Lead prices, occurrence, extraction and use

Lead is a chemical element with the element symbol Pb (Latin plumbum) and the ordinal number 82. It is a toxic heavy metal and is available in the 4. Main group or 14. IUPAC group (carbon group) and 6. Period of the periodic table. Lead is easily deformable and has a comparatively low melting point.

The isotopes 206Pb, 207Pb, and 208Pb are the heaviest stable atoms, making Lead the highest mass and atomic element yet stable. All lead isotopes have the magic proton number 82, which causes this stability. 208Pb even has a so-called double magical core because it also has the magical neutron number 126.

Since the lead isotopes -206, -207 and -208 are the end products of the three natural decay series of radioactive elements, relatively much lead has arisen; it is therefore common in the earth's crust compared to other heavy elements (mercury, gold, etc.).

 

History

In the early Bronze Age, lead was used alongside antimony and arsenic to make bronze from alloys with copper until tin became widely accepted. Already the Babylonians knew lead vases. The Assyrians had to introduce lead (abāru), which is documented by Tiglat-pileser I. among other things as a tribute from Melidu. The Romans used the metal as a material for vessels, as a sling, for seals (hence the name) and water pipes.

Even the Roman author Vitruvius considered the use of lead for drinking water pipes to be harmful to health; he recommended using clay pipes as far as possible; Nevertheless, drinking water pipes made of lead were in use until the 1970s, which is also expressed in the English word plumber ("pipe publisher"). From today's perspective, the addition of lead as a sweetener to the wine was particularly alarming (so-called "lead sugar", see also lead (II) acetate). In Westphalia, the Romans gained until their retreat after the Varus battle lead. The composition of the isotopes typical for different sites shows that the lead for the production of Roman lead coffins, which were found in the Rhineland, comes from the northern Eifel. Since some lead ores contain an economically usable portion of silver, the extraction of lead and silver has been linked with each other since antiquity. The Roman lead processing has led to a detectable pollution to this day: ice cores from Greenland show between the 5. Century BC Chr. And the 3. Century n. Chr. A measurable increase of the lead content in the atmosphere. Even later, lead had an important meaning. It has been used, for example, for the bordering of leaded glass windows, for example in churches or for the covering of lead roofs.

Lead became especially important after the invention of the firearms for the military as material for projectiles of handguns. Since the soldiers made their own projectiles, it was not uncommon for them to steal all the lead they could find to make projectiles.
Alchemical symbol for lead

Lead also played an important role in alchemy. Due to its similarity to gold (similarly soft and heavy), lead was considered to be a good starting material for gold synthesis (synthesis as a color change from gray to yellow). The alchemical symbol for lead is a stylized sickle (♄), since it has been assigned to the god and planet Saturn since ancient times as a planetary metal.

With the beginning of the industrial revolution, lead was then used in large quantities for the chemical industry, eg. B. for the sulfuric acid production in Bleikammerverfahren or the lining of equipment for explosives production needed. It was then the most important non-ferrous metal.

In an attempt to determine the Earth's age by measuring the lead to uranium ratio in rock samples, US geochemist Clair Cameron Patterson, for example, found that 1950 was contaminated with large quantities of lead from the atmosphere without exception. As a source, he was able to prove the Tetraethylblei used as an anti-knock agent in fuels. According to Patterson, the atmosphere in front of 1923 contained almost no lead at all. Based on these findings, he fought all his life for reducing the release of lead into the environment. His efforts eventually led to 1970 entering the US Clean Air Act with stricter emission regulations. 1986 was the sale of leaded gasoline in the United States, in Germany by the Gasoline Lead Law gradually from 1988, completely banned in the EU from 2001. As a result, lead levels in the blood of Americans dropped almost immediately by 80 percent. However, since lead remains practically eternal in the environment, today every human being has about 600 times more of the metal in their blood than they did before 1923. 2000 is still releasing around 100000 tons of it legally into the atmosphere every year. The main culprits are mining, metal industry and manufacturing industry. Lead-acid battery for motor vehicles.

In 2009, the amount of lead won in non-ferrous metals came fourth after aluminum, copper and zinc. It is mainly used for car batteries (lead accumulators) (60% of total production).

