The structure of the palladium atom. Extraction, properties and application of palladium Palladium precious metal or not

Noble metal of the platinum group, silvery in color, does not tarnish in air. Discovered by the English chemist and mineralogist W.Kh. Wollaston, who discovered palladium in native platinum in 1803. Malleable and malleable. More fusible than platinum, easily rolled and drawn into wire. Melting point 1552°C. Paramagnetic. Soluble in HNO 3 , in hot concentrated H 2 SO 4 and aqua regia. Palladium has an extremely high affinity for hydrogen, being able to absorb 900 times its own volume of hydrogen in powder form. Compared to other platinum metals, it is less resistant to oxidizing agents.

Finding

Palladium occurs as an admixture in many sulfides and silicates of ultramafic and mafic rocks. Some coals are enriched with palladium up to 10%, an increased concentration is observed in manganese ores, in phosphorites, in plant ash. The content of palladium is increased in ultramafic rocks and rocks containing Cu, Ni, and Te sulfides. Usually found in nature as an impurity in native platinum, with which it forms a disordered solid solution; sometimes found in its placers in the form of rounded grains. As a rule, it contains impurities of platinum, iridium, gold, silver. Palladium platinum contains 19-40% palladium, palladium stannoplatinum - 17-21%, polyxene - up to 6%, ferroplatinum - up to 13%, iridide platinum - up to 4%. It can also be found as an admixture to native gold (in Brazil, for example, a rare variety of native gold was found ( porpecite), containing 8-11% palladium). It is formed in the zone of oxidation of primary sources of platinum and directly in placers as a result of hypergene transformation of platinum minerals. In iron meteorites, up to 7.7 grams per ton of matter. palladium, in stone - up to 3.5 gr.
Since placer deposits of native palladium are very rare, the main raw materials for its associated production are nickel and copper sulfide ores (Norilsk district, etc.)

Location

In Russia, native palladium is mined together with platinum from deposits associated with ultrabasic massifs. Pure palladium was first extracted from native platinum in 1840 in the Urals (in 1843 a medal weighing 46.88 g was minted from the first palladium).

• On Wed. In the Urals, deposits of native platinum containing palladium are known in the Nizhny Tagil region.
• On the Konder Ridge (Khabarovsk Territory, Russia).
• Bushveld massif, Sev. Eastern Prov., South Africa (in the zone of oxidation of platinum deposits).
• In chromites of the "Great Dyke", Zimbabwe.
• Nickel deposits, pcs. New Southern Wales, Australia.
• Copper-nickel deposit Sudbury in Prov. Ontario, and the Thompson deposit in Prov. Manitoba (Canada).
• Placers of the San Juan and Atrato rivers, Colombia.
• Placers in pcs. Minas Gerais, Brazil

Palladium (English) PALLADIUM) - Pd

CLASSIFICATION

PHYSICAL PROPERTIES

Translation into other languages

Instruction

If there are samples of sufficiently pure metals that are similar in appearance (for example, palladium, platinum, silver), then they can be relatively easily separated from each other by determining the density of each of the samples. Since the density of pure silver is approximately 10.5 grams / cubic centimeter, it is about 12 grams (more precisely, 12.02), and platinum is approximately 21.4 grams. But, of course, this method is admissible only for very pure substances, in which the content of impurities is relatively small.

You can unmistakably distinguish palladium from the same platinum by trying a piece of the substance in hot nitric acid. Palladium will dissolve, platinum will not. It dissolves only in the famous "royal vodka" (a mixture of hydrochloric and nitric acids), and when heated. In cold "royal vodka" the reaction is very slow.

Geologists as well as analytical chemists widely use the quality of noble metals on the touchstone. It is a specially made plate from a certain type of silicon shale. Such a touchstone has the following properties: it is very hard, resistant to aggressive substances (including strong acids and their mixtures), has a fine-grained structure.

A qualitative analysis (sample) on this stone is done as follows: they take the tested metal (or its alloy) and carry it out, with a rather noticeable pressure, over the surface of the plate. The trail should be clearly visible, have a length of about 2 centimeters. Then they act on the trace with a specially prepared reagent and observe what the result will be.

