London-listed Rainbow Rare Earths has made progress with the ongoing rare earth oxide separation work under way at the back-end pilot plant, which is located at the facilities of Rainbow’s technical partner K-Technologies (K-Tech) in Florida, in the US, with group separation of the rare earth elements (REEs) achieved in the initial ion exchange testwork.

The back-end plant process uses continuous ion exchange (CIX) and continuous ion chromatography (CIC) to produce separated rare earth oxides.

The application of this established technology has been pioneered by K-Tech in the rare earths space and replaces traditional solvent extraction, which uses toxic and flammable solvents and diluents and requires more than 100 separate stages, Rainbow points out.

As previously announced, the optimal feed for the back-end process has been determined by Rainbow and K-Tech as a cerium-depleted mixed rare earth carbonate, which provides a higher-grade feedstock to the back-end separation circuit.

The initial separation at the back-end pilot plant has been achieved using the mixed rare earth carbonate successfully produced from phosphogypsum from the Phalaborwa rare earth project in Limpopo, South Africa.

This material, which includes cerium, was previously shipped to K-Tech from the front-end pilot plant located at the Johannesburg facilities of national mineral research organisation the Council for Mineral Technology (Mintek).

Cerium depletion test work is ongoing at both K-Tech and Mintek and the cerium-depleted carbonate, once available, is expected to produce better results in the CIX or CIC separation circuits.

The back-end plant process comprises three main stages.

The current focus of the pilot plant test work at K-Tech is to optimise the second stage of the chromatography process to produce a 99.5% neodymium and praseodymium product. This will be followed by CIC testing to separate and purify the separate dysprosium and terbium oxides.

In addition, the production of a separated and purified samarium, europium, gadolinium (SEG) oxide product will be evaluated and followed up.

Initial indications are that Phalaborwa could produce about 500 t/y of a saleable SEG product which, in addition to the previously announced offtake for the residual gypsum, provides the potential for an additional revenue stream for the project with minimal capital and operating costs.

“I am very pleased with the continued progress to date validating our front-end process flow sheet and the K-Tech CIX or CIC process flow sheet for the back-end. The back-end process is on track to deliver separated high purity rare earth oxides of neodymium and praseodymium, dysprosium and terbium, the four most economically important rare earth elements due to their crucial role in the green energy transition.

“It is also notable that we have achieved positive separation in the chromatography circuit of the SEG group of rare earth oxides, which could add another very saleable product and revenue stream to Rainbow at minimal cost,” says CEO George Bennett.

He acclaims that the four rare earths that will be produced at Phalaborwa are all designated as critical minerals further to their role in the transition to the green economy.

“As vital components of permanent magnets, these REEs are used within electric vehicles and wind turbines, as well as many other advanced technologies including those required for strategic defence purposes, such as guided missiles, drones, electronic displays, sonar and jet fighter engines.

“The SEG rare earths are samarium (used in magnets), europium (used in optical displays) and gadolinium (used in medical and nuclear applications),” Bennet explains.