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, small bricks, figurines, and various household items were made from lead. 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? This is the most commonly found galena and the formula is PbS. Otherwise, galena is called lead luster. The 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, and it is easy to roll into 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 its chemical properties, it is a low-active 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.” What is the specific heat of lead? 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 the earth's crust - only 0.0016% by mass. 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. Sheaths for telephone cables and parts of batteries 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. Building blocks, statues of noble people were made from it, and coins were minted. 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 didn't just make 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, which contain large quantities of 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 the 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.

High levels of it in the body lead to mental retardation, 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(English Lead, French Plomb, German Blei) has been known since the 3rd - 2nd millennium BC. in Mesopotamia, Egypt and other ancient countries, where large bricks (ingots), statues of gods and kings, seals and various household items were made from it. Bronze was made from lead, as well as tablets for writing with a sharp, hard object. At a later time, the Romans began to make water pipes from lead. In ancient times, lead was associated with the planet Saturn and was often called Saturn. In the Middle Ages, due to its heavy weight, lead played a special role in alchemical operations; it was credited with the ability to easily turn into gold. Until the 17th century. Lead was often confused with tin. In ancient Slavic languages ​​it was called tin; this name is preserved in modern Czech (Olovo).

The origin of the word "lead" is unclear. In the old days, lead was not always clearly distinguished from tin. In most Slavic languages ​​(Bulgarian, Serbo-Croatian, Czech, Polish) lead is called tin. Our “lead” is found only in the languages ​​of the Baltic group: svinas (Lithuanian), svin (Latvian). For some unfortunate translators, this led to funny misunderstandings, for example, about “tin batteries” in cars. The English name for lead, lead, and the Dutch word, lood, are probably related to our word “to tin.” The Latin plumbum (also of unclear origin) gave rise to the English word plumber - plumber (once pipes were caulked with soft lead. And another confusion associated with lead. The ancient Greeks called lead “molybdos” (the name was preserved in the modern Greek language). Hence - Latin molibdaena: in the Middle Ages this was the name for lead luster PbS, and the rarer molybdenum luster (MoS 2), and other similar minerals that left a black mark on a light surface. The same mark was left by graphite and lead itself. Thin lead rods could be written on. on parchment; it is not for nothing that in German a pencil is called Bleistift, i.e. lead rod.

Lead, along with gold, silver, copper, tin, iron and mercury, is one of the seven metals known since ancient times. It is believed that people first smelted lead from ores 8 thousand years ago. Excavations in ancient Egypt have uncovered silver and lead artifacts in burials from before the dynastic period. Similar finds made in Mesopotamia date back to the same time.

Thin lead plates were used to cover the wooden hulls of ancient ships. One such Greek ship, built in the 3rd century. BC, was found in 1954 at the bottom of the Mediterranean Sea near Marseille. The Romans also made pipes from lead, 3 meters long and of different, but strictly defined diameters (there were 15 options in total). This is the first example of standardized industrial production in history.

In the Middle Ages, the roofs of churches and palaces were often covered with lead plates that were resistant to weathering. Back in 669, the roof of the monastery church in York was covered with lead, and in 688, the bishop in Northumberland ordered the roof and walls of the church to be sheathed with lead plates. The famous stained glass windows in cathedrals were assembled using lead frames with grooves in which plates of colored glass were secured. Following the example of the Romans, both water and drainage pipes were made from lead. So, in 1532, square lead drain pipes were installed in the Palace of Westminster.

When firearms were introduced, large quantities of lead were used to make bullets and shot, and lead also became associated with lethal danger. At first, shot was cast in split molds. In 1650, the English Prince Rupert invented a faster and more convenient method. He discovered that if a little arsenic was added to lead and the alloy was poured through a kind of large colander into a tank of water, the shot balls were formed into regular spherical shapes. And after Johannes Gutenberg invented a way to print books using movable metal type in 1436, printers for hundreds of years cast letters from the so-called lead-based typographical alloy (with an admixture of tin and antimony).

Of the lead compounds, red lead Pb 3 O 4 and basic lead carbonate (lead white) have been used since ancient times as red and white paint. Almost all the paintings of the old masters were painted with paints based on white lead.

Introduction

Lead-- element of the main subgroup of the fourth group, the sixth period of the periodic table of chemical elements D.I. Mendeleev, with atomic number 82. Denoted by the symbol Pb (Latin: Plumbum).

The simple substance lead is a malleable, relatively fusible metal. Pure lead is silvery-white, but in air it quickly becomes covered with a bluish-gray coating. Melting point +327.4 0 C, boiling point +1725 0 C, density - 11.34 g/cm 3 .

Lead exhibits oxidation states +2 and +4. In both oxidation states, lead can exhibit metallic and non-metallic properties.

origin of name

The origin of the word "lead" is unclear. In most Slavic languages ​​(Bulgarian, Serbo-Croatian, Czech, Polish) lead is called tin. A word with the same meaning, but similar in pronunciation to “lead,” is found in the languages ​​of the Baltic group: љvinas (Lithuanian), svins (Latvian), as well as in the East Slavic languages ​​- Ukrainian (svinets) and Belarusian (svinets).

The Latin plumbum gave the English word plumber - plumber (in Ancient Rome, water pipes were made of this metal as the most suitable for casting), and the name of the Venetian prison with a lead roof - Piombe. Products made from this metal (coins, medallions) were used in Ancient Egypt, lead water pipes - in Ancient Rome. Lead is referred to as a specific metal in the Old Testament. Lead smelting was the first metallurgical process known to man. Until 1990, large amounts of lead were used (together with antimony and tin) for casting typographical fonts, and also in the form of tetraethyl lead to increase the octane number of motor fuel.

Lead- a rare mineral, a native metal of the class of native elements. Malleable, relatively fusible metal of silver-white color with a bluish tint. Known since ancient times. Very plastic, soft (can be cut with a knife, scratched with a fingernail). Nuclear reactions produce numerous radioactive isotopes of lead.

See also:

STRUCTURE

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. Twin crystals according to (111). It is found in small rounded grains, scales, balls, plates and thread-like formations.

PROPERTIES

Lead has a fairly low thermal conductivity, it is 35.1 W/(m K) at 0 °C. The metal is soft, can be cut with a knife, and is easily scratched with a fingernail. On the surface it is usually covered with a more or less thick film of oxides; when cut, a shiny surface is revealed, which fades over time in air. Melting point - 600.61 K (327.46 °C), boils at 2022 K (1749 °C). Belongs to the group of heavy metals; its density is 11.3415 g/cm 3 (+20 °C). As the temperature increases, the density of lead decreases. Tensile strength - 12-13 MPa (MN/m2). At a temperature of 7.26 K it becomes a superconductor.