If the drawn line is left by palladium or its alloy, then when it is exposed to a reagent consisting of a mixture of "aqua regia" and a 10% solution of potassium iodide, a bright, clearly distinguishable red-brownish spot quickly appears. This is because during the chemical reaction, the substance K2PdCl4 is formed - potassium tetrachloropalladate.

Helpful advice

Palladium is widely used in organic synthesis (catalyst), in electroplating and electrical engineering, medicine, and in the manufacture of high-precision measuring instruments. By adding even the smallest amounts of palladium to gold, it acquires strength and a characteristic color ("white gold"). Palladium is a precious metal and therefore is used in trading on the exchange and over-the-counter markets.

Once upon a time, platinum was not appreciated, because they did not know how to process it. Due to its resemblance to silver, and platinum is a silvery metal, it was called the contemptuous word "silver".

Often, rings or earrings are stored in old caskets inherited from. The items themselves are already valuable, as they are antique, but they can also turn out to be platinum! It’s not surprising that you want to appreciate them, but you don’t want to take them out of the house for any reason. You can try to do it yourself.

Properties of platinum

Before proceeding with the steps to determine platinum, you need to know how it differs from other noble metals. The first thing to do is to estimate the weight. Given the location of platinum in the periodic table, you can see that it is one of the heaviest metals, only osmium with iridium have a higher density. For jewelry works, platinum is used not lower than the 850th test, which means that the pure precious metal in the product is not less than 85%. Given that usually the sample of products made of silver or gold is lower, therefore, there are fewer of these metals themselves in the product.

No chemicals in everyday life affect platinum, which means that traces of iodine or acetic acid will not remain on the product. Neither water nor air oxidize this metal; it is one of the most chemically inert elements. Liquid bromine and "aqua regia" (a mixture of two concentrated acids, hydrochloric and nitric), are able to dissolve platinum. But this is a very slow process. Ordinary household burners are not able to melt the metal, as it melts at temperatures above 1768 degrees.

How to recognize platinum yourself

The method that is most acceptable in domestic conditions,

Palladium (lat. Palladium) in the periodic system is denoted by the symbol Pd - a chemical element with atomic number 46 and atomic mass 106.42. It is an element of the second triad (platinum metals) of the secondary subgroup, the eighth group of the fifth transitional period of the periodic system of Dmitry Ivanovich Mendeleev. Palladium is a silver-white noble metal similar in appearance to silver, but their similarities do not end there, because the forty-sixth element is the lightest of the platinum metals. In terms of density (12.02 g/cm3), palladium is closer to silver (10.49 g/cm3) than to its related platinum (21.5 g/cm3). Palladium is a heavy, refractory, malleable metal that is easily rolled into foil and drawn into thin wire.

Natural palladium consists of six stable isotopes: 102Pd (1.00%), 104Pd (11.14%), 105Pd (22.33%), 106Pd (27.33%), 108Pd (26.46%) and 110Pd ( 11.72%). The longest-lived artificial radioactive isotope is 107Pd, with a half-life of seven million years. Many isotopes of palladium are produced in comparatively small amounts in the fission of uranium and plutonium nuclei. In modern nuclear reactors, 1 ton of nuclear fuel with a burnup of 3% contains about 1.5 kg of palladium.

Palladium was discovered by the English physician and chemist William Wollaston in 1803 while studying raw platinum brought from South America, in that part of it that is soluble in aqua regia. Having dissolved the ore, Wollaston neutralized the acid with a solution of NaOH, after which he precipitated platinum from the solution by the action of ammonium chloride NH4Cl (ammonium chloroplatinate precipitates). Mercury cyanide was then added to the solution to form palladium cyanide. Pure palladium was isolated from cyanide by heating. Only a year later, Wollaston reported to the Royal Society that he had discovered palladium and another new noble metal, rhodium, in raw platinum. The very name of the new element - palladium (Palladium) Wollaston derived from the name of the minor planet Pallas (Pallas), discovered shortly before (1801) by the German astronomer Olbers.

