Chemical composition of copper and copper alloys

1. Pure copper
      Pure copper is a rose-red metal, which turns purple after a copper oxide film forms on the surface. Therefore, industrial pure copper is often called red copper or electrolytic copper. The density is 8-9g/cm3, and the melting point is 1083°C. Pure copper has good electrical conductivity and is widely used in the manufacture of wires, cables, brushes, etc.; it has good thermal conductivity and is often used to manufacture magnetic instruments and meters that must be protected from magnetic interference, such as compasses and aviation instruments; it has excellent plasticity and is easy to process by hot pressing and cold pressing, and can be made into copper materials such as tubes, rods, wires, strips, strips, plates, and foils. Pure copper products are divided into two types: smelted products and processed products. See Table 1 and Table 2 respectively.

Table 1 Grades, composition and uses of smelting copper

Table 2 Groups, grades and components of processed copper

2. Copper Alloys
(1) Brass
      Brass is an alloy of copper and zinc. The simplest brass is a copper-zinc binary alloy, called simple brass or ordinary brass. By changing the zinc content in brass, brass with different mechanical properties can be obtained. The higher the zinc content in brass, the higher its strength and slightly lower its plasticity. The zinc content of brass used in industry does not exceed 45%. A higher zinc content will cause brittleness and deteriorate the alloy properties.
      In order to improve certain properties of brass, brass with other alloying elements added to single brass is called special brass. Commonly used alloying elements include silicon, aluminum, tin, lead, manganese, iron and nickel. Adding aluminum to brass can increase the yield strength and corrosion resistance of brass and slightly reduce its plasticity. Brass containing less than 4% aluminum has good comprehensive properties such as processing and casting. Adding 1% tin to brass can significantly improve the brass's ability to resist seawater and marine atmospheric corrosion, so it is called "naval brass". Tin can also improve the cutting performance of brass. The main purpose of adding lead to brass is to improve machinability and wear resistance. Lead has little effect on the strength of brass. Manganese brass has good mechanical properties, thermal stability and corrosion resistance; adding aluminum to manganese brass can also improve its performance and obtain castings with smooth surfaces. Brass can be divided into two categories: casting and pressure processing. The chemical composition of commonly used processing brass is shown in Table 3.

Table 3 Chemical composition of commonly used brass

(2) Bronze
      Bronze is the earliest alloy used in history. It originally refers to copper-tin alloy. It is called bronze because of its blue-gray color. In order to improve the processing and mechanical properties of the alloy, other alloying elements such as lead, zinc, and phosphorus are added to most bronzes. Since tin is a scarce element, many tin-free Wuxi bronzes are also used in industry. They are not only cheap but also have the required special properties. Wuxi bronzes mainly include aluminum bronze, beryllium bronze, manganese bronze, silicon bronze, etc. In addition, there are ternary or quaternary bronzes with more complex compositions. Now, copper alloys other than brass and white copper (copper-nickel alloy) are called bronze.
      Tin bronze has higher mechanical properties, better corrosion resistance, friction reduction, and good casting properties; it is less sensitive to overheating and gas, has good welding properties, is non-ferromagnetic, and has a small shrinkage coefficient. Tin bronze has higher corrosion resistance than brass in the atmosphere, seawater, fresh water, and steam. Aluminum bronze has higher mechanical properties than tin bronze and is more wear-resistant, corrosion-resistant, cold-resistant, heat-resistant, non-ferromagnetic, has good fluidity, no segregation tendency, and can produce dense castings. Adding elements such as iron, nickel and manganese to aluminum bronze can further improve the various properties of the alloy.
Bronze is also divided into two categories: pressure processing and casting products. The chemical composition of commonly used processing bronze is shown in Table 4

Table 4 Chemical composition of commonly used bronze

(3) Nickel
      white is a copper-based alloy with nickel as the main added element. It is silvery white and is called nickel white. The copper-nickel binary alloy is called ordinary nickel white. The copper-nickel alloy with manganese, iron, zinc and aluminum is called complex nickel white. Pure copper plus nickel can significantly improve strength, corrosion resistance, electrical resistance and thermoelectric properties. Industrial nickel white is divided into structural nickel white and electrical nickel white according to its performance characteristics and uses, which meet various corrosion resistance and special electrical and thermal properties respectively. Nickel white is mostly processed into nickel white by pressure. The groups and chemical compositions of commonly processed nickel white are shown in Table 5.