RESERVES AND PRODUCTION

The content in the earth's crust is 1.6 10 −3% by weight. Native lead is rare; the range of rocks in which it is found is quite wide: from sedimentary rocks to ultramafic intrusive rocks. In these formations it often forms intermetallic compounds (for example, zvyagintsevite (Pd,Pt) 3 (Pb,Sn), etc.) and alloys with other elements (for example, (Pb + Sn + Sb)). It is part of 80 different minerals. The most important of them are: galena PbS, cerussite PbCO 3, anglesite PbSO 4 (lead sulfate); of the more complex ones - tillite PbSnS 2 and betechtinite Pb 2 (Cu,Fe) 21 S 15, as well as lead sulfosalts - jamesonite FePb 4 Sn 6 S 14, boulangerite Pb 5 Sb 4 S 11. Always found in uranium and thorium ores, often having a radiogenic nature.

To obtain lead, ores containing galena are mainly used. First, a concentrate containing 40-70 percent lead is obtained by flotation. Then, several methods are possible for processing the concentrate into werkbley (blank lead): the formerly widespread method of mine reduction smelting, the method of oxygen-suspended cyclone electrothermal smelting of lead-zinc products (KIVTSET-TSS), the Vanyukov smelting method (melting in a liquid bath) developed in the USSR. . For smelting in a shaft (water jacket) furnace, the concentrate is first sintered and then loaded into a shaft furnace, where lead is reduced from the oxide.

Werkbley, containing more than 90 percent lead, undergoes further purification. First, zeigerization and subsequent sulfur treatment are used to remove copper. Arsenic and antimony are then removed by alkaline refining. Next, silver and gold are isolated using zinc foam and the zinc is distilled off. Treatment with calcium and magnesium removes bismuth. As a result, the impurity content drops to less than 0.2%[

ORIGIN

It forms impregnations in igneous, mainly acidic rocks; in deposits of Fe and Mn it is associated with magnetite and hausmannite. Found in placers with native Au, Pt, Os, Ir.

Under natural conditions, it often forms large deposits of lead-zinc or polymetallic ores of the stratiform type (Kholodninskoye, Transbaikalia), as well as skarn (Dalnegorskoye (formerly Tetyukhinskoye), Primorye; Broken Hill in Australia) type; galena is often found in deposits of other metals: pyrite-polymetallic (Southern and Middle Urals), copper-nickel (Norilsk), uranium (Kazakhstan), gold ore, etc. Sulfosalts are usually found in low-temperature hydrothermal deposits with antimony, arsenic, and also in gold deposits (Darasun, Transbaikalia). Lead minerals of the sulfide type have a hydrothermal genesis, minerals of the oxide type are common in weathering crusts (oxidation zones) of lead-zinc deposits. Lead is present in clarke concentrations in almost all rocks. The only place on earth where rocks contain more lead than uranium is the Kohistan-Ladakh arc in northern Pakistan.

APPLICATION

Lead nitrate is used to produce powerful mixed explosives. Lead azide is used as the most widely used detonator (initiating explosive). Lead perchlorate is used to prepare a heavy liquid (density 2.6 g/cm³) used in flotation beneficiation of ores, and it is sometimes used in high-power mixed explosives as an oxidizing agent. Lead fluoride alone, as well as together with bismuth, copper, and silver fluoride, is used as a cathode material in chemical current sources.

Lead bismuthate, lead sulfide PbS, lead iodide are used as cathode material in lithium batteries. Lead chloride PbCl 2 as a cathode material in backup current sources. Lead telluride PbTe is widely used as a thermoelectric material (thermo-emf 350 μV/K), the most widely used material in the production of thermoelectric generators and thermoelectric refrigerators. Lead dioxide PbO 2 is widely used not only in lead batteries, but also on its basis many backup chemical current sources are produced, for example, lead-chlorine cell, lead-fluorescent cell and others.

Lead white, basic carbonate Pb(OH) 2 PbCO 3, dense white powder, is obtained from lead in air under the influence of carbon dioxide and acetic acid. The use of lead white as a coloring pigment is now not as widespread as before, due to its decomposition under the influence of hydrogen sulfide H 2 S. Lead white is also used for the production of putty, in the technology of cement and lead carbonate paper.

Lead arsenate and arsenite are used in insecticide technology to kill agricultural pests (gypsy moth and cotton boll weevil).

Lead borate Pb(BO 2) 2 H 2 O, an insoluble white powder, is used to dry paintings and varnishes, and, along with other metals, as coatings on glass and porcelain.

Lead chloride PbCl 2, white crystalline powder, is soluble in hot water, solutions of other chlorides and especially ammonium chloride NH 4 Cl. It is used to prepare ointments for treating tumors.

Lead chromate PbCrO4 is known as chrome yellow dye and is an important pigment for making paints, for dyeing porcelain and fabrics. In industry, chromate is used mainly in the production of yellow pigments.

Lead nitrate Pb(NO 3) 2 is a white crystalline substance, highly soluble in water. This is a binder of limited use. In industry, it is used in matchmaking, textile dyeing and printing, antler dyeing and engraving.

Since lead absorbs γ radiation well, it is used for radiation protection in X-ray facilities and in nuclear reactors. In addition, lead is considered as a coolant in projects of advanced fast neutron nuclear reactors.

Lead alloys are widely used. Pewter (tin-lead alloy), containing 85-90% Sn and 15-10% Pb, is moldable, inexpensive and used in the manufacture of household utensils. Solder containing 67% Pb and 33% Sn is used in electrical engineering. Alloys of lead and antimony are used in the production of bullets and typographic fonts, and alloys of lead, antimony and tin are used for figured casting and bearings. Lead-antimony alloys are commonly used for cable sheaths and electric battery plates. There was a time when cable sheaths used a significant portion of the world's lead production, due to the good moisture-proof properties of such products. However, lead was subsequently largely replaced from this area by aluminum and polymers. Thus, in Western countries, the use of lead on cable sheaths fell from 342 thousand tons in 1976 to 51 thousand tons in 2002. Lead compounds are used in the production of dyes, paints, insecticides, glass products and as an additive to gasoline in the form of tetraethyl lead (C 2 H 5) 4 Pb (a moderately volatile liquid, the vapors of which in small concentrations have a sweetish fruity odor, in large concentrations - an unpleasant odor; Tm = 130 °C, Tb = +80 °C/13 mmHg; density 1.650 g/cm³; nD2v = 1.5198; miscible with organic solvents, easily penetrates the skin; = 0.005 mg/m³; LD50 = 12.7 mg/kg (rat, oral)) to increase octane number.

Used to protect patients from radiation from X-ray machines.

