London-listed Rainbow Rare Earths has completed a process flowsheet to efficiently extract rare earth elements from the phosphogypsum stacks at its Phalaborwa project, in South Africa.
Rainbow developed the extraction process alongside US-based K-Technologies, following extensive test work by the Australian Nuclear Science and Technology Organisation and at K-Tech’s facility.
The company says the rare earths extraction from phosphogypsum is impressive because it has historically proven to be technically, environmentally and economically challenging.
The extraction method delivers an overall recovery rate of between 65% and 70% of the contained rare earths, which compares favourably with the overall recovery of separated rare earth oxides through standard processes.
Rainbow and K-Tech plan on jointly patenting the process and applying it to more rare earth projects in future.
Now that this milestone has been achieved, Rainbow will focus on completing the technical feasibility study on the Phalaborwa project, which is poised to be one of the lowest-cost global producers of separated rare earth oxides.
Rainbow CEO George Bennett comments that, in working closely with K-Tech, the company has identified and confirmed a novel process that will allow for valuable rare earth oxides recovery, on a low capital expenditure and operational expenditure basis.
He adds that, while the configuration of this new flowsheet is innovative, each individual stage is well tested on a commercial basis, with the required equipment and reagents being readily available.
THE METHOD
Following leaching of the phosphogypsum with sulphuric acid and subsequent rapid concentration of the rare earths in the pregnant leach solution, the concentrated rare earths solution is upgraded in K-Tech's proprietary continuous ion exchange (CIX) and continuous ion chromatography (CIC) process to deliver high-purity oxides of the target magnet rare earths, namely neodymium, praseodymium, dysprosium and terbium.
CIX and CIC have both been applied commercially in multiple applications since their development in the 1980s.
These processes are now found globally in the food, biotech, chemical, water treatment, pharmaceutical and mining industries. Several of these industrial installations are found in South Africa.
The CIX/CIC process has several economic and environmental advantages over the conventional solvent extraction route, which include:
- Nine process stages are required for the CIC separation, versus hundreds of stages in the solvent extraction (SX) method, depending on the desired product mix;
- No hazardous or toxic solvents are required, whereas they are integral to the SX process;
- Capital and operating costs are significantly lower for CIX/CIC compared with SX; and
- Working capital requirements for CIX/CIC are minimised when compared with SX, owing to the shorter time required for the production and delivery of saleable product.