Copper extraction follows two main routes depending on the type of ore being mined. Sulfide ores, which contain copper bonded to sulfur, are processed with heat in a method called pyrometallurgy. Oxide ores, where copper is bonded to oxygen, are processed with water-based chemical solutions in a method called hydrometallurgy. Most copper starts as rock containing less than 1% actual copper, and global ore grades have dropped roughly 40% since 1991, meaning more rock needs to be processed for the same amount of metal.
Getting Ore Out of the Ground
Before any chemical processing begins, the copper-bearing rock has to be physically removed from the earth. Open-pit mining is the most common method. Workers blast and excavate enormous terraced pits, sometimes reaching depths of 1,500 feet below the surface rim. As upper layers of ore are depleted, progressively deeper benches are cut into the pit walls to access fresh material. This approach generates large volumes of waste rock and overburden (the soil and vegetation sitting on top of the ore body).
Underground mining is used when the ore sits too deep for an open pit to be practical. A vertical shaft is sunk down to the ore body, and horizontal tunnels called drifts branch out from the shaft at various depths. Ore is brought up to the surface for processing, and some waste rock is returned underground as fill. Underground mining disturbs less surface area but is more expensive to operate.
Processing Sulfide Ores With Heat
Sulfide ores go through a multi-stage process that uses physical separation, intense heat, and finally electricity to produce pure copper. This is the dominant pathway for most of the world’s copper production.
Froth Flotation
The crushed ore first enters a flotation tank, where it’s mixed with water and chemical reagents. Collectors, typically a class of compounds called xanthates, coat the copper mineral particles and make them repel water. A frother (often an industrial alcohol) creates a layer of bubbles on the surface. The water-repelling copper particles attach to these bubbles and float to the top, where they’re skimmed off as a copper-rich froth. The waste rock sinks. This step concentrates the copper from less than 1% up to around 25 to 35%, making the next stages far more efficient.
Smelting
The dried concentrate is fed into a smelting furnace along with a silica-based flux. Inside, temperatures are high enough to melt everything into a molten bath. The iron and other impurities in the ore react with the flux and float to the top as slag, which is periodically drained off and discarded. What settles to the bottom is called matte, a molten mixture of copper sulfide and iron sulfide, with sulfur leaving the furnace as sulfur dioxide gas.
Converting
The matte is poured into a large cylindrical vessel called a converter, where air or oxygen-enriched air is blown through the molten material. This burns off the remaining iron and sulfur in stages. First, the iron sulfide is oxidized into iron oxide and sulfur dioxide. The iron oxide combines with added flux to form more slag, which is skimmed away. Once enough relatively pure copper sulfide (called “white metal”) accumulates, a final blast of air oxidizes the copper sulfide itself, driving off the last sulfur as sulfur dioxide and leaving behind what’s known as blister copper, which is 98 to 99% pure.
Electrolytic Refining
Blister copper is cast into large slabs and placed in tanks of acidic solution. An electric current is passed through the solution, dissolving copper from the impure slab and depositing it onto a thin starter sheet of pure copper on the opposite side of the tank. Impurities like gold, silver, and platinum fall to the bottom as a valuable sludge that’s recovered separately. The finished copper cathodes are 99.99% pure.
Processing Oxide Ores With Chemistry
Oxide ores take an entirely different path. Instead of heat, the process relies on chemical reactions in water-based solutions at ordinary temperatures. It unfolds in three stages: heap leaching, solvent extraction, and electrowinning, often shortened to SX-EW.
Heap Leaching
Crushed oxide ore is stacked in massive heaps on an impermeable pad, usually lined with heavy plastic to prevent contamination of the surrounding soil. A dilute sulfuric acid solution is dripped over the top of the heap and allowed to trickle down through the ore. As the acid percolates through, it dissolves the copper out of the rock. The copper-laden solution, called a “pregnant” leach solution, collects at the bottom and is pumped to the next stage.
This is not a fast process. Oxide minerals leach relatively quickly, with copper recoveries of 75 to 95% achievable within 30 to 100 days. But depending on the specific minerals involved, leach cycles can range from about 90 days to as long as 3 years to recover 70 to 90% of the copper. Dump leaching of low-grade waste rock can take even longer.
Solvent Extraction
The pregnant leach solution contains copper, but it’s too dilute and impure to use directly. In solvent extraction, it’s mixed with an organic solvent that selectively binds to copper ions and pulls them out of the acidic solution. The copper is then stripped from the organic solvent into a clean, highly concentrated acidic solution. The now-barren leach solution is recycled back to the heap.
Electrowinning
The concentrated copper solution is pumped into electrolytic cells, where an electric current pulls copper out of the solution and deposits it onto stainless steel or copper starter cathodes. The process is similar to the electrolytic refining used for sulfide ores, but it starts from a solution rather than an impure metal slab. The result is the same: cathodes of 99.99% pure copper ready for sale.
How Much Copper Comes From Recycling
Not all copper comes from freshly mined ore. Scrap copper from old wiring, plumbing, electronics, and industrial equipment is melted down and reprocessed, requiring significantly less energy than extracting copper from rock. Currently, recycled scrap accounts for a meaningful share of total supply, and that share is growing. Mining company BHP estimates scrap will make up around 40% of total copper consumption by 2035 and roughly half by 2050, driven in part by the fact that high-grade ore deposits are becoming harder to find. Global mined copper supply may peak in the late 2020s at just over 24 million metric tons before declining, even as demand is projected to rise from about 27 million metric tons today to 33 million by 2035.
Environmental Costs of Extraction
Copper smelting produces large quantities of sulfur dioxide, a gas that causes acid rain and respiratory problems. Modern smelters capture this gas and convert it into sulfuric acid, which is then sold (often back to leaching operations). But capture rates vary enormously. Roughly half of the world’s smelters capture less than 84% of the sulfur dioxide they produce, and about 10% capture none at all. The Ilo smelter in Peru, for example, once emitted sulfur dioxide at levels several times larger than the total output of many European nations, capturing only 30% of its yield. Modernization efforts have since reduced those emissions significantly.
Open-pit mining also transforms landscapes on a massive scale, stripping vegetation, diverting waterways, and generating billions of tons of waste rock and tailings over a mine’s lifetime. Heap leach operations carry the risk of acid solutions leaking into groundwater if pad liners fail. These environmental pressures, along with declining ore grades, are a major reason the industry is investing more heavily in recycling and in technologies that reduce water and energy use per ton of copper produced.