Table 5 Groups and components of processed white copper

Properties and Applications of Copper and Copper Alloys

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 world's copper is refined from copper sulfide ore. 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 1083Co. Pure copper is light rose or light red. Copper has many valuable physical and chemical properties, such as high thermal conductivity, strong chemical stability, high tensile strength, easy welding, corrosion resistance, plasticity and ductility. Pure copper can be drawn into very fine copper wire and made into very thin copper foil.
      Copper can form alloys with metals such as zinc, tin, lead, manganese, cobalt, nickel, aluminum, and iron. The alloys formed are mainly divided into three categories: brass is a copper-zinc alloy, bronze is a copper-tin alloy, and white copper is a copper-cobalt-nickel alloy.
      Pure copper is a tough, soft, ductile, purple-red and shiny metal. One gram of copper can be drawn into a 3,000-meter-long filament or pressed into more than 10 square meters of almost transparent copper foil. Pure copper has high electrical and thermal conductivity, second only to silver, but is much cheaper than silver.
      The color of copper is very similar to gold, but it is reddish, and the color of copper ions is blue. It is highly toxic, but copper processed by a specific method is not toxic.
      Copper is stable in dry air and can maintain its metallic luster. But in humid air, a layer of patina (basic copper carbonate) will form on the surface to protect the inner copper from oxidation.

2. Copper smelting

      Copper-containing minerals are relatively common, most of which have bright and eye-catching colors, such as golden chalcopyrite CuFeS ₂ , bright green malachite CuCO ₃ Cu(OH) ₂ , dark blue azurite 2CuCO ₃ Cu(OH) ₂ , cuprite Cu ₂ O, chalcocite Cu ₂ S, 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.
      Copper ore mined from copper mines becomes copper concentrate or copper ore sand with a higher copper grade after mineral processing. Copper concentrate needs to be smelted and extracted before it can become refined copper and copper products.

1. There are two types of copper used in the copper ore processing
         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 to make special alloys, metal wires and wires. The latter is used to make other alloys, copper pipes, 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 (CuFeS ₂ ), bornite (Cu ₅ FeS ₄ ) and chalcocite (Cu ₂ S), etc.
  · Oxide ore-----such as cuprite (Cu ₂ O), malachite [CuCO ₃ Cu(OH) ₂ ], azurite [2CuCO ₃ Cu(OH) ₂ ], chrysocolla (CuSiO ₃ 2H ₂ O), etc.
  · Native copper-----Copper ore with a copper content of about 1% (0.5% to 3%) is worth mining, because the flotation method can remove part of the gangue and other impurities in the ore, and obtain a concentrate with a higher copper content (8% to 35%).

• The smelting process of copper ore:
        The process of smelting copper from copper ore is relatively complicated. Taking chalcopyrite as an example, first, the 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°C. As a result, 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↑. Part of the iron sulfide is converted into oxide: 2FeS+3O2=2FeO+2SO2↑. Cu2S and the remaining FeS, etc. melt together to form "matte" (mainly formed by the dissolution of Cu2S and FeS, its copper content is between 20% and 50%, and its sulfur content is between 23% and 27%), and FeO and SiO2 form slag: FeO+SiO2=FeSiO3. The slag floats on the molten copper matte and is easy to separate, thereby removing some impurities. Then the copper matte is moved into a converter, and after adding flux (quartz sand), air is blown in for blowing (1100-1300°C). Since iron has a greater affinity for oxygen than copper, and copper has a greater affinity for sulfur than iron, the FeS in the copper matte is first converted into FeO, combined with the flux to form slag, and then Cu2S is converted into Cu2O, which reacts with Cu2S to form crude copper (copper content is about 98.5%). 2Cu2S＋3O2=2Cu2O＋2SO2↑, 2Cu2O+Cu2S=6Cu+SO2↑, then the crude copper is moved into a reverberatory furnace, flux (quartz sand) is added, and air is passed in to oxidize the impurities in the crude copper, and form slag with the flux and remove it. After the impurities are removed to a certain extent, heavy oil is sprayed in, and the reducing gases such as carbon monoxide produced by the combustion of heavy oil reduce cuprous oxide to copper at high temperature. The refined copper obtained contains about 99.7% copper.

