Peak has developed and successfully demonstrated a three stage process for Ngualla’s weathered bastnaesite mineralisation to produce high purity separated rare earth products aligned to market demand.
Three stage process developed by Peak for Ngualla’s rare earth mineralisation and pilot plant status as at May 2016.
Stage 1: Beneficiation
Run of mine (ROM) mineralisation is crushed, ground and classified through a comminution circuit targeting the initial liberation of the major gangue mineral barite. The classified slurry is then conditioned before proceeding to the Barite Pre-flotation Circuit consisting of roughing and two stages of cleaning. This circuit targets and removes greater than 90% of barite which is the major gangue mineral present whilst rejecting approximately 45% of the ROM mass for a minimal loss of rare earths. The tailings (reject) stream from this circuit is thickened and pumped to the Tailings Storage Facility (TSF).
The product from the Barite Pre-flotation is sent to a regrind stage to improve liberation of bastnaesite from the iron gangue minerals (predominantly goethite/limonite) before proceeding into the Rare Earth Flotation Circuit. This circuit, consisting of roughing and four stages of cleaning, targets bastnaesite directly and rejects iron and quartz to the tails. The overall beneficiation process achieves a mass rejection of 95% to produce a 45% REO grade concentrate.
The beneficiation flowsheet was successfully piloted from September to December 2015. A total of 56 dry tonnes of typical weathered bastnaesite mineralisation was treated to produce 2 tonnes of mineral concentrate grading 45% REO, demonstrating the process is robust whilst providing vital operating and design parameters for the BFS.
The development plans envisage a multi-stage processing plant using the Stage 1 comminution and beneficiation process to be on site at Ngualla with the open pit mine.
Stage 2: Leach Recovery
Peak has developed a bespoke selective leach recovery process to extract, purify and produce a rare earth solution as feed for the final separation stage of the process.
The selective leach process is a key factor in Ngualla’s low operating and capital costs and aligns the final products to the high demand magnet metal rare earth market. The process minimises the dissolution of low value cerium and impurities such as iron, reducing reagent consumption and the need for extensive further purification.
The process uses very low strength acid (<1%) in a small sized plant of modular design and polymer plastic tanks for leach and purification.
Selective Leach Recovery flowsheet developed by Peak for Ngualla’s high grade mineral concentrate
Stage 3: Rare Earth Separation Plant
The ability to produce high purity separated rare earth products adds significant value to Ngualla’s production and allows access to wider end use markets.
To this end, Peak commissioned Australia’s leading rare earth separation experts, ANSTO Minerals, to undertake a Separation Pilot Plant at their research facility at Lucas Heights near Sydney, using a feed solution prepared from a bulk sample of Ngualla’s mineralisation. The pilot plant successfully produced a range of separated and high purity rare earth products and provided Peak with important engineering data.
Peak plans to produce three high purity separated rare earth products:
A high purity (99.9%) neodymium-praseodymium oxide
A combined mid-heavy rare earth carbonate
A combined lanthanum and cerium carbonate
The full scale leach recovery and separation plant will be situated in the European Union to take advantage of ready supplies of bulk reagents and support infrastructure.