Pyrometallurgy - definition and methods of obtaining metals

mining industry

Pyrometallurgy

This is a branch of mining metallurgy. It consists of the heat treatment of minerals, metallurgical ores and concentrates to effect physical and chemical transformations in the materials allowing the recovery of valuable metals.[1] Pyrometallurgical processing can produce marketable products such as pure metals, intermediates or alloys suitable as feed for further processing. Examples of elements recovered by pyrometallurgical processes include oxides of less reactive elements such as iron, copper, zinc, chromium, can, and manganese.[2]

Pyrometallurgical processes generally fall into one or more of the following categories:[ citation needed

]

• calcination,
• frying
• fuse
• cleaning

Most pyrometallurgical processes require an input of energy to maintain the temperature at which the process occurs. Energy is usually produced in the form of combustion or electrical heat. When sufficient material is present in the feed to maintain the process temperature solely by an exothermic reaction (i.e., without the addition of fuel or electrical heat), the process is called "autogenous". When processing some sulfide ores, the exothermic nature of their combustion is used.

Frying

Main article: Roasting (metallurgy)

Roasting consists of thermal gas-solid reactions that may include oxidation, reduction, chlorination, sulfation and pyrohydrolysis.

The most common example of roasting is the oxidation of metal sulfide ores. The metal sulfide is heated in the presence of air to a temperature that allows oxygen in the air to react with the sulfide to form sulfur dioxide gas and solid metal oxide. The solid product from roasting is often called " calcined"

".
In oxidative roasting, if the temperature and gas conditions are such that the sulfide feedstock is completely oxidized, the process is known as " dead roasting
".
Sometimes, as in the case of reverberatory or electric melting furnace feedstock pre-treatment, the firing process is carried out with less oxygen than required to completely oxidize the feedstock. In this case, the process is called " partial roasting
" because the sulfur is only partially removed.
Finally, if the temperature and gas conditions are controlled so that the sulfides in the feedstock react to form metal sulfates instead of metal oxides, the process is known as " sulfation roasting
".
Sometimes the temperature and gas conditions can be maintained such that the mixed sulfide feedstock (such as feedstock containing both copper sulfide and iron sulfide) reacts so that one metal forms the sulfate and the other forms the oxide, a process known as " spot roasting
" or “
selective sulfation
”.

Industrial methods for obtaining metals

There are several ways to obtain metals in industry. Their use depends on the chemical activity of the element obtained and the raw materials used. Some metals occur in nature in pure form, while others require complex technological procedures to isolate them. The extraction of some elements takes several hours, while others require many years of processing under special conditions. Common methods for obtaining metals can be divided into the following categories: reduction, roasting, electrolysis, decomposition.

There are also special methods for obtaining rare elements, which involve creating special conditions in the processing environment.

This may include ionic decrystallization of the structural lattice or, conversely, a controlled polycrystallization process that allows the production of a specific isotope, radioactive irradiation and other non-standard exposure procedures.

They are used quite rarely due to the high cost and lack of practical application of the selected elements. Therefore, let us dwell in more detail on the main industrial methods of producing metals. They are quite varied, but all are based on the use of chemical or physical properties of certain substances.

Main methods of obtaining metals

One of the main ways to obtain metals is their reduction from oxides. It is one of the most common metal compounds found in nature. The reduction process takes place in blast furnaces under high temperatures and with the participation of metallic or non-metallic reducing agents. From metals, elements with high chemical activity are used, for example, calcium, magnesium, aluminum.

Fuse

Main article: Smelting

Melting involves thermal reactions in which at least one product is a molten phase.

Metal oxides can be smelted by heating with coke or coal (a form of carbon), a reducing agent which releases oxygen in the form of carbon dioxide leaving the purified mineral. Concerns about carbon dioxide production are only a recent concern following the identification of the enhanced greenhouse effect.

Carbonate ores are also smelted using charcoal, but sometimes it is necessary to calcinate the former.[ citation needed

]

Other materials may be added as a stream, promoting the melting of oxide ores and promoting the formation of slag as the flux reacts with impurities such as silicon compounds. [ citation needed]

]

Smelting usually occurs at temperatures above the metal's melting point, but processes vary significantly depending on the ore used and other factors.[ citation needed

]

PYROMETALLURGY

PYROMETALLURGY (from the Greek ru-fire and metallurgy), a set of high-temperature processes for the production and refining of metals and their alloys. Until the end 19th century metals were obtained only using pyrometallurgical methods. processes; At present, despite the rapid progress of new directions - hydrometallurgy and electrometallurgy, pyrometallurgy retains a leading position. In the largest production volumes of cast iron and steel, only pyrometallurgical is used. redistributions. Pyrometallurgical method to obtain basic part of Cu, Pb, Ni, Ti and other important metals, and, in addition, in many. technol. pyrometallurgical schemes processes are combined with hydro- and electrometallurgical ones.

According to the target attribute, pyrometallurgical. processes can be divided into preparatory, concentration and purification from base. masses of impurities, obtaining metals from their compounds, deep purification of metals (refining).

