Dissolution of molybdenite roasting flue dust in sulfuric acid: kinetics and mechanism for molybdenum and rhenium leaching

The present study dealt with the hydrometallurgical dissolution of molybdenum (Mo) and rhenium (Re) along with co-existing metal impurities from the molybdenite roasting flue dust using sulfuric acid as the lixiviant medium. The parametric influence of agitation speed, acid concentration, temperature, time, and pulp density in metals’ dissolution was examined along with the thermodynamic studies on targeted critical metals (Mo and Re). Dissolution efficiency of metals at an optimized condition of pulp density, 10 wt./vol.%; H 2 SO 4 concentration, 1.0 mol/L; temperature, 90 °C; and time, 90 min was found to be 96% Mo, 93% Re, 98% Cu, 92% Ca, and 99% Na after 90 min. Progress in metals’ dissolution significantly increased with the temperature raised from 30 to 90 °C revealing that the dissolution was an exothermic process. Whereas progress in metals’ dissolution with time indicated that the reaction mechanism changed from diffusion-controlled to chemically-controlled. This was further confirmed by the determined values of apparent activation energy of E a(Mo) , 35.5 kJ/mol and E a(Re) , 21.5 kJ/mol indicating the reaction driven by an intermediate-controlled mechanism. Subsequently, selective recovery of Re and Mo from the leach liquor has been proposed through a pH-swing in solvent extraction using tri-butyl phosphate as the potential organic extractant, yielding high-purity alkaline solutions.