Mechanochemical Destruction Of Chlorinated Organic Pollutants By Fe/Fe₃O₄ And Its Resource Utilization

In this study,Fe/Fe₃O₄ mixture was first applied as an additive to achieve the highly-effective mechanochemical destruction（MCD）of two chlorinated organic pollutants（COPs）,hexachloroethane（HCE）and hexachlorobenzene（HCB）.The MCD mechanism of Fe/Fe₃O₄ was investigated by means of XRD and XPS characterization,and the conclusion is that MCD of COPs occurred mainly via the reduction by Fe,Fe₃O₄ and Fe/Fe₃O₄,the oxidation of Fe₃O₄ and reduction of Fe O（formed owing to the oxidation of Fe by oxygen-containing species）may also contribute to the COPs destruction.Fe/Fe₃O₄ mixture exhibited a higher dechlorination rate（DR）than other three effective additives(i.e.,Fe/SiO_2,Mg/Al₂O₃ and Al/Al₂O₃ mixture),due to the electrical property of Fe₃O₄ and its electron transfer with Fe.The effects of different mass fraction of Fe₃O₄(MF_mag),air atmosphere（pure oxygen,air and pure nitrogen）and water contents on the destruction of COPs were investigated.As the results showed that the COPs destruction was significantly impacted by the MF_magand achieved the maximum level with an MF_magof 70%.The DR of COPs in the atmosphere of air was higher than those of pure oxygen and pure nitrogen because of the oxygen vacancy in Fe₃O₄and oxidation of Fe（Fe was oxidized to FeO）.The presence of water dramatically inhibited the COPs destruction owing to the decrease of collision energy and its competition for the active sites in Fe and Fe₃O₄.As expected,the DR of COPs increased with rotation speed,the mass ratio of ball to reactant and additive to pollutant.The analysis of intermediates indicates that HCB destruction was mainly via dechlorination and polymerization,while HCl cleavage also played an important role in HCE destruction,the degradation pathways of HCE and HCB were given.The reuse of excessive ball additive Fe/Fe₃O₄ mixture in MCD of COPs was studied.The results showed that Fe/Fe₃O₄ can activate persulfacte（PMS and PDS）to efficiently degrade iopamidol（IPM）in water.The mechanism of action of Fe/Fe₃O₄/PMS（PDS）was preliminarily discussed,and the mechanism was deduced as follows:Fe²⁺or Fe（II）activated PMS（PDS）to produce sulfate radical(SO₄^·-)that efficiently degrade IPM.The effects of different doze of Fe/Fe₃O₄,concentration of PMS（PDS）and solution initial p H on the degradation of IPM were investigated.The conclusions showed that the IPM degradation was significantly affected by the doze of Fe/Fe₃O₄ and achieved the maximum level with a doze of 0.05 g.The IPM degradation efficiency increased with increasing PMS（PDS）concentration and realized the maximum with 20 mg·L^-1PMS（PDS）.The solution initial p H had a great effect on the degradation of IPM,the IPM degradation efficiency reached the maximum when the p H was 6.According to the intermediates of IPM degradation determined by LC-MS,the degradation pathway was given.This study demonstrates that Fe/Fe₃O₄ mixture is a suitable additive for MCD process,the excessive Fe/Fe₃O₄ was resued to realize the harmless and the resource-free of mechanochemical destruction of COPs by Fe/Fe₃O₄.