Pb lead. The use of lead metal in the national economy and construction

Lead is a soft, heavy, silvery-gray metal that is lustrous but loses its luster fairly quickly. On a par with and refers to the elements known to mankind since ancient times. Lead was used very widely, and even now its use is extremely diverse. So, today we will find out whether lead is a metal or non-metal, as well as a non-ferrous or ferrous metal, learn about its types, properties, applications and extraction.

Lead is an element of group 14 of the table of D. I. Mendeleev, located in the same group with carbon, silicon and tin. Lead is a typical metal, but inert: it reacts extremely reluctantly even with strong acids.

The molecular weight is 82. This not only indicates the so-called magic number of protons in the nucleus, but also the large weight of the substance. The most interesting qualities of the metal are associated precisely with its large weight.

The concept and features of lead metal are discussed in this video:

Concept and features

Lead is a fairly soft metal. normal temperature, it is easy to scratch or flatten. Such ductility makes it possible to obtain sheets and bars of metal of very small thickness and any shape. Malleability was one of the reasons why lead has been used since antiquity.

Lead water pipes of ancient Rome are well known. Since then, this kind of water supply has been installed more than once and in more than one place, but it did not work for so long. Which, no doubt, saved a considerable amount human lives, since lead, alas, upon prolonged contact with water, eventually forms soluble compounds that are toxic.

Toxicity is the very property of the metal, due to which they try to limit its use. Metal vapors and many of its organic and inorganic salts are very dangerous for both the environment and people. Basically, of course, the workers of such enterprises and residents of the area around the industrial facility are at risk. 57% is emitted together with large volumes of dusty gas, and 37% - with converter gases. There is only one problem with this - the imperfection of purification plants.

However, in other cases, people become victims of lead contamination. Until recently, tetraethyl lead has been the most effective and popular gasoline stabilizer. During the combustion of fuel, it was released into the atmosphere and polluted it.

But lead has another, extremely useful and necessary quality- the ability to absorb radioactive radiation. Moreover, the metal absorbs the hard component even better than the soft one. A lead layer 20 cm thick is capable of protecting against all types of radiation known on Earth and in near space.

Advantages and disadvantages

Lead combines properties that are extremely useful, turning into an irreplaceable element, and frankly dangerous, which make its use a very difficult task.

The advantages from the point of view of the national economy include:

• fusibility and malleability - this allows you to form metal products of any degree of complexity and any subtlety. So, for the production of sound-absorbing membranes, lead plates with a thickness of 0.3–0.4 mm are used;
• lead is able to form an alloy with other metals (including, etc.) which under normal conditions do not alloy with each other, its use as a solder is based on this quality;
• metal absorbs radiation. Today, all elements of protection against radiation - from clothing to the decoration of X-ray rooms and rooms at test sites, are made from lead;
• the metal is resistant to acids, second only to noble gold and silver. So it is actively used for lining acid-resistant equipment. For the same reasons, pipes are made from it for the transfer of acid and for effluents in hazardous chemical plants;
• the lead battery has not yet lost its importance in electrical engineering, as it allows you to get a high voltage current;
• low cost - lead is 1.5 times cheaper than zinc, 3 times copper, and almost 10 times tin. This explains the very great advantage of using lead, and not other metals.

The disadvantages are:

• toxicity - the use of metal in any type of production is a danger to personnel, and in case of accidents it is an extreme danger to the environment and the population. Lead belongs to substances of the 1st hazard class;
• Lead products should not be disposed of as normal trash. They require disposal and are sometimes very costly. Therefore the question of recycling metal is always up to date;
• lead is a soft metal, so it can be used as structural material can not. Considering all his other qualities, this should rather be considered a plus.

Properties and characteristics

Lead is a soft, malleable, but heavy and dense metal. The molecular lattice is cubic, face-centered. Its strength is low, but its ductility is excellent. The physical characteristics of the metal are as follows:

• density at normal temperature 11.34 g/cc;
• melting point - 327.46 C;
• boiling point - 1749 C;
• resistance to tensile load - 12–3 MPa;
• resistance to compressive load - 50 MPa;
• Brinell hardness - 3.2–3.8 HB;
• thermal conductivity - 33.5 W / (m K);
• resistivity is 0.22 ohm-sq. mmm.

Like any metal, it conducts electric current, although, it should be noted, it is much worse than copper - almost 11 times. However, the metal has another interesting property: at a temperature of 7.26 K, it becomes a superconductor and conducts electricity without any resistance. Lead was the first element to exhibit this property.

In air, a piece of metal or a product made of it is rather quickly passivated by an oxide film, which successfully protects the metal from external influences. And the substance itself is not prone to chemical activity, which is why it is used in the manufacture of acid-resistant equipment.

Paints containing lead compounds are almost as resistant to corrosion. Due to toxicity, they are not used indoors, but they are successfully used in painting bridges, for example, frame structures, and so on.

The video below will show you how to make pure lead:

Structure and composition

In the entire temperature range, only one modification of lead is isolated, so both under the influence of temperature and over time, the properties of the metal change quite naturally. No abrupt transitions, when the qualities change dramatically, were noted.

Metal production

Lead is quite common, forms several industrially significant minerals - galena, cerussite, anglesite, so its production is relatively cheap. pyrometallurgical and hydrometallurgical methods. The second method is safer, but it is used much less frequently, since it is more expensive, and the resulting metal still needs to be finished at a high temperature.

Production by the pyrometallurgical method includes the following stages:

• ore mining;
• crushing and enrichment mainly by the flotation method;
• smelting in order to obtain crude lead - reduction, hearth, alkaline, and so on;
• refining, that is, cleaning black lead from impurities and obtaining pure metal.

Despite the same production technology, equipment can be used in a variety of ways. It depends on the metal content in the ore, production volumes, product quality requirements, and so on.

Read about the use and price for 1 kg of lead below.

Application area

The first - the manufacture of water pipes and household items, fortunately, dates back to quite ancient times. Today, metal enters the home only with a protective layer and in the absence of contact with food, water and humans.

• But the use of lead for alloys and as solder began at the dawn of civilization and continues to this day.
• Lead is a metal of strategic importance, especially since bullets have been cast from it. Ammunition for small arms and sporting weapons is still made only from lead. And its compounds are used as explosives.
• 75% of the metal produced in the world is used for the production of lead batteries. The substance continues to be one of the main elements of chemical current sources.
• The corrosion resistance of the metal is exploited in the manufacture of acid-resistant equipment, pipelines, as well as protective sheaths for power cables.
• And, of course, lead is used in the equipment of X-ray rooms: wall, ceiling, floor cladding, protective partitions, protective suits - everything is made with lead. At test sites, including nuclear ones, metal is indispensable.

The cost of metals is determined on several exchanges of world importance. The most famous is the London Metal Exchange. The cost of lead in October 2016 is $2,087.25 per ton.

Lead is a metal very much in demand in modern industry. Some of its qualities - corrosion resistance, the ability to absorb hard radiation - are completely unique and make the metal indispensable despite its high toxicity.

This video will tell you what happens if you pour lead into water:

Lead is in many ways an ideal metal, because it has a lot of advantages important for industry. The most obvious of them is the relative ease of obtaining it from ores, which is explained by the low melting point (only 327°C). When processing the most important lead ore - galena - the metal is easily separated from sulfur. To do this, it is enough to burn galena mixed with coal in air.

Due to its high ductility, lead is easily forged, rolled into sheets and wire, which makes it possible to use it in the engineering industry for the manufacture of various alloys with other metals. The so-called babbits (bearing alloys of lead with tin, zinc and some other metals), printing alloys of lead with antimony and tin, and lead-tin alloys for soldering various metals are widely known.

