Since the 2015 closure of Mountain Pass in California, the United States has not had an economical domestic supply of rare earth elements (REEs). Research involving coal and coal-related materials as alternatives sources of REEs has been growing owning to that each is enriched in REEs relative to average crustal abundance. However, the issue arises that REEs content in any given coal or coal-related material is variable from sample to sample. In order to know which coal and coal related-materials are worth being utilized as a REE resource, a precise analytical procedure must be first developed. Here we present such an analytical procedure that would be able to quantify down to the part per billion level of REEs in any given coal or coal related-materials. Our procedure first involved digesting solid coal or coal-related material via microwave acid digestion. After the digestion, inductively couple mass spectrometry (ICP-MS) was utilized in order to precisely quantify each REE concentration of the material. REE isotopes with the least interferences and isobaric overlaps were chosen for the ICP-MS analysis. A REE certified reference material (CRM) was always used to monitor the sample preparation procedure and instrument performance. For samples with very low REEs concentration, the iron hydroxide (Fe(OH)<sub>3</sub>) co-precipitation method was used to pre-concentrate REEs. Coal and coal fly ash samples collected at various sites in both the Southwest and Midwest of the United States were analyzed for REEs by using above analytical protocol. Our study reveals an increase in the total rare earth concentration in the coal fly ash versus the unburnt coal, with the average REE concentration among the coal fly ash being 91.07 ppm and the average REE concentrations among the coals being 53.10 ppm.

Analytical procedure for precise detection of rare earth elements in coal and coal-related materials

2019 Spring National Meeting

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