In nature, the chemical elements metals can be both in free form (in the form of a simple substance) and in bound form (become part of complex substances). In this regard, the ways and methods of obtaining metal are different, let's consider the main ones.
Chemically inactive metals, standing in a series of voltages after hydrogen (for example, copper, mercury, gold, silver, platinum) are found on Earth both in free and in bound form. Metals standing in a series of voltages up to hydrogen under natural conditions, as a rule, are contained in a bound form. Metal compounds found in nature are otherwise called minerals.
The accumulation of metal-containing minerals that are part of rocks and sedimentary rocks suitable for industrial processing are called ores..
If the metal in natural conditions is in a free form, then its production is reduced only to its separation with waste rock. In this case, well-known physical methods for separating mixtures are used.
In compounds, metals are in an oxidized form, and therefore, to isolate them from ores, it is necessary to use reduction processes. The extraction of metals from ores is carried out by the metallurgical industry or metallurgy. At the same time, depending on the method used for the reduction of metals from compounds, pyrometallurgy, hydrometallurgy and electrometallurgy are distinguished.
Pyrometallurgy covers processes for obtaining metals from ores by means of reduction reactions carried out at high temperature.
The raw materials for obtaining metals are mainly ores containing their oxides. Coal or CO (carbothermy), active metals (metalothermy), H 2 (hydrothermy) and Si (siliconthermy) are used as a reducing agent.
ZnO + C = Zn + CO
Fe 2 O 3 + 3CO \u003d 2Fe + 3CO 2
Cr 2 O 3 + 2Al \u003d 2Cr + Al 2 O 3
Ca + 2CsCl = CaCl 2 + 2Cs
TiCl 4 + 2Mg \u003d Ti + 2MgCl 2
MoO 3 + 3H 2 \u003d Mo + 3H 2 O
WO 3 + 3H 2 \u003d W + 3H 2 O
Carbon used in the form of coke, at appropriate high temperatures, can reduce almost any metal, even such active as alkali, alkaline earth, magnesium or aluminum. However, in practice, these metals are not obtained by carbothermy, since they form strong chemical compounds, carbides, with excess carbon.
With the help of carbothermy, metals such as Fe, Cu, Zn, Co, Ni, Mn, Cr are usually obtained. The carbides of these metals are fragile and easily decompose when heated.
Carbon(II)-oxide as a reducing agent is more effective than coke, since it is in a gaseous state and is able to provide a large contact area for the reactants.
With the help of hydrothermy, the following metals are obtained - molybdenum, tungsten, rhenium. The advantage of this method is that it produces metals of high purity.
In metallothermy, one of the most active reducing agents is aluminum, which is explained by the high enthalpy of formation of its oxide.
H (Al 2 O 3) \u003d -1700 kJ / mol. Aluminum is used to obtain metals such as chromium, iron, cobalt, nickel.
It can even be used to obtain alkali and alkaline earth metals, since the enthalpies of formation of their oxides are much lower than H(Al 2 O 3). But, as a rule, these metals are obtained in other ways, since their oxides with Al 2 O 3 easily form aluminates:
3CaO + 2Al \u003d Al 2 O 3 + 3Ca
CaO + Al 2 O 3 \u003d Ca (AlO 2) 2
summary equation
4 CaO + 2Al \u003d Ca (AlO 2) 2 + 3Ca
If the ore contains metal sulfide, then it is converted into oxide by oxidative roasting:
2ZnS + 3O 2 = 2ZnO + 2SO 2
4FeS 2 + 11O 2 = 2Fe 2 O 3 + 8SO 2
For the same purpose, carbonate ores are also pre-calcined:
ZnCO 3 \u003d ZnO + CO 2
FeCO 3 \u003d FeO + CO 2
Hydrometallurgy covers methods for obtaining metals from solutions of their salts. In this case, the metal compound, which is part of the ore or feedstock, is first transferred into a solution using suitable reagents, and then this metal is removed from this solution by chemical means.
So, for example, when copper ore containing copper (II) oxide is treated with dilute sulfuric acid, copper goes into solution in the form of sulfate:
CuO + H 2 SO 4 \u003d CuSO 4 + H 2 O
The copper is then removed from the solution by displacement with iron powder:
CuSO 4 + Fe \u003d Cu + FeSO 4
Au, Ag, Zn, Cd, Mo and other metals are obtained by a similar method.
4Au + O 2 + 8NaCN + 2H 2 O \u003d 4Na + 4NaOH
2Na + Zn = Na 2 + 2Au
Electrometallurgy covers methods for obtaining metals by electrolysis of solutions or melts of their compounds:
2Al 2 O 3 \u003d 4Al + 3O 2
2NaCl \u003d 2Na + Cl 2
2KCl \u003d 2K + Cl 2
In this way, the most active metals are obtained, which, when reduced with hydrogen, coal, aluminum, form chemical compounds with these substances.
by electrolysissalt solutions receive low-active metals, which are in the series of voltages after hydrogen:
СuCl 2 \u003d Cu + Cl 2
The electrolysis of solutions is used to obtain low-active metals of high purity.
