磁性介孔碳负载纳米零价铁的制备及其去除高盐废水中Cr(Ⅲ)有机配合物

Preparation of magnetic mesoporous carbon loaded nano zero⁃valent iron for removal of Crorganic complexes from high⁃salt wastewater

采用液相还原法制备了磁性介孔碳(Fe_(3)O_(4)@C)负载纳米零价铁(nano zero-valent iron,nZVI)复合材料(Fe_(3)O_(4)@C-nZVI),并将其用于高盐水中Cr(Ⅲ)-EDTA(EDTA:乙二胺四乙酸)的去除。扫描电镜、透射电镜、X射线衍射等表征表明nZVI成功负载且分散良好,可磁性分离,在碳层保护下nZVI稳定性强,有利于材料的重复利用。nZVI的加人大大提高了Fe_(3)O_(4)@C-nZVI对Cr(Ⅲ)-EDTA的吸附能力,在pH=4.0、反应温度为25℃时,Fe_(3)O_(4)@C-nZVI对Cr(Ⅲ)-EDTA的最大吸附量为10.24 mg·g^(-1),显著高于Fe_(3)O_(4)@C(4.31 mg·g^(-1))。吸附Cr(Ⅲ)-EDTA的过程更符合Langmuir模型和准二级动力学模型。Fe_(3)O_(4)@C-nZVI对Cr(Ⅲ)-EDTA的吸附能力随着溶液pH值的增加先增加后减小;低浓度络合剂(EDTA、柠檬酸)会促进Cr(Ⅲ)-EDTA的吸附,而络合剂浓度增加时则表现为抑制;高浓度阳离子(Na^(+)、K^(+)、Ca^(2+))会促进Cr(Ⅲ)-EDTA的吸附。Fe_(3)O_(4)@C-nZVI在盐和络合剂环境中对Cr(Ⅲ)-EDTA仍表现出显著的吸附效果。经过3次再生循环后,Fe_(3)O_(4)@C-nZVI对Cr(Ⅲ)-EDTA的吸附量达6.90 mg·g^(-1)。X射线光电子能谱分析表明,Fe_(3)O_(4)@C-nZVI通过表面Fe(Ⅲ)与Cr(Ⅲ)-EDTA之间的配位作用形成FedO-EDTA-Cr(Ⅲ)配合物从而将Cr(Ⅲ)-EDTA去除,随后通过离子置换作用将Cr(Ⅲ)置换出来,置换出的Cr(Ⅲ)会与表面氧化铁共沉淀为Cr_(x)Fe_(1-x)(OH)_(3),进而沉积在nZVI表面被去除。

Magnetically mesoporous carbon(Fe_(3)O_(4)@C)/nano-zerovalent iron(nZVI)composites(Fe_(3)O_(4)@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 Fe_(3)O_(4)@C-nZVI was 10.24 mg·g^(-1) at pH=4.0,25℃,which was remarkably higher than that of Fe_(3)O_(4)@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 Fe_(3)O_(4)@C-nZVI.The adsorption capacity of Fe_(3)O_(4)@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^(+),Ca^(2+))in the solution will promote the adsorption of Cr(Ⅲ)-EDTA.Fe_(3)O_(4)@C-nZVI still showed significant adsorption of Cr(Ⅲ)-EDTA in a salt and complexant environment.The adsorption saturated Fe_(3)O_(4)@C-nZVI was regenerated by 0.1 mol·L^(-1) HCl solution,the adsorption of Cr(Ⅲ)-EDTA by Fe_(3)O_(4)@C-nZVI reached 6.90 mg·g^(-1) after three regeneration cycles.X-ray photoelectron spectrum analysis of Fe_(3)O_(4)@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 Cr_(x)Fe_(1-x)(OH)_(3) deposited on the nZVI surface.