Copper ore mined from copper mine becomes copper concentrate or copper ore with high copper grade after beneficiation, and copper concentrate needs smelting commission to become refined copper and copper products. The earliest source of copper ore is malachite.
1, ore processing
Classification and properties of copper ore;
The raw material of copper smelting is copper ore. Copper mines can be divided into three categories:
(1) sulfide minerals, such as chalcopyrite (CuFeS2), bornite (Cu5FeS4) and chalcocite (Cu2S).
(2) Oxidized minerals, such as chalcopyrite (Cu2O), malachite [Cu(OH)_ CO _], azurite [2CuO3 Cu (OH) 2], chrysocolla (CuSiO3 2H2O), etc.
(3) native copper. Copper ore with copper content of about 1% (0.5% ~ 3%) has mining value, because some impurities such as gangue in the ore can be removed by flotation, and the concentrate with higher copper content (8% ~ 35%) can be obtained.
2. Melting process
(1) pyrometallurgical copper smelting
Cathode copper, electrolytic copper, is produced by smelting and electrolytic refining, and is generally suitable for high-grade copper sulfide ores. Pyrometallurgical smelting generally involves raising the raw ore containing several percent or several thousandths of copper to 20% ~ 30% by beneficiation, and smelting matte as copper concentrate in a closed blast furnace, reverberatory furnace, electric furnace or flash furnace. The matte (matte) produced is then sent to a converter to be blown into coarse copper, and then oxidized and refined in another reverberatory furnace to remove impurities. The process is short and adaptable, and the recovery rate of copper can reach 95%. However, the sulfur in the ore is discharged as sulfur dioxide waste gas in matte making and blowing stages, which is difficult to recover and easy to cause pollution.
Copper smelting from copper mine: Take chalcopyrite as an example. First, concentrate sand, flux (limestone, sand, etc. ) and fuel (coke, charcoal or anthracite) are mixed and put into a "closed" blast furnace for smelting at about 1000℃. So part of the sulfur in the ore becomes SO_ (used to make sulfuric acid), and most impurities such as arsenic and antimony become volatile substances such as As_O_ and Sb_O_, which are removed: 2CuFeS_+O_=Cu_S+2FeS+SO_↑. Part of iron sulfide is converted into oxide: 2fes+3o _ = 2feo+2so _ = Cu_S, and the rest of fes will be melted together to form matte (mainly formed by mutual dissolution of Cu_S and FeS, with copper content between 20% and 50% and sulfur content between 23% and 27%), and feo and SiO_ will form slag. The slag floats on the molten matte and is easy to separate, thus removing some impurities. Then move matte into converter, add flux (quartz sand) and blow air for smelting (1100 ~1300℃). Because the affinity of iron for oxygen is greater than that of copper, and the affinity of copper for sulfur is greater than that of iron, FeS in matte is first transformed into FeO, which combines with flux to form slag, and then Cu_S is transformed into Cu_O, and Cu_O reacts with Cu_S to produce crude copper (with a copper content of about 98.5%). 2Cu_S+3O_=2Cu_O+2SO_↑, 2Cu_O+Cu_S=6Cu+SO_↑, then move the crude copper into the reverberatory furnace, add the flux (quartz sand), and introduce air to oxidize the impurities in the crude copper, and form slag with the flux to remove them. After impurities are removed to a certain extent, heavy oil is injected, and cuprous oxide is reduced to copper at high temperature by reducing gases such as carbon monoxide generated by heavy oil combustion. The refined copper obtained contains about 99.7% copper.
In addition to copper concentrate, waste copper is one of the main raw materials for copper smelting, including old waste copper and new waste copper. Old copper scrap comes from old equipment and machines, abandoned buildings and underground pipelines. The new scrap copper comes from the scrap copper abandoned by the processing plant (the proportion of copper production is about 50%), and the supply of scrap copper is generally stable. Waste copper is divided into: bare copper: the grade is above 90%; Scrap copper (wires): copper-containing materials (old motors, circuit boards); Copper produced from waste copper and other similar materials is also called recycled copper.
(2) Copper hydrometallurgy
A ship is suitable for low-grade copper oxide, and the refined copper produced is called electrodeposited copper. Modern hydrometallurgy includes sulfation roasting-leaching-electrowinning, leaching-extraction-electrowinning and bacterial leaching, which is suitable for heap leaching, tank leaching or in-situ leaching of low-grade complex ores, copper oxide ore and copper-bearing waste ores. Wet smelting technology is being gradually popularized, and it is expected to reach 20% of the total output by the end of this century. The introduction of hydrometallurgy greatly reduces the smelting cost of copper.