Metallurgy, on Wigu Hill bastnaesite 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 have over 25 years of Rare Earth experience working on research and testwork programs developing economic process routes for various Rare Earth materials.

Montero’s strategy to become the first Rare Earth Element (“REE”) producer in Africa required embarking on a series of early preliminary metallurgical testwork and analysis on the mineralised carbonatite material from Wigu Hill. In early as 2010 the initial mapping of Wigu Hill demonstrated the potential for a significant mineralized system where 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 reason for starting the testwork at 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, obtained from the Twiga and Tembo zones at Wigu Hill, to the Mintek facility in Johannesburg in June, 2010 followed by a second sample in July, 2011. These un-weathered and course grained bastnaesite 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 samples were initially sent for mineralogical analysis, crushed and assayed and then submitted for a program of mineral processing testwork which included; screening tests, gravity tests, magnetic susceptibility tests, X-ray sorting, and flotation tests. The target was to upgrade the run of mine mineralized carbonatite material to a rare earth mineral concentrate (essentially a bastnaesite mineral concentrate) which could potentially be sold as is to interested parties or become the feed stock to a hydrometallurgical refinery for the processing and sale of rare earth chemical grade products. This mineral processing testwork is still 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 bastnaesite mineral concentrate from the mining and mineral processing plant followed by a precipitation stage to produce a Mixed Rare Earth Oxide (“MREO”) or chloride chemical saleable product, and;
  • Stage 2 Refining – The continued processing of the MREO concentrate solution and the extraction via Solvent Extraction (SX) and Ion Exchange (“IE”) technology the individual REE’s as metals or chemical compounds.

To view a conceptual illustration of the flowsheet currently being tested 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 elements as saleable chemical products. Details are outlined below.

Stage 1 Refinery Testwork
Leaching tests were performed using a variety of leaching agents and from this it was determined that a hydrochloric acid (“HCl”) leach process was the most chemically efficient for the Wigu Hill bastnaesite-rich material. Following the success of the initial program a second and more recently, a third stage of leaching tests is currently being performed to provide further optimization information for the leaching process developed. The third stage optimization tests will provide a definitive process route for the leaching of the Wigu Hill mineralized carbonatite. Acid consuming gangue material is dissolved using hydrochloric acid in order to expose the bastnaesite-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.

The results to date are encouraging and in addition to optimizing the main leaching processes, the program includes detailed mineralogy of the residues from the various stages. Testwork is also evaluating the potential for regenerating spent hydrochloric acid and caustic soda consumed in the process. The program includes working with a SysCAD mass balance program that is 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 2012 to define the process route to take MREO feedstock and produce individual, pure rare earth chemicals or metals. Once completed, this testwork program will lead to a feasibility study for the Stage 2 Refinery and the upgrade of the Stage 1 Refinery to a larger production of REE chemicals and metals.

The Stage 1 hydrometallurgical Refinery optimization testwork will be completed 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 mixed rare earth 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 or metals for sale.

Montero is currently assembling an expert metallurgical and hydrometallurgical team to undertake this work and has sent out enquiries to engineering companies to undertake the feasibility and eventual construction of the REE refinery.