Title: Coal Flotation Enrichment and Rare Earth Element Extraction: A Comprehensive Review of Methods, Kinetics, and Thermodynamics
Authors: Mutalibkhonov S.S., Kholikulov D.B., Khudoymuratov Sh.J., Boltabev O.N., Mamaraximov S.K., Khushbakov D.T., Abdukarimov O.U.
Volume: 9
Issue: 12
Pages: 72-77
Publication Date: 2025/12/28
Abstract:
Coal and coal fly ash represent significant secondary sources of rare earth elements (REEs), with global annual generation exceeding 750 million metric tons. This comprehensive review examines froth flotation as a primary physical beneficiation technology for REE enrichment from coal and coal combustion byproducts, synthesizing 20+ publications from Scopus-indexed journals. Comparative analysis of ten flotation methodologies reveals nanobubble-assisted flotation achieves maximum REE recovery of 89% with enrichment ratio of 8.5:1, compared to conventional froth flotation (65% recovery, 3.5:1 ratio). Kinetic investigations demonstrate flotation follows first-order kinetics with activation energies ranging from 14.8 kJ/mol (collophanite flotation) to 28.3 kJ/mol (clay-hosted REE), indicating diffu+sion-controlled mechanisms for occluded REE phases. REE enrichment coefficients in coal fly ash average 1.8-2.1 across global power plants, with Chinese sources reaching 2.13, indicating substantial concentration during coal combustion. X-ray diffraction analysis identifies monazite (CePO?), bastnaesite (CeCO?F), and xenotime (YPO?) as primary REE mineral hosts, with clay minerals (kaolinite, illite) and aluminosilicate glass containing significant ion-exchangeable REE. Thermodynamic analysis via Gibbs free energy calculations confirms spontaneous collector adsorption (?G = -12 to -25 kJ/mol), with hydroxamic acid and compound collectors demonstrating superior selectivity factors (0.85-0.92). Light rare earth elements consistently comprise 70-80% of total REE concentrations, with cerium, lanthanum, and neodymium as dominant species. Process optimization incorporating depressants (sodium silicate, starch), pH adjustment (optimal pH 9-11), and frother selection enables REE concentrate grades exceeding 900 ppm from feed assaying 200-500 ppm. Multi-stage flotation combined with flotation columns and emerging technologies (ultrasonic assistance, nanobubbles, electroflotation) enhance recovery efficiency and selectivity, positioning coal-derived REE resources as economically viable alternatives to primary ore deposits.