Distribution and Speciation of Rare Earth Elements in Coal Fly Ash from the Qianxi Power Plant, Guizhou Province, Southwest China

Abstract

Coal fly ash (CFA), hazardous to the environment and human health, has been considered to be a potential alternative source for rare earth elements (REEs) in recent years. However, information on how REEs distribute and occur in coal fly ash is still incomplete. In this work, particle size analysis, inductively coupled plasma–mass spectrometry, scanning electron microscopy, and electron probe microanalysis were applied to study the occurrence and distribution of REEs in a fly ash sample from the Qianxi coal-fired power plant in Guizhou province. The results show that the REEs content in the CFA was 630.51 ppm. Wet grinding-enhanced leaching experiments revealed that a part of the rare earth particles was encapsulated within the glass body. These rare earth particles could be liberated and released to a certain extent by wet grinding, which would increase the acid-leaching recovery of REEs from 23.49% to 41.68%. This study classifies the speciation of REEs in coal fly ash as (1) amorphous glassy particles with REE minerals or compounds encapsulated inside; (2) amorphous glassy particles with REEs distributed throughout; and (3) discrete REE minerals or compounds. The results of this study are a basis for developing an economically viable and environmentally sustainable technology for recovering REEs from CFA.

Separation of coal combustion residue for critical element extraction and other bulk uses

“…Franus et al 7 reported 500–600 mg kg −1 of total REEs in some Polish fly ash, a similar concentration (630 mg kg −1 ) was reported by Wu et al 8 for a fly ash sample from the Guizhou province of China. Blissett et al 9 compared six fly ash samples from the UK and Poland, and found that the concentration of REEs varied from 246 to 481 mg kg −1 .…”

Potential Future Alternative Resources for Rare Earth Elements: Opportunities and Challenges

“…Table 4 presents the potential of these alternative REE resources. A big country like China uses about 4 billion tons of coal for its power plants to generate electricity which produces about 500-550 million tons of fly ash [85]. Coal and coal combustion products such as fly ash, bottom ash, and incinerator ash are found to contain significant amounts of REE as most coal samples contain minor amounts of rhabdophane, Nd, Ce, La (PO4).H2O, monazite, (Ce, La, Th, Nd)PO4, and xenotime (Y, Er)PO4 [86].…”

Ecological and Health Risks Attributed to Rare Earth Elements in Coal Fly Ash

“…Coal fly ash (CFA), a byproduct of coal burning in thermal power plants, has recently gained attention as a potential resource for REYs [ 9 , 10 , 11 ]. While challenges exist regarding low concentrations and extraction complexities since REYs are encapsulated within glassy particles [ 12 ], ongoing research and technological advancements are making it increasingly feasible to recover REYs from this unconventional source [ 13 ]. Further, this could contribute to more sustainable REY supply chains.…”

“…However, CFA poses a severe risk to both the environment [ 14 , 15 , 16 ] and human health due to its composition and potential for leaching [ 17 , 18 , 19 , 20 , 21 ] and dispersion [ 22 , 23 , 24 ]. The danger from CFA arises from the presence of various toxic substances, particularly heavy metal(loid)s (HMs), including As, Pb, Hg, Cd, Cr, and Ni [ 12 , 25 ]. These HMs are naturally present in coal and become concentrated in the ash during combustion.…”