London-listed Rainbow Rare Earths has signed a memorandum of understanding (MoU) with the Mosaic Company to jointly conduct a preliminary economic assessment (PEA) related to the extraction of rare earth elements (REEs) from Mosaic’s phosphogypsum stack, in Brazil. 

Mosaic is an integrated producer of concentrated phosphate and potash, with its phosphogypsum stack being located in the Uberaba area of Minas Gerais.

Rainbow expects the Uberaba stack to have a similar grade and REE make-up to that of its Phalaborwa project, in South Africa, because both operations involve a hard-rock carbonatite phosphate deposit being mined and processed into a phosphate slurry before being processed into phosphoric acid.

The Uberaba phosphogypsum stack contains valuable REEs that occur as byproducts of phosphoric acid production.

While the hard-rock carbonatite does not contain rare earths in sufficient quantities to be mined for these elements alone, the plant processes it undergoes serve to concentrate the quantity of rare earths contained therein, resulting in higher concentrations of rare earths than are in the original hard rock.

This process also subjects the material to sulphuric acid and heat, which effectively leads to ‘cracked’ chemical phosphogypsum material at Phalaborwa and which is expected to have achieved the same at the Uberaba stack.

The benefit of this is that it can render the rare earths associated with the phosphogypsum amenable to direct acid leaching, which allows for a simpler hydrometallurgical process to produce separated and purified rare earth oxides.

Rainbow plans to develop a process flowsheet in conjunction with Mosaic, which will incorporate the proprietary technology developed at Phalaborwa to extract the REEs. Thereafter, the companies will collaborate on producing a PEA of this opportunity.

Rainbow CEO George Bennett says the agreement with Mosaic represents a major opportunity for Rainbow to apply the proprietary extraction technology it developed in conjunction with K-Tech, to become a multi-asset producer of REEs from secondary sources.

“The geographic diversification of our portfolio further de-risks Rainbow as one of the only rare earth development companies with multiple near-term production opportunities and aligns with our aim to be a forerunner in the establishment of an independent and ethical supply chain of the REEs that are driving the green energy transition,” he adds.

In turn, Mosaic senior VP Corrine Ricard says Mosaic has made considerable strides over the years in advancing gypsum reuse, with the Rainbow collaboration work being a natural extension of that.

“As we execute our mission to help the world grow the food it needs, the opportunity to further harness shared value out of the coproducts we produce benefits Mosaic and its stakeholders,” she notes.