Study on the Enrichment of Rare Earth Elements Between Coals and Their By-products at Coal-fired Power Plants

Abstract

Rare earth elements (REE) play an important role in industrial applications. As unbalanced between supply and demand of REE increases, it has stimulated the global search for alternative non-traditional rare earth sources. Coal and coal by-products are considered as potential rare earth sources. In this study, the content of rare earth elements in coal and its by-products of four typical coal-fired power plants in China were determined by inductively coupled plasma-mass spectrometry (ICP-MS) method. The results show that the outlook coefficients of rare earth elements in four coals and their combustion products are higher than 0.7. The total content of critical rare earth elements is more than 30%. The rare earth content in fly ash of three power plants is higher than the world average, and it has great potential to recover rare earth elements. Rare earth elements from La to Lu, that is, as the atomic number is from low to high, the distribution of rare earth elements are also decreased from left to right. The content of rare earth elements in different coal types is different. With the increase of ash content in coal, the content of rare earth elements increases. The rare earth elements are highly positively correlated with the main components of ash (Si, Al and Fe), indicating that rare earth elements may be mainly exist in inorganic minerals. The content of rare earth elements in fly ash and slag is significantly higher than that in raw coal. The enrichment ratio and enrichment factor of the rare earth elements are larger than that of the slag, indicating that the rare earth elements are easily enriched in the fly ash after the raw coal is burned. The mass balance rate of rare earth elements in the combustion process of coal in four power plants is estimated. Except for the small escape of Ce,Y, Er, Yb and Lu elements of A and C power plant, the mass balance rate of other elements and total rare earth in other power plants are between 0 and 81.2%. Therefore, it can be concluded that, the rare earth elements are mainly concentrated in the slag and fly ash during coal combustion.