Rainbow Rare Earth, Mosaic begin economic assessment on REE extraction in Brazil

Rainbow Rare Earths (LON: RBW), in collaboration with Mosaic, has kicked off work on an economic assessment (EA) for the recovery of rare earth elements (REEs) from the Uberaba phosphogypsum project in Brazil.

The EA, says Rainbow, is intended to allow for both parties to understand the project’s economics ahead of considering a partnership to potentially replace the current non-binding memorandum of understanding between the parties.

Mosaic, the world’s leading producer of concentrated phosphates and potash crop nutrients, is the project’s owner.

According to Rainbow, the Uberaba phosphogypsum contains valuable REEs that occur as byproducts of the phosphoric acid (phosacid) production operations on site, and its pioneering IP can be applied to recover these minerals.

The material is similar in nature to its Phalaborwa project in South Africa, in that it’s based on a hard rock carbonatite phosphate deposit, which is mined to initially produce a phosphate slurry feed that is then processed into phosacid using sulphuric acid, the company said.

This process, it added, delivers phosphogypsum material that contains most of the REE present in the phosphate slurry feed.

While public data is not available on the size of the Uberaba resource, initial indications are that it could be significantly larger than Phalaborwa, Rainbow has said. In addition, Mosaic’s phosacid operations are ongoing and are based on long-life phosphate mines, meaning that new phosphogypsum is deposited on the stacks annually.

“Uberaba is an exciting project for Rainbow, given the technical similarities with Phalaborwa; however, it represents a significantly larger economic opportunity over the long-term due to the sheer scale of the planned annual feed rate and the long-term nature of the underlying phosphate deposit,” George Bennett, CEO of Rainbow, commented in a news release Tuesday.

As at Phalaborwa, the Uberaba phosphogypsum is amenable to direct acid leaching, with test work to date demonstrating that between 31% and 65% of the REE can be readily extracted, Rainbow said on its website.

Assay work has returned grades of between 0.45% and 0.79% total rare earth oxides, with Nd/Pr being 24.5% of the rare earths basket, plus economic quantities of Dy and Tb. The average grade, which will be used in the EA, is 0.58% TREO.

EA details

Under the existing MOU, Rainbow and Mosaic have developed a process flowsheet for extracting REEs from the Uberaba stack for the EA work.

The flowsheet would receive phosphogypsum from the Uberaba phosacid process facility and treat the material for REE extraction. The chemically processed and cleaned phosphogypsum stream is then returned to Mosaic’s facility.

The EA envisages an operation processing capacity totalling 4.3 million tonnes of phosphogypsum per annum, which is around twice the annual size of Phalaborwa.

As at Phalaborwa, the EA is based on the establishment of a single hydrometallurgical plant on site, which will refine the material into separated rare earth oxides of +99% purity, Rainbow said.

The EA will be based on an initial project life of 15 years. Due to the life of mine of the underlying phosphate resource feeding the phosacid plant at Uberaba, recovery of rare earths can be expected to extend for a far longer period.

The third-party costs of $230,000 to develop the EA will be shared equally between Rainbow and Mosaic, as the companies had agreed in the MOU.