Metallic lead is a very good protection against all types of radioactive radiation and X-rays. It is introduced into the rubber of the apron and protective gloves of the radiologist, delaying X-rays and protecting the body from their destructive effects. Protects from radioactive radiation and glass containing oxides of lead. Such lead glass makes it possible to control the processing of radioactive materials with the help of a "mechanical arm" - a manipulator.

When exposed to air, water and various acids, lead exhibits greater stability. This property allows it to be widely used in the electrical industry, especially for the manufacture of batteries and cable cuttings. The latter are widely used in the aircraft and radio industries. The stability of lead allows it to be used to protect copper wires of telegraph and telephone lines from damage. Thin lead sheets cover iron and copper parts exposed to chemical attack (baths for the electrolysis of copper, zinc and other metals).

Lead and electrical engineering

Especially a lot of lead is consumed by the cable industry, where telegraph and electric wires are protected from corrosion during underground or underwater laying. A lot of lead is also used in the manufacture of low-melting alloys (with bismuth, tin and cadmium) for electrical fuses, as well as for precise fitting of contacting parts. But the main thing, apparently, is the use of lead in chemical current sources.

Since its inception, the lead battery has undergone many design changes, but its basis has remained the same: two lead plates immersed in a sulfuric acid electrolyte. Lead oxide paste is applied to the plates. When the battery is charged, hydrogen is released on one of the plates, reducing the oxide to metallic lead, and on the other, oxygen is released, converting the oxide into peroxide. The whole structure is converted into a galvanic cell with electrodes made of lead and lead peroxide. In the process of discharging, the peroxide deoxidizes, and metallic lead turns into an oxide. These reactions are accompanied by the appearance of an electric current that will flow through the circuit until the electrodes become the same - covered with lead oxide.

The production of alkaline batteries has reached gigantic proportions in our time, but it has not displaced lead batteries. The latter are inferior to alkaline ones in strength, they are heavier, but they give a higher voltage current. So, to power the autostarter, you need five cadmium-nickel batteries or three lead batteries.

The battery industry is one of the largest consumers of lead.

One can, perhaps, say that lead was at the origins of modern electronic computing technology.

Lead was one of the first metals to become superconductive. By the way, the temperature below which this metal acquires the ability to pass electric current without the slightest resistance is quite high - 7.17 ° K. (For comparison, we point out that for tin it is 3.72, for zinc - 0.82, for titanium - only 0.4 ° K). The winding of the first superconducting transformer built in 1961 was made of lead.

One of the most spectacular physical "tricks" is based on the superconductivity of lead, first demonstrated in the 30s by the Soviet physicist V.K. Arkadiev.

According to legend, the coffin with the body of Mohammed hung in space without supports. Of course, no one of sober-minded people believes this. However, something similar happened in Arkadiev's experiments: a small magnet hung without any support over a lead plate, which was in liquid helium, i.e. at a temperature of 4.2°K, much lower than the critical temperature for lead.

It is known that when the magnetic field changes in any conductor, eddy currents (Foucault currents) arise. Under normal conditions, they are quickly extinguished by resistance. But, if there is no resistance (superconductivity!), these currents do not fade and, naturally, the magnetic field created by them is preserved. The magnet above the lead plate, of course, had its own field and, falling on it, excited a magnetic field from the plate itself, directed towards the field of the magnet, and it repelled the magnet. This means that the task was to pick up a magnet of such a mass that this repulsive force could keep it at a respectful distance.

In our time, superconductivity is a huge area of ​​scientific research and practical application. Of course, it is impossible to say that it is associated only with lead. But the importance of lead in this area is not limited to the examples given.

One of the best conductors of electricity - copper - can not be transferred to a superconducting state. Why this is so, scientists do not yet have a consensus. In experiments on the superconductivity of copper, the role of an electrical insulator is assigned. But an alloy of copper and lead is used in superconducting technology. In the temperature range 0.1...5°K, this alloy exhibits a linear dependence of resistance on temperature. Therefore, it is used in instruments for measuring extremely low temperatures.

Lead and transport

And this theme consists of several aspects. The first is lead-based anti-friction alloys. Along with the well-known babbits and lead bronzes, a lead-calcium ligature (3 ... 4% calcium) often serves as an anti-friction alloy. Some solders have the same purpose, which are distinguished by a low content of tin and, in some cases, the addition of antimony. Alloys of lead with thallium begin to play an increasingly important role. The presence of the latter increases the heat resistance of bearings, reduces the corrosion of lead by organic acids formed during the physical and chemical destruction of lubricating oils.

The second aspect is the fight against detonation in engines. The detonation process is similar to the combustion process, but its speed is too high ... In internal combustion engines, it occurs due to the breakdown of molecules of hydrocarbons that have not yet burned down under the influence of growing pressure and temperature. Decaying, these molecules add oxygen and form peroxides, which are stable only in a very narrow temperature range. It is they who cause detonation, and the fuel ignites before the necessary compression of the mixture in the cylinder is reached. As a result, the engine starts to “jump”, overheat, black exhaust appears (a sign of incomplete combustion), burnout of the pistons accelerates, the connecting rod-crank mechanism wears out more, power is lost ...

The most common antiknock agent is tetraethyl lead (TES) Pb (C 2 H 5) 4 - a colorless toxic liquid. Its action (and other organometallic antiknock agents) is explained by the fact that at temperatures above 200 ° C, the molecules of the antiknock substance decompose. Active free radicals are formed, which, reacting primarily with peroxides, reduce their concentration. The role of the metal formed during the complete decomposition of tetraethyl lead is reduced to the deactivation of active particles - the products of the explosive decomposition of the same peroxides.

The addition of tetraethyl lead to fuel never exceeds 1%, but not only because of the toxicity of this substance. An excess of free radicals can initiate the formation of peroxides.

An important role in the study of the processes of detonation of motor fuels and the mechanism of action of antiknock agents belongs to scientists from the Institute of Chemical Physics of the USSR Academy of Sciences, headed by Academician N.N. Semenov and Professor A.S. Falcon.

Lead and war

Lead is a heavy metal with a density of 11.34. It was this circumstance that caused the massive use of lead in firearms. By the way, lead projectiles were used in antiquity: the slingers of Hannibal's army threw lead balls at the Romans. And now bullets are cast from lead, only their shell is made from other, harder metals.

Any additive to lead increases its hardness, but quantitatively the effect of additives is unequal. Up to 12% antimony is added to lead used for the manufacture of shrapnel, and no more than 1% arsenic is added to gunshot lead.

Without initiating explosives, not a single rapid-fire weapon will work. Heavy metal salts predominate among the substances of this class. Use, in particular, lead azide PbN 6 .

All explosives are subject to very stringent requirements in terms of safe handling, power, chemical and physical resistance, and sensitivity. Of all the known initiating explosives, only “mercury fulminate”, azide and lead trinitroresorcinate (TNRS) “pass” all these characteristics.

Lead and Science

In Alamogordo - the site of the first atomic explosion - Enrico Fermi rode in a tank equipped with lead protection. To understand why it is lead that protects against gamma radiation, we need to turn to the essence of the absorption of short-wave radiation.

