Abstract
Tungsten (W), a rare metal, is categorized as a Critical and Strategic Raw Material (CRM) by the European Union (EU), with the highest economic importance of all selected CRMs since 2014. Tungsten and its derivatives are extracted from their commercial raw materials, mainly wolframite [(Fe,Mn)WO(4)] and scheelite (CaWO(4)) ores. Subsequently to mining and mineral processing, the W ore is submitted to thermal treatment and hydrometallurgy under aggressive conditions (high pressure and temperature), which are usually applied for the extraction of tungsten compounds. This paper aims to investigate a thermal route for scheelite processing using various selected chemical agents, resulting in a W-bearing material that is capable of being leached under softer conditions. In this context, a thermodynamic study of the interaction between FeWO(4), MnWO(4) and CaWO(4) and various chemical reagents is described. The thermochemical calculations and data modeling show that, among other considerations, the reaction of CaWO(4) with magnesium chloride (MgCl(2)) can lead to the formation of magnesium tungsten oxide (MgWO(4)), which appears to be more easily leachable than CaWO(4). Experimental tests of the reaction of scheelite with MgCl(2) appear to validate the thermodynamic predictions with satisfactory process kinetics at temperatures from 725 to 775 °C.