Preparation Of Supported Zero Valent Iron Sulfide By Carbothermal Reduction Of Limonite And Its Degradation Of Azo Dye Wastewater

Sulfide zero valent iron（S-ZVI）is a composite material coated with sulfide zero valent iron（ZVI）,which can effectively improve the selectivity and degradation rate of S-ZVI for target pollutants.Currently,S-ZVI is mainly prepared by liquid phase reduction and ball milling methods.Due to its production costs,sample preservation,operational safety,and mass production issues,the practical application of S-ZVI materials in environmental remediation is limited.Therefore,it is urgent to develop new processes to achieve low-cost preparation of S-ZVI.In this paper,limonite was used for carbothermal reduction to prepare loaded zero valent iron sulfide,which was used to degrade azo wastewater.The reaction mechanism of carbothermal reduction of limonite and sulfurizer to prepare S-ZVI was studied.The phase analysis during the carbothermal reduction process shows that goethite（Fe O（OH））in limonite will first be removed from the crystalline water to become Fe₂O₃,and then gradually reduced to Fe₃O₄ and Fe O,eventually forming Fe;The sulfiding agent reacts with Fe in a reducing atmosphere to form pyrrhotite(Fe_1-xS).The effects of curing agent type and dosage,anthracite dosage,calcination temperature and time on the degradation performance of S-ZVI for methyl orange were studied.The results showed that sulfur had the best effect.Increasing the amount of sulfur,increasing the preparation temperature,increasing the amount of anthracite,and prolonging the preparation time,the degradation efficiency of S-ZVI on methyl orange showed a trend of first increasing and then decreasing.Finally,the optimal conditions for the preparation of S-ZVI were obtained:sulfur content of 3%,preparation temperature of 1000℃,preparation time of 60 min,and anthracite content of 25%.X-ray diffraction（XRD）,scanning electron microscopy,and energy dispersive spectroscopy（SEM-EDS）were used to analyze the phase transition and micromorphology of limonite and sulfurizer during carbothermal reduction,and the C and S contents of S-ZVI under various preparation conditions were tested.The experimental results show that increasing the preparation temperature and prolonging the preparation time are beneficial for the reduction of iron minerals to generate S-ZVI.However,excessive preparation temperature and time can lead to the aggregation and growth of S-ZVI particles,reducing the degradation effect of S-ZVI on methyl orange.The S-ZVI prepared under the optimal conditions was subjected to X-ray diffraction,scanning electron microscopy,and energy spectrum analysis.The results showed that the S-ZVI particles were loaded on the surface of quartz in a core-shell structure,with particle sizes mainly distributed between 200 and 400 nm.The effect of degradation conditions on S-ZVI degradation of methyl orange was studied.The results showed that reducing the initial p H value of methyl orange solution,increasing the amount of S-ZVI,decreasing the concentration of methyl orange,and increasing the water bath temperature could accelerate the degradation rate of S-ZVI for methyl orange.The degradation efficiency of 2.5 g/L S-ZVI for methyl orange solution with an initial concentration of 500 mg/L was 96.22%.The decolorization reaction of methyl orange follows a pseudo first order kinetic model,with a good curve fitting degree.The apparent activation energy of this reaction E_a=57.33 k J/mol.The mechanism analysis showed that methyl orange was mainly degraded into p-aminodimethylaniline and sulfanilic acid.