Effect of coexisting ions on crystal phase transformation of nanoscale zero-valent iron in chromium-containing solutions
When nanoscale zero-valent iron(nZVI)reacts with hexavalent chromium[Cr(Ⅵ)]in water,its own structure also changes,which affects its efficacy and properties.In this paper,the effect of coexistence of heavy metal ions(Co2+,Cd2+,Ni2+,Cu2+)and anions(Cl-,CO32-,NO3,SO42-)in Cr(Ⅵ)solution on the crystal phase transformation of nZVI was mainly investigated.Results showed that the coexistence of heavy metal ions can promote the oxidation of nZVI and promote the compositions of nZVI to lepidocrocite(γ-FeOOH)and goethite(α-FeOOH).The effect of coexisting anions on the crystal phase of nZVI is related to concentration of chromium and anions.When Cr was 10 mg·L-1,the four anions all inhibited the oxidation of nZVI;when Cr was 20 mg·L-1,NO3-,SO42-promoted the oxidation of nZVI,CO32-inhibited the oxidation of nZVI,low concentration of Cl-(20 mg·L-1)promotes the crystal phase transformation of nZVI,high concentration of Cl-(200 mg·L-1)inhibits the transformation of Fe(0)into the mixture of γ-FeOOH and maghemite/magnetite(γ-Fe2O3/Fe3O4).When Cr(Ⅵ)＞50 mg·L-1,the oxidation of nZVI is inhibited,and the four anions have no obvious effect at this time.This study had important significance for studying the relationship between the structure and removal efficiency of nZVI under complex environmental systems.
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