Preparation Of Dispersed Nano Zero-valent Iron For Removal Of Hexavalent Chromium From Groundwater

Cr (VI), as one of the common heavy metals in contaminated soil andgroundwater, has always been paid much attention to. In recent years, nanozero-valent iron (nZVI) has been proved to be an efficient method to treat Cr (VI)polluted groundwater. The major challenges for environmental applications of nZVIare its strong tendency of agglomeration, rapid sedimentation and consequentlylimited mobility of nanoparticles in the aquatic environment. To solve these problems,this paper used sodium alginate to modify nano zero-valent iron. Dispersed nZVI wassuccessfully prepared by the liquid phase reduction method, and then batchexperiments were conducted to compare the efficiency of the removal of Cr (VI). Theresults show that, SA-Fe has better mobility and excellent Cr (VI) removal efficiency.The main contents are as follows:The SA-Fe was a sphere with a diameter less than100nm. By using SEM, XRD,XPS, it could be inferred that the Fe particles were embedded in the polymer materialand exiseted as amorphous state.In order to examine the stability and mobility of SA-Fe and CMC-Fe, zetapotential was measured and the column experiment was conducted. SA-Fe had ahigher absolute zeta potential than the CMC-Fe. Sodium alginate, as a dispersant,increased the electrostatic repulsion between nanoscale zero-valent iron and enhancedthe steric hindrance by dispersing the particles to achieve better stability. After1.5pore water effluent, the Fe concentration in effluent of SA-Fe was greater than theCMC-Fe’s, which demonstrated that SA-Fe migrated faster.The dosage of nZVI, the pH value and the initial concentration of Cr (VI) hadeffect on the removal rate of Cr (VI). Generally, the presence of low concentration ofNO3-had no negative influence on the removal rate. The lower pH, lower initialconcentration of Cr (VI) and higher dosage of nZVI were favorable for Cr (VI)removal.Cr(VI) reduction kinetic followed a pseudo-first-order reaction. The apparentrate constant(Kobs) reduced with Cr (Ⅵ) initial concentration increasing. With an initial Cr (VI) concentration of10mg/L,15mg/L,20mg/L, the corresponding Kobswere0.29968min-1,0.10044min-1,0.03215.min-1respectively. The change of pHvalue strongly affected the Kobsand the Kobsincreased from0.04598min-1to0.09156min-1with the pH decreasing from9to6. Under the same condition, the KobsofSA-Fe was greater than that of CMC-Fe. By XPS analysis, the presence of Cr (Ⅲ)suggested that Fe0indeed reduced Cr (Ⅵ) and the hydroxide precipitates of Cr (Ⅲ)produced.