Rainbow Rare Earths has chosen solvent extraction (SX) as the final separation method for its Phalaborwa rare earths project, in Limpopo, a decision the company says removes a key uncertainty in the development schedule and allows it to finalise the process flowsheet ahead of construction, which is planned to start in 2027.

The company said the choice of SX follows a detailed assessment of separation options for the high-grade mixed rare earth product produced through its in-house process to recover rare earth elements (REE) from phosphogypsum.

Rainbow said the determination of the final route enabled completion of the definitive feasibility study (DFS) and kept the timeline for first production in 2028 unchanged.

Rainbow appointed ANSTO, the Australian research and minerals testing organisation, to model the two-stage SX circuit needed to produce separated neodymium-praseodymium (NdPr) oxide and a mixed rare earth carbonate containing medium and heavy rare earths.

The company said ANSTO previously carried out initial testwork for Phalaborwa and was familiar with the project, while Rainbow continued to work with METC Engineering on the associated engineering design.

"We are pleased to announce this important derisking step for Rainbow via the determination that SX offers the optimal route to final separation for our proposed +99.5% purity products, being a separated NdPr oxide and a samarium, europium, gadolinium plus other heavy rare earths (SEG+) product, combining the full suite of medium and heavy rare earths.

“The ability to design a small and efficient SX circuit has been enabled via the successes we have achieved in optimising the front-end flowsheet, and we are confident that Phalaborwa will retain its status as a low-capital intensity project," Rainbow CEO George Bennett said.

"SX is the industry standard for REE separation and purity and we have sought expert insight from Australia's ANSTO, who have designed most of the SX circuits for new Western REE projects in development. Our team has extensive experience with ANSTO, as we have worked together historically as lead process engineers on numerous studies, including the Lofdal, Ngualla and Songwe Hill rare earth projects, as well as having designed and built various uranium projects together that also utilise continuous ion exchange (CIX) and SX circuits in their design.

“We are very comfortable with these technologies and are pleased to finalise the process design for Phalaborwa, which will allow for the timely completion of the Phalaborwa DFS,” Rainbow technical director Dave Dodd added.

The company said it had previously focused on continuous ion chromatography as the separation method, as outlined in its earlier economic studies. It explained that a reduction in the volume of material fed to the separation circuit, made possible by incorporating a CIX stage for impurity removal and a cerium depletion step, meant SX could now be considered a practical alternative.

Rainbow said the impurity-rejection step allowed for a simpler and smaller SX circuit compared with traditional plants that could require many hundreds of stages.

According to the ANSTO prefeasibility report commissioned by the company, Phalaborwa will need only two small SX circuits - one for the NdPr oxide and one for the mixed medium and heavy rare earth product.

Rainbow said the circuits will contain about 75 mixer settlers in total, compared with traditional plants that often contain about 1 500 or more, and that the project, therefore, continued to align with its stated goal of maintaining low capital requirements.

The company said continuous ion chromatography remained a viable separation option but SX offered a more rapid and commercially proven pathway. Rainbow said the finalisation of the separation method meant the project design could now be completed and that the overall schedule remained on track.

It said that although development had taken longer than expected, the proposed timeline was still faster than that of most conventional mining projects, which could take up to 20 years from initial discovery to first production.

Rainbow also issued corrected annual production figures for the mix of medium and heavy rare earths that will make up the SEG+ product.

The company said the figures initially published on November were based on extraction results from a single batch of gypsum that was not representative of the full resource. It said the revised estimates, based on the Joint Ore Reserves Committee-compliant resource, lower the expected output of gadolinium and yttrium but raise the estimate for dysprosium, resulting in a total SEG+ production estimate of 718 t/y.

The company said it calculated that the value of the corrected SEG+ production, based on mid-market European prices and a payability assumption of 70%, would be about $160-million a year. It said this compared with the $80-million in its interim economic study from December 2024, which reflected expected revenue from separated dysprosium and terbium at full payability.