1. The natural properties of copper

Copper is one of the earliest ancient metals discovered by humans. Humans began to use copper more than 3,000 years ago. Copper in nature is divided into natural copper, copper oxide ore and copper sulfide ore. The reserves of natural copper and copper oxide are small. Now more than 80% of the copper in the world is refined from copper sulfide ore. The copper content of this ore is extremely low, generally around 2-3%. Metal copper, element symbol CU, atomic weight 63.54, specific gravity 8.92, melting point 1083Co. Pure copper is light rose or reddish. Copper has many valuable physical and chemical properties, such as high thermal conductivity, strong chemical stability, high tensile strength, easy welding, and corrosion resistance, plasticity, and ductility. Pure copper can be drawn into very thin copper wire to make very thin copper foil.

Copper can form alloys with metals such as zinc, tin, lead, manganese, cobalt, nickel, aluminum, iron, etc. The alloys formed are mainly divided into three categories: brass is a copper-zinc alloy, bronze is a copper-tin alloy, and cupronickel is a copper-cobalt-nickel alloy. .

Pure copper is a tough, soft, ductile, purplish-red and shiny metal. 1 gram of copper can be drawn into a 3,000-meter-long filament, or pressed into an almost transparent copper foil of more than 10 square meters. Pure copper has high electrical and thermal conductivity, second only to silver, but much less expensive.

The color of copper is much like gold, but reddish, and the color of copper ions is blue. Highly toxic, however, copper processed by specific processing methods is not toxic.

Copper is stable in dry air and retains its metallic luster. But in humid air, a layer of patina (basic copper carbonate) will be formed on the surface to protect the inner layer of copper from being oxidized.

2. Smelting of copper

Copper-containing minerals are more common, and most of them have bright and eye-catching colors, such as: golden yellow chalcopyrite CuFeS2, bright green malachite CuCO3Cu(OH)2, dark blue azurite 2CuCO3Cu(OH)2, Cuprite Cu2O, chalcocite Cu2S, etc., these ores are roasted in air to form copper oxide CuO, and then reduced with carbon to obtain metallic copper. In addition, bornite is also a very common copper ore.

The copper ore mined from the copper ore is processed into copper concentrate or copper ore with higher copper content after beneficiation.

Processing of copper ore

There are two types of copper used in industry: electrolytic copper (containing 99.9% to 99.95% copper) and refined copper (containing 99.0% to 99.7% copper). The former is used in the electrical industry for the manufacture of special alloys, metal wires and wires. The latter are used to make other alloys, copper tubes, copper plates, shafts, etc.

Classification and properties of copper ore:

The raw material for copper smelting is copper ore. Copper ore can be divided into three categories:

·Sulfide ore-----such as chalcopyrite (CuFeS2), bornite (Cu5FeS4) and chalcocite (Cu2S).

·Oxide ore-----such as cuprite (Cu2O), malachite [CuCO3Cu(OH)2], azurite [2CuCO3Cu(OH)2], malachite (CuSiO32H2O), etc.

·Natural copper----The content of copper in copper ore is about 1% (0.5%~3%), it has mining value, because the flotation method can remove some impurities such as gangue in the ore, and get Concentrate sand with high copper content (8% to 35%).

The smelting process of copper ore:

