GOLD PROCESSING
The doré dilemma
Whether it is comminution , process control , cyanide alternatives or real-time grade measurement , gold miners are investing in a new breed of technologies in an effort to retain their existing production profiles and clean up the industry ’ s act , Dan Gleeson reports
The Metso Outotec Elution and Goldroom plant can be delivered standalone or as part of a holistic gold process solution to enable onsite production of gold doré
Gold miners are facing a losing battle when it comes to applying conventional technology to today ’ s orebodies .
As grades plunge , geological and metallurgical complexity increases and the list of ‘ investorapproved ’ jurisdictions gets smaller , many miners are looking for alternative routes to extract , liberate and recover the precious metal .
There are various areas in the flowsheet miners can look to for potential boosts , several of which IM explores in this feature .
Ore to doré
The recent launch of a compact Elution and Goldroom plant has completed Metso Outotec ’ s run-of-mine ore to doré process flowsheet at the same time as provide a standardised solution for the forming of concentrated eluate to be processed for gold recovery by electrowinning .
Announced in August and in keeping with other modular moves the company has made within the mineral processing and metallurgy field , the plant design is based on preengineered modules to reduce engineering , delivery and construction , as well as commissioning time and investment cost .
The plant represents the final step in the gold process flowsheet , where the gold cyanide complex is desorbed from the activated carbon , recovered as a metal in the electrowinning cells and refined to doré gold bars in the gold room . The activated carbon is regenerated for reuse in the cyanide leaching section .
According to Jan van Niekerk , Director , Gold Process Solutions at Metso Outotec , the company has delivered elution plants in the past , but used a third-party provider that “ increased the number of interfaces that had to be managed ” and meant the company assumed guarantees for a plant it did not design or build .
“ That is part of the reason why we developed the solution ourselves ,” he told IM .
The Metso Outotec Elution and Goldroom plant can be delivered standalone or as part of a holistic gold process solution to enable on-site production of gold doré . The company offers compact plant flowsheet designs based on ZADRA or AARL technologies , with the plant itself featuring a heat recovery circuit to minimise energy consumption and efficient carbon dewatering to maximise carbon regeneration and minimise energy losses .
“ Most other suppliers only offer the elution part of the gold room or parts thereof ,” van Niekerk said . “ We can offer a full ore to doré package .”
Clients are likely to yield further benefits of this complete flowsheet offering by bolting on Metso Outotec digital solutions for effective process control , according to van Niekerk .
The company ’ s CIL Optimizer can , it says , provide the most efficient carbon pumping scenario within the plant flowsheet , while its CarbonSense in-situ measurement system helps minimise gold solution losses in carbon-in-pulp ( CIP ) and carbon-in-leach ( CIL ) circuits by enabling reliable and repeatable online monitoring of carbon concentration . Operators can also layer on the Courier ® 6G SL on-stream analyser for direct measurement of gold .
All these elements can be finetuned in HSC Chemistry ® , a software solution Metso Outotec has used in countless metallurgical processes in various commodities to carry out effective modelling and simulation . In the elution scenario , specifically , HSC Chemistry allows dynamic modelling of the plant ’ s acid wash , elution and electrowinning circuits .
Also within the HSC Chemistry software is the ability to construct and use a digital twin of a plant – modelled with data from either the operating plant in question or similar operating plants – to provide operators with the ability to test out different parameters to improve recoveries and efficiencies .
Ma ’ aden in Saudi Arabia is one gold miner to have taken advantage of such modelling capabilities , according to van Niekerk .
The Elution and Goldroom plant solution comes with four levels of automation : standard ,
26 International Mining | NOVEMBER / DECEMBER 2021