Obtaining metals in their pure form. Basic methods for obtaining metals
Metals in nature can be found in the form of minerals, rocks, and aqueous solutions. Only a few (Au, Pt, partly Ag, Cu, Hg) are found in a free state.
Mineral– an individual substance with a specific crystal structure (for example, chalk, marble is calcium carbonate). Rock - a mixture of minerals. A rock containing 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 obtaining metals, the ore is enriched (concentrated), i.e., separated from waste rock.
There are various methods for beneficiating ores. The most commonly used methods are flotation, gravity and magnetic.
For example, the copper content in exploited ores usually does not exceed 1%, so preliminary enrichment is necessary. It is achieved by using the ore flotation method, based on the various adsorption properties of the surfaces of sulfur metal particles and the silicate-type waste rock surrounding them. If in water containing a small admixture of a low-polar organic substance (for example, pine oil), you shake the powder of finely ground copper ore and blow air through the entire system, then the particles of copper sulfide will rise up along with air bubbles 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 flotation, it is possible not only to separate ore from waste rock, but also to separate individual minerals of polymetallic ores.
Metallurgical processes are divided into pyrometallurgical and hydrometallurgical.
Pyrometallurgy– reduction of metals from their compounds (oxides, sulfides, etc.) in 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 = 2 ZnO + 2SO 2 ; 2PbS + 3O 2 = 2 PbO + 2SO 2;
ZnO + C = Zn + CO; PbO + C = Pb + CO.
For example, cast iron and steel are produced using the pyrometallurgical method.
However, not all metals can be obtained by reducing their oxides with coal or CO, so stronger reducing agents are used: hydrogen, magnesium, aluminum, silicon. For example, metals such as chromium, molybdenum, iron are obtained aluminothermy :
3Fe 3 O 4 + 8Al = 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 solution of sulfuric acid:
(CuOH) 2 CO 3 + 2H 2 SO 4 = 2CuSO 4 + 3H 2 O + CO 2.
Copper is isolated from the resulting sulfate solution either by electrolysis or by the action of metallic iron:
Fe + CuSO 4 = 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:
2H 2 O – 4 e –→ O 2 + 4H + .
Active metals (alkali 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 due to its fragility caused by the presence of impurities. After the development of cleaning methods, the use of titanium increased sharply. The purity of materials is especially important in electronics, computer technology and nuclear energy.
Refining– a metal purification process based on the difference in the physical and chemical properties of the metal and impurities.
All methods of metal purification can be divided into chemical and physical-chemical.
Chemical methods purification involves the interaction of metals with certain reagents, which form precipitates or gaseous products with basic metals or impurities. To obtain high-purity nickel, iron, and titanium, thermal decomposition of volatile metal compounds is used (carboxyl process, iodide process).
Consider, for example, the production of zirconium. In a closed system there are iodine vapors and raw zirconium. The temperature in the reaction vessel is 300 ºС. At this temperature, volatile zirconium tetraiodide is formed on the zirconium surface:
Zr (sol)+ 2I 2 (g) ↔ ZrI 4 (g).
The reaction vessel contains a tungsten filament heated to 1500 ºC. Due to the high reversibility of this reaction, zirconium iodide is deposited on the tungsten filament and decomposes to form zirconium.
Physico-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 electrolyzer:
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. The metal with the most positive potential, i.e. nickel, is first deposited on the cathode. Thus, as a result of refining, nickel is deposited on the cathode, copper falls into sludge, and zinc goes into solution.
By electrolysis of molten compounds, aluminum, magnesium, sodium, lithium, beryllium, calcium, as well as alloys of some metals are obtained. The largest-scale electrolytic process in the chemical industry is the electrolysis of a NaCl solution to produce chlorine gas 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 NaOH solution), manganese dioxide from a MnSO 4 solution, etc.
Widely used zone melting , which consists in the fact that the heating zone and, accordingly, the zone of molten metal slowly moves along the ingot (rod). Some impurities are concentrated in the melt and collected at the end of the ingot, others at the beginning of the ingot. After repeated runs, the initial and final parts of the ingot are cut off, leaving the cleaned middle part of the metal.
Metal alloys
Alloy – 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, are studied by one of the branches of inorganic chemistry - metal chemistry .
