Rainbow Rare Earths has announce positive results from the ongoing phased test work programme at the Phalaborwa Project, in South Africa.

“We are delighted by this positive test work and are very reassured that results received to date continue to demonstrate Phalaborwa’s robust fundamentals. The studies have identified several key opportunities for capital and operating cost savings as well as underscoring the significant environmental benefits of the Project,” said George Bennett, Rainbow Rare Earths CEO.

The test work is being conducted in conjunction with ANSTO Minerals in Australia, a world-leading critical and strategic metals processing expert (ANSTO), and K-Technologies, the processing technology developer located in the USA (K-Tech). “The potential to participate further downstream in the value chain and produce rare earth oxides with 99.5-99.9% purity has been confirmed by K-Tech’s study, which also highlights flexibility for phased project development if required,” explained Bennett.

The results of the test work are enabling Rainbow to develop an economic rare earths extraction flowsheet currently as part of the feasibility study for the project. Results to date have provided the company with additional optimisation opportunities to explore, which can reduce both operating and capital costs for the project. The next phase of the test work programme is now underway, which includes several trade-off and project optimisation studies.

Strong recoveries and optimisation opportunities

The test work at ANSTO has confirmed that a simple acid leaching process is expected to allow 65-70% of the rare earths contained in the Phalaborwa gypsum stacks to be recovered in solution, with an average 66% leach recovery reported from preliminary metallurgical variability test work.

“As a team, we have led numerous projects through this vital development phase and recognise the enormous benefits of implementing the correct trade-offs and optimising to the greatest extent possible in order to deliver a successful end result,” added Bennett.

The K-Tech purification and separation desktop study has confirmed the ability to deliver separated rare earths with over 99% purity oxides from the leach solution.  Phalaborwa will be unique in producing separated Neodymium and Praseodymium (NdPr) oxide, Dysprosium (Dy) oxide and Terbium (Tb) oxide on site.  This will allow the full value of the rare earths to be realised – a 47% increase in revenue over the expected sales price for a mixed rare earth carbonate.

Trade-off studies have started at both ANSTO and K-Tech to determine the optimal method to maximise the grade of rare earth elements in the leach solution prior to the final K-Tech separation step, whilst managing the build-up of impurities present in the gypsum stacks that could impact overall rare earth recovery. Increasing the leach solution grade by recycling the leach solution will significantly reduce both operating and capital costs. “I firmly believe that we have the right people in place to take Phalaborwa’s development forward, with significant experience throughout the asset lifecycle from optimisation, feasibility and development to plant construction and commissioning.”

Reduced capital and operating costs

The Phosphogypsum will be hydraulically reclaimed from the stacks and pumped into the processing facility, reducing cost per tonne compared to traditional hard rock mining.

Nano filtration will successfully recycle over 60% of the sulphuric acid required to recover the rare earths to the leach solution, reducing operating and capital costs and minimising leach solution flows into the downstream K-Tech separation circuit.

Potential identified for phased development providing versatility: the K-Tech study has shown that a cerium-depleted mixed rare earth carbonate could be produced at Phalaborwa as an initial phase if required at a lower up-front capital cost.

Sulphuric acid remains the lixiviant (leaching liquid) of choice following this test work, owing to the low cost and availability of the reagent in the local area, and the simpler materials of construction requirements.

With a slight elevation to the temperature of the sulphuric acid leach solution, recovery is optimised with a 12-hour leach residence period, providing significant operating and capital cost savings compared to the initial 24-hours leach residence period originally envisaged at atmospheric temperature.

Environmental benefits

Water neutralisation test work has confirmed the ability to treat the existing water from the stacks and reuse it in a closed circuit as plant process water. This not only reduces the substantial legacy issue of acid water from historic work (prior to the company’s involvement) but will also reduce overall freshwater usage in the flowsheet. “By getting this stage of process flowsheet definition right, investigating the highlighted optimisation and trade-off opportunities identified by our considerable work to date, we aim to realise the full value of Phalaborwa and develop a responsible, independent Western rare earths supply chain,” Bennett said.

Very low levels of radioactivity have been confirmed within the gypsum extracted, significantly below the International Atomic Energy Agency (IAEA) guidelines, therefore exempting the Project from regulation pertaining to radioactivity. “I am proud that we have delivered significant progress in unlocking this opportunity at Phalaborwa for Rainbow’s stakeholders in an exceptionally short time frame since the Project was first secured in December 2020,” Bennett concluded.