Chalcopyrite ( ) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS<sub>2</sub> and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green-tinged black.
On exposure to air, chalcopyrite tarnishes to a variety of oxides, hydroxides, and sulfates. Associated copper minerals include the sulfides bornite (Cu<sub>5</sub>FeS<sub>4</sub>), chalcocite (Cu<sub>2</sub>S), covellite (CuS), digenite (Cu<sub>9</sub>S<sub>5</sub>); carbonates such as malachite and azurite, and rarely oxides such as cuprite (Cu<sub>2</sub>O). It is rarely found in association with native copper. Chalcopyrite is a conductor of electricity.
Copper can be extracted from chalcopyrite ore using various methods. The two predominant methods are pyrometallurgy and hydrometallurgy, the former being the most commercially viable. It was sometimes historically referred to as "yellow copper".
Identification
Chalcopyrite is often confused with pyrite and gold since all three of these minerals have a yellowish color and a metallic luster. Some important mineral characteristics that help distinguish these minerals are hardness and streak. Chalcopyrite is much softer than pyrite and can be scratched with a knife, whereas pyrite cannot be scratched by a knife. However, chalcopyrite is harder than gold, which, if pure, can be scratched by copper. Additionally, gold is malleable, while chalcopyrite is brittle.
Chemistry
thumb|237x237px|The [[unit cell of chalcopyrite. Copper is shown in pink, iron in blue and sulfur in yellow.]]
thumb|Microscopic picture of chalcopyrite|186x186px
Natural chalcopyrite has no solid solution series with any other sulfide minerals. There is limited substitution of zinc with copper despite chalcopyrite having the same crystal structure as sphalerite.
Minor amounts of elements such as silver, gold, cadmium, cobalt, nickel, lead, tin, and zinc can be measured (at parts per million levels), likely substituting for copper and iron. Selenium, bismuth, tellurium, and arsenic may substitute for sulfur in minor amounts. Chalcopyrite can be oxidized to form malachite, azurite, and cuprite. The unit cell is twice as large, reflecting an alternation of Cu<sup>+</sup> and Fe<sup>3+</sup> ions replacing Zn<sup>2+</sup> ions in adjacent cells. In contrast to the pyrite structure chalcopyrite has single S<sup>2−</sup> sulfide anions rather than disulfide pairs. Another difference is that the iron cation is not diamagnetic low spin Fe(II) as in pyrite.
In the crystal structure, each metal ion is tetrahedrally coordinated to 4 sulfur anions. Each sulfur anion is bonded to two copper atoms and two iron atoms.
Chalcopyrite is present in the supergiant Olympic Dam Cu-Au-U deposit in South Australia.
Chalcopyrite may also be found in coal seams associated with pyrite nodules, and as disseminations in carbonate sedimentary rocks.
Extraction of copper
thumb|315x315px|Copper [[flash smelting process, a pyrometallurgical method of copper extraction from chalcopyrite]]
Copper metal is predominantly extracted from chalcopyrite ore using two methods: pyrometallurgy and hydrometallurgy. The most common and commercially viable method, pyrometallurgy, involves "crushing, grinding, flotation, smelting, refining, and electro-refining" techniques. Crushing, leaching, solvent extraction, and electrowinning are techniques used in hydrometallurgy. Specifically in the case of chalcopyrite, pressure oxidation leaching is practiced.
Pyrometallurgical processes
The most important method for copper extraction from chalcopyrite is pyrometallurgy. Pyrometallurgy is commonly used for large scale, copper rich operations with high-grade ores. This is because Cu-Fe-S ores, such as chalcopyrite, are difficult to dissolve in aqueous solutions. The extraction process using this method undergoes four stages:
- Isolating desired elements from ore using froth flotation to create a concentration
- Creating a high-Cu sulfide matte by smelting the concentration
- Oxidizing/converting the sulfide matte, resulting in an impure molten copper
- Refining by fire and electrowinning techniques to increase purity of resultant copper by melting the flotation concentrate in a 1250°C furnace to create a new concentrate (matte) with about 45–75% copper. This is because of the extracting challenges which arise from the 1:1 presence of iron to copper, resulting in slow leaching kinetics.