History of calcium

Calcium was discovered in 1808 by Humphry Davy, who, by electrolysis of slaked lime and mercury oxide, obtained calcium amalgam, as a result of the process of distillation of mercury from which the metal remained, which received the name calcium. in latin lime sounds like calx, it was this name that was chosen by the English chemist for the discovered substance.

Calcium is an element of the main subgroup II of group IV of the period of the periodic system of chemical elements D.I. Mendeleev, has atomic number 20 and an atomic mass of 40.08. The accepted designation is Ca (from Latin - Calcium).

Physical and chemical properties

Calcium is a reactive, soft, silver-white alkali metal. Due to the interaction with oxygen and carbon dioxide, the surface of the metal tarnishes, so calcium needs a special storage regime - a tightly closed container in which the metal is poured with a layer of liquid paraffin or kerosene.

Calcium is the most well-known of the trace elements necessary for a person, the daily requirement for it is from 700 to 1500 mg for a healthy adult, but it increases during pregnancy and lactation, this must be taken into account and calcium should be taken in the form of drugs.

Being in nature

Calcium has a very high chemical activity, therefore, in a free (pure) form, it does not occur in nature. However, it is the fifth most common in the earth's crust, in the form of compounds it is found in sedimentary (limestone, chalk) and rocks(granite), a lot of calcium contains feldspar anorite.

It is widely distributed in living organisms, its presence is found in plants, animal and human organisms, where it is present mainly in the composition of teeth and bone tissue.

Calcium absorption

An obstacle to the normal absorption of calcium from foods is the consumption of carbohydrates in the form of sweets and alkalis, which neutralize hydrochloric acid stomach to dissolve calcium. The process of calcium absorption is quite complicated, so sometimes it is not enough to get it only with food, an additional intake of the microelement is necessary.

Interaction with others

To improve the absorption of calcium in the intestines, it is necessary, which tends to facilitate the process of calcium absorption. When taking calcium (in the form of supplements) in the process of eating, absorption is blocked, but taking calcium supplements separately from food does not affect this process in any way.

Almost all of the body's calcium (1 to 1.5 kg) is found in the bones and teeth. Calcium is involved in the processes of nervous tissue excitability, muscle contractility, blood clotting processes, is part of the nucleus and membranes of cells, cell and tissue fluids, has anti-allergic and anti-inflammatory effects, prevents acidosis, activates a number of enzymes and hormones. Calcium is also involved in the regulation of cell membrane permeability and has the opposite effect.

Signs of calcium deficiency

Signs of a lack of calcium in the body are such, at first glance, unrelated symptoms:

• nervousness, mood deterioration;
• cardiopalmus;
• convulsions, numbness of the limbs;
• growth retardation and children;
• high blood pressure;
• delamination and fragility of nails;
• pain in the joints, lowering the "pain threshold";
• profuse menstruation.

Causes of calcium deficiency

The causes of calcium deficiency can be unbalanced diets (especially starvation), low calcium content in food, smoking and addiction to coffee and caffeinated drinks, dysbacteriosis, kidney disease, thyroid gland, pregnancy, lactation periods and menopause.

Excess calcium, which can occur with excessive consumption of dairy products or uncontrolled intake of drugs, is characterized by severe thirst, nausea, vomiting, loss of appetite, weakness, and increased urination.

The use of calcium in life

Calcium has found application in the metallothermic production of uranium, in the form of natural compounds it is used as a raw material for the production of gypsum and cement, as a means of disinfection (everyone knows bleach).

Although calcium is very widely distributed in the globe It does not occur in the free state in nature.

Before we learn how pure calcium can be obtained, let's get acquainted with natural calcium compounds.

Calcium is a metal. IN periodic system Mendeleev calcium (Calcium), Ca has atomic number 20 andlocated in group II. This is a chemically active element, it easily interacts with oxygen. Has a silvery white color.

Natural calcium compounds

Calcium compounds are found almost everywhere.

calcium carbonate, or calcium carbonate – it is the most common calcium compound. His chemical formula-CaCO 3. Marble, chalk, limestone, shell rock - all these substances contain calcium carbonate with a small amount of impurities. There are no impurities at all in calcite, the formula of which is also CaCO 3.

calcium sulphate also called calcium sulfate. The chemical formula of calcium sulfate CaSO 4. The mineral gypsum known to us is the crystalline CaSO 4 2H 2 O.

calcium phosphate, or calcium salt of phosphoric acid. It is the material from which the bones of humans and animals are built. This mineral is called tricalcium phosphate Ca 3 (PO 4) 2.

Calcium chlorideCaCl 2, or calcium chloride, occurs in nature in the form of CaCl 2 · 6H 2 O crystalline hydrate. When heated, this compound loses water molecules.

calcium fluoride CaF 2, or calcium fluoride, can be found naturally in the mineral fluorite. And pure crystalline calcium difluoride is called fluorspar.

But not always natural calcium compounds have the properties that people need. Therefore, man has learned to artificially transform such compounds into other substances. Some of these artificial compounds are even more familiar to us than natural ones. An example is slaked Ca (OH) 2 and quicklime CaO, which have been used by humans for a very long time. Many building materials such as cement, calcium carbide, and bleach also contain artificial calcium compounds.

What is electrolysis

Probably, almost every one of us has heard of a phenomenon called electrolysis. We will try to give the simplest description of this process.

If an electric current is passed through aqueous solutions of salts, then as a result of chemical transformations, new chemicals are formed. The processes that occur in a solution when an electric current is passed through it are called electrolysis. All these processes are studied by a science called electrochemistry. Of course, the electrolysis process can only take place in a medium that conducts current. Aqueous solutions acids, bases and salts are such a medium. They are called electrolytes.

