Metallurgy, on Wigu Hill material
An update on the mineral processing and metallurgical testwork performed to date on the bastnaesite-rich carbonatite material from the Wigu Hill Rare Earth Project in Tanzania. In early 2010, Montero approached Mintek, an internationally recognized metallurgical research and testwork facility in Johannesburg, South Africa, to test the Wigu Hill carbonatite for recovery of Rare Earths. Mintek has over 25 years of experience working performing research and testwork developing economic process routes for various Rare Earth mineralizations.
Montero’s strategy is to become the first Rare Earth (“REE”) materials producer in Africa which required embarking on a series of early-stage metallurgical testwork on the mineralised carbonatite material from Wigu Hill. Early in 2010, the initial mapping of Wigu Hill demonstrated a potential for a significant REE mineralized system. The major challenge would be the mineral beneficiation, hydrometallurgy, and production of saleable rare earths. A research program to identify, test and determine the critical path to rare earth production was the justification for starting the testwork in parallel with such an early stage in the exploration program. In 2010, Montero established a team led by Mike Evans that worked with Mintek on an extensive literature research program to identify:
1) a minerals processing route to produce a bastnaesite mineral concentrate and 2) a hydrometallurgical process route for the production of saleable rare earth products.
Montero delivered the first representative bulk sample to the Mintek facility in Johannesburg on June 2010 followed by a second sample in July 2011. These unweathered, course grained bastnäsite-rich samples were taken from trenches and pits in the Twiga and Tembo Zones where Montero has subsequently completed a NI 43-101 Inferred Resource Estimate (see news release dated 12/09/2011).
1) Preliminary Minerals Processing Testwork to produce a bastnaesite mineral concentrate
The basnasite-rich samples from Wigu Hill were initially sent for mineralogical analysis, crushed, assayed by element and chemical analysis, and then subjected to a mineral processing testwork program which included tests such as; screening, gravity separation, magnetic susceptibility, X-ray sorting, and flotation. The objective was to upgrade the run of mine (ROM) mineralized carbonatite material to a bastnäsite-rich mineral concentrate. This mineral concentrate potentially could be sold “as is” to downstream REE processors, or alternatively, become a feed stock to a hydrometallurgical refinery designed to process this bastnäsite concentrate into a variety of saleable rare earth chemical products. At present, this testwork program on mineral processing remains in progress.
2) Preliminary Hydrometallurgical Refinery Testwork to produce saleable Rare Earth chemicals
The detailed literature work enabled the team to develop a hydrometallurgical flowsheet with a two-stage Rare Earth Refinery recovery process;
- Stage 1 Refining – The leaching of the bastnäsite mineral concentrate from the mining and mineral processing plant followed by a precipitation stage to produce a Mixed Rare Earth Oxide (“MREO”) or chloride saleable product, , and;
- Stage 2 Refining –The continued processing of the MREO concentrate solution and the extraction via Solvent Extraction (SX) and/or Ion Exchange (“IE”) technology to separate the individual REE’s.
To view a conceptual illustration of the flowsheet currently being evaluated click here
In early 2011, Mintek initiated a Hydrometallurgical Refinery testwork program to develop a leaching and extraction process for the production of high purity rare earth saleable chemical products. Details are outlined below.
Stage 1 Refinery Testwork
Leaching tests were performed using a variety of leaching lixiviants. From this testwork program, it was determined that a leach process using hydrochloric acid (“HCl”) was the most efficient for the Wigu Hill bastnäsite-rich material. Acid consuming gangue material is dissolved using hydrochloric acid in order to expose the bastnäsite-rich material. The residue is then leached with caustic soda to remove the silica and expose the rare earths minerals for subsequent dissolution in a further hydrochloric acid leach. Following the success of this initial test work program, a second stage program was completed, and more recently, a third stage of leaching tests is currently being performed to provide further optimization information for the leaching process. The third stage optimization tests will provide a definitive process route for the leaching of the Wigu Hill mineralized carbonatite.
The results to date are encouraging. In addition to optimizing the main leaching processes, the testwork program included detailed mineralogy of the residues from the various process stages. Testwork also evaluated the potential for recycling the spent hydrochloric acid and caustic soda reagent streams, modelling the process with SysCAD mass balance software. SysCAD was used to model the bulk leaches and the phases to produce a MREO saleable product. The final product of this process will also provide a feed solution for the Stage 2 Refining testwork.
Stage 2 Refinery Testwork
Montero and Mintek will embark on a testwork program that will commence in early 2013 to define the process route to take the MREO feedstock and produce individual, pure rare earth chemicals. On completion of this testwork program, the target is to complete a feasibility study for the Stage 2 Refinery and the upgrade of the Stage 1 Refinery to a larger production of REE chemicals.
The Stage 1 hydrometallurgical Refinery optimization testwork is targetted for completion by year end and presented by Mintek for evaluation by Montero. This will generate sufficient data to form the Design Basis for a Feasibility Study. The deliverables of this feasibility study will be a “Demonstration Plant” for a Leaching and Mixed Rare Earth Oxide (“MREO”) refinery facility targeting the production of 3,000-5,000 tpa of MREO chemical products for sale. The facility will also provide pregnant solution for solvent extraction testwork leading to the Feasibility Study of the Stage 2 Refinery that will target production of the individual rare earth chemicals for sale.
Montero has an expert metallurgical and hydrometallurgical team to undertake this work.