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

作　　者：Agnes Modiga Orevaoghene Eterigho-Ikelegbe Samson Bada 

机构地区：[1]DSI-NRF SARChI Clean Coal Technology Research Group,School of Chemical and Metallurgical Engineering,Faculty of Engineering and the Built Environment,University of the Witwatersrand,Private Bag X3,Wits,Johannesburg 2050,South Africa [2]Mintek,200 Malibongwe Drive,Randburg 2194,South Africa

出　　处：《International Journal of Coal Science & Technology》2024年第5期36-47,共12页国际煤炭科学技术学报(英文)

基　　金：The research was also supported by the National Research Foundation(NRF)of South Africa's SARChI Clean Coal Technology Grant(86421)。

摘　　要：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℃,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 microscopyenergy 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.

关 键 词：Acid leaching CAUSTIC MINERALOGICAL Pre-digestion REE recovery Ultrasonic 

分 类 号：P61[天文地球—矿床学]