Navigation
- Solving combined problems based on the quantitative characteristics of a substance
- Problem solving. The law of the constancy of the composition of substances. Calculations using the concepts of "molar mass" and "chemical amount" of a substance
- Solving computational problems based on the quantitative characteristics of matter and stoichiometric laws
- Solving computational problems based on the laws of the gaseous state of matter
- Electronic configuration of atoms. The structure of the electron shells of atoms of the first three periods
11.3. Chemical properties of metals
11.4.
Various types of naturally occurring minerals suitable for the production of metals on an industrial scale are called ores.
All methods for separating metals from ores are based on their reduction according to the equation
Men+ + n e → Me0 ,
where n is the valency of the metal.
Graphite, carbon monoxide (II) CO, hydrogen, active metals are used as reducing agents, electricity and etc.
There are the following ways to obtain metals from ores.
1) pyrometallurgical− carbothermic, metal-thermal;
2) electrometallurgical;
3) hydrometallurgical.
pyrometallurgical the method consists in applying high temperatures in the process of metal reduction. Most often, these are reduction processes with more active metals: Al, Mg, Ca, Na, etc. (metallothermy), silicon (silicathermy), reduction with hydrogen, metal hydrides, etc.
carbothermic method - reduction of metal oxides with carbon or carbon monoxide CO at high temperatures:
Cu2O + C→ 2Cu + CO
In blast furnaces, carbon oxide is used as a reducing agent.
Fe2 O3 + 3CO → 2Fe + 3CO2
In metallothermic method as reducing agents use more active metals at high temperatures (Al, Mg, Ca, etc.). This method produces titanium, uranium, vanadium:
TiCl4 + 2Mg → Ti + 2MgCl2
Not all metals can be obtained by reduction with carbon or carbon monoxide (II) CO. For example, the reaction Cr2 O3 + 3CO = 2Cr+3CO2, G ° = 274.6 kJ/mol, cannot proceed even at fairly high temperatures, while aluminothermy is easily feasible.
Chemistry. Proc. allowance |
11. GENERAL CHARACTERISTICS OF METALS
11.4. Methods for obtaining metals from ores
If aluminum is used as a reducing agent, then this method is called aluminothermy:
Cr2 O3 + 2Al→ 2Cr + 2Al2 O3
Some metals (for example, manganese) form carbides with carbon, therefore, in this case, silicon is a more economical method.
catothermy:
MnO2 + Si Т → Mn + SiO2
Hydrogen reduction is carried out, as a rule, when it is necessary to obtain a relatively pure metal. Hydrogen is used, for example, to obtain pure iron, tungsten from WO3, rhenium from
NH4 ReO4 , osmium from (NH4 )2 OsCl6 etc.
Pyrometallurgy is usually referred to as chlorine metallurgy. The essence of the method lies in the chlorination of raw materials in the presence of a reducing agent or without it and further processing of the resulting metal chlorides, for example:
TiO2 + C + 2Cl2 = TiCl4 + CO2
TiCl4 + 2Mg = Ti + 2MgCl2
The advantages of the chlorination method are: high speed process, the completeness of the use of raw materials, the possibility of separating a large number of components due to the different volatility and thermal stability of chlorides.
Electrometallurgy- technology based on the application electrical energy for the recovery of metals.
Electrometallurgy includes the processes of obtaining metals by electrothermal and electrolysis methods.
In the first case, the electric current serves as a source of high temperatures (for example, steel smelting in electric furnaces); in the second, it is used for the direct separation of metals from compounds.
Such active metals as K, Na, Ca, Mg, Al, etc., are obtained by electrolysis of melts of their compounds. For example, during the electrolysis of a sodium chloride melt, metallic sodium and chlorine gas are obtained:
molten salt NaCl, anode C (graphite):
(− ) K Na+ + e → Na0 − restoration,
(+) А 2Cl− − 2 e → Cl2 − oxidation.
Chemistry. Proc. allowance |
11. GENERAL CHARACTERISTICS OF METALS
11.4. Methods for obtaining metals from ores
Obtaining aluminum is a complex process associated with great difficulties. The main feedstock - aluminum oxide Al2 O3 - does not conduct electricity and has a very high melting point (about 2050 o C). Therefore, a molten mixture of cryolite Na3 AlF6 and aluminum oxide is subjected to electrolysis. A mixture containing about 10% wt. Al2 O3 melts at 960 o C and has electrical conductivity, density and viscosity, the most favorable for the process. To further improve these characteristics, additives AlF3 , CaF2 , MgF2 are added to the composition of the mixture. Due to this, electrolysis is possible at 950 ° C.
The electrolytic cell for aluminum smelting is an iron casing lined with refractory bricks from the inside. Its bottom (under), assembled from blocks of compressed coal, serves as a cathode. Anodes (one or more) are located on top: these are aluminum frames filled with coal briquettes. The cells are installed in series, each series consists of 150 or more cells.