The electrodes are immersed in the electrolyte. The negatively charged electrode is called the cathode. A positively charged electrode is called an anode. When an electric current passes through the electrolyte, electrolysis occurs. As a result of electrolysis, the constituents of dissolved substances settle on the electrodes. At the cathode they are positively charged, at the anode they are negative. But on the electrodes themselves, secondary reactions can occur, as a result of which a secondary substance is formed.

We see that with the help of electrolysis, chemical products are formed without the use of chemical reagents.

How is calcium obtained

In industry, calcium can be obtained by electrolysis of molten calcium chloride CaCl 2 .

CaCl 2 \u003d Ca + Cl 2

In this process, a bath made of graphite is the anode. The bath is placed in an electric oven. An iron rod moving along the width of the bath, and also having the ability to rise and fall, is the cathode. The electrolyte is molten calcium chloride, which is poured into the bath. The cathode is lowered into the electrolyte. This is how the electrolysis process begins. Molten calcium forms under the cathode. When the cathode rises, calcium solidifies at the point of contact with the cathode. So gradually in the process of raising the cathode, calcium builds up in the form of a rod. Then the calcium rod is beaten off from the cathode.

Pure calcium was first obtained by electrolysis in 1808.

Calcium is also obtained from oxides by aluminothermic reduction. .

4CaO + 2Al -> CaAl 2 O 4 + Ca

In this case, calcium is obtained in the form of steam. This vapor is then condensed.

Calcium has a high chemical activity. That is why it is widely used in industry for the reduction of refractory metals from oxides, as well as in the production of steel and iron.

Introduction

Properties and uses of calcium

1 Physical properties

2 Chemical properties

3 Application

Getting calcium

1 Electrolytic production of calcium and its alloys

2 Thermal preparation

3 Vacuum-thermal method for obtaining calcium

3.1 Aluminothermic method of calcium reduction

3.2 Silicothermic method of calcium reduction

Practical part

Bibliography

Introduction

Chemical element Group II of the periodic system of Mendeleev, atomic number 20, atomic mass 40.08; silver-white light metal. A natural element is a mixture of six stable isotopes: 40Ca, 42Ca, 43Ca, 44Ca, 46Ca and 48Ca, of which 40 is the most common Ca (96.97%).

Ca compounds - limestone, marble, gypsum (as well as lime - a product of burning limestone) have been used in construction since ancient times. Until the end of the 18th century, chemists considered lime to be a simple substance. In 1789, A. Lavoisier suggested that lime, magnesia, barite, alumina and silica are complex substances. In 1808, G. Davy, subjecting a mixture of wet slaked lime with mercury oxide to electrolysis with a mercury cathode, prepared an amalgam of Ca, and after driving mercury out of it, he obtained a metal called "Calcium" (from Latin calx, genus case calcis - lime) .

The ability of calcium to bind oxygen and nitrogen made it possible to use it for cleaning inert gases and as a getter (A getter is a substance that serves to absorb gases and create a deep vacuum in electronic devices.) in vacuum radio equipment.

Calcium is also used in the metallurgy of copper, nickel, special steels and bronzes; they are associated with harmful impurities of sulfur, phosphorus, excess carbon. For the same purposes, calcium alloys with silicon, lithium, sodium, boron, and aluminum are used.

In industry, calcium is obtained in two ways:

) By heating a briquetted mixture of CaO and Al powder at 1200 ° C in a vacuum of 0.01 - 0.02 mm. rt. Art.; released by the reaction:

CaO + 2Al = 3CaO Al2O3 + 3Ca

Calcium vapor condenses on a cold surface.

) By electrolysis of a melt of CaCl2 and KCl with a liquid copper-calcium cathode, an alloy of Cu - Ca (65% Ca) is prepared, from which calcium is distilled off at a temperature of 950 - 1000 ° C in a vacuum of 0.1 - 0.001 mm Hg.

) A method has also been developed for obtaining calcium by thermal dissociation of calcium carbide CaC2.

Calcium is very common in nature in the form of various compounds. In the earth's crust, it occupies the fifth place, accounting for 3.25%, and is most often found in the form of limestone CaCO 3, dolomite CaCO 3MgCO 3, gypsum CaSO 42H 2O, Phosphorite Ca 3(PO 4)2 and fluorspar CaF 2, not counting a significant proportion of calcium in the composition of silicate rocks. Sea water contains an average of 0.04% (wt.) calcium.

In this term paper the properties and application of calcium are studied, as well as the theory and technology of vacuum-thermal methods for its production are also considered in detail.

. Properties and uses of calcium

.1 Physical properties

Calcium is a silvery white metal, but tarnishes in air due to the formation of an oxide on its surface. It is a ductile metal harder than lead. Crystal cell ?-form Ca (stable at ordinary temperature) face-centered cubic, a = 5.56 Å . Atomic radius 1.97 Å , ionic radius Ca 2+, 1,04Å . Density 1.54 g/cm 3(20°C). Above 464 °C stable hexagonal ?-form. mp 851 °C, tbp 1482 °C; temperature coefficient of linear expansion 22 10 -6 (0-300°C); thermal conductivity at 20 °C 125.6 W/(m K) or 0.3 cal/(cm s °C); specific heat capacity (0-100 °C) 623.9 j/(kg K) or 0.149 cal/(g °C); electrical resistivity at 20 °C 4.6 10 -8ohm m or 4.6 10 -6 ohm cm; temperature coefficient of electrical resistance 4.57 10-3 (20 °C). Modulus of elasticity 26 Gn/m 2(2600 kgf/mm 2); tensile strength 60 MN/m 2(6 kgf/mm 2); elastic limit 4 MN/m 2(0.4 kgf/mm 2), yield strength 38 MN/m 2(3.8 kgf/mm 2); elongation 50%; Brinell hardness 200-300 MN/m 2(20-30 kgf/mm 2). Calcium of sufficiently high purity is plastic, well pressed, rolled and can be machined.