The forty-sixth element, due to a number of its remarkable physical and chemical properties, has found wide application in many areas of science and life. So some types of laboratory glassware are made from palladium, as well as parts of equipment for separating hydrogen isotopes. Alloys of palladium with other metals find a very valuable application. For example, alloys of the forty-sixth element with silver are used in communication equipment (contact manufacturing). Temperature controllers and thermocouples use alloys of palladium with gold, platinum and rhodium. Certain alloys of palladium are used in jewelry, dentistry (dentures) and even used to make parts for pacemakers.

When applied to porcelain, asbestos and other supports, palladium serves as a catalyst for a number of redox reactions, which is widely used in the synthesis of a number of organic compounds. The palladium catalyst is used to purify hydrogen from traces of oxygen, as well as oxygen from traces of hydrogen. A solution of palladium chloride is an excellent indicator of the presence of carbon monoxide in the air. Palladium coatings are applied to electrical contacts to prevent sparking and increase their corrosion resistance (palladium).

In jewelry, palladium is used both as a component of alloys and on its own. In addition, the Bank of Russia mints palladium commemorative coins in very limited quantities. Not a large number of palladium is consumed for medical purposes - the preparation of cytostatic drugs - in the form of complex compounds, similar to cis-platinum.

Biological properties

Scientists definitely cannot say anything about the biological role of palladium in living organisms, perhaps further studies of the properties of this platinoid will reveal its significance in certain biological processes.

Nevertheless, the role of this element in medicine is quite large. So in some countries (including Russia) a certain amount of palladium is used to obtain cytostatic drugs - in the form of complex compounds, similar to cis-platinum. Immediately after the discovery of the cytostatic effect of platinum by Rosenberg, scientists around the world began to study this phenomenon and synthesize more and more effective and safe platinum compounds for medical purposes. In recent years, the world's leading medical institutions and large companies have been trying to find bioactive drugs among other compounds of the platinum group, including palladium. This noble metal kills and slows down the growth of cancer cells no worse than platinum, but it is almost ten times less toxic. Anticancer drugs based on palladium are undergoing the latest clinical trials and may soon be in service with oncologists.

Another rather important purpose of palladium and its alloys is associated with the high biological compatibility of this metal - the manufacture of medical instruments, parts of pacemakers and dentures. Even now, the use of traditional base alloys based on cobalt, nickel and chromium for orthopedic dentistry is significantly reduced due to the frequent occurrence of adverse reactions in a number of patients sensitive to the influence of base metals.

What will replace obsolete materials? The answer is obvious - noble metal alloys, including platinoids and palladium in particular. One of these alloys is palladant ("Superpal"), containing 60% palladium and 10% gold. The alloy has a beautiful silver-gray metallic color, reliable strength characteristics, and is biologically compatible. In maxillofacial surgery, it is used for the manufacture of extended bridges. Another alloy containing palladium is plagodent ("Super KM"). 98% consists of precious metals (except for palladium contains gold and platinum), has a light yellow color and is intended for the manufacture of cast prostheses, inlays, semi-crowns, bridges, mainly with a ceramic or glass-ceramic coating.

Palladium is also used in the food industry. After it became clear in a number of countries that nickel was the cause of a surge in allergies in the population, many blamed dishes made from this material. However, subsequent studies refuted this hypothesis and established the true cause of the allergic reaction - nickel was found in food, and more specifically in margarine made from vegetable oil. The fact is that according to the technological process, the oil must become solid, for this it is hydrogenated, that is, the molecules are saturated with hydrogen using a catalyst. Nickel played the role of such for a long time. To intensify the process, the catalyst powder is intensively mixed with vegetable oil at high temperature, and then the catalyst is removed by filtration, however, nickel is not completely removed, and if a failure occurs in the process, then a rather large amount of this allergen enters the final product.

