Recent global geopolitical tensions have exacerbated the scarcity of rare-earth elements (REEs), which are critical across many industries. REE-rich coal fly ash (CFA), a coal combustion residual, has been proposed as a potential source. Conventional REE-CFA recovery methods are energy- and material-intensive and leach elements indiscriminately. This study has developed a new valorization process based on the ionic liquid (IL) betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf₂N]) for preferential extraction of REEs from different CFAs. Efficient extraction relies on [Hbet][Tf₂N]’s thermomorphic behavior with water: upon heating, water and the IL form a single liquid phase, and REEs are leached from CFA via a proton-exchange mechanism. Upon cooling, the water and IL separate, and leached elements partition between the two phases. REEs were preferentially extracted over bulk elements from CFAs into the IL phase and then recovered in a subsequent mild-acid stripping step, regenerating the IL. Alkaline pretreatment significantly improved REE leaching efficiency from recalcitrant Class-F CFAs, and additional betaine improved REE and bulk element separation. Weathered CFA showed slightly higher REE leaching efficiency than unweathered CFA, and Class-C CFA demonstrated higher leaching efficiency but less selective partitioning than Class-F CFAs. Significantly, this method consistently exhibits a particularly high extraction efficiency for scandium across different CFAs.

中文翻译：

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使用可回收离子液体从粉煤灰中优先回收稀土元素

最近的全球地缘政治紧张局势加剧了稀土元素 (REE) 的稀缺性，稀土元素对许多行业都至关重要。富含 REE 的粉煤灰 (CFA)，一种煤燃烧残余物，已被提议作为潜在来源。传统的 REE-CFA 回收方法是能源和材料密集型的，并且会不加选择地浸出元素。本研究开发了一种基于离子液体 (IL) 甜菜碱双（三氟甲基磺酰基）亚胺 ([Hbet][Tf ₂ N]) 的新工艺，用于从不同的 CFA 中优先提取 REE。高效提取依赖于[Hbet][Tf ₂N] 与水的热变形行为：加热后，水和离子液体形成单一液相，稀土元素通过质子交换机制从 CFA 中浸出。冷却后，水和离子液体分离，浸出的元素在两相之间分配。REE 优先于 CFA 中的整体元素提取到 IL 相，然后在随后的弱酸汽提步骤中回收，再生 IL。碱性预处理显着提高了顽固的 F 类 CFA 的 REE 浸出效率，额外的甜菜碱改善了 REE 和大块元素的分离。风化 CFA 显示出比未风化 CFA 略高的 REE 浸出效率，C 级 CFA 显示出更高的浸出效率，但比 F 级 CFA 的选择性分配更低。显着地，