1.2 Chemical properties

Calcium is an active metal. So under normal conditions, it easily interacts with atmospheric oxygen and halogens:

Ca + O 2= 2 CaO (calcium oxide) (1)

Ca + Br 2= CaBr 2(calcium bromide). (2)

With hydrogen, nitrogen, sulfur, phosphorus, carbon and other non-metals, calcium reacts when heated:

Ca + H 2= CaH 2(calcium hydride) (3)

Ca + N 2= Ca 3N 2(calcium nitride) (4)

Ca + S = CaS (calcium sulfide) (5)

Ca + 2 P \u003d Ca 3R 2(calcium phosphide) (6)

Ca + 2 C \u003d CaC 2 (calcium carbide) (7)

Calcium interacts slowly with cold water, and very vigorously with hot water, giving a strong base Ca (OH) 2 :

Ca + 2 H 2O \u003d Ca (OH) 2 + H 2 (8)

Being an energetic reducing agent, calcium can take away oxygen or halogens from oxides and halides of less active metals, i.e. it has reducing properties:

Ca + Nb 2O5 = CaO + 2 Nb; (9)

Ca + 2 NbCl 5= 5 CaCl2 + 2 Nb (10)

Calcium reacts vigorously with acids with the release of hydrogen, reacts with halogens, with dry hydrogen to form CaH hydride 2. When calcium is heated with graphite, CaC carbide is formed 2. Calcium is obtained by electrolysis of molten CaCl 2or aluminothermic reduction in vacuum:

6СаО + 2Al = 3Ca + 3CaO Al2 ABOUT 3 (11)

Pure metal is used to reduce Cs, Rb, Cr, V, Zr, Th, U compounds to metals, for steel deoxidation.

1.3 Application

Calcium is increasingly used in various industries. IN Lately he acquired great importance as a reducing agent in the production of a number of metals.

Pure metal. Uranium is obtained by reducing uranium fluoride with calcium metal. Titanium oxides, as well as oxides of zirconium, thorium, tantalum, niobium, and other rare metals can be reduced with calcium or its hydrides.

Calcium is a good deoxidizer and degasser in the production of copper, nickel, chromium-nickel alloys, special steels, nickel and tin bronzes; it removes sulfur, phosphorus, carbon from metals and alloys.

Calcium forms refractory compounds with bismuth, so it is used to purify lead from bismuth.

Calcium is added to various light alloys. It contributes to the improvement of the surface of the ingots, fineness and reduction of oxidizability.

Bearing alloys containing calcium are widely used. Lead alloys (0.04% Ca) can be used to make cable sheaths.

Antifriction alloys of Calcium with lead are used in engineering. Calcium minerals are widely used. So, limestone is used in the production of lime, cement, silicate brick and directly as a building material, in metallurgy (flux), in chemical industry for the production of calcium carbide, soda, caustic soda, bleach, fertilizers, in the production of sugar, glass.

Chalk, marble, Icelandic spar, gypsum, fluorite, etc. are of practical importance. Due to the ability to bind oxygen and nitrogen, calcium or calcium alloys with sodium and other metals are used to purify noble gases and as a getter in vacuum radio equipment. Calcium is also used to produce hydride, which is a source of hydrogen in the field.

2. Getting calcium

There are several ways to obtain calcium, these are electrolytic, thermal, vacuum thermal.

.1 Electrolytic production of calcium and its alloys

The essence of the method lies in the fact that the cathode initially touches the molten electrolyte. At the point of contact, a liquid drop of metal that wets the cathode is formed, which, when the cathode is slowly and evenly raised, is removed from the melt together with it and solidifies. In this case, the solidifying drop is covered with a solid film of electrolyte, which protects the metal from oxidation and nitriding. By continuously and carefully lifting the cathode, the calcium is drawn into the rods.

2.2 Thermal preparation

calcium chemical electrolytic thermal

· Chloride process: the technology consists of melting and dehydrating calcium chloride, melting lead, obtaining a double alloy of lead - sodium, obtaining a ternary alloy of lead - sodium - calcium, and diluting the ternary alloy with lead after removing salts. The reaction with calcium chloride proceeds according to the equation

CaCl 2 + Na 2Pb 5=2NaCl + PbCa + 2Pb (12)

· Carbide process: the basis for obtaining a lead-calcium alloy is the reaction between calcium carbide and molten lead according to the equation

CaC 2+ 3Pb = Pb3 Ca+2C. (13)

2.3 Vacuum-thermal method for obtaining calcium

Raw material for vacuum thermal process

The raw material for the thermal reduction of calcium oxide is lime obtained by roasting limestone. The main requirements for raw materials are as follows: lime must be as pure as possible and contain a minimum of impurities capable of being reduced and converted into metal along with calcium, especially alkali metals and magnesium. Calcination of limestone should be carried out until the carbonate is completely decomposed, but not before it is sintered, since the reducibility of the sintered material is lower. The fired product must be protected from absorption of moisture and carbon dioxide, the release of which during recovery reduces the performance of the process. The technology of burning limestone and processing the burnt product is similar to the processing of dolomite for the silicothermic method of obtaining magnesium.

.3.1 Aluminothermic method of calcium reduction

The diagram of the temperature dependence of the change in the free energy of oxidation of a number of metals (Fig. 1) shows that calcium oxide is one of the most durable and difficult to reduce oxides. It cannot be reduced by other metals in the usual way - at a relatively low temperature and atmospheric pressure. On the contrary, calcium itself is an excellent reducing agent for other difficult-to-reduce compounds and a deoxidizing agent for many metals and alloys. The reduction of calcium oxide with carbon is generally impossible due to the formation of calcium carbides. However, due to the fact that calcium has a relatively high vapor pressure, its oxide can be reduced in vacuum with aluminum, silicon, or their alloys according to the reaction

CaO + Me? Ca + MeO (14).

