Crystallization behaviour and growth mechanisms of spinel crystals in vanadium slag with high MgO content

Abstract

Increasing the MgO content in vanadium slag is a prerequisite for implementing slag splashing to protect the furnace. The increase in MgO content will inevitably cause changes in the phase structure of vanadium slag, thereby affecting the extraction of vanadium. In this study, the effect of MgO on the crystallization behavior of the spinel phase in vanadium slag was systematically investigated. It was found that the spinel phases in vanadium slag with high MgO content were mainly FeV₂O₄, Fe₂TiO₄, MgV₂O₄ and Mg₂TiO₄, and the nucleation and growth rates of the above crystals increased significantly with the increase of FeO/SiO₂ ratio and MgO content. With the increase of FeO/SiO₂ from 1 to 3, the combined crystallization rate of Fe₂TiO₄, FeV₂O₄, and Mg₂TiO₄ increased by two orders of magnitude, and the total spinel crystallization rate of MgV₂O₄ and spinel also increased by one order of magnitude. The effect of the MgO content on the crystallization of the crystals was not as significant as the FeO/SiO₂ ratio. The optimum crystallization temperature of the total spinel in vanadium slag is determined with MgV₂O₄, which has the highest melting point, and the optimum crystallization temperature interval is 1500–1650 K. During the cooling process of the vanadium slag, MgV₂O₄ is first crystallized, then Mg₂TiO₄ and FeV₂O₄, and finally Fe₂TiO₄. When the cooling rate is 5 K min⁻¹ and the temperature drops from 1773 K to 1623 K, the average grain size of the spinel gradually increases, and the growth of the spinel in vanadium slag with high MgO content is controlled by the supply.