London-listed Rainbow Rare Earths has announced progress with its Phalaborwa pilot plant, with rare earth oxide (REO) separation now under way at the facilities of Rainbow’s technical partner, K-Technologies (K-Tech), in Florida, in the US.

This back-end plant process uses continuous ion exchange and continuous ion chromatography to produce separated REOs, which replaces traditional solvent extraction that uses toxic and flammable solvents and requires more than 100 separate stages.

The process will produce all four of the critical rare earths used in permanent magnets, including neodymium and praseodymium, dysprosium and terbium.

Some bench-scale testwork carried out by K-Tech is already showing positive REO separation in line with expectations. K-Tech has since started continuously running the rare earth separation processing plant.

Meanwhile, the front-end pilot plant, which is based at the Council for Mineral Technology’s facility, in Johannesburg, South Africa, has reached successful completion of two planned campaigns, from which about 5.75 kg of mixed rare earth carbonate has been shipped in five batches.

The pilot plant process involves a continual optimisation to deliver the most efficient final flowsheet for commercial-scale operations. 

The front-end plant will start running on a continuous basis from January 15, producing increased volumes of mixed rare earth carbonate to ship to K-Tech over the course of the first quarter.

As part of the front-end process, Rainbow has worked with K-Tech to establish the optimal mixed rare earth product for the back-end plant.

Rainbow explains that the additional front-end plant process removes certain unwanted elements, providing a higher-grade feedstock into the back-end separation unit.

The inclusion of this extra processing step does not add any significant capital or operating expenditure to the front-end flowsheet but reduces the quantity of mixed rare earths to be processed in the separation circuit by about 40%, resulting in capital and operating cost benefits overall.

Rainbow CEO George Bennett says that, while the company has experienced some delays from the original timetable owing to further beneficiation of mixed rare earth sulphate to produce a cerium-depleted carbonate, as well as two mechanical issues at K-Tech which took longer to resolve than expected over the holiday period, these delays have not affected the integrity of the process flowsheet. Bennett adds that the process flowsheet is progressing as planned.

He expects to report more pilot plant milestones during the first quarter of this year.

In turn, K-Tech CEO Tom Baroody says separation of the Phalaborwa material is progressing as planned, with the delivery of four separated REOs on US soil being a major milestone in the development of an independent supply chain of critical rare earths in the West.

Rainbow is recovering rare earths from phosphogypsum stacks at the Phalaborwa project, in South Africa’s Limpopo province. The rare earths are recovered as a by-product of phosphoric acid production, with the original source rock for both deposits being a hard rock carbonatite.

The Phalaborwa preliminary economic assessment has confirmed strong base line economics for the project, including a net present value of $627-million and a payback period of less than two years.

The project is expected to reach commercial production in 2026, five years after work began on the project.