Rare-Earth Elements Extraction from Low-Alkali Desilicated Coal Fly Ash by (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> + H<sub>2</sub>SO<sub>4</sub>
Andrei Shoppert,
Dmitry Valeev,
Julia Napol’skikh,
Irina Loginova,
Jinhe Pan,
Hangchao Chen,
Lei Zhang
Affiliations
Andrei Shoppert
Department of Non-Ferrous Metals Metallurgy, Ural Federal University, Yekaterinburg 620002, Russia
Dmitry Valeev
Laboratory of Sorption Methods, Vernadsky Institute of Geochemistry and Analytical Chemistry, The Russian Academy of Sciences, Moscow 119991, Russia
Julia Napol’skikh
Department of Non-Ferrous Metals Metallurgy, Ural Federal University, Yekaterinburg 620002, Russia
Irina Loginova
Department of Non-Ferrous Metals Metallurgy, Ural Federal University, Yekaterinburg 620002, Russia
Jinhe Pan
Key Laboratory of Coal Processing & Efficient Utilization, Ministry of Education, School of Chemical Engineering and Technology, China University of Mining & Technology, Xuzhou 221116, China
Hangchao Chen
Key Laboratory of Coal Processing & Efficient Utilization, Ministry of Education, School of Chemical Engineering and Technology, China University of Mining & Technology, Xuzhou 221116, China
Lei Zhang
Key Laboratory of Coal Processing & Efficient Utilization, Ministry of Education, School of Chemical Engineering and Technology, China University of Mining & Technology, Xuzhou 221116, China
Coal fly ash (CFA) obtained from pulverized coal furnaces is a highly refractory waste that can be used for alumina and rare-earth elements (REEs) extraction. The REEs in this type of CFA are associated with a mullite and amorphous glassy mass that forms a core-shell structure. In this research, it was shown that complete dissolution of amorphous aluminosilicates from the mullite surface with the formation of the low-alkali mullite concentrate prior to sulfuric acid leaching with the addition of (NH4)2SO4 helps to accelerate the extraction of REEs. The extraction degree of Sc and other REEs reaches 70–80% after 5 h of leaching at 110 °C and acid concentration of 5 M versus less than 20% for the raw CFA at the same conditions. To study the leaching kinetics of the process, the effects of temperature (90–110 °C), liquid-to-solid ratio (5–10), and leaching time (15–120 min) on the degrees of Al and rare-earth elements (REEs) extraction were evaluated. After 120 min of leaching at 110 °C and L/S ratio = 10, the extraction of Al was found to be lower than 30%. At the same time, total REEs (TREE) and Fe extraction were greater than 60%, which indicates that a part of the TREE was transferred into the acid soluble phase. After leaching, the residues were studied by laser diffraction (LD), X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM-EDS) to evaluate the leaching mechanism and the solubility of Al- and Fe-containing minerals, such as mullite, hematite, and amorphous aluminosilicate.
