An investigation into the sodium molybdate leaching of molybdenum calcine

The ammonia leaching-purification-crystallization process is the conventional treatment method of molybdenum calcine. This process generates large amounts of nitrogen-containing wastewater and exhaust gases. Based on the self-coordination principle of Mo, where MoO₃ with low-polymerization ability combines with Na₂MoO₄ into highly polymerized polymolybdates, this study proposes a novel, green leaching process using Na₂MoO₄ for the selective extraction of Mo from molybdenum calcine. Leaching conditions were optimized, and the reaction mechanism was elucidated through the identification of solids using XRD, EDS mapping, XPS, and Raman spectroscopy. Results show that under optimal conditions, the leaching efficiency reached 98.6 %. Molybdenum from MoO₃, PbMoO₄, and FeMoO₄ phases in the calcine was effectively extracted, while Fe and Pb oxides remained in the leach residue as PbO and Fe₂O₃·1.2H₂O, respectively. In the leachate, Mo existed primarily as Mo₇O₂₄⁶⁻, HMo₇O₂₄⁵⁻, and MoO₄²⁻. This study presents an environmentally friendly process for extracting Mo from molybdenum calcine.