Selectro Test 3: scandium recovery to 91.8%, heavy rare earths to 84%, at half the reagent dose

This Cashu Research note was commissioned and paid for by Mount Ridley Mines Ltd, a relevant context when assessing the report’s rating and valuation. Its central conclusion is that the company’s third Selectro leach test improved recoveries while using materially less reagent, strengthening the process case for Mount Ridley’s Grass Patch project.

On 17 September 2026, Mount Ridley reported the third and final leach test in its initial Selectro programme on the Grass Patch composite. Test 3 used half the reagent dose applied in Tests 1 and 2, yet produced the programme’s best recoveries: scandium recovery reached 91.8%, heavy rare earth recovery averaged 84% and reached up to 86%, while light rare earth recovery averaged 77% and reached up to 81%.

Gallium moved in the opposite direction at the lower dose, falling to 41.5% from 55.8%. The result was nevertheless materially better than the HCl baseline, which produced zero gallium recovery. The test used the same unbeneficiated 8-sample T3803 composite from five historical diamond holes, tested at Nagrom’s Kelmscott laboratory without process optimisation.

The operating conditions are central to the report’s interpretation. Leaching took place at low temperature and atmospheric pressure, with maximum recoveries reached in under four hours of a 24-hour test. The company has not yet found the lower limit of reagent concentration, leaving open the possibility of further gains at an even lower dose.

Cashu Research describes the combination as unusual because leach testing normally involves a trade-off between reagent use and metal recovery. In this case, scandium recovery rose by nearly 12 percentage points from Test 2, while every rare earth except terbium improved; terbium remained flat at 83.1%. Because Selectro is designed as a closed loop with lower reagent cost than HCl, the report says that halving the dose also halves the volume requiring recycling.

The broader point is that Selectro appears tunable rather than dependent on a single result. Across three tests, scandium recovery moved from 62.1% to 80.0% and then 91.8% by changing the leaching regime rather than the feed. Gallium responded differently at the lower concentration, suggesting that reagent settings can be adjusted toward the metals that matter most economically.

That flexibility has not yet been demonstrated on beneficiated material. Flotation testwork is underway following the confirmation by TIMA on 6 August that the mineralogy is phosphate-hosted. The next bulk-sample programme is intended to test reduced-reagent conditions and a flotation-followed-by-leaching flow sheet on beneficiated feed.

The recovery improvement also changes the resource conversion discussion. At 91.8% recovery, the report calculates that 47,357 tonnes of contained scandium would yield about 43,500 tonnes of recoverable metal, compared with roughly 37,900 tonnes at the 80% recovery assumption used in the initiation. The difference is about 5,600 tonnes, achieved without changing the resource itself.

Cashu Research therefore maintains its A$0.144 price target and reiterates its Speculative Buy rating. The target was built on A$4,000 per tonne of contained scandium, with no value assigned to gallium, rare earths or the Selectro process. The report says Test 3 does not change the target arithmetic, but does improve the probability that the resource can become a project.

Cashu Research places the 91.8% scandium recovery favourably against the listed developers discussed in the report. Sunrise’s Syerston feasibility study assumes 88% recovery using high-pressure acid leaching at around 250°C, while Scandium International’s Nyngan work returned 70% to 80% overall recovery and averaged 75% in atmospheric acid-bake tests. Laboratory studies on red mud have reported 90% to 95% scandium extraction in hot, strong acid, but those results have not reached commercial scale.

The report’s rare earth interpretation may be just as important. Grass Patch is not an ionic clay deposit: TIMA identified rare earths in xenotime, crandallite and monazite, minerals that ordinarily require high-temperature acid cracking. Recovering an average 84% of heavy rare earths from phosphate minerals under ambient conditions is presented as the result that could make Selectro relevant beyond Mount Ridley’s own ore.

The process remains unproven away from the Grass Patch composite. Every result so far comes from one 8-sample composite, so the planned test on third-party material is the critical validation step. Oak Ridge and Fraunhofer programmes disclosed in August are identified as the first external checks, but third-party feed has not yet been tested.

There are also commercial and technical hurdles. The reagent must remain protected through secrecy or a complete patent filing; the provisional intellectual-property position has a PCT deadline of August 2027, while a potential licensee would want granted claims rather than only a priority date. Bench recoveries must survive bulk sampling and pilot work, with impurities and downstream separation quantified. A 91.8% leach recovery is not automatically a 91.8% recovery to oxide.

For now, Cashu Research carries Selectro at zero in its valuation and will not change that treatment until a trial on someone else’s ore is published. The report identifies a successful third-party trial, followed by bulk and pilot validation, as the evidence that could move licensing from a plausible opportunity to a demonstrated business. Against a last close of A$0.042 on 16 September 2026, the maintained A$0.144 target implies about 243% upside in the research house’s framework, but that view depends on the process surviving tests that have not yet been completed.