Molybdates Formation Pathways and Their Roles on Thermal Oxidation of Molybdenite Concentrates

The mainstream oxidative roasting method is facing challenges in processing low-grade molybdenite (MoS₂) concentrates, calling for deep understandings toward the behaviors of impurities. This study took pure minerals and reagents as the objects and conducted elaborate experiments and theoretical calculations into the formations of molybdates and their influences on MoS₂ oxidation. The emphasis are on the reactions under local O₂-absent conditions and the sintering of MoS₂ caused by molybdates of Ca, Fe, Cu, or Pb. It was found that molybdates could directly form from MoO₂ or MoS₂ without O₂ at 600 °C to 650 °C, due to the promotion of reactivity and reducibility of MoO₂ when combining with impurity metals. The produced molybdates would lower the melting point, dissolve in liquid MoO₃, and migrate to oxidation interface to form a sintering layer that inhibits O₂ diffusion. Overall, this study has discovered new pathways of molybdates formation and new effects of segregation on the sintering and established evolution patterns of bulk MoS₂ concentrate during roasting, which may be significant complements to the fundamentals of classical molybdenum metallurgy.