GOLD PROCESSING
addressing the new cyanide destruction requirements in a cost-effective manner , BQE Water became the industry leader in cyanide recovery through its expertise in SART ( sulphidisation , acidification , recycling and thickening ) technology ,” BQE says . “ Together , our combined expertise will enable BQE Water to offer complete cyanide management services .”
A golden game changer
Metso Outotec ’ s hydrometallurgical business may have its roots fixed in the base metals industry , but in the last decade it has been gaining a reputation for outperforming its peers in the gold CIL sector .
According to Teemu Ritasalo , Director , Hydrometallurgical Equipment and Plants at Metso Outotec , the company ’ s gold processing expertise was born out of Outotec and tied to a key pressure oxidation ( POX ) project to address the processing needs of refractory ore sources in 2011 .
“ This project led to us developing our own inhouse refractory POX autoclave offering ,” he told IM . “ This proved very successful where we were able to supply the whole plant based on our OKTOP ® design .”
Adding South Africa-based Biomin and its BIOX ® technology to the portfolio in late 2015 further bolstered the company ’ s POX , biooxidation technology and roasting portfolio , and led to the company moving into the cyanidebased leaching arena .
The first CIL reactor deliveries based on the OKTOP agitator design were carried out in that same year – one going to Argentina and another going to Turkey – and , over the last seven years , the company ’ s R & D team ( now under Metso Outotec ) has been working to refine and differentiate this OKTOP CIL Reactor technology from other offerings on the market .
Metso Outotec is now in the position where it is combining various system improvements it has made over this timeframe into a single package that , it claims , can reduce gold losses caused by activated carbon breakage and electric energy consumption by up to 50 % when compared with other hydrofoil agitator-based designs .
The “ next generation ” of Metso Outotec ’ s agitated OKTOP CIL Reactor for gold cyanide leaching and recovery provides a new agitation system that saves power , a new carbon measurement system that allows automation of the plant , and many other enhancements , according to Jan Van Niekerk , Director for Gold Processing Solutions at Metso Outotec .
“ We have also passed the Planet Positive designation , which is becoming more and more important for our clients , many of whom are looking for energy-efficient designs whenever selecting equipment ,” he said .
Metso Outotec carried out the retrofit of two reactors with an OKTOP agitator and FlowBottom solution at Dragon Mining ’ s Svartliden operation in Sweden
The Planet Positive portfolio focuses on the most environmentally efficient technologies – of which there are more than 100 – in Metso Outotec ’ s offering , responding to the sustainability requirements of its customers in the industries it serves . The customer requirements relate to energy or water efficiency , reduction of emissions , circularity and safety , the company says .
It ’ s easy to see the credentials on show when breaking down the single package CIL offering .
The patented OKTOP FlowBottom technology on board this new generation of OKTOP CIL Reactor assists in solids suspension , lowering the agitational requirement needed for full suspension conditions dramatically and bringing several benefits , such as homogeneous suspension of solids with reduced mixing power and decreased carbon attrition and related gold losses , according to the company .
It is well known that carbon attrition and nonideal carbon management can result in gold being lost in carbon fines and to the solution , with the former mainly being abrasion-related . While the attrition rate depends on ore and carbon characteristics , it is always proportional to the mixing power intensity . The reduction in required mixing power input provided by the novel tank bottom structure of FlowBottom , therefore , can potentially reduce these gold losses .
OKTOP SandSense™ , meanwhile , controls the agitation speed dynamically to produce just the right amount of energy needed for the mixing
task in any given time , according to Metso Outotec . This solution reduces wear , improves
energy consumption and detects upstream problems , the company adds .
The CarbonSense™ in-situ measurement system helps minimise gold solution losses . When combined with the CIL optimizer – which controls the gold CIL circuit to always achieve optimal processing conditions – it maximises the recovery of gold from the ore . It also automatically monitors and controls carbon concentration and cyanide dosing using continuous data measurement , according to Metso Outotec .
Add to this the optional Courier ® 6G SL onstream analyser for direct measurement of gold from ore feed , concentrate , and tailings streams , and it ’ s easy to see that the ‘ whole is greater than the sum of the parts ’ in this equation .
Metso Outotec has established and proven these solutions in more than just the lab , as Ritasalo explained .
A greenfield operation in Saudi Arabia has already installed a 3,000 cu . m OKTOP CIL Reactor with all the additional functionality mentioned above , demonstrating its efficiency and performance with slurry and carbon-loaded inputs .
And , in Sweden at Dragon Mining ’ s Svartliden mine , the company can reflect on a retrofit solution that has proven OKTOP ’ s credentials .
“ This mine had some issues in the cyanide leaching section with their previous agitators , experiencing heavy solid accumulation and sanding issues ,” Ritasalo said . Estimates were that the company was losing about 10-15 % of operational volume due to sanding .
He continued : “ They wanted to retrofit those cyanide leaching reactors with an upgraded mixing solution without increasing the mixing power of those reactors .
“ Our FlowBottom design was viewed as a good option to make the reactors perform more efficiently , while avoiding sanding and accumulation , and consuming the same amount of power .”
The company has been able to carry out the retrofit of these two reactors with an OKTOP agitator and FlowBottom solution , which reduced the mixing intensity and power consumption within the circuit without a drop in performance , according to Ritasalo .
“ It is that digital monitoring and control element , on top of the energy-efficient agitator design , that has resulted in a very positive outcome ,” he said .
Van Niekerk sees Metso Outotec ’ s digital solutions continuing to get the most out of its plant in the gold processing space , starting at the plant optimisation and design levels with the capabilities of its digital twin , Geminex , before moving onto other operational solutions .
“ The digital integration will be the game changer , reducing the dependency on the plant operator and allowing remote access to plant operation that is becoming more important in the environment and world we are moving into ,” he
International Mining | NOVEMBER / DECEMBER 2022