Extractability and mineralogical evaluation of rare earth elements from Waterberg Coalfield run-of-mine and discard coal

IF 6.9 1区 工程技术 Q2 ENERGY & FUELS
Agnes Modiga, Orevaoghene Eterigho-Ikelegbe, Samson Bada
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Abstract

This study explores the extraction of rare earth elements (REEs) from high-ash run-of-mine and discard coal sourced from the Waterberg Coalfield. Three distinct methods were employed: (1) ultrasonic-assisted caustic digestion; (2) direct acid leaching; and (3) ultrasonic-assisted caustic-acid leaching. Inductively coupled plasma mass spectrometry was utilized to quantify REEs in both the coals and resultant leachates. Leaching the coals with 40% NaOH at 80 °C, along with 40 kHz sonication, yielded a total rare earth element (TREE) recovery of less than 2%. Notable enrichment of REEs was observed in the run-of-mine and discard coal by 17% and 19%, respectively. Upon employing 7.5% HCl, a recovery of less than 11.0% for TREE was achieved in both coal samples. However, leaching the caustic digested coal samples with 7.5% HCl significantly enhanced the TREE recovery to 88.8% and 80.0% for run-of-mine and discard coal, respectively. X-ray diffraction analysis identified kaolinite and quartz as the predominant minerals. Scanning electron microscopy-energy dispersive microanalysis revealed monazite and xenotime as the REE-bearing minerals within the coal samples. These minerals were found either liberated, attached to, or encapsulated by the clay-quartz matrices. Further mineralogical assessments highlighted the increased REE concentrations in coals post-caustic digestion and subsequent recovery during acid leaching. This increase was attributed to the partial dissolution of kaolinite encapsulating the RE-phosphates and the digestion of REE-bearing minerals. Notably, undissolved REE-bearing elements in the caustic-acid-leached coal indicated the necessity of harsh leaching conditions to augment REE recovery from these coal samples.

Abstract Image

瓦特贝格煤田采煤和弃煤中稀土元素的可提取性和矿物学评价
本研究探讨了从沃特伯格煤田的高灰分原煤和弃煤中提取稀土元素(REEs)的方法。采用了三种不同的方法:(1) 超声波辅助苛性钠消化法;(2) 直接酸浸法;(3) 超声波辅助苛性钠-酸浸法。利用电感耦合等离子体质谱法对煤炭和浸出液中的 REEs 进行量化。在 80 °C 下用 40% 的 NaOH 和 40 kHz 的超声波对煤炭进行浸出,其稀土元素总回收率低于 2%。在原煤和弃煤中观察到的稀土元素富集率分别为 17% 和 19%。在使用 7.5% HCl 时,两个煤样中的 TREE 回收率均低于 11.0%。然而,用 7.5% HCl 浸取经过苛性钠消化的煤样后,矿前煤和废弃煤的 TREE 回收率分别显著提高到 88.8% 和 80.0%。X 射线衍射分析确定高岭石和石英为主要矿物。扫描电子显微镜-能量色散显微分析显示,煤样中的独居石和氙石是含 REE 的矿物。这些矿物或被释放出来,或附着在粘土-石英基质上,或被粘土-石英基质包裹。进一步的矿物学评估表明,在苛性钠消化后和随后的酸浸出过程中,煤炭中的 REE 浓度有所增加。这种增加可归因于包裹稀土磷酸盐的高岭石的部分溶解和含稀土元素矿物的消化。值得注意的是,苛性碱-酸浸出煤中未溶解的含 REE 元素表明,必须在苛刻的浸出条件下才能提高这些煤样的 REE 回收率。
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来源期刊
CiteScore
11.40
自引率
8.40%
发文量
678
审稿时长
12 weeks
期刊介绍: The International Journal of Coal Science & Technology is a peer-reviewed open access journal that focuses on key topics of coal scientific research and mining development. It serves as a forum for scientists to present research findings and discuss challenging issues in the field. The journal covers a range of topics including coal geology, geochemistry, geophysics, mineralogy, and petrology. It also covers coal mining theory, technology, and engineering, as well as coal processing, utilization, and conversion. Additionally, the journal explores coal mining environment and reclamation, along with related aspects. The International Journal of Coal Science & Technology is published with China Coal Society, who also cover the publication costs. This means that authors do not need to pay an article-processing charge.
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