Direct synthesis of highly reactive nanostructured scheelite from enriched wolframite and calcium oxide through planetary ball milling

Nanostructured scheelite (CaWO4) was synthesized directly from enriched wolframite (Fe1-xMnxWO4) ore (55.18 % WO3) and lime (CaO) by energetic planetary milling, with no need of high-temperature calcination. After 48 h milling, wolframite was fully converted into nanostructured CaWO4. The mechanochemically derived products, when refluxed overnight in boiling Na2CO3 0.7 M at atmospheric pressure, showed practically complete (> 95 %) dissolution of the calcium tungstate, leaving CaCO3 in the solid residue. In contrast, the very same leaching treatment, when applied to either bare enriched wolframite or pure micro-crystalline CaWO4, did cause a scarse or little solubilization of tungsten. These results confirm the much higher reactivity of nanostructured scheelite in leaching treatments. The observed mechanochemical synthetic route may lead to less energy-intensive and lower environmental impact of tungsten-bearing minerals processing.