Abstract:The phase composition and microstructure of alkaline vanadium slag were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD). A crystallization model of spinel was established to calculate the effects of basicity (the mass ratio of CaO to SiO₂) and P₂O₅ on crystal growth rates and precipitation patterns. Based on the crystal size distribution (CSD) theory, the size distribution and growth mechanisms of spinel crystals in alkaline vanadium slag at different temperatures were investigated. The results revealed that, at a cooling rate of 5 K/min, the mean grain size of spinel increased from 12.77 to 21.52 μm as the temperature decreased from 1748 to 1598 K, with spinel growth being controlled by the interface. At 1548 K, the spinel particle size reached 31.04 μm, indicating a supply-controlled growth mechanism as the temperature decreased from 1598 to 1548 K. Increased P₂O₅ content hindered the crystal growth, while an increase in basicity promoted nucleation and growth. Furthermore, MnCr₂O₄ preferentially crystallized and grew in alkaline vanadium slag.

Key words: alkaline vanadium slag; CaO content; P₂O₅ content; spinel; crystallization; kinetics