Modern Mining November 2015

MINING News

Pilot plant for Ngualla rare earth project operational

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 libera­ tion of the bastnasite from iron-bearing gangue minerals. A second stage of stan­ dard 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 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 (PFS). According to Peak, the ability to pro­ duce 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 PFS. This is because of decreased transportation costs of the lower mass concentrate; a reduction in acid consuming gangue mineral content; and a significant reduction in the size of the downstream leach recovery plant. The 66-tonne sample of weathered bastnasite 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 of mill feed. Three metallurgical laboratories were requested to provide proposals for the construction and operation of a pilot plant using the two-stage flowsheet. ALS in Perth was selected based on its piloting experience, available equipment and tech­ nical expertise in rare earth flotation. Milling of the bulk sample and opera­ tion 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 tonnes of high grade concentrate to be used for the downstream leach recovery pilot plant scheduled to commence in the first quarter of 2016. 

Commissioning of the barite prefloat circuit of the pilot plant (photo: Peak Resources).

ASX-listed Peak Resources reports that piloting of the beneficiation flowsheet has commenced on a 66-tonne bulk sample of typical weathered bastnasite mineralisa­ tion collected from the Ngualla rare earth project in Tanzania. The selection and piloting of the beneficiation flowsheet is an integral part of the Bankable Feasibility Study (BFS) and – says Peak – demonstrates its commitment to move towards the com­ mercialisation of the Ngualla project. Located 147 km from the city of Mbeya on the edge of the East African Rift Valley in southern Tanzania, the project is centered on the Ngualla carbonatite. Peak’s Managing Director, Darren Townsend, commented: “ The com­ mencement 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 com­

mencement of this key work programme.” Peak is developing Ngualla in conjunc­ tion with its partners Appian and IFC. Ngualla is a large high-grade rare earth deposit that is particularly rich in the high growth magnet metals neodymium and praseodymium. After extensive evaluation of two alter­ native beneficiation flowsheets developed specifically for Ngualla’ s unique minerali­ sation, a two-stage flotation process with an intermediate regrind step has been selected on the basis of operational advan­ tages 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 tech­ niques. Typically, this process stage rejects Kamwendo has been CEO of ZCI Limited since November 2011 and is a member of the board of the Copperbelt Development Foundation, African Copper’s ultimate par­ ent company. He has been CEO of several engineering companies including his own multi-disciplinary consulting firm. He has previously chaired the boards of the Engineering Institution of Zambia, the Environmental Council of Zambia, the National Savings and Credit Bank, the Copperbelt University and ZCI Limited. He also served on a Presidential Commission of Enquiry into university education in Zambia. 

Senior appointments at African Copper African Copper has appointed Boikobo Paya, currently a Non-executive Director of African Copper, as Non-executive Chairman of the company in succession to Roy Corrans who retired from the Board with effect from 30 September 2015. It has also announced the appointment of Thomas Kamwendo as Chief Executive Officer with immediate effect. Paya, a Botswana national, was the Per­ manent Secretary in the Botswana Ministry of Minerals, Energy andWater Resources from October 2010 to August 2014. He was also the Deputy Permanent Secretary in the same ministry, responsible for thewater and energy sectors, a post he held from October 2008.

8  MODERN MINING  November 2015