It was possible to solve this problem thanks to the developments of scientists from the Petrochemical Institute named after A.V. Topchiev. They managed to create a catalyst based on palladium deposited on aluminum oxide. This introduction made it possible to solve several problems at once: palladium is inert and safe for humans, in addition, it is many times more effective than nickel, which means that it needs a thousand times less. There are other advantages of the palladium catalyst - it is easier to remove from the final product and the structure of the molecules of the latter is "deciphered" by the body more easily than in the case of a nickel catalyst, so "palladium" margarine is easier to digest.

It is known that palladium is often used by jewelers in alloys with other precious metals. So alloys of the 583rd and 750th tests, called "white gold", can contain ten percent or more palladium. In our country, the government officially established palladium 500 and 850 samples. These samples are most common in jewelry.

Another popular palladium sample is 950. This is due to the fact that such a sample is made of metal wedding rings, as an alternative to rhodium-plated white gold rings. The fact is that rhodium is quickly erased from the surface of the ring, and not everyone will be able to renew the expensive coating every year. Palladium rings have exactly the same appearance as gold rings, but do not require annual renewal. In addition to standard palladium alloys, decorative compounds of palladium with indium are sometimes used in jewelry production, forming a wide range of colors from golden to lilac. However, products made from such an alloy are very rare.

In 1988, for the first time, 25-ruble coins were minted from palladium in the series “1000th Anniversary of Old Russian Coinage, Literature, Architecture, Baptism of Russia”. On a coin weighing 31.1 g of the highest 999 test, a monument to Prince Vladimir Svyatoslavovich in Kyiv is depicted. In Basel, at the International Numismatic Exhibition, this series was recognized as the best program of the year, receiving the first prize for the quality of execution.

The release of such coins was limited and did not last long, for this reason the coins have a high collectible value. The most valuable are two series of coins (1993-1994 issue): “The first Russian round-the-world trip. 1803-1806 "-" Sloop "Hope"" with a portrait of I.F. Kruzenshtern, "Sloop" Neva "(Yu.F. Lisyansky)". The second series “The First Russian Antarctic Expedition. 1819-1821 "-" Sloop "Mirny" (M.P. Lazarev)", "Sloop" Vostok "(F. F. Bellingshausen)". Also presented are coins of the series "Russia and World Culture" - "A. Rublev, M. P. Mussorgsky”, coins of the “Russian Ballet” series and dedicated to Russian monarchs.

There are many awards and prizes in the world that are awarded to outstanding scientists. There is a William Hyde Wollaston medal made of pure palladium. This award was established almost two centuries ago (1831) by the London Geological Society and was initially made of gold. Only in 1846, the famous English metallurgist Johnson extracted pure palladium from Brazilian palladium gold, which was intended exclusively for the manufacture of this medal. Among those awarded the Wollaston medal was Charles Darwin, and in 1943 the medal was awarded to the Soviet scientist Academician Alexander Evgenievich Fersman for his outstanding mineralogical and geochemical research. Now this medal is kept in the State Historical Museum.

However, this is not the only palladium medal. The second, awarded for outstanding work in the field of electrochemistry and the theory of corrosion processes, was established by the American Electrochemical Society. In 1957, this award was awarded to the works of the largest Soviet electrochemist, Academician A.I. Frumkin.

The merits of William Wollaston include not only the discovery of palladium (1803) and rhodium (1804), the production of the first pure platinum (1803), but also the discovery of ultraviolet radiation independent of J. Ritter. In addition, Wollaston designed a refractometer (1802) and a goniometer (1809).

The palladium industry in Russia appeared relatively late. It was not until 1922 that the State Refinery produced the first batch of Russian refined palladium. This marked the beginning of the industrial production of palladium in our country.

It is known that palladium is able to enhance the anti-corrosion properties of even such a metal resistant to aggressive environments, like titanium. The addition of palladium in just 1% increases the resistance of titanium to sulfuric and hydrochloric acids. So for a year in hydrochloric acid, a plate made of a new alloy loses only 0.1 millimeters of its thickness, while pure titanium thins by 19 millimeters over the same period. A solution of calcium chloride does not affect the alloy at all, while titanium annually loses up to two millimeters in an aggressive environment. What is the secret of such an alloy? The fact is that the acid interacts primarily with palladium and immediately the surface of the second component of the alloy is covered with the thinnest oxide film - the part, as it were, puts on a protective shirt. This phenomenon was called by scientists the self-passivation (self-protection) of metals.

