School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
College of Engineering, Chemical Engineering, California State University, Long Beach, Long Beach, California 90840, United States.
Environ Sci Technol. 2021 Jul 6;55(13):9209-9220. doi: 10.1021/acs.est.1c00630. Epub 2021 Jun 23.
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][TfN]) for preferential extraction of REEs from different CFAs. Efficient extraction relies on [Hbet][TfN]'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.
最近的全球地缘政治紧张局势加剧了稀土元素（REEs）的稀缺性，这些元素在许多行业都至关重要。富稀土的粉煤灰（CFA）是一种煤燃烧的残余物，已被提议作为一种潜在的来源。传统的 REE-CFA 回收方法是能源和材料密集型的，并且无差别地浸出元素。本研究基于离子液体（IL）双（三氟甲基磺酰基）亚胺甜菜碱（[Hbet][TfN]）开发了一种从不同 CFA 中优先提取 REE 的新型增值工艺。有效的提取依赖于[Hbet][TfN]与水的热致相转变行为：加热时，水和 IL 形成单一液相，REEs 通过质子交换机制从 CFA 浸出。冷却后，水和 IL 分离，浸出元素在两相之间分配。REEs 优先从 CFA 进入 IL 相并在随后的温和酸浸出步骤中回收，从而再生 IL。碱性预处理显著提高了难处理的 F 类 CFA 中 REE 的浸出效率，并且额外的甜菜碱提高了 REE 和大量元素的分离。风化的 CFA 显示出比未风化的 CFA 略高的 REE 浸出效率，而 C 类 CFA 表现出比 F 类 CFA 更高的浸出效率但选择性分配较低。值得注意的是，这种方法在不同的 CFA 中对钪始终表现出特别高的提取效率。
