Natural lead compounds. Lead and its properties

DEFINITION

Lead- eighty-second element periodic table. Designation - Pb from the Latin "plumbum". Located in the sixth period, IVA group. Refers to metals. The core charge is 82.

Lead - bluish white heavy metal(Fig. 1). When cut, the lead surface shines. In air it becomes covered with a film of oxides and because of this it becomes dull. It is very soft and can be cut with a knife. Has low thermal conductivity. Density 11.34 g/cm3. Melting point 327.46 o C, boiling point 1749 o C.

Rice. 1. Lead. Appearance.

Atomic and molecular mass of lead

Relative molecular weight of the substance(M r) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and relative atomic mass element(A r) - how many times the average mass of atoms of a chemical element is greater than 1/12 of the mass of a carbon atom.

Since in the free state lead exists in the form of monatomic Pb molecules, the values ​​of its atomic and molecular masses coincide. They are equal to 207.2.

Isotopes of lead

It is known that in nature lead can be found in the form of four stable isotopes 204 Pb, 206 Pb, 207 Pb and 208 Pb. Their mass numbers are 204, 206, 207 and 208, respectively. The nucleus of an atom of the lead isotope 204 Pb contains eighty-two protons and one hundred and twenty-two neutrons, and the rest differ from it only in the number of neutrons.

There are artificial unstable isotopes of lead with mass numbers from 178 to 215, as well as more than ten isomeric states of nuclei, among which the longest-lived isotopes 202 Pb and 205 Pb, the half-lives of which are 52.5 thousand and 15.3 million years, respectively.

Lead ions

The outer energy level of the lead atom has four electrons, which are valence electrons:

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 6s 2 6p 2 .

As a result of chemical interaction, lead gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion:

Pb 0 -2e → Pb 2+ ;

Pb 0 -4e → Pb 4+ .

Lead molecule and atom

In the free state, lead exists in the form of monoatomic Pb molecules. Here are some properties characterizing the lead atom and molecule:

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

(nm, coordination numbers are given in parentheses) Pb 4+ 0.079 (4), 0.092 (6), Pb 2+ 0.112 (4), 0.133 (6).

The lead content in the earth's crust is 1.6-10 3% by mass, in the World Ocean 0.03 µg/l (41.1 million tons), in rivers 0.2-8.7 µg/l. Known approx. 80 containing lead, the most important of them is galena, or lead luster, PbS. Small industrial Anglesite PbSO 4 and cerus-site PbCO 3 are important. Lead is accompanied by Cu, Zn; Cd, Bi, Te and other valuable elements. Nature background of 2·10 -9 -5·10 -4 μg/m 3 . The body of an adult contains 7-15 mg of lead.

Properties. Lead metal is bluish-gray in color and crystallizes into facets. cubic Cu type lattice, a - = 0.49389 nm, z = 4, space. Fm3m group. Lead is one of the fusible, heavy; m.p. 327.50 °C, bp. 1751 °C; density, g/cm 3: 11.3415 (20 °C), 10.686 (327.6 °C), 10.536 (450 °C), 10.302 (650 °C), 10.078 (850 °C);26.65 J/( K); 4.81 kJ/,177.7 kJ/;64.80 JDmol K); , Pa: 4.3·10 -7 (600 K), 9.6·10 -5 (700 K), 5.4·10 -2 (800 K). 1.2·10 -1 (900 K), 59.5 (1200 K), 8.2·10 2 (1500 K), 12.8·10 3 (1800 K). Lead is a poor conductor of heat and electricity; 33.5 W/(m K) (less than 10% of Ag); temperature coefficient linear expansion of lead (purity 99.997%) in the temperature range 0-320 °C is described by the equation: a = 28.15·10 -6 t + 23.6·10 -9 t 2 °C -1 ; at 20°C r 20.648 μOhm cm (less than 10% of r Ag), at 300 °C and 460 °C, respectively. 47.938 and 104.878 μΩ cm. At -258.7°C r of lead drops to 13.11·10 -3 μΩ·cm; at 7.2 K it goes into the superconducting state. Lead is diamagnetic, mag. susceptibility -0.12·10 -6. IN liquid state lead is fluid, h in the temperature range 330-800 °C varies within 3.2-1.2 mPa s; g in the range of 330-1000 °C is in the range of (4.44-4.01)·10 -3 N/m.