Lead - Pb

CLASSIFICATION

Strunz (8th edition)	1/A.05-20
Nickel-Strunz (10th edition)	1.AA.05
Dana (7th edition)	1.1.21.1
Dana (8th edition)	1.1.1.4
Hey's CIM Ref	1.30

Lead is a chemical element with atomic number 82 and the symbol Pb (from the Latin plumbum - ingot). It is a heavy metal with a density greater than that of most ordinary materials; Lead is soft, malleable and melts at relatively low temperatures. Freshly cut lead has a bluish-white tint; it dulls to a dull gray when exposed to air. Lead has the second highest atomic number of the classically stable elements and stands at the end of the three major decay chains of the heavier elements. Lead is a relatively non-reactive post-transition element. Its weak metallic character is illustrated by its amphoteric nature (lead oxides and lead react with both acids and bases) and tendency to form covalent bonds. Lead compounds are typically in the +2 rather than +4 oxidation state, typically with lighter carbon group members. Exceptions are mainly limited to organic compounds. Like the lighter members of this group, lead tends to bind to itself; it can form chains, rings and polyhedral structures. Lead is easily extracted from lead ores and was already known to prehistoric people in Western Asia. The main ore of lead, galena, often contains silver, and interest in silver contributed to the large-scale extraction of lead and its use in ancient Rome. Lead production declined after the fall of the Roman Empire and did not reach the same levels until the Industrial Revolution. Currently, global lead production is about ten million tons per year; secondary production from processing accounts for more than half of this amount. Lead has several properties that make it useful: high density, low melting point, ductility, and relative inertness to oxidation. Combined with its relative abundance and low cost, these factors led to the widespread use of lead in construction, plumbing, batteries, bullets, scales, solders, tin-lead alloys, fusible alloys, and radiation shielding. At the end of the 19th century, lead was recognized as highly toxic, and since then its use has been gradually reduced. Lead is a neurotoxin that accumulates in soft tissue and bone, damaging the nervous system and causing brain disorders and, in mammals, blood disorders.

Physical properties

Atomic properties

The lead atom has 82 electrons arranged in the electron configuration 4f145d106s26p2. The combined first and second ionization energies—the total energy required to remove two 6p electrons—are close to the energy of tin, lead's upper neighbor in the carbon group. It's unusual; Ionization energies generally move down the group as the element's outer electrons become further away from the nucleus and more shielded by smaller orbitals. The similarity of ionization energies is due to the reduction of lanthanides - a decrease in the radii of elements from lanthanum (atomic number 57) to lutetium (71) and the relatively small radii of elements after hafnium (72). This is due to poor shielding of the nucleus by lanthanide electrons. The combined first four ionization energies of lead exceed those of tin, contrary to predictions of periodic trends. Relativistic effects, which become significant in heavier atoms, contribute to this behavior. One such effect is the inert pair effect: the 6s electrons of lead are reluctant to participate in bonding, making the distance between nearby atoms in crystalline lead unusually long. The lighter carbon groups of lead form stable or metastable allotropes with a tetrahedrally coordinated and covalently bonded diamond cubic structure. The energy levels of their outer s and p orbitals are close enough to allow mixing with the four sp3 hybrid orbitals. In lead, the inert pair effect increases the distance between its s and p orbitals, and the gap cannot be bridged by the energy that will be released by additional bonds after hybridization. Unlike the diamond cubic structure, lead forms metallic bonds in which only p-electrons are delocalized and shared between Pb2+ ions. Therefore, lead has a face-centered cubic structure, like the divalent metals of equal size, calcium and strontium.

Large volumes

Pure lead has a bright silver color with a hint of blue. It fades on contact with moist air and its shade depends on the prevailing conditions. Characteristic properties of lead include high density, ductility, and high resistance to corrosion (due to passivation). The dense cubic structure and high atomic weight of lead results in a density of 11.34 g/cm3, which is greater than that of common metals such as iron (7.87 g/cm3), copper (8.93 g/cm3) and zinc ( 7.14 g/cm3). Some rarer metals have higher densities: tungsten and gold have a density of 19.3 g/cm3, and osmium, the densest metal, has a density of 22.59 g/cm3, almost twice that of lead. Lead is a very soft metal with a Mohs hardness of 1.5; it can be scratched with a fingernail. It is quite malleable and somewhat plastic. Lead's bulk modulus, a measure of its ease of compressibility, is 45.8 GPa. For comparison, the bulk modulus of aluminum is 75.2 GPa; copper – 137.8 GPa; and mild steel – 160-169 GPa. Tensile strength at 12-17 MPa is low (for aluminum it is 6 times higher, for copper it is 10 times higher, and for mild steel it is 15 times higher); it can be strengthened by adding a small amount of copper or antimony. Lead's melting point, 327.5 °C (621.5 °F), is low compared to most metals. Its boiling point is 1749 °C (3180 °F), the lowest of the carbon group elements. The electrical resistivity of lead at 20 °C is 192 nanometers, which is almost an order of magnitude higher than that of other industrial metals (copper at 15.43 nΩ·m, gold 20.51 nΩ·m and aluminum at 24.15 nΩ·m). Lead is a superconductor at temperatures below 7.19 K, the highest critical temperature of all Type I superconductors. Lead is the third largest elemental superconductor.

Isotopes of lead

Natural lead consists of four stable isotopes with mass numbers 204, 206, 207 and 208, and traces of five short-lived radioisotopes. The large number of isotopes is consistent with the fact that the number of lead atoms is even. Lead has a magic number of protons (82), for which the nuclear shell model accurately predicts a particularly stable nucleus. Lead-208 has 126 neutrons, another magic number that may explain why lead-208 is unusually stable. Given its high atomic number, lead is the heaviest element whose natural isotopes are considered stable. This title was previously held by bismuth, which has atomic number 83, until it was discovered in 2003 that its only original isotope, bismuth-209, decays very slowly. The four stable isotopes of lead could theoretically undergo alpha decay into mercury isotopes, releasing energy, but this has never been observed; their predicted half-lives range from 1035 to 10189 years. Three stable isotopes occur in three of the four major decay chains: lead-206, lead-207, and lead-208 are the end products of the decay of uranium-238, uranium-235, and thorium-232, respectively; these decay chains are called uranium series, actinium series and thorium series. Their isotopic concentration in a natural rock sample is highly dependent on the presence of these three parent isotopes of uranium and thorium. For example, the relative abundance of lead-208 can vary from 52% in normal samples to 90% in thorium ores, so the standard atomic mass of lead is given in only one decimal place. Over time, the ratio of lead-206 and lead-207 to lead-204 increases as the former two are supplemented by the radioactive decay of heavier elements, while the latter is not; this allows lead-to-lead bonds to occur. As uranium decays into lead, their relative amounts change; this is the basis for creating uranium-lead. In addition to the stable isotopes that make up almost all of the lead that exists naturally, there are trace amounts of several radioactive isotopes. One of them is lead-210; although its half-life is only 22.3 years, only small amounts of this isotope are present in nature because lead-210 is produced through a long decay cycle that begins with uranium-238 (which has been present on Earth for billions of years). The decay chains of uranium-235, thorium-232 and uranium-238 contain lead-211, -212 and -214, so traces of all three of these lead isotopes are naturally found. Small traces of lead-209 arise from the very rare cluster decay of radium-223, one of the daughter products of natural uranium-235. Lead-210 is particularly useful in helping to identify the age of samples by measuring its ratio to lead-206 (both isotopes present in the same decay chain). A total of 43 lead isotopes were synthesized, with mass numbers 178-220. Lead-205 is the most stable with a half-life of about 1.5×107 years. [I] The second most stable is lead-202, which has a half-life of about 53,000 years, longer than any naturally occurring trace radioisotope. Both are extinct radionuclides that were produced in stars along with stable isotopes of lead but have long since decayed.