During electrolysis, aluminum is released at the cathode, and oxygen is released at the anode. Aluminum, which has a higher density than the original melt, is collected at the bottom of the cell; from here it is periodically released. As the metal is released, new portions of aluminum oxide are added to the melt. The oxygen released during electrolysis interacts with the carbon of the anode, which burns out, forming CO and CO2.
Hydrometallurgy- a technology that produces metals from ores using aqueous solutions of special reagents (acids, alkalis, salts), which transfer metals from an insoluble state in the ore to a water-soluble state. Further, the metal is isolated from aqueous solutions either by reducing it with a more active metal, or by electrolysis (if the metal is inactive), or by extraction with organic compounds.
For example, consider getting copper:
CuO (t) + H 2SO 4 (l) \u003d CuSO 4 (l) + H 2O (l)
From the resulting solution, copper can be isolated, for example, by reduction with iron:
CuSO4 + Fe = Cu + FeSO4
The hydrometallurgical method separates Ag, Au, Pb and other metals from the waste rock contained in the ore:
4Au + O2 + 8NaCN + 2H2O = 4Na + 4NaOH
2Na + Zn = Na2 + 2Au
Chemistry. Proc. allowance |
11. GENERAL CHARACTERISTICS OF METALS
11.4. Methods for obtaining metals from ores
A special place in hydrometallurgy is occupied by extraction - the extraction of a valuable component of a solution using a solvent that is not miscible with the solution. At present, a whole branch of metallurgy has been created that uses various chemical extractants in the separation of metals from mixtures.
11.5. Obtaining metals of high purity
FROM By increasing the purity of metals, their characteristics are significantly improved. They become more ductile, heat and electrically conductive, more difficult to corrode, etc.
Obtaining high-purity metals is a very complex problem, which has not been solved for all metals. There are a number of cleaning methods, let's look at some of them.
At vacuum melting- the metal is melted in a vacuum, which allows you to get rid of a number of volatile and low-melting impurities of various metals, non-metals, gases. This method does not give very greater degree metal purity.
Thermal decomposition of metal iodides used to purify very refractory metals that form volatile compounds with iodine, such as zirconium, titanium, chromium, etc. The metal to be purified is placed in a crucible
And add iodine. When heated, the metal interacts with yo-
House. In this case, a volatile metal iodide is formed (for example, TiJ4), which, in contact with a hot grid of pure titanium, decomposes under the influence of high temperature, and the purified titanium settles on it:
TiJ 4 1 300− 1 500 D С→ Ti + 2J 2
IN the result is a pure metal, and the iodine is captured and recycled back into the process.
This method makes it possible to selectively isolate individual metals from their mixtures and obtain metals of a sufficiently high degree of purity.
Electrochemical refining based on the application of the process
owls of electrolysis with a soluble anode, for example, when cleaning blister copper from impurities.
IN an electrolytic bath is poured with a solution of copper sulfate CuSO 4 and install a massive anode of blister copper, and a cathode of refined copper in the form of a thin plate. During electrolysis, the copper of the anode passes
in solution and then reduced at the cathode:
CuSO4 solution, anode - blister copper, cathode - refined copper,
(+) A Cu0 - 2 e \u003d Cu2 + (in solution),
(–)K Cu2+ + 2 e = Cu0 (remains on the cathode).
Chemistry. Proc. allowance |
11.5. Obtaining high purity metals
The electrolysis is carried out at low speeds to ensure the selective deposition of copper on the cathode, while impurities of other metals remain in the electrolyte solution.
Electrolysis is carried out until the anode is completely dissolved, and the cathode turns from a thin plate into a massive bar of pure refined copper.
Zone melting makes it possible to obtain metals of a very high degree of purity.
A metal ingot in the form of a rod placed in a crucible is moved at a low speed (5–10 mm/h) through an electric furnace. In this case, a very small area of the ingot is melted, located in the heating zone in this moment. As the crucible moves, the molten zone moves from one end of the ingot to the other.
The purification process is based on the fact that the solubility of impurities in the liquid phase is much higher than in the solid phase. As the ingot, and hence the melt zone moves slowly along the ingot, the impurities are removed by the melt zone and moved to the end of the ingot.
By repeating the described process many times, a high purity metal is obtained with impurities collected at one end of the ingot, which is cut off and subjected to further purification in order to more completely extract the pure metal from them.
Control questions and tasks
1. What are the features of the electronic structure of atoms of metallic elements? What explains the relatively weak bond between the valence electrons of metal atoms and the nucleus?
2. Which elements are metals in the Periodic Table of the Elements? How do their properties change over the period, over the group?
3. What are the characteristic physical properties of metals? From
what do they depend on?
4. What is a metallic bond? By what means is it carried out?
5. What metals should not be stored in air? Why? Write the equations for the reactions of these metals with oxygen. What are the resulting compounds called?
