IM 2022 November/December 22 NovemberDecember22 | Page 77

HEAP LEACHING & SX

primary copper sulphides .

Antofagasta ’ s solution leverages chloridebased reagents and 20-years of knowledge leaching secondary sulphides .

Like Nuton , it also has a large mine site test to reference .

Called Cuprochlor ^® -T, the proprietary process has undergone five years of intense development leading to the point where the company is open to talking about its potential .

It leverages off the first iteration of leaching technology Antofagasta devised for secondary sulphides – Cuprochlor .

Cuprochlor , which is now working at the Michilla mine in Chile ( which Antofagasta sold in 2016 ), effectively binds together the particles of mineral – particularly fine in the case of Michilla – into a porous but manageable material that can then be heap leached . The agglomeration is achieved by mixing the mineral and leach solution with chloride salts and sulphuric acid , which react to form a plaster-like paste .

Over the years , the process has been refined , going on to consistently deliver recovery rates of around 90 %.

Sitting on an expansive base of primary sulphide resources – mainly chalcopyrite – and the success of Cuprochlor , Antofagasta began a series of tests around five years ago , adjusting variables such as temperature , reagent concentrations and particle size to see if the

chloride leaching process could be adapted for the treatment of primary sulphides .

Temperature proved to be one of the keys , with tests showing that by elevating the temperature of the heap to around 30 ° C , Cuprochlor-T was able to stimulate the required chemical reaction for recovering copper from primary sulphides such as chalcopyrite .

Another key differentiator between the two chloride leaching technologies is the “ reagent recipe ” and particle size distribution ( PSD ), Alan Muchnik , VP Strategy & Innovation for Antofagasta , told IM earlier this year .

“ Providing a constant temperature throughout the process is very important , but the real innovation is the approach we have used ,” he said . “ It involves a combination of factors , including , among others , the recipe for reagent concentrations and the required PSD .”

While not wanting to reveal the ‘ secret sauce ’, Muchnik said the PSD consideration goes beyond the usual P80 industry reference point .

It is this balance that has landed the company with recoveries of over 70 % after approximately 200 days of leaching on the heap in test work .

During the March quarter of 2022 , the company finalised a large-scale pilot program to validate the technology , conducting industrialscale trials at Centinela using a 40,000-t heap of the site ’ s primary sulphides . The results were consistent with previous test work , giving recoveries of 70 % over that same timeframe .

“ This new technology will potentially unlock value from previously uneconomic mineral resources and bring forward the profitable processing of ore otherwise scheduled to be mined in many years ’ time or that was previously considered to be uneconomic ,” the company said recently .

While Rio is looking outside of the group for potential leaching applications , Antofagasta is lining projects up internally .

It is progressing studies for the primary sulphide orebody that lies below the Zaldívar reserves , in Chile , to evaluate if Cuprochlor-T leaching is a viable processing route .

The company added : “ An alternative is for idle leach pad and SX-EW capacity to be used to process material using the Cuprochlor-T technology , and one area of flexibility is that the existing EW plant can process blended solutions from both oxide and chloride leach . This allows the technology to be gradually deployed during the life of each mine as appropriate for the specific situation and the use of this option is being investigated by Centinela and Antucoya ( both in Chile ) as part of their annual mine planning processes .”

Lain ’ s leaching alternative

In Spain , another leaching alternative is about to get a mine site try out on an industrial scale .

Monday , Nov . 28 2022 10am EST / 4pm CET

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NOVEMBER / DECEMBER 2022 | International Mining 73