 120min,the acid leaching liquid-to-solid ratio was 7,the acid leaching temperature was 70℃and the hydrochloric acid concentration was 5 mol/L,and the leaching rate under this condition was 135.76%.PAFC was prepared from the acid leaching solution,and the effects of different polymerization pH,polymerization temperature and polymer Al/Fe molar ratio on the flocculation effect of PAFC were studied.The effects of flocculation concentration and flocculation pH during the flocculation process were investigated.XRD,FTIR and SEM were used to characterize the structure and performance of the PAFC.In addition,the aged landfill leachate was used as the target,and the indexes of COD,UV₂₅₄ and chromaticity of the self-made PAFC and the commercial PAFC were compared.The results showed that the PAFC prepared under the conditions of pH 2.5,polymerized Al/Fe molar ratio of 8,and polymerization temperature of 70℃had the best flocculation effect on the aged landfill leachate.The self-made PAFC and commercial PAFC under the flocculation conditions of 1.2 g/L and pH of 6,the COD removal rate was 72.2%and73.0%respectively;the UV₂₅₄ removal rate was respectively 79.2%and 79.9%,the chroma removal rate was 82.9%and 85.7%,respectively.Moreover,the flocculation mechanism of PAFC with metallic luster and mesh was mainly completed by electric neutralization adsorption,bridging effect and net trapping and sweeping.NaP1 zeolite and SFO@NaP1 zeolite were prepared via alkali fusion hydrothermal method.The effects of different mass ratios of ARM and NaOH,alkali fusion temperature and alkali fusion time on the synthetic crystallinity of NaP1 zeolite were investigated.Moreover,the effect of different composite ratio of SFO@NaP1 zeolite on adsorption performance.The structure and properties of NaP1 zeolite and SFO@NaP1 zeolite were characterized by XRD,FTIR,XPS and SEM.Methylene blue solution was used as simulated wastewater,and the adsorption performance of NaP1 zeolite and SFO@NaP1zeolite were studied,and their regeneration performance was investigated.The suitable conditions for alkali fusion were m（ARM）:m（NaOH）of 1:1.5,alkali fusion temperature of 650℃and alkali fusion time of 60 min.The optimal conditions for hydrothermal synthesis of zeolite were liquid-solid ratio of 10,hydrothermal time of 7 h and hydrothermal temperature of 120℃.NaP1 zeolite and SFO@NaP1 zeolite have been successfully synthesized,and both have excellent adsorption properties.The removal efficiency and adsorption capacity of NaP1 zeolite and SFO@NaP1 zeolite under the dosage of 1 g/L,the initial pH of 7,the initial concentration of 50 mg/L and the adsorption temperature of 25℃were 97.1%,95.4%,48.7 mg/g,47.9 mg/g,respectively.The adsorption of MB on NaP1 zeolite and SFO@NaP1 zeolite was an exothermic process that followed the pseudo-second-order kinetic model.However,NaP1 zeolite conformed to Freundlich isotherm model,while SFO@NaP1 zeolite belonged to Langmuir isotherm model.The adsorption capacity of MB on NaP1 zeolite and SFO@NaP1 zeolite with a saturation magnetization of 1.61 emu/g after three regenerations were 34.5 mg/g and 33.2mg/g,respectively.The adsorption mechanism of NaP1 zeolite and SFO@NaP1 zeolite with specific surface areas of 79.30 m²/g and 78.86 m²/g,respectively,was caused by electrostatic attraction,hydrogen bonding and pore diffusion.