6. What metals are resistant to oxidation by atmospheric oxygen? Why?
7. What is the acid-base character of metal oxides? How does it change in a period with an increase in the ordinal number of an element?
8. How does the nature of metal oxides depend on the degree of oxidation of the element that forms these oxides?
9. Name the methods of obtaining metals from ores.
Chemistry. Proc. allowance |
11. GENERAL CHARACTERISTICS OF METALS
Control questions and tasks
10. What substances are used as metal reducing agents
in pyrometallurgical method?
11. How does the purity of a metal affect its physical properties?
12. Name the getter methods pure metals, their features.
Student competencies
know the classification of metals and their presence in nature; physical and chemical properties of metals; methods for obtaining metals from ores - pyrometallurgical, electrometallurgical, hydrometallurgical; methods for obtaining metals of high purity;
be able to distinguish the features of the electronic structure of metals from non-metals; determine and explain the reason for the change in the chemical activity of metals by groups and periods of the table of D. I. Mendeleev; check experimentally the chemical activity of metals when they interact with acids, atmospheric oxygen and other oxidizing agents; explain the characteristic physical properties of metals in terms of metallic bonding; draw up equations of redox processes in the production of metals by electrometallurgical, hydrometallurgical and other methods; explain the essence of the process of cleaning metals by electrolytic refining and write down the equations of the corresponding chemical reactions.
Chemistry. Proc. allowance |
In his daily life is surrounded by various metals. Most of the items we use contain these chemicals. This all happened because people found a variety of ways to obtain metals.
What are metals
Inorganic chemistry deals with these valuable substances for people. Obtaining metals allows a person to create more and more perfect technology that improves our lives. What are they? Before considering the general methods for obtaining metals, it is necessary to understand what they are. Metals are a group chemical elements in the form of simple substances with characteristic properties:
Thermal and electrical conductivity;
High plasticity;
Glitter.
A person can easily distinguish them from other substances. A characteristic feature of all metals is the presence of a special brilliance. It is obtained by reflecting incident light rays onto a surface that does not transmit them. Shine is a common property of all metals, but it is most pronounced in silver.
To date, scientists have discovered 96 such chemical elements, although not all of them are recognized by official science. They are divided into groups depending on their characteristic properties. So the following metals are distinguished:
Alkaline - 6;
Alkaline earth - 6;
Transitional - 38;
Lungs - 11;
Semimetals - 7;
Lanthanides - 14;
Actinides - 14.
Obtaining metals
In order to make an alloy, it is necessary first of all to obtain metal from natural ore. Native elements are those substances that are found in nature in a free state. These include platinum, gold, tin, mercury. They are separated from impurities mechanically or with the help of chemical reagents.
Other metals are mined by processing their compounds. They are found in various fossils. Ore is minerals and rocks, which include metal compounds in the form of oxides, carbonates or sulfides. To obtain them, chemical processing is used.
Recovery of oxides with coal;
Obtaining tin from tin stone;
Burning sulfur compounds in special furnaces.
To facilitate the extraction of metals from ore rocks, various substances called fluxes are added to them. They help remove unwanted impurities such as clay, limestone, sand. As a result of this process, low-melting compounds called slags are obtained.
In the presence of a significant amount of impurities, the ore is enriched before smelting the metal by removing a large part of the unnecessary components. The most widely used methods for this treatment are flotation, magnetic and gravity methods.
alkali metals
Mass production of alkali metals is a more complex process. This is due to the fact that they are found in nature only in the form of chemical compounds. Since they are reducing agents, their production is accompanied by high energy costs. There are several ways to extract alkali metals:
Lithium can be obtained from its oxide in a vacuum or by electrolysis of its chloride melt, which is formed during the processing of spodumene.
Sodium is extracted by calcining soda with coal in tightly closed crucibles or by electrolysis of a chloride melt with the addition of calcium. The first method is the most laborious.
Potassium is obtained by electrolysis of a melt of its salts or by passing sodium vapor through its chloride. It is also formed by the interaction of molten potassium hydroxide and liquid sodium at a temperature of 440°C.
Cesium and rubidium are mined by reducing their chlorides with calcium at 700-800°C or zirconium at 650°C. Obtaining alkali metals in this way is extremely energy intensive and expensive.
Differences between metals and alloys
There is practically no fundamentally clear boundary between metals and their alloys, since even the purest, simplest substances have some proportion of impurities. So what is the difference between them? Almost all metals used in industry and in other sectors of the national economy are used in the form of alloys obtained purposefully by adding other components to the main chemical element.
Alloys
The technique requires a variety of metallic materials. At the same time, pure chemical elements are practically not used, since they do not have the properties necessary for people. For our needs, we have invented different ways to obtain alloys. This term refers to a macroscopically homogeneous material that consists of 2 or more chemical elements. In this case, metal components predominate in the alloy. This substance has its own structure. In alloys, the following components are distinguished:
A base consisting of one or more metals;
Small additions of modifying and alloying elements;
Unremoved impurities (technological, natural, random).