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

• Pyrometallurgy: Cathode copper,
        also known as electrolytic copper, is produced through smelting and electrolytic refining, which is generally suitable for high-grade copper sulfide ores. Pyrometallurgy generally involves first increasing the copper content of a few percent or a few thousandths of the original ore to 20-30% through ore dressing, and then using it as copper concentrate for matte smelting in a closed blast furnace, reverberatory furnace, electric furnace or flash furnace. The resulting molten matte (matte) is then sent to a converter for blowing into crude copper, and then oxidized and refined in another reverberatory furnace to remove impurities, or cast into anode plates for electrolysis, to obtain electrolytic copper with a grade of up to 99.9%. This process is short and adaptable, and the copper recovery rate can reach 95%, but 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 is prone to pollution. In recent years, pyrometallurgy has gradually developed towards continuous and automated development, such as the silver method, the Noranda method, and the Mitsubishi method in Japan. 
        In addition to copper concentrate, scrap copper is one of the main raw materials for refined copper, including old scrap copper and new scrap copper. Old scrap copper comes from old equipment and old machines, abandoned buildings and underground pipes; new scrap copper comes from copper scraps discarded by processing plants (the output ratio of copper materials is about 50%). Generally, the supply of scrap copper is relatively stable. Scrap copper can be divided into: bare scrap copper: grade above 90%; yellow scrap copper (wires): copper-containing materials (old motors, circuit boards); copper produced from scrap copper and other similar materials is also called recycled copper.

• Hydrometallurgy:
        A ship is suitable for low-grade copper oxide, and the refined copper produced is called electrolytic copper. Modern hydrometallurgy includes sulfuric acid roasting-leaching-electrolytic, leaching-extraction-electrolytic, bacterial leaching and other methods, which are suitable for heap leaching, tank leaching or in-situ leaching of low-grade complex ores, copper oxide ores, and copper-containing waste ores. Hydrometallurgy technology is being gradually 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.

• Characteristics of the two processes: pyrometallurgical and hydrometallurgical copper production processes 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 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 technology has considerable advantages, but its scope of application is limited. Not all copper mines can be smelted using this process. However, through technical improvements, more and more countries, including the United States, Chile, Canada, Australia, Mexico and Peru, have applied this process to more copper mines in recent years. The improvement of hydrometallurgical technology and the promotion of its application have reduced the production cost of copper, increased the production capacity of copper mines, increased the supply of social resources in the short term, and caused a relative surplus of total social supply, which has a pulling effect on prices.

3. Copper production and consumption

1. Distribution of copper resources:
         The world's copper resources are mainly distributed in North America, Latin America and Central Africa. At present, the world's proven reserves total 350 million tons, of which Chile accounts for 24%, the United States accounts for 16.9%, the Commonwealth of Independent States accounts for 10.15%, Zaire accounts for 7.39%, Zambia accounts for 4.55%, Peru accounts for 3.41%, and America accounts for 60% of the world's reserves. China's copper production is concentrated in East China, and the region's copper production accounts for 51.84% of the country's total production, of which Anhui and Jiangxi provinces account for about 30%. The main consumption of copper is in East China and South China, and the consumption of the two accounts for about 70% of the country's total consumption.

2. Main uses of copper:
         Copper is a red metal and also a green metal. It is called a green metal mainly because it is durable, easy to remelt and resmelt, and therefore relatively cheap to recycle.
         In the 1960s, the largest market for copper was the electrical and electronic market, accounting for about 28% of the total. In 1997, these two markets became the second largest end-user of copper consumption, with a 25% share. In many electrical products (such as wires, busbars, transformer windings, heavy motors, telephone wires and telephone cables), the service life of copper is quite long, and only after 20 to 50 years can the copper in it be recycled. Other electrical and electronic products containing copper (such as small appliances and consumer electronics) have a shorter service life, generally 5-10 years. Commercial electronic products and large electrical products are usually recycled because they contain other precious metals in addition to copper. Despite this, the recycling rate of small electronic consumer products is still quite low because they contain almost no copper.
         With the rapid development of science and technology in the field of electronics, some old copper-containing products are becoming increasingly obsolete. For example, in the 1980s, telephone switching stations and central business offices were the main sources of copper and copper alloy scrap, but the advent of digital switching has made these bulky, metal-intensive items increasingly obsolete. 
         Transportation equipment is the third largest market for copper, accounting for about 13% of the total, which is basically the same as in the 1960s. Although the importance of transportation has not changed, the way copper is used has changed significantly. For many years, automotive radiators were the most important end user in this area; however, the use of copper in automotive appliances and electronics has increased rapidly, while the use in the heat exchanger market has declined. The average life of a car is 10-15 years, and almost all of the copper (including radiators and wiring) is recycled before it is completely disassembled and recycled.
         Industrial machinery and equipment is another major application market where copper tends to have a longer service life. However, copper use in this market has not grown and now accounts for only 12% of total use, compared to 21% in the 1960s. The relative importance of consumer and general products has also fallen from 13% in the 1960s to 9% in the 1970s. Coins and ammunition are the main end users in this area. Bullets are rarely recycled, some coins can be melted down, and many are kept by collectors or savers and cannot be recycled.

