Comprehensive Understandings of Rare Earth Element (REE) Speciation in Coal Fly Ashes and Implication for REE Extractability
Comprehensive Understandings of Rare Earth Element (REE) Speciation in Coal Fly Ashes and Implication for REE Extractability
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DOI：
10.1021/acs.est.9b00005
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发表时间：
2019-05-07
影响因子：
11.4
通讯作者：
Tang, Yuanzhi
中科院分区：
文献类型：
--
作者：
Liu, Pan;Huang, Rixiang;Tang, Yuanzhi
近年来，从煤飞灰（CFA）中回收稀土元素（REE）被认为是一种有前途的资源回收选择。然而，CFA 中 REE 形态的定量信息及其与 REE 可提取性的相关性尚未明确。本研究通过采用从微观到整体尺度的多种分析和光谱技术并结合热力学计算，系统地研究了四个代表性 CFA 样品中的 REE 形态与可萃取性关系。鉴定了一系列含稀土元素的相，例如稀土氧化物、稀土元素磷酸盐、磷灰石、锆石和含稀土元素的玻璃相。稀土元素可以以离散颗粒的形式存在，也可以以封装在玻璃相中的颗粒形式存在，或者分布在整个玻璃相中。尽管由于每种方法的固有局限性，通过 X 射线吸收光谱和酸浸定量的 REE 形态存在一定的差异，但这两种方法都显示出相当大比例的 REE 氧化物、REE 磷酸盐、磷灰石和含 REE 的 Fe 氧化物。这项研究有助于深入了解 CFA 中的 REE 形态-分布-可提取性关系，并有助于识别与 REE 形态量化相关的不确定性。它还为复杂环境样品中稀土元素形态的未来研究提供了通用方法，并为开发有效的稀土元素回收技术奠定了知识基础。
In recent years, recovery of rare earth elements (REEs) from coal fly ashes (CFAs) has been considered as a promising resource recovery option. Yet, quantitative information on REE speciation in CFAs and its correlation with REE extractability are not well established. This study systematically investigated the REE speciation-extractability relationship in four representative CFA samples by employing multiple analytical and spectroscopic techniques across the micro to bulk scale and in combination with thermodynamic calculations. A range of REE-bearing phases are identified, such as REE oxides, REE phosphates, apatite, zircon, and REE-bearing glass phase. REEs can occur as discrete particles, as particles encapsulated in the glass phase, or distribute throughout the glass phase. Although certain discrepancies exist on the REE speciation quantified by X-ray adsorption spectroscopy and acid leaching due to intrinsic limitations of each method, both approaches show significant fractions of REE oxides, REE phosphates, apatite, and REE-bearing Fe oxides. This study contributes to an in-depth understanding of the REE speciation-distribution-extractability relationship in CFAs and can help identify uncertainties associated with the quantification of REE speciation. It also provides a general methodology for future studies on REE speciation in complex environmental samples and a knowledge basis for the development of effective REE recovery techniques.