The waste is over: how to meet the copper needs of a green economy

Natural compounds containing copper

Pure copper, which is what its nuggets represent, is found in nature in very small quantities. Copper is mainly found in nature in the form of various compounds, the most common of which are the following.

• Bornite is a mineral that got its name in honor of the Czech scientist I. Born. This is a sulfide ore, the chemical composition of which is characterized by its formula - Cu5FeS4. Bornite has other names: variegated pyrite, copper purple. In nature, this ore is presented in two polymorphic forms: low-temperature tetragonal-scalenohedral (temperature less than 228 degrees) and high-temperature cubic-hexaoctahedral (more than 228 degrees). This mineral can have different types depending on its origin. Thus, exogenous bornite is a secondary early sulfide, which is very unstable and is easily destroyed by weathering. The second type, endogenous bornite, is characterized by variable chemical composition, which may contain chalcocite, galena, sphalerite, pyrite and chalcopyrite. Theoretically, minerals of these types can contain from 25.5% sulfur, more than 11.2% iron and over 63.3% copper, but in practice this content of these elements is never maintained.
• Chalcopyrite is a mineral whose chemical composition is characterized by the formula CuFeS2. Chalcopyrite, which is of hydrothermal origin, was previously called copper pyrite. Along with sphalerite and galena, it is included in the category of polymetallic ores. This mineral, which, in addition to copper, contains iron and sulfur, is formed as a result of metamorphic processes and can be present in two types of copper ores: contact-metasomatic type (skarns) and mountain metasomatic (greisens).
• Chalcocite is a sulfide ore, the chemical composition of which is characterized by the formula Cu2S. This ore contains a significant amount of copper (79.8%) and sulfur (20.2%). This ore is often referred to as “copper lustre”, due to the fact that its surface appears as a shiny metal, ranging in shades from lead-gray to completely black. In copper-bearing ores, chalcocite appears as dense or fine-grained inclusions.

Chalcopyrite

In nature, there are also rarer minerals that contain copper.

• Cuprite (Cu2O), a member of the oxide group of minerals, can often be found in places where there is malachite and native copper.
• Covelline is a sulfide rock formed metasomatically. This mineral, whose copper content is 66.5%, was first discovered at the beginning of the last century in the vicinity of Vesuvius. Now covellite is actively mined in deposits in countries such as the USA, Serbia, Italy, and Chile.
• Malachite is a mineral well known to everyone as an ornamental stone. Surely everyone has seen products made from this beautiful mineral in the photo or even owns them. Malachite, which is very popular in Russia, is copper carbonate or copper dihydrocoxcarbonate, which belongs to the category of polymetallic copper-containing ores. The malachite found indicates that there are deposits of other minerals containing copper nearby. In our country, a large deposit of this mineral is located in the Nizhny Tagil region; previously it was mined in the Urals, but now its reserves there are significantly depleted and are not being developed.
• Azurite is a mineral that is also called “copper blue” due to its blue color. It is characterized by a hardness of 3.5–4 units; its main deposits are developed in Morocco, Namibia, Congo, England, Australia, France and Greece. Azurite is often intergrown with malachite and occurs in places where deposits of sulfide-type copper-bearing ores are located nearby.

Malachite

Materials scientist

To obtain copper, copper ores are used (copper content - 1...6%), as well as waste of copper and its alloys.

Copper in nature is found in the form of sulfur compounds (CuS, Cu2S), oxides (CuO, Cu2O), hydrocarbonates (Cu(OH)2), carbon dioxide compounds (CuCO3) in sulfide ores and native copper metal.

The most common ores are copper pyrite and copper luster, containing 1...2% copper.

90% of primary copper is obtained by pyrometallurgical method, 10% by hydrometallurgical method.

The hydrometallurgical method is the production of copper by leaching it with a weak solution of sulfuric acid and subsequent separation of copper metal from the solution. The method is used when processing low-grade ores; it does not allow the extraction of precious metals along with copper.

The production of copper by the pyrometallurgical method consists of beneficiation, roasting, smelting for matte, purging in a converter, and refining.

Enrichment of copper ores is carried out by flotation and oxidative roasting.

The flotation method is based on the use of different wettability of copper-containing particles and waste rock. The essence of flotation is the selective adhesion of certain mineral particles suspended in an aqueous medium to the surface of air bubbles, with the help of which these mineral particles rise to the surface. The method allows you to obtain copper powder concentrate containing 10...35% copper.