In general, an attempt is made to reduce the burden on humans and the environment with lead and thus lead poisoning. In addition to the ban on leaded gasoline, RoHS directives have restricted the use of lead in electrical and electronic equipment as of 2002. 1989 completely prohibited lead-based coatings and coatings, and the use of leaded ammunition was partially banned in some states as of 2005. As a material for water pipes, lead has already been banned from 1973, however, there is still no law for the removal of lead pipes from existing properties, which is why the Federal Council 2017 a ban on lead-containing drinking water pipes demanded.

occurrence

Lead occurs in the earth's crust with a content of about 0,0018% and occurs rather rarely dignified, that is in elemental form. Nevertheless, around 200 sites for solid lead are known worldwide (2017), including in Argentina, Ethiopia, Australia, Belgium, Brazil, the People's Republic of China, Germany, Finland, France, Georgia, Greece, Greenland, Italy, Canada, Kazakhstan, Kyrgyzstan, Mexico, Mongolia, Namibia, Norway, Austria, Poland, Russia, Sweden, Slovenia, the Czech Republic, Ukraine, the US Virgin Islands, the United Kingdom and the United States of America (USA).

Also in rock samples of the Mid-Atlantic Ridge, more precisely at the northeastern edge of the "Markov depth" within the "Sierra Leone Fracture Zone" (Sierra Leone threshold), as well as outside the earth on the moon in Mare Fecunditatis could be found lead.

At each locality, the isotopic composition deviates slightly from the averages given above, so that a precise analysis of the isotopic composition can be used to determine the site of the discovery and to conclude that the archeological findings indicate old trade routes. In addition, lead may also contain different foreign substances such as silver, copper, zinc, iron, tin and / or antimony depending on the location.

In lead ore, lead is usually present as galena (lead sulfide PbS, galena). This mineral is also the most significant commercial source for the extraction of new lead. Further lead minerals are cerussite (lead (II) carbonate, PbCO3, also white lead ore), crocoite (lead (II) chromate, PbCrO4, also red lead ore) and anglesite (lead (II) sulfate, PbSO4, also lead vitriol). The lead minerals with the highest lead concentration in the compound are lithargite and massicotite (up to 92,8%) and minium (up to 90,67%). Altogether so far 514 lead liners are known (state: 2017).

The economically minable reserves are estimated worldwide at 67 million tons (2004 level). The largest deposits are found in the People's Republic of China, the USA, Australia, Russia and Canada. In Europe, Sweden and Poland are the countries with the highest incidence.

Also in Germany was in the northern Eifel (Rescheid / pits Wohlfahrt and Schwalenbach, Mechernich / mine Günnersdorf and open pit / Virginia, Bleialf), in the Black Forest, in the Harz (Goslar / Rammelsberg), in Saxony (Freiberg / Muldenhütten), at the lower Lahn (Bad Ems, Holzappel), and in Westphalia (Ramsbeck / Sauerland) in the past lead ore mined, smelted and refined.

The most important source of lead today is the recycling of old lead products. Therefore, there are only two primary smelters in Germany that produce lead from ore, the Binsfeldhammer lending mill in Stolberg (Rhld.) And Metaleurop in Nordenham near Bremerhaven. All other huts produce so-called secondary lead by working up old lead (especially from used car batteries).

Recovery

By far the most important lead mineral is galena. This often occurs associated with the sulphides of other metals (copper, bismuth, zinc, arsenic, antimony, etc.), which are naturally present as an impurity of the raw lead up to a proportion of 5%.

The ore, processed by crushing, classifying and flotation up to 60% mineral content, is converted into metallic lead in three different industrial processes. The processes of Röder reduction and the roasting reaction increasingly take a back seat and are replaced by direct melting, which on the one hand can be made more economical and on the other hand, are more environmentally friendly.
Röstreduktionsarbeit

This process proceeds in two stages, roasting and reduction. During roasting, the finely comminuted lead sulfide is placed on a traveling grate and 1000 ° C hot air pushed through. It reacts with the oxygen of the air in an exothermic reaction to lead (II) oxide (PbO) and sulfur dioxide. This is expelled via the roasting gases and can be used for sulfuric acid production. The lead oxide is liquid under these conditions and flows downwards. It can be sintered there.

(Röstarbeit)

Subsequently, the reduction of the lead oxide with the aid of coke to metallic lead takes place. This is done in a shaft furnace similar to that used in the blast furnace process. Slag-forming additives such as lime are added.

 (Reduction work)

The countries with the largest lead promotion (2006)

Rank	Country	Flow rates (in 1000 t)	Rank	Country	Flow rates (in 1000 t)
1	People's Republic of China	950	11	Sweden	33,9
2	Australia	642	12	Kazakhstan	33
3	United States	445	13	Morocco	31,3
4	Peru	306,2	14	Russia	24
5	Mexico	118,5	15	Iran	22
6	Canada	76,7	16	North Korea	20
7	Ireland	65,9	17	Bulgaria	19
8	India	39,8	18	Turkey	18,7
9	Poland	38	19	Romania	15
10	South Africa	37,5	20	Brazil	14,7

Röstreaktionsarbeit

This process is mainly used for PbS-enriched lead ores and enables lead generation in one step. The sulphide ore is only incompletely roasted. Subsequently, the lead sulfide / lead oxide mixture is further heated to exclude air. The lead oxide reacts with the remaining PbS without addition of a further reducing agent to lead and sulfur dioxide:

(Röstarbeit)

(Reaction work).