It is metal alloys that are the main structural material. There are more than 5000 of them in technology.
Despite such a variety of alloys, those based on iron and aluminum are of the greatest importance for people. They are the most common in everyday life. The types of alloys are different. Moreover, they are divided according to several criteria. So applied various ways alloy manufacturing. According to this criterion, they are divided into:
Cast, which are obtained by crystallization of the melt of mixed components.
Powder, created by pressing a mixture of powders and subsequent sintering at high temperature. Moreover, often the components of such alloys are not only simple chemical elements, but also their various compounds, such as titanium or tungsten carbides in hard alloys. Their addition in certain quantities changes the materials.
Methods for obtaining alloys in the form of a finished product or blank are divided into:
Foundry (silumin, cast iron);
Deformable (steels);
Powder (titanium, tungsten).
Alloy types
Methods for obtaining metals are different, while the materials made thanks to them have different properties. In the solid state of aggregation, alloys are:
Homogeneous (homogeneous), consisting of crystals of the same type. They are often referred to as single phase.
Heterogeneous (heterogeneous), called multiphase. When they are obtained, a solid solution (matrix phase) is taken as the base of the alloy. The composition of heterogeneous substances of this type depends on the composition of its chemical elements. Such alloys may contain the following components: solid solutions interstitials and substitutions, chemical compounds (carbides, intermetallic compounds, nitrides), crystallites of simple substances.
Alloy properties
Regardless of which methods of obtaining metals and alloys are used, their properties are completely determined by the crystal structure of the phases and the microstructure of these materials. Each of them are different. The macroscopic properties of alloys depend on their microstructure. In any case, they differ from the characteristics of their phases, which depend solely on the crystal structure of the material. The macroscopic homogeneity of heterogeneous (multiphase) alloys is obtained as a result of a uniform distribution of phases in the metal matrix.
The most important property of alloys is weldability. Otherwise, they are identical to metals. So, alloys have thermal and electrical conductivity, ductility and reflectivity (shine).
Varieties of alloys
Various methods of obtaining alloys have allowed man to invent a large number of metallic materials with different properties and characteristics. According to their purpose, they are divided into the following groups:
Structural (steel, duralumin, cast iron). This group also includes alloys with special properties. So they are distinguished by intrinsic safety or anti-friction properties. These include brass and bronze.
For pouring bearings (babbitt).
For electric heating and measuring equipment (nichrome, manganin).
For the production of cutting tools (will win).
In production, people also use other types of metallic materials, such as low-melting, heat-resistant, corrosion-resistant and amorphous alloys. Magnets and thermoelectrics (telurides and selenides of bismuth, lead, antimony, and others) are also widely used.
Iron alloys
Almost all the iron smelted on Earth is directed to the production of simple iron. It is also used in the production of pig iron. Iron alloys have gained their popularity due to the fact that they have properties that are beneficial to humans. They were obtained by adding various components to a simple chemical element. So, despite the fact that various iron alloys are made on the basis of one substance, steels and cast irons have different properties. As a result, they find a variety of applications. Most steels are harder than cast iron. Various methods for obtaining these metals make it possible to obtain different grades (brands) of these iron alloys.
Improvement of alloy properties
By fusing certain metals and other chemical elements, materials with improved characteristics can be obtained. For example, pure aluminum is 35 MPa. Upon receipt of an alloy of this metal with copper (1.6%), zinc (5.6%), magnesium (2.5%), this figure exceeds 500 MPa.
By combining various chemical substances in different proportions, metal materials with improved magnetic, thermal or electrical properties can be obtained. The main role in this process is played by the structure of the alloy, which is the distribution of its crystals and the type of bonds between atoms.
Steels and cast irons
These alloys are obtained by and carbon (2%). In the production of alloyed materials, nickel, chromium, and vanadium are added to them. All ordinary steels are divided into types:
Low-carbon (0.25% carbon) is used for the manufacture of various structures;
High-carbon (more than 0.55%) is intended for the production of cutting tools.
Various grades of alloyed steels are used in mechanical engineering and other products.
An alloy of iron with carbon, the percentage of which is 2-4%, is called cast iron. This material also contains silicon. Various products with good mechanical properties are cast from cast iron.
Non-ferrous metals
In addition to iron, other chemical elements are used to make various metallic materials. As a result of their combination, non-ferrous alloys are obtained. In people's lives, materials based on:
Copper, called brass. They contain 5-45% zinc. If its content is 5-20%, then brass is called red, and if 20-36% - yellow. There are alloys of copper with silicon, tin, beryllium, aluminum. They are called bronzes. There are several types of such alloys.
Lead, which is a common solder (tretnik). In this alloy, 2 parts of tin fall on 1 part of this chemical. In the production of bearings, babbitt is used, which is an alloy of lead, tin, arsenic and antimony.
Aluminum, titanium, magnesium and beryllium, which are light non-ferrous alloys with high strength and excellent mechanical properties.
