The ore will be processed through a beneficiation and hydrometallurgical facility collocated on site to produce a high purity, dysprosium rich, mixed RE carbonate for export.
The xenotime mineralisation found at Browns Range is rich in dysprosium and other high value heavy rare earth oxides2 (HREO). The xenotime, in combination with the mainly silica host rock, allows the ore to be upgraded, up to 30 times through the beneficiation process with excellent recoveries. This recovery and upgrade ratio has resulted in a competitive pre-production capital cost estimate.
Stage one: test
The pilot plant will consist of all the processing steps detailed in the Project’s Definitive Feasibility Study (DFS) and in stage three below. However, the plant will be downsized to a capacity to process 60,000tpa of ore at 1.19% total rare earth oxides1 (TREO) through the beneficiation plant, and 3,200tpa of xenotime concentrate at 20% TREO through the hydrometallurgical process. The final product will contain 49,000kg dysprosium in 590,000kg TREO within a mixed RE carbonate per annum.
The pilot plant will be modularised and containerised where possible, to facilitate a compressed site construction period and allow it to be transported to undertake testwork at other projects if required.
Stage two: develop
Produce a premium product
Significant opportunity exists to reduce downstream solvent extraction (SX) separation costs, by separating yttrium in the hydrometallurgical process.
Removing approximately 90% of the yttrium results in less mixed RE carbonate being produced, and less material required to be processed through the downstream SX separation process.
With current market signals indicating that sale of the yttrium oxide is likely to be limited for the foreseeable future, this step will increase the percentage of the dysprosium in the mixed RE carbonate product from 9% Dy/TREO to around 20% Dy/TREO.
Completion of initial testwork at ANSTO Minerals has indicated that removal of yttrium, lanthanum and cerium can be achieved through a relatively simple addition to the hydrometallurgical process. Any further studies will progress in line with funding.
Stage three: full scale
The full scale beneficiation plant will process 585,000tpa of ore to produce a high grade mineral concentrate to feed into the hydrometallurgical plant. The process consists of:
- a crushing and grinding circuit; and
- a combination of wet high gradient magnetic separation, and flotation.
The overall beneficiation circuit delivers outstanding recoveries of 91% dysprosium and 87% TREO at a 20% TREO mineral concentrate grade.
The proposed hydrometallurgical plant will use conventional unit processes to treat 16,700tpa of mineral concentrate from the beneficiation plant. The hydrometallurgical plant processes include:
- sulphation bake followed by water leach;
- purification of the leach liquor to remove deleterious elements; and
- carbonate precipitation step to precipitate a mixed RE carbonate.
The hydrometallurgical plant will produce 279,000kg of dysprosium contained with 3,127,000kg of TREO, in 6,000,000kg of mixed RE carbonate per annum.
These processes and the final production numbers do not take into account the yttrium rejection test work and flowsheet development to be completed during stage two.
Mixed RE carbonate
Following feedback from a number of potential offtake partners and toll-separators, Northern Minerals will produce a mixed RE carbonate which is the preferred feedstock for downstream processing by SX.
¹TREO = Total Rare Earth Oxides – La2O3, CeO2, Pr6O11, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb4O7, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, Y2O3²HREO = Heavy Rare Earth Oxides – Total of Sm2O3, Eu2O3, Gd2O3, Tb4O7, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, Y2O3