High-temperature oxidation behavior of ferrovanadium (FeV 2 O 4 ) and ferrochrome (FeCr 2 O 4 ) spinels is crucial for the application of spinel as an energy material, as well as for the clean usage of high-chromium vanadium slag. Herein, the nonisothermal oxidation behavior of FeV 2 O 4 and FeCr 2 O 4 prepared by high-temperature solid-state reaction was examined by thermogravimetry and X-ray diffraction (XRD) at heating rates of 5, 10, and 15 K/min. The apparent activation energy was determined by the Kissinger–Akahira–Sunose (KAS) method, whereas the mechanism function was elucidated by the Malek method. Moreover, in-situ XRD was conducted to deduce the phase transformation of the oxidation mechanism for FeV 2 O 4 and FeCr 2 O 4 . The results reveal a gradual increase in the overall apparent activation energies for FeV 2 O 4 and FeCr 2 O 4 during oxidation. Four stages of the oxidation process are observed based on the oxidation conversion rate of each compound. The oxidation mechanisms of FeV 2 O 4 and FeCr 2 O 4 are complex and have distinct mechanisms. In particular, the chemical reaction controls the entire oxidation process for FeV 2 O 4 , whereas that for FeCr 2 O 4 transitions from a three-dimensional diffusion model to a chemical reaction model. According to the in-situ XRD results, numerous intermediate products are observed during the oxidation process of both compounds, eventually resulting in the final products FeVO 4 and V 2 O 5 for FeV 2 O 4 and Fe 2 O 3 and Cr 2 O 3 for FeCr 2 O 4 , respectively.
Owing to its low grade and complex dissemination, the efficient recovery of vanadium from stone coal vanadium ore remains highly challenging. To address this issue, this study proposes a novel approach, referred to as "narrow particle-fraction wüstite (Fe 1- x O) solid solution magnetization," which enables highly efficient vanadium enrichment from stone coal vanadium ore through the use of precisely controlled narrow particle-fraction Fe 1- x O. During roasting under a reducing atmosphere, vanadium-bearing components are thermally activated and diffuse into the Fe–O lattice of residual granular Fe 1- x O through the product layer, resulting in the formation of a ferrimagnetic Fe 3 O 4 –FeV 2 O 4 (Fe 3- x V x O 4 ) solid solution. Subsequently, the Fe 3- x V x O 4 phase is separated using low-intensity magnetic separation. Taken the stone coal vanadium ore with a V 2 O 5 content of 0.95 wt% as the raw material, under optimized Fe 1- x O particle size fractions and roasting parameters, the magnetic separation process yielded over 87% vanadium recovery in the concentrate, with a V 2 O 5 grade exceeding ten times that of the raw tailings, the processing volume required for the subsequent hydrometallurgical vanadium extraction process reduced by nearly 90%. Mechanistic analyses (SEM–EDS, EPMA, VSM, CLSM, and XRD) confirmed that the in situ-formed Fe 3- x V x O 4 solid solution served as an efficient magnetic carrier for vanadium in stone coal vanadium ore. Therefore, this approach provides a sustainable pathway for the efficient conversion of stone coal vanadium ore.
The calcium‑magnesium composite roasting – acid leaching process represents a sustainable alternative for vanadium extraction from vanadium slag, yet its underlying mechanism remains insufficiently understood. This study systematically investigates the phase transformation and dissolution behavior within the FeV 2 O 4 –CaO–MgO system to clarify the role of MgO. Results reveal its critical dual role: it promotes the formation of acid-soluble calcium‑magnesium vanadate (Ca 5 Mg 4 V 6 O 24 ), yet concurrently facilitates the formation of insoluble magnesium‑iron vanadates (e.g., Mg 2 FeV 3 O 11 ), thereby severely compromising leaching efficiency. The formation of the low-melting-point compound CaMgV 2 O 7 can also inhibit extraction via phase encapsulation. As a result, vanadium recovery demonstrates a pronounced non-monotonic dependence on MgO content, with a well-defined efficiency maximum under optimal conditions. These findings elucidate the phase-transformation mechanism governing leaching performance and establish a fundamental basis for the rational design of efficient vanadium recovery processes.
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