Naib. A common preparatory operation is firing, which is carried out at a temperature below the melting temperature of raw materials and products in order to change the composition, remove harmful impurities and/or enlarge dusty materials (agglomerating roasting, or agglomeration). According to the purpose and nature of the processes occurring, they are distinguished: oxidize. roasting leading to the production of oxides or sulfates (sulfatizing roasting) upon interaction. sulfide materials with atmospheric oxygen (for example, roasting of copper and molybdenum concentrates, sulfatizing roasting of zinc concentrates); will restore. roasting to obtain lower oxides or metals by interaction. source materials with coal or other reducing agents (for example, magnetizing roasting of iron ores with the addition of coal to convert Fe2O3 into Fe3O4 before electromagnetic enrichment); calcining roasting to obtain metal oxides from their hydrates, carbonates or other compounds that decompose at high temperatures; roasting with the addition of solid or liquid reagents (for example, sintering tungsten concentrates with soda to obtain solution Na2WO4 in water, sulfatization of concentrates and industrial products containing Nb, Ta and other rare metals, using H2SO4) and other methods firing

The concentration of metals is achieved by transferring them and base. masses of waste rock into different phases that are easily separated from one another. The most important method of concentration is smelting, carried out at a temperature sufficient to melt (the whole or the main part) of the starting material and products. During melting, two or more immiscible liquid layers are formed, differing in density - metal, slag (alloy of oxides), matte (alloy of sulfides), molten salts, etc. Will restore. smelting is carried out using a reducing agent, most often solid carbon-containing (coke, coal). Products will be restored. metal melts melt and slag, sometimes other phases. The distribution of metals and impurities between layers depends on the ease of their reduction. When restored. smelting iron ores (blast furnace process), lead, tin and other concentrates, the extracted metal turns into metallic. phase, impurities in slag or matte, while when smelting ilmenite concentrate (FeTiO3) the target product is slag with a high Ti content, and in metallic. the melt passes to the base. impurity-Fe.

The base is oxidizing. smelting (oxidizing agent - oxygen) of sulfide ores, concentrates and industrial products. products (reflective, shaft and electric smelting of copper and copper-nickel concentrates and ores for matte, converting nickel and copper-nickel matte, etc.) lies in the difference in the affinity of metals for oxygen and sulfur. With a lack of S, Cu, Ni, Co and other non-ferrous metals are concentrated in the matte, and the main. part of Fe, Ca, Si, Al, Mg, etc. goes into slag. The reduction-sulfidation smelting of oxidized nickel ores is based on the same difference.

Dr. a group of concentration processes is based on the separation of metal in the form of vapor (or volatile compound) from the base. mass of the starting material, in a solid or liquid state. Basic examples: fuming process - distillation of Pb, Zn, Cd, SnS and SnO by blowing liquid slag with a mixture of air and coal dust; Waelz process - distillation of Zn from dispersed material mixed with coke at a temperature that excludes melting; chlorination of titanium slag, loparite and zircon concentrates to produce volatile TiCl4, NbOCl3, TaCl5, ZrCl4.

To remove the bulk of impurities, distillation and other processes based on decomposition are used. volatility conn. target metal and impurities (distillation of MoO3, TiCl4, sublimation of ZrCl4, vacuum distillation of Mg and MgCl2 from titanium sponge, etc.). Differences in volatility increase selectivity. reduction, oxidation or other methods (for example, selective reduction of ZrCl4 in a mixture with HfCl4 to non-volatile ZrCl3, selective reduction of NbCl5 in a mixture with TaCl5 to non-volatile NbCl3). Naib. An effective way to separate substances with different boiling points is rectification (for example, purification of TiCl4 from SiCl4, separation of TaCl5 and NbCl5, etc.).

Obtaining metals from compounds. carry out dif. methods. If conn. metal has a fairly low thermal temperature. stability, metal can be obtained from it without the use of thermal reducing agents. dissociation. In this way, for example, Fe, Ni, Co and other metals are obtained from their carbonyls, W and Mo from their chlorides. Metals with low affinity for oxygen are produced by oxidation of their sulfides (converting copper matte to blister copper, obtaining Hg by oxidizing roasting of HgS). In other cases, electrolysis in molten salts is used (for example, the production of Al from Al2O3, Mg from MgCl2, Ta from Ta2O5, Zr from K2ZrF6) or using reducing agents. With the help of reducing agents, metals are most often obtained from oxides and halides. When producing metals from oxides, CO, CH4, products of incomplete combustion or interaction are used. with water vapor from coal or natural gas. gas (reduction of Fe oxides), H2 (reduction of W, Mo, Fe, Cu oxides), carbon (production of Ni, Fe, W). The most stable oxides are reduced with carbon (carbothermic method) in a vacuum (for example, obtaining Nb and Ta) or metals (see Metallothermy) that have the greatest affinity for oxygen (aluminothermic method for obtaining Nb and Ta, reduction of Ti and Zr oxides calcium or CaH2, U oxides calcium or Mg, etc.). Halides are reduced with metals or H2 (reduction of TiCl4 and ZrCl4 with magnesium or sodium, BeF2magnesium, UF4magnesium or calcium, sodium thermal reduction of K2TaF7, K2NbF7, K2ZrF6, etc.).

