Australian small-cap mineral explorer Mount Ridley Mines says a proprietary leaching process it brought under its roof when it made metallurgist Chris Larder chief technology officer in July this year has demonstrated high rare earth, scandium and gallium recoveries in independent testing of samples from its cornerstone project near Esperance in southern Western Australia.
What it is now calling the Selectro leach process achieved significantly higher average returns than industry-standard hydrochloric acid, or HCI, leach testing, according to Mount Ridley. Respected Perth metallurgical and assaying laboratory Nagrom did the testing.
Mount Ridley said Selectro recorded 77-83% heavy rare earth element (terbium, dysprosium, yttrium) and 70-77% light REE (neodymium, praseodymium) recoveries on the same composite sample material as Nagrom used for HCI assessment for a baseline. Scandium recovery of 80% was a “pivotal result for one of the largest scandium resources globally, significantly outperforming the HCl baseline test”.
Gallium recovery at 56% compared with zero metal recovery with the HCI leach.
The sample material came from Grass Patch at Mount Ridley’s namesake flagship property about 25km north of Esperance. The company has outlined JORC inferred resources at Grass Patch of 367.98 million tonnes grading 57.3ppm scandium, 838.7Mt at 29.3ppm gallium and 122.5Mt at 889ppm total rare earth oxides.
ASX-listed Mount Ridley has a current market value of cA$47 million.
“These are the first metallurgical testwork results the company has produced since the definition of our HREE, scandium and gallium mineral resources and the establishment of the current management team and corporate strategy,” CEO Allister Caird said.
“The Selectro process results validate what we believed to be true about Grass Patch – that we have a genuinely polymetallic system where all three critical minerals can be recovered from a single leach process.”
Mount Ridley has said its “breakthrough leaching technology” was developed over about 10 years by Larder, who the company brought in as metallurgy and processing technical adviser in April. Three months later he became its inaugural CTO.
Larder’s more than three decades in mineral processing, flowsheet design and pilot plant development included periods spent working for Lynas Corporation on Mt Weld’s RE flowsheet and for Alcoa at its Wagerup alumina refinery, now the focus of a proposed US$200 million gallium plant.
“Mount Ridley is focused on fast-tracking the definition of a scalable, integrated processing pathway with the objective of reducing development timelines and enhancing overall project value,” Mount Ridley said in April when welcoming Larder on board.
“This includes engagement with international partners and the assessment of technology opportunities to support downstream development.”
In May when it announced metallurgical testwork had started at Nagrom, Mount Ridley said it was “progressing toward a processing solution that encompasses beneficiation extraction and separation of its regolith-hosted and collocated heavy rare earth, scandium and gallium mineralisation”.
Neither announcement mentioned Selectro.
Now it is Mount Ridley’s “proprietary hydrometallurgical technology developed to recover multiple critical minerals through a single leach process”.
“The process was developed with a focus on achieving high metal recoveries using lower-cost reagents, while incorporating reagent recycling through a closed-loop processing system,” the company said.
“The initial results represent a pivotal technical milestone for the company, demonstrating the ability of its wholly owned Selectro process to recover HREE, LREE, scandium and gallium from unbeneficiated Grass Patch material through a single proprietary leach process.
“As beneficiation and optimisation studies progress the company believes there is significant opportunity to further improve process performance and expedite future commercial development.”