Story

The honor of discovering palladium belongs to the Englishman William Hyde Wollaston, who isolated the new metal from the raw platinum of South American mines in 1803. Who is the man who is named after the pure palladium medal awarded annually by the Geological Society of London?

At the end of the eighteenth century, William Wollaston was one of the many obscure London doctors who practiced in poor working-class areas. A job that did not bring income could not suit an intelligent and enterprising young man. In those days, the doctor had to have the skills not only of a physician, but also to master the pharmaceutical business, which in turn required an excellent knowledge of chemistry. W.H. Wollaston turned out to be an excellent chemist - studying platinum, he invented new way manufacture of platinum tableware and set up its production. It is worth mentioning that in those years, platinum glassware for chemical laboratories was a necessity, because the hype around scientific discoveries was the same as in the time of the alchemists around the philosopher's stone. It is no coincidence that at the turn of the XVIII and XIX centuries. discovered about 20 new chemical elements!

It is not surprising that the Englishman's new enterprise began to bring him a considerable income, sufficient to leave the unpromising medical practice. Products manufactured by Wollaston were in demand far beyond the foggy Albion, allowing the Englishman to engage in new chemical research without worrying about the money issue. Improving the technique of refining and cleaning platinum from impurities, the chemist came to the idea of ​​the possibility of the existence of platinum-like metals.

The platinum that Wollaston had to work with was a by-product obtained from the washing of gold sands in the distant Colombian Republic. In addition to gold, it contained mercury impurities, which had to be removed. He dissolved raw platinum in aqua regia, after which he precipitated only platinum from the solution - with especially pure ammonia NH4Cl. It was then that Wollaston noted that the precipitated solution had a pink hue, which impurities such as gold and mercury could not give. By adding zinc to the colored solution, the chemist obtained a black precipitate, which he dried and then dissolved in aqua regia. It turned out that only part of the black powder was dissolved. Diluting the concentrate with water, Wollaston added potassium cyanide, as a result of which a copious orange precipitate formed, which turned gray when heated. The gray precipitate was fused into metal, which was less than mercury in specific gravity. Having dissolved the resulting metal in nitric acid, Wollaston obtained a soluble part, which was palladium and an insoluble part, from which he isolated another platinoid, rhodium.

Rhodium got its name from the Greek word "pink", because rhodium salts give the solution pink color. As for palladium, Wollaston named it after an earlier astronomical discovery. Shortly before the discovery of palladium and rhodium (in 1802), the German astronomer Olbers discovered a small planet in the solar system and named it Pallas in honor of the ancient Greek goddess of wisdom, Pallas Athena.

What did Wollaston do after the discovery of a new element? He did not immediately announce this, but circulated an anonymous advertisement for the sale of the new palladium metal in the store of the mineral dealer Forster. The message about a new noble metal - "new silver" interested many, including the chemist Richard Cheneviks. Having a typical hot-tempered and uncontrollable Irish character, Chenevix wanted to expose the "fraudulent trick" and, neglecting the high price, bought a palladium bar and began to analyze it.

Soon the Irishman suggested that the metal was not at all new element, and is made of platinum by fusion with mercury according to the method of the Russian scientist A. A. Musin-Pushkin. This opinion Cheneviks hastened to express - first in a report read before members of the Royal Society of London, and then in the general press. In response, the anonymous advertiser announced that he was willing to pay £20 to anyone who could artificially prepare the new metal using Chenevix's proposed method. However, other chemists, and even Chenevix himself, with all their efforts, could not find either mercury or platinum in palladium ...

Only some time later, Wollaston officially announced that he was the author of the discovery of palladium and described a method for obtaining it from raw platinum. At the same time, he reported on the discovery and properties of another platinum metal - rhodium. In addition, he said that he was the anonymous seller of the new metal, who set a premium for its artificial preparation.

Such an interesting and extraordinary person was William Hyde Wollaston - a little-known London doctor and a world famous chemist - the discoverer of palladium and rhodium.

