Department of Energy, Environmental and Chemical Engineering, Washington University , St. Louis, Missouri 63130, United States.
Environ Sci Technol. 2014;48(1):299-306. doi: 10.1021/es403777w. Epub 2013 Dec 18.
Heterogeneous coprecipitation of iron and aluminum oxides is an important process for pollutant immobilization and removal in natural and engineered aqueous environments. Here, using a synchrotron-based small-angle X-ray scattering technique, we studied heterogeneous nucleation and growth of Fe(III) (hydr)oxide on quartz under conditions found in acid mine drainage (at pH = 3.7 ± 0.2, [Fe(3+)] = 10(-4) M) with different initial aqueous Al/Fe ratios (0:1, 1:1, and 5:1). Interestingly, although the atomic ratios of Al/Fe in the newly formed Fe(III) (hydr)oxide precipitates were less than 1%, the in situ particle size and volume evolutions of the precipitates on quartz were significantly influenced by aqueous Al/Fe ratios. At the end of the 3 h experiments, with aqueous Al/Fe ratios of 0:1, 1:1, and 5:1, the average radii of gyration of particles on quartz were 5.7 ± 0.3, 4.6 ± 0.1, and 3.7 ± 0.3 nm, respectively, and the ratio of total particle volumes on quartz was 1.7:3.4:1.0. The Fe(III) (hydr)oxide precipitates were poorly crystallized, and were positively charged in all solutions. In the presence of Al(3+), Al(3+) adsorption onto quartz changed the surface charge of quartz from negative to positive, which caused the slower heterogeneous growth of Fe(III) (hydr)oxide on quartz. Furthermore, Al affected the amount of water included in the Fe(III) (hydr)oxides, which can influence their adsorption capacity. This study yielded important information usable for pollutant removal not only in natural environments, but also in engineered water treatment processes.
铁和铝氧化物的异质共沉淀是自然和人为水环境污染中污染物固定和去除的重要过程。在这里，我们使用基于同步加速器的小角 X 射线散射技术，在酸性矿山排水（pH = 3.7 ± 0.2，[Fe(3+)] = 10(-4) M）条件下研究了铁（III）（水合）氧化物在石英上的异质成核和生长，初始水相 Al/Fe 比（0:1、1:1 和 5:1）不同。有趣的是，尽管新形成的 Fe(III)（水合）氧化物沉淀物中 Al/Fe 的原子比小于 1%，但沉淀在石英上的原位颗粒尺寸和体积演变明显受水相 Al/Fe 比的影响。在 3 小时实验结束时，水相 Al/Fe 比为 0:1、1:1 和 5:1 时，沉淀在石英上的颗粒的转动半径平均值分别为 5.7 ± 0.3、4.6 ± 0.1 和 3.7 ± 0.3nm，且石英上总颗粒体积比分别为 1.7:3.4:1.0。Fe(III)（水合）氧化物沉淀结晶较差，在所有溶液中均带正电荷。在 Al(3+)存在的情况下，Al(3+)吸附在石英上使石英的表面电荷从负变为正，从而导致 Fe(III)（水合）氧化物在石英上的异质生长较慢。此外，Al 影响 Fe(III)（水合）氧化物中包含的水量，从而影响其吸附能力。本研究为污染物去除提供了重要信息，不仅在自然环境中，而且在人为水处理过程中都可用。