The process of smelting copper from copper ore is complex. Taking chalcopyrite as an example, firstly, concentrate sand, flux (limestone, sand, etc.) and fuel (coke, charcoal or anthracite) are mixed, put into a "closed" blast furnace, and smelted at about 1000 ℃. Therefore, part of the sulfur in the ore becomes SO2 (used to make sulfuric acid), and most of the impurities such as arsenic and antimony become volatile substances such as AS2O3 and Sb2O3 and are removed: 2CuFeS2+O2=Cu2S+2FeS+SO2↑. A part of iron sulfide is transformed into oxide: 2FeS+3O2=2FeO+2SO2↑. Cu2S and the remaining FeS are melted together to form "matte" (mainly formed by mutual dissolution of Cu2S and FeS, its copper content is between 20% and 50%, and its sulfur content is between 23% and 27%. between), FeO and SiO2 form slag: FeO+SiO2=FeSiO3. The slag floats on the molten matte and is easy to separate, thereby removing a part of the impurities. Then transfer the matte into the converter, add flux (quartz sand) and blow air to carry out blowing (1100～1300℃). Since iron has a greater affinity for oxygen than copper, and copper has a greater affinity for sulfur than iron, FeS in matte is first converted into FeO, combined with the flux to form slag, and then Cu2S is converted into Cu2O, and Cu2O and Cu2S reacts to produce blister copper (with a copper content of about 98.5%). 2Cu2S+3O2=2Cu2O+2SO2↑, 2Cu2O+Cu2S=6Cu+SO2↑, then move the blister copper into the reverberatory furnace, add flux (quartz sand), and let in air to oxidize the impurities in the blister copper, and form slag with the flux. remove. After the impurities are removed to a certain extent, heavy oil is injected, and the reducing gases such as carbon monoxide generated by the combustion of the heavy oil reduce the cuprous oxide to copper at high temperature. The obtained refined copper contains about 99.7% copper.

copper smelting process

The development of copper metallurgy technology has gone through a long process, but so far copper smelting is still dominated by fire-based smelting, and its output accounts for about 85% of the world's total copper output. Modern hydrometallurgical technology is gradually being promoted. The introduction of copper has greatly reduced the smelting cost of copper. Pyrometallurgy and hydrometallurgy (SX-EX).

Fire copper smelting:

Cathode copper is produced by melting smelting and electrolytic refining, that is, electrolytic copper, which is generally suitable for high-grade copper sulfide ore. Pyro smelting is generally to first increase the raw ore containing a few percent or a few thousandths of copper to 20-30% through beneficiation. Matte smelting, the resulting molten matte (matte) is then sent to a converter for blowing into blister copper, and then oxidized and refined to remove impurities in another reverberatory furnace, or cast into an anode plate for electrolysis, and the grade is as high as 99.9%. of electrolytic copper. The process is short and adaptable, and the recovery rate of copper can reach 95%. However, because the sulfur in the ore is discharged as sulfur dioxide waste gas in the two stages of matte making and blowing, it is not easy to recover, and it is easy to cause pollution. In recent years, molten pool smelting such as silver method and Nolanda method and Japan's Mitsubishi method have emerged, and pyrometallurgy has gradually developed towards continuous and automated development.

In addition to copper concentrate, copper scrap is one of the main raw materials for refining copper, including old copper scrap and new scrap copper. Old scrap copper comes from old equipment and machines, abandoned buildings and underground pipes; new scrap copper comes from processing The copper scraps discarded by the factory (the output ratio of copper materials is about 50%), the general supply of scrap copper is relatively stable, and the scrap copper can be divided into: bare copper: the grade is above 90%; yellow copper (wire): containing Copper material (old motors, circuit boards); copper produced from scrap copper and other similar materials, also known as recycled copper.

Hydrometallurgy:

A boat is suitable for low-grade copper oxide, and the refined copper produced is called electro-deposited copper. Modern wet smelting methods include sulfated roasting-leaching-electrowinning, leaching-extracting-electrowinning, bacterial leaching, etc., which are suitable for heap leaching and tank leaching of low-grade complex ores, copper oxide ores, and copper-containing waste ores. ground leaching. Hydrometallurgical smelting technology is gradually being promoted, and it is expected to reach 20% of the total output by the end of this century. The introduction of hydrometallurgy has greatly reduced the smelting cost of copper.

The characteristics of the two processes of fire and wet methods

(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 has limitations and is subject to the grade and type of ore.

(3) The cost of the former is higher than that of the latter.

It can be seen that the hydrometallurgical smelting technology has considerable advantages, but its scope of application is limited, and not all copper ore smelting can use this process. However, through technological improvements, more and more countries, including the United States, Chile, Canada, Australia, Mexico and Peru, have applied this process to more copper smelting in recent years. The improvement of hydrometallurgy technology and the promotion of its application have reduced the production cost of copper, improved the capacity of copper mines, and increased the supply of social resources in the short term, resulting in a relative surplus of the total social supply, which has a pulling effect on prices.