Copper ores and concentrates containing large amounts of sulfur are subjected to oxidative roasting. In the process of heating the concentrate or ore to 700...800 0C in the presence of atmospheric oxygen, sulfides are oxidized and the sulfur content is reduced by almost half the original value. Only poor concentrates (with a copper content of 8...25%) are fired, and rich (25...35% copper) concentrates are melted without firing.

After roasting, the ore and copper concentrate are smelted into matte, which is an alloy containing copper and iron sulfides (Cu2S, FeS). The matte contains 20...50% copper, 20...40% iron, 22...25% sulfur, about 8% oxygen and admixtures of nickel, zinc, lead, gold, and silver. Depending on the chemical composition of the ore and its physical state, matte is produced either in shaft furnaces, if the raw material is lump copper ore containing a lot of sulfur, or in reverberatory furnaces, if the starting product is powdered flotation concentrate. Most often, smelting is carried out in fiery reverberatory furnaces. The temperature in the smelting zone is 1450 0C.

The resulting copper matte, in order to oxidize sulfides and iron, is subjected to blowing with compressed air in horizontal converters with side blast. The resulting oxides are converted into slag, and sulfur into SO2. Heat in the converter is released due to chemical reactions without fuel supply. The temperature in the converter is 1200…1300 ºC. Thus, the converter produces blister copper containing 98.4...99.4% copper, 0.01...0.04% iron, 0.02...0.1% sulfur and a small amount of nickel, tin, antimony, silver, gold. This copper is poured into a ladle and poured into steel molds or a casting machine.

Blister copper is refined to remove harmful impurities, followed by fire and then electrolytic refining.

The essence of fire refining of blister copper is the oxidation of impurities that have a greater affinity for oxygen than copper, removing them with gases and converting them into slag. After fire refining, copper with a purity of 99...99.5% is obtained. It is poured into molds and ingots are obtained for further smelting of alloys (bronze and brass) or ingots for electrolytic refining.

Electrolytic refining is carried out to obtain copper free of impurities (99.95% Cu).

Electrolysis is carried out in baths where the anode is made of fire-refined copper, and the cathode is made of thin sheets of pure copper. The electrolyte is an aqueous solution of CuSO4 (10...16%) and H2SO4 (10...16%).

When a direct current is passed, the anode dissolves, the copper goes into solution, and copper ions are discharged at the cathodes, depositing a layer of pure copper on them.

Impurities are deposited at the bottom of the bath in the form of sludge, which is processed to extract metals: silver, antimony, selenium, tellurium, gold, etc...

The cathodes are unloaded after 5...12 days, when their mass reaches 60...90 kg. They are thoroughly washed and then melted in electric furnaces.

Copper by purity is divided into grades: M0 (99.95% Cu), M1 (99.9%), M2 (99.7%), M3 (99.5%), M4 (99%).

Extraction methods

Copper is mined by open and closed methods. The first is relevant if the ore is located in a thickness of up to 500 meters. For deeper deposits, special underground mines are built. Pure copper is obtained mainly by the pyrometallurgical method, less often by the hydrometallurgical method.

The pyrometallurgical technique is conventionally divided into two stages, and uses chalcopyrite (copper sulfate) as the feedstock. The first stage is flotation or oxidative roasting. The purpose of this technology is the enrichment of copper ore, which has a high sulfur concentration. During processing, sulfur is removed up to 1%, other metals contained in the ore are converted into oxide compounds.

Chemical formulas of the process:

• ZnS + 1.5O2 = ZnO + SO2 + Q – the reaction occurs at a temperature exceeding +800 degrees;
• ZnS + 2O2 = ZnSO2 + Q – the optimal temperature varies within +600/+700 degrees.

After this, the enriched ore is melted in shaft furnaces at a temperature of + 14,500 degrees, transforming into an alloy consisting of iron and copper sulfides (matte). To improve quality, converter blowing is carried out without fuel supply. The copper content in this alloy is approximately 91%. The second stage is refining, after which the copper component increases to 99.9%.