Practical use So far, he has found only an aluminothermic method for obtaining calcium, since it is much easier to reduce CaO with aluminum than with silicon. There are different views on the chemistry of the reduction of calcium oxide with aluminum. L. Pidgeon and I. Atkinson believe that the reaction proceeds with the formation of calcium monoaluminate:

CaO + 2Al = CaO Al 2O3 + 3Ca. (15)

V. A. Pazukhin and A. Ya. Fisher indicate that the process proceeds with the formation of tricalcium aluminate:

CaO + 2Al = 3CaO Al 2O 3+ 3Ca. (16)

According to A. I. Voynitsky, the formation of pentacicium trialuminate is predominant in the reaction:

CaO + 6Al = 5CaO 3Al 2O3 + 9Ca. (17)

Latest research, A. Yu. Taits and AI Voynitsky found that the aluminothermic reduction of calcium proceeds stepwise. Initially, the release of calcium is accompanied by the formation of 3CaO AI 2O 3, which then reacts with calcium oxide and aluminum to form 3CaO 3AI 2O 3. The reaction proceeds according to the following scheme:

CaO + 6Al = 2 (3CaO Al 2O 3)+ 2CaO + 2Al + 6Ca

(3CaO Al 2O 3) + 2CaO + 2Al = 5CaO 3Al 2O 3+ 3Са

CaO + 6A1 \u003d 5CaO 3Al 2O 3+ 9Ca

Since oxide reduction occurs with the release of vaporous calcium, and the remaining reaction products are in a condensed state, it is possible to easily separate and condense it in the cooled sections of the furnace. The main conditions necessary for the vacuum-thermal reduction of calcium oxide are high temperature and low residual pressure in the system. The relationship between temperature and the equilibrium vapor pressure of calcium is given below. The free energy of reaction (17), calculated for temperatures 1124-1728°K, is expressed as

F T \u003d 184820 + 6.95T-12.1 T lg T.

Hence the logarithmic dependence of the equilibrium elasticity of calcium vapor (mm Hg)

Lg p \u003d 3.59 - 4430 \ T.

L. Pidgeon and I. Atkinson determined experimentally the equilibrium vapor pressure of calcium. A detailed thermodynamic analysis of the reduction reaction of calcium oxide with aluminum was carried out by I. I. Matveenko, who gave the following temperature dependences of the equilibrium pressure of calcium vapor:

lgp Ca(1) \u003d 8.64 - 12930\T mm Hg

lgp Ca(2) \u003d 8.62 - 11780\T mm Hg

lgp Ca(3 )\u003d 8.75 - 12500\T mm Hg.

The calculated and experimental data are compared in Table. 1.

Table 1 - The effect of temperature on the change in the equilibrium elasticity of calcium vapor in systems (1), (2), (3), (3), mm Hg.

Temperature °С Experimental data Calculated in systems(1)(2)(3)(3 )1401 1451 1500 1600 17000,791 1016 - - -0,37 0,55 1,2 3,9 11,01,7 3,2 5,6 18,2 492,7 3,5 4,4 6,6 9,50,66 1,4 2,5 8,5 25,7

It can be seen from the data presented that interactions in systems (2) and (3) or (3") are under the most favorable conditions. This is consistent with observations, since pentascalcium trialuminate and tricalcium aluminate predominate in the residues of the charge after the reduction of calcium oxide with aluminum.

Equilibrium elasticity data show that the reduction of calcium oxide with aluminum is possible at a temperature of 1100-1150 ° C. To achieve a practically acceptable reaction rate, the residual pressure in the Rost system must be below the equilibrium P equals , i.e., the inequality Р equals >P ost , and the process must be carried out at temperatures of the order of 1200°. Studies have established that at a temperature of 1200-1250 ° high utilization (up to 70-75%) and low specific consumption of aluminum (about 0.6-0.65 kg per kg of calcium) is achieved.

According to the above interpretation of the chemistry of the process, the optimal composition is the mixture designed for the formation of 5CaO 3Al in the residue 2O 3. To increase the degree of use of aluminum, it is useful to give some excess of calcium oxide, but not too much (10-20%), otherwise this will adversely affect other process indicators. With an increase in the degree of aluminum grinding from particles of 0.8-0.2 mm to minus 0.07 mm (according to V. A. Pazukhin and A. Ya. Fisher), the use of aluminum in the reaction increases from 63.7 to 78%.

The use of aluminum is also affected by the mode of charge briquetting. A mixture of lime and aluminum powder should be briquetted without binders (to avoid outgassing in a vacuum) at a pressure of 150 kg/cm 2. At lower pressures, the use of aluminum decreases due to segregation of molten aluminum in overly porous briquettes, and at higher pressures, due to poor gas permeability. The completeness and speed of recovery also depend on the packing density of the briquettes in the retort. When laying them without gaps, when the gas permeability of the entire charge is low, the use of aluminum is significantly reduced.

Figure 2 - Scheme for obtaining calcium by vacuum-thermal method.

Technology of alumino-thermal way

The technological scheme for the production of calcium by the aluminothermic method is shown in fig. 2. Limestone is used as a raw material, and aluminum powder prepared from primary (better) or secondary aluminum is used as a reducing agent. Aluminum used as a reducing agent, as well as raw materials, should not contain impurities of easily volatile metals: magnesium, zinc, alkalis, etc., capable of evaporating and turning into condensate. This must be taken into account when choosing grades of recycled aluminum.

According to the description of S. Loomis and P. Staub, in the USA, at the New England Lime Co. plant in Canaan (Connecticut), calcium is obtained by the aluminothermic method. Lime of the following typical composition is used, %: 97.5 CaO, 0.65 MgO, 0.7 SiO 2, 0.6 Fe 2Oz + AlOz, 0.09 Na 2O+K 2Oh, 0.5 the rest. The calcined product is ground in a Raymond mill with a centrifugal separator, the fineness of grinding is (60%) minus 200 mesh. As a reducing agent, aluminum dust is used, which is a waste in the production of aluminum powder. Burnt lime from closed hoppers and aluminum from drums are fed to the dosing scales and then to the mixer. After mixing, the mixture is briquetted in a dry way. At the mentioned plant, calcium is reduced in retort furnaces, which were previously used to obtain magnesium by the silicothermic method (Fig. 3). Furnaces are heated with generator gas. Each furnace has 20 horizontal retorts made of refractory steel containing 28% Cr and 15% Ni.

