Integrative Study Assessing Space and Time Variations with Emphasis on Rare Earth Element (REE) Distribution and Their Potential on Ashes from Commercial (Colombian) Coal

• Type: Article in International Scientific Journal
• Date: 2022

Authors

Aurora Futuro Silva (Author) FEUP; Ana Santos (Author) FCUP; Alexandra Guedes (Author) FCUP; David Frech (Author) Other; Bruno Valentim (Author) FCUP

Journal

Title: Minerals

Vol. 46

Pages: 1-194

Publisher: MDPI

Indexing

ISI Web of Knowledge - 4 Citations

Scopus - 6 Citations

Other information

Authenticus ID: P-00W-1T5

DOI: 10.3390/min12020194

Abstract (EN): The increasing demand for rare earth elements (REEs), which is associated with their economic importance and the supply risk, has motivated the research for alternative secondary sources of these elements. Coal and coal combustion ash have been pointed out as promising REE raw materials. This research seeks to understand REE fractionation, from feed coals to ashes, considering seasonal variations, and to assess the trends within the ash fractions that can be used for further beneficiation processes. Colombian commercial feed coals, combustion ashes, and their respective fractions were sampled from a Portuguese power plant and were characterized via petrographical, mineralogical, and chemical analyses. The total REE concentrations in the feed coals studied range between 6.97 and 23.15 ppm, while, in the ashes, they vary from 159.9 to 266.6 ppm. Fly ash (FA) from electrostatic precipitator (ESP) presented higher concentrations than the bottom (BA) and economizer (ECO) ashes. Furthermore, REEs and the LREE/HREE ratio increased slightly towards the back rows of the ESP. In the feed coals, the REEs are significantly correlated with ash, and they occur in micrometric phosphate minerals intermixed with clays. In the ashes, the REEs were mostly detected in micrometric particles, with P and Al-Si as the major components. The results from the fractioned samples show that the REEs were enriched in the fine (<25 mu m) and nonmagnetic fractions of the ESP FA. A single trial combining sieving and magnetic separation enabled the attainment of a REE recovery of 53%, and a final enrichment factor of 1.25. Coal combustion ashes and their respective size fractions are promising REE raw materials; however, the REE oxide concentrations are below the economical cutoff of 1000 ppm.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 32