LSE-listed Rainbow Rare Earths has started operations at its Johannesburg pilot plant, marking the final phase of process testwork for the Phalaborwa rare earths project in South Africa.

The operation is designed to validate the company’s optimised flowsheet and generate data to support the definitive feasibility study (DFS) and third-party project finance validation.

The pilot plant will operate the full-scale leach circuit, producing pregnant leach solution (PLS) that feeds a continuous ion exchange (CIX) and impurity removal circuit developed using Rainbow’s intellectual property.

The bulk feed sample generated will be used for off-site solvent extraction (SX) testwork, confirming the separation process for high-purity neodymium/praseodymium (NdPr) oxide, as well as other medium and heavy rare earths, such as samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and yttrium (SEG+).

Rainbow expects the pilot operations to continue throughout the first half of this year.

“This new piloting operation is the final phase of process testwork for Phalaborwa, as it will demonstrate the project flowsheet that has been considerably updated over the past 18 months through a number of key optimisations.

“These efficiencies further reinforce the project’s position at the bottom of the industry cost curve to deliver high-purity (more than 99.5%) separated NdPr oxide and SEG+ products. The pilot operations are important to the finalisation of the DFS this year and ensure the long-term success of the Phalaborwa project,” Rainbow Rare Earths CEO George Bennett said.

The Phalaborwa project is unique in that it will be the first commercial operation to recover rare earth elements (REEs) from phosphogypsum, a byproduct of phosphoric acid production. This approach reduces the costs, risks and timelines typically associated with traditional mining projects.

The pilot plant will also provide essential data for the DFS, including process flowsheet development, mass balance, equipment sizing and capital and operating costs.

The pilot plant is operating at Rainbow’s in-house laboratory premises at Mintek, South Africa’s national mineral research organisation. This follows a previous pilot plant operation concluded in mid-2024, which contributed to a series of significant optimisations in the Phalaborwa flowsheet. These include the addition of a CIX circuit for impurity rejection, subsequent impurity precipitation steps and a simplification of the SX separation process.

The leach process has been optimised through large-scale locked cycle tests, which have reduced the number of leach stages from three to two, cut the residence time from 32 hours to eight, lowered the number of filters from 14 filters at 180 m² to seven filters at 163 m² and significantly reduced heating requirements. These improvements are expected to positively impact both capital and operating costs.

The pilot plant will produce the bulk feed sample required for off-site SX testwork, allowing Rainbow to finalise product specifications for NdPr oxide and SEG+ products. These specifications are critical to concluding offtake agreements for the high-demand products.

The company reported that the outlook for the REE market remains strong, with pricing for NdPr oxide having risen to more than $100/kg following significant increases in medium and heavy REE prices, which are subject to Chinese export controls.

Rainbow highlighted that Phalaborwa’s ability to produce a full range of economically and strategically important REEs has secured backing from the US International Development Finance Corporation as a contributor to supply chain resilience.