Understanding the reaction mechanisms of Mg2B2O5-Fe3O4 and Mg2B2O5-Na2CO3-Fe3O4 systems under different atmospheres

Abstract

Ludwigite ore is a strategic and characteristic resource characterized by its multi-mineral intergrowth, serving as the primary raw material for the current boron industry in China. However, its comprehensive and efficient utilization presents challenges due to the complex mineralogical composition and mineral associations. Mineral phase reconstruction of ludwigite ore through soda-ash roasting has proven to be an efficient approach for activating and separating boron and iron. Nevertheless, the transformation behavior of boron and iron and physicochemical properties of reaction products are significantly affected by the amount of soda-ash and the roasting atmosphere, and the underlying reaction mechanism remains unclear. In this study, the reaction behaviors of Mg₂B₂O₅-Fe₃O₄ and Mg₂B₂O₅-Na₂CO₃-Fe₃O₄ systems under different roasting atmospheres were investigated to better understand the reaction mechanism involved in the soda-ash roasting of ludwigite ore. The results showed that Fe₃O₄ was oxidized to Fe₂O₃ and it hardly reacted with Mg₂B₂O₅, while in the presence of soda-ash, it reacted with Mg₂B₂O₅ to generate NaBO₂ and MgO, and then Fe₂O₃ further reacted with MgO to form MgFe₂O₄ (air atmosphere). The roasting behavior under nitrogen and weakly reducing atmospheres was found to be similar. In the absence of soda-ash, Fe₃O₄ showed a slight reaction with Mg₂B₂O₅, resulting in the formation (Mg, Fe)₂FeBO₅ by solid–solid interfacial reaction. When soda-ash was present, Mg₂B₂O₅ reacted with Na₂CO₃ to yield NaBO₂ and MgO, after which Fe₃O₄ further reacted with MgO to form Mg_xFe_3-xO₄ and Mg_yFe_1-yO via isomorphic substitution.