If you arrange the metals in order of increasing their chemical interaction with each other, you will get the following series:
– the components do not interact with each other either in liquid or solid state;
– the components dissolve mutually in the liquid state, and form a eutectic in the solid state (mechanical mixture);
– components form liquid and solid solutions of any composition with each other (systems with unlimited solubility);
– the components form one or more metal compounds between themselves, 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 chemical changes occurring in the system.
Chemical transformations in a system can be judged by the nature of changes in various physical properties - melting and crystallization temperatures, vapor pressure, viscosity, density, hardness, magnetic properties, electrical conductivity of the system, depending on its composition. Of the various types of physicochemical analysis, the most commonly used is thermal analysis . During the analysis, they build and study fusibility diagrams, which represent a graph of the dependence of the melting temperature of the system on its composition.
To construct a fusibility diagram, take two pure substances and prepare mixtures of different compositions from them. Each mixture is melted and then cooled slowly, noting the temperature of the cooling alloy at certain intervals. In this way a cooling curve is obtained. In Fig. 1. cooling curves of a pure substance are shown (1) and alloy ( 2 ). The transition of a pure substance from a liquid to a solid state is accompanied by the release of crystallization heat, therefore, until all the liquid crystallizes, the temperature remains constant (section bс, curve 1 ). Further cooling of the solid proceeds uniformly.
When cooling the melt (solution), the cooling curve has a more complex form (Fig. 1, curve 2). In the simplest case of cooling a melt of two substances, a uniform decrease in temperature first 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 a 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 separate, the composition of the liquid melt changes, and its solidification temperature continuously decreases as crystallization occurs. The heat released during crystallization somewhat slows down the cooling process 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`s`. When crystallization ends, a further drop in temperature is observed.
Based on the cooling curves of mixtures of different compositions, a fusibility diagram is constructed. Let's look at the most typical of them.
Related information.
And in the form of various compounds. In a free state, there are metals in nature that are difficult to oxidize with atmospheric oxygen, for example, platinum, gold, silver, and much less commonly, mercury, copper, etc.
Native metals are usually found in small quantities as grains or inclusions in rocks. Occasionally there are also quite large pieces of metal - nuggets. Thus, the largest copper nugget found weighed 420 tons, silver - 13.5 tons, and gold - 112 kg.
Most metals in nature exist in a bound state in the form of various chemical natural compounds - minerals. Very often these are oxides, for example iron minerals: red iron ore, brown iron ore, magnetic iron ore Fe3O4. Often the minerals are sulfide compounds, for example lead luster PbS, zinc blende, or galena ZnS, cinnabar HgS.
Minerals are part of rocks and ores. Ores are natural formations containing minerals in which metals are found in quantities technologically and economically suitable for the production of metals in industry.
Based on the chemical composition of the mineral included in the ore, oxide, sulfide and other ores are distinguished.
Usually, before obtaining metals from ore, it is pre-enriched - waste rock, impurities, etc. are separated, resulting in the formation of a concentrate that serves as raw material for metallurgical production.
Metallurgy is the science of methods and processes for the production of metals from ores and other metal-containing products, the production of alloys and the processing of metals. The most important branch of heavy industry involved in the production of metals and alloys has the same name.
Depending on the method of obtaining metal from ore (concentrate), there are several types of metallurgical production.
Pyrometallurgy - methods of ore processing based on chemical reactions occurring at high temperatures (Greek pyros - fire).
Pyrometallurgical processes involve roasting, in which metal compounds contained in ores, in particular sulfides, are converted into oxides, and sulfur is removed in the form of sulfur oxide (1V) SO2, for example:
2СuS + 3O2 = 2СuО + 2SO2
and smelting, in which the reduction of metals from their oxides occurs with the help of coal, hydrogen, carbon monoxide (P), a more active metal, for example:
2СuО + С = 2Сu + СO2
Сr2O3 + 2Аl = Аl2O3 + 2Сr
If aluminum is used as the reducing metal, the corresponding reduction process is called aluminothermy. This method of obtaining metals was proposed by the Russian scientist N. N. Beketov.
Nikolai Nikolaevich Beketov
Russian physical chemist. Contributed to the development of physical chemistry as an independent field of science. He discovered the chemical process of displacement of metals from solutions of their salts under the influence of other metals and hydrogen.
Hydrometallurgy- methods for obtaining metals based on chemical reactions occurring in solutions.
