THE NOLANS NdPr PROJECT - DEVELOPING A FLOWSHEET WORKING WITH ORE CHARACTERISTICS TO OPTIMSE PROJECT OUTCOMES

摘要

Arafura Resources' flagship project and key focus is the Nolans Rare Earth Project, one of the world's largest and most intensively explored rare earth deposits, located in the Northern Territory of Australia, close to the Stuart Highway and about 130 km by road from Alice Springs. The rare earths are associated mainly with apatite (a calcium phosphate mineral), monazite (a rare earth phosphate), and allanite (a calcium and rare earth silicate mineral). The Project has undergone extensive development over the last 15 years including multiple test work and piloting programs and numerous feasibility studies aimed at developing an efficient flowsheet for the treatment of the Nolans ore to produce rare earth oxide products. Three major flowsheet developments have been undertaken on the road to the definitive feasibility study (DFS) and Project financing. In the first flowsheet iteration, known as hydrochloric acid pre-Ieach, the apatite concentrate was pre-leached with hydrochloric acid to dissolve the calcium phosphate prior to sulphation of the rare earth minerals using a sulphuric acid baking process. The "cracked" rare earths were solubilised in water, and impurities (Fe, Al, Th) removed as a solid residue prior to uranium recovery by ion exchange, and precipitation of the rare earths as a mixed carbonate precipitate. The mixed carbonate was dissolved in hydrochloric acid as feed to a solvent extraction rare earth separation process, to produce five 99% purity rare earth oxide products (Cerium oxide, Didymium oxide, a mixed heavy rare earth oxide, Lanthanum oxide and a mixed Samarium, Europium and Gadolinium oxide). The hydrochloric acid used in pre-Ieach was regenerated from a residual calcium chloride solution formed following phosphate precipitation from the pre-Ieach liquor to produce a calcium phosphate product.Evaluation of the hydrochloric acid pre-Ieach flowsheet showed excellent metallurgical performance but at extremely high capital and operating costs, and therefore an alternative flowsheet was developed. The second flowsheet iteration, known sulphuric acid pre-Ieach with double sulphate precipitation (SAPL-DSP) carried out a pre-Ieach of the phosphate concentrate using recycled water leach liquor high in sulphuric acid, to dissolve the phosphate. The resulting gypsum rich pre-Ieach residue was then cracked with sulphuric acid and fed to water leach with the water leach liquor recycled to pre-Ieach. The pre-Ieach liquor, rich in rare earths, was fed to DSP to recover the contained rare earth elements. The resultant rare earth sulphate precipitate, rich in rare earth phosphates, required conversion to a hydroxide prior to production of a cerium product in a selective hydrochloric acid leach which also produced the rare earth chloride feed for separation. Rare earth separation then produced a 99% pure mixed heavy rare earth carbonate, a 99.9% pure NdPr oxide, and a 99% pure lanthanum oxide product using solvent extraction. Again, the SAPL-DSP flowsheet provided good metallurgical performance but operating costs, particularly reagent consumption, was high and capital costs were also above the level needed to provide satisfactory Project returns. Working with the orebody characteristics, Arafura has subsequently developed and demonstrated the viability, over the last four years, of a phosphoric acid pre-Ieach (PAPL) flowsheet which works with the mineralisation to minimise both capital and operating costs and provide significant improvements to Project outcomes. This paper provides a technical overview of the PAPL process in comparison to previous flowsheets as well as an insight into the significant piloting efforts recently completed which demonstrate the technical viability of the Project. Finally, a snapshot will be provided on the results of the recently completed DFS and the planned Project activities aiming for production from the Nolans Project in the near future.