The gamma rays accompanying radioactive decay come from the nucleus, whose energy is almost a million times greater than that which is "collected" in the outer shell of the atom. Naturally, gamma rays are immeasurably more energetic than light rays. When meeting with matter, a photon or a quantum of any radiation loses its energy, and this is how its absorption is expressed. But the energy of the rays is different. The shorter their wave, the more energetic they are, or, as they say, tougher. The denser the medium through which the rays pass, the more it delays them. Lead is dense. Hitting the surface of the metal, gamma quanta knock out electrons from it, for which they spend their energy. The larger the atomic number of an element, the more difficult it is to knock an electron out of its outer orbit due to the greater force of attraction by the nucleus.

Another case is also possible, when a gamma-quantum collides with an electron, imparts to it a part of its energy and continues its movement. But after the meeting, it became less energetic, more "soft", and in the future it is easier for a layer of a heavy element to absorb such a quantum. This phenomenon is called the Compton effect after the American scientist who discovered it.

The harder the rays, the greater their penetrating power - an axiom that does not require proof. However, scientists who relied on this axiom were in for a very curious surprise. It suddenly turned out that gamma rays with an energy of more than 1 million eV are retained by lead not weaker, but stronger than less hard ones! The fact seemed to contradict the evidence. After conducting the most subtle experiments, it turned out that a gamma-quantum with an energy of more than 1.02 MeV in the immediate vicinity of the nucleus “disappears”, turning into an electron-positron pair, and each of the particles takes away with it half of the energy spent on their formation. The positron is short-lived and, colliding with an electron, turns into a gamma-quantum, but of lower energy. The formation of electron-positron pairs is observed only in high-energy gamma quanta and only near the "massive" nucleus, that is, in an element with a higher atomic number.

Lead is one of the last stable elements of the periodic table. And of the heavy elements, it is the most accessible, with a technology of extraction that has been worked out for centuries, with explored ores. And very plastic. And very easy to handle. This is why lead radiation shielding is the most common. A fifteen to twenty centimeter layer of lead is enough to protect people from the effects of radiation from any known to science kind.

Let us briefly mention one more aspect of the service of lead to science. It is also associated with radioactivity.

There are no lead parts in the watches we use. But in cases where time is measured not in hours and minutes, but in millions of years, lead is indispensable. Radioactive transformations of uranium and thorium culminate in the formation of stable isotopes of element No. 82. In this case, however, different lead is obtained. The decay of the isotopes 235 U and 238 U ultimately leads to the isotopes 207 Pb and 206 Pb. The most common thorium isotope, 232 Th, completes its transformations with the 208 Pb isotope. By establishing the ratio of lead isotopes in the composition of geological rocks, you can find out how long a particular mineral exists. In the presence of highly accurate instruments (mass spectrometers), the age of the rock is determined according to three independent determinations - according to the ratios 206 Pb: 238 U; 207Pb: 235U and 208Pb: 232Th.

Lead and culture

Let's start with the fact that these lines are printed with letters made of lead alloy. The main components of printing alloys are lead, tin and antimony. It is interesting that lead and tin began to be used in book printing from its first steps. But then they did not constitute a single alloy. The German pioneer Johann Guttenberg cast tin letters into lead molds, as he considered it convenient to mint molds from soft lead that could withstand a certain number of tin pours. The current tin-lead printing alloys are designed to meet many requirements: they must have good casting properties and low shrinkage, be sufficiently hard and chemically resistant to inks and wash-off solutions; during remelting, the composition must remain constant.

However, the service of lead to human culture began long before the appearance of the first books. Painting appeared before writing. For many centuries, artists have used lead-based paints, and they still have not gone out of use: yellow - lead crown, red - red lead and, of course, white lead. By the way, it is because of the white lead that the paintings of the old masters seem dark. Under the action of hydrogen sulfide microimpurities in the air, white lead turns into dark lead sulfide PbS...

For a long time, the walls of pottery were covered with glazes. The simplest glaze is made from lead oxide and quartz sand. Now the sanitary supervision prohibits the use of this glaze in the manufacture of household items: the contact of food products with lead salts must be excluded. But in the composition of majolica glazes intended for decorative purposes, relatively low-melting lead compounds are used, as before.

Finally, lead is part of the crystal, more precisely, not lead, but its oxide. Lead glass is brewed without any complications, it is easily blown and cut, it is relatively easy to apply patterns and ordinary cutting, in particular, to it. Such glass refracts light rays well and therefore finds application in optical devices.

By adding lead and potash (instead of lime) to the mixture, a rhinestone is prepared - glass with a brilliance greater than that of precious stones.

Lead and medicine

Once in the body, lead, like most heavy metals, causes poisoning. Nevertheless, lead is needed by medicine. Since the time of the ancient Greeks remained in medical practice lead lotions and plasters, but this is not limited to the medical service of lead.

Bile is needed not only for satirists. The organic acids contained in it, primarily glycocholic C 23 H 36 (OH) 3 CONHCH 2 COOH, as well as taurocholic C 23 H 36 (OH) 3 CONHCH 2 CH 2 SO 3 H, stimulate liver activity. And since the liver does not always work with the accuracy of a well-established mechanism, these acids are needed by medicine. They are isolated and separated with lead acetate. The lead salt of glycocholic acid precipitates, while taurocholic acid remains in the mother liquor. After filtering the precipitate, the second drug is also isolated from the mother liquor, again acting with a lead compound - the main acetic salt.

But the main work of lead in medicine is connected with diagnostics and radiotherapy. It protects doctors from constant x-ray exposure. For almost complete absorption of X-rays, it is enough to put a layer of lead 2 ... 3 mm in their path. That is why the medical personnel of X-ray rooms are dressed in aprons, mittens and helmets made of rubber, which contains lead. And the image on the screen is observed through lead glass.

These are the main aspects of the relationship of mankind with lead - an element known from ancient times, but even today serving man in many areas of his activity.

Wonderful pots thanks to lead

The production of metals, especially gold, was considered a "sacred art" in ancient Egypt. The conquerors of Egypt tortured its priests, extorting from them the secrets of smelting gold, but they died keeping the secret. The essence of the process, which the Egyptians so guarded, found out many years later. They treated gold ore with molten lead, which dissolved precious metals, and thus extracted gold from the ores. This solution was then subjected to oxidative roasting and the lead was converted to oxide. The main secret of this process was the firing pots. They were made from bone ash. During melting, lead oxide was absorbed into the walls of the pot, while entraining random impurities. And at the bottom there was a pure alloy.

Use of lead ballast

On May 26, 1931, Professor Auguste Piccard was supposed to take to the skies on a stratospheric balloon of his own design - with a pressurized cabin. And got up. But, while developing the details of the upcoming flight, Piccard unexpectedly ran into an obstacle that was not at all a technical order. As ballast, he decided to take on board not sand, but lead shot, which required much less space in the gondola. Upon learning of this, the officials in charge of the flight categorically forbade the replacement: the rules say “sand”, nothing else is allowed to be thrown on people's heads (with the exception of only water). Piccard decided to prove the safety of his ballast. He calculated the force of friction of lead shot against the air and ordered that this shot be dropped on his head from the highest building in Brussels. The complete safety of "lead rain" has been demonstrated clearly. However, the administration ignored the experience: "The law is the law, it says sand, which means sand, not shot." The obstacle seemed insurmountable, but the scientist found a way out: he announced that "lead sand" would be in the gondola of the stratospheric balloon as ballast. By replacing the word "shot" with the word "sand", the bureaucrats were disarmed and no longer hindered Piccard.

