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LEAD- a chemical element of group IV of the periodic table. Relative atomic mass ( A r = 207.2) is an average of the masses of several isotopes: 204Pb (1.4%), 206Pb (24.1%), 207Pb (22.1%) and 208Pb (52.4%). The last three nuclides are the end products of natural radioactive transformations of uranium, actinium and thorium. More than 20 radioactive isotopes of lead are also known, of which the longest-lived ones are 202 Pb and 205 Pb (with half-lives of 300 thousand and 15 million years). In nature, short-lived isotopes of lead with mass numbers 209, 210, 212, and 214 are also formed with half-lives of 3.25 hours, 27.1 years, 10.64 hours, and 26.8 minutes, respectively. The ratio of different isotopes in different samples of lead ores may vary slightly, which makes it impossible to determine the value for lead A r with greater precision.
There is not much lead in the earth's crust - 0.0016% by mass, but this one of the heaviest metals is much more common than its closest neighbors - gold, mercury and bismuth. This is because different isotopes of lead are end products of the decay of uranium and thorium, so lead content in the earth's crust has slowly increased over billions of years.
There are many ore deposits rich in lead, and the metal is easily separated from the minerals. In total, more than a hundred lead minerals are known. Of these, the main ones are galena (lead luster) PbS and the products of its chemical transformations - anglesite (lead vitriol) PbSO 4 and cerussite ("white lead ore") PbCO 3. Less common are pyromorphite (“green lead ore”) PbCl 2 3Pb 3 (PO 4) 2, mimetite PbCl 2 3Pb 3 (AsO 4) 2, crocoite (“red lead ore”) PbCrO 4, wulfenite (“yellow lead ore ”) PbMoO 4 , Stolzite PbWO 4 . Lead ores often also contain other metals - copper, zinc, cadmium, silver, gold, bismuth, etc. In the place of occurrence of lead ores, soil (up to 1% Pb), plants and water are enriched with this element.
In the highly oxidizing alkaline environment of the steppes and deserts, the formation of lead dioxide, the mineral plattnerite, is possible. And extremely rare native metallic lead.
Story.
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, to “tin batteries” in cars. The English name for lead and the Dutch word for lead are probably related to our "tinker". The Latin plumbum (also of unclear origin) gave the English word plumber - a plumber (once pipes were minted 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 given to the 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 write on parchment, not without reason in German pencil - Bleistift, i.e. lead rod.
Lead, together with gold, silver, copper, tin, iron and mercury, is one of the seven metals known from ancient times. These metals were compared with the then known planets (Saturn corresponded to lead). It is believed that for the first time people smelted lead from ores 8 thousand years ago. Excavations in ancient Egypt have unearthed silver and lead artifacts in burials prior to the dynastic period. Similar finds made in Mesopotamia date back to the same time. Joint finds of silver and lead items are not surprising. Even in prehistoric times, the attention of people was attracted by beautiful heavy crystals of lead luster. Deposits of this mineral were found in the mountains of Armenia, in the central regions of Asia Minor. And the mineral galena often contains significant impurities of silver. If you put pieces of this mineral in a fire, the sulfur will burn out and molten lead will flow (charcoal prevents lead from oxidizing). Already many millennia before the new era in Mesopotamia, Egypt, statues were cast from it.
In the VI century. BC. rich deposits of galena were discovered in Lavrion, a mountainous area near Athens. During the Punic Wars (264-146 BC), numerous lead mines operated on the territory of modern Spain, which were laid by the Greeks and Phoenicians. Later they were developed by the Romans; Roman engineers used lead to make ancient plumbing pipes. The ancient Greek historian Herodotus (5th century BC) wrote about a method of strengthening iron and bronze staples in stone slabs by filling holes with fusible lead. Later, during the excavations of Mycenae, lead brackets were found in the stone walls.
When obtaining lead, ancient metallurgists first calcined the ore, while reactions took place
2PbS + 3O 2 ® 2PbO + 2SO 2 and PbS + 2O 2 ® PbSO 4 . Then the temperature was raised, which led to the smelting of lead:
PbS + 2PbO ® 3Pb + SO 2 ; PbS + PbSO 4 ® 2Pb + 2SO 2 . The first melting furnaces, made of clay and stones, were very primitive. They tried to install them on the slopes of the hills, where the winds blow, which help the firing. Smelted lead, as a rule, contained silver - sometimes up to 0.5% or more. With slow cooling of such a melt, pure lead first crystallizes, and the liquid is enriched in silver - up to about 2%. To isolate silver, the cupellation method was used: molten lead was oxidized in a porous clay vessel - fonts, and its oxide was then again reduced to metal. The mechanism of this process was studied only in 1833.
