The enhanced extraction of rare earth elements from coal gangue and coal fly ash

Abstract

Rare earth elements (REEs) are unrenewable, uneven distributed and less productive worldwide, but technological-critical and strategic important. Searching for alternative REEs resource has motivated many interests and technological advancement. The recent example was studies launched by U.S. on the recovery of REEs from coal and coal byproducts, since substantial REEs have been found in coal recourses despite in their lower occurrence. The extraction of REEs from coal and coal products face many technological challenges because REEs mainly exist in the inorganic lattice structure of coal and its byproducts, such as silicon-aluminum oxides. In this study, coal gangue and fly ash were selected as two representative coal by-products to extract REEs. The extraction of their REEs was alternative to the direct conventional acid leaching procedure. In this study, the realization of the CFA activation was initialized before moving-on to the conventional acid leaching. The activation of selected coal byproducts was subject to the calcination at the elevated temperatures using sodium carbonate (Na 2 CO 3 ). Studies regarding effects of the temperature and the Na 2 CO 3 dosage during the calcination as well as pH adjustment during leaching on the following-up maximize the extraction efficiency of REEs were intensively investigated. The results showed that the best practices achieved by 93.2% and 95.8% for coal fly ash and coal gangue in the extraction efficiency of REEs, upon the mixing molar ratio of silicon-aluminum oxides in coal byproducts and sodium carbonate at 1:1, the calcination temperature at 850°C and the acid leaching pH at 2.