London-listed Rainbow Rare Earths has started a prefeasibility study (PFS) for the Uberaba project, in Brazil, in conjunction with partner NYSE-listed Mosaic Company.  

Following the positive outcome of an economic assessment in March, which confirmed Uberaba as a second major development opportunity for Rainbow, the decision was made to proceed with a PFS. 

The appointment of SRK Consulting to complete a mineral resource estimate (MRE) is the first of a number of leading technical consultants expected to be engaged for the study, Rainbow points out.

The Uberaba project is located in the Minas Gerais state of Brazil where Mosaic is currently mining phosphate rock and producing phosphoric acid for use in the fertiliser industry.

The PFS will focus on building a processing plant on site to process the phosphogypsum waste residue at a yearly throughput of about 2.7-million tonnes over an initial project life of 30 years, with an originally modelled head grade of about 5 100 parts per million total rare earth oxides, and the potential to extend the life of the project owing to the underlying long life of the phosphate feedstock at Uberaba.

Rainbow has leveraged the proprietary intellectual property (IP) developed for the Phalaborwa rare earths project to establish a flowsheet for Uberaba, in conjunction with further testwork between Rainbow and Mosaic, demonstrating the potential to replicate and apply the Phalaborwa process at other phosphogypsum projects.

Mosaic is currently shipping a further about 6 t of phosphogypsum feedstock to Rainbow’s laboratory and pilot plant in South Africa for further testwork and piloting.

The project will produce separated neodymium and praseodymium oxide and a samarium, europium and gadolinium plus mixed rare earth carbonate that is rich in medium and heavy rare earth elements (REEs), each at 99.5% purity.

As announced in March, the Uberaba economic assessment demonstrated a post-tax net present value of $916-million, a post-tax internal rate of return of 45%, average earnings before interest, taxes, depreciation and amortisation of $217-million a year over a 30-year life-of-mine and a payback of 1.7 years, using spot rare earth pricing reported by Argus Media at the time.

“Following the successful results of the economic assessment and the signing of the joint development agreement with Mosaic, we are pleased to continue our partnership with the start of the PFS and appointment of SRK Consulting to complete the Joint Ore Reserves Committee-compliant MRE for the Uberaba project,” says Rainbow CEO George Bennett.

“Uberaba is expected to demonstrate the value of Rainbow’s proprietary IP across other phosphogypsum projects. Strategically situated in Brazil, a crucial hub for rare earths supply chain independence and the focus of extensive US government support for the industry, and with the potential to deliver near-term REE production in the lowest-cost quartile, Uberaba represents a valuable opportunity for Rainbow to further leverage the expertise we have developed at Phalaborwa,” he adds.