ABx testing shows heavy rare earths recovered by cold water leaching

The first leach-test results from ABx Group’s rare earth elements mineralisation at its Tasmanian bauxite project have confirmed the rare earths can be leached by cold water, with enhanced reaction times and recoveries if ammonium sulphate is added to the mix. Importantly, the heavy rare earth elements are enriched in the precipitate and deleterious elements are depleted and only very low radioactive elements remain in the concentrate.

ABx says a commercially attractive concentrate may be achieved from the company’s rare earth element mineralisation which would make the predominantly bauxite project even more economically viable. 

The recipe ABx used was to collect composite bulk samples from across the mineralised zone that were then soaked in cold distilled water at approximately 12 degrees Celsius for 24 hours. The cloudy liquids were then filtered-off using a 125-micron sieve and placed in a drying oven at 105 degrees Celsius. After drying, the bulk samples and the precipitates were assayed by a commercial lab and results showed that all rare earths, apart from cerium were significantly enriched in the precipitate with a strong depletion of deleterious elements such as calcium, phosphorus and manganese. Significantly, the radioactive elements uranium and thorium were very low grade in all fractions analysed. 

The rare earths mineralisation is a fortuitous and unexpected value-add to ABx’s Tasmanian bauxite project, especially as they are relatively free of the radioactive elements which means a simple bulk rare earth concentrate can likely be produced and sold to existing processing plant operators. ABx now believes it has discovered “water-soluble” rare earths that can be concentrated into a saleable precipitate simply by low-cost leaching with dilute water-based solutions.

Intriguingly, there was a 400 per cent enrichment of sulphur in the precipitate which was unexpected. The company suggests this may indicate soluble rare earths may be leached more strongly by dilute sulphate solutions.  A test using dilute solution of ammonium sulphate and water is in progress to test this concept.

ABx says the results are consistent with ionic adsorption clay type of rare earths mineralisation. Importantly, the mineralisation is enriched in the super-magnetic rare earth elements neodymium, praseodymium, terbium and dysprosium which are strategically important, high-priced metals needed for electric vehicles, wind turbines, smart phones and military electronics.  The fact that the leaching process trialled by ABx is not favourable for the recovery of cerium is not an issue according to management, as some buyers prefer low cerium concentrates.

ABx Operations Manager, Nathan Towns said; “This research work will continue to provide a better understanding of the potential of our rare earth element mineralisation. The current results support our interpretations that the REE occurs as ionic substances that are loosely bound to clays and are therefore relatively easy to leach and precipitate a concentrate that is saleable. The mineralisation appears to be Ionic Adsorption Clay deposits which have been a major source of low-cost REE production in southern China until recently”

ABx says it is one of only three publicly listed companies in the world targeting ionic adsorption clay-type rare earth element deposits. Currently there are only five producing heavy rare earths mines in the world and they are all in China. ASX-listed Northern Minerals’ pilot plant in northern Western Australia is also capable of producing heavies such as dysprosium which is a key rare earth element for electric engines.

ABx is now conducting further metallurgical tests on bulk samples to confirm the deposit type and will continue assembling results to design a low-cost concentration method for its particular type of rare earths mineralisation.

Prices for the four super-magnet heavy rare earths are still rising strongly and have more than doubled in the last twelve months which makes this style of mineralisation where the rare earth elements are loosely ionically bound to clay minerals quite advantageous as it can be developed, processed and sold rapidly.  

With high demand and a tight supply, ABx will be keenly assessing the value of its easily processed rare earths that may be lurking in and around its bauxite deposit.

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