Abstract
Vanadium is a critical metal with physical and chemical properties that are highly advantageous for a broad spectrum of modern industrial applications. Primary applications are in the manufacturing of high-grade steels and high-performance alloys for aerospace, biomedical and nuclear applications. Vanadium redox flow batteries (VRFBs) are also emerging as a key technology for grid-scale energy storage. The global demand for vanadium is projected to increase substantially in the coming years, with a World Bank report projecting annual global demand to increase by >180% by 2050 (relative to 2018). The primary source of vanadium is vanadium titanomagnetite ores, which make up about 88% of the world’s vanadium production. Nearly 70% of vanadium extracted globally is obtained from steel slags produced by smelting titanomagnetite ores. However, the availability of this resource is determined by the economic outlook for steel, making it largely inelastic to evolving vanadium demand. This creates the need to explore new alternative primary sources of vanadium. However, a key challenge associated with vanadium ores is their low grade (typically, 0.2-1 wt% of V2O5 in the concentrated ore). In addition to titanomagnetite sources, vanadium can also be found in a range of other geological deposits. Here, we report an investigation into the potential extraction of vanadium from a newly identified weathered silicaceous hematite deposit in the Northern Territory of Australia. Notably, ROM material from this deposit contains up to 0.9% V2O5, at Fe;V ratios of < 60:1. Finely-dispersed silica inclusions are also present, at bulk levels of 43%. Sodium roasting and water leaching remains the most widely implemented process for primary vanadium extraction. Therefore, initial investigations have pursued this route utilising Na2CO3 as the roasting additive. Comprehensive initial characterisation of the material was conducted via XRF (X-ray fluorescence) and XRD (X-ray diffraction) analyses. XRD analysis revealed the presence of silicon dioxide, hematite, goethite and various clay mineral phases in the initial ore. SEM-EDS (scanning electron microscopy/energy-dispersive X-ray spectrometry) analysis confirmed that vanadium is associated with the iron-containing phase, with a pronounced enrichment of the element at the interfaces of pores and cracks of particles. Pulverised ore samples were mixed with Na2CO3 at various V:Na ratios. However, it was found that increasing the Na content reduced V extraction efficiency from ~30% for a blank roast down to < 15% extraction at an Na:V ratio of 4:1. It is believed that this somewhat surprising finding is due to the formation of liquid-phase sodium silicates during the roasting process, which impede V extraction by encapsulating vanadium from the matrix, thus preventing subsequent leaching in water. The V extraction efficiencies achieved from blank-roasted samples were notably higher than from any Na-roasted samples. This unexpected result suggests that inherent components present in the ore can react with V-containing phases at high temperature to form water-soluble vanadates. The findings of this research indicate that traditional Na2CO3 roasting may not be suitable for high-efficiency V extraction from silicon-rich primary ores. However, alternative roast-dopants (such as those present in the native ore), may present a viable alternative route.