Direct smelting process

Modern lead manufacturing processes are based on direct smelting processes that have been optimized for environmental compatibility and cost-effectiveness (eg the QSL process). Advantageous is the continuous process control with limitation to a reaction space, which occurs as the only emitter for pollutants - in comparison, the classical production methods have the sintering as an additional emitting step. Roasting and reduction take place in parallel in a reactor. The lead sulfide is not fully roasted, similar to the roast reaction process. Part of the lead is thus formed by reaction of the lead sulfide with lead oxide. Since the reactor is slightly inclined, lead and lead-containing slag flow off. This passes through the reduction zone, blown into the coal dust and the lead oxide is reduced to lead. When roasting, pure oxygen is used instead of air. This considerably reduces the volume of exhaust gases, which on the other hand have a higher concentration of sulfur dioxide compared to conventional methods. Their use for sulfuric acid production is thus simpler and more economical.

refining

Lead rolls, electrolytically refined, 99,989%

The resulting lead contains 2-5% other metals, including copper, silver, gold, tin, antimony, arsenic, bismuth in varying proportions. The purification and marketing of some of these by-products, in particular of the silver contained up to 1% in the lead lead, contributes significantly to the economics of lead recovery.

The pyrometallic refining of lead is a multi-step process. By melting in the presence of sodium nitrate / sodium carbonate or air, antimony, tin and arsenic are oxidized and can be deducted as lead antimonates, stannates and arsenates from the surface of the molten metal (antimony smear). Copper as well as possibly contained zinc, nickel and cobalt are removed from the raw metal by seigers of the factory lead. The sulfur content also drops considerably. Depending on the Parkes process, silver may be precipitated from the lead by the addition of zinc and the precipitation of the forming Zn-Ag mixed crystals ("parking etching"), while the importance of the older Pattinson process has declined considerably (see also Preparation of silver, silver look). Bismuth can be stripped from the surface of the lead melt by the Kroll-Betterton process by alloying with calcium and magnesium as bismuth foam.

Further purification can be carried out by electrolytic refining, but this process is more expensive due to the high energy demand. Although lead is a non-noble element, it has a more negative standard potential than hydrogen in the electrochemical series. However, this has a high overvoltage on lead electrodes, so that an electrolytic deposition of metallic lead from aqueous solutions is possible, see electrolytic lead refining.

Refined lead comes as lead or standardized metallurgical lead with 99,9- to 99,97% purity (eg Eschweiler Raffiné) or as fine lead with 99,985 to 99,99% lead (DIN 1719, obsolete) on the market. According to the intended use, designations such as cable lead for the alloy with approx. 0,04% copper are also widespread. Current standards such as DIN EN 12659 are no longer familiar with these common names.

Physical Properties

Lead is a base metal with a standard electrode potential of about -0,13 V. However, it is nobler than many other commodity metals such as iron, zinc or aluminum. It is a diamagnetic heavy metal with a density of 11,3 g / cm³, which crystallizes face centered cubic and thus has a cubic dense sphere packing with the space group Fm3m (space group number 225). The lattice parameter for pure lead is 0,4950 nm (equivalent to 4,95 Å) for 4 formula units per unit cell.

This is the basis for the pronounced ductility of the metal and the low Mohs hardness of 1,5. It is therefore easy to roll sheets or form wires, but because of their low hardness are only slightly resistant. A diamond-like modification, as known from the lighter homologs of the group 14, does not occur in lead. This is due to the relativistic instability of Pb-Pb binding and the low tendency to be tetravalent.

Fresh lead samples are from greyish white to metallic white in color and show a typically metallic luster, which decreases very rapidly due to superficial oxidation. The color changes to dark gray and becomes dull. On paper, the soft metal leaves a (lead) gray line. For this reason, lead was written and painted earlier. The name "pencil" has been preserved to this day, although graphite has been used for a long time.

The melting point of the lead is 327 ° C, its boiling point is 1740-1751 ° C (values ​​differ in technical literature: 1740 ° C, 1746 ° C, 1751 ° C). Lead, as a typical metal, conducts both heat and electricity, but this is much worse than other metals (see Lead Electrical Conductivity: 4,8 · 106 S / m, Silver: 62 · 106 S / m). Below 7,196 K, lead does not show any electrical resistance, it becomes a type I superconductor. The speed of sound in lead is about 1200 m / s, in the literature the values ​​scatter something, probably due to different purity or processing.