Lead was also used to purify gold and silver by cupellation. To do this, the precious metal to be purified was alloyed with lead. Lead and other impurities were easily oxidized at high temperature; the resulting oxides were blown away by an air stream, and partially absorbed into the pores of the font, and an ingot of pure silver or gold remained at the bottom. The lead oxide could then be turned back into a metal by heating it with charcoal. Archaeological finds in Ur and Troy testify that cupellation was known in the northwest of Asia Minor already in the first half of the 3rd millennium BC. And the Greek craftsmen managed to extract almost all the silver from the lead mined in Lavrion: according to modern analyzes, only 0.02% of it remained in lead! The art of the ancient metallurgists is worthy of surprise: after all, they had neither the ability to control the temperature at different stages of the process, nor to carry out chemical analyzes. And yet, there was a lot of unextracted lead in the mine dumps. Even better results were achieved by Roman metallurgists, halving the residual amount of silver. Of course, they were not worried about the purity of the lead, but about the completeness of the extraction of the precious metal from it. Moreover, as the Greek historian Strabo testifies, by processing the old dumps in Lavrion, the Romans were able to extract quite a lot of both lead and silver, leaving about two million tons of waste ore in the dumps. After that, the mines were abandoned for almost two millennia, but in 1864 they began to process the dumps again - now for the sake of only silver (about 0.01% of it remained in them). At modern metallurgical enterprises, hundreds of times less silver is left in lead.
Ancient potters, grinding the lead luster with clay and water, doused the clay vessels to be fired with this mixture. At high temperatures, the surface of the vessel was covered with fusible lead glass. In 1673, the English glassmaker George Ravenscroft, adding lead oxide to the composition of the glass, invented crystal glass, which melts easily, is perfectly workable and has a special brilliance that brings it closer to real rock crystal. Later, by fusing pure white sand, potash and lead oxide, they obtained a rhinestone (on behalf of the jeweler Strass, who lived at the end of the 18th century) - a type of glass with such a strong luster that it imitated a diamond well, and with an admixture of various pigments - other precious stones.
The wooden hulls of ancient ships were sheathed with thin lead plates. One such Greek ship, built in the 3rd c. 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 ever example of standardized industrial production. First, a plate was cast from lead, wrapped around a wooden rod, and the seam was sealed with tin-lead solder (its composition has remained virtually unchanged since then). Leaks were often found in the pipes, and they had to be repaired. Until now, during excavations in Italy and England, such pipes are found in very good condition. The Roman architect and engineer Marcus Vitruvius Pollio recommended replacing lead pipes with ceramic pipes made of fired clay. He drew attention to the sickness of the workers involved in the smelting of lead and believed that lead "deprives the blood of its strength." However, not everyone shared this opinion. So, the Roman statesman, scientist and writer Pliny, the author of the famous "Natural History", wrote about the benefits of lead preparations, that lead ointment helps to remove scars, heal ulcers and eye diseases.
In the Middle Ages, the roofs of churches and palaces were often covered with weather-resistant lead plates. As early as 669, the roof of the monastery church in York was covered with lead, and in 688 the bishop in Northumberland ordered that the roof and walls of the church be sheathed with lead plates. The famous stained-glass windows in the cathedrals were assembled using lead frames with grooves in which plates of colored glass were strengthened. Made of lead, following the example of the Romans, and plumbing, as well as drainage pipes. So, in 1532, square-section lead drainpipes were installed in the Palace of Westminster. All these products in those days were not rolled, but cast in molds, on the bottom of which finely sifted sand was poured. Over time, a strong protective layer appeared on lead products - patina. Some lead-lined medieval spiers have survived for nearly seven hundred years. Unfortunately, the fire of 1561 in London destroyed such a spire of the greatest St. Peter's Cathedral.
When firearms appeared, large quantities of lead were used to make bullets and shot, and lead also began to be associated with mortal danger: “Destructive lead will whistle around me” (A. Pushkin), “For your trench, another fighter put his chest under evil lead” ( K. Simonov). First, the shot was cast in detachable molds. In 1650, the English Prince Rupert invented a faster and more convenient way. He discovered that if a little arsenic was added to lead, and the alloy was poured through a sort of large colander into a tank of water, balls of shot were formed into regular spherical shapes. And after in 1436 Johannes Gutenberg invented a way to print books using movable metal characters, printers for hundreds of years cast letters from the so-called lead-based printing 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 are painted with paints prepared on the basis of white lead. The original was the old method of obtaining them: pots with strong vinegar were placed in manure, and thin lead plates twisted into a spiral were hung over them. Decaying, the manure gave heat (it is necessary for enhanced evaporation of acetic acid) and carbon dioxide. The joint action of these substances on lead, as well as atmospheric oxygen, gave white. In addition to toxicity, these whites darken over time, as they react with traces of hydrogen sulfide, which is always present in the air: 2PbCO 3 Pb (OH) 2 + 3H 2 S ® 3PbS + 2CO 2 + 4H 2 O. When restoring such paintings, darkened areas carefully treated with a solution of H 2 O 2, which converts black sulfide into white sulfate: PbS + 4H 2 O 2 ® PbSO 4 + 4H 2 O. Currently, poisonous lead white has been replaced by more expensive, but harmless titanium white. Pigments containing lead have limited use (for example, as pigments for art oil paints): lead crown lemon 2PbCrO 4 PbSO 4, lead crown yellow 13PbCrO 4 PbSO 4 , red lead-molybdate crown 7PbCrO 4 PbSO 4 PbMoO 4 .
lead properties.
Lead usually has a dirty gray color, although its fresh cut has a bluish tint and shines. However, the shiny metal is quickly covered with a dull gray oxide protective film. The density of lead (11.34 g / cm 3) is one and a half times that of iron, four times that of aluminum; even silver is lighter than lead. Not without reason, in Russian, “lead” is a synonym for heavy: “A rainy night, darkness spreads across the sky with lead clothes”; “And how the lead went to the bottom” - these Pushkin lines remind us that the concept of oppression, heaviness is inextricably linked with lead.