WITH wine is soft, flexible, and easily rolled into thin sheets. according to Brinell 25-40 MPa; s rise 12-13 MPa, s compress approx. 50 MPa; relates elongation at break 50-70%. Significantly increase lead Na, Ca and Mg, but reduce its chemical. durability. increases the anti-corrosion resistance of lead (to the action of H 2 SO 4). With Sb, the acid resistance of lead to H 2 SO 4 also increases. Bi and Zn reduce the acid resistance of lead, and Cd, Te and Sn also increase the fatigue resistance of lead. There is practically no solution in lead. N 2, CO, CO 2, O 2, SO 2, H 2.

In chem. Lead is quite inert. Standard lead -0.1265 V for Pb 0 /Pb 2+ . When dry, it does not oxidize; when wet, it fades, becoming covered with a film that turns into presence. CO 2 in the main 2PbCO 3 ·Pb(OH) 2. C lead forms the series: Pb 2 O, PbO (), PbO 2, Pb 3 O 4 () and Pb 2 O 3 (see). At room temperature, lead does not react with dilute. sulfuric and hydrochloric acids, since the sparingly soluble films of PbSO 4 and PbC1 2 formed on its surface prevent further. Conc. H 2 SO 4 (>80%) and HC1 at heating. interaction with lead to form r-rim compounds. Pb(HSO 4) 2 and H 4 [PbCl 6]. Lead is resistant to hydrofluoric acid, aqueous solutions NH 3 and many others. org. to-there. The best lead diluents. HNO 3 and CH 3 COOH. In this case, Pb(NO 3) 2 and Pb(CH 3 COO) 2 are formed. Lead is noticeably dissolved. also in lemon, formic and wine juices.

Pb + PbO 2 + 2H 2 SO 4 : 2PbSO 4 + 2H 2 O

When interacting Pb(IV) and Pb(II) salts are formed, respectively. plumbates(IV) and plumbites(II),eg Na 2 PbO 3, Na 2 PbO 2. Lead dissolves slowly. in conc. solution with the release of H 2 and the formation of M 4 [Pb(OH) 6 ].

When heated, lead reacts with, forming. With hydronitrous acid, lead gives Pb(N 3) 2, with heating - PbS (see Lead chalcogenides). not typical for lead. In some areas, PbH 4 -colorless tetrahydride is found. , easily decomposes into Pb and H 2; formed by the action of dil. hydrochloric acid for Mg 2 Pb. See also, Organolead compounds.

Receipt. Basic The source of lead is polymetallic sulfide. . Lead and other concentrates are produced selectively from those containing 1-5% Pb. Lead concentrate usually contains 40-75% Pb, 5-10% Zn, up to 5% Cu, as well as Bi. OK. 90% of lead is obtained using a technology that includes the following stages: agglomerating sulfide concentrates, mine reduction. melting of sinter and rough lead. Autogenous smelting processes are being developed to utilize combustion heat.

Agglomerating with traditional Lead production is carried out on straight-line machines with blowing or by sucking it out. In this case, PbS is oxidized primarily. in liquid state: 2PbS + 3O 2: 2PbO + 2SO 2. Fluxes (SiO 2, CaCO 3, Fe 2 O 3) are added to the charge, which, reacting with each other and with PbO, form a liquid phase that cements the charge. In the finished agglomerate, lead is mainly concentrated in lead silicate glass, occupying up to 60% of the volume of the agglomerate. Zn, Fe, Si, Ca crystallize in the form of complex compounds, forming a heat-resistant frame. Effective (working) area of ​​agglomeration. cars 6-95 m 2.

The finished agglomerate contains 35-45% Pb and 1.2-3% S, part of the cut is in the form. Sinter productivity sintering machines depend on the S content in the charge and range from 10 (poor concentrates) to 20 t/(m 2 · day) (rich concentrates); in terms of burned S, it is in the range of 0.7-1.3 t/(m 2 · day). Part containing 4-6% SO 2 is used for the production of H 2 SO 4. The utilization rate of S is 40-50%.

The resulting agglomerate is sent for reduction. smelting in mines. for lead smelting it is a rectangular shaft formed by water-cooled boxes (caissons). (or air-oxygen mixture) is supplied through a special nozzles (tuyeres) located around the entire perimeter in the bottom. a series of caissons. The melting mixture includes mainly agglomerate and, sometimes, lump recycled and secondary raw materials are loaded. Ud. sinter melting 50-80 t/(m 2 day). Direct extraction of lead in crude oil 90-94%.

