Extraction of tungsten and molybdenum from waste alloy assisted by a recyclable roasting additive: β-MnO2

Extraction of molybdenum (Mo) and tungsten (W) from waste alloy significantly impacts the alleviation of resource shortage and ecological environment. In this study, Mn additive was utilized as a recyclable roasting aid to convert Mo and W for facilitating extraction, by considering thermodynamic calculations. The effect of β-MnO2 as a roasting additive on the phase evolution of Mo, W, and Mn elements and the optimal process conditions were evaluated by XRD, SEM-EDS, thermal analysis, and alkali leaching experiments. Notably, Mo and W in the alloy waste got oxidized and converted into soluble MnMoO4 and MnWO4, respectively, under the conditions of roasting temperature of 750 °C, β-MnO2 amount of 75% of waste alloy mass, and time of 1 h. During alkaline leaching, 100.00% Mo and 99.59% W in the roasted product were extracted, which was accompanied with the precipitation of leached residue of α-MnO2, Mn3O4, and Mn2O3 from Mn present in the leach liquor (NaOH concentration 2 mol⋅L−1, solid–liquid ratio 10% (w/v), time 5 h, temperature 90 °C). When the recycled leached residue was employed in the next roasting process, the leaching efficiency of Mo and W was maintained above 98.56%. Moreover, the reaction mechanisms of roasting and leaching were investigated by kinetics study. Roasting with β-MnO2 fundamentally reduced the production cost with the high extraction efficiency of Mo and W, and the flue gas recovery process was no longer required, which is beneficial to industrial application.