Red Metal Limited (ASX: RDM) has announced significant advancements in the potential for low-cost processing at its Sybella rare earths discovery, located 20 kilometers southwest of Mount Isa. Optimized bottle roll pH optimisation leach tests on air core and RC percussion drill chip samples from the eastern Kary Zone have demonstrated the viability of using weaker and lower-cost sulphuric acid at pH levels between 2.0 and 2.5 to achieve favorable Magnet Rare Earth Oxide (MREO) extractions. The company’s research has also identified a potentially low-cost in-heap pathway to strip iron impurities from the pregnant leach liquor.
These findings have validated and significantly improved upon past results, establishing clear pH set points for definitive column leach tests on recently drilled diamond core samples. Leach data strongly supports the application of heap leach processing to extract MREO from the weathered granite ores of the Kary Zone.
Specifically, at pH 2.0, a large portion of the weathered Kary Zone ores achieved neodymium and praseodymium extractions ranging from 76% to 81%, terbium extractions averaging 43% to 60%, and dysprosium extractions ranging from 38% to 55%. The sulphuric acid consumption was low, ranging from 17 to 22 kg/tonne, with low aluminum impurity extractions (3-6%) and very low iron impurity extractions (1-2%).
The study has also shown that neutralizing the pH of the leach liquor with time leads to the precipitation of iron oxides and a step-change reduction in iron impurities. This iron oxide precipitation reaction is acid generating, allowing MREO extractions to be maintained while reducing acid addition.
Managing Director Rob Rutherford stated that these optimized leach tests have shown strong rare earths extractions at weaker acid strengths, enhancing the deposit’s economic potential. Column leach test work is slated to commence in the coming months to provide definitive data on crushed rock, simulating a heap leach setting.
Furthermore, geological mapping has expanded the interpreted surface area of the Kary Zone, potentially increasing its near-surface potential. Further test work, including column leach tests and additional intermittent bottle roll tests are planned.
