Sequestration Of Tungstate From Wastewater By Nano-zero-valent Iron (nZVI) And Sulfided Nano-zero-valent Iron (S-nZVI)

The discharge of heavy metal wastewater not only pollutes the environment,but also is a waste of resources.Nano-zero-valent iron(nZVI)is widely used in the treatment of heavy metal pollution because of its large specific surface area,high reactivity,strong adsorption and wide adaptability.Sulfided nano-zero-valent iron(S-nZVI)is a modified nZVI,which improves the dispersibility of nZVI,reduces its oxidation rate,improves the reactivity,and increases its removal efficiency of pollutants.Presently,nZVI and S-nZVI have been widely used as a new functional repair material in the treatment of heavy metal wastewater.In this paper,nZVI was prepared by liquid phase reduction method,and S-nZVI was synthesized by the stepwise synthesis method.A comparative study was conducted on the effects of tungstate(W(VI))sequestration between nZVI and S-nZVI.The external variables on the removal efficiency such as W(VI)initial concentration,nZVI and S-nZVI dosage and coexisting oxyacid ion(NO3-?SO42-?SiO32-?PO43-)interference were investigated.The reaction products were characterized by X-ray electron spectroscopy(XPS)and high-resolution transmission electron microscopy(TEM).The relevant research conclusions are as follows.1)The freshly prepared nZVI has a staggered chain structure,and S-nZVI synthesized by the "two-step method" also exhibits a similar structure.Both nZVI and S-nZVI particles exhibit a core-shell" structure.The main components of the nuclear" are both Fe(0),however the "shell"of nZVI is mainly composed of iron(hydrogen)oxideandthe "shell" of S-nZVI is sulfide or iron(hydrogen)oxide.2)When the dosage of nZVI is 0.3 g·L-1 and the initial concentration of W(?)is 20 mg·L-1,the removal efficiency is better,andW(?)is finally reduced to W(?)by nZVI;The coexistence of oxyacid groups have different effects on the removal of W(?).NO3-and SO42-have little effect on the removal of W(?),however the case of SiO32-and PO43-is different.As the concentration of SiO32-or PO43-increases,the inhibitory effect on W(?)removal is more pronounced.When the molar ratio of SiO32-or PO43-to W(?)is 10:1,W(?)in the water body cannot be substantially removed.The results of TEM and XPS analysis showed that the coexistence of oxyacid groups changed the surface microstructure of nZVI to varying degrees,affecting the content of W(?)in the product.3)When the dosage of S-nZVI is 0.3 g·L-1 and the initial concentration of W(?)is 20 mg·L-1,the removal efficiency is better and W(?)is reduced to W(?)by S-nZVI;The coexistence of different concentrations of oxyacid ions changed the removal efficiency of W(?)to varying degrees.NO3-and SO42-have little effect on the removal of W(?).The existence of SiO32-or PO43-inhibited W(VI)removal by S-nZVI in water,and the higher the concentration,the greater the degree of inhibition.Compared with the results of nZVI,it is found that the effect of SiO32-and PO43-on the W(VI)removal by S-nZVI is significantly reduced.