The hydrometallurgical method is based on leaching. To do this, the ore is crushed into small pieces and filled with solvents:

The result is a solution in which copper and other metals are released. Process formulas:

• CuO+H2SO4>CuSO4+H2O – leaching with sulfuric acid;
• CuSO4+2Fe2SO4>4FeSO4+2CuSO+S – use of iron sulfate;
• Cu2S + 2 Fe2 (SO4)3>2 CuSO4 + 4 FeSO4 + S – leaching with iron sulfate.

The resulting solution undergoes subsequent processing to extract the metal. For example, the cementation technique can be used: CuSO4 + Fe>FeSO4 + Cu. Here pieces of iron are added to the composition, replacing the copper component in sulfate salts.

Technology

Bessemerizing is an iron smelting process that produces steel of relatively high quality. It should be noted that such technology is used extremely rarely today. This is due to the emergence of quite a large number of modern technologies that make it possible to obtain higher quality steel in less time.

The entire Bessemer steel production process can be divided into several main stages:

1. Cast iron is poured into the converter through the neck. An important point is that in this position the device must be in a horizontal position, since there is a possibility that the nozzle will be filled with metal. Nozzles are necessary to blow through the charge. It is the oxidation of impurities and their removal as slag that makes it possible to obtain steel of improved quality.
2. The next stage is to start the blast and turn the converter into a vertical position.
3. In order to ensure the oxidation of harmful impurities and excess carbon, the metal is blown with air. At this stage, slag is formed, with which unnecessary chemicals are removed.
4. After a sufficiently long period of purging, the converter is turned over again into a horizontal position, and the purging of molten metal stops.
5. The molten metal is drained into a ladle and deoxidized by adding special substances.

At the time of the start of purging the composition, active oxidation of manganese and silicon occurs. At the initial stage, carbon is practically not oxidized. This is due to the fact that this component reacts exclusively to exposure to high temperatures. In addition, the process of oxidation of impurities is influenced by thermodynamic factors that determine the activity of oxygen transfer to the sites of the Bessemer process.

Considering this technology, we note the following points:

1. At the first stage, a large number of different slags are formed, which contains a high concentration of silica. The time interval for the first stage is 2-5 minutes.
2. The second stage of the Bessemer production process provides the most favorable conditions for carbon oxidation. An example is an increase in operating temperature to approximately 2000 degrees Celsius. The duration of this stage is approximately 13 minutes. At the end of this stage, the temperature drops to approximately 1600 degrees Celsius.
3. High quality steel can be achieved using various bessemerization methods. It all depends on the characteristics of the composition of the scrap used and the concentration of the cream in the composition.
4. In order to eliminate the possibility of metal overblowing, the active air supply is stopped already at the second stage.
5. Only at the third stage can active oxidation of iron be noted, which causes the release of brown smoke. This stage begins at the moment when the carbon concentration is less than 0.1%.

As previously noted, the Bessemer method of steel production has become widespread due to its high productivity. Foundries quite often install equipment that has a charge of about 35 tons.

Bessemer method of steel smelting

Today, the Bessemer method of steel production is practically not used, which is due to the low quality of the resulting metal and its fairly high cost.

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Biological value for humans

Copper belongs to the category of vital elements, and the body of an adult contains about 100 grams of this metal. A reassessment of the toxicity of this substance was carried out in 2003 by the World Health Organization. Studies have found that copper is not a cause of diseases of the digestive tract, and does not provoke the development of Wilson-Konovalov disease (hepatocerebral dystrophy affecting the liver and brain), as previously thought. Scientists have concluded that a lack of copper is more harmful to human health than its excess.

The bactericidal properties of copper have been known for a long time, and recent studies in this area have confirmed the effectiveness of the metal in the prevention of swine flu and infection by Staphylococcus aureus. In experiments, it was found that 99% of pathogenic bacteria die on a copper surface within 2 hours. Therefore, copper and its alloys are widely used for water disinfection. In Europe, door handles, locks, hinges and railings are made from this metal, which are installed in medical institutions and public places.

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Features of copper ores

Copper-containing ores are characterized as multi-element. The most common connections are with:

• iron;
• gray;
• copper.

The following may be present in minor concentrations:

• nickel;
• gold;
• platinum;
• silver.

Deposits all over the world have approximately the same set of chemical elements in the ore composition; they differ only in their percentages. To obtain pure metal, various industrial methods are used. Almost 90% of metallurgical enterprises use the same method for producing pure copper - pyrometallurgical.