How to get
The main methods for obtaining metals and alloys:
Foundry, in which the solidification of various molten components occurs. To obtain alloys, pyrometallurgical and electrometallurgical methods of obtaining metals are used. In the first variant, thermal energy obtained in the process of fuel combustion is used to heat the raw material. The pyrometallurgical method produces steel in open-hearth furnaces and cast iron in blast furnaces. With the electrometallurgical method, the raw materials are heated in induction or electric arc furnaces. At the same time, the raw material is disintegrated very quickly.
Powder, in which the powders of its components are used to make the alloy. Thanks to pressing, they are given a certain shape, and then sintered in special furnaces.
Metals in nature can be in the form of minerals, rocks, aqueous solutions. Only a few (Au, Pt, partly Ag, Cu, Hg) occur in the free state.
Mineral- an individual substance with a specific crystalline structure (for example, chalk, marble is calcium carbonate). Rock - a mixture of minerals. A rock that contains a significant amount of metals is called ore. Aqueous solutions – ocean and sea water; mineral water(in solutions, metals are in the form of salts).
Metallurgy is a science that studies and develops industrial methods for obtaining metals from ores.
Before receiving metals, the ore is enriched (concentrated), i.e., separated from the waste rock.
There are various ways to enrich ores. The most commonly used flotation, gravity and magnetic methods.
For example, the content of copper in exploited ores usually does not exceed 1%, so preliminary enrichment is necessary. It is achieved by using the method of flotation of ores, based on the different adsorption properties of the surfaces of the particles of sulphurous metals and the surrounding waste rock of the silicate type. If in water containing a small admixture of a low-polarity organic substance (for example, pine oil), we shake up the powder of finely ground copper ore and blow air through the entire system, then the particles of copper sulfide, together with air bubbles, will rise up and flow over the edge of the vessel in the form of foam, and silicate particles will settle to the bottom. This is the basis of the flotation enrichment method, with the help of which more than 100 million tons of sulfur ores of various metals are processed annually. Enriched ore - concentrate - usually contains from 20 to 30% copper. With the help of selective (selective) flotation, it is possible not only to separate the ore from the waste rock, but also to separate the individual minerals of polymetallic ores.
Metallurgical processes are divided into pyrometallurgical and hydrometallurgical.
Pyrometallurgy– reduction of metals from their compounds (oxides, sulfides, etc.) under anhydrous conditions at high temperatures.
When processing sulfide ores, sulfides are first converted into oxides by roasting, and then the oxides are reduced with coal or CO:
ZnS + 3O 2 \u003d 2 ZnO + 2SO 2; 2PbS + 3O 2 \u003d 2 PbO + 2SO 2;
ZnO + C = Zn + CO; PbO + C = Pb + CO
The pyrometallurgical method produces, for example, cast iron and steel.
However, not all metals can be obtained by reducing their oxides with carbon or CO, so stronger reducing agents are used: hydrogen, magnesium, aluminum, silicon. For example, metals such as chromium, molybdenum, iron are aluminothermy :
3Fe 3 O 4 + 8Al \u003d 9Fe + 4Al 2 O 3.
Hydrometallurgy - extraction of metals from ores using aqueous solutions of certain reagents.
For example, an ore containing a basic salt (CuOH) 2 CO 3 is treated with a sulfuric acid solution:
(CuOH) 2 CO 3 + 2H 2 SO 4 \u003d 2CuSO 4 + 3H 2 O + CO 2.
From the resulting sulfate solution, copper is isolated either by electrolysis or by the action of metallic iron:
Fe + CuSO 4 \u003d Cu + FeSO 4.
The displacement of one metal by another from a solution of its salt is called in technology cementation.
Copper, zinc, cadmium, nickel, cobalt, manganese and other metals are obtained electrolysis salt solutions. The discharge of metal ions from solutions occurs at the cathode:
Cu+2+2 e -= Cu 0 .
These processes use insoluble anodes, which usually release oxygen:
2H2O-4 e -→ O 2 + 4H + .
Active metals (alkaline and alkaline earth) are obtained by electrolysis of melts, since these metals are soluble in water:
(cathode, -): Mg +2 + 2 e -= Mg 0 ; (anode, +): 2Cl – – 2 e -= Cl 2 0 .
Methods for cleaning metals
The properties of metals depend on the content of impurities in them. For example, titanium has not been used for a long time because of the fragility due to the presence of impurities. After the development of purification methods, the use of titanium has increased dramatically. Of particular importance is the purity of materials in electronic, computer technology and nuclear power.
Refining- the process of cleaning metals, based on the difference in physical and chemical properties metal and impurities.
All methods of cleaning metals can be divided into chemical and physico-chemical.
Chemical Methods purifications consist in the interaction of metals with various reagents that form precipitates or gaseous products with base metals or impurities. To obtain high-purity nickel, iron, titanium, thermal decomposition of volatile metal compounds is used (carboxylic process, iodide process).