Chemistry

A large volume of lead exposed to moist air forms a protective layer of varying composition. Sulfite or chloride may also be present in urban or marine environments. This layer renders a large volume of lead effectively chemically inert in the air. Fine-powdered lead, like many metals, is pyrophoric and burns with a bluish-white flame. Fluorine reacts with lead at room temperature to form lead(II) fluoride. The reaction with chlorine is similar, but requires heating, since the resulting chloride layer reduces the reactivity of the elements. Molten lead reacts with chalcogens to form lead(II) chalcogenides. The lead metal is not attacked by dilute sulfuric acid, but is dissolved in a concentrated form. It reacts slowly with hydrochloric acid and vigorously with nitric acid to form nitrogen oxides and lead(II) nitrate. Organic acids such as acetic acid dissolve lead in the presence of oxygen. Concentrated alkalis dissolve lead and form plumbites.

Inorganic compounds

Lead has two main oxidation states: +4 and +2. The tetravalent state is common to the carbon group. The divalent state is rare for carbon and silicon, minor for germanium, important (but not predominant) for tin, and more important for lead. This is explained by relativistic effects, in particular the inert pair effect, which occurs when there is a large difference in electronegativity between lead and oxide, halide or nitride anions, resulting in significant partial positive charges on lead. As a result, there is a stronger contraction of the 6s orbital of lead than the 6p orbital, which makes lead very inert in ionic compounds. This is less applicable to compounds in which lead forms covalent bonds with elements of similar electronegativity, such as carbon in organoleptic compounds. In such compounds, the 6s and 6p orbitals are the same size, and sp3 hybridization is still energetically favorable. Lead, like carbon, is predominantly tetravalent in such compounds. The relatively large difference in electronegativity of lead(II) at 1.87 and lead(IV) is 2.33. This difference highlights the opposite trend of increasing stability of the +4 oxidation state with decreasing carbon concentration; tin, by comparison, has values ​​of 1.80 in the +2 oxidation state and 1.96 in the +4 state.

Lead(II) compounds are characteristic of inorganic lead chemistry. Even strong oxidizing agents such as fluorine and chlorine react with lead at room temperature, forming only PbF2 and PbCl2. Most are less ionic than other metal compounds and are therefore largely insoluble. Lead(II) ions are usually colorless in solution and are partially hydrolyzed to form Pb(OH)+ and finally Pb4(OH)4 (in which the hydroxyl ions act as bridging ligands). Unlike tin(II) ions, they are not reducing agents. Methods for identifying the presence of Pb2+ ion in water usually rely on the precipitation of lead(II) chloride using dilute hydrochloric acid. Since the chloride salt is slightly soluble in water, an attempt is then made to precipitate lead(II) sulfide by bubbling hydrogen sulfide through the solution. Lead monoxide exists in two polymorphs: red α-PbO and yellow β-PbO, the latter only stable above 488 °C. This is the most commonly used lead compound. Lead(II) hydroxide can only exist in solution; it is known to form plumbite anions. Lead usually reacts with heavier chalcogens. Lead sulfide is a semiconductor, photoconductor, and extremely sensitive infrared detector. The other two chalcogenides, lead selenide and lead telluride, are also photoconductors. They are unusual in that their color becomes lighter the lower the group. Lead dihalides are well described; these include diastatide and mixed halides such as PbFCl. The relative insolubility of the latter is a useful basis for the gravimetric determination of fluorine. Difluoride was the first solid ion-conducting compound to be discovered (in 1834 by Michael Faraday). Other dihalides decompose when exposed to ultraviolet or visible light, especially diiodide. Many lead pseudohalides are known. Lead(II) forms a large number of halide coordination complexes such as 2-, 4- and n5n-chain anion. Lead(II) sulfate is insoluble in water, like sulfates of other heavy divalent cations. Lead(II) nitrate and lead(II) acetate are highly soluble, and this is used in the synthesis of other lead compounds.

Several inorganic lead(IV) compounds are known, and they are usually strong oxidizing agents or exist only in strongly acidic solutions. Lead(II) oxide gives a mixed oxide upon further oxidation, Pb3O4. It is described as lead(II,IV) oxide or structurally 2PbO·PbO2 and is the best known mixed valence lead compound. Lead dioxide is a strong oxidizing agent, capable of oxidizing hydrochloric acid to chlorine gas. This is because the expected PbCl4 to be produced is unstable and spontaneously decomposes to PbCl2 and Cl2. Similar to lead monoxide, lead dioxide is capable of forming foamed anions. Lead disulfide and lead diselenide are stable at high pressures. Lead tetrafluoride, a yellow crystalline powder, is stable, but less so than difluoride. Lead tetrachloride (yellow oil) decomposes at room temperature, lead tetrabromide is even less stable, and the existence of lead tetraiodide is disputed.

Other oxidation states

Some lead compounds exist in formal oxidation states other than +4 or +2. Lead(III) can be produced as an intermediate between lead(II) and lead(IV) in larger organoleptic complexes; this oxidation state is unstable because both the lead(III) ion and the larger complexes containing it are radicals. The same applies to lead(I), which can be found in such species. Numerous mixed oxides of lead (II, IV) are known. When PbO2 is heated in air, it becomes Pb12O19 at 293°C, Pb12O17 at 351°C, Pb3O4 at 374°C and finally PbO at 605°C. Another sesquioxide, Pb2O3, can be produced at high pressure along with several non-stoichiometric phases. Many of these show defective fluorite structures in which some oxygen atoms are replaced by voids: PbO can be seen as having this structure, with every alternate layer of oxygen atoms missing. Negative oxidation states can occur as Zintl phases, as in either the case of Ba2Pb, with lead formally being lead(-IV), or as in the case of oxygen-sensitive ring-shaped or polyhedral cluster ions, such as the trigonal bipyramidal ion Pb52-i, where two lead atoms are lead (- I), and three are lead (0). In such anions, each atom sits on a polyhedral vertex and contributes two electrons to each covalent bond at the edge of their sp3 hybrid orbitals, with the remaining two being an outer lone pair. They can be formed in liquid ammonia by reducing lead with sodium.

Organolead compound

Lead can form multi-linked chains, a property it shares with its lighter homologue, carbon. Its ability to do this is much less because the Pb-Pb bond energy is three and a half times lower than that of the C-C bond. With itself, lead can build metal-to-metal bonds up to the third order. With carbon, lead forms organolead compounds similar to but usually less stable than typical organic compounds (due to the weakness of the Pb-C bond). This makes the organometallic chemistry of lead much less broad than that of tin. Lead preferentially forms organic compounds (IV), even if this formation begins with inorganic lead(II) reagents; very few organolate(II) compounds are known. The best characterized exceptions are Pb 2 and Pb (η5-C5H5)2. The lead analogue of the simplest organic compound, methane, is plumbane. Plumbane can be produced by the reaction between metallic lead and atomic hydrogen. Two simple derivatives, tetramethyladine and tetraethyl alide, are the best known organolead compounds. These compounds are relatively stable: tetraethylide begins to decompose only at 100 °C or when exposed to sunlight or ultraviolet radiation. (Tetraphenyl lead is even more thermally stable, decomposing at 270 °C). With sodium metal, lead readily forms an equimolar alloy, which reacts with alkyl halides to form organometallic compounds such as tetraethyl alide. The oxidizing nature of many organometallic compounds is also exploited: lead tetraacetate is an important laboratory oxidation reagent in organic chemistry, and tetraethyl alide has been produced in greater quantities than any other organometallic compound. Other organic compounds are less chemically stable. For many organic compounds there is no lead analogue.

