Crews at the Safford and Morenci operations are leading the charge on the effort to utilize covers to maximize the Leach the Last Drop effort . Over the last year and a half , they have experimented with different types , sizes and densities of cover material , each presenting advantages and challenges during installation and removal . The material ’ s unwieldiness in bulk and its vulnerability to environmental stresses , such as wind and long-term sun exposure , are among the realities that have tested the fail-fast agile process , but the cover teams remain tenacious and resourceful .
“ Safford ’ s leaching employees embraced this project as their own and have been committed to its success ,” said Justin Bingham , Superintendent-Hydromet Leaching at Safford . “ They meet with leadership regularly to provide updates , share new ideas and get support for making improvements to the process .”
The Safford team worked with a vendor to design and implement a mechanized spool that makes it easier to roll out the plastic for installation . They also use the Low Altitude Authorization and Notification Capability – a resource for drone pilots – to get detailed wind and weather updates for planning covers installation during adverse conditions .
“ The practices around installing covers have vastly improved from where we were when we started the initiative in late 2021 ,” said Jackie Steeples , Manager Processing-Operational Improvement .
According to Cory Stevens , President , Freeport- McMoRan Mining Services , a new mechanized covers installation product is pending for 2023 , but installation is only half the battle . Safford and Morenci also have evaluated various mechanized solutions for efficiently removing covers without damage , so they can be reused . Some vendor-provided devices as well as in-house mechanisms designed and fabricated by Freeport employees have proven successful .
To address quality issues , the sites have experimented with various sizes and thicknesses of plastic sheeting . Also under evaluation are string-reinforced products as well as products with built-in drip lines , which would remove a step from the typical installation sequence of drip line followed by covers .
New skill sets developed
As crews define what their best day of covers management looks like , that information is shared with other cover crews across the company . The project affords ample opportunities for employees to become skilled on new types of equipment and technology , building bench strength in the process .
“ This process continues to evolve for the better ,” Bingham said . “ Our crews continue testing new ideas and implementing those that improve efficiency , and we as the leadership continue to support and provide them with the tools they need .”
While cover crews winnow out products and processes for their regimen , metallurgists and geotechnical engineers gather drilling , sampling and temperature data from the targeted leaching areas , and some early results appear to validate the impact of covers on pad temperature .
“ At Safford , we have measured temperatures at three depths within similar material on the Lone Star leach pad , capturing readings from covered and uncovered areas ,” said Pip Killian , Senior Metallurgist-Safford . “ Our temperature tracking confirms we are able to heat our newly placed Lone Star material to 20 feet below the leach pad surface .”
Killian said that readings from 2 feet deep showed temperature shifts of 2 to 3 degrees Fahrenheit . At 10 feet , they ranged from 5 to 7 degrees , and at 20 feet , they were as high as 7 to 11 degrees , leading to the logical follow-up question .
“ If covering the pad results in greater heat , does higher heat correlate to better recovery ?” Todd Morman , Innovation Engineer II-Safford , rhetorically asked . “ Thermo monitoring devices buried in the pad and samples from the test areas will help us answer that .”
Recovery of Covered , Uncovered Material Compared
It already was theorized that adding heat should improve the process , but the data work stream of Leach to the Last Drop seeks to produce the metrics confirming it does and by how much . In late summer 2022 , Safford began reviewing preliminary drill data on copper recovery from covered versus uncovered material .
“ With the instrumentation in the stockpiles , we ’ re trying to prove to ourselves that these covers are really doing what we want them to do ,” Chase Zenner , Senior Metallurgist-Technology Center said . “ As the data comes in , we ’ re trying to build confidence and buy-in from all the sites that this really is working and making a difference for us .”
At Safford , 80 percent of the copper in the site ’ s mostly oxide ore normally is recoverable , and after 150 days under leach , about 85 percent of that 80 percent is recovered , Morman explained .
“ In this covers experiment , a section of leach pad is covered , while another is left uncovered , and then thermal sensors are put in both sections ,” Morman said . “ After a 150-day leach cycle , samples are pulled and sent to the lab for chemical assay . Covered samples are compared with uncovered samples to determine if a recovery rate higher than 85 percent is being achieved and sustained .”
Verifying a higher temperature directly leads to higher recovery values , especially on a large scale , would boost confidence in implementing covers as part of standard leaching practice . Now , in early 2023 , that verification has begun to materialize , although it has varied from site to site , depending on mineralogy .
“ There ’ s a pretty strong correlation that covers do increase pad temperature , and we ’ re quantifying how much additional recovery the heat actually gives us in newly placed stockpiles ,” said Josh Andres , Chief Innovation Engineer .
Safford is leading the effort to provide that proof .
“ Safford has the drilling campaign to measure recovery results before and after the depletion of the copper during the leach cycle , comparing recovery from covered areas with that from uncovered areas of similar ore ,” Morman said . “ They will be the first site to publish a thermal reaction data set representing the impact of covers .”
While covers are proving their value in helping achieve that , other techniques also are in play to boost the effort .
“ Thermal covering is just one of the tools in our experiment , and we ’ re starting to realize the big difference it makes ,” Stevens said . “ But we ’ re also leaching side slopes , re-leaching older areas , injecting solution deep into stockpiles , and identifying additives that further enhance all these practices . It ’ s a mix of many tools for increasing our success potential with Leach to the Last Drop .”