Lead in the paint industry

White lead was able to produce 3 thousand years ago. Their main supplier in the ancient world was the island of Rhodes in the Mediterranean Sea. There were not enough paints then, and they were extremely expensive. The celebrated Greek painter Nikias once eagerly awaited the arrival of whitewash from Rhodes. The precious cargo arrived at the Athenian port of Piraeus, but a fire suddenly broke out there. The flames engulfed the ships on which the white was brought. When the fire was extinguished, the frustrated artist climbed onto the deck of one of the stricken ships. He hoped that not all the cargo was lost, but at least one barrel with the paint he needed could have survived. Indeed, barrels of whitewash were found in the hold: they did not burn out, but were heavily charred. When the barrels were opened, the artist's surprise knew no bounds: they did not have white paint, but bright red! So the fire in the port suggested a way to make a wonderful paint - minium.

Lead and gases

When melting one or another metal, one has to take care of removing gases from the melt, since otherwise a low-quality material is obtained. This is achieved by various technological methods. The smelting of lead in this sense does not cause any trouble to metallurgists: oxygen, nitrogen, sulfur dioxide, hydrogen, carbon monoxide, carbon dioxide, hydrocarbons do not dissolve in either liquid or solid lead.

Lead in construction

In ancient times, when building buildings or defensive structures, stones were often fastened with molten lead. In the village of Stary Krym, the ruins of the so-called lead mosque, built in the 14th century, have survived to this day. The building got its name because the gaps in the masonry are filled with lead.

Lead Restrictions

Currently, the industry around the world is going through another stage of transformation associated with the tightening of environmental standards - there is a general rejection of lead. Germany has severely restricted its use since 2000, the Netherlands since 2002, and European countries such as Denmark, Austria and Switzerland have banned the use of lead altogether. This trend will become common to all EU countries in 2015. The US and Russia are also actively developing technologies that will help find an alternative to the use of lead.

Its widespread use in industry has resulted in lead contamination being found everywhere. Consider the most important components of the biosphere, such as air, water and soil.

Let's start with the atmosphere. With air, a small amount of lead enters the human body - (only 1-2%), but most of the lead is absorbed. The largest emissions of lead into the atmosphere occur in the following industries:

• metallurgical industry;
• mechanical engineering (production of accumulators);
• fuel and energy complex (production of leaded gasoline);
• chemical complex (production of pigments, lubricants, etc.);
• glass enterprises;
• canning production;
• woodworking and pulp and paper industry;
• defense industry enterprises.

Undoubtedly, the most significant source of lead pollution in the atmosphere is motor vehicles using leaded gasoline.

It has been proven that an increase in the content of lead in drinking water causes, as a rule, an increase in its concentration in the blood. A significant increase in the content of this metal in surface waters is associated with its high concentration in wastewater from ore processing plants, some metallurgical plants, mines, etc.

From contaminated soil, lead enters agricultural crops, and together with food - directly into the human body. An active accumulation of this metal was noted in cabbage and root crops, and in those that are widely eaten (for example, in potatoes). Some types of soils strongly bind lead, which protects ground and drinking water, plant products from pollution. But then the soil itself gradually becomes more and more contaminated, and at some point the destruction of soil organic matter can occur with the release of lead into the soil solution. As a result, it will be unsuitable for agricultural use.

Thus, due to global environmental pollution with lead, it has become a ubiquitous component of any plant and animal food. In the human body, most of the lead comes from food - from 40 to 70% in different countries. Plant foods generally contain more lead than animal products.

As already mentioned, it's all the fault industrial enterprises. Naturally, in the production facilities themselves, dealing with lead, the environmental situation is worse than anywhere else. According to the results of official statistics, among occupational intoxications, lead ranks first. In the electrical industry, non-ferrous metallurgy and mechanical engineering, intoxication is due to the excess of the MPC of lead in the air working area 20 or more times. Lead causes extensive pathological changes in the nervous system, disrupts the activity of the cardiovascular and reproductive systems.

Lead (Pb from lat. Plumbum) is a chemical element that is in Group IV of the Periodic Table. Lead has many isotopes, more than 20 of which are radioactive. Lead isotopes are products of the decay of uranium and thorium, so the lead content in the lithosphere has gradually increased over millions of years and is now about 0.0016% by mass, but it is more abundant than its closest relatives such as gold and. Lead is easily isolated from ore deposits. The main sources of lead are galena, anglesite and cerussite. In ore, lead often coexists with other metals, such as zinc, cadmium, and bismuth. In its native form, lead is extremely rare.

Lead - interesting historical facts

The etymology of the word "lead" is still not exactly clear and is the subject of very interesting research. Lead is very similar to tin, they were often confused, so in most West Slavic languages, lead is tin. But the word "lead" is found in Lithuanian (svinas) and Latvian (svin) languages. Lead translated into English lead, into Dutch lood. Apparently, this is where the word “tinkering” came from, i.e. cover the product with a layer of tin (or lead). The origin of the Latin word Plumbum, from which the English word plumber is derived, is also not fully understood. The fact is that once water pipes were “sealed” with lead, “sealed” (French plomber “seal with lead”). By the way, this is where the well-known word “filling” comes from. But the confusion does not end there, the Greeks always called lead “molybdos”, hence the Latin “molibdaena”, it is easy for an ignorant person to confuse this name with the name chemical element molybdenum. So in ancient times they called shiny minerals that leave a dark mark on a light surface. This fact has left its mark on the German language: "pencil" in German is called Bleistift, i.e. lead rod.
Mankind has been familiar with lead since time immemorial. Archaeologists have found lead products smelted 8000 years ago. In ancient Egypt, statues were even cast from lead. In ancient Rome, water pipes were made of lead, it was he who predetermined the first environmental catastrophe in history. The Romans had no idea about the dangers of lead, they liked the malleable, durable and easy-to-work metal. It was even believed that lead added to wine improved its taste. Therefore, almost every Roman was poisoned with lead. We will discuss the symptoms of lead poisoning below, but for now we will only indicate that one of them is mental disorder. Apparently, all these crazy antics of noble Romans and countless crazy orgies originate from here. Some researchers even believe that lead was almost the main reason for the fall of Ancient Rome.
In ancient times, potters ground lead ore, diluted it with water, and poured clay objects over the resulting mixture. After firing, such vessels were covered with a thin layer of shiny lead glass.
In 1673, the Englishman George Ravenscroft improved the composition of glass by adding lead oxide to the initial components and thus obtained a fusible, shiny glass that was very similar to natural rock crystal. And at the end of the 18th century, Georg Strass fused white sand, potash and lead oxide together in the manufacture of glass, obtaining such a clean and shiny glass that it was difficult to distinguish it from diamond. Hence the name "rhinestones" came from, in fact a fake for precious stones. Unfortunately, among his contemporaries, Strass was known as a fraud and his invention was forgotten until, at the beginning of the 20th century, Daniel Swarovski was able to turn the production of rhinestones into an entire fashion industry and art direction.
After the advent and widespread use of firearms, lead began to be used to make bullets and shot. Printing letters were made from lead. Lead was previously part of white and red paints, they were used by almost all ancient artists.

lead shot

Chemical properties of lead in brief

Lead is a dull gray metal. However, its fresh cut shines well, but unfortunately almost instantly becomes covered with a dirty oxide film. Lead is a very heavy metal, it is one and a half times heavier than iron, and four times heavier than aluminum. Not without reason in Russian the word "lead" is to some extent a synonym for gravity. Lead is a very fusible metal, it melts already at 327 ° C. Well, this fact is known to all fishermen who easily melt the weights they need. Also, lead is very soft, it can be cut with an ordinary steel knife. Lead is a very inactive metal, it is not difficult to react with it or dissolve it even at room temperature.
Organic lead derivatives are highly toxic substances. Unfortunately, one of them, tetraethyl lead, has been widely used as an octane booster in gasoline. But on the other hand, fortunately, tetraethyl lead is no longer used in this form, chemists and production workers have learned to increase the octane number in safer ways.

