School of Environmental Science and Engineering, Guangdong University of Technology, Guangzhou 510006, China.
School of Environmental Science and Engineering, Guangdong University of Technology, Guangzhou 510006, China.
Sci Total Environ. 2019 Dec 15;696:133966. doi: 10.1016/j.scitotenv.2019.133966. Epub 2019 Aug 18.
Understanding the redistribution and retention of chromium(VI) (Cr(VI)) co-precipitated with silicate-containing ferrihydrite during aging is essential to the stabilization and immobilization of Cr(VI) in nature. In this work, Cr(VI) was removed by co-precipitated with silicate-containing ferrihydrite with various Si/Fe ratios at different precipitating pH. The co-precipitates were characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy before and after aging for 9 days at 80 °C. Results showed that silicate not only competed with Cr(VI) adsorbed on ferrihydrite surface by forming inner-sphere complexes, but also inhibited ferrihydrite transforming into more stable and compact iron phases. Ferrihydrite only transformed to hematite at pH 5.0, and converted to hematite and goethite at pH 7.5 and 10.0. Cr(VI) was initially removed by silicate-containing ferrihydrite with the removal efficiencies > 99.64% at initial pH of 5.0, and it was obviously incorporated into hematite and goethite during the transformation of ferrihydrite. The transformation products influenced the redistribution of Cr(VI), which was beneficial to the retention of Cr(VI) inside the co-precipitates, but not conducive to the adsorption for Cr(VI). The findings that Cr(VI) was removed by a common and metastable precursor of silicate-containing ferrihydrite can promote understanding of three-dimensional transfer and behavior of Cr(VI) during the transformation of silicate-containing ferrihydrite.
了解铬(VI)（Cr(VI)）与含硅铁氢氧化物共沉淀后在老化过程中的再分配和保留对于 Cr(VI)在自然界中的稳定和固定化至关重要。在这项工作中，通过在不同沉淀 pH 值下用不同 Si/Fe 比与含硅铁氢氧化物共沉淀去除 Cr(VI)。共沉淀物在老化 9 天后在 80°C 下用 X 射线衍射、透射电子显微镜、傅里叶变换红外光谱和 X 射线光电子能谱进行了表征。结果表明，硅酸盐不仅通过形成内圈络合物与吸附在铁氢氧化物表面的 Cr(VI)竞争，而且还抑制铁氢氧化物转化为更稳定和致密的铁相。铁氢氧化物仅在 pH 5.0 下转化为赤铁矿，而在 pH 7.5 和 10.0 下转化为赤铁矿和针铁矿。Cr(VI)最初通过含硅铁氢氧化物以初始 pH 值为 5.0 时去除效率>99.64%，并且在铁氢氧化物转化过程中明显掺入赤铁矿和针铁矿中。转化产物影响 Cr(VI)的再分配，这有利于 Cr(VI)在共沉淀物内部的保留，但不利于 Cr(VI)的吸附。发现 Cr(VI)是通过含硅铁氢氧化物的常见和亚稳前体去除的，这可以促进对含硅铁氢氧化物转化过程中 Cr(VI)的三维迁移和行为的理解。