Lead melts very easily - at 327.5 ° C, boils at 1751 ° C and is noticeably volatile already at 700 ° C. This fact is very important for those working in lead mining and processing plants. Lead is one of the softest metals. It scratches easily with a fingernail and rolls into very thin sheets. Lead alloys with many metals. With mercury, it gives an amalgam, which, with a small content of lead, is liquid.
According to its chemical properties, lead is an inactive metal: in the electrochemical series of voltages, it stands directly in front of hydrogen. Therefore, lead is easily displaced by other metals from solutions of its salts. If a zinc stick is dipped into an acidified solution of lead acetate, lead is released on it in the form of a fluffy coating of small crystals, which has the old name "Saturn tree". If the reaction is halted by wrapping the zinc in filter paper, larger lead crystals will grow.
The most typical oxidation state for lead is +2; lead(IV) compounds are much less stable. In dilute hydrochloric and sulfuric acids, lead practically does not dissolve, including due to the formation of an insoluble chloride or sulfate film on the surface. With strong sulfuric acid (at a concentration of more than 80%), lead reacts with the formation of soluble hydrosulfate Pb (HSO 4) 2, and in hot concentrated hydrochloric acid, dissolution is accompanied by the formation of complex chloride H 4 PbCl 6 . Lead is easily oxidized with dilute nitric acid:
Pb + 4HNO 3 ® Pb (NO 3) 2 + 2NO 2 + H 2 O. The decomposition of lead (II) nitrate when heated is a convenient laboratory method for obtaining nitrogen dioxide:
2Pb(NO 3) 2 ® 2PbO + 4NO 2 + O 2 .
In the presence of oxygen, lead also dissolves in a number of organic acids. Under the action of acetic acid, a readily soluble acetate Pb (CH 2 COO) 2 is formed (the old name is “lead sugar”). Lead is also noticeably soluble in formic, citric and tartaric acids. The solubility of lead in organic acids may have previously led to poisoning if food was cooked in tin-plated or lead-soldered utensils. Soluble lead salts (nitrate and acetate) in water are hydrolyzed:
Pb (NO 3) 2 + H 2 O Pb (OH) NO 3 + HNO 3. A suspension of basic lead acetate ("lead lotion") has limited medical use as an external astringent.
Lead slowly dissolves in concentrated alkalis with hydrogen evolution: Pb + 2NaOH + 2H 2 O ® Na 2 Pb (OH) 4 + H 2, which indicates the amphoteric properties of lead compounds. White lead(II) hydroxide, which is easily precipitated from solutions of its salts, is also soluble in both acids and strong alkalis:
Pb (OH) 2 + 2HNO 3 ® Pb (NO 3) 2 + 2H 2 O; Pb (OH) 2 + 2NaOH ® Na 2 Pb (OH) 4. When standing or heating, Pb (OH) 2 decomposes with the release of PbO. When PbO is fused with alkali, plumbite of the composition Na 2 PbO 2 is formed.
From an alkaline solution of sodium tetrahydroxoplumbate Na 2 Pb (OH) 4, lead can also be displaced by a more active metal. If a small aluminum granule is placed in such a heated solution, a gray fluffy ball is quickly formed, which is saturated with small bubbles of evolving hydrogen and therefore floats up. If aluminum is taken in the form of a wire, the lead released on it turns it into a gray "snake".
When heated, lead reacts with oxygen, sulfur and halogens. So, in reaction with chlorine, PbCl 4 tetrachloride is formed - a yellow liquid that smokes in air due to hydrolysis, and when heated, it decomposes into PbCl 2 and Cl 2. (The halides PbBr 4 and PbI 4 do not exist, since Pb (IV) is a strong oxidizing agent that would oxidize bromide and iodide anions.) Finely ground lead has pyrophoric properties - it flares up in air. With prolonged heating of molten lead, it gradually turns first into yellow oxide PbO (lead litharge), and then (with good air access) into red minium Pb 3 O 4 or 2PbO PbO 2. This compound can also be considered as the lead salt of ortholeadic acid Pb 2 . With the help of strong oxidizing agents, for example, bleach, lead (II) compounds can be oxidized to dioxide:
Pb (CH 3 COO) 2 + Ca (ClO) Cl + H 2 O ® PbO 2 + CaCl 2 + 2CH 3 COOH. Dioxide is also formed when red lead is treated with nitric acid:
Pb 3 O 4 + 4HNO 3 ® PbO 2 + 2Pb (NO 3) 2 + 2H 2 O. If brown dioxide is heated strongly, then at a temperature of about 300 ° C it will turn into orange Pb 2 O 3 (PbO PbO 2), at 400° C - into red Pb 3 O 4, and above 530° C - into yellow PbO (decomposition is accompanied by the release of oxygen). In a mixture with anhydrous glycerin, lead litharge slowly reacts within 30-40 minutes to form a water-resistant and heat-resistant solid putty, which can be used to glue metal, glass and stone.