Consider, for example, the production of zirconium. In a closed system are iodine vapor and raw zirconium. The temperature in the reaction vessel is 300 ºС. At this temperature, volatile zirconium tetraiodide is formed on the surface of zirconium:
Zr (tv) + 2I 2 (g) ↔ ZrI 4 (g).
The reaction vessel contains a tungsten filament heated to 1500 ºС. Due to the high reversibility of this reaction, zirconium iodide is deposited on the tungsten filament and decomposed to form zirconium.
Physical and chemical methods include electrochemical, distillation, crystallization and other purification methods.
Electrolysis is widely used in the metallurgy of light and non-ferrous metals. This method is used to purify many metals: copper, silver, gold, lead, tin, etc.
Consider, for example, the refining of black nickel, which contains impurities of zinc and copper and serves as an anode in an electrolytic cell:
E 0 Zn 2+ / Zn = - 0.76 V; E 0 Cu 2+ / Cu = .34 V; E 0 Ni 2+ / Ni = - 0.25 V.
At the anode, the metal with the most negative potential dissolves first. Because
E 0 Zn 2+ / Zn< E 0 Ni 2+ / Ni< E 0 Cu 2+ / Cu ,
then zinc dissolves first, and then the base metal - nickel:
Zn-2 e-→ Zn 2 + , Ni - 2 e– → Ni 2 + .
The copper impurity, which has a more positive potential, does not dissolve and precipitates (sludge) in the form of metal particles. The solution will contain Zn 2+ and Ni 2+ ions. On the cathode, the metal with the most positive potential, i.e., nickel, is deposited first. Thus, as a result of refining, nickel is deposited on the cathode, copper precipitates into the sludge, and zinc goes into solution.
Electrolysis of melts of compounds produces aluminum, magnesium, sodium, lithium, beryllium, calcium, as well as alloys of some metals. To the largest scale electrolytic process in chemical industry refers to the electrolysis of a NaCl solution with the production of gaseous chlorine at the anode, hydrogen at the cathode and an alkali solution in the cathode space. In addition, electrolysis produces fluorine from a melt of a mixture of HF and NaF, hydrogen and oxygen from water (to reduce ohmic losses, electrolysis is carried out in a solution of NaOH), manganese dioxide from a solution of MnSO 4, etc.
Widely used zone melting , which consists in the fact that the heating zone and, accordingly, the zone of molten metal slowly move along the ingot (rod). Some impurities are concentrated in the melt and are collected at the end of the ingot, others - at the beginning of the ingot. After multiple runs, the initial and final parts of the ingot are cut off, leaving the cleaned middle part of the metal.
metal alloys
Alloy – it is a system with metallic properties, consisting of two or more metals (one component may be a non-metal).
Questions of the chemical interaction of metals with each other, as well as with non-metals, if the products of their interaction retain metallic properties, studies one of the sections inorganic chemistry – metal chemistry .
If you arrange the metals in order of increasing their chemical interaction with each other, you get the following series:
– the components do not interact with each other either in the liquid or in the solid state;
- the components mutually dissolve in the liquid state, and form a eutectic in the solid state (mechanical mixture);
– components form with each other liquid and solid solutions of any composition (systems with unlimited solubility);
- the components form one or more metal compounds with each other, called intermetallic (system with the formation of a chemical compound).
To study the physical properties of alloys, depending on their composition, physicochemical analysis is widely used. This makes it possible to detect and study the chemical changes occurring in the system.
Chemical transformations in the system can be judged by the nature of the change in various physical properties - melting and crystallization temperatures, vapor pressure, viscosity, density, hardness, magnetic properties, electrical conductivity of the system, depending on its composition. From various kinds physicochemical analysis is more often used thermal analysis . During the analysis, they build and study melting charts, which are a plot of the melting point of the system versus its composition.
To build a melting diagram, two pure substances are taken and mixtures of various compositions are prepared from them. Each mixture is melted and then slowly cooled, noting the temperature of the cooling alloy at regular intervals. In this way a cooling curve is obtained. On fig. 1. shows the cooling curves of a pure substance (1) and alloy ( 2 ). The transition of a pure substance from a liquid to a solid state is accompanied by the release of the heat of crystallization, therefore, until the entire liquid crystallizes, the temperature remains constant (section bc, curve 1 ). Further, the cooling of the solid proceeds evenly.
When the melt (solution) is cooled, the cooling curve has a more complex form (Fig. 1, curve 2). In the simplest case of cooling a melt of two substances, at first, a uniform decrease in temperature occurs until crystals of one of the substances begin to separate from the solution. Since the crystallization temperature of the solution is lower than that of the pure solvent, the crystallization of one of the substances from the solution begins above the crystallization temperature of the solution. When crystals of one of the substances are isolated, the composition of the liquid melt changes, and its solidification temperature continuously decreases as it crystallizes. The heat released during crystallization somewhat slows down the course of cooling and therefore, starting from the point l on the curve 2, the steepness of the cooling curve line decreases. Finally, when the melt becomes saturated with respect to both substances , crystallization of both substances begins simultaneously. This corresponds to the appearance of a horizontal section on the cooling curve b`c`. When crystallization ends, a further drop in temperature is observed.