Being in nature

Palladium is one of the rarest metals, its average concentration in the earth's crust is 1∙10-6% by weight, but this is twice as much as gold contained in the earth's crust (5∙10-7%). William Wollaston had to extract palladium from grains of Columbian native platinum, the only mineral known at that time to contain palladium. Nowadays, geochemists can name about 30 minerals that include this noble metal.

Like platinum, the forty-sixth element occurs in its native form (unlike the rest of the platinoids), while it may contain impurities of other metals: platinum, gold, silver and iridium. In appearance, it is rather difficult to distinguish it from native platinum, but it is much lighter and softer than it. Quite often, palladium itself is an impurity in native gold or platinum. Thus, palladium platinum containing 40% palladium was found in the ores of Norilsk, and in Brazil (Minas Gerais state) a very rare and little-studied variety of native gold was found - palladium gold or porpecite. In appearance, this mineral is very difficult to distinguish from pure gold, because it contains only 10% palladium.

About a third of the minerals containing palladium are little studied, some of them do not even have a name, this is due to the fact that the minerals of all platinum metals form microinclusions in ores and are difficult to study. One such mineral is allopalladium. This silvery-white mineral with a metallic sheen is very rare. All components of this mineral have not yet been fully identified, however, spectral analysis showed the content of mercury, platinum, ruthenium and copper in it. The most famous palladium minerals are palladite PdO, stannopalladite Pd3Sn2, stibiopalladite Pd3Sb (contains PtAs2 impurities), braggite (Pd, Pt, Ni) S (16-20% palladium), tarite PdHg. The last of these minerals was found back in 1925 in the diamond placers of British Guinea. Its composition was established by conventional chemical analysis: 34.8% Pd and 65.2% Hg.

The largest placer deposits of platinum metals (including palladium) are located in Russia - in the Urals. Other palladium-rich countries include the United States (Alaska), Colombia and Australia.

However, the main supplier of the forty-sixth element was the deposits of nickel and copper sulfide ores, in which palladium is a by-product of processing. After all, its content in such ores is three times greater than that of platinum itself, not to mention its other satellites. Large deposits of such ores are located in Africa (Transvaal) and Canada. In our country, the richest deposits of copper-nickel ores are located in the Arctic (Norilsk, Talnakh).

Palladium is found not only in the bowels of our planet, as evidenced by the chemical analysis of space "guests". So, in iron meteorites, up to 7.7 grams of palladium per ton of substance, and in stone - up to 3.5 grams. And on the Sun, it was discovered simultaneously with helium back in 1868.

It is not surprising that, having the richest reserves of platinum metal ores, Russia is one of the world's largest producers and exporters of palladium, as well as platinum, nickel and copper. Leadership in this area among Russian companies belongs to MMC Norilsk Nickel. Enterprises owned by the company are mining valuable metals on the Taimyr and Kola Peninsulas. The development of deposits in the Krasnoyarsk Territory is underway. It is believed that the deposit of the Taimyr Peninsula is one of the richest in the world in terms of palladium content in sulfide ores. For this reason, Norilsk Nickel is the owner of the largest palladium reserves in the world.

Application

Another very valuable property of palladium is its relatively low price. So in the late sixties of the last century, it cost about five times less than platinum. Over time, the price of the forty-sixth element rose, but so did the prices of other precious metals. It is this quality of palladium that makes it the most promising of all platinum metals, expanding the scope of its use.

Palladium, like other platinum metals, is an excellent catalyst. In its presence, many practically important reactions begin and proceed at low temperatures, for example, the processes of fat hydrogenation and oil cracking. Palladium accelerates the hydrogenation processes of many organic products much better than such a proven catalyst as nickel. The forty-sixth element is used as a catalyst in the production of acetylene, many pharmaceuticals, sulfuric, nitric, acetic acids, fertilizers, explosives, ammonia, chlorine, caustic soda and other products of organic synthesis.