3. Copper Recycling
         Copper is very durable. It conducts electricity and generally does not corrode or deteriorate over time. As a result, copper is often used to make products that have a relatively long lifespan. In 1997, the construction industry accounted for approximately 42% of all copper consumed in the United States, up 22% from 1960. Homes also use significantly more copper today than they did 50 or 100 years ago. 
         A building's infrastructure can be expanded or modernized, but the copper wire, copper pipes, and brass fittings in a home or office rarely need to be replaced. Because copper has a relatively long lifespan and homes contain less copper than current building structures, there is only a small amount of copper scrap in the building and construction industry. 
         For building copper wire, copper pipe, and copper fittings, the scrap recycling rate (i.e., the ratio of scrap to total copper consumption) is relatively low compared to steel, aluminum, and plastics. This is because packaging products (which are the main end-users of steel, aluminum, and plastics) have a cycle of only a few weeks and can be recycled several times a year. On the other hand, copper products generally have a relatively long lifespan. This affects the supply of copper scrap for recycling.

4. Appendix: Copper recycling in the U.S. market
         Copper and copper alloys are easy to recycle. In 1997, 1.45 million tons of copper were recovered from scraps processed in the United States, and in the same year the United States also exported 379,000 tons of copper and copper alloys. The total amount of primary refined copper extracted from domestic mines and foreign raw materials in the United States is 20 tons. About 2/3 of the copper-containing scraps are new scraps, and 1/3 are old scraps. 
         The United States has a developed infrastructure that can provide copper scraps to smelters, metallurgical plants, copper rolling mills, foundries, ingot plants and other places. These processing plants need copper scraps for processing or to save costs. In 1997, about 19% of copper was processed in furnaces. Most of the copper smelted in the United States comes from primary smelters associated with mining operations. Most of these plants do not use copper scraps, although some use a small amount of copper scraps to control the temperature of molten copper in converters. In the United States, there are two secondary smelters, Chemetco in Illinois and Southern Electric Equipment in Georgia, which mainly process copper scrap. The raw material for these plants is old copper scrap without impurities, which must be upgraded before recycling.
         Most of the primary refineries in the United States rely on blister copper and positive electrodes from primary smelters as their main source of raw material supply. However, there are a small number of refineries that process high-grade No. 1 copper scrap or purchase blister copper or positive electrodes from copper scrap. Generally, ingots obtained by fire smelting or negative electrodes obtained from secondary raw materials are not used everywhere. Most of this raw material is used in copper rolling mills. Secondary cathodes may not be suitable for the production of fine wires, so they are originally used only for the production of home wires. Some secondary cathodes are also mixed with cathodes from primary smelters and used in the production of other wires and cables.
         Southern Cable Works uses high-grade copper scrap to produce cathodes, which are used in the production of wires and cables together with purchased negative electrodes. Warrenton Refinery is another copper scrap processing plant that mainly produces fire-refined ingots. Reading Industries and Cerro Copper operate scrap mills that supply pipe mills. Canada's Noranda and Asarco both use high-grade scrap in their primary smelters. U.S. refineries process about 10% of the country's recycled copper. 
         Copper mills are the largest consumers of copper scrap in the United States, accounting for more than 50% of the total copper scrap consumption in the United States. These mills use both copper scrap and alloy copper scrap. This raw material must be high-grade because it is only smelted once and not refined. Much of the scrap is new. For example, a large portion of the copper scrap used in alloy rod mills is recycled copper from consumers. Scrap is also a major source of raw material for copper rod and sheet producers, but pipe mills use purchased copper rather than taxed copper. Scrap contains an average of about 56% of the raw material required by copper mills in the United States.
         Ingot producers and foundries rely on scrap for copper, and in 1997, scrap accounted for 93% of their copper needs. The raw material requirements for producing cast products are generally less stringent than those for producing gold-plated or drawn products, so ingot producers and foundries can use lower-grade copper and copper alloy scrap. 
         Copper has a high intrinsic value, which makes it quite economical to recycle. The infrastructure needed by scrap collectors, traders, processors and consumers is not supported by the city government and there is no compensation program. 
         When copper mills collect copper scrap from consumers, the price of the scrap is only 90% of the metal value of the scrap. For example, when copper rod mills adjust their prices, they set a "sale price for brass rod metal value" and a "recycling price to consumers." In the U.S. futures market, copper scrap is generally sold at a price slightly lower than the copper price set by the Comex market.

