| Zero valent iron(ZVI)is widely used in industrial wastewater treatment,groundwater remediation and other fields due to its low cost,strong electronic supply capacity and nontoxicity.However,the accumulation of iron(hydr)oxides on the surface of iron significantly reduces the activity of the ZVI and this becomes more severe when the pH environment is more basic.After decades of development,scholars have proposed many modification techniques for ZVI,including pretreatment,weak magnetic field,bimetallic,loading method,and sulfidation.Sulfidation is a modification technology that can effectively improve the reactivity of ZVI.The essence is that a layer of iron sulfide(FeSx)is loaded on the surface of ZVI.FeSx on the surface of sulfide-modified zero-valent iron(SZVI)not only has good electron transport properties,but also can slow down the formation of iron oxide to a certain extent.However,the FeSx phase will inevitably be consumed during storage or disposal of pollutants.Although it can be used to reduce some pollutants,this will continue to weaken the advantages brought by sulfidation.Compared with FeSx,copper-containing sulfides not only have higher oxidation resistance,but also have stronger electron transport properties.Considering that,copper cation was introduced to the FeSx phases to prepare copper-doped sulfides with improved durability.In this study,we successfully prepared copper-doped SZVI(Cu-SZVI).The composition and structure have been clearly confirmed by a combination of several techniques,including Raman spectroscopy and X-ray powder diffraction,and the main component of its sulfide was Cu5FeS4.Cr(Ⅵ)removal experiments show that the inorganic copper source for the preparation of’ Cu-SZVI does not affect the properties of the prepared materials.The removal effect of sulfides on Cr(Ⅵ)is very poor,indicates that the main reducing agent of SZVI are the primary reductants Fe(1 and the secondary reductants Fe(Ⅱ),etc.The results of Cr(Ⅵ)sequestration in respike experiments showed Cu-SZVI occupies higher Cr(Ⅵ)removal capacity(82.83 mg/g)and longer effective longevity,which was significantly better than SZVI(57.54 mg/g)and ZVI(8.23 mg/g).The operational pH tolerance is improved for SZVI after doping copper,more than 99%of Cr(Ⅵ)can be removed by Cu-SZVI within 90 min at pHini 4-9,which showed CuSZVI possesses better operational pH tolerance and high environmental applicability.The pH of actual wastewater varies greatly,and it is difficult to maintain the pH in a range that is conducive to the removal of pollutants by materials,so materials with pH tolerance are of practical significance.The effect of air aging on the reactivity of the material shows that CuSZVI can still completely remove Cr(Ⅵ)within 90 minutes after aging in air for 30 days.Compared with the fresh material,the pseudo-first-order kinetic constant decreases by 34.00%,while the decrease rate of szvi is 61.21%,indicating that the sulfide on the surface of Cu-SZVI is more resistant to air oxidation.The characterization analysis of the material during the removal of Cr(Ⅵ)showed that compared with SZVI,the valence state and surface morphology of the sulfur species of CuSZVI changed less,and less sulfate ions were released into the reaction solution,which fully proved that the sulfide of Cu-SZVI is more stable.The essence of higher reactivity after copper doping is the modification of sulfide,which improves the stability of sulfide and improves its electron transport performance.After 90 minutes of Cr(Ⅵ)removal by by Cu-SZVI and SZVI,chromium mainly exists as Cr(Ⅲ),the removal trends of total chromium and Cr(Ⅵ)are basically the same,and the concentration of total iron has been at a low level,indicating that the removal mechanism of Cr(Ⅵ)is reduction,adsorption and co-precipitation.Cu-ZVI has no copper environmental risk.This work proposes a new way to modify SZVI by doping a secondary cation,which can be used to further explore new SZVI materials based on specific needs. |
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