Chemical properties

In the air, lead is passivated by formation of a layer of lead oxide and thus protected against further oxidation. Therefore, fresh cuts initially shine metallic, but they quickly start to form a matt surface. In a finely divided state, lead is highly flammable (pyrophoric lead).

Also in various acids lead is insoluble by passivation. Thus, lead is resistant to sulfuric acid, hydrofluoric acid and hydrochloric acid, since insoluble lead salts form with the anions of the respective acid. Therefore, lead for certain applications has a certain importance in chemical apparatus engineering.

In contrast, lead is soluble in nitric acid (lead (II) nitrate is water-soluble), hot, concentrated sulfuric acid (formation of the soluble Pb (HSO4) 2 complex), acetic acid (only in the presence of air) and hot alkalis.

In water that does not contain oxygen, metallic lead is stable. In the presence of oxygen, however, it dissolves slowly, so that leaking drinking water pipes can pose a health hazard. On the other hand, if the water contains many hydrogencarbonate and sulfate ions, which is usually associated with high water hardness, a layer of basic lead carbonate and lead sulfate forms after some time. This protects the water from the lead, but even then some lead from the lines in the water over.

isotope

Naturally occurring lead is an average of about 52,4% of the isotope 208Pb, about 22,1% of 207Pb, about 24,1% of 206Pb, and about 1,4% 204Pb. The composition is slightly different depending on the deposit, so that an analysis of the isotopic composition, the lead origin can be determined. This is important for historical finds from lead and knowledge of past trade relations.

The first three isotopes are stable. 204Pb is a primordial radionuclide. It decomposes by emitting alpha radiation with a half-life of 1,4 · 1017 years (140 quadrillion years) in 200Hg. 208Pb has a double magic core; it is the heaviest stable nuclide. (The even heavier, long-lasting 209Bi is unstable according to recent measurements and decays with a half-life of (1,9 ± 0,2) 1019 years (19 trillion years) emitting alpha particles into 205Tl.) Its very slow decay is due to the fact that with Z = 83, it has only one proton more than the magic proton number of 82 and the magic neutron number 126, which is very similar to the double magic lead nucleus with 208 nucleons).

The stable isotopes of naturally occurring lead are the end products of the uranium and thorium decay series, respectively: 206Pb is the final nuclide of the uranium-radium series beginning with 238U, 207Pb is the end of the uranium-actinium series beginning at 235U, and 208Pb is the end the Thorium series starting with the 244Pu or 232Th. This series of decays leads to the effect that the ratio of the lead isotopes in a sample is not constant over time in the absence of a material exchange with the environment. This can be used for the age determination by the uranium-lead or thorium-lead method, which is due to the long half-lives of uranium and thorium isotopes in contrast to the radiocarbon method just for dating millions of years old samples suitable. In addition, the effect leads to differentiated isotope signatures in lead from different deposits, which can be used for proof of origin.

Furthermore, there are 33 unstable isotopes and 13 unstable isomers from 178Pb to 215Pb, either artificially produced or found in the decay series of uranium or thorium, such as 210Pb in the uranium-radium series. The longest-lived isotope among them is 205Pb with a half-life of 153 million years.

Usage

The largest lead consumers are the USA, Japan, Germany and the People's Republic of China. Consumption is heavily dependent on the economy in the car industry, where approximately 60% of the world's lead demand is used in its accumulators. Further 20% are processed in the chemical industry.

radiation shielding

Because of its high atomic mass, lead is suitable in sufficiently thick layers or blocks for shielding against gamma and X-radiation; It absorbs X-ray and gamma radiation very effectively. Lead is cheaper and easier to process, for example, as a soft sheet, than even "atom-heavier", denser metals. Therefore, it is generally used in radiation protection (eg, nuclear medicine, radiology, radiotherapy) for shielding. One example is the lead apron worn by doctors and patients during x-rays. Leaded glass is also used for radiation protection.

In the hospital sector, as a technical indication for structural facilities with shielding function such as walls, doors, windows, the lead thickness equalization is common and often written down in order to calculate the effectiveness of radiation protection and radiation exposure.

Lead is therefore z. B. also used for anti-scatter grid.

A special application is the shielding of gamma spectrometers for precision dosimetry. For this lead with the lowest possible intrinsic radioactivity is needed. The natural content of radioactive 210Pb is disturbing. It is lower, the longer the smelting time lies, because with the smelting the mother nuclides from the uranium-radium series (companion in the ore) are separated from the lead. The 210Pb therefore decays from the time of smelting on with its half-life of 22,3 years, without new emulation. Therefore, historic lead items such as trim weights from sunken ships or historical cannon balls are sought for the production of low-radiation lead for the production of such shields. There are also other research institutions that need this old lead for similar reasons.

