Modes of occurrence of rare earth-bearing minerals in South African coal and ash samples using electron microscopy

IF 4.9 2区工程技术 Q1 ENGINEERING, CHEMICAL

Minerals Engineering Pub Date : 2025-05-20 DOI:10.1016/j.mineng.2025.109436

Sanki Biswas, Nicola J. Wagner, Ofentse M. Moroeng

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引用次数: 0

Abstract

Rare earth elements and yttrium (REY) are crucial for modern technologies. This study investigated the modes of occurrence, mineral hosts, and distribution in coal and laboratory-derived coal-ash samples from the Soutpansberg Coalfield (South Africa) using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), mineral liberation analysis (MLA), X-ray diffraction (XRD), and inductively coupled plasma mass spectrometry (ICP-MS). The mineral composition of the studied coal primarily comprises of silicates, predominantly kaolinite (avg. 24.1 wt%; whole coal basis), quartz (avg. 13.6 wt%), alongside carbonates (avg. 12.9 wt%) and pyrite (∼0.1 wt%). Although the coal-ash samples also have silicates (avg. 78.9 wt%), phosphates (monazite, xenotime), titanium oxides, and zircon. Average REY concentrations are 241.3 mg/kg in the coal and 468.3 mg/kg in the coal-ash, reaching a maximum of 957.4 mg/kg with multi-day multi-acid digestion, suggesting enhanced liberation.

Backscattered electron (BSE) images obtained via SEM-EDS and MLA reveal monazite and xenotime as the major REY-bearing minerals in both the coal and coal-ash samples, with some REY hosted by carbonates. In the coal, micron-scale REY-bearing minerals are adsorbed onto the surfaces of major and minor minerals such as quartz, kaolinite, zircon, and Ti-oxides. The REY-bearing minerals in the coal-ash are encapsulated within new phases, likely amorphous or aluminosilicates. The LREY and MREY are associated with monazite, quartz, carbonate, zircon, and Ti-oxide phases, and HREY with xenotime. Particles ∼ 1 μm in size show better liberation, which may potentially enhance extractability. MLA offers higher-resolution imaging than SEM-EDS, enabling better identification of micron-size REY particles.

These findings underscore the importance of understanding REY mineralogical associations and liberation dynamics to optimize extraction and enhancing resource recovery from coal and its by-products.

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利用电子显微镜研究南非煤和灰样品中含稀土矿物的赋存模式

稀土元素和钇（REY）对现代技术至关重要。本文利用扫描电子显微镜、能量色散x射线能谱（SEM-EDS）、矿物解离分析（MLA）、x射线衍射（XRD）和电感耦合等离子体质谱（ICP-MS）研究了南非South pansberg煤田煤和实验室衍生煤灰样品的赋存模式、矿物宿主和分布。研究煤的矿物组成主要由硅酸盐组成，主要是高岭石（平均24.1% wt%）；全煤基)，石英（平均13.6 wt%），以及碳酸盐（平均12.9 wt%）和黄铁矿（约0.1 wt%）。尽管煤灰样品也含有硅酸盐（平均78.9%）、磷酸盐（独居石、xenotime）、氧化钛和锆石。煤中REY的平均浓度为241.3 mg/kg，煤灰中REY的平均浓度为468.3 mg/kg，经过多日多酸消化，REY的浓度最高可达957.4 mg/kg，表明REY的释放增强。通过SEM-EDS和MLA获得的背散射电子（BSE）图像显示，煤和煤灰样品中主要含REY矿物为独居石和xenotime，部分REY矿物为碳酸盐。在煤中，微尺度的含rey矿物吸附在石英、高岭石、锆石、钛氧化物等主要矿物和次要矿物的表面。煤灰中的含稀土矿物被包裹在新的相中，可能是无定形的或铝硅酸盐。LREY和MREY具有独居石、石英、碳酸盐、锆石和钛氧化物相，而HREY具有xenotime相。粒径为1 μm的颗粒具有较好的解离性，有可能提高可提取性。MLA提供比SEM-EDS更高分辨率的成像，能够更好地识别微米尺寸的REY颗粒。这些发现强调了了解REY矿物学关联和释放动力学对于优化煤炭及其副产品的开采和提高资源回收率的重要性。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Minerals Engineering 工程技术-工程：化工

CiteScore

8.70

自引率

18.80%

发文量

519

审稿时长

81 days

期刊介绍： The purpose of the journal is to provide for the rapid publication of topical papers featuring the latest developments in the allied fields of mineral processing and extractive metallurgy. Its wide ranging coverage of research and practical (operating) topics includes physical separation methods, such as comminution, flotation concentration and dewatering, chemical methods such as bio-, hydro-, and electro-metallurgy, analytical techniques, process control, simulation and instrumentation, and mineralogical aspects of processing. Environmental issues, particularly those pertaining to sustainable development, will also be strongly covered.