Lead dioxide is a strong oxidizing agent. A jet of hydrogen sulfide directed at dry dioxide ignites; concentrated hydrochloric acid is oxidized by it to chlorine:
PbO 2 + 4HCl ® PbCl 2 + Cl 2 + H 2 O, sulfur dioxide - to sulfate: PbO 2 + SO 2 ® PbSO 4, and Mn 2+ salts - to permanganate ions: 5PbO 2 + 2MnSO 4 + H 2 SO 4 ® 5PbSO 4 + 2HMnO 4 + 2H 2 O. Lead dioxide is formed and then consumed during charging and subsequent discharge of the most common acid batteries. Lead(IV) compounds have even more typical amphoteric properties. So, insoluble brown hydroxide Pb (OH) 4 is easily soluble in acids and alkalis: Pb (OH) 4 + 6HCl ® H 2 PbCl 6; Pb (OH) 4 + 2NaOH ® Na 2 Pb (OH) 6. Lead dioxide, reacting with alkali, also forms a complex plumbate (IV):
PbO 2 + 2NaOH + 2H 2 O ® Na 2. If PbO 2 is alloyed with solid alkali, a plumbate of composition Na 2 PbO 3 is formed. Of the compounds in which lead(IV) is a cation, tetraacetate is the most important. It can be obtained by boiling red lead with anhydrous acetic acid:
Pb 3 O 4 + 8CH 3 COOH ® Pb (CH 3 COO) 4 + 2Pb (CH 3 COO) 2 + 4H 2 O. When cooled, colorless lead tetraacetate crystals stand out from the solution. Another way is the oxidation of lead (II) acetate with chlorine: 2Pb (CH 3 COO) 2 + Cl 2 ® Pb (CH 3 COO) 4 + PbCl 2. Water tetraacetate instantly hydrolyzes to PbO 2 and CH 3 COOH. Lead tetraacetate finds use in organic chemistry as a selective oxidizing agent. For example, it very selectively oxidizes only some hydroxyl groups in cellulose molecules, while 5-phenyl-1-pentanol is oxidized by the action of lead tetraacetate with simultaneous cyclization and the formation of 2-benzylfuran.
Organic lead derivatives are colorless, highly toxic liquids. One of the methods for their synthesis is the action of alkyl halides on an alloy of lead with sodium:
4C 2 H 5 Cl + 4PbNa ® (C 2 H 5) 4 Pb + 4NaCl + 3Pb. By the action of gaseous HCl, one alkyl radical after another can be cleaved from tetrasubstituted lead, replacing them with chlorine. R 4 Pb compounds decompose on heating to form a thin film of pure metal. This decomposition of tetramethyllead was used to determine the lifetime of free radicals. Tetraethyl lead is an antiknock motor fuel.
Getting lead.
The amount of lead produced is continuously increasing. If in 1800 about 30,000 tons were received all over the world, then in 1850 - 130,000 tons, in 1875 - 320,000 tons, in 1900 - 850,000 tons, in 1950 - almost 2 million tons, and now a year about 5 million tons are mined. In terms of production, lead ranks fourth among non-ferrous metals - after aluminum, copper and zinc.
The main source of lead is polymetallic sulfide ores containing from 1 to 5% lead. The ore is concentrated to a lead content of 40 - 75%, then it is roasted: 2PbS + 3O 2 ® 2PbO + 2SO 2 and the lead is reduced with coke and carbon monoxide (II). A more economical, so-called autogenous, method consists in carrying out the reaction PbS + 2PbO ® 3Pb + SO 2 (PbO is formed during partial roasting of PbS). Lead obtained from ore contains from 3 to 7% impurities in the form of copper, antimony, arsenic, tin, aluminum, bismuth, as well as gold and silver. Their removal (or isolation, if it is economically viable) requires complex and time-consuming operations. Lead can also be purified by electrochemical refining. The electrolyte is an aqueous solution of lead fluorosilicate PbSiF 6 . Pure lead settles on the cathode, and impurities are concentrated in the anode sludge, which contains many valuable components, which are then isolated.
Lead in the human body.
Lead compounds are poisonous. But this was not immediately obvious. In the past, covering pottery with lead glaze, making lead water pipes, using white lead (especially for cosmetic purposes), and using lead pipes in vapor condensers in distilleries have all led to lead accumulation in the body. The ancient Greeks knew that wine and sour juices could not be kept in glazed earthenware vessels (the glaze contained lead), but the Romans ignored this rule. James Lind, who in 1753 recommended lemon juice to the English Admiralty as a remedy for scurvy for sailors on a long voyage, warned against storing the juice in glazed pottery. Nevertheless, cases of poisoning, including fatal ones, were observed for the same reason two hundred years later.
Lead enters the body through the gastrointestinal tract or the respiratory system and is then carried by the blood throughout the body. Moreover, inhalation of lead dust is much more dangerous than the presence of lead in food. In the air of cities, the content of lead averages from 0.15 to 0.5 µg/m 3 . In areas where polymetallic ores processing facilities are located, this concentration is higher.
Lead accumulates in the bones, partially replacing calcium in Ca 3 (PO 4) 2 phosphate. Getting into soft tissues - muscles, liver, kidneys, brain, lymph nodes, lead causes a disease - plumbism. Like many other heavy metals, lead (in the form of ions) blocks the activity of certain enzymes. It was found that their activity decreases 100 times with an increase in the concentration of lead in the blood by 10 times - from 10 to 100 micrograms per 100 ml of blood. At the same time, anemia develops, the hematopoietic system, kidneys and brain are affected, intelligence decreases. A sign of chronic poisoning is a gray border on the gums, a disorder of the nervous system. Lead is especially dangerous for children, as it causes developmental delays. At the same time, tens of millions of children around the world under the age of 6 have lead poisoning; the main reason is the ingestion of paint containing lead into the mouth. The calcium salt of ethylenediaminetetraacetic acid can serve as an antidote for poisoning. In a poisoned organism, calcium is replaced by lead ions, which are held very firmly in this salt and are excreted in this form.