Hydrometallurgical processes include the stage of transferring insoluble metal compounds from ores into solutions, for example, copper, zinc and uranium salts are transferred into solution by the action of sulfuric acid, and molybdenum and tungsten compounds are transferred by treatment with a soda solution, followed by the reductive separation of metals from the resulting solutions using other metals or electric current.
Electrometallurgy- methods for producing metals based on electrolysis, i.e., the separation of metals from solutions or melts of their compounds by passing a direct electric current through them. This method is used mainly for the production of very active metals - alkali, alkaline earth and aluminum, as well as for the production of alloy steels. It was by this method that the English chemist G. Davy first obtained potassium, sodium, barium and calcium.
Humphry Davy
(1778-1829)
English chemist and physicist. One of the founders of electrochemistry. By electrolysis of salts and alkalis he obtained potassium, sodium, barium, calcium, amalgam (a solution of metal in mercury) of strontium and magnesium.
Microbiological methods for obtaining metals, which use the vital activity of certain types of bacteria, deserve great attention. For example, so-called thionic bacteria are capable of converting insoluble sulfides into soluble sulfates. In particular, this bacterial method is used to extract copper from its sulfide ores directly at their location. Next, the working solution enriched with copper(II) sulfate is supplied for hydrometallurgical processing.
1. Native metals.
Lesson content lesson notes supporting frame lesson presentation acceleration methods interactive technologies Practice tasks and exercises self-test workshops, trainings, cases, quests homework discussion questions rhetorical questions from students Illustrations audio, video clips and multimedia photographs, pictures, graphics, tables, diagrams, humor, anecdotes, jokes, comics, parables, sayings, crosswords, quotes Add-ons abstracts articles tricks for the curious cribs textbooks basic and additional dictionary of terms other Improving textbooks and lessonscorrecting errors in the textbook updating a fragment in a textbook, elements of innovation in the lesson, replacing outdated knowledge with new ones Only for teachers perfect lessons calendar plan for the year; methodological recommendations; discussion program Integrated LessonsMost metals are found in nature as part of compounds in which the metals are in a positive oxidation state, which means that in order to obtain them in the form of a simple substance, it is necessary to carry out a reduction process.
But before restoring a natural metal compound, it is necessary to convert it into a form that can be processed, for example, the oxide form, followed by the reduction of the metal. The pyrometallurgical method is based on this. Is it the reduction of metals from their ores at high temperatures using non-metallic reducing agents? coke, carbon monoxide (II), hydrogen; metal? aluminum, magnesium, calcium and other metals. .
Demonstration experiment 1. Obtaining copper from oxide using hydrogen.
Cu +2O + H2 = Cu0 + H2O (hydrothermy)
Demonstration experiment 2. Production of iron from oxide using aluminum.
Fe+32O3 +2Al = 2Fe0 + Al2O3 (aluminothermy)
To obtain iron in industry, iron ore is subjected to magnetic enrichment: 3Fe2 O3 + H2 = 2Fe3O4 + H2O or 3Fe2O3 + CO = 2Fe3O4 + CO2, and then a reduction process takes place in a vertical furnace:
Fe3O4 + 4H2 = 3Fe + 4H2O
Fe3O4 + 4CO = 3Fe + 4CO2
View media lecture. (CD)
The hydrometallurgical method is based on the dissolution of a natural compound in order to obtain a solution of a salt of this metal and the displacement of this metal by a more active one. For example, the ore contains copper oxide and is dissolved in sulfuric acid:
CuO + H2SO4 = CuSO4 + H2O, then carry out a substitution reaction
CuSO4 + Fe = FeSO4 + Cu.
Demonstration experiment 3. Interaction of iron with copper sulfate solution.
In this way, silver, zinc, molybdenum, gold, vanadium and other metals are obtained.
Electrometallurgical method.
These are methods of producing metals using electric current (electrolysis). View a fragment of the media lecture. (CD)
This method produces aluminum, alkali metals, and alkaline earth metals. In this case, melts of oxides, hydroxides or chlorides are subjected to electrolysis:
NaCl -> Na+ + Cl?
cathode Na+ + e > Na0 ¦ 2
anode 2Cl? ?2e > Cl20 ¦ 1
overall equation: 2NaCl = 2Na + Cl2
A modern, cost-effective method for producing aluminum was invented by the American Hall and the Frenchman Héroult in 1886. It involves electrolysis of a solution of aluminum oxide in molten cryolite. Molten cryolite dissolves Al2O3, just as water dissolves sugar. The electrolysis of a “solution” of aluminum oxide in molten cryolite occurs as if the cryolite were only a solvent, and the aluminum oxide? electrolyte.