The effect of lead on the human body and symptoms of poisoning

All lead compounds are highly toxic. The metal enters the body with food or inhaled air and is carried by the blood. Moreover, inhalation of vapors of lead compounds and dust is much more dangerous than its presence in food. Lead tends to accumulate in the bones, partially replacing calcium in this case. With an increase in the concentration of lead in the body, anemia develops, the brain is affected, which leads to a decrease in intelligence, and in children it can cause irreversible developmental delays. It is enough to dissolve one milligram of lead in a liter of water and it will become not only unsuitable, but also dangerous for drinking. Such a low amount of lead also poses a certain danger, neither the color nor the taste of the water changes. The main symptoms of lead poisoning are:

• gray border on the gums,
• lethargy,
• apathy,
• memory loss,
• dementia,
• vision problems,
• early aging.

Lead Application

Yet, despite the toxicity, there is no way to abandon the use of lead due to its exceptional properties and low cost. Lead is mainly used for the production of battery plates, which currently consumes about 75% of the lead mined on the planet. Lead is used as sheathing for electrical cables due to its ductility and resistance to corrosion. This metal is widely used in the chemical and oil refining industries, for example, for lining reactors in which sulfuric acid is produced. Lead has the ability to delay radioactive radiation, which is also widely used in energy, medicine and chemistry. In lead containers, for example, radioactive elements are transported. Lead goes into the production of bullet cores and shrapnel. Also, this metal finds its application in the production of bearings.

Lead statue of Saint Martin in Bratislava

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

History reference. Lead was known for 6-7 thousand years BC. e. the peoples of Mesopotamia, Egypt and other countries of the ancient world. He served for the manufacture of statues, household items, tablets for writing. The Romans used lead pipes for plumbing. The alchemists called Lead Saturn and designated it as the sign of this planet. Compounds Lead - "lead ash" РbО, white lead 2РbСО 3 ·Рb(OH) 2 were used in ancient Greece and Rome as components of medicines and paints. When firearms were invented, lead began to be used as a material for bullets. The toxicity of lead was noted as early as the 1st century AD. e. Greek physician Dioscorides and Pliny the Elder.

Distribution of lead in nature. Lead content in earth's crust(Clark) 1.6 10 -3% by weight. The formation in the earth's crust of about 80 lead-bearing minerals (the chief among them is galena PbS) is associated mainly with the formation of hydrothermal deposits. Numerous (about 90) secondary minerals are formed in the oxidation zones of polymetallic ores: sulfates (anglesite PbSO 4), carbonates (cerussite PbCO 3), phosphates [pyromorphite Pb 5 (PO 4) 3 Cl].

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

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

Chemical properties of lead. The configuration of the outer electron shells of the Pb 6s 2 6р 2 atom, in accordance with which it exhibits the oxidation states +2 and +4. Lead is relatively inactive chemically. The metallic luster of a fresh lead cut gradually disappears in air due to the formation of a very thin film of PbO, which protects against further oxidation.

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

In the absence of O 2 , water at room temperature does not act on Lead, but it decomposes hot water vapor to form lead oxide and hydrogen. Corresponding to the oxides PbO and PbO 2, the hydroxides Pb (OH) 2 and Pb (OH) 4 are amphoteric in nature.

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

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

Getting Lead. Metallic lead is obtained by oxidative roasting of PbS, followed by the reduction of PbO to crude Pb ("werkble") and refining (purification) of the latter. Oxidative roasting of the concentrate is carried out in continuous sintering belt machines. During the firing of PbS, the reaction prevails:

2PbS + ZO 2 \u003d 2PbO + 2SO 2.

In addition, a little PbSO 4 sulfate is also obtained, which is converted into PbSiO 3 silicate, for which quartz sand is added to the mixture. At the same time, sulfides of other metals (Cu, Zn, Fe) present as impurities are also oxidized. As a result of firing, instead of a powdery mixture of sulfides, an agglomerate is obtained - a porous sintered continuous mass, consisting mainly of oxides PbO, CuO, ZnO, Fe 2 O 3. Pieces of agglomerate are mixed with coke and limestone, and this mixture is loaded into a water jacket furnace, into which air is supplied under pressure from below through pipes (“tuyeres”). Coke and carbon monoxide (II) reduce PbO to Pb already at low temperatures (up to 500 °C). At higher temperatures, the following reactions take place:

CaCO 3 \u003d CaO + CO 2

2PbSiO 3 + 2CaO + C \u003d 2Pb + 2CaSiO 3 + CO 2.

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

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

Lead in the body. Plants absorb lead from soil, water and atmospheric fallout. Lead enters the human body with food (about 0.22 mg), water (0.1 mg), dust (0.08 mg). The safe daily level of lead intake for humans is 0.2-2 mg. It is excreted mainly with feces (0.22-0.32 mg), less with urine (0.03-0.05 mg). The human body contains on average about 2 mg of lead (in some cases - up to 200 mg). In the inhabitants of industrialized countries, the content of lead in the body is higher than in the inhabitants of agrarian countries, in the townspeople it is higher than in the countryside. The main depot of Lead is the skeleton (90% of the total Lead in the body): 0.2-1.9 µg/g accumulates in the liver; in the blood - 0.15-0.40 mcg / ml; in hair - 24 mcg / g, in milk - 0.005-0.15 mcg / ml; is also found in the pancreas, kidneys, brain and other organs. The concentration and distribution of lead in the body of animals are close to those established for humans. With an increase in the level of lead in the environment, its deposition in the bones, hair, and liver increases.

Poisoning with lead and its compounds is possible in the mining of ores, smelting lead, in the production of lead paints, in printing, pottery, cable production, in the production and use of tetraethyl lead, etc. Household poisoning occurs rarely and is observed when eating products that have been stored in earthenware, glazed with red lead or litharge. Lead and its inorganic compounds in the form of aerosols penetrate the body mainly through Airways, to a lesser extent through gastrointestinal tract and skin. Lead circulates in the blood in the form of highly dispersed colloids - phosphate and albuminate. Lead is excreted mainly through the intestines and kidneys. Violation of porphyrin, protein, carbohydrate and phosphate metabolism, deficiency of vitamins C and B 1 , functional and organic changes in the central and autonomic nervous system, and the toxic effect of lead on the bone marrow play a role in the development of intoxication. Poisoning can be latent (the so-called carriage), proceed in mild, moderate and severe forms.

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

Lead is a chemical element with atomic number 82 and symbol Pb (from the Latin plumbum - ingot). It is a heavy metal with a density greater than that of most conventional materials; lead is soft, malleable, and melts at relatively low temperatures. Freshly cut lead has a bluish-white hue; it dulls to a dull gray when exposed to air. Lead has the second highest atomic number of the classically stable elements and is at the end of the three main decay chains of the heavier elements. Lead is a relatively non-reactive post-transition element. Its weak metallic character is exemplified by its amphoteric nature (lead and lead oxides react with both acids and bases) and tendency to form covalent bonds. Lead compounds are usually in the +2 oxidation state rather than +4, typically with the lighter members of the carbon group. Exceptions are mainly limited to organic compounds. Like the lighter members of this group, lead tends to bond with 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 and use of lead in ancient Rome. Lead production declined after the fall of the Roman Empire and did not reach the same levels until the Industrial Revolution. At present, the world production of lead 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 the relative abundance and low cost, these factors have led to the widespread use of lead in construction, plumbing, batteries, bullets, weights, solders, pewter, 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 phased out. Lead is a neurotoxin that accumulates in soft tissues and bones, damaging the nervous system and causing brain and blood disorders in mammals.

