Tanzania – Piloting of the beneficiation flowsheet has commenced on a 66 t bulk sample of typical weathered bastnasite mineralisation collected from ASX-listed rare earths junior Peak Resources' Ngualla rare earth project in Tanzania.

Commissioning of the barite prefloat circuit
Commissioning of the barite prefloat circuit

The 66 t of weathered bastnaesite mineralisation was collected from eight trenches excavated at Ngualla earlier in the year and transported to Perth, Western Australia. This material has been selected to be representative of the first five years mill feed.

Milling of the bulk sample and operation of the first stage barite flotation has now commenced.

The overall operation of the plant will continue until the end of the calendar year, producing in excess of 2 t of high grade concentrate to be used for the downstream leach recovery pilot plant scheduled to commence in the first quarter of 2016.

The beneficiation pilot plant will provide essential operating data to assist in the engineering of the commercial scale operation by Peak’s bankable feasibility study (BFS) Lead Engineer, Amec Foster Wheeler, as well as providing appropriate samples to third party equipment and reagent vendors.

The flowsheet selected for the treatment and upgrading of the Ngualla mineralisation, which is being piloted by ALS Metallurgy, consists of two stage flotation with intermediate regrinding.

The flowsheet, using standard flotation cells and readily available reagents, is a simple, robust and effective means of achieving an up to 8 times upgrade of the run of mine (RoM) grade of rare earths.

The selection and piloting of the beneficiation flowsheet is an integral part of the BFS and demonstrates Peak’s commitment to move towards the commercialisation of the Ngualla project.

The Peak Resources team on site
The Peak Resources team on site

The ability to produce a high grade/low mass mineral concentrate is expected to have a profound impact on the overall project economics by reducing both operating and capital costs compared to the prefeasibility study via:

  • Decreased transportation costs of the lower mass concentrate
  • Reduction in acid consuming gangue mineral content– notably iron oxides and hydroxides
  • Significantly reducing the downstream leach recovery plant size

“The commencement of the beneficiation pilot plant is another key milestone in the development of the Ngualla Project. My congratulations go to the Peak technical team and their consultants for the commencement of this key work program,” says Peak Resources MD Darren Townsend.

Beneficiation Flowsheet

The homogenised 66 t sample of typical weathered bastnasite mineralisation
The homogenised 66 t sample of typical weathered bastnasite mineralisation

After extensive evaluation of two alternative beneficiation flowsheets developed specifically for Ngualla’s unique mineralisation, a two stage flotation process with an intermediate regrind step has been selected on the basis of operational advantages and lower operating costs.

The flowsheet takes advantage of a significant proportion of the gangue (waste) mineralisation being in the form of relatively large barite particles. An initial coarse grind (-75 microns) is employed to liberate the barite and allow its selective removal using standard flotation techniques.  Typically this process stage rejects greater than 95% of the barite whilst losing only around 10% of the rare earth bearing bastnasite.

The barite depleted concentrate is then screened, thickened and sent to a regrind mill where the particle size is reduced to less than 45 microns. This provides liberation of the bastnasite from iron bearing gangue minerals.  A second stage of standard flotation is then undertaken at a temperature of 50°C using dispersants, gangue depressants and a hydroxamic acid as a rare earth collector.

The selected flowsheet is the result of continuous, incremental improvements achieved in the beneficiation process, with test work delivering concentrate grades of between 30% and to 50% rare earth oxide (REO). These grades represent a two to three fold improvement over the 16.3% REO concentrate attained in the preliminary feasibility study.

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