KEY POINTS
• Pilot scale testwork applying a well-established Grate Kiln technology demonstrates energy efficiency and adaptability for vanadium roasting.
• Process optimisation by roasting a concentrate representative of average early years mine production, has resulted in vanadium roast / leach extractions up to 94.9%.
• Roasting testwork conducted on concentrate representative of the average forecast for later years of processing produced optimum vanadium roast / leach extraction at 92.2%. Both results provide significant improvements compared to a traditional rotary kiln flowsheet as typically applied in vanadium processing.
• Completion of the pilot scale roasting program now enables the BFS engineering design for the concentrate preparation and grate kiln areas to be updated.
• Testwork was partly funded by the Australian Government’s Cooperative Research Centre – Projects scheme entitled: “Production of 99.95% Pure Vanadium Pentoxide and Vanadium Electrolytes”.
Australian Vanadium Limited (ASX: AVL, “the Company” or “AVL”) is pleased to advise that pilot scale pyrometallurgical testwork at the Metso testing facilities in the US has been completed and reported. The testwork comprised detailed testing and optimisation work on pelletised concentrates produced by AVL’s 30 tonne Crushing, Milling and Beneficiation (CMB) testwork program. The pyrometallurgical work has confirmed the initial successful pilot test results announced in July 20201 and is a significant step towards the Company’s goal to design, build and operate the world’s lowest cost primary vanadium operation which will be located in Western Australia’s Mid-West region.
The concentrates used as feed for the pyrometallurgical test program were generated during AVL’s CMB pilot testwork in 2019. An early years (Y0-5) blend typical of the average of the first five years of forecast production and a later scheduled average blend (LOM) were campaigned separately. Vanadium recovery from the CMB circuit was exceptional, at 69% for Y0-5 and 76% for LOM, reflecting the unique characteristics of the AVL Gabanintha orebody. The concentrate grades achieved at the target particle grind size P80 of 75 µm were similar.
Albeit the concentrates have similar chemistry they differ in mineralogy. Hematite is the dominant iron mineral in the Y0-5 concentrate whereas magnetite is dominant in LOM concentrate . These minerals are both hosts for vanadium and behave differently in the roast-leach process. Roasting testwork was centred around optimising process conditions for each of these two blends.
The full pyrometallurgical test program was completed in February 2021, after some delays due to COVID-19 and repairs to the kiln. The key process parameter for vanadium extraction from either the hematite or magnetite rich blend was the kiln operating temperature. Figure 2 illustrates the degree to which vanadium leach extraction changed when testing a range of potential kiln temperatures.
The effectiveness of the roast process over a range of relatively short residence times was demonstrated at an optimal temperature (see Figure 3). By testing a range of potential commercial roasting durations no appreciable difference in vanadium leach extraction resulted, indicating a robust process and rapid completion of the salt-vanadium reaction.
LOM magnetite rich pellets showed a marginally lower, but more consistent and repeatable vanadium roast-leach extraction, averaging 92% at the selected roast temperature. LOM blend material provided more than 9% higher vanadium recovery from the CMB circuit compared to the Y0-5 blend, more than offsetting its slightly lower roast performance.
The concentrates used for the pilot work were generated in the CMB pilot program and are impressively low in impurities. Silica, for example, was at 1.83% SiO2 (0.86% Si) in the Y0-5 concentrate and 1.68% SiO2 (0.79% Si) in the LOM concentrate. The objective for the pyrometallurgical roast is to maximise vanadium solubilisation and minimise extraction of silicon and aluminium present in the concentrate. This ensures a high-quality vanadium product. AVL has
previously reported that for Y0-5 only 4.2% silicon and almost no aluminium3 extraction occurred. This trend continued for the LOM concentrates with only 3.8% silicon extraction and again almost no aluminium.
The overall vanadium recovery forecast for the entire process is regarded as exceptional due to a combination of favourable ore characteristics and significant technical development by AVL.
Completion of Pyrometallurgical Testwork and Implications for the BFS
With completion and reporting of the pyrometallurgical testwork program, AVL’s engineers are in the process of updating the design of the grate kiln area to support the BFS.
Ongoing work related to the Company’s CRC-P Research Program for production of high purity vanadium products is aimed at further increasing efficiency and improving certainty in the vanadium purification flowsheet design, which will be part of the Australian Vanadium Project Processing Plant near Geraldton.
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