Peer into an Arizona copper mine. Deeper. Beneath deposits that can be mined and processed more readily lies chalcopyrite – the most plentiful source of copper in Arizona and around the world. But recovering copper from chalcopyrite requires considerable effort and cost. Streamlining recovery methods could unlock more of this resource for power systems and other urgent needs. 

Phoenix-based mining company Freeport-McMoRan is funding a $1.2 million University of Arizona research effort to improve the efficiency and sustainability of chalcopyrite (pronounced KAL-koh-py-rite) recovery. The project is led by Isabel Barton, associate professor in the U of A School of Mining Engineering and Mineral Resources.  

“The more you rely on electrical parts or systems, the more copper you need. If we're going to supply enough copper for the world, we have to be able to process chalcopyrite,” Barton said. 

The team began the project in 2023 and expects to conclude in two more years. The researchers are investigating the complicated factors that make chalcopyrite dissolve inconsistently – generally poorly – during leaching, the chemical process that pulls copper from rock. By analyzing how chalcopyrite’s composition and structure affect this process, the team aims to improve extraction methods and boost copper yields from leaching. 

Those advances could boost domestic copper production and reduce reliance on overseas processing. As advanced computing increases electricity demand and countries worldwide expand power capacity, pressure is mounting to upgrade transmission systems – driving demand for the copper needed to move energy efficiently at scale. 

In addition to carrying electricity for traditional and renewable systems, copper is used for plumbing, roofing, climate control, industrial machinery and electric vehicle components. 

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“Copper powers our whole lives. It’s the element we use the most in daily life, but it ends up being taken for granted,” said Sarah Patterson, a U of A mining and geological engineering doctoral student who is collaborating with Barton.  

Copper is a major driver of Arizona’s economy, with the state producing 70% of the nation’s supply, according to the U.S. Geological Survey. A U of A report indicates that Freeport-McMoRan produces roughly 80% of Arizona’s copper ore.  

The company has partnered with the U of A for nearly two decades and, in addition to funding research, has donated more than $6 million to the university since 2005 for scholarships, academic programs and campus facilities. 

The price of uncertainty 

Heap leaching is a common way to extract copper from near-surface ores such as malachite and azurite. For these deposits, miners crush the rock and spread it across large, lined pads to prevent contamination. A sulfuric acid solution dissolves the copper-bearing minerals as it filters downward. The metal-rich solution is then collected and purified, producing usable copper. Dissolving the metal directly into a liquid solution avoids more energy-intensive methods and can recover large amounts of copper.  

But unlike these soft surface ores, chalcopyrite does not dissolve well in sulfuric acid, making it a poor match for heap leaching. 

“It is very insoluble. If you try to leach it by conventional methods, you'll get somewhere between 0 and about 20% recovery,” Barton said. 

Since leaching becomes inefficient at deeper levels of the deposit, miners change methods as they reach the chalcopyrite level. The rock is crushed, ground and processed to produce a concentrate, which is then sent to a smelter – often in China – for high-temperature extraction of the metal. The process is costly and environmentally demanding. Some chalcopyrite, found through testing to be too resistant to break down, eventually ends up in tailings or waste piles.  

These economic and social costs are driving research that will empower Freeport-McMoRan to adapt and tailor heap leaching methods for different chalcopyrite ore types – improving local copper recovery while reducing energy use, waste and overall processing costs. By linking chalcopyrite’s composition, structure and associated minerals to leaching behavior, the researchers hope to identify practical adjustments – such as altering solution chemistry, timing or pre-treatment steps – that could make heap leaching more effective for different types of chalcopyrite deposits. Achieving this, however, will require a deeper understanding of the mineral’s complex behavior under different conditions.  

“There's enormous literature and decades of research, and yet we haven't actually established a lot of the basic phenomena,” Barton said, citing as an example the ongoing debate about the conditions under which passivation, the formation of a non-reactive surface layer, occurs on the chalcopyrite. 

Passivation varies dramatically with solution chemistry, the compounds produced during leaching, and with the internal structure of the chalcopyrite. These complexities, along with other unresolved variables, mean that researchers have yet to reach consensus on the underlying mechanisms or how they influence leaching across different types of ore. 

“These are basic things that we should know. But, as a matter of fact, we don't – at least not consistently enough to apply to all sorts of different chalcopyrite,” Barton said. 

Moving the field forward 

At this stage, the collaborators are assembling a large dataset on chalcopyrite from sites and geologic settings around the world, cataloging major and trace element composition and other characteristics tied to how electrons move through the mineral. That electronic behavior plays a central role in copper extraction. 

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“When you remove an electron, the structure has to adjust in a way that kicks the copper into the solution,” Barton said. 

In addition to analyzing and logging natural samples, the researchers are synthesizing chalcopyrite in the lab with carefully controlled compositions. By creating these lab-grown samples, they can better isolate the effects of specific trace elements and mineral combinations. 

This trace element analysis is aided by an extremely specialized laser mass spectrometry system housed in the Lowell Mineral Characterization Facility. A few years ago, the U of A became the first university in the nation to install this type of instrument, Barton said. It fires pulses roughly 1,000 times faster than conventional systems. The rapid pulses limit heat dissipation, allowing precise trace-element measurements without destroying chalcopyrite samples – a challenge with standard laser-based techniques. 

“Between the dataset and our synthetic studies, I think we will be able to have a much clearer idea of what factors influence chalcopyrite leaching, in which ways,” Barton said.  

The need to study the minerals that occur in contact with or adjacent to chalcopyrite grains, forming interfaces where chemical reactions are concentrated, adds another layer of complexity. At these boundaries, sulfide minerals – compounds of sulfur and metals such as pyrite – interact with chalcopyrite during leaching, either hastening or slowing copper release.  

“We've started disentangling exactly what effects different sulfides have. We’re seeing a few trends, but we need a lot more samples,” Barton said, adding that the team is working toward clear links between trace elements, associated sulfide minerals and chalcopyrite’s semiconducting properties and leaching behavior.  

The collaboration has already provided interesting insights, said Mitchell Catling, Freeport-McMoRan’s manager of metallurgy. 

“The research is informing our ‘Leach to the Last Drop’ initiative, aimed at extracting more copper from existing stockpiles, by improving knowledge of sulfide leaching and the impact of natural ore impurities,” Catling said. 

Patterson said the researchers will contribute to the field by examining chalcopyrite holistically, as it occurs in real mining environments, rather than as a simplified, stand-alone mineral. Having worked on the project since its inception, beginning while earning her U of A master’s degree, she believes dedicating years to this detailed project is valuable preparation for a career as a research scientist. It’s helping her connect laboratory analyses to broader economic and industry impacts. 

“It's really boiling it down to micro characteristics that have macro consequences,” she said. “Working on that scale is rewarding, and it feels direct.”