Rainbow Rare Earth, Mosaic study REEs in Brazil

First production of mixed rare earth sulphate at Phalaborwa.

Rainbow Rare Earths (LSE: RBW) and fertilizer giant Mosaic (NYSE: MOS) are testing the economics of recovering rare earth elements (REEs) from waste stacks at their Uberaba phosphogypsum joint venture project in Brazil.

Public data isn’t available on the size of the Uberaba resource, but initial indications are that it could be significantly larger than Rainbow’s Phalaborwa project in South Africa, according to the company. While Phalaborwa reprocesses old stacks from a closed operation, the stacks at Underaba and Mosaic’s stacks across Florida are constantly growing as a by-product of fertilizer production. Rainbow says its pioneering method can be applied to recover REEs.

“Uberaba is an exciting project for Rainbow, given the technical similarities with Phalaborwa,” Rainbow CEO George Bennett said in a news release. “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.”

The study envisages an operation processing capacity totalling 4.3 million tonnes of phosphogypsum per annum, which is around twice the annual size of Phalaborwa. The work could lead to a partnership replacing the current non-binding memorandum of understanding between the companies. 

REEs in phosphate 

The Uberaba phosphogypsum contains valuable REEs that occur as byproducts of the phosphoric acid (phosacid) production operations on site.  The material at Underaba is similar in nature to that at Phalaborwa 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. 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.

Study details

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

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.

As at Phalaborwa, the study 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 study is to 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 study will be shared equally between Rainbow and Mosaic.