Effects and mechanisms of ternary solution of NaOH-Na2CO3-Na2SO4 on the recovery of molybdenum from residues containing multiple molybdates

Abstract

The recovery of molybdenum from secondary resources containing multiple molybdates is limited by low recovery efficiency. In this work, detailed investigations have been carried out to deeply and selectively recover Mo from volatilization residues of molybdenite concentrate. Characterizations show that the molybdenum is present as MoO3 and mixed molybdates of La, Ce, Nd, Fe, Ba, Ca, Mg, Sr etc. Leaching experiments involving various conditions were then performed to dissolve Mo from the residues. The leaching efficiency of Mo could not attain a high level until a ternary solution was used. Specifically, 98.4% of Mo and 13.1% of Si could be dissolved with 160 g/L NaOH, 20 g/L Na2CO3 and 30 g/L Na2SO4 at 95 °C for 120 min at liquid to solid ratio of 6:1 mL/g, while rare earths were enriched and totally kept in leach residues. Furtherly, thermodynamic calculations about the dissolution reactions involving various molybdates and leaching agents were conducted. The leaching mechanisms of Mo with ternary solution were revealed based on the calculations and SEM-EDS analysis. Generally, this work may provide not only a new strategy for the recovery of Mo from complex secondary resources, but also new insights into the leaching mechanisms of Mo in the aspect of thermodynamics.