The purpose of smelting is to extract as much lead as possible from the rough material, and remove Zn and waste material to the slag. Basic Ration of shaft smelting of lead agglomerate: PbO + CO: Pb + + CO 2. As a quality, . is introduced into the mixture. Some of the lead is reduced directly by it. For lead, a weakly reducing agent is required. (O 2 10 -6 -10 -8 Pa). Consumption per mass of agglomerate during shaft smelting is 8-14%. Under these conditions, Zn and Fe are not reduced and turn into slag. present in the agglomerate in the form of CuO and CuS. under conditions of shaft smelting, it is easily reduced to and turns into lead. With a high content of Cu and S in the agglomerate during shaft smelting, self-forming occurs. matte phase.

Basic slag-forming components of slag (80-85% by weight of slag) - FeO, SiO 2, CaO and ZnO - are sent for further processing to extract Zn. Up to 2-4% Pb and ~20% Cu pass into the slag, the content of these respectively. 0.5-3.5 and 0.2-1.5%. Formed during shaft smelting (and agglomeration) serves as the feedstock for the extraction of rare and.

The basis of autogenous lead smelting processes is exothermic. solution PbS + O 2 : Pb + SO 2, consisting of two stages:

2PbS + 3O2 : 2PbO + 2SO 2 PbS + 2PbO: 3Pb + SO 2

Advantages of autogenous methods over traditional ones. technology: agglomeration is excluded. , eliminates the need to dilute the concentrate with fluxes, which reduces slag yield, uses heat from and eliminates (partial) consumption, increases SO 2 extraction, which simplifies their use and increases plant safety. The industry uses two autogenous processes: KIVTsET-TSS, developed in the USSR and implemented at the Ust-Kamenogorsk plant and in Italy at the Porto Vesme plant, and the American QSL process.

Melting technology using the KIVTSET-TSS method: finely ground, well-dried charge containing concentrate, recycled and, using a burner, is injected with technical O 2 into the melting chamber, where lead is obtained and slag is formed. (contain 20-40% SO 2) after purification, returned to the smelting charge, they enter the production of H 2 SO 4. The rough lead and slag will be separated through. the partition leaks into the electrothermal. settling furnace, from where they are released through tapholes. fed into the charge for excess in the smelting zone.

The QSL process is carried out in a converter-type unit. divided by a partition into zones. Granules are loaded in the melting zone. concentrate, smelting and technical O2. The slag enters the second zone, where, using tuyeres, it is blown with a pulverized coal mixture for lead. In all methods of melting the main a quantity of Zn (~80%) goes into slag. To extract Zn, as well as the remaining lead and certain rare metals, the slag is processed by fuming or rolling.

Rough lead obtained in one way or another contains 93-98% Pb. Impurities in rough lead: Cu (1-5%), Sb, As, Sn (0.5-3%), Al (1-5 kg/t), Au (1-30%), Bi (0.05 -0.4%). Crude lead is purified pyrometallurgically or (sometimes) electrolytically.

Pyrometallurgical method, the rough lead is successively removed: 1) copper by two operations: segregation and with the help of elemental S, forming Cu 2 S. Preliminary. (rough) purification from Cu to a content of 0.5-0.7% is carried out in reflective or electrothermal with deep lead, having a temperature difference in height. interaction on the surface with lead sulfide concentrate to form Cu-Pb matte. The matte is sent to copper production or independently. hydrometallurgical processing.

2) Tellurium-action metallic. Na present NaOH. selective interaction with Te, forming Na 2 Te, floating to the surface and dissolving in NaOH. The melt goes for processing to extract Te.

3), and antimony-oxidation of them or O 2 is reflected. at 700-800 °C, or NaNO 3 in the presence. NaOH at 420 °C. Alkaline melts are sent to hydrometallurgical plants. processing NaOH from them and extracting Sb and Sn; As is removed in the form of Ca 3 (AsO 4) 2, which is sent for burial.

4) and gold using Zn, which selectively reacts with dissolved lead; AuZn 3, AgZn 3 are formed, floating to the surface. The resulting residues are removed from the surface for the last. processing them into

Properties of lead

There is not only beet or cane, but also lead. This is the name of one of the metal compounds.

Acetate looks like a sweet food additive - small white or powder, highly soluble in water.

However, lead sugar not sweet, and eating it is not recommended. The substance contains poison, which are metal ions.

Acetate is used only in veterinary medicine externally, as it has astringent properties.

The toxicity of some lead compounds, oddly enough, is used for the benefit of humans, but not insects.

A metal-containing substance called arsenate is a poison for field pests such as the cotton weevil and gypsy moth.

There is a whole range of harmless combinations of lead with other elements.

In combination with metal, which has drying properties, paintings are treated with the substance so that the paint becomes empty faster.

