Department of Chemical and Biochemical Engineering, University of Iowa, Iowa City, Iowa 52242, USA.
Analyst. 2013 Jan 21;138(2):451-60. doi: 10.1039/c2an36318f.
Airborne fly ash from coal combustion may represent a source of bioavailable iron (Fe) in the open ocean. However, few studies have focused on Fe speciation and distribution in coal fly ash. In this study, chemical imaging of fly ash has been performed using a dual-beam focused ion beam/scanning electron microscope (FIB/SEM) system for a better understanding of how simulated atmospheric processing can modify the morphology, chemical composition and element distribution within individual particles. A novel approach has been applied for cross-sectioning fly ash particles with the FIB in order to explore element distribution within the interior of individual particles. Our results indicate that simulated atmospheric processing can cause disintegration of aluminosilicate glass, a dominant material in fly ash particles. Fe present in the inner core of fly ash spheres within the aluminosilicate phase is more easily mobilized compared with Fe oxides present as surface aggregates on the exterior of fly ash spheres. Fe dissolution depends strongly on Fe speciation in fly ash particles. The approach for preparation of a cross-sectioned specimen described here opens up new opportunities for particle microanalysis, particularly with respect to inorganic refractive materials like fly ash and mineral dust.
燃煤飞灰中的空气传播飞灰可能代表了开阔海洋中生物可用铁（Fe）的一个来源。然而，很少有研究集中于研究煤飞灰中 Fe 的形态和分布。在这项研究中，采用双束聚焦离子束/扫描电子显微镜（FIB/SEM）系统对飞灰进行了化学成像，以便更好地了解模拟大气处理如何改变单个颗粒内部的形态、化学成分和元素分布。应用了一种新的方法，通过 FIB 对飞灰颗粒进行了横截面切割，以探索单个颗粒内部的元素分布。我们的结果表明，模拟大气处理会导致铝硅酸盐玻璃的解体，而铝硅酸盐玻璃是飞灰颗粒中的主要物质。与作为飞灰球体外部表面聚集体存在的 Fe 氧化物相比，存在于铝硅酸盐相中的飞灰球体内部核心中的 Fe 更容易被迁移。Fe 的溶解强烈依赖于飞灰颗粒中的 Fe 形态。这里描述的用于制备横截面样本的方法为颗粒微分析开辟了新的机会，特别是对于飞灰和矿物粉尘等无机折射材料。
