Environmentally Sustainable Production of Critical Metals: A mineralogical approach to tungsten recovery

Tungsten, due to its economic importance and high supply risk, is classified as a critical metal. Approximately 70% of tungsten production is derived from scheelite (CaWO₄). High-quality resources are largely depleted, and the utilization of low-grade ores is now attracting considerable attention. Scheelite is commonly associated with the gangue minerals quartz, calcite, fluorite, and/or barite and these must be removed during ore processing. Currently, separating scheelite from gangue minerals to produce a concentrate is typically carried out via a flotation process. The froth flotation process exploits physicochemical surface properties of ore and gangue materials and is most effective when mineral surfaces with different surface free energies are present. Removing fluorite (CaF₂) can be particularly challenging. Cleavage surfaces of scheelite (112) and fluorite (111) have similar calcium active sites (i.e., very close Ca–Ca distance, despite significantly different Ca²⁺ densities), that induce similar surface physicochemical characteristics, and consequently similar flotation behaviour when conventional reagents are used. Hence, a deep understanding of responses and mechanisms involved is needed in order to develop a suitable framework for ore processing.

This and similar challenges will be addressed within the “Environmentally sustainable production of critical metals” project recently begun at the University of Tasmania within CODES (Centre of Ore Deposit and Earth Sciences). This project has strong industry collaboration and aims to provide new pathways to critical metal processing for materials from existing mines and from waste materials. The project includes multiple study sites in Tasmania. A geology-based, mineral characterisation approach is planned to help improve ore definition and production of tungsten at several sites. In addition, studies of flotation characteristics will be carried out to help optimise reagent choices and suggest alternate processing routes to separate scheelite from gangue phases. Waste materials will also be characterised to highlight potential uses, e.g., use in acidity reduction, road base, building materials etc.