One of the largest ore mines produces 17 million tons of copper per year

The design of this process also makes it possible to obtain metal from recycled materials, which is a significant advantage for industry. Since the deposits belong to the group of non-renewable deposits, reserves decrease every year, ores become poorer, and their extraction and production becomes expensive. This ultimately affects the price of the metal on the international market. In addition to the pyrometallurgical method, there are other methods:

• hydrometallurgical;
• fire refining method.

Chemical properties

In low humidity conditions, copper exhibits almost no special chemical properties. However, upon contact with water and carbon dioxide, it quickly enters into an oxidative reaction, and a film forms on its surface, protecting it from destruction. Oxidation also occurs when heated to 375 degrees.

The metal reacts actively with non-metals of the halogen group, selenium and sulfur. Paired with the latter, for example, it ignites. Copper with valency I and II is involved in the creation of complex compounds (double salts and ammonia mixtures) that are highly stable and used in many industrial fields.

Copper production

After mining the ore, the next problem arises: how to extract the necessary material from it? There are several ways.

One of the oldest technologies involved burning malachite ores with limited air access. The mass placed in pots, mixed with coal, burned, releasing carbon monoxide. Which led to achieving the desired result - obtaining copper that was sufficiently pure for its time.

It is clear that over the past centuries, methods and methods of ore processing have undergone major changes, driven by the goal of achieving the most optimal results for any type of primary raw material. That is why modern metallurgy is based on three main methods for producing copper.

Pyrometallurgical method

Based on high-temperature processes, the pyrometallurgical method is ideally suited for sulfide ores, which are sometimes quite poor in copper concentration. It allows you to extract metal even with a content of 0.5%.

But first of all, the feedstock is enriched during the flotation process. Its essence lies in thoroughly grinding the ore, filling it with water, and adding complex organic flotation reagents. They envelop mineral particles containing copper alloys, giving them non-wetting.

At the second stage of this process, foam is created in the solution, the bubbles of which pick up particles coated with organic matter. This happens under the influence of air flow, as a result of which the formations float to the surface, from where they are later taken up. The foam saturated with copper compounds is collected, squeezed out and dried.

After which the resulting concentrate is fired at a temperature of 14,000 C. This is necessary to remove sulfur and oxidize sulfides. Then high-temperature (14,0000 - 15,0000C) smelting is carried out in shaft furnaces to produce an alloy of iron and copper - matte. Next, in the process of Bessemer smelting in a converter under the influence of oxygen, the oxide is obtained, and then the blister copper itself, containing 90.95% of the metal. In this case, sulfur turns into an acid residue, and iron into silicate slag.

You can obtain pure copper from a rough substance using:

• fire refining,
• electrolysis,
• exothermic reduction reaction under the influence of hydrogen.

Hydrometallurgical method

To extract copper and a number of other metals from polymetallic ores containing less than 0.5% of the desired mineral, the hydrometallurgical method is used.

The extracted minerals are dissolved using non-concentrated sulfuric acid or ammonia. Copper is obtained from the resulting liquids during the displacement reaction. Metallic iron is used to carry out the reaction.

Electrolysis method

The method is designed to obtain pure copper through an electrolytic reaction.

Its technology is to produce pure copper thin sheet cathodes and thick plate anodes from blister copper. Placed then in a bath filled with copper sulfate, they react under the influence of electric current. Copper dissolves on the anodes and is deposited on the cathodes. Released impurities are removed by chemical methods.

Copper pipes

Application area

Copper plate is widely used in construction, automobile, ship and railway industries.

Copper sheets are used in the construction of roofs, facades, fences and fences. And due to the bactericidal nature of the metal surface of copper products, items are made for use in hospitals: doors, handles, handrails, railings and even dishes.

Copper pipe is intended for transporting liquid and air media in water and gas supply systems, heating, air conditioning, as well as in heat exchangers and refrigeration units. In addition to household utilities, such pipes are used in shipbuilding and energy.

Copper wire is used for the production of cable products and wires with low resistance and special magnetic properties.

Copper tape is used in instrument making, electrical engineering and radio electronics, in the manufacture of conductors, windings, and power transformers.

Copper rod is also often used in the construction and industrial industries. It can be used to prepare bearings, window lifters, water stop fittings, and decorative structures in architecture and the interior of buildings.

