GOLD PROCESSING
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 said . “ These solutions will continue to be refined as more and more sites and applications use them .”
Manifold processing advantages
With gold prices continuing to hover around quarterly record highs , many yellow metal producers are seeking to increase production , leveraging new technology and processes where appropriate .
For many gold mines , high pressure grinding rolls ( HPGRs ) offer the ideal solution thanks to a track record of removing bottlenecks and inefficiencies created by traditional milling , reducing energy and water costs , and enhancing gold recovery , according to Bjorn Dierx , Global Product Manager – Enduron ® HPGR at Weir Minerals .
Gold is traditionally located in reasonably hard ore and , therefore , requires substantial time in
The Enduron HPGR solution at the Kışladağ heap leach operation , in Turkey , is expected to increase gold recovery by approximately 4 %, which returns the investment in less than one year , according to Bjorn Dierx
grinding mills to produce a suitable particle size for mineral liberation , leading to high consumption of the mill ’ s liners and grinding media .
However , the inter-particle compression of a HPGR is highly effective at reducing competent ores when deployed for tertiary comminution , significantly increasing the throughput of downstream mills while reducing the circuit ’ s overall energy consumption by up to 40 %, according to Dierx .
“ Moreover , with declining ore grades and more complex orebodies , the advantages of utilising HPGRs in gold processing applications are manifold ,” he said .
There are some projects processing ore with a Bond Work Index of 22-24 kWh / t , placing substantial requirements on traditional milling technology and leading to higher energy consumption .
“ HPGRs offer miners an effective way to increase production while keeping energy costs low and maintaining profitability ,” Dierx said .
When the gold is recovered by heap leaching , miners can also reduce their water consumption to further minimise operating costs , he said , adding that heap leaching consumes less than 0.3 tonnes of water for one tonne of ore .
In heap leaching applications , typically the most efficient configuration is to have a HPGR perform tertiary grinding immediately prior to recovery , avoiding the need for a ball mill with the help of a partial product recycling system ( PPR ).
“ The PPR consists of splitter plates under the
rolls that return combined edge and centre product streams back to the head feed hopper ; they can be flexibly adjusted to maintain stable leach pad feeding conditions , despite changing feed conditions ,” Dierx explained .
HPGRs are highly effective for heap leaching because the high pressure that particles experience between the HPGR ’ s tyres introduces ‘ micro-cracks ’ or fractures , allowing the leaching chemicals to effectively diffuse through the particles and liberate the gold ore . As sound heap stability and percolation is required , microfines should be mitigated , hence the PPR system safeguards the most optimal product gradation .
Tuprag , Eldorado Gold ’ s subsidiary in Turkey , recently partnered with Weir Minerals to optimise its Kışladağ heap leach operation and improve its gold recovery , leading to an increased heap leach life . The final flowsheet included a 2.4-m diameter by 2.2-m long Enduron HPGR with PPR with the capacity to process 4,200 t / h .
This simplified flowsheet replaced five existing tertiary crushers of which liners would have an average lifetime of around one month with a crusher availability of 85 %. Contrastingly , the HPGR tyres have a wear life close to 18 months , with the HPGR achieving an asset availability of more than 95 %, according to Weir Minerals .
“ The Enduron HPGR solution is expected to increase gold recovery by approximately 4 %, which returns the investment in less than one year ,” Dierx said .
While these figures vary from site-to-site , independent research has indicated that , compared with conventional cone crushing , the HPGR can provide up to 10-11 % additional gold extraction , the company says .
“ Kışladağ represents one of the largest brownfield Enduron HPGRs Weir Minerals has ever installed ,” Dierx said . “ In a tight regulatory environment in which fewer greenfield projects are being approved , HPGRs offer miners a way to uplift mill capacity in circuits without the need for expensive , time-consuming civil engineering to make space for new equipment .”
When working on brownfield projects , equipment usually needs to be installed in a very tight space to avoid expanding the current footprint on site . This limits the opportunities to blend and homogenise material streams , making feed segregation inevitable . Skewing is , therefore , mandatory for efficient grinding in these challenging conditions , according to Dierx .
“ Unless a HPGR can dynamically accommodate these changing feed conditions , its tyres will wear unevenly and , more importantly , it won ’ t be able to exert sufficient press force to exceed the material ’ s compressive strength across the full operating gap , which , in turn , reduces the grind quality in a single pass ,” he said .
68 International Mining | NOVEMBER / DECEMBER 2022