Direct Tungsten Extraction from Scheelite in a Molten Salt Media

<p>Tungsten is a basic metal commodity that is classified as critical raw material (CRM) by the European Commission (EC) with the highest economical importance compared to other CRM. Thanks to its unique properties, secure W supply is critical to all industrial applications involving cutting or component wear, such as mining, machining, construction, tools and dies. Other important uses are in high-strength steels and high-temperature alloys, chemicals, mill products and lighting filaments. The production of W metal or carbide to be used in end products, requires a reduction process of the oxide which has been previously extracted from the primary (ores) resources by complex and energy intensive hydrometallurgical processes.</p><p>In the frame of the EC-funded TARANTULA project (GA 821159), innovative methods to obtain W metal directly from scheelite raw material have been investigated. The process comprises two steps, i.e., selective chlorination of the W ore in a molten chloride media using gaseous reactants, and subsequent electrolysis of the dissolved W electroactive species from the same reaction media. The chlorination of natural scheelite in a molten chloride has been demonstrated in the equimolar NaCl-KCl mixture at a working temperature of 727 °C, using both Cl₂ (g) and HCl (g). The dissolved W species in the molten chloride were found to be tri-tungstate: W₃O₁₀²⁻ and/or the chloro-complex, as e.g., W₃O₁₀Cl₂⁴⁻. Subsequent electrolysis trials demonstrated the recovery of WC₂ deposits on a carbonaceous cathode, while the anode reaction was evidenced to include the discharge of the oxide ions from the dissolved tri-tungstate species.</p>