Metal

Lead is predominantly used as metal or alloy. Unlike previous times, when lead was one of the most important and widely used metals, today one tries to replace lead with other non-toxic elements or alloys. However, because of its important properties, especially its corrosion resistance and high density as well as its ease of manufacture and processing, it still has great importance in the industry. For example, elements of similar or even higher density are either even more problematic (mercury, uranium) or very rare and expensive (tungsten, gold, platinum).

Electrical Engineering

Lead-acid battery for motor vehicles

Most lead is used today for chemical energy storage in the form of lead-acid batteries (eg for cars). A car battery contains a lead and a lead (IV) oxide electrode and dilute sulfuric acid (37%) as the electrolyte. The Pb2 + ions formed in the electrochemical reaction form insoluble lead (II) sulfate in the sulfuric acid. Recharging is possible through the reverse reaction of lead (II) sulfate to lead and lead (IV) oxide. One advantage of the lead-acid battery is the high nominal voltage of one battery cell of 2,06 Volt.

Engineering

Since lead has a high density, it is used as a weight. Colloquially, there is therefore the term "lead heavy" for very heavy things. Lead weights have been used as balancing weights for balancing car wheels, among others. But this is since the 1. July 2003 on new cars and since the 1. July 2005 prohibited on all cars (up to 3,5 t); the lead weights have been replaced by zinc or copper weights. Further applications utilizing high density are: lead strings for tightening curtains and dipping weights to balance the buoyancy of divers and equipment while diving. In addition, lead is used as a vibration damper in vibration-sensitive (auto) parts, for stabilizing ships and for special applications of sound insulation.

apparatebau

Lead is chemically very resistant by passivation and resists among others sulfuric acid and bromine. Therefore, it is used as corrosion protection in apparatus and container construction. One early important application was the lead-acid process for producing sulfuric acid, since lead was the only known metal that resisted sulfuric acid vapor. Even earlier plants and rooms for the production of nitroglycerine were lined with lead on the floor and wall. Lead has also been widely used to encase cables for environmental protection, such as telephone cables. Today, lead is mostly by plastics, eg. As PVC, has been replaced, but is still used today in cables in refineries, since it is insensitive to hydrocarbons.

Construction industry

Since lead is easy to process and pour, lead has been used frequently in the past for metallic objects. The most important lead products included pipes. Due to the toxicity of lead compounds which may be formed from lead (lead poisoning), however, lead tubes have not been used since the 1970 years. Despite a formed carbonate layer in the pipes, the lead continues to dissolve in the drinking water. Experience has shown that the limit value of the applicable drinking water ordinance is no longer complied with after just a few meters.

Further use in building found lead for connecting stones by embedded metal brackets or metal dowels, such as to attach hinges to a stone door sill or an iron railing on a stone staircase. This technique is still widely used in restoration. For example, at the top of the spire in St. Stephen's Cathedral in Vienna or the bridge in Mostar. Also for window frames, z. B. to medieval church windows, lead rods were often used. Lead (rolled lead) is also used as a roof covering (eg the main domes of the Hagia Sophia) or for roof closures (eg in the famous "lead chambers", the former prison of Venice and in Cologne Cathedral) as well as for the enclosure of roof openings , Also, in the past, paint and anti-corrosive paints were added to lead, especially paints for metal surfaces. Even today, lead in existing buildings is a building pollutant that needs to be taken into account, as it can still be found in many older building and plant components.

pneumatic controls

A special application of lead pipes was from the late 19. Century pneumatic controls for organs (pneumatic action), pneumatic art pianos and, as a special and very successful application, the control of the link trainer, the first widespread flight simulator. The advantages of lead pipes (cheap, stable, flexible, small space requirement for the necessary extensive bundles of tubes, solderable, mechanically easy to process, durable) were decisive for this.

Military technology

An important customer for lead metal was and is the military. Lead serves as a base material for projectiles, both for spin and for firearms. Chopped lead was fired in so-called grape-shot. The reason for the use of lead was and is on the one hand the high density and thus high penetrating power and on the other hand the easy production by casting. Nowadays, the lead is usually surrounded by a jacket (hence "coat bullet") made of a copper alloy (Tombak). Advantages are above all a higher achievable bullet speed at which an uncoated lead bullet can no longer be used due to its softness, and the prevention of lead deposits inside the barrel of a firearm. However, lead-free ammunition is also available.

body repair

Before the advent of modern 2 component putty, lead or lead-tin alloys have been used to fill vehicle body damage and repair sites due to their low melting point. For this purpose, the material was soldered onto the damaged area with a soldering torch and flux. Subsequently, the spot was sanded as when filling. This has the advantage that the lead, in contrast to putty a firm bond with the sheet enters and joins in thermal expansion of its longitudinal extent. Since the resulting vapors and dusts are toxic, this process is hardly used today except for the restoration of historic vehicles.