— Lead chromate, sunny color. It is used for dyeing fabrics.

— Batteries cannot function without metal sulfate.

— Tetraethyl lead serves as an additive to engine fuel and improves quality parameters.

— Without metal sulfide, it is not possible to fire dishes and products made from.

— Lead chloride slows down the growth of tumors, therefore it is used by doctors as an ointment.

This is the application lead chemical compounds. In its pure form, the element is useful in industry.

Use of lead

The metal is not noble, but it helps to obtain precious metals in their pure form. The process is called cupellation.

In the process of melting the mixture and lead under the influence of oxidation, the precious metal is separated without any impurities.

Lead is added and in mixtures that are used as solders.

They are used for soldering parts together. Lead itself is not distinguished by aesthetic beauty.

Without contact with air, it is shiny, blue-white. But as soon as the metal reacts with oxygen in the atmosphere, it loses its luster and becomes covered with an opaque, cloudy film. So, from an aesthetic point of view, lead is of no value.

But the element with serial number 82c is the hero of many literary works. Writers love the epithet “lead.”

Usually, it means the incredible weight of something. For example, the phrase “ lead feet"is interpreted as limbs that cannot be moved due to the feeling of heaviness in them.

Metal No. 82 is indeed not light, but it is far from the heaviest known substance. For example, a piece of lead floats on the surface.

So, more precisely, another literary use of the image of the element. The term “lead” is used in relation to color.

People often say “leaden complexion.” This means that the covers have an unhealthy gray-blue color, the same color that metal acquires when it comes into contact with air.

In the translation of some texts you can find the phrase “tin batteries”.

These are the costs of translating texts in Lithuanian, Latvian, and Bulgarian by not entirely competent people.

The fact is that the word lead simply does not exist in many countries. This element is called tin.

Even ancient people confused two similar metals. True, tin millennia ago did not have the honor of representing any planet.

Other metals, known since time immemorial, were divided by ancient people into celestial bodies. It's no secret what Mars symbolized. Lead began to represent Saturn.

The earth is literally crammed with the 82nd element and this applies not only to natural metal reserves, but also to communication systems.

Properties of lead save power lines and telegraph wires from corrosion. They often have to be laid not through the air, but under bodies of water or, simply, underground.

Plumbing systems cannot do without blue and white metal. In them lead element– material for locking devices. They prevent unplanned access to sewers, for example.

The amount of lead in the external environment affects the crime rate. US scientists came to this conclusion.

They surveyed all the states of the country, correlated the numbers and identified a pattern.

Where the metal concentration is maximum, 4 times more offenses are committed than in areas with lower levels of element No. 82.

Pundits even found an explanation for the statistics. They assumed that metal lead contributes to the disruption of neural connections in the brain, destroys some chemical compounds, essential for normal operation organ.

Perhaps this helps reprogram a person to more non-standard and aggressive behavior.

By the way, lead in the history of mankind was often associated precisely with aggression. Metal was used in torture.

Lily in molten form on the skin, mouth. In India, the alloy was poured into the ears of representatives of the lower caste if they overheard the conversations of their higher brothers.

And in Venice they did it for dangerous criminals lead ceilings cameras on top floor prisons.

In the heat they were burning hot - the prisoners were languishing from the temperatures and stuffiness. In cool weather, on the contrary, the rooms were very cold.

But, fortunately, now metal No. 82 is used mainly for good purposes. Basic lead miner- China.

In the Celestial Empire, about 2 million tons of the element are mined per year. For comparison, all Russian reserves are equal to only 17 million tons. Most of them are hidden in the depths of the Primorsky, Altai, and Krasnoyarsk territories.

Lead is a metal that has been known since ancient times. Man has been using it since 2-3 thousand BC, and it was first discovered in Mesopotamia. There they made small bricks, figurines, and various household items. Even then, people obtained bronze using this element, and also made it for writing with sharp objects.

What color is the metal?

It is an element of group IV of period 6 of the periodic table, where it has the serial number 82. What is lead in nature? It is the most commonly found galena and the formula is PbS. Otherwise, galena is called lead luster. pure element is a soft and malleable metal of a dirty gray color. In air, its cut quickly becomes covered with a small layer of oxide. Oxides reliably protect the metal from further oxidation in both wet and dry environments. If a metal surface coated with oxides is cleaned, it will acquire a shiny tint with a blue tint. This cleaning can be done by pouring the lead in a vacuum and sealing it into a vacuum flask.

