Research status and prospect of rare earth elements in coal

As a strategic resource, rare earths are widely used in the defense industry and high-tech fields. As a major producer and exporter of rare earths, traditional rare earth resource of China has been declining. Therefore, expanding China's reserves of rare earth resources has important economic value and strategic significance. Rare earth elements can be enriched in coal under specific geological conditions, and even reach industrial grades. In recent years, coal geologists have carried out lots of researches on rare earth elements in coal and have made great progress. In this paper, the content of rare earth elements in 125 samples from Ordos in Xinjiang, Muli in Qinghai, Yuanyang Lake in Ningxia and other places were measured,and combined with previous data, the distribution characteristics of rare earth elements in coal, occurrence state, enrichment factors, and migration laws during combustion were measured, and the separation and extraction methods of rare earth elements in fly ash were summarized, which provides theoretical basis for the resource utilization of rare earth elements in coal and coal fly ash. The content of rare earth elements in coal in China is much higher than that in America. The Erlian-Hailaer basin and southwestern Sichuan-Yunnan-Guangxi region are the two metallogenic belts of rare earth deposits in coal. Rare earth elements mainly exist in coal in the form of rare earth minerals, organic compounds and adsorbed ions. The enrichment of rare earth elements in coal may be the result of superposition of sediment sources, transport medium, sedimentary environments, weathering leaching and magmatic activities in different periods. During coal combustion, rare earth elements, as nonvolatile elements, are further enriched in fly ash and bottom ash. Rare earth elements in coal fly ash are present in glass, REY-bearing minerals and amorphous carbon. Different types and sources of coal fly ash may be suitable for different methods of physical separation and chemical extraction. As major coal producer and consumer in the world, China has natural advantages in extracting rare earth elements from coal and fly ash. Therefore, enhancing study on the extraction of rare earth elements from coal and combustion products, and building industrial extraction of rare earth elements of the pilot plant have prospective prospect.