Figure 3 - Retort furnace for calcium production

Retort length 3 m, diameter 254 mm, wall thickness 28 mm. Reduction occurs in the heated part of the retort, and condensation occurs in the cooled end protruding from the speech. The briquettes are introduced into the retort in paper bags, then the condensers are inserted and the retort is closed. Air is pumped out by mechanical vacuum pumps at the beginning of the cycle. Then the diffusion pumps are connected and the residual pressure is reduced to 20 microns.

The retorts are heated up to 1200°. After 12 hours. after loading, the retorts are opened and unloaded. The resulting calcium has the form of a hollow cylinder of a dense mass of large crystals deposited on the surface of a steel sleeve. The main impurity in calcium is magnesium, which is reduced in the first place and is mainly concentrated in the layer adjacent to the sleeve. The average content of impurities is; 0.5-1% Mg, about 0.2% Al, 0.005-0.02% Mn, up to 0.02% N, other impurities - Cu, Pb, Zn, Ni, Si, Fe - are found in the range of 0.005-0.04%. A. Yu. Taits and A. I. Voinitsky used a semi-factory electric vacuum furnace with coal heaters to obtain calcium by the aluminothermic method and achieved a degree of aluminum utilization of 60%, a specific aluminum consumption of 0.78 kg, a specific charge consumption of 4.35 kg, respectively, and a specific electricity consumption 14 kWh per 1 kg of metal.

The resulting metal, with the exception of magnesium impurity, was distinguished by a relatively high purity. On average, the content of impurities in it was: 0.003-0.004% Fe, 0.005-0.008% Si, 0.04-0.15% Mn, 0.0025-0.004% Cu, 0.006-0.009% N, 0.25% Al.

2.3.2 Silicothermic reduction method calcium

The silicothermic method is very tempting; the reducing agent is ferrosilicon, the reagent is much cheaper than aluminum. However, the silicothermic process is more difficult to implement than the aluminothermic one. The reduction of calcium oxide by silicon proceeds according to the equation

CaO + Si = 2CaO SiO2 + 2Ca. (18)

The equilibrium elasticity of calcium vapor, calculated from the values ​​of free energy, is:

°С1300140015001600Р, mm Hg st0.080.150.752.05

Therefore, in a vacuum of the order of 0.01 mm Hg. Art. reduction of calcium oxide is thermodynamically possible at a temperature of 1300°. In practice, to ensure an acceptable speed, the process should be carried out at a temperature of 1400-1500°.

The reduction reaction of calcium oxide with silicoaluminum proceeds somewhat easier, in which both aluminum and silicon of the alloy serve as reducing agents. It has been established experimentally that reduction with aluminum predominates at the beginning; moreover, the reaction proceeds with the final formation of bCaO 3Al 2Oz according to the scheme outlined above (Fig. 1). Silicon reduction becomes significant at higher temperatures when most of the aluminum has reacted; the reaction proceeds with the formation of 2CaO SiO 2. In summary form, the reduction reaction of calcium oxide with silicoaluminum is expressed by the following equation:

mSi + n Al + (4m +2 ?) CaO \u003d m (2CaO SiO 2) + ?n(5CaO Al 2O3 ) + (2m +1, 5n) Ca.

Research by A. Yu. Taits and A. I. Voinitsky found that calcium oxide is reduced by 75% ferrosilicon with a metal yield of 50-75% at a temperature of 1400-1450 ° in a vacuum of 0.01-0.03 mm Hg. Art.; silicoaluminum containing 60-30% Si and 32-58% Al (the rest is iron, titanium, etc.) reduces calcium oxide with a metal yield of approximately 70% at temperatures of 1350-1400 ° in a vacuum of 0.01-0.05 mm Hg . Art. Experiments on a semi-factory scale proved the fundamental possibility of obtaining calcium on lime with ferrosilicon and silicoaluminum. The main hardware difficulty is the selection of a lining that is resistant to this process.

When solving this problem, the method can be implemented in industry. Decomposition of calcium carbide Production of metallic calcium by decomposition of calcium carbide

CaC2 = Ca + 2C

should be regarded as promising. In this case, graphite is obtained as the second product. W. Mauderly, E. Moser, and W. Treadwell, having calculated the free energy of formation of calcium carbide from thermochemical data, obtained the following expression for the vapor pressure of calcium over pure calcium carbide:

ca \u003d 1.35 - 4505 \ T (1124 - 1712 ° K),

lgp ca \u003d 6.62 - 13523 \ T (1712-2000 ° K).

Apparently, commercial calcium carbide decomposes at much higher temperatures than follows from these expressions. The same authors report thermal decomposition of calcium carbide in compact pieces at 1600-1800° in a vacuum of 1 mm Hg. Art. The yield of graphite was 94%, calcium was obtained in the form of a dense coating on the refrigerator. A. S. Mikulinsky, F. S. Morii, R. Sh. Shklyar to determine the properties of graphite obtained by the decomposition of calcium carbide, the latter was heated in a vacuum of 0.3-1 mm Hg. Art. at a temperature of 1630-1750°. The resulting graphite differs from Acheson's in larger grains, higher electrical conductivity, and lower bulk density.

