Mkango Resources has announced the results of further metallurgical optimisation test work completed as part of the ongoing pre-feasibility study for the Songwe Hill rare earth project in Malawi.

Caustic conversion and hydrochloric acid dissolution test work was undertaken at Nagrom, Australia on the residue from the previous bulk leach of a rare earth concentrate. This concentrate was produced via flotation of a representative composite sample of drill core from the project. The results indicate that recoveries may be significantly enhanced by including a caustic conversion step in the flow sheet.

During the caustic conversion step, the bulk leach residue was contacted with a 50% sodium hydroxide solution at 100ºC for a 4 hour period. Upon cooling, the solids were filtered, washed and then dissolved in 5% hydrochloric acid.

Other metallurgical optimisation is ongoing, including the incorporation of a gangue pre-leach step to provide a clean solution for hydrochloric acid recycling along with improvements to the flotation stage. With respect to the latter, recent test work has demonstrated an increase in heavy rare earth recoveries to a level similar to light rare earth recoveries.

William Dawes, Chief Executive Officer of Mkango stated: “These increased leach recoveries could potentially have a significant impact on the economics of the project, in particular the increase in recoveries for neodymium, praseodymium, europium and dysprosium which account for a large proportion of the in-situ value for Songwe Hill.”

Songwe Hill’s favourable mineralogy, comprising synchysite and apatite that is anomalously enriched in heavy rare earths, means that high capital and energy intensive kilns will not be required in the flow sheet, in contrast to projects dominated by monazite, xenotime or other refractory REE minerals. Plant design will comprise conventional technology largely comprised of tanks, pumps and filters, and will be modular, facilitating the potential for future expansions, the latter underpinned by significant resource base. The use of low strength acid will enable the use of plastics or composite materials for tanks and pipework, and will facilitate acid recycling using cheaper sulphuric acid.

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