Assessment of the potential of polish fly ashes as a source of rare earth elements

Abstract

Polish energy sector is based on processing of fossil fuels, especially hard coal and lignite. The production of energy from fossil fuels generates large amounts of waste, among which fly ash is distinguished.As the demand for REY increased, alternative sources of these elements began to be desired, including apatite phosphogypsum and ashes from hard coal and lignite combustion.The article presents the results of a comprehensive physicochemical study of 16 Polish fly ashes. The objective was to (i) assess their usefulness as potential alternative sources of rare earth elements and (ii) demonstrate the relationship of rare earth elements with phase and chemical composition, which may be useful in attempts to recover these metals from ashes.The share of REY in the studied Polish fly ashes originating from hard coal combustion is at the level of 300–360 ppm, rarely 500 ppm and, converted to REO oxides, is lower than the value of 1000 ppm considered as the border limit allowing the successful recovery of these metals from low-carbonated coal.Polish fly ashes can be included in the REY prospective raw materials due to the values of the Coutl prospective coefficient, which range from 0.93 to 1.37 (the average Coutl is 1.10), and this coefficient is characterized by low variability (V = 11%).Significant positive and high values of the REY correlation coefficient with the dominant phase components of fly ash (mullite, amorphous enamel) may indicate the desirability of their separation for obtaining these metals, in particular MREY and HREY.Significant positive and high values of the REY correlation coefficient with chemical components such as TiO2, Al2O3, P2O5 and K2O of fly ash may indicate the desirability of grain separation rich in these ingredients to obtain rare earth elements.