3. Practical part

The daily outflow of magnesium from the electrolyzer for a current of 100 kA was 960 kg when the bath was fed with magnesium chloride. The voltage on the cell jester is 0.6 V. Determine:

)Current output at the cathode;

)The amount of chlorine obtained per day, provided that the current output at the anode is equal to the current output at the kode;

)Daily filling MgCl 2into the electrolyzer, provided that the loss of MgCl 2 occur mainly with sludge and sublimation. Amount of sludge 0.1 per 1 ton of Mg containing MgCl 2 in sublimation 50%. The amount of sublimation is 0.05 t per 1 t of Mg. The composition of the poured magnesium chloride, %: 92 MgCl2 and 8 NaCl.

.Determine the current output at the cathode:

m etc =I ?k mg · ?

?=m etc \I ?k mg \u003d 960000\100000 0.454 24 \u003d 0.881 or 88.1%

.Determine the amount of Cl received per day:

x \u003d 960000g \ 24 g \ mol \u003d 40000 mol

Converting to volume:

х=126785.7 m3

3.a) We find pure MgCl 2, for the production of 960 kg Mg.

x \u003d 95 960 \ 24.3 \u003d 3753 kg \u003d 37.53 tons.

b) losses with sludge. From the composition of magnesium electrolyzers, %: 20-35 MgO, 2-5 Mg, 2-6 Fe, 2-4 SiO 2, 0.8-2 TiO 2, 0.4-1.0 C, 35 MgCl2 .

kg - 1000 kg

m shl \u003d 960 kg - mass of sludge per day.

Per day 96 kg of sludge: 96 0.35 (MgCl2 with sludge).

c) losses with sublimates:

kg - 1000 kg

kg sublimates: 48 0.5 = 24 kg MgCl 2 with sublimates.

All you need to fill in Mg:

33.6+24=3810.6 kg MgCl2 per day

Bibliography

Fundamentals of Metallurgy III

<#"justify">metallurgy of Al and Mg. Vetyukov M.M., Tsyplokov A.M.

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Among all the elements of the periodic system, several can be distinguished, without which it is not only possible to develop various diseases in living organisms, but it is generally impossible to live and grow normally. One of these is calcium.

Interestingly, when it comes to this metal, as a simple substance, it does not have any benefit for a person, even harm. However, one has only to mention the Ca 2+ ions, as immediately there is a mass of points characterizing their importance.

Position of calcium in the periodic table

The characterization of calcium, like any other element, begins with an indication of its position in the periodic system. After all, it makes it possible to learn a lot about this atom:

• nuclear charge;
• the number of electrons and protons, neutrons;
• oxidation state, higher and lower;
• electronic configuration and other important things.

The element we are considering is located in the fourth large period of the second group, main subgroup and has serial number 20. Also chemical table Mendeleev shows the atomic weight of calcium - 40.08, which is the average value of the existing isotopes of this atom.

The oxidation state is one, always constant, equal to +2. CaO formula. The Latin name for the element is calcium, hence the symbol for the atom Ca.

Characterization of calcium as a simple substance

Under normal conditions, this element is a metal, silvery-white in color. Calcium formula as a simple substance- Sa. Due to its high chemical activity, it is able to form many compounds belonging to different classes.

in solid state of aggregation is not part of the human body, therefore it is important for industrial and technical needs (mainly chemical syntheses).

It is one of the most common metals in terms of its share in the earth's crust, about 1.5%. It belongs to the group of alkaline earths, since when dissolved in water it gives alkalis, but in nature it occurs in the form of multiple minerals and salts. A lot of calcium (400 mg/l) is included in sea water.

Crystal cell

The characteristic of calcium is explained by the structure of the crystal lattice, which can be of two types (since there is an alpha and a beta form):

• cubic face-centric;
• volume-centric.

The type of bond in the molecule is metallic, at the lattice sites, like all metals, there are atom-ions.

Being in nature

There are several basic substances in nature that contain this element.

1. Sea water.
2. Rocks and minerals.
3. Living organisms (shells and shells, bone tissues and so on).
4. Groundwater in the earth's crust.

The following types of rocks and minerals can be identified, which are natural springs calcium.

1. Dolomite is a mixture of calcium and magnesium carbonate.
2. Fluorite is calcium fluoride.
3. Gypsum - CaSO 4 2H 2 O.
4. Calcite - chalk, limestone, marble - calcium carbonate.
5. Alabaster - CaSO 4 0.5H 2 O.
6. Apatity.

In total, about 350 different minerals and rocks that contain calcium are isolated.

How to get

For a long time, it was not possible to isolate the metal in a free form, since its chemical activity is high, you will not find it in nature in its pure form. Therefore, until the 19th century (1808), the element in question was another mystery that the periodic table carried.

Calcium as a metal was able to synthesize the English chemist Humphrey Davy. It was he who first discovered the features of the interaction of melts of solid minerals and salts with electric shock. To date, still the most relevant way to obtain this metal is the electrolysis of its salts, such as:

• a mixture of calcium and potassium chlorides;
• a mixture of fluoride and calcium chloride.

It is also possible to extract calcium from its oxide using the aluminothermic method common in metallurgy.

Physical properties

The characterization of calcium in terms of physical parameters can be described in several points.

1. Aggregate state - under normal conditions, solid.
2. Melting point - 842 0 С.
3. The metal is soft and can be cut with a knife.
4. Color - silvery-white, brilliant.
5. It has good conductive and heat-conducting properties.
6. With prolonged heating, it passes into a liquid, then a vapor state, losing its metallic properties. Boiling point 1484 0 С.

The physical properties of calcium have one feature. When pressure is applied to a metal, at some point in time it loses its metallic properties and ability to conduct electricity. However, with a further increase in exposure, it is restored again and manifests itself as a superconductor, several times higher than the rest of the elements in terms of these indicators.

Chemical properties

The activity of this metal is very high. Therefore, there are many interactions in which calcium enters. Reactions with all non-metals are common for him, because as a reducing agent he is very strong.