Lead can easily enter the body with drinking water if it comes into contact with metal: in the presence of carbon dioxide, soluble bicarbonate Pb (HCO 3) 2 slowly passes into the solution. In ancient Rome, where lead pipes were used to supply water, such poisoning was very common, as analysis of the remains of the Romans indicates. Moreover, it was mostly wealthy Romans who were poisoned, who used plumbing, stored wine, olive oil and other products in leaded vessels, and used lead-containing cosmetics. It is enough that there is only one milligram of lead in a liter of water - and drinking such water becomes very dangerous. This amount of lead is so small that it does not change the smell or taste of water, and only accurate modern instruments can detect it.
Some historians also explain the morbidity of a number of Russian tsars with lead poisoning. In 1633, the construction of a water pipe was completed in the Moscow Kremlin. Water came into it from a well in the lower floor of the Sviblova tower, which stood at the confluence of the Neglinnaya and Moscow rivers. Water was pumped from the well with the help of a lifting machine - a platoon (since then this Kremlin tower has been called Vodovzvodnaya). The car was driven by horses. Water was pumped into a large tank, and from there the water itself flowed through pipes to the royal kitchen, gardens, and other places. The pipes were made of lead; the inside of the water tank was also lined with lead sheets so that water from it would not seep into the cracks. Especially a lot of lead accumulated in the water during the night, after its motionless standing in the lead tank and pipes.
The Kremlin's "lead plumbing" worked for a little over 100 years - it was destroyed by a fire in 1737. And during the operation of this plumbing, Russian tsars lived less than usual. So, the Tsar and Grand Duke Ivan V Alekseevich, the son of Tsar Alexei Mikhailovich and his first wife, Miloslavskaya, lived only 29 years. Shortly before his death, he looked like a decrepit old man. From childhood, he was, as they wrote then, "weak and sickly, weak in body and mind, stuttered, mournful in head, suffered from scurvy and eye disease." Of the six brothers of the king, five did not live to be 20 years old. Some scientists believe that these are the consequences of lead poisoning. But the sixth brother, Peter Alekseevich, the future Peter I, escaped poisoning - he spent his childhood and adolescence not in the Kremlin, but in villages near Moscow. And later, he rarely visited the Kremlin - he fought a lot, traveled around Europe, and then completely transferred the capital to the banks of the Neva. By the way, the first water pipe in St. Petersburg, which provided water for the palaces and fountains of the Summer Garden, was wooden. His pipes were made from logs with holes drilled into them. Peter used lead for military purposes - for casting bullets.
And here is how modern medical reference books write about lead poisoning: lethargy, apathy, memory loss, dementia praecox, visual impairment, patients look older than their years. Surprisingly reminiscent of the old description of Tsar Ivan Alekseevich!
Once upon a time, they were poisoned not only with “lead water”. Lead was widely used in the manufacture of dishes (lead glaze), lead white, which was used to paint the walls of houses. This use of lead is now strictly prohibited. White, for example, make zinc or titanium. Nevertheless, people in industrialized countries have more lead in their bodies than people in backward and developing countries, and people in urban areas have more lead than people in rural areas. The difference can be huge - hundreds of times.
Lead pollution acquired in the 20th century. global character. Even in the snows of Greenland, its content has increased five times over a hundred years, and in the centers of large cities in the soil and plants there is 25 times more lead than on the outskirts! Lead pollution occurs in lead mining areas, as well as in processing areas and on motorways, especially if leaded gasoline is still being used. A lot of lead settles at the bottom of lakes in the form of hunting shot. Every year, more than half a million tons of this poisonous metal enters the oceans with wastewater. And who has not seen used batteries thrown into garbage cans, or even simply into ditches! As long as lead is cheap, collecting and processing its waste is unprofitable. The low solubility of most lead compounds, fortunately, does not allow it to accumulate in significant amounts in water. In the waters of the World Ocean, it contains an average of 0.03 μg / l (3 10 -9%). There is little on average lead in living matter - 10-4%.
The use of lead.
Despite the toxicity of lead, it is impossible to refuse it. Lead is cheap - half the price of aluminum, 11 times cheaper than tin. After the French physicist Gaston Plante invented the lead accumulator in 1859, millions of tons of lead have since been used to make accumulator plates; Currently, up to 75% of all lead produced in a number of countries is used for these purposes! The use of lead for the manufacture of a very poisonous antiknock agent, tetraethyl lead, is gradually decreasing. The ability of tetraethyl lead to improve the quality of gasoline was discovered by a group of young American engineers in 1922; in their search, they were guided by the periodic table of elements, systematically approaching the most effective means. Since then, the production of tetraethyl lead has grown continuously; the maximum falls on the end of the 1960s, when hundreds of thousands of tons of lead were emitted with exhaust annually in the USA alone - one kilogram per inhabitant! In recent years, the use of leaded gasoline has been banned in many regions and its production has been declining.
