The tests produced two products through conventional acid leaching technology, both of which contained significant quantities of the most valuable heavy rare earth elements.
A high grade mixed rare earth carbonate product contained 59% rare earths in total, with 7% of these in the heavy category.
The second product stripped out light rare element cerium to leave a heavy rare earth enriched mixed hydroxide concentrate with 55% total rare earths and 18% of the heavier elements.
The simple, low temperature acid leaching achieved recoveries of up to 90% and above of Neodymium, Europium, Terbium, Dysprosium and Yttrium, all of which are seen as critical components in the next wave of consumer products, electronics and clean energy applications.
Under the proposed flow sheet, Mkango added it should be able to use a modular plant design for processing with conventional technology.
This will mean lower capital expenditure and make expansion easier and cheaper.
William Dawes, Mkango's chief executive, said today's announcement was a major milestone for the company.
"We delineated the Indicated and Inferred mineral resource estimate late last year which goes a long way towards de-risking the project geologically.
"Now we need to look at how we extract the rare earths and demonstrate that we can produce a saleable product.
"Today's announcement is a major stepping stone towards that."
It was significant that during the flotation, leaching and purification steps the overall proportion of heavy rare earths was maintained and enhanced in the case of the hydroxide product, he added.
The next stage is to produce samples of concentrate on a larger scale to facilitate discussions with refineries and offtakers.
Dawes says the progress at Songwe Hill so far has been such that the company believes it has a very real chance of getting into production.
"We have a strong platform for growth in a major undeveloped and world class rare earths mineral province in Malawi in a commodity that will be very important to the growth plans of future emerging market economies i.e consumer electronics and clean energy.
"So, we are in the right place, have got the resource, have got the flow sheet, and now have demonstrated we can produce products."
The next step, he said, will be to refine the flow sheet as part of pre-feasibility study (NYSE:PFS) and to continue discussions with potential offtake partners and refineries.
At a 1% cut-off, Songwe Hill has a NI 43-101 compliant indicated resource of 13.2mt grading 1.62% total rare earths (TREO), with 18.6mt at 1.38% in the inferred category.
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