1. At normal conditions easily reacts with the formation of the corresponding binary compounds with: halogens, oxygen.
2. When heated: hydrogen, nitrogen, carbon, silicon, phosphorus, boron, sulfur and others.
3. In the open air, it immediately interacts with carbon dioxide and oxygen, therefore it becomes covered with a gray coating.
4. Reacts violently with acids, sometimes with ignition.

Interesting properties of calcium are manifested when it comes to it in the composition of salts. So, beautiful caves growing on the ceiling and walls are nothing more than formed over time from water, carbon dioxide and bicarbonate under the influence of processes inside groundwater.

Considering how active the metal is in its normal state, it is stored in laboratories, like alkaline ones. In a dark glass container, with a tightly closed lid and under a layer of kerosene or paraffin.

A qualitative reaction to the calcium ion is the color of the flame in a beautiful, saturated brick-red color. It is also possible to identify a metal in the composition of compounds by insoluble precipitates of some of its salts (calcium carbonate, fluoride, sulfate, phosphate, silicate, sulfite).

metal connections

The types of metal compounds are as follows:

• oxide;
• hydroxide;
• calcium salts (medium, acidic, basic, double, complex).

Calcium oxide known as CaO is used to create a building material (lime). If you extinguish the oxide with water, you get the corresponding hydroxide, which exhibits the properties of an alkali.

big practical value have exactly different calcium salts, which are used in different sectors of the economy. What kind of salts exist, we have already mentioned above. Let us give examples of the types of these compounds.

1. Medium salts - CaCO 3 carbonate, Ca 3 phosphate (PO 4) 2 and others.
2. Acidic - hydrosulfate CaHSO 4.
3. The main ones are bicarbonate (CaOH) 3 PO 4.
4. Complex - Cl 2.
5. Double - 5Ca (NO 3) 2 * NH 4 NO 3 * 10H 2 O.

It is in the form of compounds of this class that calcium is important for biological systems, since salts are the source of ions for the body.

Biological role

Why is calcium important for the human body? There are several reasons.

1. It is the ions of this element that are part of the intercellular substance and tissue fluid, participating in the regulation of the mechanisms of excitation, the production of hormones and neurotransmitters.
2. Calcium accumulates in the bones, tooth enamel in an amount of about 2.5% of the total body weight. This is quite a lot and plays an important role in strengthening these structures, maintaining their strength and stability. The growth of the body without it is impossible.
3. Blood clotting also depends on the ions in question.
4. It is part of the heart muscle, participating in its excitation and contraction.
5. It is a participant in the processes of exocytosis and other intracellular changes.

If the amount of calcium consumed is not enough, then the development of diseases such as:

• rickets;
• osteoporosis;
• blood diseases.

The daily norm for an adult is 1000 mg, and for children from 9 years old 1300 mg. In order to prevent an overabundance of this element in the body, the indicated dose should not be exceeded. Otherwise, intestinal diseases may develop.

For all other living beings, calcium is no less important. For example, although many do not have a skeleton, the external means of strengthening them are also formations of this metal. Among them:

• shellfish;
• mussels and oysters;
• sponges;
• coral polyps.

All of them carry on their backs or, in principle, form in the process of life some kind of external skeleton that protects them from external influences and predators. Its main constituent is calcium salts.

Vertebrate animals, like humans, need these ions for normal growth and development and receive them with food.

There are many options with which it is possible to make up for the missing norm of the element in the body. Best of all, of course, natural methods - products containing the desired atom. However, if for some reason this is insufficient or impossible, the medical path is also acceptable.

So, the list of foods containing calcium is something like this:

• dairy and sour-milk products;
• fish;
• greenery;
• cereals (buckwheat, rice, whole grain flour pastries);
• some citrus fruits (oranges, tangerines);
• legumes;
• all nuts (especially almonds and walnuts).

If you are allergic to some products or you can’t use them for another reason, then calcium-containing preparations will help to replenish the level of the desired element in the body.

All of them are salts of this metal, which have the ability to be easily absorbed by the body, quickly absorbed into the blood and intestines. Among them, the most popular and used are the following.

1. Calcium chloride - solution for injection or for oral administration to adults and children. It differs in the concentration of salt in the composition, it is used for "hot injections", because it causes just such a sensation when injected. There are forms with fruit juice to facilitate ingestion.
2. Available as tablets (0.25 or 0.5 g) and solutions for intravenous injection. Often in the form of tablets contains various fruit additives.
3. Calcium lactate - available in tablets of 0.5 g.

Compounds of calcium.

Cao- calcium oxide or quicklime, it is obtained by decomposition of limestone: CaCO 3 \u003d CaO + CO 2 is an oxide of an alkaline earth metal, therefore it actively interacts with water: CaO + H 2 O \u003d Ca (OH) 2

Ca(OH) 2 - calcium hydroxide or slaked lime, so the reaction CaO + H 2 O \u003d Ca (OH) 2 is called lime slaking. If the solution is filtered, lime water is obtained - this is an alkali solution, so it changes the color of phenolphthalein to crimson.

Hydrated lime is widely used in construction. Its mixture with sand and water is a good binding material. Under the action of carbon dioxide, the mixture hardens Ca (OH) 2 + CO 2 \u003d CaCO3 + H 2 O.

At the same time, part of the sand and the mixture turns into silicate Ca (OH) 2 + SiO 2 \u003d CaSiO 3 + H 2 O.

The equations Ca (OH) 2 + CO 2 \u003d CaCO 2 + H 2 O and CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2 play an important role in nature and in shaping the appearance of our planet. Carbon dioxide in the form of a sculptor and architect creates underground palaces in the strata of carbonate rocks. It is capable of moving hundreds and thousands of tons of limestone underground. Along cracks in rocks, water containing dissolved in it carbon dioxide, falls into the thickness of limestone, forming cavities - castra caves. Calcium bicarbonate exists only in solution. Groundwater moves in the earth's crust, evaporating water under suitable conditions: Ca (HCO3) 2 \u003d CaCO3 + H 2 O + CO 2 , this is how stalactites and stalagmites are formed, the formation scheme of which was proposed by the famous geochemist A.E. Fersman. There are a lot of castra caves in the Crimea. Science studies them speleology.

