Reaction behavior of associated rare earth minerals during coal-based reduction

In order to ascertain the reaction behavior of rare earth minerals in coal-based reduction, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analyses were applied to investigate the rare earth minerals in Bayan Obo. The occurrence state and regularity of rare earth elements were analyzed under different reduction time. The results reveal that rare earth elements in rare earth minerals exist in RE(CO3)F (bastnaesite) and REPO4 (monazite). In this research, at 1,498 K with a C/O molar ratio (i.e., molar ratio of fixed carbon in the coal to reducible oxygen in the ore) of 2.5, rare earth minerals primarily decompose into RE2O3 at 5 min. When the time is extended to 10 min, solid-phase reactions occur among RE2O3, CaO, and SiO2, and the resultant is cerium wollastonite (CaO·2RE2O3·3SiO2). At reaction time >20 min, rare earth elements mainly exist in cerium wollastonite (CaO·2RE2O3·3SiO2), and the grain size varies in the range of 10–30 μm. The results show that coal-based reduction is efficient to recover rare earth minerals in reduced materials.