Study On The Preparation Of Silicate-supported Iron-copper Sulfide By Carbothermic Reduction From Limonite And Its Removal Of Hexavalent Chromium And Chloramphenicol In Water

Water pollution is a serious threat to ecological safety and human health,so more and more researchers pay close attention to it.Zero-valent iron（ZVI）is widely used in water pollution treatment because of its low price and excellent electronic supply capacity.However,the surface of ZVI is prone to passivation membrane with poor electron transfer performance,which greatly inhibits the reactivity of ZVI and reduces the selectivity and removal rate of the target contaminants.In this study,Si O₂@S-ZVI-Cu,a silicate-supported copper ferrous sulfide material,was prepared by carbon thermal reduction using cheap and readily available limonite as an iron source,and applied to the removal of hexavalent chromium（Cr（VI））and the activation of persulphate（PS）to degrade chloramphenicol（CAP）in water.The main findings are as follows:The mechanism of preparation of Si O₂@S-ZVI-Cu from limonite and Cu Fe S₂ by carbon thermal reduction was investigated.Thermodynamic analysis shows that the reduction process of limonite is Fe O（OH）→Fe₂O₃→Fe₃O₄→Fe O→Fe,and the pyrolysis of limonite into Fe S,Cu₂S and S₂.At temperatures of about 1000℃,the mixed decomposition reaction of limonite and Cu Fe S₂ is balanced,resulting in Fe,Fe S,Cu₂S,and Cu.Preparation conditions were optimized using Cr（VI）as a model pollutant.The optimum preparation conditions were 6%Cu Fe S₂,20%anthracite,1000℃and 60 min.Si O₂@S-ZVI-Cu prepared under these conditions was characterized and showed that Si O₂@S-ZVI-Cu is a silicate-loaded micron size particle with a large specific surface area,a core shell structure,a core of ZVI-Cu,and an outer layer of Cu Fe sulfide.The effects of degradation conditions on the removal of Cr（VI）from Si O₂@S-ZVI-Cu were investigated.The results showed optimal degradation conditions of p H=4.0,0.5 g/L for Si O₂@S-ZVI-Cu,10 mg/L for Cr（VI）initial solution,28℃reaction temperature and 88.54%removal of Cr（VI）within 80 min.The copper ion content of the solution after reaction was0.00189 mg/L and secondary contamination was not introduced.Mechanistic analysis showed that Cr（VI）was reduced to Cr（III）and then deposited on the surface of Si O₂@S-ZVI-Cu in the form of Fe Cr₂O₄ and Cr（OH）₃.Si O₂@S-ZVI-Cu prepared under optimal conditions was used to activate PS to degrade CAP.The results showed 96.16%degradation of CAP in 60 min at PS 3.0 m M,Si O₂@S-ZVI-Cu 0.4 g/L,reactive solution p H 6.2,CAP concentration 20 mg/L and reaction temperature28℃.Stability tests showed that Si O₂@S-ZVI-Cu was a high quality PS activator.Secondary contamination was not introduced in the solution with a Cu content of 0.0034 mg/L.SO₄^·-is the main active radical that degrades CAP.The degradation mechanism analysis revealed that both ZVI and copper were involved in PS activation.CAP can be broken down into small molecules by the Si O₂@S-ZVI-Cu/PS system,but not completely mineralized,with a solution toxicity of 79%,much less than CAP（100%）.Analysis of intermediate products by liquid chromatography mass spectrometry（LC-MS）suggests that the degradation pathways of CAP are denitrification,dehydroxylation and dechlorination.