Al2O3 -> AlAlO3 -> Al3+ + AlO33–
cathode Al3+ +3e -> Al 0 ¦ 4
anode 4AlO33– – 12 e -> 2Al2O3 +3O2 ¦ 1
overall equation: 2Al2O3= 4Al + 3O2.
Thermal decomposition of compounds.
Iron reacts with carbon monoxide (II) at elevated pressure and temperature 100-2000, forming pentacarbonyl: Fe + 5CO = Fe (CO)5
Iron pentacarbonyl is a liquid that can be easily separated from impurities by distillation. At a temperature of about 2500, carbonyl decomposes, forming iron powder: Fe (CO)5 = Fe + 5CO.
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.
Non-metallic substances include carbon monoxide, hydrogen and coking coals. The essence of the reduction procedure is that a more active chemical element or compound displaces the metal from the oxide and reacts with oxygen. Thus, the output is a new oxide and pure metal. This is the most common method of producing metals in modern metallurgy.
Roasting is only an intermediate method of obtaining a pure element. It involves burning metal sulfide in an oxygen environment, resulting in the formation of an oxide, which is then subjected to a reduction procedure. This method is also used quite often, since sulfide compounds are widespread in nature. Direct production of pure metal from its sulfur compounds is not used due to the complexity and high cost of the technological process. It is much easier and faster to carry out double processing, as indicated above.
Electrolysis, as a method of producing metals, involves passing current through a molten metal compound. As a result of the procedure, pure metal is deposited on the cathode, and other substances are deposited on the anode. This method is applicable to metal salts. But it is not universal for all elements. The method is suitable for the production of alkali metals and aluminum. This is due to their high chemical activity, which, under the influence of electric current, makes it easy to break the bonds established in the connections. Sometimes the electrolytic method of obtaining metals is used for alkaline earth elements, but they no longer lend themselves so well to this treatment, and some do not completely break the bond with the non-metal.
The last method - decomposition occurs under the influence of high temperatures, which make it possible to break the bonds between elements at the molecular level. Each connection will require its own temperature level, but in general the method does not contain any tricks or features. The only point: the metal obtained as a result of processing may require a sintering procedure. But this method allows you to obtain an almost 100% pure product, since catalysts and other chemicals are not used for its implementation. In metallurgy, methods for producing metals are called pyrometallurgical, hydrometallurgical, electrometallurgical and thermal decomposition. These are the four methods given above, only named not according to chemical, but according to industrial terminology.
How metal is obtained in industry
The method of metal production largely depends on its distribution in the bowels of the earth. Mining mainly occurs in the form of ore with a certain percentage of elements. High-grade ores can contain up to 90% metal. Low-grade ores, which contain only 20-30% of the substance, are sent to a processing plant before processing.
Only noble metals are found in nature in their pure form and are mined in the form of nuggets of various sizes. Chemically active elements are found either in the form of simple salts or in the form of polyelement compounds, which have a very complex chemical structure, but generally quite simply decompose into their components under a certain influence. Metals of medium and low activity under natural conditions form oxides and sulfides. Less commonly, they can be found in complex acid-metal compounds.
Before obtaining pure metal, one or more procedures are often carried out to decompose complex substances into simpler ones. It is much easier to isolate one product from a two-element compound than from a multi-element complex formation. In addition, the technological process requires careful control, which is very difficult to ensure when we are talking about a large number of impurities with different properties.
As for the environmental side of the issue, the electrochemical method for producing metals can be considered the cleanest, since during its implementation no substances are released into the atmosphere. Otherwise, metallurgy is one of the most harmful industries for nature, so in the modern world much attention is paid to the problem of creating waste-free equipment.
Already, many factories have abandoned the use of open-hearth furnaces in favor of more modern electric models. They consume much more energy, but do not emit fuel combustion products into the atmosphere. Recycling of metals is also very important. For this purpose, special collection points are equipped in all countries where you can hand over used parts made of ferrous and non-ferrous metals, which will then be sent for recycling. In the future, they will be used to make new products that can be used in accordance with their intended purpose.
