REPROCESSING AND RETREATMENT
A mixture of Imhoflot V-cells ( for higher yield to concentrate ) and G-cells ( for increased grade from fine concentrates ) were used on the Codelco-owned Andina plant in Chile , Maelgywn says
Production gains
Higher commodity prices bode well for new and old mine developments alike , with quite often the quickest and ‘ greenest ’ way to increase output involving processing mineralised waste piles from past operations . Dan Gleeson examines some of the technologies helping facilitate this growth
The ‘ quick buck ’ is usually made in the mining industry by leveraging existing assets when technology , commodity prices and company strategy start to change for the better .
This is best displayed in tailings and mine waste projects , where the marginal tonnes , pounds , or ounces of output on site can quickly be turned around to bolster a company ’ s cash proceeds .
Miners are , arguably , in that sweet spot , benefitting from a plethora of new technology developed within or outside of the industry , markedly higher commodity prices than 12 months ago and , in the wake of COVID-19 , a different way of approaching projects within existing portfolios .
Making a modular move
Maelgwyn has been part of the tailings reprocessing space for decades with two technologies applicable to this segment of the market : the Aachen High-Shear Reactor for gold tailings and the Imhoflot Advanced Reactor Flotation for fine ( -20 μm ) base metal recovery .
Both have found application globally in tailings retreatment projects where the low price point and high recoveries make them an attractive option . In the last year , Maelgwyn has brought further value to this product range by launching modular designs to both increase the installation speed and reduce the footprint of the Aachen and Imhoflot solutions .
Gold reprocessing – Mine Waste Solutions , Harmony , South Africa Harmony Gold Mining acquired the Mponeng mine and Mine Waste Solutions ( MWS ) tailings reprocessing facility from AngloGold Ashanti in 2020 .
MWS has been operating Aachen reactors for its tailings retreatment efforts since 2018 , with recoveries typically in the order of 50 % from a head grade of 0.3 g / t , according to Maelgywn .
The company explains the Aachen process : “ The dissolution of gold in cyanide is a galvanic reaction with kinetics controlled by the diffusion of reagents ( cyanide and oxygen ) to the gold particle surface , and dissolution products away from the surface . The importance of thinning the Nernst layer to speed diffusion and removal of by-product passivation layers can often be forgotten in gold leaching , however optimising these can improve gold dissolution dramatically .”
The Aachen uses high-shear conditions inside the reactor to refresh gold surfaces and maintain high dissolved oxygen levels without additional oxygen consumption , according to the company . The optimisation of this leach tank chemistry
through the retrofit of an Aachen module to the side of a tank has made the reactors a popular choice in gold tailings reprocessing .
Where the gold is contained in sulphide inclusions , the Aachen will oxidise sulphides to make gold amenable to leaching at a price point suitable for tailings projects , which pressure oxidation or bio oxidation struggle to compete with , Maelgwyn says .
Maelgwyn offers the Aachen system as a rental option with ongoing support and spare parts included . Recently , it has boosted the digitisation of its systems to offer remote process optimisation to clients alongside the technology .
Tim Sambrook , Global Business Development Manager at Maelgywn , says containerised oxygen plants can be added as part of the Aachen Integrated System , which further reduces client operating costs by some 30-40 % and offers the plant resilience from oxygen supply disruption .
Codelco Andina Copper Tailings reprocessing , Chile In 2013 , Codelco wanted to form a joint venture to monetise the copper value in its tailings . The copper tailings were made up of chalcopyrite in the -20 μm fraction , so had low recoveries when processed through conventional flotation cells whose bubble-particle energy is optimised for recovery in the -106 + 38 μm size range , Maelgwyn explained .
The tailings reprocessing plant needed to have a high throughput while maintaining a small physical footprint , so the Imhoflot cells with their small size per cu . m / h throughput proved a good match , the company said . With a low operating mass due to not retaining the pulp for a long residence time , the Imhoflot cells , unlike conventional cells , allowed civil engineering costs to be kept to a minimum and reduced overall project capital expenditure .
A mixture of V-cells ( for higher yield to concentrate ) and G-cells ( for increased grade from fine concentrates ) were used on the Andina plant : n Rougher – 4 x 4.5 m diameter V-cells ( 4 x IMF-
V45s ); n First cleaner and first cleaner scavenger – 4 x 2.5 m diameter V-cells ( 4 x IMF-V25s ); and n Second cleaner and second cleaner scavenger – 3 x 1.8 m diameter G-cells ( 3 x IMF-G18s ). Overall plant throughput was 600 cu . m / h ( 220 t / h ) and took the tailings to a saleable concentrate ( 26.2 % Cu ) at an 80 % recovery , Maelgwyn said .
52 International Mining | APRIL 2021