When refining metals, differences in their chemistry are used. St. Vakh, in coefficient. distribution between the solid phase and the melt, in the volatility of metals and impurities or their compounds. To be elected oxidation of impurities (C, Si, Mn, P, S, etc.) is the basis for the production of steel from cast iron (see Iron alloys) - by oxidation with air oxygen or blast enriched with it (converter processes) or oxides contained in ore or scrap (open-hearth process), metal impurities. the melt turns into slag or gases. The high affinity of Cu for S is used in the fine refining of Pb; after adding a small amount of elemental S, solid Cu2S sulfide floats to the surface of the molten Pb.

The basis of segregation purification of metals is the separation of impurities from the melt when the temperature decreases. Examples include the purification of Pb from Cu, Sn from Fe, etc. Distillation. Metals that have a fairly high volatility (Hg, Cd, As, Zn, etc.) are subjected to purification. In some cases, distillation is carried out in a vacuum (Li, Rb, Cs, etc.).

When cleaning from impurities that are more volatile than the base metal, the latter is melted in a vacuum. This method is used in the metallurgy of W, Mo, Nb, Ta, Ti, Zr, etc. Deep purification of metals is ensured by chemical transport reactions (transfer reactions) - reversible reactions, accompanied by the transfer of the base metal from one temperature zone to another as a result formation and decomposition will be in between. gaseous conn. (e.g. purification of Ni in the form of tetracarbonyl, Ti and Zr in the form of tetraiodides). The purest metals are obtained using directional crystallization and zone melting processes based on the enrichment of crystals released from the melt with impurities that increase the melting temperature of the metal, and the melt with impurities that lower it. These purification methods are used to obtain single crystals of W, Mo, Ga, Al, Sn, etc.

Pyrometallurgical processes are carried out in various furnaces. type using various types of heating (see Furnaces). In recent years, autogenous processes have been developing, in which the required temperature is maintained due to the exothermic heat released. districts, for example roasting of sulfide concentrates in a fluidized bed, flash smelting with oxygen or hot air blast, the Noranda and Mitsubishi processes, smelting in a liquid bath, etc. (see Copper).

An important direction for improving pyrometallurgical processes - reducing their harmful impact on the environment, associated with the introduction of waste-free technologies, with the reduction and neutralization of waste and emissions.

Lit.: Vanyukov A.V., Zaitsev V.Ya., Theory of pyrometallurgical processes, M., 1973; Sevryukov N.H., Kuzmin B.A., Chelishchev E.V., General metallurgy, 3rd ed., M., 1976; Zelikman AH, Metallurgy of rare metals, M., 1980; Vanyukov A.V., Utkin N.I., Complex processing of copper and nickel raw materials, Chelyabinsk, 1988. G. M. Voldman.

Equipment

Various equipment is used for production and processing:

1. For heat treatment - furnaces, smelters, forges.
2. To change the roughness of surfaces - grinding machines, sandblasting.
3. To create recesses, process edges, ends - slotting, drilling, milling machines.
4. To give a simple or complex cylindrical shape - lathes.
5. For cutting workpieces - saws, laser or waterjet cutters.

Modern equipment is equipped with automatic control systems, which speeds up production and minimizes physical costs on the part of humans.

Homemade horn (Photo: Instagram / vetal7070)

Copper production in Russia and the world

According to analytical agencies, the Russian Federation confidently occupies fifth position among countries engaged in the mining and production of pure copper. Copper production in Russia on average per year is 860 thousand tons. The basis of the modern structure of copper production is made up of three large holdings: OJSC MMC Norilsk Nickel (Norilsk Nickel), LLC UGMKHolding (UMMC) and CJSC Russian Copper Company (RMK). These companies carry out a full production cycle from ore mining to the production of finished ingots, rolled products and wire. Each holding includes several enterprises equipped with the most advanced production technologies. Thanks to dynamic development, last year it was possible to increase copper production by seven percent.

Global copper production is fairly consolidated. Almost 35% of this metal is produced by the five largest companies. These include:

• Codelco (Chile).
• Freeport-McMoRan (USA).
• Glencore (Switzerland).
• BHP Billiton (Australia).
• Southern Copper (Mexico).

These companies obtain almost 80% of copper from primary raw materials (that is, they carry out a full processing cycle) and produce 20% as a result of processing incoming scrap. In Europe, the largest copper producers are: Poland, Portugal and Bulgaria. Each plant is capable of producing a wide range of copper products. Despite the current crisis, copper still remains a sought-after metal. One of the serious disadvantages inherent in this production is environmental problems. Assessments of emissions from copper smelters showed high levels of ambient air pollution. It contains a large number of chemical compounds harmful to health (cadmium, mercury, arsenic, lead, nitrogen oxides and carbon).

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.