Customs

An old oracle custom that the Romans used to cultivate is lead casting, in which liquid lead (nowadays also alloyed with tin) is solidified in cold water. Prospects about the future are to be made on the basis of the random forms. Today, the custom is still happily practiced at New Year to get a (not necessarily taken seriously) outlook on the coming year.

Watersports

When diving lead weights are used for taring; The high density surplus (well 10 g / cm³) compared to water provides compact downforce, so that a diver can float even in shallow water. The use of lead as a weight also benefits from the comparatively low price: Based on the world market prices for July 2013 metals, lead has an excellent price-to-weight ratio. They are used in the form of plates on the soles of an armored diving suit, threaded as rounded blocks on a wide waist belt or - modern - as shotgun pellets in the pockets of a buoyancy compensator. Opening the buckle or the pockets (below) allows the ballast to be dropped quickly if necessary.

The keel ballast of sailing yachts is preferably made of lead. Iron scrap is cheaper, but also less dense, which is not optimal for today's slender keels. In addition to the density is a further advantage that lead does not rust and therefore does not degenerate even in case of damage in the keel fairing.

Alloy component

Lead is also used in some important alloys. By alloying other metals, depending on the metal, the hardness, the melting point or the corrosion resistance of the material change. The most important lead alloy is the hard lead, a lead-antimony alloy, which is considerably harder and therefore mechanically stronger than pure lead. Traces of some other elements (copper, arsenic, tin) are usually contained in hard lead and also significantly affect the hardness and strength. Hartblei is used, for example, in apparatus engineering, where it depends not only on chemical resistance but also on stability.

Another lead alloy is the Letternmetall, a lead alloy containing 60-90% lead, which contains antimony and tin as further constituents. It is used for letters in classic letterpress printing, but today does not matter anymore in the mass production of printed materials, but at best for bibliophile editions. In addition, lead in bearings is used as a so-called bearing metal.

Lead plays a role as an alloy component in soft solder, which is used, inter alia, in electrical engineering. In soft solders tin is the most important component besides lead. The use of lead in solders has been around 1998 20.000 tons worldwide. The EU directive 2002 / 95 / EG RoHS banishes lead since July 2006 largely from the soldering technique. For special applications, however, there are a number of exceptions.

Lead is a common secondary component in brass. There a lead content (up to 3%) helps to improve the machinability. Also in other alloys, such as. As gunmetal, lead may be included as a minor component. It is therefore advisable, after prolonged standing, not to drink the first water coming out of brass fittings because of some dissolved lead.

Lead free

Lead-containing products and applications are either completely replaced (such as tetraethyl lead in gasoline) or the lead content is limited by limits to a value corresponding to the technical impurity (eg tin and solder). These products are often called "lead-free". Limits exist among others in the legislation around the so-called RoHS (Directive 2011 / 65 / EU), which provides for 1000 ppm (0,1%). Strenger is the limit for 100 ppm packaging (94 / 62 / EC directive).

The political will to replace the lead also applies where the use would be technically or economically attractive due to the properties, the health risk is low and recycling with reasonable effort would be possible (eg lead as a roofing).

leaded glass

Because of the shielding effect of the lead, the cone of cathode ray tubes (ie, the "back" part of the tube) for television, computer screens, etc., is lead glass. The lead absorbs the soft X-rays inevitably produced in cathode ray tubes. For this purpose, lead is not yet safe to replace, therefore the RoHS directive is not applied here. Due to this shielding effect, glass with a very high lead content is also used in radiology and in radiation protection (for example in window panes). Furthermore, lead glass is used as a so-called lead crystal because of its high refractive index for high quality glassware.

toxicity

Elemental lead can be absorbed via the lungs, especially in the form of dust. In contrast, lead is hardly absorbed through the skin. Therefore, elemental lead in a compact form is not toxic to humans. Metallic lead forms a dense, poorly water-soluble protective layer of lead carbonate in the air. Toxic are dissolved lead compounds as well as lead dust that can enter the body through ingestion or inhalation. Particularly toxic are organoble compounds, eg. As tetraethyllead, which are highly lipophilic and are rapidly absorbed through the skin.