Origin and prevalence

In space

The abundance of lead per particle in the Solar System is 0.121 ppm (parts per billion). This figure is two and a half times higher than platinum, eight times higher than mercury, and 17 times higher than gold. The amount of lead in the universe is slowly increasing as the heaviest atoms (all of which are unstable) gradually decay into lead. The abundance of lead in the solar system has increased by about 0.75% since its formation 4.5 billion years ago. The solar system isotope abundance table shows that lead, despite its relatively high atomic number, is more abundant than most other elements with atomic numbers greater than 40. Primordial lead, which contains the isotopes lead-204, lead-206, lead-207, and lead -208- were mainly created through repeated neutron capture processes that occur in stars. The two main capture modes are s- and r-processes. In the s process (s stands for slow), the captures are separated by years or decades, allowing less stable nuclei to undergo beta decay. A stable nucleus of thallium-203 can capture a neutron and become thallium-204; this substance undergoes beta decay, yielding stable lead-204; when it captures another neutron, it becomes lead-205, which has a half-life of about 15 million years. Further entrapments lead to the formation of lead-206, lead-207 and lead-208. When another neutron is captured, lead-208 becomes lead-209, which quickly decays to bismuth-209. When another neutron is captured, bismuth-209 becomes bismuth-210, whose beta decays to polonium-210 and alpha decays to lead-206. The cycle therefore ends at lead-206, lead-207, lead-208 and bismuth-209. In the r-process (r stands for "fast"), captures happen faster than the nuclei can decay. This occurs in environments with a high density of neutrons, such as a supernova or the merger of two neutron stars. The neutron flux can be on the order of 1022 neutrons per square centimeter per second. The R process does not form as much lead as the s process. It tends to stop once neutron-rich nuclei reach 126 neutrons. At this point, the neutrons are located in full shells in the atomic nucleus, and it becomes more difficult to energetically contain more of them. When the neutron flux subsides, their beta nuclei decay into stable isotopes of osmium, iridium and platinum.

On the ground

Lead is classified as a chalcophile according to the Goldschmidt classification, meaning it typically occurs in combination with sulfur. It is rarely found in its natural metallic form. Many lead minerals are relatively light and, over the course of Earth's history, remained in the crust rather than sinking deeper into the Earth's interior. This explains the relatively high lead level in the bark, 14 ppm; it is the 38th most abundant element in the cortex. The main lead mineral is galena (PbS), which is mainly found in zinc ores. Most other lead minerals are related to galena in some way; boulangerite, Pb5Sb4S11, is a mixed sulfide derived from galena; anglesite, PbSO4, is a product of galena oxidation; and serusite or white lead ore, PbCO3, is a product of the decomposition of galena. Arsenic, tin, antimony, silver, gold, copper and bismuth are common impurities in lead minerals. World lead resources exceed 2 billion tons. Significant reserves of lead have been discovered in Australia, China, Ireland, Mexico, Peru, Portugal, Russia and the United States. Global reserves - resources that are economically viable to extract - amounted to 89 million tons in 2015, 35 million of which are in Australia, 15.8 million in China, and 9.2 million in Russia. Typical background concentrations of lead do not exceed 0.1 μg/m3 in the atmosphere; 100 mg/kg in soil; and 5 µg/L in fresh water and sea water.

Etymology

The modern English word "lead" is of Germanic origin; it comes from Middle English and Old English (with a long sign above the vowel "e", indicating that the vowel sound of that letter is long). The Old English word comes from a hypothetical reconstructed Proto-Germanic *lauda- (“lead”). According to accepted linguistic theory, this word "gave birth" to descendants in several Germanic languages ​​with exactly the same meaning. The origin of Proto-Germanic *lauda is not clear within the linguistic community. According to one hypothesis, this word is derived from Proto-Indo-European *lAudh- (“lead”). Another hypothesis is that the word is a loanword from Proto-Celtic *ɸloud-io- ("lead"). The word is related to the Latin plumbum, which gave the element the chemical symbol Pb. The word *ɸloud-io- may also be the source of Proto-Germanic *bliwa- (which also means "lead"), from which German Blei is derived. The name of the chemical element is not related to the verb of the same spelling, derived from Proto-Germanic *layijan- (“to lead”).

Story

Background and early history

Metal lead beads dating back to 7000-6500 BC found in Asia Minor may represent the first example of metal smelting. At the time, lead had few (if any) uses due to its softness and dull appearance. The main reason for the spread of lead production was its association with silver, which could be produced by burning galena (a common lead mineral). The ancient Egyptians were the first to use lead in cosmetics, which spread to ancient Greece and beyond. The Egyptians may have used lead as a sinker in fishing nets and in making glazes, glasses, enamels, and jewelry. Various civilizations in the Fertile Crescent used lead as a writing material, as a currency, and in construction. Lead was used in the ancient Chinese royal court as a stimulant, as currency, and as a contraceptive. In the Indus Valley Civilization and Mesoamericans, lead was used to make amulets; Eastern and Southern African peoples used lead in wire drawing.

Classical era

Because silver was widely used as a decorative material and medium of exchange, lead deposits began to be worked in Asia Minor from 3000 BC; later lead deposits were developed in the Aegean and Lorion regions. These three regions collectively dominated the production of mined lead until approximately 1200 BC. Since 2000 BC, Phoenicians have worked in the mines of the Iberian Peninsula; by 1600 BC Lead mining existed in Cyprus, Greece and Sicily. Rome's territorial expansion in Europe and the Mediterranean, as well as the development of mining, led to the area becoming the largest producer of lead in the classical era, with annual production reaching 80,000 tons. Like their predecessors, the Romans obtained lead primarily as a by-product of silver smelting. The leading producers were Central Europe, Britain, the Balkans, Greece, Anatolia and Spain, accounting for 40% of global lead production. Lead was used to make water pipes in the Roman Empire; The Latin word for this metal, plumbum, is the source of the English word plumbing. The metal's ease of handling and resistance to corrosion has led to its widespread use in other applications, including pharmaceuticals, roofing materials, currency and military supplies. Writers of the time such as Cato the Elder, Columella and Pliny the Elder recommended lead vessels for the preparation of sweeteners and preservatives added to wine and food. Lead gave a pleasant taste due to the formation of "lead sugar" (lead(II) acetate), while copper or bronze vessels could impart a bitter taste to food due to the formation of verdigris. This metal was by far the most common material in classical antiquity, and It is appropriate to refer to the (Roman) Age of Lead. Lead was as widely used to the Romans as plastic is to us. The Roman author Vitruvius reported on the health hazards lead may pose, and modern writers have suggested that lead poisoning played an important role in it. the decline of the Roman Empire.[l] Other researchers have criticized such claims, pointing out, for example, that not all stomach pains were caused by lead poisoning. According to archaeological research, Roman lead pipes increased lead levels in tap water, but such an effect "is unlikely to have occurred." really harmful." Victims of lead poisoning began to be called "Saturnines", in honor of the terrible father of the gods, Saturn. By association with this, lead was considered the “father” of all metals. Its status in Roman society was low because it was easily accessible and cheap.

