An advanced analytical assessment of rare earth element concentration, distribution, speciation, crystallography and solid-state chemistry in fly ash
An advanced analytical assessment of rare earth element concentration, distribution, speciation, crystallography and solid-state chemistry in fly ash
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DOI：
10.1016/j.sab.2020.105950
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发表时间：
2020-08
期刊：
影响因子：
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通讯作者：
I. Okeme;P. Martin;Christopher P. Jones;R. Crane;T. Ojonimi;K. Ignatyev;T. Scott
中科院分区：
文献类型：
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作者：
I. Okeme;P. Martin;Christopher P. Jones;R. Crane;T. Ojonimi;K. Ignatyev;T. Scott
粉煤灰是一种很有前途的稀土元素替代来源。然而，目前缺乏关于含稀土矿物相及其与其他飞灰组分的关联的信息，这对从飞灰中回收稀土至关重要。本文利用一系列实验室和同步加速器x射线分析技术，对尼日利亚模拟飞灰样品中的REE、U和Th的质量分数、分布、晶体学和固态化学进行了表征，为未来的提取方法奠定了基础。对45个样品进行全酸消化后的电感耦合等离子体质谱分析显示，可回收的平均总稀土含量在442 mgkg - 1和625 mgkg - 1之间，包括超过30%的临界稀土Nd， Eu, Tb, Dy， Y和Er。粉煤灰样品中稀土元素最常与分离的独居石、xenotime和含y锆石矿物颗粒相关，其中独居石最多，可通过重选进行选矿。利用同步辐射分析技术对从复合样品中分离出的独居石颗粒进行分析，发现其具有核-壳模式，壳富含共定域的Ce、Nd和La，而核富含U和Th。发现铈在独居石中以三价和四价混合氧化态存在，高温燃烧过程使独居石结构非晶化。结果表明，粉煤灰中REE、U、Th在独居石中具有较强的协同作用和物理分布；这些知识随后可以用于优化或开发更具选择性、成本效益和环保的溶剂萃取方法，通过瞄准飞灰独居石颗粒中强共域和表面结合的REE。
Fly ash represents a promising alternative source of rare earth elements (REE). However, information on REE containing mineral phases and their association with other fly ash components, vital for REE recovery from fly ash, is currently lacking. Herein, the mass fraction, distribution, crystallography and solid-state chemistry of REE, U and Th in Nigerian simulated fly ash samples were characterised using a range of laboratory and synchrotron x-ray based analytical techniques to underpin future extraction methodologies. Inductively coupled plasma mass spectrometry following full-acid digest of forty-five samples revealed recoverable average total REE content which ranged between 442 mgkg−1and 625 mgkg−1, comprising over 30 wt% of the critical REE Nd, Eu, Tb, Dy, Y and Er. These REE within the fly ash samples were found to be most frequently associated with discrete monazite, xenotime and Y-bearing zircon mineral particles, with the former the most detected, which could be beneficiated through gravity separation. Analysis of monazite particles isolated from the composite samples through a complimentary suite of analytical synchrotron radiation techniques revealed a core-shell pattern, with the shell rich in colocalised Ce, Nd and La, and the core enrich in both U and Th. Ce in monazite was found to exist in a mixed trivalent and tetravalent oxidation state, with the monazite structure amorphized due to the high temperature combustion process. Such results demonstrate the strong co-association and physical distribution of REE, U and Th within monazite in fly ash; knowledge of which can subsequently be used to optimise or develop a more selective, cost-effective and environmentally friendly solvent extraction methodology, by targeting the strongly colocalised and surface bound REE in fly ash monazite particles.