Abstract:Oxidizing roasting of molybdenite with lime can significantly reduce SO₂ pollution compared with the traditional roasting without lime. However, the calcine is subsequently leached by sulfuric acid, resulting in serious equipment corrosion and abundant non-recyclable CaSO₄ slag. In this work, a novel process, in which the molybdenite was roasted with CaCO₃ followed by (NH₄)₂CO₃ solution leaching, was proposed to improve the art of lime roasting-sulfuric acid leaching. Oxidizing roasting of molybdenite with CaCO₃ was investigated through thermodynamic calculation, thermogravimetric analysis and roasting experiments. The results show that the products of the oxidizing reaction of MoS₂ in the presence of CaCO₃ and O₂ are CaSO₄, CaMoO₄ and CO₂ at 573-1000 K. The MoS₂ conversion rate achieves approximately 99% and the sulfur-retained rate attains approximately 95% with a CaCO₃-to-MoS₂ molar ratio of 3.6 at 500 °C for 1 h by adding 5% mineralizer A (mass fraction). The leaching results show that the leaching rate of Mo reaches 98.2% at 85 °C for 7 h with a (NH₄)₂CO₃ concentration of 600 g/L and a liquid-solid ratio of 10 mL/g. The results presented are potential to develop a novel cleaner technique for ammonium molybdate production.

Key words: molybdenite; limestone; ammonium carbonate; oxidizing roasting; leaching