Interaction with acids

Sulfuric and hydrochloric acids have a very weak effect on lead, but the metal easily dissolves in nitric acid. All metal chemical compounds that may be soluble are poisonous. It is obtained mainly from ores: first, lead luster is burned until it turns into lead oxide, and then this substance is reduced with coal to pure metal.

General Element Properties

The density of lead is 11.34 g/cm3. This is 1.5 times the density of iron and four times that of lightweight aluminum. It is not without reason that in Russian the word “lead” is synonymous with the word “heavy”. Lead melts at a temperature of 327.5 o C. The metal becomes volatile already at an ambient temperature of 700 C°. This information is very important for those who work in the mining of this metal. It is very easy to scratch even with a fingernail, it is easy to roll it in thin sheets. This is a very soft metal.

Interaction with other metals, heating

The specific heat capacity of lead is 140 J/kg. According to their own chemical properties it is a low-reactive metal. In the voltage series it is located in front of hydrogen. Lead is easily replaced from its salts by other metals. For example, you can conduct an experiment: dip a zinc stick into a solution of acetate of this element. Then it will settle on the zinc stick in the form of fluffy crystals, which chemists call “Saturn wood.” How many specific heat lead equal to? What does this mean? This figure is 140 J/kg. This means the following: to heat a kilogram of metal by 1 o C, 140 Joules of heat are required.

Distribution in nature

There is not so much of this metal in earth's crust- only 0.0016% by weight. However, even this value shows that it is more abundant than mercury, bismuth and gold. Scientists attribute this to the fact that various lead isotopes are decay products of thorium and uranium, so the lead content in the Earth's crust has slowly increased over millions of years. At the moment, many lead ores are known - this is the already mentioned galena, as well as the results of its chemical transformations.

The latter include lead sulfate, cerussite (another name is white mimetite, stoltsite. The ores also contain other metals - cadmium, copper, zinc, silver, bismuth. Where lead ores occur, not only the soil is saturated with this metal, but also water bodies, plants. What is lead in nature? It is always a specific compound. This metal is also found in ores of radioactive metals - uranium and thorium.

Heavy metal in industry

The most commonly used in industry is a compound of lead and tin. Ordinary solder called "tertiary" is widely used for connecting pipelines and electrical wires. This compound contains one part lead and two parts tin. Shells for telephone cables, battery parts may also contain lead. The melting point of some of its compounds is very low - for example, alloys with cadmium or tin melt at 70 o C. Fire-fighting equipment is made from such compounds. Metal alloys are widely used in shipbuilding. They are usually colored light gray. Ships are often coated with tin and lead alloys to protect against corrosion.

Meaning for people of the past and application

The Romans used this metal to make pipes in pipelines. In ancient times, people associated lead with the planet Saturn, and therefore it was previously called Saturn. In the Middle Ages, due to its heavy weight, the metal was often used for alchemical experiments. He was often credited with the ability to turn into gold. Lead is a metal that was very often confused with tin, which continued until the 17th century. And in ancient Slavic languages ​​it bore this name.

It has reached the modern Czech language, where this heavy metal is called olovo. Some linguistic experts believe that the name Plumbum is associated with a specific Greek area. The Russian origin of the word “lead” is still unclear to scientists. Some linguists associate it with the Lithuanian word "scwinas".

The traditional use of lead in history is in the manufacture of bullets, shotgun pellets, and various other projectiles. It was used because it was cheap and had a low melting point. Previously, when making gun shot, a small amount of arsenic was added to the metal.

Lead was also used in Ancient Egypt. It was made from building blocks, statues of noble people, coins were minted in full force. The Egyptians were sure that lead had special energy. They made small plates out of it and used them to protect themselves from ill-wishers. And the ancient Romans not only did water pipes. They also produced cosmetics from this metal, without even suspecting that they were signing their own death warrant. After all, when lead entered the body every day, it caused serious illnesses.

What about the modern environment?

There are substances that kill humanity slowly but surely. And this applies not only to the unenlightened ancestors of antiquity. Sources of toxic lead today are cigarette smoke and urban dust from residential buildings. Vapors from paints and varnishes are also dangerous. But the greatest harm comes from car exhaust gases, large quantities containing lead.

But not only residents of megacities are at risk, but also those who live in villages. Here the metal can accumulate in soils and then end up in fruits and vegetables. As a result, humans receive more than a third of lead through food. In this case, only powerful antioxidants can serve as an antidote: magnesium, calcium, selenium, vitamins A, C. If you use them regularly, you can reliably neutralize yourself from the harmful effects of the metal.