In chemical production equipment, a palladium catalyst is most often used in the form of “niello” (in a finely dispersed state, palladium, like all platinum metals, becomes black) or in the form of PdO oxide (in hydrogenation apparatuses). Since the seventies of the XX century, palladium has been actively used by the automotive industry in catalysts for afterburning exhaust gases (neutralizers). By the way, neutralizers are necessary not only for cleaning car exhaust gases, but also for cleaning any gas emissions, for example, at thermal power plants. Industrial installations of this purpose are used in the USA, some EU countries and Japan.

Due to the fact that hydrogen actively diffuses through palladium, the latter is used for deep purification of hydrogen. Under low pressure, the gas is passed through palladium tubes closed on one side, heated to 600 ° C. Hydrogen quickly passes through palladium, and impurities (water vapor, hydrocarbons, oxygen, nitrogen) are retained in the tubes. To reduce the cost of the process, not pure palladium is used, but its alloys with other metals (silver, yttrium).

Palladium and alloys based on it are widely used in electronics - for coatings resistant to sulfides. A certain amount of this metal is used for the production of high-precision precision resistance rheochords (aerospace and military equipment), including in the form of an alloy with tungsten (for example, PdV-20M). In its pure form, palladium is found in ceramic capacitors with high temperature stability, which are used in the production of pagers, mobile phones, computers, widescreen TVs and other electronic devices. Palladium chloride PdCl2 is used as an activating agent in the galvanic metallization of dielectrics - in particular, the deposition of copper on the surface of laminated plastics in the production of printed circuit boards in electronics.

The forty-sixth element is also needed in jewelry, both as a component of alloys and by itself. For example, the well-known concept of "white gold" refers to an alloy of gold, palladium and some other elements. For example, "white gold" of the 583rd test contains 13% palladium, and the white precious metal of the 750th test has the following composition: Au - 75%, Ag - 4%, Pd - 21% (for this sample, the composition may vary). "Pure" palladium Jewelry have in their composition an admixture of ruthenium of 5%.

Palladium is used for the manufacture of special chemical glassware (for example, for the production of hydrofluoric acid) - stills, vessels, pump parts, retorts. Part of the metal is spent on the manufacture of corrosion-resistant parts of high-precision measuring instruments.

In the glass industry, palladium alloys are used in crucibles for melting glass, in spinnerets for the production of rayon and viscose thread.

Palladium and its alloys are also used in medicine - the manufacture of medical instruments, parts of pacemakers, dentures. In some countries, a small amount of palladium is used to obtain cytostatic drugs - in the form of complex compounds, similar to cisplatin.

Production

We know that William Hyde Wollaston isolated palladium while studying the latest methods of refining platinum. Dissolving raw platinum in aqua regia and precipitating only pure noble metal from the solution with ammonia, the chemist noted the unusual pink color of the solution. A color of this kind could not be explained by the presence of known impurities in raw platinum, from which Wollaston concluded that some platinum metals were present in the samples of the ore he studied.

Having acted on the resulting solution of an unusual color with zinc, the English chemist obtained a black precipitate, which he dried and tried to re-dissolve in aqua regia. However, not all of the powder was dissolved. Diluting this solution with water and adding potassium cyanide (in order to avoid the precipitation of small amounts of platinum remaining in the solution), William Wollaston obtained an orange precipitate, which turned gray when heated, and when fused turned into a drop of metal, which the scientist tried to dissolve in nitric acid. The soluble part was palladium.

In such a complex and obscure language, the scientist himself described the discovery of a new metal. Modern methods obtaining pure palladium from natural raw materials, based on the separation of chemical compounds of platinum metals, is very complex and time consuming. Most refining firms and corporations are reluctant to share their trade secrets. We can only say that the production of palladium is one of the stages in the processing of raw platinum and the production of platinum metals. The metal is obtained according to the following scheme: from the filtrate remaining after precipitation of (NH4)2, as a result of refining, a sparingly soluble complex compound dichlorodiammine palladium Cl2 is obtained, it is purified from impurities of other metals by recrystallization from a solution of NH4Cl. By calcining this compound in a reducing atmosphere of hydrogen, palladium is obtained in the form of a sponge:

Cl2 + H2 → Pd + 2NH3 + 2HCl

Sponge palladium is alloyed in a high frequency vacuum electric furnace. By reducing solutions of palladium salts, fine-crystalline palladium is obtained - palladium black. The electrodeposition of palladium is carried out from nitrite and phosphate acid electrolytes, in particular using Na2.