Used in construction calcium carbonate CaCO3- this is chalk, limestone, marble. All of you have seen our railway station: it is finished with white marble brought from abroad.

experience: blow through a tube into a solution of lime water, it becomes cloudy .

Ca(OH) 2 + CO 2 = CaCO 3 + H 2 ABOUT

Adds acetic acid to the formed precipitate, effervescence is observed. carbon dioxide is released.

CaCO 3 +2CH 3 COOH \u003d Ca (CH 3 SOO) 2 +H 2 O + CO 2

THE TALE ABOUT THE CARBONATE BROTHERS.

Three brothers live on earth
From the Carbonate family.
The older brother is a handsome MARBLE,
Glorious in the name of Karara,
Excellent architect. He
He built Rome and the Parthenon.
Everyone knows LIMESTONE,
That's why it's named like that.
Famous for his work
Building a house behind the house.
Both able and able
The younger soft brother MEL.
How to draw, look
This CaCO 3!
Brothers love to frolic
Burn in a hot oven
CaO and CO 2 are then formed.
It's carbon dioxide
Each of you is familiar with him,
We breathe it out.
Well, this is Sao -
Hot burnt quicklime.
Add water to it
Thoroughly mixing
To avoid trouble
We protect our hands
Cool mixed LIME, but SLAKED!
milk of lime
The walls are whitewashed easily.
The bright house cheered up
Turning lime into chalk.
Hocus pocus for the people:
One has only to blow through the water,
How easy it is
Turned into milk!
Now it's pretty smart.
I get soda
Milk plus vinegar. Ay!
Foam is pouring over the edge!
All in worries, all in work
From dawn to dawn -
These brothers the Carbonates,
These CaCO 3!

Repetition: CaO– calcium oxide, quicklime;
Ca(OH) 2 - calcium hydroxide (slaked lime, lime water, milk of lime, depending on the concentration of the solution).
General - the same chemical formula Ca (OH) 2. Difference: lime water is a transparent saturated solution of Ca (OH) 2, and milk of lime is a white suspension of Ca (OH) 2 in water.
CaCl 2 - calcium chloride, calcium chloride;
CaCO 3 - calcium carbonate, chalk, shell rock marble, limestone.
L/R: collections. Next, we demonstrate the collection of minerals available in the school laboratory: limestone, chalk, marble, shell rock.
CaS0 4 ∙ 2H 2 0 - hydrated calcium sulfate, gypsum;
CaCO 3 - calcite, calcium carbonate is part of many minerals that cover 30 million km 2 on earth.

The most important of these minerals is limestone. Shell rocks, limestones of organic origin. It goes to the production of cement, calcium carbide, soda, all kinds of lime, in metallurgy. Limestone is the backbone of the construction industry and many building materials are made from it.

Chalk it's not just tooth powder and school chalk. It is also a valuable additive in the production of paper (coated - highest quality) and rubber; in the construction and repair of buildings - as a whitewash.

Marble is a dense crystalline rock. There is color - white, but most often various impurities color it in different colors. Pure white marble is rare and is mainly used by sculptors (statues of Michelangelo, Rodin. In construction, colored marble is used as a facing material (Moscow metro) or even as the main building material of palaces (Taj Mahal).

In the world of interesting "MAUSOLEUM" Taj Mahal ""

Shah Jahan from the Mughal dynasty held in fear and obedience almost all of Asia. In 1629, Mumzat Mahal, Shah Jahan's beloved wife, died at the age of 39 during childbirth on a campaign (it was their 14th child, all of them boys). She was unusually beautiful, bright, intelligent, the emperor obeyed her in everything. Before her death, she asked her husband to build a tomb, take care of the children, and not marry. The saddened king sent his messengers to all big cities, the capitals of neighboring states - to Bukhara, Samarkand, Baghdad, Damascus, in order to find and invite the best craftsmen - in memory of his wife, the king decided to erect the best building in the world. At the same time, messengers sent to Agra (India) plans for all the best buildings in Asia and the best building materials. They even brought malachite from Russia and the Urals. The chief masons came from Delhi and Kandahar; architects - from Istanbul, Samarkand; decorators - from Bukhara; gardeners from Bengal; the artists are from Damascus and Baghdad, and the well-known master Ustad-Isa was in charge.

Together, over 25 years, a melomarble structure was built, surrounded by green gardens, blue fountains and a red sandstone mosque. 20,000 slaves erected this miracle of 75 m (with a 25-storey building). Nearby, he wanted to build a second mausoleum of black marble for himself, but did not have time. He was overthrown from the throne by his own son (2nd, and he also killed all his brothers).

The ruler and ruler of Agra spent the last years of his life looking out of the narrow window of his dungeon. 7 years so the father admired his creation. When his father went blind, his son made him a system of mirrors so that his father could admire the mausoleum. He was buried in the Taj Mahal, next to his Mumtaz.

Those entering the mausoleum see cenotaphs - false tombs. The places of eternal rest of the great khan and his wife are located below, in the basement. Everything there is encrusted with precious stones that glow as if alive, and the branches of fabulous trees, intertwined with flowers, adorn the walls of the tomb with intricate patterns. Turquoise-blue lapis lazuli, green-black nephrites and red amethysts processed by the best carvers sing the love of Shah Jahal and Mumzat Mahal.

Every day tourists rush to Agra who want to see the true wonder of the world - the mausoleum of the Taj Mahal, as if hovering above the ground.

CaCO 3 - this is the building material of the external skeleton of mollusks, corals, shells, etc., egg shells. (illustrations or Animals of the coral biocenosis” and display of a collection of sea corals, sponges, shell rock).