Confusion with tin and antimony

In the classical era (and even before the 17th century), tin was often not distinguished from lead: the Romans called lead plumbum nigrum (“black lead”) and tin plumbum candidum (“light lead”). The connection between lead and tin can be traced in other languages: the word "olovo" in Czech means "lead", but in Russian the related olovo means "tin". In addition, lead is closely related to antimony: both elements usually occur in the form of sulfides (galena and stibnite), often together. Pliny incorrectly wrote that stibnite produces lead instead of antimony when heated. In countries such as Turkey and India, the original Persian name for antimony referred to antimony sulfide or lead sulfide, and in some languages ​​such as Russian it was called antimony.

Middle Ages and Renaissance

Lead mining in Western Europe declined after the fall of the Western Roman Empire, with Arabian Iberia being the only region with significant lead output. The greatest production of lead was observed in South and East Asia, especially in China and India, where lead mining increased greatly. In Europe, lead production only began to revive in the 11th and 12th centuries, where lead was again used for roofing and piping. Since the 13th century, lead has been used to create stained glass. In the European and Arabic traditions of alchemy, lead (the symbol of Saturn in the European tradition) was considered an impure base metal that, by separating, purifying and balancing its constituent parts, could be transformed into pure gold. During this period, lead was increasingly used to contaminate wine. The use of such wine was prohibited in 1498 by order of the Pope, as it was considered unfit for use in sacred rites, but it continued to be drunk, leading to mass poisonings until the end of the 18th century. Lead was a key material in parts of the printing press, which was invented around 1440; printing workers routinely inhaled lead dust, causing lead poisoning. Firearms were invented around the same time, and lead, although more expensive than iron, became the main material for making bullets. It was less dangerous to iron gun barrels, had a higher density (which allowed for better velocity retention), and its lower melting point made bullets easier to produce since they could be made using wood fire. Lead, in the form of Venetian pottery, was widely used in cosmetics among Western European aristocracies, as bleached faces were considered a sign of modesty. The practice later expanded to white wigs and eyeliner and only disappeared during the French Revolution in the late 18th century. A similar fashion appeared in Japan in the 18th century with the advent of the geisha, a practice that continued throughout the 20th century. “White faces epitomized the virtue of Japanese women,” and lead was commonly used as a bleaching agent.

Outside Europe and Asia

In the New World, lead began to be produced soon after the arrival of European settlers. The earliest recorded production of lead dates back to 1621 in the English colony of Virginia, fourteen years after its founding. In Australia, the first mine opened by colonists on the continent was the leading mine in 1841. In Africa, lead mining and smelting was known in the Benue-Taure and lower Congo Basin, where lead was used for trade with Europeans and as currency by the 17th century, long before the Scramble for Africa.

Industrial Revolution

In the second half of the 18th century, the Industrial Revolution took place in Britain, and later in continental Europe and the United States. This was the first time that the rate of lead production anywhere in the world exceeded that of Rome. Britain was a leading producer of lead, however, it lost this status by the mid-19th century with the depletion of its mines and the development of lead mining in Germany, Spain and the United States. By 1900, the United States led the world in lead production, and other non-European countries—Canada, Mexico, and Australia—began significant lead production; production outside Europe increased. A significant portion of the demand for lead was for plumbing and paint—lead paint was regularly used back then. During this time, more people (the working class) were exposed to metals and cases of lead poisoning increased. This led to research into the effects of lead consumption on the body. Lead was found to be more dangerous in its smoke form than the solid metal. A link has been found between lead poisoning and gout; British physician Alfred Baring Garrod noted that a third of his patients with gout were plumbers and artists. The effects of chronic lead exposure, including mental disorders, were also studied in the 19th century. The first laws aimed at reducing lead poisoning in factories were introduced in the 1870s and 1880s in the United Kingdom.

New time

Further evidence of the threat posed by lead was discovered in the late 19th and early 20th centuries. The mechanisms of harm were better understood, and lead blindness was documented. Countries in Europe and the United States have begun efforts to reduce the amount of lead that people come into contact with. The United Kingdom introduced compulsory inspections in factories in 1878 and appointed the first factory health inspector in 1898; as a result, a 25-fold reduction in cases of lead poisoning was reported from 1900 to 1944. The last major human exposure to lead was the addition of tetraethyl ether to gasoline as an anti-knock agent, a practice that began in the United States in 1921. It was phased out in the United States and the European Union by 2000. Most European countries banned lead paint, commonly used for its opacity and water resistance for interior decoration, by 1930. The impact was significant: in the last quarter of the 20th century, the percentage of people with excess levels of lead in their blood dropped from more than three-quarters of the United States population to just over two percent. The main lead product by the end of the 20th century was the lead-acid battery, which posed no immediate threat to humans. From 1960 to 1990, lead production in the Western Bloc increased by a third. The Eastern Bloc's share of global lead production tripled from 10% to 30% from 1950 to 1990, with the Soviet Union being the world's largest lead producer in the mid-1970s and 1980s and China beginning extensive lead production in the late 20s. -th century. Unlike European communist countries, China was largely a non-industrialized country in the mid-20th century; in 2004, China surpassed Australia as the largest lead producer. As with European industrialization, lead had negative health effects in China.

Production

Lead production is increasing worldwide due to its use in lead-acid batteries. There are two main categories of products: primary, from ores; and secondary, from scrap. In 2014, 4.58 million tons of lead were produced from primary production, and 5.64 million tons from secondary production. This year, the top three producers of mined lead concentrate were led by China, Australia and the United States. The top three producers of refined lead are led by China, the USA and South Korea. According to a 2010 report by the International Association of Metal Experts, the total amount of lead used accumulated, released or dispersed into the environment at a global level per capita is 8 kg. A significant portion of this volume occurs in more developed countries (20-150 kg per capita) rather than in less developed countries (1-4 kg per capita). The production processes for primary and secondary lead are similar. Some primary manufacturing plants are now supplementing their operations with lead sheets, a trend that is likely to increase in the future. With adequate production methods, secondary lead is indistinguishable from primary lead. Scrap metal waste from the construction trade is usually quite clean and can be remelted without the need for smelting, although distillation is sometimes required. Thus, the production of secondary lead is cheaper in terms of energy requirements than the production of primary lead, often by 50% or more.

