HEAP LEACHING & SX
A crucial combination
Grade depletion , rising operating costs and increasing ESG requirements are all contributing to a pyrometallurgical re-think . Dan Gleeson checks in with those in the heap leaching and solvent extraction markets to find out how they are making the most of these new opportunities
It is not just falling ore grades and high pyrometallurgical processing options that has miners re-evaluating leaching plans as part of their strategic ambitions ; the potential to mine deposits in a more environmentally friendly manner where water and energy use are reduced is another reason why firms are looking to heap leaching and solvent extraction ( SX ) in tandem .
And , with an assortment of new technologies moving from the lab to the mine site , the metal processing dynamic is changing .
A leaching R & D legacy
More than a few companies and technology providers claim to have solved the primary copper sulphide leaching conundrum , but only one has close to 30 years of R & D and the Rio Tinto name behind it .
Nuton is the latest to table a solution to treat primary copper sulphides such as chalcopyrite , with Rio having introduced the company to the sector earlier this year in an attempt at growing its copper business .
At its centre is a portfolio of proprietary copper leach related technologies and capability that , Nuton says , offer the potential to economically unlock known low-grade copper sulphide resources , copper bearing waste and tailings , and achieve higher copper recoveries on oxide and transitional material . This allows for a
significantly increased copper production outcome , according to the company .
One of the key differentiators of Nuton is the potential to deliver leading environmental performance , including more efficient water usage , lower carbon emissions and the ability to reclaim mine sites by reprocessing mine waste , it claims .
Adam Burley , Rio Tinto ' s Nuton venture lead , said at the core of Nuton is an elevated temperature bioleaching process that can , in the right thermochemical conditions , deliver “ peak ” copper recovery from primary sulphides such as
chalcopyrite .
“ Taking advantage of naturally-occurring processes , we have nurtured a culture of
Earlier this year , Atalaya Mining approved the construction of the first phase of an industrialscale plant using E-LIX at its Proyecto Riotinto mine , in Spain
microorganisms that establish and thrive in those optimised conditions ,” he told IM . “ The elevated temperatures are generated by the work of the bacteria ; under the base case , we don ’ t need to heat the heap from external sources , which can often be financially and environmentally costly .” This leaching foundation is enhanced by a range of “ additives ” and expertise that can , for example , deal with high precipitation and cold weather climates .
Having assembled and extensively tested this portfolio , Nuton and Burley are confident enough to state expectations of delivering greater than 80 % copper recoveries from chalcopyrite ore with its process .
“ This is , from our understanding , some way above the next best leaching technologies available ,” Burley said .
The testing behind such numbers is extensive , dating back to 1994 when the company carried out its pilot heap leach operation and developed its initial predictive modelling capabilities at the Kennecott copper mine in Utah , in the US .
“ Since that time , we ’ ve conducted hundreds of column tests across tens of orebodies ,” Burley said . “ We have run columns at a range of scales –
NOVEMBER / DECEMBER 2022 | International Mining 71