- 01Test 3: half-dose; Sc 91.8%, HREE 84%, LREE 77%.
- 02Grass Patch unbeneficiated; base for flotation tests.
- 03Ga 41.5% at low dose; element responses differ.
Mount Ridley Mines (ASX: MRD) has delivered its strongest scandium and rare earth element (REE) recoveries to date from the wholly owned Selectro process, with its third leach test achieving better results despite using half the reagent dose applied in the previous two tests.
Selectro Test 3 lifted scandium recovery to 91.8% from 80%, while heavy REE recoveries reached as high as 86% and averaged about 84%.
Light REE recoveries reached as high as 81% and averaged about 77%, with the work completed on the same unbeneficiated Grass Patch composite used in earlier testing and without process optimisation.
The result provides Mount Ridley with a new basis for reagent optimisation, flotation, and bulk sample work as it advances the patent-pending Selectro process at its Grass Patch project in Western Australia.
Lower Reagent Dose
The halved reagent dose in Test 3 produced stronger HREE and LREE recoveries than Test 2, including an increase in average HREE recovery from 78.5% to 84% and an increase in scandium recovery from 80% to 91.8%.
Mount Ridley attributed the improvement to molecular tuning of the Selectro leaching chemistry, which allows the composition of the leaching molecule to be adjusted towards targeted metals.
Gallium recovery moved in the opposite direction, falling to about 41.5% from 55.8% in Test 2 at the lower reagent dose, highlighting different responses among individual elements.
“These results are particularly encouraging given they have been achieved on unbeneficiated Grass Patch material at this early stage of the test work program,” managing director Allister Caird said.
“Combined with the scale of the existing mineral resources at Grass Patch, […] they give us confidence as we advance Selectro into flotation concentrate and bulk sample testing.”
Process Optimisation
The metallurgical test work was undertaken by Nagrom at its Kelmscott laboratory using a 16.8kg homogenised composite prepared from five historical Grass Patch diamond drill holes.
Comparative testing used representative dry-weight aliquots of about 90 grams, with Selectro and hydrochloric acid baseline tests each conducted over a 24-hour leach period at atmospheric pressure.
The Selectro tests achieved maximum recoveries in under four hours, while Mount Ridley has not yet established the lower limit of reagent concentration that can be used by the process.
Mount Ridley considers the latest work a foundation for further optimisation because it was completed on unbeneficiated material, with the balance between scandium, HREE, LREE, and gallium recovery still to be refined.
Flotation Test Work
Flotation test work on Grass Patch material is underway and will determine the beneficiation approach used before Selectro moves into bulk sample testing.
Earlier mineralogical work identified the REE in the tested composite as being predominantly hosted in discrete phosphate minerals, including xenotime, crandallite group phosphates and monazite/rhabdophane.
Mount Ridley plans to incorporate the Test 3 results into updated process economics and scoping assumptions, while further work will test whether lower reagent concentrations can retain or improve targeted recoveries.
Bulk sample testing will then assess both the reduced-reagent approach demonstrated in Test 3 and flotation-beneficiated feed, with Mount Ridley also planning to validate the Selectro process on third-party material.
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