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 digest...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.展开更多
基金The research was also supported by the National Research Foundation(NRF)of South Africa's SARChI Clean Coal Technology Grant(86421)。
文摘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.