Physical properties

Atomic Properties

The lead atom has 82 electrons arranged in the 4f145d106s26p2 electronic configuration. The combined first and second ionization energies - the total energy required to remove two 6p electrons - is close to that of tin, the top neighbor of lead in the carbon group. It's unusual; ionization energies generally go down the group as the element's outer electrons become more distant 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 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 periodic trends predicted. Relativistic effects, which become significant in heavier atoms, contribute to this behaviour. One such effect is the inert pair effect: the 6s electrons of lead are reluctant to participate in bonding, making the distance between the nearest atoms in crystalline lead unusually long. The lighter lead carbon groups 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 the same size, calcium and strontium.

Large volumes

Pure lead has a bright silvery color with a hint of blue. It tarnishes on contact with moist air, and its hue depends on the prevailing conditions. The 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 common metals such as iron (7.87 g/cm3), copper (8.93 g/cm3) and zinc ( 7.14 g/cm3). Some of the rarer metals are more dense: tungsten and gold are 19.3 g/cm3, while 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 ductile. The bulk modulus of lead, 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 (6 times higher for aluminum, 10 times higher for copper, and 15 times higher for mild steel); it can be enhanced by adding a small amount of copper or antimony. The melting point of lead, 327.5°C (621.5°F), is low compared to most metals. Its boiling point is 1749 °C (3180 °F) and is the lowest of the carbon group elements. The electrical resistance 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.

Lead isotopes

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 its only primordial isotope, bismuth-209, was discovered in 2003 to decay very slowly. The four stable isotopes of lead could theoretically undergo alpha decay into mercury isotopes releasing energy, but this has not been observed anywhere, with predicted half-lives ranging 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 final decay products 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 for lead-lead bonds. 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 naturally occurring lead, 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 found in nature because lead-210 is produced by a long decay cycle that starts with uranium-238 (which has been 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 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 especially useful to help identify the age of samples by measuring its ratio to lead-206 (both isotopes are present in the same decay chain). A total of 43 isotopes of lead 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 natural 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 humid 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. Finely 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. Lead metal is not attacked by dilute sulfuric acid, but is dissolved in concentrated form. It reacts slowly with hydrochloric acid and vigorously with nitric acid with the formation of 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, negligible for germanium, important (but not predominant) for tin, and more important for lead. This is due to relativistic effects, in particular the effect of inert pairs, which occurs when there is a large difference in electronegativity between lead and oxide, halide or nitride anions, resulting in significant partial positive charges of lead. As a result, there are more strong compression 6s orbitals of lead than 6p orbitals, making lead quite 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 between lead(II) at 1.87 and lead(IV) is 2.33. This difference highlights the reversal of the increase in stability of the +4 oxidation state with decreasing carbon concentration; tin, for comparison, has values ​​of 1.80 in the +2 oxidation state and 1.96 in the +4 state.

Lead(II) compounds are characteristic of non organic chemistry lead. Even strong oxidizers such as fluorine and chlorine react with lead at room temperature to form only PbF2 and PbCl2. Most of them are less ionic than other metal compounds and are therefore largely insoluble. Lead(II) ions are usually colorless in solution and partially hydrolyze 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 the Pb2+ ion in water usually rely on the precipitation of lead(II) chloride using dilute hydrochloric acid. Because 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 is only stable above 488 °C. It is the most commonly used lead compound. Lead hydroxide (II) can exist only 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; they 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 the 2-, 4- and anion of the n5n chain. Lead(II) sulfate is insoluble in water, like the sulfates of other heavy divalent cations. Lead(II) nitrate and lead(II) acetate are very soluble, and this is used in the synthesis of other lead compounds.

Several inorganic lead(IV) compounds are known, and they are usually strong oxidizers or only exist 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 to a lesser extent 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 obtained as an intermediate between lead(II) and lead(IV) in larger organoleptic complexes; this oxidation state is unstable, since 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 obtained 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 viewed as having this structure, with every alternate layer of oxygen atoms missing. Negative oxidation states can occur as Zintl phases, as either in the case of Ba2Pb, where lead is formally lead(-IV), or as in the case of oxygen-sensitive ring or polyhedral cluster ions such as the trigonal bipyramidal ion Pb52-i, where two lead atoms - lead (- I), and three - lead (0). In such anions, each atom is at the polyhedral vertex and contributes two electrons to each covalent bond at the edge of their sp3 hybrid orbitals, with the other two being the outer single pair. They can be formed in liquid ammonia by the reduction of lead with sodium.

Organic lead

Lead can form multiply 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-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 predominantly forms organic compounds (IV), even if this formation begins with inorganic lead (II) reagents; very few organolate(II) compounds are known. The most well-characterized exceptions are Pb 2 and Pb (η5-C5H5)2. The lead analogue of the simplest organic compound, methane, is a plumbane. Plumban can be obtained in the reaction between metallic lead and atomic hydrogen. Two simple derivatives, tetramethyladine and tetraethylidelide, 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 easily forms an equimolar alloy, which reacts with alkyl halides to form organometallic compounds such as tetraethylide. The oxidizing nature of many organoorganic compounds is also exploited: lead tetraacetate is an important laboratory reagent for oxidation in organic chemistry, and tetraethyl elide 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 that of platinum, eight times higher than that of mercury, and 17 times higher than that of 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 more than 40. Primordial lead, which contains the isotopes lead-204, lead-206, lead-207, and lead-208-, was mainly created as a result of repeated neutron capture processes that occur in stars. The two main capture modes are s- and r-processes. In the s process (the s stands for "slow"), the captures are separated by years or decades, allowing the 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 another neutron is captured, it becomes lead-205, which has a half-life of about 15 million years. Further captures lead to the formation of lead-206, lead-207 and lead-208. When captured by another neutron, lead-208 becomes lead-209, which quickly decays into bismuth-209. When another neutron is captured, bismuth-209 becomes bismuth-210, whose beta decays into polonium-210, and whose alpha decays into lead-206. The cycle therefore ends at lead-206, lead-207, lead-208 and bismuth-209. In the r process (r stands for "fast"), the captures are faster than the nuclei can decay. This happens 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 generate as much lead as the s process. It tends to stop as soon as neutron rich nuclei reach 126 neutrons. At this point, neutrons are located in full shells in the atomic nucleus, and it becomes more difficult to energetically accommodate 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 by the Goldschmidt classification, which means that it usually 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, have remained in the crust rather than sinking deeper into the Earth's interior. This explains the relatively high level of lead in the bark, 14 ppm; it is the 38th most common element in the bark. 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 an oxidation product of galena; and serusite or white lead ore, PbCO3, is a decomposition product of galena. Arsenic, tin, antimony, silver, gold, copper, and bismuth are common impurities in lead minerals. World lead resources exceed 2 billion tons. Significant lead deposits have been found in Australia, China, Ireland, Mexico, Peru, Portugal, Russia and the United States. Global reserves - resources that are economically viable to extract - in 2015 amounted to 89 million tons, 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" (lead) is of Germanic origin; it comes from Middle English and Old English (with a longitude over the vowel "e" to signify that the vowel of that letter is long). The Old English word comes from a hypothetical reconstructed Proto-Germanic *lauda- ("lead"). According to the 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 in the linguistic community. According to one hypothesis, this word is derived from Proto-Indo-European *lAudh- ("lead"). According to another hypothesis, the word is a loanword from Proto-Celtic *ɸloud-io- ("lead"). This word is related to the Latin plumbum, which gave this element the chemical symbol Pb. The word *ɸloud-io- may also be the source of the Proto-Germanic *bliwa- (which also means "lead"), from which the German Blei derives. The name of a 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 uses (if any) due to its softness and fading appearance. The main reason for the spread of lead production was its association with silver, which can be obtained 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, as well as in glazes, glasses, enamels, and jewelry. Various civilizations of the Fertile Crescent used lead as a writing material, as currency, and in construction. Lead was used in the ancient Chinese royal court as a stimulant, as a currency, and as a contraceptive. In the Indus Valley Civilization and the Mesoamericans, lead was used to make amulets; Eastern and South African peoples used lead in wire drawing.