Since 2006 inhalable fractions of lead and inorganic lead compounds have been classified as carcinogenic by the MAK Commission of the Deutsche Forschungsgemeinschaft:

Lead arsenate and lead chromate in the 1 category ("Substances that cause cancer in humans and are thought to contribute to cancer risk." Epidemiological studies provide reasonable evidence for a link between human exposure and the onset of cancer. ")
Lead and other inorganic lead compounds other than lead arsenate and lead chromate in the 2 category ('Substances to be regarded as carcinogenic to humans, because sufficient results from long-term animal studies or evidence from animal studies and epidemiological studies are considered to contribute to Cancer risk. ").

Lead accumulates in the body even when taking the smallest amounts, which are taken over a longer period steadily, as it is z. B. embedded in bone and is excreted only very slowly. Lead can cause chronic intoxication, including headaches, fatigue, emaciation, and defects in blood, nervous and muscular systems. Lead poisoning is especially dangerous for children and pregnant women. It can also cause fruit damage and inability to produce. In extreme cases, lead poisoning can lead to death. The toxicity of lead is based inter alia on a disorder of hemoglobin synthesis. It inhibits several enzymes and thus hinders the incorporation of iron into the hemoglobin molecule. As a result, the oxygen supply of the body cells is disturbed.

Lead glass and lead glaze is not suitable for eating and drinking vessels, as vinegar (acid) can dissolve lead as a water-soluble lead acetate from the silicate composite. When car engines still ran on gasoline with lead tetraethyl, the vegetation near roads and in the cities was contaminated with lead, as oxide dust. Rough and recessed surfaces, such as the collection around the stem of an apple, are traps for dust.

Lead pollution of the environment

Air

The lead pollution of the air is mainly caused by lead-containing dusts: the main sources are the lead-producing industry, the burning of coal and, until a few years ago, especially the car traffic due to the combustion of leaded fuels in car engines - by reaction with the halogenated hydrocarbons added to the gasoline the lead tetraethyl added in addition to lower amounts of lead (II) chloride and lead (II) bromide especially lead and lead (II) oxide. As a result of the ban on lead-containing fuels, the corresponding air pollution has declined significantly in recent years.

Lead contamination by lead dust is currently highest at work in lead-producing and processing plants. Even when cleaning and removing old Mennige paintings by sandblasting leads to lead dust. The lead dioxide dust resulting from lead refining and the burning of coal could be reduced by suitable filters. Another source that is negligible in terms of quantity is the incineration of household waste in waste incineration plants.

Sportsmen and other shooters are exposed to significant burdens due to (heavy) metals contained in the muzzle or detonator fire, including lead, antimony, copper and mercury; [48] precaution can be provided by operating appropriate extraction equipment on shooting ranges and by using lead-free Ammunition to be taken.

ground

Even soils can be contaminated with lead. The mean lead content of the continental crust is 15 mg / kg. Soils naturally contain between 2 and 60 mg / kg lead; if they are formed from lead-containing rocks, the content can be significantly higher. The majority of the lead contamination of soils is anthropogenic, the sources are manifold. The majority of the entry takes place via lead from the air, which come with the rain or by dry deposition in the soil. For Germany and the year 2000 the atmospheric input into soils was estimated at 571 t lead / year. Another source is contaminated fertilizer, both mineral fertilizer (136 t Pb / a), especially ammonium saltpeter, and manure (182 t Pb / a). Sewage sludge (90 t Pb / a) and compost (77 t Pb / a) also contribute to the lead contamination of the soils. [51] There is also a significant input from lead shot ammunition. For contaminated sites, such. As in former locations of lead-producing industries or in the vicinity of old lead-sheathed cables, the soil can also have a high lead load. There is a particularly large lead diversification in the town of Santo Amaro da Purificação in Brazil.

Water

The lead contamination of rivers and lakes is mainly due to leaching of lead from polluted soils. The release of small amounts of lead by the rain from lead materials, such as lead slabs, contributes to the lead contamination of the waters. The direct pollution of waters by the lead industry and the lead mining plays (at least in Germany) due to the construction of sewage treatment almost no longer matter. The annual entry of lead into water has decreased in Germany from about 900 t in the year 1985 to about 300 t in the year 2000. In Germany, the limit since the 1. December 2013 10 μg / L (formerly 25 μg / L); the basis of the measurement is a sample representative of the average weekly water consumption by consumers (see Drinking Water Ordinance).

food

Through exposure to lead from air, soil and water, the metal enters the food chain of humans through fungi, plants and animals. Particularly high levels of lead contamination can be found in various fungi. On the leaves of plants, lead deposits as dust, which was characteristic of the environment of roads with a lot of car traffic, as gasoline was still lead. This dust can be removed by careful washing. Additional sources may be leaded ammunition in hunted animals. Lead can also change from lead-containing glazes of ceramic vessels into food. In fresh fruits and vegetables in the vast majority of cases lead and cadmium are not or only in very small traces detectable.