Soft and ductile lead, which does not rust in the presence of moisture, is an indispensable material for the manufacture of sheaths of electrical cables; up to 20% of lead is spent for these purposes in the world. Low-level lead is used for the manufacture of acid-resistant equipment for the chemical industry, for example, for lining reactors in which hydrochloric and sulfuric acids are produced. Heavy lead retains radiation that is harmful to humans, and therefore lead screens are used to protect workers in X-ray rooms, and radioactive preparations are stored and transported in lead containers. Lead is also contained in babbitt bearing alloys, "soft" solders (the most famous is "tretnik" - an alloy of lead and tin).
In construction, lead is used to seal joints and create earthquake-resistant foundations. In military technology - for the manufacture of shrapnel and bullet cores.
Ilya Leenson
Literature:
History of Technology. Vol. I–V. Oxford: Clarendon Press, 1956–1958
Chisolm J.J. Lead Poisoning. Scientific American, 1971, February
Lead. Geneva: UN and WHO Press, 1980
Polyansky N.G. Lead. M., "Science", 1986
Davydova S.L., Pimenov Yu.T., Milaeva E.R. Mercury, tin, lead and their organic derivatives in the environment. Astrakhan, 2001
Lead is often called one of the most ancient metals in terms of history, since mankind learned how to mine and process it as early as 6400 BC. The "industrial" scale of lead processing was noted in Ancient Rome (about 80 thousand tons annually), which was explained by the availability of this metal and the ease of its smelting. The Romans made pipes from it for their water pipes, but even then they knew about the toxicity of the substance.
Physical properties of lead
Lead is a heavy metal with an atomic mass of 207.2 g/mol. At the same time, clean it is so soft that it can be cut with a knife. The main physical characteristics of lead:
- density (n.a.) - 11.3415 g / cm³
- melting temperature - 327.46°C (600.61 K)
- boiling point - 1749°C (2022 K)
- thermal conductivity (at 300 K) – 35.3 W/(m K)
- tensile strength - 12-13 MPa
Lead: chemical properties
In chemical compounds, the element Pb reaches two oxidation states: +2 and +4, in which it is able to exhibit both metallic and non-metallic properties. Soluble lead salts are represented by:
- acetate Pb (CH 3 COO) 2
- nitrate Pb (NO 3) 2
- sulfate PbSO 4
- chromate PbCrO 4
At ordinary temperatures, lead does not dissolve in pure water, which cannot be said about water saturated with oxygen. Also, the Pb element quickly dissolves in dilute nitric acid and concentrated sulfuric acid. Diluted sulfuric acid has no effect on lead, while hydrochloric acid has little effect. As for alkaline media, in them, as well as in acidic solutions, lead is converted into a reducing agent. At the same time, water-soluble lead, in particular its acetate, is very toxic.
Lead Application
Pure lead is used in medicine (X-ray machines), geology (its isotopes help determine the age of rocks), but it is most widely used in compounds:
- lead sulfides and iodides are used in the manufacture of batteries
- nitrates and azides - for the manufacture of explosives
- dioxides and chlorides - for chemical current sources
- arsenites and arsenates - in agriculture for the destruction of harmful insects
- tellurides - for the production of thermoelectric generators and refrigeration units
It is also known that lead delays radiation, which is explained by its ability to perfectly absorb g-radiation. As a result, Pb is the main element for the manufacture of radiation shielding materials used in the creation of nuclear reactors and X-ray installations.
Lead (Latin name plumbum) is a chemical element, a metal with atomic number 82. In its pure form, the substance has a silvery, slightly bluish tint.
Due to the fact that lead is widely distributed in nature, it is easy to mine and process, this metal has been known to mankind since ancient times. It is known that people used lead as early as the 7th millennium BC. Lead was mined and processed in ancient Egypt and later in ancient Rome. Lead is quite soft and pliable, so even before the invention of smelting furnaces, it was used to make metal objects. For example, the Romans made pipes from lead for the water supply network.
In the Middle Ages, lead was used as a roofing material and for the production of seals. For a long time, people did not know about the dangers of the substance, so it was mixed into wine and used in construction. Even into the 20th century, lead was added to printing ink and gasoline additives.
Lead properties
In nature, lead is most often found in the form of compounds that are part of ores. Ores are mined, and then a pure substance is isolated industrially. The metal itself, as well as its compounds, have unique physical and chemical properties, which explains the widespread use of lead in various industries.
Lead has the following properties:
- very soft, obedient metal that can be cut with a knife;
- heavy, denser than iron;
- melts at relatively low temperatures (327 degrees);
- oxidizes rapidly in air. A piece of pure lead is always covered with a layer of oxide.
Lead toxicity
Lead has one unpleasant feature: it and its compounds are toxic. Lead poisoning is chronic: with constant intake into the body, the element accumulates in the bones and organs, causing serious disorders. 
For a long time, the volatile compound tetraethyl lead was used to improve gasoline, which caused environmental pollution in cities. Now in civilized countries the use of this additive is prohibited.
Lead Application
The toxicity of lead is now well known. At the same time, lead and its compounds can be of great benefit if used rationally and competently.
