Copper is one of the earliest ancient metals discovered by human beings. As early as 3000 years ago, people began to use copper. Copper in nature is divided into natural copper, copper oxide and copper sulfide. The reserves of natural copper and copper oxide are very small. At present, more than 80% of copper in the world is extracted from copper sulfide ore, and the copper content of this ore is extremely low, generally around 2-3%. Metallic copper, element symbol CU, atomic weight 63.54, specific gravity 8.92, melting point 1083 Co. Pure copper is light rose or reddish. Copper has many valuable physical and chemical properties, such as high thermal conductivity, mechanical stability, high tensile strength, easy welding, corrosion resistance, plasticity and ductility. Pure copper can be drawn into thin copper wire and made into thin copper foil. It can form alloys with metals such as zinc, tin, lead, manganese, cobalt, nickel, aluminum, iron, etc. The formed alloys are mainly divided into three categories: brass is copper-zinc alloy, bronze is copper-tin alloy, and white copper is copper-cobalt-nickel alloy.
2. Copper smelting
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.
A. Copper ore processing
Industrial copper includes electrolytic copper (containing 99.9% ~ 99.95% copper) and refined copper (containing 99.0% ~ 99.7% copper). The former is used to make special alloys, wires and wires in the electrical industry. The latter is used to manufacture other alloys, copper tubes, copper plates, shafts, etc.
A. 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 [CuCO3Cu(OH)2], azurite [2CuCO3Cu(OH)2], chrysocolla (CuSiO32H2O), 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.
B. the smelting process of copper ore;
The process of extracting copper from copper ore is very complicated. Taking chalcopyrite as an example, firstly, 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℃. Therefore, a part of sulfur in the ore becomes SO2 (used to make sulfuric acid), and most impurities such as arsenic and antimony become volatile substances such as AS2O3 and Sb2O3 and are removed: 2 cufs 2+O2 = cu2s+2 FeS+SO2↑. Part of iron sulfide is converted into oxide: 2fes+3o2 = 2feo+2so2 ↑. Cu2S and the remaining FeS melt together to form matte (mainly formed by mutual dissolution of Cu2S and FeS, with copper content between 20% and 50% and sulfur content between 23% and 27%), and FeO and SiO2 form slag: FeO+SiO 2 = FeSiO 3. 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 iron has a greater affinity for oxygen than copper, and copper has a greater affinity for sulfur than iron, FeS in matte is first transformed into FeO, which combines with flux to form slag, and then Cu2S is transformed into Cu2O, and Cu2O reacts with Cu2S to produce crude copper (with a copper content of about 98.5%). 2cu2s+3o2 = 2cu2o+2so2 = 2cu2o+cu2s = 6cu+SO2 = =, then move the crude copper into a reverberatory furnace, add flux (quartz sand), and introduce air to oxidize impurities in the crude copper, which will form slag with the flux and be removed. 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.
B. Copper smelting process
The development of copper-gold technology has gone through a long process, but so far the smelting of copper is still dominated by pyrometallurgy, and its output accounts for about 85% of the world's total copper production. Modern hydrometallurgy technology is gradually popularized, and the introduction of hydrometallurgy greatly reduces the smelting cost of copper. Pyrolysis and hydrometallurgy (SX-EX).
A. pyrometallurgical copper smelting:
Cathode copper, electrolytic copper, is produced by smelting and electrolytic refining, and is generally suitable for high-grade copper sulfide ores. Generally, pyrometallurgical process is to raise the raw ore containing a few percent or a few thousandths of copper to 20-30% as copper concentrate after beneficiation, and carry out matte smelting in a closed blast furnace, reverberatory furnace, electric furnace or flash furnace, and then send the generated matte (matte) into a converter to be blown into crude copper, and then oxidize and refine it in another reverberatory furnace to remove impurities, or the process is short and has strong adaptability. 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. In recent years, molten pool smelting such as Baiyin process and Noranda process, as well as Mitsubishi process and pyrometallurgical process in Japan, have gradually developed to continuity and automation.
The production process is roughly as shown in the figure:
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.
B. 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.
The wet smelting process is as follows:
C. Comparison of characteristics between pyrometallurgy and wet process Compared with pyrometallurgy and wet copper production process, pyrometallurgy and wet copper production process have the following characteristics:
(1) The smelting equipment of the latter is simpler, but the impurity content is higher, which is a beneficial supplement to the former.
(2) The latter is limited by the grade and type of ore.
(3) The cost of the former is higher than that of the latter.
It can be seen that wet smelting technology has considerable advantages, but its application scope is limited, and not all copper mines can adopt this technology. However, through technical improvement, in recent years, more and more countries, including the United States, Chile, Canada, Australia, Mexico and Peru, have applied this process to more copper smelting. The improvement of hydrometallurgy technology and the popularization of its application have reduced the production cost of copper, improved the productivity of copper mines, and increased the supply of social resources in a short time, resulting in a relative surplus of total social supply, which has a pulling effect on prices.