Water pipes made of lead pipes can pollute the drinking water. They have not been installed in Germany until the 1970 years. Lead pipes are still to be found, especially in old buildings in some regions of northern and eastern Germany. According to Stiftung Warentest, the lead levels of tap water were above the current legal limit for more than 5% of the samples of water from these buildings. The same applies to Austria and concerns house supply lines of the water supplier and lines in the house, which are the property of the homeowner. From lead-containing crockery, lead can be dissolved out by sour foods (fruit, wine, vegetables).

Water line fittings (stopcocks, fittings, angle valve, mixer) are usually made of brass or gunmetal. Brass is added for good machinability 3% lead, gunmetal contains 4-7%. Whether lead and other heavy metal ions (Cu, Zn, Ni) pass into water to a relevant extent depends on the water quality: water hardness, pH, oxygen, salinity. With 2013, the limit value for lead in drinking water has been lowered to 0,01 mg / L. Basically, after prolonged standing of the water in the line, about overnight, by running the water pipe of about one minute (flushing) before removal for drinking water purposes, the content of all ions migrated from the conduit wall can be reduced.

Analytics

Classical qualitative determination of lead
Evidence by crystallization

Lead ions can be represented as lead (II) iodide in a microscopic detection reaction. The sample is dissolved in dilute hydrochloric acid and carefully evaporated to crystallization. The residue is taken up with a drop of water and then with a crystal of a water-soluble iodide, eg. As potassium iodide (KI), added. After a short time, microscopic, yellow, hexagonal leaflets of the lead (II) iodide are formed.

Qualitative proof in the separation process

Since lead does not precipitate quantitatively as PbCl2 upon addition of HCl, it can be detected in both the HCl group and the H2S group. The PbCl2 can be precipitated by adding potassium iodide according to the above reaction as yellow PbI2, as well as with K2Cr2O7 as a yellow lead chromate, PbCrO4.

After introducing H2S into the hydrochloric acid sample, divalent lead precipitates in the form of black PbS. This is detected after digestion with (NH4) SX and addition of 4 M HNO3 as PbI2 or PbCrO4.

Instrumental quantitative analysis of lead

For trace analysis of lead and its organ derivatives, a number of methods are available. However, new and improved methods are constantly being presented in the literature, also with regard to the often required preconcentration. A not to be underestimated problem is the sample processing.
Atomic absorption spectrometry (AAS)

Among the various AAS techniques, the quartz tube and graphite tube technology provides the best results for the lead analysis of lead compounds. Often, lead is converted to the volatile lead hydride, PbH4, using NaBH2. This is passed into a quartz cuvette and then electrically heated to above 900 ° C. The sample is atomized and the absorbance at 283,3 nm is measured using a hollow cathode lamp. A detection limit of 4,5 ng / ml was achieved. The AAS also likes to use an air-acetylene torch (F-AAS) or microwave-induced plasma (MIP-AAS) for atomization.

Atomic Emission Spectrometry (AES)

In the AES, microwave-induced plasma (MIP-AES) and inductively coupled argon plasma (ICP-AES) have proven themselves for atomization. The detection takes place at the characteristic wavelengths 283,32 nm and 405,78 nm. The detection limit of 3 pg / g was determined for trimethyl lead, (CH3) 0,19Pb + using the MIP-AES. [61] The ICP-AES provides a detection limit for lead in drinking water of 15,3 ng / ml.

Mass spectrometry (MS)

In nature, four stable isotopes occur at different rates for lead. For mass spectrometry, the isotope 206Pb is often used. With the help of ICP quadrupole MS, this urinary isotope could be determined with a detection limit of 4,2 pg / g.

photometry

The most widely used method for the photometric detection of lead is the so-called dithizone method. Dithizone is a bidentate, aromatic ligand and forms at pH 9-11,5 with Pb2 + ions a red complex whose absorbance at 520 nm (ε = 6,9 104 l / mol · cm) is measured. Bismuth and thallium interfere with the determination and should first be precipitated or extracted quantitatively.

voltammetry

The subtractive anodic stripping voltammetry (SASV) is ideal for the electrochemical determination of traces of lead. The actual voltammetric determination is preceded by a reductive enrichment period on a rotating Ag-disk electrode. This is followed by the actual determination by measuring the oxidation current when scanning a potential window from -800 mV to -300 mV. Subsequently, the measurement is repeated without previous enrichment and the resulting curve is subtracted from the first measurement. The height of the remaining oxidation peak at -480 mV correlates with the amount of lead present. A detection limit of 50 pM lead in water was determined.

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