HEAP LEACHING & SX
Capstone publicly announced in July that Jetti ’ s catalytic technology had boosted both the economics of the operation as well as the dump leach performance on site .
A plan to increase cathode production further is being implemented , with the goal of generating high margins from material previously considered as waste at Pinto Valley ’ s 25 MIb / y ( 11,340 t / y ) electrowinning plant , which is currently operating at only circa-20 % of capacity .
Capstone said in its press release : “ The plan is to increase cathode production to 300-350 MIb from residual and high-grade waste over the next two decades .”
A technical report detailing such developments is due out next year .
Reviewing this project , Outwin said : “ The results from the commercial operation at Pinto Valley match very well with the outcomes from the pilot test programs we ’ ve been operating , as well as the significant amount of large scale laboratory test work we ’ ve conducted over the years .
“ The doubling of cathode production at Pinto Valley could be representative of how the technology can perform , however , it is difficult to give specific guidance as every mine is different and has different mineralogy .”
Where are we likely to see the technology next ? Outwin laid a few metaphorical breadcrumbs for interested parties to follow .
“ The nature of the technology means that it is particularly suited to those operations that have large volumes of chalcopyrite stockpiles or mineable resources , surrounded by existing SX-EW plants with spare capacity ,” he said . “ Many of these mines are located in regions where there are constraints on the availability of water such as Chile , Peru , Mexico and the US .
“ Jetti is in advanced testing programs with some of the largest copper mines in the world , including 20 mines in the Americas .”
ROL options
Having first announced the development of its Rapid Oxidative Leaching ( ROL ) technology in May 2015 , FLSmidth has since been on a mission to roll out the process across the base and precious metal industry .
ROL leaches 97-99 % of copper directly on-site in six to eight hours , from concentrates as low as 5 % Cu , according to FLSmidth . In gold , meanwhile , it has the potential to unlock the value of undeveloped refractory gold deposits with less than 3 g / t Au head grade , the company claims .
Unlike other refractory processing techniques , ROL uses the application of mechanical energy coupled with oxidation under atmospheric conditions . The process relies on stirred media reactors to accelerate the oxidation of sulphide minerals , which eliminates the need for ultrafine grinding , high temperatures and high pressure which , FLSmidth says , makes the process energy saving and cost-effective .
“ In copper , the existing orebodies are becoming lower grade , they are deeper , and they are more complicated to process ,” the company said . “ The ROL technology makes it possible to recover more copper from low-grade concentrates .”
This also applies to orebodies with high arsenic concentrations , as they too can be handled in an environmentally safe and economically viable way with ROL , FLSmidth added .
Gary Roy , Director , Process Line ROL Technology , Mining at FLSmidth , told IM that the initial demonstration testing for ROL on a site in South America achieved good copper leach recoveries , but , due to the COVID-19 pandemic , there had been delays in getting further site testing completed .
He said : “ FLSmidth has continued to develop the ROL technology , and is actively doing work in copper , gold and zinc projects .
“ The company has tested a half a dozen refractory gold ores and achieved 50-98 % sulphide oxidation , leading to a significant increase in downstream gold leach recoveries on each of these projects .”
Although COVID has continued to hamper siterelated ROL activities , the bench testing of ores remains very active , according to Roy . This includes existing heap leach operations processing oxide material that plan on transitioning into the sulphide orebody over the next five to 10 years .
“ For these orebodies , ROL presents a unique opportunity to allow leaching of copper sulphides and to continue to utilise the existing SX-EW plants ,” he said .
Solving the silica issue
Earlier this year , Protea Mining Chemicals , a subsidiary of Omnia Holdings , said it had become the first in its field to develop a solution that helps copper and cobalt mines reduce product contamination – improving metal purity levels – and maximise throughput in the SX process .
This solution took six years to develop and was carried out in partnership with chemicals manufacturers and copper and cobalt miners in the Democratic Republic of the Congo , Omnia said .
IM delved deeper , touching base with Mike Smith , Managing Director of Protea Mining , to find out more .
“ Silica is present in orebodies to varying degrees and , when leached into solution , can result in significant operational challenges during processing of such ores ,” he said . “ Solvent extraction processes tend to be hardest hit by this contaminant and , in extreme cases , these plants fail completely .”
Apart from the costs incurred in replacing lost reagents , such failures result in production downtime with consequent reductions in copper sales for the sites concerned , Smith explained .
“ Silica contamination has , therefore , been an issue that mines have grappled with for decades with
numerous attempts being made to address this problem with limited degrees of success ,” he said . With no industry-wide solution in sight , most companies have reluctantly accepted the contamination issue despite the impact on process efficiency , the significant processing challenges it introduces and the periodic production losses incurred , according to Smith . That is until recently . Protea , together with global chemical manufacturers , has been developing a sustainable solution to this problem . The answer lies in adopting a “ holistic approach that accounts for the nature of the ore , the metallurgical process employed together with its specific peculiarities and nuances , application of a proprietary chemical reagent , and optimising the reagent suite interactions and dependencies ”, Smith said .
It is the combination of addressing all these factors that results in the problem being resolved .
“ By working with visionary customers that were willing to provide uninhibited access to their plants and operations to Protea Mining Chemicals , an immensely successful solution was developed ,” Smith said .
The solution , now commercially available through Protea Mining Chemicals , is currently being employed at SX operations in the DRC , according to Smith .
The many benefits include : n Elimination of “ continuity flipping ”; n Improvement in phase disengagement time ; n Improved stability and subsequent increased uptime in SX ; and n Lower organic : aqueous ratios .
These factors result in an increased level of copper production with an associated increase in revenue , according to Smith , with other benefits including a reduction in organic losses and contamination , resulting in lower reagent consumption with associated cost savings ; and improved cathode quality to maximise revenue ( reducing silica contamination and other impurity entrainment to EW ).
Bio-based SX
Metso Outotec is seeking to solve another one of the base metal industry ’ s challenges using a bio-based diluent in solvent extraction .
In January , Outotec ( since merged with Metso to become Metso Outotec ) announced it and Neste had verified the use of Neste Renewable Isoalkane™ for extracting metals in hydrometallurgical processes .
This diluent , based on Neste ’ s NEXBTL technology and produced entirely from bio-based waste and residue raw materials , was put through its paces during laboratory studies and pilot trials at the Metso Outotec Research Center in Pori , Finland , and Neste ’ s Technology Center in Porvoo , Finland , confirming the high level performance of the product for copper SX .
“ Thanks to its renewable origins and being readily biodegradable , the bio-based diluent reduces environmental risk and has a remarkably smaller carbon footprint over its life cycle when compared to fossil equivalents ,” Outotec said at the time .
60 International Mining | NOVEMBER / DECEMBER 2020