classical era

Since 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 combined dominated the production of mined lead until about 1200 BC. Since 2000 BC, the Phoenicians have been working on the deposits in 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 the mining industry, led the area to become the largest lead producer in the classical era, with annual production reaching 80,000 tons. Like their predecessors, the Romans obtained lead mainly as a by-product of silver smelting. The leading miners were Central Europe, Britain, the Balkans, Greece, Anatolia and Spain, which accounted for 40% of world lead production. Lead was used to make water pipes in the Roman Empire; the Latin word for this metal, plumbum, is the source English word plumbing (plumbing). The metal's ease of handling and resistance to corrosion has led to its widespread use in other areas, including pharmaceuticals, roofing, 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 "sugar of lead" (lead(II) acetate), whereas copper or bronze vessels could give food a bitter taste due to the formation of verdigres. This metal was by far the most common material in classical antiquity, and it is appropriate to refer to the (Roman) Lead Era. Lead was in common use for the Romans as plastic is for us. The Roman author Vitruvius reported on the dangers that lead could pose to health, and modern writers have suggested that lead poisoning played an important role in the decline of the Roman Empire.[l]Other researchers have criticized such claims, pointing out, for example, that not all abdominal pain was caused by lead poisoning.According to archaeological research, Roman lead pipes increased lead levels in tap water, but such an effect "would hardly have been really harmful." Victims of lead poisoning became known as "saturnines," after the fearsome father of the gods, Saturn. association with this, lead was considered the "father" of all metals. His status in Roman society was low as he was easily available and cheap.

Tin and antimony confusion

In the classical era (and even until the 17th century), tin was often indistinguishable from lead: the Romans called lead plumbum nigrum ("black lead"), and tin plumbum candidum ("light lead"). The connection between lead and tin can also be traced in other languages: the word "olovo" in Czech means "lead", but in Russian the related tin means "tin". In addition, lead is closely related to antimony: both elements usually occur as sulfides (galena and stibnite), often together. Pliny wrote incorrectly 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 largest production of lead was observed in South and East Asia, especially in China and India, where lead mining increased greatly. In Europe, lead production began to revive only in the 11th and 12th centuries, where lead was again used for roofing and piping. Beginning in the 13th century, lead was used to create stained glass windows. In the European and Arabic traditions of alchemy, lead (the symbol of Saturn in the European tradition) was considered an impure base metal, which by separating, purifying and balancing it constituent parts could be converted into pure gold. During this period, lead was increasingly used to contaminate wine. The use of such wine was banned in 1498 by order of the Pope, as it was considered unsuitable for use in sacred rites, but it continued to be drunk, leading to mass poisoning until the end of the 18th century. Lead was a key material in parts of the printing press, which was invented around 1440; print workers routinely inhaled lead dust, which caused lead poisoning. Firearms were invented around the same time, and lead, despite being more expensive than iron, became the main material for making bullets. It was less damaging to iron gun barrels, had a higher density (contributing to better velocity retention), and its lower melting point made it easier to manufacture bullets as they could be made using wood fire. Lead, in the form of Venetian pottery, was widely used in cosmetics among the Western European aristocracy, as bleached faces were considered a sign of modesty. This practice later expanded to white wigs and eyeliners and only disappeared during the French Revolution, at the end of the 18th century. A similar fashion appeared in Japan in the 18th century with the advent of geishas, ​​a practice that continued throughout the 20th century. "White faces embodied the virtue of Japanese women", while lead was commonly used as a bleach.

Outside Europe and Asia

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

Industrial Revolution

In the second half of the 18th century, the Industrial Revolution took place in Britain, and then 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 the leading producer of lead, however, it lost this status by the middle of the 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 was the world leader in lead production, and other non-European countries—Canada, Mexico, and Australia—began significant lead production; production outside of Europe increased. A large proportion of lead demand was for plumbing and paint—lead paint was then regularly used. During this time, more people (the working class) came into contact with metals and there was an increase in cases of lead poisoning. This led to research into the effects of lead intake on the body. Lead proved to be more dangerous in its smoke form than the solid metal. An association has been found between lead poisoning and gout; British physician Alfred Baring Garrod noted that a third of his gout patients were plumbers and artists. The consequences of chronic exposure to lead, including mental disorders, were also studied in the 19th century. The first laws to reduce the incidence of lead poisoning in factories were enacted 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 have been better understood, and lead blindness has also been documented. Countries in Europe and the US have launched efforts to reduce the amount of lead people come into contact with. In 1878, the United Kingdom introduced mandatory examinations in factories and appointed the first factory medical 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 originated 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 due to its opacity and water resistance, to decorate interiors by 1930. The impact has been significant: in the last quarter of the 20th century, the percentage of people with excess blood lead levels dropped from over 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. Between 1960 and 1990, lead production in the Western Bloc increased by a third. The share of global lead production in the Eastern Bloc tripled from 10% to 30% from 1950 to 1990, when the Soviet Union was the world's largest lead producer in the mid-1970s and 1980s, and China began extensive lead production in the late 20s. th century. Unlike the European communist countries, in the middle of the 20th century China was mostly a non-industrialized country; in 2004, China surpassed Australia as the largest producer of lead. As with European industrialization, lead has taken its toll on health in China.

Production

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

Main

Most lead ores contain a low percentage of lead (rich ores have a typical lead content of 3-8%), which must be concentrated for recovery. During the initial processing, the ores are usually subjected to crushing, separation of dense media, grinding, froth flotation and drying. The resulting concentrate with a lead content of 30-80% by weight (typically 50-60%) is then converted to (impure) lead metal. There are two main ways to do this: a two-stage process involving roasting followed by extraction from the blast furnace, carried out in separate vessels; or a direct process in which the extraction of the concentrate takes place in a single vessel. The latter method has become more common, although the former is still significant.

Two step process

First, the sulfide concentrate is roasted in air to oxidize lead sulfide: 2 PbS + 3 O2 → 2 PbO + 2 SO2 ore. This crude lead oxide is reduced in a coke oven to an (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 on top of the melt and are removed. Metallic silver and gold are removed and recovered economically by the Parkes process, in which zinc is added to lead. Zinc dissolves silver and gold, both of which, without mixing with lead, can be separated and recovered. Desilvered lead is released by bismuth using the Betterton-Kroll method, treating it with metallic calcium and magnesium. The obtained bismuth-containing slags 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 dissolves and is deposited on the cathode, leaving the vast majority of the impurities in solution.

direct process

In this process, lead ingot and slag are obtained directly from lead concentrates. 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 the fluxes. Thus, the lead monoxide is reduced to lead metal in the middle of the lead monoxide rich slag. Up to 80% of lead in highly concentrated initial concentrates can be obtained in the form of ingots; the remaining 20% ​​form a slag rich in lead monoxide. For low grade raw materials, all lead can be oxidized to high grade slag. Metallic lead is further produced from high grade (25-40%) slags by incineration or subsea fuel injection, by an auxiliary electric furnace, or a combination of both methods.

