• Selectro recovered 91.9 per cent of the aluminium and 96.7 per cent of the iron from a Darling Range bauxite composite supplied by Australian Silica Quartz Group.
  • The result is from a first-pass laboratory test on a roughly one kilogram composite that the company says is not intended to represent the deposit as a whole.
  • Mount Ridley intends to accelerate design and construction of a Selectro demonstration plant, and says it remains funded for this.

Mount Ridley Mines Limited (ASX:MRD) has announced the first third-party test of Selectro, its wholly owned, patent-pending leach process. The sample was a bauxite composite supplied by Australian Silica Quartz Group Ltd (ASX:ASQ) from its Darling Range bauxite project in Western Australia. It is also the first application of Selectro to a feed from outside Mount Ridley's Grass Patch Complex. Testwork was conducted by Australian Laboratory Services (ALS), and the company says the result was achieved on a first-pass basis, with the chemistry not yet optimised for bauxite.

The results

The composite had a head grade of 41.9 per cent aluminium as alumina and 13.6 per cent iron as iron oxide. Selectro recovered 91.9 per cent of the aluminium and 96.7 per cent of the iron, which the company rounds to 92 per cent and 97 per cent. Mount Ridley says these are recoveries of metal extracted to solution, calculated from residue and head assays, and that the test was run below 100 degrees Celsius.

The dried leach residue was about 25 per cent of the original feed mass and was predominantly silica, with more than 90 per cent of the silica remaining in the residue. The company describes it as small, neutral in pH and silica-rich, in contrast to the caustic, iron-rich red mud produced by conventional Bayer refining. It adds that iron can be precipitated from the leach solution by a simple pH adjustment, which could Yield an iron oxide product that may be saleable.

What the sample does and does not represent

The composite was blended from 16 vacuum drill samples taken from four holes across the Athena and Ceres prospects, which ASX-listed Australian Silica Quartz collected in 2013 and 2014, giving a sample of about one kilogram. Mount Ridley states that it has not independently verified the drilling, sampling or survey data, and that the composite is not intended to represent the deposit as a whole. These limits matter when reading the recoveries, which describe one small sample rather than a resource.

Comparison with the Bayer process

The release compares Selectro with Bayer digestion, which it says runs at about 145 degrees Celsius for gibbsite-rich bauxite such as Darling Range ore. The company cites red mud generation of 1 to 1.5 tonnes per tonne of alumina, and says Selectro could suit high reactive silica bauxite, which is often uneconomic under Bayer, as well as smaller deposits too small for a conventional refinery. These are the company's views and have not been demonstrated at scale. The industry statistics in the release, such as global aluminium output and red mud stockpiles, are background from the company and not results of this test.

One statement in the release, that calcined alumina is achieved by molten salt electrowinning, appears to describe aluminium smelting rather than alumina refining, so readers should treat that passage with caution.

Next steps and conditions

Mount Ridley lists several next steps. It plans to optimise the chemistry for bauxite and demonstrate separation and purification to recover aluminium and iron products, either in-house or with industry partners. Flotation testwork on Grass Patch feed is complete with assays pending, after which concentrates will be treated with Selectro. The company expects further third-party testing ahead of the first quarter of 2027 timeframe it previously indicated, and says gallium results from the bauxite are expected within a week using a more sensitive assay method.

It also intends to accelerate the design and construction of a Selectro demonstration plant, and says it remains funded for this. Licensing to refiners is described by the company as the most direct route to adoption, alongside strategic partnerships and government programmes.

The release contains forward-looking statements, and there is no certainty that laboratory performance will carry over to a pilot or commercial scale, or that any commercial arrangement will follow.