Using Green Method To Synthesis NZVI Apply For Chromium Remediation And Its Transportability Under Environmental Impact Factors Conditions

Currently,chromium(Cr)is used in industrial production because of its wide applicability,and the discharge of electroplating wastewater,the stacking of Cr slag caused by industrial production makes the problem of Cr pollution serious.Dealing with hexavalent chromium(Cr(?))pollution in natural waters or in the soil is more difficult than other pollutants,because Cr(?)is difficult to degrade and endanger human health through bioaccumulation.Therefore,considering the hazards of Cr(?),many researchers have considered reducing the toxicity of Cr(?)by reducing Cr(?)to Cr(?).Nano zero-valent iron(nZVI)has reducibility,reactivity and adsorption properties,which is an ideal material for removing heavy metal pollution.However,the chemical synthesis of nZVI has the characteristics of easy agglomeration and poor transportability,which reduces the reaction performance of nZVI.Therefore,this study used diatomite(DE)as a stabilizer and green tea extract(tea polyphenols;GT)as a reducing agent to obtain modified nano-iron particles(GT-nZVI@DE)through green synthesis.The mobility of GT-nZVI@DE in heterogeneous porous media,the remediation effect in soil environment and the reaction mechanism with Cr(?)were studied.And also studied the effect of inorganic molecule phosphate(PO₄^3-),organic molecule humic acid(HA)and sulfide metal(ferrous sulfide(FeS)/pyrite(FeS₂))to the reactivity and mobility of GT-nZVI@DE remediates Cr(?),which are widely exist in nature.The main conclusions of this article as follows:(1)The green method was used to prepare GT-nZVI@DE nanocomposite and its reactivity and mobility with Cr(?)were studied:using DE as the carrier and GT as the reducing agent,a series of GT-nZVI@DE with different loading ratios(Fe/DE)was successfully prepared,and characterized by a variety of analysis methods,its possible structure is DE(?-Fe⁰/organic).The nZVI are successfully loaded in the porous structure of DE,its stability and mobility are better than the green synthetic blank nano zero-valent iron without DE loaded(GT-nZVI).The transport behavior of GT-nZVI@DE mainly depends on the proportion of sand and soil in the water-saturated heterogeneous porous medium.In particular,a two-point kinetic model is used to reveal the transport mechanism of GT-nZVI@DE in soil.At the same time,compared with GT-nZVI(about 400mg·g^-1),GT-nZVI@DE(Fe/DE=10)nanocomposite(796.5mg·g^-1)shows better Cr(?)removal ability,and adding GT-nZVI@DE(98.37mg·g^-1),the ability of immobilize Cr(1.12mg·g^-1)is improved by soil.The stability of GT-nZVI@DE reacted with Cr(?)is better than GT-nZVI,which also leads to GT-nZVI@DE still has a certain degree of mobility after reacting with Cr(?),and it is found that the load of DE is increased GT-nZVI ability of adsorb Cr(?).In addition,XRD and XPS analysis identified the morphology of Cr(?)after the reaction(i.e.FeOCr₂O₃,Cr₂O₃,Cr(OH)₃).(2)Taking GT-nZVI@DE composite material(Fe/DE=10)as the research subject,the effects of p H,initial Cr concentration,PO₄^3-and HA on the remediate of Cr by GT-nZVI@DE were investigated.Firstly,the effect of p H on the stability of GT-nZVI@DE composites and the effect of initial Cr concentrations on its transportability and removal effect were investigated.After determining the Cr/Fein remediation,the effect of PO₄^3-and HA on the efficiency of Cr(?)remediation by GT-nZVI@DE was also studied.And through a series of analysis methods to reveal the possible mechanism.The results show that:p H has no obvious effect on the particle size of the GT-nZVI@DE,and high Cr concentration could inhibit the reduction of Cr by the GT-nZVI@DE.Meanwhile,PO₄^3-will inhibit the removal of Cr by GT-nZVI@DE,and the higher concentration of PO₄^3-,the more obvious the competitive adsorption will have between PO₄^3-and Cr,and the stronger inhibitory effect will have.Similarly,HA has an inhibitory effect on Cr immobilization by GT-nZVI@DE.There is an interesting phenomenon that HA increased the proportion of reduction in the removal amount during the Cr immobilization,which was attributed to HA as an electron donor to provide the electrons to reduce Cr(?).Under the inhibition of PO₄^3-and HA,GT-nZVI@DE still maintains a high Cr(?)removal capacity(216.8mg·g^-1).In addition,when PO₄^3-and HA coexist,heterogeneous agglomeration will occur to reduce the inhibitory effect of these two factors on the removal of Cr by GT-nZVI@DE.And because of heterogeneous agglomeration between PO₄^3-,HA and GT-nZVI@DE under the condition of Cr(?),reducing the transportability of GT-nZVI@DE.(3)Using ferric chloride(FeCl₃·6H₂O;exclude the influence of sulfate ions in the sample on the experimental results)and GT to synthesis GT-nZVI,the effect of GT-nZVI on Cr(?)remediation and the stability reacted with Cr(?)were investigated.And through XRD analysis the possible mechanism.The results show that FeS or FeS₂ will heterogeneous aggregate with GT-nZVI under the condition of Cr(?),thereby reducing the transportability of GT-nZVI in sand column.In addition,FeS and FeS₂ can significantly improve GT-nZVI removing Cr(?)in aqueous solution,especially the reduction ability of Cr(?).This is mainly due to the hydrolysis of FeS and FeS₂ to produce Fe²⁺and S^2-/S₂^2-as an electron donor to reduce Cr(?).In particular,FeS has a greater impact on GT-nZVI removing Cr(?)and the co-transport of GT-nZVI and Cr(?)in the quartz sand column than FeS₂,especially,at p H=6.00.The effluent of Cr(?)in the FeS system is lower than that of FeS₂,which is attributed to the rapid and high rate of dissolved iron produced by FeS in aqueous solution.This study shows that GT-nZVI@DE is a potential nanocomposite for Cr remediation in soil,which can provide ideas for other related research.Moreover,DE widely exists in soil and available easily,so it can be better used in actual production.Under the effect of HA and PO₄^3-,GT-nZVI@DE composite can still show a good ability to immobilize Cr(?)in the soil,so provides a theoretical basis for GT-nZVI@DE used in natural containing HA and PO₄^3-.In addition,the coexist of pyrite confirms that GT-nZVI@DE can immobilize Cr better in the soil.