Synthesis of scheelite nanoparticles by mechanically assisted solid-state reaction of wolframite and calcium carbonate

Nanostructured scheelite (CaWO4) was synthesized by calcination in air of enriched wolframite (Fe1-xMnxWO4) ore and calcium carbonate (CaCO3). The effects of process parameters such as milling conditions of the solid reactants, calcination in flowing or static air, and use of stoichiometric excess of calcium carbonate on wolframite conversion into scheelite were studied by X-Ray Diffraction (XRD) and field emission gun scanning electron microscopy (FEG SEM). The intimate mixing and associated decrease in the diffusion path by high-energy planetary ball milling (PBM) were responsible for the conversion of most of wolframite into nanostructured scheelite after 2 h at 600 °C, with no need of calcium carbonate stoichiometric excess. Complete conversion of PBM wolframite:CaCO3 mixtures into nanosized scheelite, iron oxide and carbon dioxide was accomplished after 2 h at 700 °C. The nanostructured scheelite obtained from wolframite is expected to be significantly more reactive in subsequent treatments (e.g., leaching) for tungsten extraction.