Fly ash derived from the combustion of an eastern Kentucky high volatile bituminous coal blend was, as discussed in previous studies, beneficiated to yield a − 75-μm product with a reduction in the carbon and spinels. The beneficiated fly ash was reacted with a strong acid in a pilot-scale unit to extract rare earth elements (REE) and other major and minor elements. In this study, polished, epoxy-bound pellets of the beneficiated and acid-extracted ashes were examined via scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Selected slices of the polished section were extracted using a focused ion beam (FIB) technology and further examined via transmission electron microscopy (TEM) and EDS. The bulk chemistry of the original feed ash (not studied by microbeam methods), the beneficiated ash, and the acid-extracted ash exhibit similar Upper Continental Crust-normalized REE patterns. The bulk chemistry indicates that the concentrations of the major oxides (aside from SiO2), REE, V, Cr, Mn, Ni, As, Rb, Sr, Zr, Ba, and Pb are less in the processed ash compared to the beneficiated ash. The fly ashes have H-type distributions (LaN < LuN) with a strong M-type (medium type: LaN/SmN < 1, GdN/LuN > 1) contribution. Among the REE and Y, SEM-EDS and TEM-EDS showed the presence of zircon with Y (and Ce, Nd, and Gd, perhaps from an adjacent monazite); xenotime; a Dy-rich xenotime-structure mineral: and monazite with light REE (La, Ce, Pr, Nd, and Sm), Gd, Dy, Er, and Th. Glassy Al-Si-rich fly ash spheres showed the presence of Ce, Nd, Sm, and Dy but no discernable minerals at the scale of the SEM view. Certain spheres showed 2- to 4-μm amorphous rims surrounding nano-crystalline cores. As with the depletion of elements in the bulk fly ash, the amorphous rims showed a relative increase in Si and a depletion or apparent elimination of other elements, including the REE. It is possible that the apparent absence of 2- to 4-μm particles may mean that these particles were totally or largely dissolved by the acid or as a consequence of multiple wash-filtration cycles to remove leachate from the spent ash. Processing of a combination of a finer size than processed in this pilot-scale investigation and/or more fractured particles, perhaps via a pre-processing step, would permit a greater penetration of the acid into the interior of the fly ash particles, leading to a greater recovery of REE.

中文翻译：

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对肯塔基州选矿粉煤灰中稀土元素中试规模酸萃取产生的废灰进行电子微束研究


正如之前的研究所讨论的，从肯塔基州东部高挥发性烟煤混合物燃烧中获得的粉煤灰被采纳产生 − 75 μm 的产品，碳和尖晶石减少。选矿飞灰在中试规模装置中与强酸反应，以提取稀土元素 （REE） 和其他主要和次要元素。在这项研究中，通过扫描电子显微镜 （SEM） 和能量色散光谱 （EDS） 检查了选矿灰和酸萃取灰烬的抛光、环氧树脂结合颗粒。使用聚焦离子束 （FIB） 技术提取抛光切片的选定切片，并通过透射电子显微镜 （TEM） 和 EDS 进一步检查。原始原料灰（未通过微束法研究）、选矿灰和酸提取灰的本体化学性质表现出相似的上大陆地壳归一化 REE 模式。本体化学表明，与选矿灰分相比，加工灰分中主要氧化物（SiO2 除外）、REE、V、Cr、Mn、Ni、As、Rb、Sr、Zr、Ba和 Pb 的浓度较低。飞灰具有 H 型分布 （LaN < LuN），具有很强的 M 型（中等型：LaN/SmN < 1，GdN/LuN > 1）贡献。在 REE 和 Y 中，SEM-EDS 和 TEM-EDS 显示存在带有 Y（以及 Ce、Nd 和 Gd，可能来自相邻的独居石）的锆石;钇钇 （xenotime）;富含 Dy 的钇石结构矿物：和具有轻质 REE（La、Ce、Pr、Nd 和 Sm）、Gd、Dy、Er 和 Th. 富含玻璃硅的飞灰球体显示存在 Ce、Nd、Sm 和 Dy，但在 SEM 视图的尺度上没有可辨别的矿物。某些球体在纳米晶核周围显示出 2 至 4 μm 的非晶边缘。 与散装飞灰中元素的消耗一样，非晶态边缘显示出 Si 的相对增加，而其他元素（包括 REE）的消耗或明显消除。明显不存在 2 至 4 μm 颗粒可能意味着这些颗粒被酸完全或大部分溶解，或者由于多次洗涤过滤循环以去除废灰烬中的渗滤液。加工比中试规模研究中加工的更细尺寸和/或更多断裂颗粒的组合，可能通过预处理步骤，将允许酸更好地渗透到飞灰颗粒内部，从而更好地回收 REE。