Harm

Every schoolchild knows what lead is. But not all adults are able to answer the question of what its harm is. Its particles enter the body through respiratory system. Next, it begins to interact with the blood, reacting with various parts of the body. The musculoskeletal system suffers the most from this. This is where 95% of all lead consumed by humans ends up.

A high level of its content in the body leads to a lag in mental development, and in adults it manifests itself in the form of depressive symptoms. Excess is indicated by absent-mindedness and fatigue. The intestines also suffer - due to lead, spasms can often occur. This heavy metal also negatively affects the reproductive system. Women find it difficult to bear a child, and men may experience problems with sperm quality. It is also very dangerous for the kidneys. According to some studies, it can cause malignant tumors. However, in amounts not exceeding 1 mg, lead can be beneficial to the body. Scientists have found that this metal can have a bactericidal effect on the organs of vision - however, you should remember what lead is and use it only in doses not exceeding the permissible ones.

As a conclusion

As already mentioned, in ancient times the planet Saturn was considered the patron saint of this metal. But Saturn in astrology is an image of loneliness, sadness and hard fate. Is this why lead is not the best companion for humans? Perhaps he should not impose his society, as the ancients intuitively assumed when they called lead Saturn. After all, the harm to the body from this metal can be irreparable.

Lead(lat. Plumbum), Pb, chemical element Group IV of Mendeleev's periodic system; atomic number 82, atomic mass 207.2. Lead is a heavy metal of a bluish-gray color, very ductile, soft (cut with a knife, scratched with a fingernail). Natural Lead consists of 5 stable isotopes with mass numbers 202 (trace), 204 (1.5%), 206 (23.6%), 207 (22.6%), 208 (52.3%). The last three isotopes are the end products of radioactive transformations 238 U, 235 U and 232 Th. At nuclear reactions Numerous radioactive isotopes of Lead are formed.

Historical reference. Lead was known 6-7 thousand years BC. e. peoples of Mesopotamia, Egypt and other countries ancient world. It was used to make statues, household items, and writing tablets. The Romans used lead pipes for water supply. Alchemists called Lead Saturn and designated it with the sign of this planet. Compounds Lead - “lead ash” PbO, lead white 2PbCO 3 ·Pb(OH) 2 were used in Ancient Greece and Rome as components of medicines and paints. When was it invented firearms, Lead began to be used as a material for bullets. The toxicity of Lead was noted back in the 1st century AD. e. Greek physician Dioscorides and Pliny the Elder.

Distribution of Lead in nature. The content of Lead in the earth's crust (clarke) is 1.6·10 -3% by mass. The formation in the earth's crust of about 80 minerals containing Lead (the main one is galena PbS) is mainly associated with the formation of hydrothermal deposits. In zones of oxidation of polymetallic ores, numerous (about 90) secondary minerals are formed: sulfates (anglesite PbSO 4), carbonates (cerussite PbCO 3), phosphates [pyromorphite Pb 5 (PO 4) 3 Cl].

In the biosphere, Lead is mainly dissipated; it is small in living matter (5·10 -5%), sea ​​water(3·10 -9%). From natural waters Lead is partly sorbed by clays and precipitated by hydrogen sulfide, so it accumulates in marine silts with hydrogen sulfide contamination and in the black clays and shales formed from them.

Physical properties of Lead. Lead crystallizes in a face-centered cubic lattice (a = 4.9389 Å) and has no allotropic modifications. Atomic radius 1.75Å, ionic radii: Pb 2+ 1.26Å, Pb 4+ 0.76Å; density 11.34 g/cm 3 (20 °C); t pl 327.4 °C; boiling point 1725 °C; specific heat capacity at 20 °C 0.128 kJ/(kg K) | thermal conductivity 33.5 W/(m K); temperature coefficient of linear expansion 29.1·10 -6 at room temperature; Brinell hardness 25-40 Mn/m2 (2.5-4 kgf/mm2); tensile strength 12-13 MN/m2, compressive strength about 50 MN/m2; relative elongation at break 50-70%. Hardening does not increase mechanical properties Lead, since its recrystallization temperature is below room temperature (about -35 ° C with a degree of deformation of 40% and above). Lead is diamagnetic, its magnetic susceptibility is -0.12·10 -6. At 7.18 K it becomes a superconductor.

Chemical properties of Lead. The configuration of the outer electron shells of the Pb atom is 6s 2 6p 2, according to which it exhibits oxidation states of +2 and +4. Lead is relatively little chemically active. The metallic luster of a fresh cut of Lead gradually disappears in the air due to the formation the thinnest film PbO, which protects against further oxidation.

