The conditions under which coal ash is formed largely dictates the association of valuables within its matrix. An optimum utilization of coal waste in commercial level is only feasible upon performing an in-depth comparative study of fly ash (FA), bottom ash (BA) and laboratory ash (LA). In the present study, two coal ash samples were acquired from a power plant in India (1200–1300 °C), whereas the one under laboratory conditions was prepared at 815 °C. The total concentrations of rare earth elements (hereafter abbreviated as REEs) were- LA (873 ppm), FA (509 ppm) and BA (373 ppm) and their respective outlook coefficients were-LA (0.78), FA (0.87) and BA (0.88). Sequential extraction revealed that the chosen LA possessed 40 % of the total REE in extractable form, whereas both FA and BA possessed only 10 % of the total REE in extractable form. Magnetically isolated Fe-containing matrix with 50 % FeO was observed in case of FA. Alkaline pre-treatment to enhance the extractability of REEs was performed using both NaOH and NaCO, under varying temperature from 400–850 °C. The optimum condition was deduced to be using NaOH at 400 °C. Sodium silicate was eliminated during water leaching, from which Si was precipitated at neutral pH. The leaching parameters were optimized on these alkali roasted coal ash samples, and 0.5 M tartaric acid at 90 °C stirred for 60 min demonstrated 75–80 % increase in leaching of REEs as compared to baseline leaching of 27 % (LA), 5 % (FA), 12 % (BA). Significant morphological change was observed post alkaline pre-treatment and acid leaching. NaOH roasting resulted in cracks and fractures on the surface of spherical BA and FA samples followed by development of pores during the leaching process. Solvent extraction was performed with 10 % (v/v) D2EHPA (di-(2-ethylhexyl) phosphoric acid) in kerosene with an additional scrubbing stage (5 % oxalic acid solution) to enhance the purity of REE extraction.

中文翻译：

---

实验室灰、底灰、粉煤灰中稀土元素的缔合和萃取性的比较研究：印度煤炭的视角


粉煤灰形成的条件很大程度上决定了其基质中贵重物质的组合。只有对飞灰 (FA)、底灰 (BA) 和实验室灰 (LA) 进行深入的比较研究，煤废弃物的商业化最佳利用才是可行的。在本研究中，两个煤灰样品是从印度的一家发电厂采集的（1200–1300°C），而实验室条件下的一个是在 815°C 下制备的。稀土元素（以下简称 REE）的总浓度为 - LA (873 ppm)、FA (509 ppm) 和 BA (373 ppm)，其展望系数分别为 - LA (0.78)、FA (0.87) 和 BA （0.88）。顺序萃取表明，所选的 LA 拥有可萃取形式的总 REE 的 40%，而 FA 和 BA 均仅拥有可萃取形式的总 REE 的 10%。在 FA 情况下，观察到具有 50% FeO 的磁隔离含铁基质。使用 NaOH 和 NaCO 在 400–850 °C 的不同温度下进行碱性预处理，以提高 REE 的提取率。推断最佳条件是在 400 °C 下使用 NaOH。硅酸钠在水浸过程中被消除，硅在中性pH下从中沉淀出来。对这些碱烤煤灰样品的浸出参数进行了优化，与 27% (LA)、5% 的基线浸出相比，0.5 M 酒石酸在 90 °C 下搅拌 60 分钟，稀土元素的浸出增加了 75–80% (FA), 12% (BA)。碱预处理和酸浸后观察到显着的形态变化。 NaOH 焙烧导致球形 BA 和 FA 样品表面出现裂纹和断裂，随后在浸出过程中产生孔隙。 使用 10% (v/v) D2EHPA（二-(2-乙基己基)磷酸）的煤油溶液进行溶剂萃取，并进行额外的洗涤阶段（5% 草酸溶液），以提高 REE 萃取的纯度。