The efforts of scientists and developers are aimed at making the most of the beneficial properties of lead, reducing its danger to humans. Lead is used in a variety of industries, including:
— in medicine and other areas where radiation protection is needed. Lead does not transmit any radiation well, so it is used as a shield. In particular, lead plates are sewn into aprons that are worn by patients for safety during x-ray examinations. The protective properties of lead are used in the nuclear industry, science, and the production of nuclear weapons;
— in the electrical industry. Lead is not very susceptible to corrosion - this property is actively used in electrical engineering. Lead-acid batteries are the most widely used. Lead plates are installed in them, immersed in an electrolyte. The galvanic process makes it possible to obtain an electric current sufficient to start a car engine. The battery industry is the largest consumer of lead in the world. In addition, lead is used to protect cables, the production of cable cabins, fuses, superconductors;
— in the military industry. Lead is used to make bullets, shot, and shells. Lead nitrate is part of explosive mixtures, lead azide is used as a detonator;
— in the production of dyes and building mixtures. Lead white, extremely common before, is now giving way to other paints. Lead is used in the production of putties, cement, protective coatings for and ceramics. 
Due to the toxicity of lead, they try to limit the use of this metal, replacing it with alternative materials. Much attention is paid to the safety of production related to lead, the disposal of products containing this element, as well as to reduce the contact of lead parts with humans and the release of substances into the environment.
physical properties. Lead is a heavy non-ferrous bluish-gray metal, its fresh fracture has a strong metallic luster. Like most metals, lead crystallizes in the regular system, producing imperfect cubes and octahedrons.
Pure lead is very soft and easily traced with a fingernail. Its hardness depends on the method of cooling and the presence of impurities. Slowly cooled lead is softer than rapidly cooled lead.
Impurities greatly change the mechanical and physicochemical properties of lead. Some additives significantly improve mechanical properties (strength, hardness, creep resistance) while maintaining high corrosion resistance.
Lead is a very ductile metal, easily forged and rolled into the thinnest foil. Due to its exceptional softness and malleability, it is easily extruded into solid and hollow cylinders at temperatures below its melting point. But at the same time, lead has such low malleability that it is almost impossible to draw a thin wire out of it, as a result of which the wire is squeezed out and pressed in the same way as lead pipes are made.
Lead lends itself well to processing, has good casting properties, but low mechanical strength and relatively high creep limit its use as a structural material.
Lead easily alloys with some metals, giving simple and complex alloys. The main lead alloys are bearing (babbits), wrought (for cable sheaths), printing alloys and solders. Lead babbits contain, in addition to the main component - lead, sodium, calcium and other elements. Tin babbits, in addition to lead and tin, contain copper, antimony, cadmium, nickel, tellurium, etc.
Lead sodium-calcium babbits have good mechanical anti-friction properties, which allows them to be used for filling bearings.
The composition of wrought lead alloys includes tin, copper, tellurium and antimony as additives.
Lead based printing alloys contain antimony, tin and copper.
To characterize the physical properties of lead, we present some numerical data borrowed from the literature.
The melting point of lead is 327°C; boiling point 1750 ° C. The saturated vapor pressure of lead, depending on the temperature, is as follows:
The bulk density of solid lead ranges from 11.273-11.48 g/cm3.
The bulk density of liquid lead varies with temperature:
The heat of fusion of lead at 327°C is 5100 j/mol*°K. The change in the heat of fusion depending on the temperature is expressed by the following relationship:
The dependence of the heat of vaporization of lead on temperature is as follows:
Average specific heat capacity of lead:
- solid:
- liquid:
Surface tension versus temperature:
Viscosity of lead as a function of temperature:
The hardness of lead according to Brinell is 3.8-4.2 kg/mm2.
Outflow pressure of high purity lead 6.6 kg/mm2. Heat flow for solid and liquid lead at different temperatures:
From the above figures it can be seen that lead is a fusible metal, but already at low temperatures it has a noticeable volatility, which increases with temperature.
From the volatility of lead and its compounds, losses in metallurgical production increase, which forces us to take a number of measures to trap lead vapors. Some impurities, such as arsenic and antimony, increase the volatility of lead.
Lead is a very fluid metal, its viscosity is only 2 times greater than that of water. Lead is a poor conductor of electric current, with respect to silver its conductivity is less than 0.1.
Chemical properties. Lead is a chemical element of group IV of the periodic system D.I. Mendeleev. Its serial number is 82. The atomic weight is 207.21. Valence 2 and 4. In completely dry air, lead does not change chemically. In humid air containing carbon dioxide, lead tarnishes, becoming covered with a film of nitrous oxide Pb2O, which slowly turns into the basic carbonate 3PbCO3 * Pb (OH) 2. Molten lead in the presence of air slowly oxidizes to nitrous oxide, which, when the temperature rises, turns into PbO oxide (litharge).
With prolonged heating of molten lead in an air atmosphere in the range from 330 to 450 ° C, the resulting litharge turns into lead trioxide Рb2О3; in the range from 450 to 470 ° C, minium Pb3O4 is formed. Both Pb2O3 and Pb3O4 decompose with increasing temperature.
The dissociation of Pb3O4 proceeds according to the reaction
The relationship between the pressure p of the dissociation of Pb3O4 and the temperature is expressed by the following figures:
All lead oxides, except PbO oxide, are unstable at elevated temperatures and dissociate into PbO and O2.
Carbon dioxide has a slight oxidizing effect on lead.
Pure water reacts with lead only in the presence of oxygen and, upon prolonged exposure, forms loose lead oxide hydrate.
