Graduate School of Creative Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan.
Faculty of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan.
J Hazard Mater. 2017 Jul 15;334:142-149. doi: 10.1016/j.jhazmat.2017.03.058. Epub 2017 Mar 27.
Hexavalent chromium (Cr(VI)) attracted researchers' interest for its toxicity, natural availability and removal difficulty. Nevertheless, its sorption mechanism is not clearly understood yet. In this work, we elucidated the sorption mechanism of the co-precipitation of chromates with ferrihydrite through quantitative analysis. The influence of Cr/Fe molar ratio on sorption was investigated by zeta potential measurements, X-ray diffraction (XRD) and X-ray adsorption fine-structure analysis (XAFS). Coprecipitation at pH 5 showed almost twice the sorption density of adsorption at pH 5. In co-precipitation, a shift of the XRD peak due to inner-sphere sorption of chromate was observed at Cr/Fe molar ratio 0.5. For adsorption, the same peak shift was confirmed at Cr/Fe molar ratio of 1. Zeta potential at pH 5 suggested that the sorption mechanism changed at Cr/Fe molar ratio 0.25 for coprecipitation and at Cr/Fe molar ratio of 1 for adsorption. Fitting of Cr and Fe K-edge extended X-ray adsorption fine-structure suggested that ferrihydrite immobilized Cr(VI) via outer sphere surface complexation for lower Cr/Fe ratios and via inner-sphere surface complexation for higher molar ratios. At higher molar ratios, bidentate binuclear CrFe bonds were well established, thus resulting in the expansion of the ferrihydrite structure.
六价铬 (Cr(VI)) 因其毒性、天然存在和去除难度而引起了研究人员的兴趣。然而，其吸附机制尚不清楚。在这项工作中，我们通过定量分析阐明了铬酸盐与水铁矿共沉淀的吸附机制。通过动电电位测量、X 射线衍射 (XRD) 和 X 射线吸收精细结构分析 (XAFS) 研究了 Cr/Fe 摩尔比对吸附的影响。在 pH 5 下共沉淀的吸附密度几乎是在 pH 5 下吸附的两倍。在共沉淀中，在 Cr/Fe 摩尔比为 0.5 时观察到由于铬酸盐的内球吸附而导致的 XRD 峰的位移。对于吸附，在 Cr/Fe 摩尔比为 1 时，相同的峰位移得到了确认。在 pH 5 时的动电电位表明，共沉淀的吸附机制在 Cr/Fe 摩尔比为 0.25 时发生变化，而吸附的吸附机制在 Cr/Fe 摩尔比为 1 时发生变化。Cr 和 Fe K 边扩展 X 射线吸收精细结构的拟合表明，对于较低的 Cr/Fe 比，水铁矿通过外球表面络合固定 Cr(VI)，对于较高的摩尔比，通过内球表面络合固定 Cr(VI)。在较高的摩尔比下，双齿双核 CrFe 键得到很好的建立，从而导致水铁矿结构的扩展。
