Research progress on the distribution and occurrence characteristics of rare earth elements in coal and coal-fired products

Rare earth elements are widely used in permanent magnet, metallurgy, hydrogen storage materials and other fields due to their special properties, and their consumption is increasing year by year. China is a big country with rare earth element reserves. By 2020, China's rare earth element mineral production in the world accounted for a decline year by year, and has rebounded in recent years, but it is necessary to find and develop other materials that can be used as a supply source of rare earth elements. Coal, as a kind of organic mineral, can enrich rare earth elements during its formation. Deeply recognizing the content and occurrence state of rare earth elements in coal is of great significance for the subsequent research on the occurrence, extraction and recovery of rare earth elements in combustion products. Scholars at home and abroad studied the content of rare earth elements in coal by era, region and coal grade, and the research on the occurrence state of rare earth elements in coal and its combustion products was summarized to clearly understand the distribution characteristics of rare earth elements in coal and its combustion products in China. Current research shows that the average rare earth element content in China's coal is twice the average rare earth element content in coal in the world. Late Permian period coal is relatively rich in rare earth elements. Rare earth elements in coal mainly exist in Portland state. The properties of rare earth elements are stable, and the coal can be enriched several times to tens of times in the combustion products after combustion, mainly in the non-magnetic fine fly ash particles. In order to improve the representativeness and accuracy of statistical data, factors such as the coverage rate of coal mining area, sample processing method and trace element testing method should be comprehensively considered in the statistics of rare earth elements content in coal. Direct observation, characterization test methods, stepwise chemical extraction methods and mathematical statistical methods were synthesized to obtain a more reliable occurrence state. China has a considerable amount of coal consumption, with the main energy supply being thermal power generation. The production of coal-fired products is huge, and rare earth elements in coal can be enriched dozens of times in coal-fired products. The distribution pattern of rare earth elements in coal-fired products of power plants is explored, and corresponding recovery processes are proposed based on the difficulty of extraction, in order to achieve the resource utilization of coal-fired products.