With oxygen it forms a series of oxides Pb 2 O, PbO, PbO 2, Pb 3 O 4 and Pb 2 O 3.

In the absence of O2, water at room temperature has no effect on Lead, but it decomposes hot water vapor to form Lead oxide and hydrogen. The hydroxides Pb(OH) 2 and Pb(OH) 4 corresponding to the oxides PbO and PbO 2 are amphoteric in nature.

The compound of Lead with hydrogen PbH 4 is obtained in small quantities under the action of dilute of hydrochloric acid on Mg 2 Pb. PbH 4 is a colorless gas that very easily decomposes into Pb and H 2. When heated, Lead combines with halogens, forming the halides PbX 2 (X-halogen). All of them are slightly soluble in water. PbX 4 halides were also obtained: PbF 4 tetrafluoride - colorless crystals and PbCl 4 tetrachloride - yellow oily liquid. Both compounds easily decompose, releasing F 2 or Cl 2; hydrolyzed by water. Lead does not react with nitrogen. Lead azide Pb(N 3) 2 is obtained by reacting solutions of sodium azide NaN 3 and Pb (II) salts; colorless needle-shaped crystals, sparingly soluble in water; upon impact or heating, it decomposes into Pb and N 2 with an explosion. Sulfur reacts with Lead when heated to form PbS sulfide, a black amorphous powder. Sulfide can also be obtained by passing hydrogen sulfide into solutions of Pb(II) salts; found in nature in the form of lead luster - galena.

In the voltage series, Pb is higher than hydrogen (normal electrode potentials are respectively -0.126 V for Pb = Pb 2+ + 2e and +0.65 V for Pb = Pb 4+ + 4e). However, Lead does not displace hydrogen from dilute hydrochloric and sulfuric acids due to the overvoltage of H 2 on Pb, as well as the formation of protective films of poorly soluble PbCl 2 chloride and PbSO 4 sulfate on the metal surface. Concentrated H 2 SO 4 and HCl act on Pb when heated, and soluble complex compounds of the composition Pb(HSO 4) 2 and H 2 [PbCl 4 ] are obtained. Nitric, acetic, and also some organic acids (for example, citric) dissolve Lead to form Pb (II) salts. According to their solubility in water, salts are divided into soluble (lead acetate, nitrate and chlorate), slightly soluble (chloride and fluoride) and insoluble (sulfate, carbonate, chromate, phosphate, molybdate and sulfide). Pb (IV) salts can be obtained by electrolysis of strongly acidified H 2 SO 4 solutions of Pb (II) salts; the most important of the Pb (IV) salts are Pb(SO 4) 2 sulfate and Pb (C 2 H 3 O 2) 4 acetate. Pb(IV) salts tend to add excess negative ions to form complex anions, for example, plumbates (PbO 3) 2- and (PbO 4) 4-, chloroplumbates (PbCl 6) 2-, hydroxoplumbates [Pb(OH) 6] 2- and others. Concentrated solutions of caustic alkalis react with Pb when heated, releasing hydrogen and hydroxoplumbites of type X 2 [Pb(OH) 4 ].

Getting Lead. Metallic Lead is obtained by oxidative roasting of PbS, followed by the reduction of PbO to raw Pb (“werkbley”) and refining (purification) of the latter. Oxidative roasting of the concentrate is carried out in sintering rooms draw machines continuous action. When firing PbS, the reaction predominates:

2PbS + ZO 2 = 2PbO + 2SO 2.

In addition, a little PbSO 4 sulfate is obtained, which is converted into PbSiO 3 silicate, for which it is added to the charge quartz sand. At the same time, sulfides of other metals (Cu, Zn, Fe), present as impurities, are also oxidized. As a result of firing, instead of a powdered mixture of sulfides, an agglomerate is obtained - a porous sintered solid mass consisting mainly of the oxides PbO, CuO, ZnO, Fe 2 O 3. Pieces of agglomerate are mixed with coke and limestone, and this mixture is loaded into a water-jacket furnace, into which pressurized air is supplied from below through pipes (“tuyeres”). Coke and carbon monoxide (II) reduce PbO to Pb already at no high temperatures(up to 500 °C). At higher temperatures the following reactions occur:

CaCO 3 = CaO + CO 2

2PbSiO 3 + 2CaO + C = 2Pb + 2CaSiO 3 + CO 2.