IV. Factors affecting copper prices

• International economic situation. The correlation between commodity market and economic situation is obvious, especially in today's world economy, which is becoming more and more globalized. Commodity market and economy have more correlation, so the price of copper is closely related to the economic situation. Copper consumption is mainly concentrated in developed industrial countries. The economic conditions of these countries, such as the United States, Japan, and Western Europe, have a greater impact on copper prices. Generally speaking, when the economic situation is good, the demand for copper increases and the price rises, and vice versa.

• Production conditions in producing countries. Chile is the country with the richest copper resources and the world's largest copper exporter. Zambia and Zaire in central Africa are also important copper producers. Almost all of the copper they produce is exported. Their production conditions have a great impact on the international copper market. The political situation in these three countries has always been unstable, and labor disputes often break out, which also has a direct impact on copper prices.

• Seasonal influence: The seasonal fluctuation of copper prices is obvious, with the lowest price in January and the highest price in August.

• The impact of industrial policies. Since copper is mainly used in electrical, electronic, construction, machinery and transportation industries, the country's industrial policies on these industries have a more important impact on copper prices.

• The price of substitutes. In the telecommunications industry, copper has always been an important raw material, but the promotion and application of optical fiber technology has challenged the status of copper. At the same time, metal materials such as aluminum have the same properties as copper and have also replaced copper in most areas of use.

• The impact of inventory. Inventory is one of the important factors affecting copper prices. Under different market conditions, companies will take different measures to increase or reduce inventory. In order to ensure the raw materials needed for production or speed up capital turnover, the government will also use the throughput reserves to stabilize the copper market at different times.

• The impact of other policies and regulations. Since the copper market is an international market with a large volume of international trade, changes in factors such as the import and export policies, exchange rate systems, and efforts to combat smuggling of relevant countries will also have an impact on copper prices.

V. Characteristics of domestic copper price trends

      Since the official launch of copper futures trading on March 11, 1993, it has become one of the more standardized and mature trading products in China. Its price has become an important guiding price for domestic copper spot trading. Looking at the trend over the past few years, domestic copper futures prices have the following characteristics:

• The Shanghai Metal Exchange and the London Metal Exchange (LME) have the same market trends and influence each other;

• The Shanghai Gold Exchange has its own technical characteristics and has not lost its independence:

• Compared with other commodities, the price fluctuation of copper futures is relatively small, and it is difficult for large investors to manipulate the market or force a liquidation maliciously.

6. Classification of Copper and Copper Products

1. Classification by form in nature:
   native copper------copper content is over 99%, but the reserves are very small;
   oxide copper ore-----there are also few of them ;
   sulfide copper ore-----copper content is extremely low, generally around 2-3%. More than 80% of the world's copper is refined from sulfide copper ore.

2. Classification by production process
   Copper concentrate - ore with a high copper content selected before smelting.
   Brussels copper - the product after smelting copper concentrate, with a copper content of 95-98%.
   Pure copper - copper with a content of more than 99% after fire refining or electrolysis. Fire refining can produce 99-99.9% pure copper, and electrolysis can make the purity of copper reach 99.95-99.99%.

3. Classification by main alloy components

• Brass - copper-zinc alloy. Brass has excellent mechanical properties and wear resistance, and can be used to make precision instruments, ship parts, gun shells, etc. Brass sounds good when struck, so musical instruments such as gongs, cymbals, bells, and trumpets are all made of brass. The alloy of copper, zinc, and tin is resistant to seawater erosion and can be used to make ship parts and balancers.

• Bronze - copper-tin alloys, etc. (Except zinc and nickel, alloys with other elements are called bronze). Bronze generally has good corrosion resistance, wear resistance, castability and excellent mechanical properties. It is used to manufacture precision bearings, high-pressure bearings, mechanical parts on ships that resist seawater corrosion, and various plates, pipes, bars, etc. Bronze also has an abnormal characteristic - "heat shrinkage and cold expansion". It is used to cast statues. After cooling, it expands, which can make the features clearer. The alloy of copper, tin and phosphorus is hard and can be made into springs.

• White copper - copper-cobalt-nickel alloy. Its color is the same as silver, shiny and not easy to rust. It is often used to make coins, electrical appliances, instruments and decorations.

4. Classification by product form: copper tubes, copper rods, copper wires, copper plates, copper strips, copper bars, copper foils, etc.