Alternatives

Research continues on a cleaner and less energy-intensive lead mining process; its main disadvantage is that either too much lead is lost as waste, or alternative methods lead to 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 technique that may have potential.

secondary method

Melting, which is an integral part of primary production, is often skipped during secondary production. This only happens when the metallic lead has undergone significant oxidation. This process is similar to primary mining 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 used lead batteries removes the sulfur by treating it with alkali and then processed in a coal-fired furnace in the presence of oxygen to form impure lead, antimony being the most common impurity. Recycling of secondary lead is similar to that of primary lead; Some refining processes may be skipped depending on the recycled material and its potential for contamination, with bismuth and silver being most commonly accepted as 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 graphite winding tool, the specific type of graphite used was called plumbago (literally for lead or lead layout).

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 are generally less common and more difficult to extract from ores. The toxicity of lead has led to the phase-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 rifle ammunition can be cast with minimal use of technical equipment; in addition, lead is denser than other common metals, which allows for better speed retention. Concerns have been raised that lead bullets used for hunting could harm the environment. Its high density and corrosion resistance have been used in a number of related applications. Lead is used as the 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 bulk and minimizes water resistance. Lead is used in scuba diving to counter the diver's ability to float. 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, in cladding, flashing, in the manufacture of gutters and downspout joints, and in roof parapets. Lead moldings are used as a decorative material for fixing lead sheets. Lead is still used in the manufacture 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 lubricity. Being practically insoluble in copper, lead forms hard globules in imperfections throughout the alloy, such as grain boundaries. At low concentrations, and also as a lubricant, the globules prevent chipping during operation of the alloy, thereby improving machinability. Bearings use copper alloys with a higher concentration of lead. Lead provides lubrication and copper provides support. Due to its high density, atomic number and formability, lead is used as a barrier to absorb sound, vibration and radiation. Lead does not have natural resonant frequencies, as a result, lead sheet is used as a soundproofing layer in 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 shielding material used in nuclear science and X-ray cameras: gamma rays are absorbed by electrons. Lead atoms are densely packed and their electron density is high; a large atomic number means that there are many electrons per atom. Molten lead has been used as 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. Lead in batteries does not come into direct human contact and is therefore associated with less of a toxicity threat. Supercapacitors containing lead-acid batteries have been installed in kilowatts and megawatts in Australia, Japan and the US in frequency control, solar smoothing and other applications. These batteries have a lower energy density and charge discharge efficiency than lithium-ion batteries, but are significantly cheaper. Lead is used in high voltage power cables as a sheath material to prevent water diffusion during thermal insulation; this use is declining as lead is phased out. Some countries are also phasing out the use of lead in electronics solders to reduce environmental pollution. hazardous waste. Lead is one of three metals used in the Oddi 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. electrical cords. It can be used on candle wicks to provide a longer, more even burn. Due to the toxicity of lead, 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 ecological effects

Biological effects

Lead has not been confirmed biological role. Its prevalence in the human body averages 120 mg in an adult - its abundance is surpassed only by zinc (2500 mg) and iron (4000 mg) among the heavy metals. Lead salts are very efficiently absorbed by the body. A small amount of lead (1%) will be stored in the bones; the rest will be excreted in urine and faeces within a few weeks of exposure. The child will only be able to excrete about a third of the lead from the body. Chronic exposure to lead can lead to lead bioaccumulation.

Toxicity

Lead is an extremely poisonous metal (whether inhaled or swallowed) affecting nearly every organ and system in the human body. At an air level of 100 mg/m3, it poses an immediate danger to life and health. Lead is rapidly 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 the 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 interacts are calcium, iron and zinc. High levels of calcium and iron tend to provide some protection against lead poisoning; low levels cause increased susceptibility.

effects

Lead can cause serious damage to the brain and kidneys and eventually lead to death. Like calcium, lead can cross the blood-brain barrier. It destroys the myelin sheaths of neurons, reduces their number, interferes with the neurotransmission pathway and reduces the growth of neurons. Symptoms of lead poisoning include nephropathy, abdominal colic, 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 male fertility. In the developing brain of a child, lead interferes with the formation of synapses in the cerebral cortex, neurochemical development (including neurotransmitters) and the organization of ion channels. Early lead exposure in children is associated with an increased risk of sleep disturbances and excessive daytime sleepiness in later childhood. High blood lead levels are associated with delayed puberty in girls. The increase and decrease in exposure to airborne lead from the combustion of tetraethyl lead in gasoline during the 20th century is associated with historical increases and decreases in crime rates, however, this hypothesis is not universally accepted.

Treatment

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

Sources of influence

Lead exposure is global problem, since the mining and smelting of lead is common in many countries of the world. Lead poisoning usually results from ingestion of lead-contaminated food or water, and less commonly from accidental ingestion of contaminated soil, dust, or lead-based paint. Products sea ​​water may contain lead if the water is exposed to industrial waters. Fruits and vegetables can be infected high content lead in the soils in which they were grown. Soil can be contaminated by particulate buildup 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 inner part pipes will be covered with a protective layer of lead carbonate or lead sulfate. Ingestion of lead paint is the main source of lead exposure in children. As paint breaks down, it flakes off, grinds to 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 its compounds. Inhalation is the second major route of exposure to lead, including for smokers and especially for lead workers. Cigarette smoke contains, among other toxic substances, radioactive lead-210. Almost all of the lead inhaled is absorbed into the body; for oral intake, the rate is 20-70%, with children absorbing more lead than adults. Dermal exposure can be significant for a narrow category of people working with organic lead compounds. The absorption rate of lead in the skin is lower for inorganic lead.

Ecology

Extraction, production, use and disposal of lead and its products have caused significant pollution of soils and waters of the Earth. Atmospheric lead emissions were at their peak during the industrial revolution, and the lead gasoline 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 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 the process of photosynthesis and preventing or killing them. Pollution of soils and plants affects microorganisms and animals. Affected animals have a reduced ability to synthesize red blood cells, which causes anemia. Analytical methods for the determination of lead in the environment include spectrophotometry, X-ray fluorescence, atomic spectroscopy, and electrochemical methods. A specific ion-selective electrode was developed based on the S,S'-methylenebis ionophore (N,N-diisobutyldithiocarbamate).

Limitation and restoration

By the mid-1980s, there had been a significant shift in the use of lead. In the United States, environmental regulations reduce or eliminate the use of lead in non-battery products, including gasoline, paint, solder, and water systems. Particulate control devices can be used in coal-fired power plants to collect lead emissions. Lead use is further restricted by the European Union Restriction of Use Directive hazardous substances. 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 of America, the Occupational Safety and Health Administration has set the acceptable lead exposure limit in the workplace at 0.05 mg/m3 over an 8-hour workday; this applies to metallic lead, inorganic lead compounds and lead soaps. National Institute The United States Occupational Safety and Health Administration recommends blood lead concentrations be below 0.06 mg per 100 g of blood. Lead can still be found in harmful amounts in ceramics, vinyl (used for laying pipes and insulating electrical cords), and Chinese brass. Older houses may still contain lead paint. White lead paint has been phased out in industrialized countries, but yellow lead chromate is still in use. Removing old paint by sanding produces dust that a person can inhale.