GOLD PROCESSING 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 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
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
( 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 .
Representative gold analysis
In the world of real-time analysis , direct measurement of gold has presented significant challenges due to its low concentration in ore .
Scantech , with its GEOSCAN GOLD analyser , believes it has got closer than any other company in achieving representative , direct measurement of the yellow metal .
The company ’ s GEOSCAN elemental analyser uses prompt gamma neutron activation analysis ( PGNAA ), which allows for the representative and independent direct measurement of elements in conveyed flows and , subsequently , the ability to make process control decisions , it says .
The technology has been well established in other industries outside of gold , leveraging a
NOVEMBER / DECEMBER 2022 | International Mining