Varieties of copper ores

There are nine geological types of copper ores of industrial importance:

• Iron-nickel ores occurring in igneous rocks.
• Cuprous sandstones and shales. Stratiform reserves account for 30% of copper reserves and therefore occupy second place in this list.
• Copper-nickel. The deposits are distinguished by a variety of shapes with large inclusions of the desired metal.
• Porphyry copper. They are the undisputed leader and provide 40% of global copper production.
• Carbonatite. They are unique in that there is only one deposit in the world; in addition, they contain alkaline compounds.
• Quartz-sulfide. They do not play a significant role in ensuring production.
• Native. They are located in oxidation areas of copper-sulfide ore mines.
• Skarn. They are located among limestones and are characterized by extreme heterogeneity of morphological structure.

Copper in the listed list of ores can be presented in sulfide, oxide or mixed form, which determines the corresponding types of deposits. Based on their structure in rocks, deposits are divided into disseminated, massive and continuous textures. In the near future, this list may be supplemented by ores lying at the bottom of seas and oceans, as well as nodules of uranium deposits.

Fire refining technology for blister copper

This method of obtaining pure copper is used when the starting material is copper scrap.

The process takes place in special reverberatory furnaces, which are fired by coal or oil. The melted mass fills the bath, into which air is blown through iron pipes:

• pipe diameter – up to 19 mm;
• air pressure – up to 2.5 atm;
• oven capacity – up to 250 kg.

During the refining process, copper raw materials are oxidized, sulfur burns out, then metals. Oxides do not dissolve in liquid copper, but float to the surface. To remove them, quartz is used, which is placed in the bath before the refining process begins and is placed along the walls.

If the scrap metal contains nickel, arsenic or antimony, the technology becomes more complicated. The percentage of nickel in refined copper can only be reduced to 0.35%. But if other components are present (arsenic and antimony), then nickel “mica” is formed, which dissolves in copper and cannot be removed.

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Stages of pyrometallurgical copper production

General methods for obtaining metal from ore

Industrial copper production using the pyrometallurgical method has advantages over other methods:

• the technology provides high productivity - it can be used to produce metal from rocks in which the copper content is even lower than 0.5%;
• allows you to efficiently process secondary raw materials;
• a high degree of mechanization and automation of all stages has been achieved;
• its use significantly reduces emissions of harmful substances into the atmosphere;
• The method is economical and effective.

Enrichment

Ore beneficiation scheme

At the first stage of production, it is necessary to prepare the ore, which is delivered to processing plants directly from the quarry or mine. Often there are large pieces of rock that must first be crushed.

This happens in huge crushing units. After crushing, a homogeneous mass is obtained, with a fraction of up to 150 mm. Pre-enrichment technology:

• raw materials are poured into a large container and filled with water;
• oxygen is then added under pressure to form foam;
• metal particles stick to the bubbles and rise to the top, and waste rock settles at the bottom;
• Next, the copper concentrate is sent for roasting.

Burning

This stage aims to reduce the sulfur content as much as possible. The ore mass is placed in a furnace where the temperature is set at 700–800

O

C. As a result of thermal exposure, the sulfur content is halved. Sulfur oxidizes and evaporates, and some of the impurities (iron and other metals) pass into an easily slag state, which will facilitate later smelting.

Roasting ore to reduce sulfur levels

This stage can be omitted if the rock is rich and contains 25–35% copper after enrichment; it is used only for low-grade ores.

Melting for matte

The matte smelting technology makes it possible to obtain blister copper, which varies by grade: from MCh1 - the purest to MCh6 (contains up to 96% pure metal). During the smelting process, the raw material is immersed in a special furnace in which the temperature rises to 1450

O

WITH.

Copper ore processing technology and black copper production

After the mass is melted, it is purged with compressed oxygen in converters. They have a horizontal appearance, and the blowing is carried out through a side hole. As a result of blowing, iron and sulfur sulfides are oxidized and converted into slag. Heat in the converter is generated due to the flow of hot mass; it does not heat up additionally. The temperature is 1300

O

WITH.

General scheme of copper smelting

At the output of the converter, a rough composition is obtained, which contains up to 0.04% iron and 0.1% sulfur, as well as up to 0.5% other metals:

• tin;
• antimony;
• gold;
• nickel;
• silver

This rough metal is cast into ingots weighing up to 1200 kg. This is the so-called anode copper. Many manufacturers stop at this stage and sell such ingots. But since copper production is often accompanied by the extraction of precious metals contained in the ore, processing plants use the technology of refining the rough alloy. In this case, other metals are released and preserved.