Hydrochloric and sulfuric acids act only on the surface of lead, since the resulting chloride (PbCl2) and sulfate (PbSO4) lead are almost insoluble and protect the underlying metal layer from further action of acids. Concentrated sulfuric acid dissolves lead only at temperatures above 200 ° C. In addition, lead is chemically resistant to the following substances; mixtures of sulfuric and nitric acids, nitroses, alkalis, ammonia and ammonia salts, chlorine and chlorine-containing solutions, hydrofluoric acid and its salts, most organic acids, potassium cyanide, phosphoric anhydride, molten borax and oils.
The best lead solvent is nitric acid.
The use of lead. Lead has a number of valuable properties that ensure its use in various fields of industry.
A very large consumer of lead is the battery industry. Lead is used to make battery plates, the grids of which are made of a lead-antimony alloy and filled with a mixture of lead and litharge. The need for lead-acid batteries is constantly increasing due to the growth in the production of cars and tractors.
In the electrical industry, lead is used in the manufacture of cables to cover them with a corrosion-resistant sheath.
Lead is used for the manufacture of chemical compounds (white, red lead, litharge, nitride) and for chemical apparatus and mechanical engineering. Lead is consumed in large quantities in the production of sulfuric acid, bleaching salts, rayon, cellulose, etc. Lead is widely used in the production of bound nitrogen, alum, in the fat and soap industries.
In metallurgical production, lead is used in many hydrometallurgical installations, in electrolytic refining and in dust collectors.
Widely used lead alloys with other metals included in a large group of bronzes, brass, babbits and solders. These alloys are used for bearings in mechanical engineering and electrical engineering. Of great importance is the typographic alloy.
Lead is better than other materials capable of absorbing gamma rays, due to which it is used in the use of atomic energy.
Lead is also used in modern military technology.
The use of lead tetraethyl as an additive to gasoline to reduce its explosiveness (anti-knock) and to improve its quality are also major lead consumption items.
In modern technology, there is a tendency to replace lead with other materials. To cover cables, instead of lead, aluminum and plastic polyethylene sheaths are used in increasing quantities.
Lead pigment products have been successfully replaced by titanium based pigments.
Lead used for anti-corrosion coatings can in some cases be replaced by synthetic chemical materials. Lead foil has been successfully replaced with aluminum foil. The introduction of zinc alloys in the printing industry. instead of lead antimony should also reduce the consumption of lead.
This video will continue the story about the properties of lead:
Electrical conductivity
The thermal and electrical conductivity of metals correlate quite well with each other. Lead does not conduct heat very well and is not one of the best conductors of electricity either: the resistivity is 0.22 ohm-sq. mm / m with a resistance of the same copper 0.017.
Corrosion resistance
Lead is a non-precious metal, however, in terms of chemical inertness, it approaches those. Low activity and the ability to be covered with an oxide film and causes decent corrosion resistance.
In a humid, dry atmosphere, the metal practically does not corrode. Moreover, in the latter case, hydrogen sulfide, carbonic anhydride and sulfuric acid - the usual "culprits" of corrosion, do not affect it.
Corrosion indicators in different atmospheres are as follows:
- urban (smog) – 0.00043–0.00068 mm/year,
- in sea (salt) - 0.00041–0.00056 mm/year;
- rural – 0.00023–.00048 mm/year.
No exposure to fresh or distilled water.
- The metal is resistant to chromic, hydrofluoric, concentrated acetic, sulfurous and phosphoric acids.
- But in dilute acetic or nitrogen with a concentration of less than 70%, it quickly collapses.
- The same applies to concentrated - more than 90%, sulfuric acid.
Gases - chlorine, sulfur dioxide, hydrogen sulfide do not affect the metal. However, under the influence of hydrogen fluoride, lead corrodes.
Its corrosion properties are affected by other metals. So, contact with iron does not affect the corrosion resistance in any way, and the addition of bismuth or reduces the resistance of the substance to acid.
Toxicity
Both lead and all its organic compounds are class 1 chemically hazardous substances. The metal is very toxic, and poisoning with it is possible in many technological processes: smelting, making lead paints, ore mining, and so on. Not so long ago, less than 100 years ago, household poisoning was no less common, since lead was even added to whitewash for the face.
The greatest danger is metal vapor and its dust, since in this state they most easily penetrate the body. The main route is the respiratory tract. Some can also be absorbed through the gastrointestinal tract and even the skin with direct contact - the same lead white and paint.
- Once in the lungs, lead is absorbed by the bloodstream, spreads throughout the body and accumulates mainly in the bones. Its main poisoning effect is associated with disturbances in the synthesis of hemoglobin. Typical signs of lead poisoning are similar to anemia - fatigue, headaches, sleep and digestion disorders, but are accompanied by constant aching pains in the muscles and bones.
- Prolonged poisoning can cause "lead paralysis". Acute poisoning provokes an increase in pressure, sclerosis of blood vessels, and so on.
The treatment is specific and long-term, since it is not easy to remove heavy metal from the body.
We will discuss the environmental properties of lead below.
Environmental performance
Lead pollution is considered one of the most dangerous. All products that use lead require special disposal, which is carried out only by licensed services.
Unfortunately, lead pollution is provided not only by the activities of enterprises, where it is at least somehow regulated. In urban air, the presence of lead vapors ensures the combustion of fuel in cars. Against this background, the presence of lead stabilizers in such, for example, familiar structures as a metal-plastic window no longer seems worthy of attention.
Lead is a metal that has. Despite the toxicity, it is used too widely in the national economy to be able to replace the metal with something.
This video will tell about the properties of lead salts:
