In situ synthesis of Fe–Mo alloys via synergistic smelting of copper slag and spent MoSi2 rods: Phase transformation and decomposition mechanism of MoSi2

The massive accumulation of copper slag and spent molybdenum disilicide rods results in significant waste of valuable metal elements such as Fe and Mo. To mitigate environmental pollution and promote metal recovery, this study proposes a synergistic smelting process for preparing ferromolybdenum alloy by utilizing spent molybdenum disilicide rods and copper slag. Through integrated analysis of thermodynamic simulations and non-isothermal kinetic experiments, the reduction behavior, phase reconstruction, and decomposition of MoSi₂ during the synergistic smelting process were systematically investigated. The magnetite phase and fayalite phase gradually decomposed under the influence of CaO and MoSi₂, following the reaction pathways: Fe₃O₄→FeO→Fe and Fe₂SiO₄→Fe_1.5Ca_0.5(SiO₃)₂→Fe. At approximately 950–1100 °C, an exothermic reaction occurred between MoSi₂ and copper slag, initiating in-situ formation of Fe₃Mo. CaO improved the thermodynamic conditions and facilitated reaction progression. After system melting, solid-liquid reactions further decomposed MoSi₂, while Mo and Si diffused into the slag, and Fe selectively captured Mo for directional enrichment. Differential scanning calorimetry analysis determined the activation energy for MoSi₂-driven copper slag reduction to be 113.470 kJ/mol, confirming MoSi₂ as an efficient reductant. Under optimal temperature conditions, the recovery rates of Mo and Fe reached 99.21 % and 85.49 %, respectively, with Fe content in the secondary slag reduced to 4.04 %. This study utilizes spent molybdenum disilicide rods as both a reductant and a molybdenum source, without introducing carbon, providing a novel strategy for the high-value and low-carbon utilization of these two solid wastes.