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OD6 metallurgy boosts rare earths processing method

Updated: Apr 18

OD6 Metals is eyeing chlor-alkali electrolysers. Credit: File

Metallurgical testing of ore from four prospects at OD6 Metals’ Splinter Rock rare earths project near Esperance in Western Australia has confirmed low acid consumption and high recoveries of valuable magnetic elements.

An average of 16kg of hydrochloric acid (HCl) was consumed per tonne of ore treated, with ore from multiple zones requiring just 6kg to 10 kg of acid per tonne. Magnetic rare earth oxides (MREO) were recovered at an average of 61 per cent, with 20 grams per litre hydrochloric acid concentration.

MREO are used to create permanent magnets, a critical component in the electrical power systems upon which the global clean energy transition hinges. The elements are non-replaceable across a variety of renewable energy applications and it is generally considered economically more positive if ore from a deposit can be processed to recover a higher percentage of MREO elements.

OD6 tested 10 samples of ore from a wide variety of clay and non-clay rock types across its 2579-square-kilometre Splinter Rock project, about 150km north-east of the deepwater port of Esperance.

The mix of ore types was selected to test the various potential mineral recovery variations across the project’s four main prospects – Prop, Centre, Scrum and Flanker. The Australian Nuclear Science and Technology Organisation (ANSTO) was selected to complete the testwork based on its vast experience with rare earths processing.

These low acid consumption numbers are very positive, validating our proposed processing route and providing confidence in future potential process economics. This represents a key value lever as we continue to tick all the major boxes that pave the way for project development success. We continue to focus on identifying the best-of-the-best Prospect areas, with our methodical and disciplined approach. OD6 Metals managing director Brett Hazelden.

The samples were leached at 10, 15 and 20g/L HCl for 24 hours at 30°C and results show that ore from each prospect returned slightly different recoveries – which is to be expected as each type of mineralisation has different optimal acid conditions.

At 20g/L HCl, the Flanker prospect returned a low acid consumption of 6kg per tonne, with a solid 65 per cent MREO recovery. The Centre prospect returned an acid consumption ranging from 6kg per tonne to 41kg a tonne, with MREO recovery of between 43 per cent and 56 per cent.

The Scrum prospect returned an acid consumption of 19kg per tonne with a 55 per cent MREO recovery and the Prop prospect returned an acid consumption ranging from 6kg per tonne to 63kg a tonne, with a MREO recovery of 49 per cent to 87 per cent.

OD6 says all recovery results are based on the four-acid soluble digestion method, which aligns with how the company reports geological drill assays and also its maiden mineral resource estimate for Splinter Rock that sits at 344 million tonnes at 1308 parts per million total rare earth oxides (TREO).

MREO make up an average of 23 per cent of the TREO grade in the ground across Splinter Rock.

Management says its latest batch of metallurgical test results advocate for a site-based chlor-alkali processing facility that will convert salt and water to produce the reagents, HCl and sodium hydroxide.

HCl is used to leach the rare earths before sodium hydroxide is used to remove impurities, precipitating a mixed rare earths product and neutralising the clays prior to in-pit disposal.

The company says a single chlor-alkali electrolyser will cost about $5.7 million and will be capable of producing about 62,000 tonnes per year of HCl and 69,000 tonnes per year of sodium hydroxide. At an average consumption of 16kg HCl per tonne of ore, it will be sufficient to treat about 4 million tonnes of ore per year.

Splinter Rock raised some eyebrows recently when Breakaway Research, a Sydney-based equities research specialist which has been profiling ASX-listed junior to mid-size companies for the past decade, rated it a potential sleeper among giants – suggesting the deposit has the potential for massive growth.

OD6 says it will review and potentially upgrade its mineral resource estimate at Splinter Rock on back of more assays in next year’s first quarter.

The news flow from the company this month is expected to include drill assays from the Centre prospect and further metallurgical leach performance metrics. Metallurgical recovery and acid consumption results for its phase-two drill program are expected before the end of this year and further results are expected for the third-phase drill program in next year’s first quarter.

On the ground at Splinter Rock, reinterpretation of airborne electromagnetics data by the CSIRO will map clay thickness and clay basin areas to guide further exploration efforts.

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