Refining using copper cathode

The technology for producing refined copper is quite simple. Its principle is even used to clean copper coins from oxides at home. The production scheme looks like this:

Refined copper ingots

• the rough ingot is placed in a bath with electrolyte;
• a solution with the following content is used as an electrolyte: copper sulfate – up to 200 g/l;
• sulfuric acid – 135–200 g/l;
• colloidal additives (thiourea, wood glue) – up to 60 g/l;
• water.

The entire electrolysis process takes place within 20–28 days. During this period, the copper cathode is removed up to 3–4 times. The weight of the plates is up to 150 kg.

How it's done: copper mining

During the refining process, dendrites can form on cathode copper - growths that reduce the distance to the anode. As a result, the speed and efficiency of the reaction decreases. Therefore, when dendrites appear, they are immediately removed.

Features of copper: its composition, structure and production technology

Copper, which belongs to non-ferrous metals, has been known for a long time. Its production was invented before people began to make iron.

According to assumptions, its active use occurred as a result of its availability and fairly simple extraction from copper-containing compounds and alloys.

So, let's look today at the properties and composition of copper, the world's leading countries in copper production, the manufacture of products from it and the features of these areas.

Copper has a high coefficient of electrical conductivity, which has increased its value as an electrical material. If previously up to half of all copper produced in the world was spent on electrical wires, now aluminum is used for these purposes as a more affordable metal. And copper itself becomes the most scarce non-ferrous metal.

This video discusses the chemical composition of copper:

The structural composition of copper includes many crystals: nickel, gold, calcium, silver, lead and many others. All metals included in its structure are distinguished by relative softness, ductility and ease of processing. Most of these crystals, when combined with copper, form solid solutions with continuous rows.

The unit cell of this metal is cubic in shape. For each such cell there are four atoms located at the vertices and the central part of the face.

Chemical composition

The composition of copper during its production may include a number of impurities that affect the structure and characteristics of the final product. At the same time, their content should be regulated both by individual elements and by their total quantity. Impurities that are found in copper include:

• Bismuth. This component negatively affects both the technological and mechanical properties of the metal. That is why it should not exceed 0.001% of the finished composition.
• Oxygen. It is considered the most undesirable impurity in copper. Its maximum content in the alloy is up to 0.008% and rapidly decreases when exposed to high temperatures. Oxygen negatively affects the ductility of the metal, as well as its resistance to corrosion.
• Manganese. In the case of the manufacture of conductive copper, this component negatively affects its conductivity. Already at room temperature it quickly dissolves in copper.
• Arsenic. This component creates a solid solution with copper and has virtually no effect on its properties. Its action is largely aimed at neutralizing the negative effects of antimony, bismuth and oxygen.
• Nickel. Forms a solid solution with copper and at the same time reduces its thermal and electrical conductivity.
• Tin. Creates a solid solution and enhances thermal conductivity.
• Selenium, sulfur. These two components have the same effect on the final product. They form a fragile connection with copper and amount to no more than 0.001%. As the concentration increases, the degree of ductility of copper sharply decreases.
• Antimony. This component is highly soluble in copper and therefore has minimal impact on its final properties. It is allowed no more than 0.05% of the total volume.
• Phosphorus. Serves as the main deoxidizer of copper, the maximum solubility of which is 1.7% at a temperature of 714°C. Phosphorus, in combination with copper, not only promotes better welding, but also improves its mechanical properties.
• Zinc. Contained in a small amount of copper, it has virtually no effect on its thermal and electrical conductivity.

The process and proper sequence of copper production will be discussed next.

physical characteristics

Copper acquires its characteristic color as a result of interaction with oxygen and the formation of a thin oxide film. Thinner plates look greenish-blue when viewed through light. The most pronounced physical properties of copper:

• high electrical and thermal conductivity (second only to silver),
• softness,
• plastic,
• easy to stretch and process,
• corrosion resistance.

Among other characteristics of copper, it is worth noting its good immunity to external natural factors (temperature, ultraviolet radiation, chemical exposure) and pleasant appearance (possibility of patination). In cases where it is necessary to use a harder material, brass and bronze are used - alloys of copper with zinc and tin, respectively. Copper products have a high density and can be rolled into wire, rod or sheet of any thickness.