Preparation of magnetic mesoporous carbon loaded nano zero-valent iron for removal of Cr(Ⅲ)organic complexes from high-salt wastewater
Magnetically mesoporous carbon(Fe3O4@C)/nano-zerovalent iron(nZVI)composites(Fe3O4@C-nZVI)were successfully prepared by a liquid-phase reduction for the effective removal of Cr(Ⅲ)-EDTA(EDTA:ethylenedi-aminetetra-acetic acid)in high-salinity wastewater.By characterization and analysis by scanning electron micro-scope(SEM)and electron microscope(TEM),the nZVI has been successfully loaded into the carbon layer without significant agglomeration and can be magnetically separated and nZVI was stable under the protection of a carbon layer which is favorable for the reuse of materials.The presence of nZVI on the adsorbents greatly improved the adsorption of Cr(Ⅲ)-EDTA and the maximum adsorption capacity of Fe3O4@C-nZVI was 10.24 mg·g-1 at pH=4.0,25 ℃,which was remarkably higher than that of Fe3O4@C(4.31 mg·g-1).The results showed that the Langmuir model and the pseudo-second-order kinetic model can better describe the adsorption of Cr(Ⅲ)-EDTA by Fe3O4@C-nZVI.The adsorption capacity of Fe3O4@C-nZVI on Cr(Ⅲ)-EDTA increased and then decreased with the increase of solu-tion pH value;low concentrations of complexing agents(EDTA,citric acid)would promote the adsorption of Cr(Ⅲ)-EDTA,whereas an increase in the concentration of the complexing agents showed inhibition;due to the charge shielding effect,high concentrations of cations(Na+,K+,Ca2+)in the solution will promote the adsorption of Cr(Ⅲ)-EDTA.Fe3O4@C-nZVI still showed significant adsorption of Cr(Ⅲ)-EDTA in a salt and complexant environment.The adsorption saturated Fe3O4@C-nZVI was regenerated by 0.1 mol·L-1 HC1 solution,the adsorption of Cr(Ⅲ)-EDTA by Fe3O4@C-nZVI reached 6.90 mg·g-1 after three regeneration cycles.X-ray photoelectron spectrum analysis of Fe3O4@C-nZVI before and after reaction showed that the adsorption mechanism was mainly through complexation between surface Fe(Ⅲ)and Cr(Ⅲ)-EDTA to form Fe(Ⅲ)-EDTA-Cr(Ⅲ)complexation products,and subsequently displaces Cr(Ⅲ)due to ionic displacement,and the displaced Cr(Ⅲ)will be removed by co-precipitation with Fe(Ⅲ)as CrxFe1-x(OH)3 deposited on the nZVI surface.
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