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Mount Ridley extraction tests show high rare earths recovery

Updated: Apr 19

Mount Ridley Mines drilling. Credit: File

Mount Ridley Mines has revealed high rare earths recovery from leach extraction tests using simple hydrochloric acid leaching on samples from its Mia and Vincent prospects, about 50km north of the Western Australian port town of Esperance.

The company says the high rare earths extraction rates were recorded from testwork on screen beneficiated sample material that employed a simple acid leach at a concentration of 25 grams per litre of hydrochloric acid inside a 24-hour leach period. It says the process yields up to 72 per cent extraction of total rare earth oxides (TREO), including up to 85 per cent of high-value magnet rare earths.

Mount Ridley commissioned testwork on 12 samples from its Mia, Jody, Winston and Vincent prospects. The testing saw samples leached with hydrochloric acid at three different strengths – 3.6g/l, 10g/l and 25g/l – for periods ranging between six and 24 hours. The company says the best results were returned when samples were leached at an acid concentration of 25g/l for 24 hours.

The news comes less than a month after management revealed a successful outcome to its pre-process screen sizing beneficiation tests on 19 samples from 15 drill holes. The tests used screens with apertures ranging between 500 microns and 25 microns and results showed optimum beneficiation was achieved by screening at 75 microns mesh size.

The process yielded average upgrades of 164 per cent from the Mia and Jody prospects and 154 per cent from Vincent, with a maximum of 202 per cent at the latter. More than 80 per cent of the TREO was contained within 50 per cent of the original sample mass.

Recent results have provided valuable metallurgical insights as the Company progresses towards a flow sheet for the Mia Prospect and the larger Mount Ridley REE Project. The weighted average drill-intersection grade at Mia now exceeds 1,500ppm TREO. It is projected that this grade may increase to above 2,400ppm TREO through simple screen beneficiation, a rate of upgrade of 160%, and now excellent acid leach test results have been returned from beneficiated test samples, showing the potential efficacy of HCl leaching to recover rare earth elements at a reasonable level of acid consumption. Mount Ridley Mines chairman Peter Christie

The company initially acquired the project area for its nickel and copper sulphide potential. However, re-analysis of more than 1100 samples from previous air-core (AC) work revealed that the majority contained significantly-elevated levels of clay-hosted rare earths that are now sought widely for their importance in the global decarbonisation energy imperative.

Clay-based rare earths have become a key focus, especially in Australia where several big discoveries have been made. The resources are typically soft and shallow and can be more easily mined at low grades with excellent economies of scale.

With a combination of methods that simultaneously enable about a 50 per cent reduction in raw feed volume and enhance feed head grade by sizing, and then greatly improving recoveries from the beneficiated material with simple acid leaching, Mount Ridley looks like it might be onto a winning process strategy.

Management says drilling is scheduled to resume at Mia next month and it expects it to lead to a maiden mineral resource estimate later in the year.

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