Identification of rare earth elements in synthetic and natural monazite and xenotime by visible-to-shortwave infrared reflectance spectroscopy

IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY
A. H. Dijkstra, W. H. Bakker, F. Deon, C. Marcatelli, M. P. Plokker, H. T. Hintzen
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Abstract

To support the role of proximal and remote sensing in geological rare earth element (REE) resource exploration, we studied the reflectance spectroscopy of synthetic single- and mixed-REE phosphate phases. Synthesis yielded monazite for the elements La to Gd, and xenotime for Dy to Lu and Y. Visible-to-shortwave infrared (350–2500 nm) reflectance spectra of synthetic single-REE monazites and xenotimes can be used to identify the ions responsible for the absorption features in natural monazites and xenotimes. Nd3+, Pr3+ and Sm3+ produce the main absorption features in monazites. In natural xenotime, Dy3+, Er3+, Ho3+ and Tb3+ ions cause the prevalent absorptions. The majority of the REE-related absorption features are due to photons exciting electrons within the 4f subshell of the trivalent lanthanide ions to elevated energy levels resulting from spin-orbit coupling. There are small (< 20 nm) shifts in the wavelengths of these absorptions depending on the nature of the ligands. The energy levels are further split by crystal field effects, manifested in the reflectance spectra as closely spaced (∼ 5–20 nm) multiplets within the larger absorption features. Superimposed on the electronic absorptions are vibrational absorptions in the H2O molecule or within [OH], [CO3]2− and [PO4]3− functional groups, but so far only the carbonate-related spectral features seem usable as a diagnostic tool in REE-bearing minerals. Altogether, our study creates a strengthened knowledge base for detection of REE using reflectance spectroscopy and provides a starting point for the identification of REE and their host minerals in mineral resources by means of hyperspectral methods.

Abstract Image

利用可见光-短波红外反射光谱鉴定合成和天然独居石和氙中的稀土元素
为了支持近距离和遥感技术在稀土元素(REE)资源地质勘探中的作用,我们研究了合成的单一和混合稀土元素磷酸盐相的反射光谱。合成单稀土元素独居石和混合稀土元素独居石的可见光至短波红外(350-2500 nm)反射光谱可用于识别天然独居石和混合稀土元素独居石中产生吸收特征的离子。Nd3+、Pr3+ 和 Sm3+ 在独居石中产生主要的吸收特征。在天然氙石中,Dy3+、Er3+、Ho3+ 和 Tb3+ 离子导致了普遍的吸收。大多数与 REE 相关的吸收特征都是由于光子激发了三价镧系离子 4f 子壳内的电子,使其在自旋轨道耦合作用下达到较高的能级。根据配体的性质,这些吸收的波长会有微小(20 nm)的偏移。能级在晶体场效应的作用下进一步分裂,在反射光谱中表现为较大吸收特征中间隔较近(∼ 5-20 nm)的多重。与电子吸收叠加的是 H2O 分子或 [OH]-、[CO3]2- 和 [PO4]3- 官能团中的振动吸收,但到目前为止,似乎只有与碳酸盐相关的光谱特征可用作含 REE 矿物的诊断工具。总之,我们的研究为利用反射光谱检测 REE 奠定了坚实的知识基础,并为利用高光谱方法识别矿物资源中的 REE 及其寄主矿物提供了一个起点。
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来源期刊
Physics and Chemistry of Minerals
Physics and Chemistry of Minerals 地学-材料科学:综合
CiteScore
2.90
自引率
14.30%
发文量
43
审稿时长
3 months
期刊介绍: Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are: -Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.) -General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.) -Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.) -Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.) -Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems -Electron microscopy in support of physical and chemical studies -Computational methods in the study of the structure and properties of minerals -Mineral surfaces (experimental methods, structure and properties)
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