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-MnO 2 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 MnMoO 4 and MnWO 4 , respectively, under the conditions of roasting temperature of 750 °C, β-MnO 2 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-MnO 2 , Mn 3 O 4 , and Mn 2 O 3 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-MnO 2 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. [Display omitted] [ABSTRACT FROM AUTHOR]