Based on the cooling curves of mixtures of different compositions, a melting diagram is constructed. Let's consider the most typical of them.
Similar information.
Methods for obtaining metals.
The vast majority of metals are found in nature in the form of compounds with other elements. Only a few metals are found in the free state, and then they are called native. Gold and platinum are found almost exclusively in native form, silver and copper - sometimes in native form, also native mercury, tin and some other metals are found. The extraction of gold and platinum is carried out either by mechanically separating them from the rock in which they are enclosed, for example, by washing with water, or by extracting them from the rock with various reagents, followed by separation of the metal from the solution.
All other metals are mined by chemical processing of their natural compounds.
Minerals and rocks containing metal compounds and suitable for the production of these metals in a factory way are called ores. The main ores are oxides, sulfides and carbonates of metals. The most important method for obtaining metals from ores is based on the reduction of their oxides with coal. If, for example, red copper ore cuprite Cu2O is mixed with coal and subjected to strong incandescence, then coal, reducing copper, will turn into carbon monoxide II, and copper will be released in the molten state Cu2O C 2Cu CO In a similar way, cast iron is smelted from them. iron ore, obtaining tin from tin stone SnO2 and the reduction of other metals from oxides.
When processing sulfur ores, sulfur compounds are first converted into oxygen compounds by firing in special furnaces, and then the resulting oxides are reduced with coal. For example, 2ZnS 3O2 2ZnO 2SO2 ZnO C ZnCO In cases where the ore is a salt of carbonic acid, it can be directly reduced with coal, like oxides, since when heated, carbonates decompose into metal oxide and carbon dioxide.
For example ZnCO3 ZnO CO2 Usually, ores, in addition to the chemical compound of this metal, contain many more impurities in the form of sand, clay, limestone, which are very difficult to melt. To facilitate the smelting of metal, various substances are added to the ore, which form low-melting compounds with impurities - slags. Such substances are called fluxes. If the admixture consists of limestone, then sand is used as a flux, which forms calcium silicate with limestone.
On the contrary, in the case of a large amount of sand, limestone serves as a flux. In many ores, the amount of waste rock impurities is so high that the direct smelting of metals from these ores is economically unprofitable. Such ores are pre-enriched, that is, part of the impurities are removed from them. Especially widespread is the flotation method of ore dressing - flotation, based on the different wettability of pure ore and waste rock.
The technique of the flotation method is very simple and basically boils down to the following. The ore, consisting, for example, of sulphurous metal and silicate waste rock, is finely ground and poured into large vats of water. Some low-polarity organic substance is added to the water, which contributes to the formation of a stable foam when the water is agitated, and a small amount of a special reagent, the so-called collector, which is well adsorbed by the surface of the mineral being floated and makes it incapable of being wetted by water.
After that, a strong stream of air is passed through the mixture from below, mixing the ore with water and added substances, and the air bubbles are surrounded by thin oil films and form foam. In the process of mixing, the particles of the floated mineral are covered with a layer of adsorbed molecules of the collector, stick to the bubbles of the blown air, rise up with them and remain in the foam, while the particles of waste rock wetted by water settle to the bottom. The foam is collected and squeezed out, obtaining an ore with a significantly higher metal content.
To restore some metals from their oxides, hydrogen, silicon, aluminum, magnesium and other elements are used instead of coal. The process of reducing a metal from its oxide with the help of another metal is called metallothermy. If, in particular, aluminum is used as a reducing agent, then the process is called aluminothermy. Electrolysis is also a very important method of obtaining metals.
Some of the most active metals are obtained exclusively by electrolysis, since all other means are not energetic enough to reduce their ions. List of used literature. 1. Basics of general chemistry. Yu.D. Tretyakov, Yu.G. Metlin. Moscow Enlightenment 1980 2. General chemistry. N.L. Glinka. Chemistry Publishing House, Leningrad branch, 1972. 3. Why and how metals are destroyed. S.A. Balezin. Moscow Enlightenment 1976 4. A manual on chemistry for applicants to universities. G.P. Khomchenko. 1976 5. Reading book on inorganic chemistry. Part 2. Compiled by V.A. Kritsman.
Moscow Enlightenment 1984 6. Chemistry and scientific and technical progress. I.N. Semenov, A.S. Maksimov, A.A. Makarenya. Moscow Enlightenment 1988
End of work -
This topic belongs to:
Metals. Metal properties
Metal groups. Currently, 105 chemical elements are known, most of them are metals. The latter are very common in nature and .. Metals he wrote solid, malleable shiny bodies. Assigning this or that .. The first of them includes ferrous metals - iron and all its alloys, in which it makes up the main part. These..
If you need additional material on this topic, or you did not find what you were looking for, we recommend using the search in our database of works:
What will we do with the received material:
If this material turned out to be useful for you, you can save it to your page on social networks:
Loading...