Basics

Most lead ores contain a low percentage of lead (high-grade ores have a typical lead content of 3-8%), which must be concentrated for extraction. During initial processing, ores typically undergo crushing, solids separation, grinding, froth flotation and drying. The resulting concentrate, containing 30-80% lead by weight (usually 50-60%), is then converted into (impure) lead metal. There are two main ways to do this: a two-step process involving firing followed by removal from the blast furnace, carried out in separate vessels; or a direct process in which the extraction of the concentrate occurs in one vessel. The latter method has become more common, although the former is still significant.

Two stage process

First, the sulfide concentrate is roasted in air to oxidize the lead sulfide: 2 PbS + 3 O2 → 2 PbO + 2 SO2 The original concentrate was not pure lead sulfide, and roasting produces lead oxide and a mixture of sulfates and silicates of lead and other metals contained in ore. This crude lead oxide is reduced in a coke oven to the (again impure) metal: 2 PbO + C → Pb + CO2. The impurities are mainly arsenic, antimony, bismuth, zinc, copper, silver and gold. The melt is treated in a reverberation furnace with air, steam and sulfur, which oxidizes impurities, with the exception of silver, gold and bismuth. Oxidized contaminants float at the top of the melt and are skimmed off. Silver and gold metal are removed and recovered economically through the Parkes process, in which zinc is added to lead. Zinc dissolves silver and gold, both of which, not mixing in lead, can be separated and recovered. Desilvered lead is liberated with bismuth by the Betterton-Kroll method, treating it with metallic calcium and magnesium. The resulting bismuth-containing slag can be removed. Very pure lead can be obtained by electrolytically treating fused lead using the Betts process. Impure lead anodes and pure lead cathodes are placed in a lead fluorosilicate (PbSiF6) electrolyte. After applying an electrical potential, the impure lead at the anode is dissolved and deposited on the cathode, leaving the vast majority of impurities in solution.

Direct process

In this process, lead ingot and slag are obtained directly from lead concentrates. The lead sulfide concentrate is melted in a furnace and oxidized to form lead monoxide. Carbon (coke or coal gas) is added to the molten charge along with fluxes. Thus, lead monoxide is reduced to metallic lead in the middle of the lead monoxide-rich slag. Up to 80% of the lead in highly concentrated feed concentrates can be obtained in the form of ingots; the remaining 20% ​​forms slag rich in lead monoxide. For low-grade raw materials, all lead can be oxidized to high-grade slag. Lead metal is further produced from high-grade (25-40%) slags by combustion or subsea fuel injection, an auxiliary electric furnace, or a combination of both methods.

Alternatives

Research continues into a cleaner, less energy-intensive lead mining process; its main disadvantage is that either too much lead is lost as waste or alternative methods result in high sulfur content in the resulting lead metal. Hydrometallurgical extraction, in which impure lead anodes are immersed in an electrolyte and pure lead is deposited on the cathode, is a method that may have potential.

Secondary method

Melting, which is an integral part of primary production, is often skipped during secondary production. This only occurs when the lead metal has undergone significant oxidation. This process is similar to the primary extraction process in a blast furnace or rotary kiln, with the significant difference being the greater variability in yields. The lead smelting process is a more modern method that can act as an extension of primary production; Battery paste from waste lead-acid batteries removes sulfur by treating it with alkali and is then treated in a coal-fired oven in the presence of oxygen, resulting in the formation of impure lead, with antimony being the most common impurity. Recycling of secondary lead is similar to processing of primary lead; Some refining processes may be skipped depending on the material processed and its potential contamination, with bismuth and silver being the most commonly accepted impurities. Of the sources of lead for disposal, lead-acid batteries are the most important sources; Lead pipe, sheet and cable sheath are also significant.

Applications

Contrary to popular belief, the graphite in wooden pencils was never made from lead. When the pencil was created as a tool for winding graphite, the specific type of graphite used was called plumbago (literally for lead or lead dummy).

Elementary form

Lead metal has several useful mechanical properties, including high density, low melting point, ductility, and relative inertness. Many metals are superior to lead in some of these aspects, but they are generally less abundant and more difficult to extract from their ores. Lead's toxicity has led to the phasing out of some of its uses. Lead has been used to make bullets since their invention in the Middle Ages. Lead is inexpensive; its low melting point means that small arms ammunition can be cast with minimal use of technical equipment; In addition, lead is denser than other common metals, which allows it to better maintain speed. Concerns have been raised that lead bullets used for hunting may be harmful to the environment. Its high density and corrosion resistance have been used in a number of related applications. Lead is used as a keel on ships. Its weight allows it to counterbalance the cocking effect of the wind on the sails; being so dense, it takes up little volume and minimizes water resistance. Lead is used in scuba diving to counteract the diver's ability to float to the surface. In 1993, the base of the Leaning Tower of Pisa was stabilized with 600 tons of lead. Because of its corrosion resistance, lead is used as a protective sheath for submarine cables. Lead is used in architecture. Lead sheets are used as roofing materials, cladding, flashing, gutters and downspout joints, and roof parapets. Lead moldings are used as a decorative material to secure lead sheets. Lead is still used in the making of statues and sculptures. In the past, lead was often used to balance car wheels; For environmental reasons, this use is being phased out. Lead is added to copper alloys such as brass and bronze to improve their machinability and lubrication properties. Being virtually insoluble in copper, lead forms hard globules in imperfections throughout the alloy, such as grain boundaries. In low concentrations, and also as a lubricant, the globules prevent the formation of chips when the alloy is worked, thereby improving machinability. Bearings use copper alloys with a higher concentration of lead. Lead provides lubrication and copper provides load-bearing support. Due to its high density, atomic number and formability, lead is used as a barrier that absorbs sound, vibration and radiation. Lead has no natural resonant frequencies, and as a result, lead sheet is used as a soundproofing layer in the walls, floors and ceilings of sound studios. Organic pipes are often made from a lead alloy mixed with varying amounts of tin to control the tone of each pipe. Lead is a radiation shielding material used in nuclear science and in X-ray cameras: gamma rays are absorbed by electrons. Lead atoms are tightly packed and their electron density is high; A high atomic number means there are many electrons per atom. Molten lead was used as a coolant for lead-cooled fast reactors. The greatest use of lead was observed at the beginning of the 21st century in lead-acid batteries. The reactions in the battery between lead, lead dioxide and sulfuric acid provide a reliable source of voltage. The lead in batteries is not exposed to direct contact with people and is therefore associated with less of a toxic threat. Supercapacitors containing lead-acid batteries have been installed in kilowatts and megawatts in Australia, Japan and the US in frequency control, solar power smoothing and other applications. These batteries have lower energy density and charge discharge efficiency than lithium-ion batteries, but are significantly less expensive. Lead is used in high voltage power cables as a sheath material to prevent water diffusion during thermal insulation; such use is decreasing as lead is phased out. Some countries are also reducing the use of lead in electronics solders to reduce environmentally hazardous waste. Lead is one of three metals used in the Oddy test for museum materials, helping to detect organic acids, aldehydes and acid gases.