Zn and Fe oxides partially transform into ZnSiO 3 and FeSiO 3, which together with CaSiO 3 form slag that floats to the surface. Lead oxides are reduced to metal. Raw Lead contains 92-98% Pb, the rest is impurities of Cu, Ag (sometimes Au), Zn, Sn, As, Sb, Bi, Fe. Cu and Fe impurities are removed by zeigerization. To remove Sn, As, Sb, air is blown through the molten metal. The separation of Ag (and Au) is carried out by the addition of Zn, which forms a “zinc foam” consisting of compounds of Zn with Ag (and Au), lighter than Pb, and melting at 600-700 °C. Excess Zn is removed from molten Pb by passing air, steam or chlorine. To remove Bi, Ca or Mg is added to liquid Pb, giving the low-melting compounds Ca 3 Bi 2 and Mg 3 Bi 2. Lead refined by these methods contains 99.8-99.9% Pb. Further purification is carried out by electrolysis, resulting in a purity of at least 99.99%.

Use of Lead. Lead is widely used in production lead acid batteries, used for the manufacture of factory equipment that is resistant to aggressive gases and liquids. Lead strongly absorbs γ-rays and X-rays, due to which it is used as a material for protection against their effects (containers for storing radioactive substances, equipment for X-ray rooms, etc.). Large quantities Lead is used to make shells electrical cables protecting them from corrosion and mechanical damage. Many lead alloys are made from Lead. Lead oxide PbO is introduced into crystal and optical glass to produce materials with a high refractive index. Red lead, chromate (crown yellow) and basic lead carbonate (lead white) are pigments of limited use. Lead chromate is an oxidizing agent used in analytical chemistry. Azide and stythiate (trinitroresorcinate) are initiating explosives. Tetraethyl lead is an anti-knock agent. Lead acetate serves as an indicator for the detection of H 2 S. 204 Pb (stable) and 212 Pb (radioactive) are used as isotopic indicators.

Lead in the body. Plants absorb Lead from soil, water and atmospheric deposition. Lead enters the human body through food (about 0.22 mg), water (0.1 mg), and dust (0.08 mg). The safe daily intake level of Lead for humans is 0.2-2 mg. It is excreted mainly in feces (0.22-0.32 mg), less in urine (0.03-0.05 mg). The human body contains on average about 2 mg of Lead (in some cases - up to 200 mg). Residents of industrialized countries have a higher level of Lead in their bodies than residents of agricultural countries, while city dwellers have higher levels of Lead than rural residents. The main depot of Lead is the skeleton (90% of the total Lead in the body): 0.2-1.9 μg/g accumulates in the liver; in the blood - 0.15-0.40 mcg/ml; in hair - 24 mcg/g, in milk - 0.005-0.15 mcg/ml; also found in the pancreas, kidneys, brain and other organs. The concentration and distribution of Lead in the body of animals are close to the values ​​​​established for humans. When Lead levels increase in environment its deposition in bones, hair, and liver increases.

Poisoning with Lead and its compounds is possible during ore mining, Lead smelting, in the production of lead paints, in printing, pottery, cable production, during the production and use of tetraethyl lead, etc. Household poisonings occur rarely and are observed when eating foods that have been stored for a long time in earthenware coated with a glaze containing red lead or litharge. Lead and his inorganic compounds enter the body in the form of aerosols mainly through Airways, to a lesser extent - through gastrointestinal tract and skin. Lead circulates in the blood in the form of highly dispersed colloids - phosphate and albuminate. Lead is excreted mainly through the intestines and kidneys. In the development of intoxication, disturbances in porphyrin, protein, carbohydrate and phosphate metabolism, deficiency of vitamins C and B1, functional and organic changes in the central and vegetative system play a role. nervous system, toxic effects of Lead on bone marrow. Poisoning can be hidden (the so-called carriage), occurring in mild, moderate and severe forms.

The most common signs of Lead poisoning: a border (a strip of lilac-slate color) along the edge of the gums, an earthy-pale coloring of the skin; reticulocytosis and other blood changes, increased content of porphyrins in the urine, the presence of Lead in the urine in quantities of 0.04-0.08 mg/l or more, etc. Damage to the nervous system is manifested by asthenia, in severe forms - encephalopathy, paralysis (mainly extensors of the hand and fingers), polyneuritis. With the so-called lead colic, sharp cramping pain in the abdomen and constipation occur, lasting from several hours to 2-3 weeks; colic is often accompanied by nausea, vomiting, and blood pressure, body temperature up to 37.5-38 °C. With chronic intoxication, damage to the liver, cardiovascular system, and disruption of endocrine functions are possible (for example, in women - miscarriages, dysmenorrhea, menorrhagia and others). Suppression of immunobiological reactivity contributes to increased overall morbidity.