More Heat , More Copper ?
Sites Test Theory with Leach Pad Covers and Other Tools
A spool-type device on the back of an ATV makes laying the covers a less daunting task .
If you ’ ve ever spent any time inside a greenhouse on a sunny day , you probably have some idea of how a sealed thermal barrier affects what ’ s under it . Things get a lot warmer . That ’ s the principle behind leach pad blanketing – or covers – as it often is referenced in discussions about Leach to the Last Drop .
In theory , every degree of temperature increase proportionally boosts copper recovery , and there ’ s enough data-driven confidence in testing that on a large scale at active operations . The thermal covering method was selected from a backlog of ideas not fully explored and now is in play across the organization as a critical component of the Leach to the Last Drop project , the objective of which is to get more copper out of stockpiles than was thought recoverable in years past .
Leaching teams across the company continue to refine this technique , intended to help accelerate copper recovery from newly placed ore , and squeeze more copper out of older ore piles .
The covers help increase heat , which maximizes the effectiveness of the leaching process .
“ Based on theoretical analysis , it was assumed that heat would drive increased recovery from leach pads by helping the leaching solution dissolve the copper faster ,” said Todd Morman , Innovation Engineer II-Safford . “ With that information coming out of the lab , there was a decision to start covering stockpiles so it ’ s been a big initiative .”
Since November 2021 , nine operations – Bagdad , Chino , Miami , Morenci , Safford , Sierrita , Tyrone , Cerro Verde and El Abra – have been covering sections of their active leach areas with clear plastic sheeting , which helps keep solar and chemically generated heat contained within the pad underneath .
Jon Ticer , Hydromet Leach Operator II , looks over the leach piles being covered .
HIGH RECOVERY AT LOW COST
“ This has been a giant experiment ,” said Cory Stevens , President , Freeport-McMoRan Mining Services . “ We ’ ve gone across all the sites and put down about 30 million square feet – over 1 square mile in total area . That represents about 20 percent of our total leach area , which could deliver us 5 to 10 percent more recovery at low cost and low carbon output .”
The actual range of increase is what Leach to the Last Drop teams are determining as they collaborate to fine-tune the recipe for optimizing recovery , particularly from ore resistant to conventional leaching methods .
“ Test scale data we ’ ve collected over the years shows that increased heat does improve recovery , especially on sulfide copper materials , which tend to be what we get the lowest recovery on ,” said Chase Zenner , Senior Metallurgist-Technology Center .
When it comes to stubborn , leaching-resistant sulfide materials , the worst culprit for many Freeport mines is chalcopyrite – a common copper sulfide extracted from the open pits .
“ The lab looked at ways to leach chalcopyrite , understanding that copper dissolves more quickly under heat ,” Morman said . “ That was the basis for the thermal covers . If we can heat up the ore as it ’ s being leached , we can get a quicker recovery , possibly even from chalcopyrite .”
For that reason , the search is on to find the right combination of thermal covers , leaching solution additives , data capture and analysis methods , and operational practices that will bring about more and quicker recovery from all types of ore in new and existing piles .
Meanwhile , crews in North and South America have been overlaying leach pads using various methods – from manual labor to ATVs to small excavators and other machines – and collaborating with drip line crews , who install drip piping before the plastic is placed over it .
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