Connections

Lead compounds are used as or in coloring agents, oxidizing agents, plastics, candles, glass and semiconductors. Lead-based dyes are used in ceramic glazes and glass, especially for reds and yellows. Lead tetraacetate and lead dioxide are used as oxidizing agents in organic chemistry. Lead is often used in PVC coatings on electrical cords. It can be used to treat candle wicks to provide a longer, more even burn. Due to lead's toxicity, European and North American manufacturers are using alternatives such as zinc. Lead glass consists of 12-28% lead oxide. It changes the optical characteristics of the glass and reduces the transmission of ionizing radiation. Lead semiconductors such as lead telluride, lead selenide, and lead antimonide are used in photovoltaic cells and infrared detectors.

Biological and environmental effects

Biological effects

Lead has no proven biological role. Its prevalence in the human body averages 120 mg in an adult—its prevalence is surpassed only by zinc (2500 mg) and iron (4000 mg) among heavy metals. Lead salts are absorbed very efficiently by the body. A small amount of lead (1%) will be stored in the bones; the rest will be excreted in urine and feces for several weeks after exposure. The child will be able to eliminate only about a third of the lead from the body. Chronic exposure to lead can lead to lead bioaccumulation.

Toxicity

Lead is an extremely toxic metal (if inhaled or ingested) that affects almost every organ and system in the human body. At levels in the air of 100 mg/m3, it poses an immediate danger to life and limb. Lead is quickly absorbed into the bloodstream. The main reason for its toxicity is its tendency to interfere with the proper functioning of enzymes. It does this by binding to sulfhydryl groups found on many enzymes or by mimicking and displacing other metals that act as cofactors in many enzymatic reactions. Among the main metals with which lead reacts are calcium, iron and zinc. High levels of calcium and iron generally provide some protection against lead poisoning; low levels cause increased susceptibility.

Effects

Lead can cause serious damage to the brain and kidneys and ultimately cause death. Like calcium, lead can cross the blood-brain barrier. It destroys the myelin sheaths of neurons, reduces their number, interferes with neurotransmission pathways and reduces neuronal growth. Symptoms of lead poisoning include nephropathy, cramping abdominal pain, and possibly weakness in the fingers, wrists, or ankles. Low blood pressure increases, especially in middle-aged and older people, which can cause anemia. In pregnant women, high levels of lead exposure can cause miscarriage. Chronic exposure to high levels of lead has been shown to reduce fertility in men. In the developing child's brain, lead interferes with the formation of synapses in the cerebral cortex, neurochemical development (including neurotransmitters), and the organization of ion channels. Early exposure to lead in children is associated with an increased risk of sleep disturbances and excessive daytime sleepiness later in childhood. High blood lead levels are associated with delayed puberty in girls. Increases and decreases in exposure to airborne lead from the combustion of tetraethyl lead in gasoline during the 20th century are associated with historical increases and decreases in crime rates, however, this hypothesis is not generally accepted.

Treatment

Treatment for lead poisoning usually involves administration of dimercaprol and succimer. Acute cases may require the use of calcium disodium edetate, a calcium chelate of ethylenediaminetetraacetic acid disodium salt (EDTA). Lead has a greater affinity for lead than calcium, causing the lead to be chelated by metabolism and excreted in the urine, leaving harmless calcium.

Sources of influence

Lead exposure is a global problem, as lead mining and smelting are common in many countries around the world. Lead poisoning usually occurs from ingestion of food or water contaminated with lead, and less commonly from accidental ingestion of contaminated soil, dust, or lead-based paint. Seawater products may contain lead if the water is exposed to industrial waters. Fruits and vegetables can be contaminated by high levels of lead in the soils in which they are grown. Soil can be contaminated by the accumulation of particulate matter from lead in pipes, lead paint, and residual emissions from leaded gasoline. The use of lead in water pipes is problematic in areas with soft or acidic water. Hard water forms insoluble layers in pipes, while soft and acidic water dissolves lead pipes. Dissolved carbon dioxide in transported water can lead to the formation of soluble lead bicarbonate; oxygenated water can similarly dissolve lead as lead(II) hydroxide. Drinking water can cause health problems over time due to the toxicity of dissolved lead. The harder the water, the more it will contain bicarbonate and calcium sulfate, and the more the inside of the pipes will be coated with a protective layer of lead carbonate or lead sulfate. Ingestion of lead paint is the main source of lead exposure in children. As the paint breaks down, it flakes off, grinds into dust, and then enters the body through hand contact or contaminated food, water, or alcohol. Ingestion of some folk remedies may result in exposure to lead or lead compounds. Inhalation is a second important route of exposure to lead, including for smokers and especially for lead workers. Cigarette smoke contains radioactive lead-210, among other toxic substances. Almost all inhaled lead is absorbed into the body; for oral administration, the rate is 20-70%, with children absorbing more lead than adults. Dermal exposure may be significant for a limited population of people working with organic lead compounds. The rate of absorption of lead into the skin is lower for inorganic lead.

Ecology

The extraction, production, use and disposal of lead and its products have caused significant pollution of the Earth's soils and waters. Atmospheric lead emissions were at their peak during the Industrial Revolution, and the gasoline lead period was in the second half of the twentieth century. Elevated lead concentrations persist in soils and sediments in post-industrial and urban areas; Industrial emissions, including those associated with coal combustion, continue in many parts of the world. Lead can accumulate in soils, especially those with high organic matter content, where it persists for hundreds to thousands of years. It can take the place of other metals in plants and can accumulate on their surfaces, thereby slowing down photosynthesis and preventing their growth or killing them. Soil and plant pollution affects microorganisms and animals. Affected animals have a reduced ability to synthesize red blood cells, causing anemia. Analytical methods for determining lead in the environment include spectrophotometry, x-ray fluorescence, atomic spectroscopy and electrochemical methods. A specific ion selective electrode was developed based on the ionophore S, S"-methylenebis (N, N-diisobutyl dithiocarbamate).

Limitation and recovery

By the mid-1980s, there was a significant shift in the use of lead. In the United States, environmental regulations are reducing or eliminating the use of lead in non-battery products, including gasoline, paints, solders and water systems. Particulate matter control devices can be used in coal-fired power plants to collect lead emissions. The use of lead is further limited by the European Union's Restriction of Hazardous Substances Directive. The use of lead bullets for hunting and sport shooting was banned in the Netherlands in 1993, resulting in a significant reduction in lead emissions from 230 tons in 1990 to 47.5 tons in 1995. In the United States, the Occupational Safety and Health Administration has set the occupational exposure limit for lead at 0.05 mg/m3 over an 8-hour workday; this applies to metallic lead, inorganic lead compounds and lead soaps. The US National Institute for Occupational Safety and Health recommends that blood lead concentrations be below 0.06 mg per 100 g of blood. Lead may still occur in harmful levels in ceramics, vinyl (used for pipe lining and electrical cord insulation) and Chinese brass. Older homes may still contain lead paint. White lead paint has been phased out in industrialized countries, but yellow lead chromate remains in use. Removing old paint by sanding produces dust that can be inhaled.