Abstract
The article covers the issues related to the characteristics, application, and some methods of rare earth elements (REEs) recovery from coal fly ashes. REEs are elements with growing demand and a very wide range of application, especially when it comes to modern technologies. The conducted analysis and price forecast proved the existing upward tendency, and this confirmed the need to search for new REE sources, among industrial waste (proecological effect). The development of the REE recovery technology would involve solving several problems related to REE speciation, optimization of factors controlling their extractivity and selection of the REE separation method from obtained extraction solutions with a very extreme pH and complicated composition. The paper presented advantages and disadvantages of usually used methods of REE separation from coal fly ashes, like physical and acid–base leaching. It was also presented alternative REE recovery techniques in the form of membrane and biological methods and based on ion liquids (ILs) or chelating agents. The directions of further modifications, which will allow the efficient REE recovery were presented. The aim of this article was to propose specific solutions based on the creation of appropriate multistage method of REE recovery. It will be a combination of magnetic and size separation, acid–base leaching (including roasting in justified cases), removal of matrix elements with ILs (Al, Si, and Fe), and finally REE membrane separation, allowing one to obtain the appropriate process efficiency.
Highlights
The rare earth elements (REEs) group consists of seventeen chemical elements, including fifteen lanthanides and yttrium and scandium [1,2]
The results suggested that the extraction of REE from the aluminosilicate glass fraction would allow the recovery of a significant amount of REEs
The above paper covered the issues related to the characteristics, application, and selected methods of REE recovery from coal fly ashes
Summary
The rare earth elements (REEs) group consists of seventeen chemical elements, including fifteen lanthanides and yttrium and scandium (occur in the same ore deposits and have similar chemical properties) [1,2] All these elements exist in the form of trace quantities in natural materials, which are unevenly distributed around the world (estimated average concentration in the Earth’s crust ranging from around 130 to 240 μg/g) [1,3]. The 4f electrons have lower energies and are a part of the ion core, lying inside, surrounded by outer valence electrons They do not participate directly in the formation of bonds with other elements and the formation of chemical compounds. The phenomenon called lanthanide contraction is caused by an increase in nuclear charge that is not completely screened by the additional
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