Other refining methods are also used, in particular, based on the use of ion exchangers.

It is known that in the mid-eighties of the last century, the annual mining and production of palladium in Western and developing countries was about 25-30 tons. No more than ten percent was obtained from recycled palladium. At the same time, the USSR accounted for up to two-thirds of the total world production of the precious metal. In our time (according to 2007 data), palladium production amounted to 267 tons, of which Russia accounted for 141 tons, South Africa - 86 tons, the USA and Canada - 31 tons, other countries - 9 tons. These statistics show that production, as well as the extraction of the forty-sixth element, is increasing, and the role of the leader still remains with our country.

Palladium products are mainly produced by stamping and cold rolling. From this metal, it is quite easy to obtain seamless pipes of the desired length and diameter. In addition, palladium is produced in ingots of 3000-3500 grams, as well as in the form of ribbons, strips, foils, wires and other semi-finished products.

The metals trading market is seeing a surge in demand for palladium. It is possible that in the near future the existing supply on the market will no longer be enough to meet the growing demand for the metal, as a result of which the price of palladium will rise even higher. Thus, palladium becomes the best investment among precious metals.

Physical properties

Palladium is a noble platinum metal with a silvery white color with a face-centered cubic lattice of the copper type (a = 0.38902 nm, z = 4). Included in the first triad of platinoids, palladium, nevertheless, in appearance is more similar to silver than to platinum. At the same time, all three metals are outwardly very similar, which cannot be said about their density. In this aspect, palladium (density 12.02 g/cm3) is much closer to silver (10.49 g/cm3) than to platinum (21.5 g/cm3).

In addition to the fact that the forty-sixth element is the lightest of the platinum metals, it is also the most fusible of them - the melting point of Pd is 1,552 ° C, while the melting point of platinum (Pt) is 1,769 ° C, the melting point of rhodium ( Rh) 1960 °C, the melting point of ruthenium (Ru) is 2250 °C, for iridium (Ir) the melting point is 2410 °C, and the melting point of osmium (Os) exceeds 3000 °C. The same situation is with the boiling point of platinum metals - the lowest is for palladium (3980 °C), for rhodium and platinum about 4500 °C, for ruthenium about 4900 °C, and for iridium (5300 °C) and osmium (5,500 °C) the highest boiling points of all platinoids.

Other temperature characteristics of the forty-sixth element: heat capacity (at a temperature of 0 ° C) 0.058 cal / (g ∙ ° C) or 0.243 kJ / (kg ∙ K); thermal conductivity 0.17 cal/(cm∙sec∙°C) or 71 W/(m∙K). The linear coefficient of thermal expansion at 0 °C is 11.67∙10-6.

similarity appearance palladium with silver and platinum, its ability to polish well, resistance to corrosion and, as a result, the absence of tarnish - all these qualities made the forty-sixth element one of the jewelry metals. In a palladium frame, precious stones stand out effectively. Watches in white gold cases are very popular. It would seem, where does palladium? The fact is, “white gold” for watch cases is gold that has been decolorized with the addition of palladium. The property of palladium to "bleach" large amounts of gold is well known. Other metals also benefit from palladium. So its addition to titanium (less than 1%) is able to turn this metal into an alloy that is absolutely resistant to aggressive environments. Pure titanium is able to resist aqua regia and nitric acid, but is unstable to concentrated hydrochloric and sulfuric acids. Alloyed with palladium, titanium calmly endures their impact.

Like platinum, palladium is a ductile and malleable metal that can be welded, rolled, drawn, stamped and drawn even at room temperature. For heated palladium, these qualities improve, it is possible to obtain the thinnest sheets, wire, seamless pipes of the required length and diameter from it. Brinell hardness 49 kgf/mm2. The modulus of normal elasticity for the forty-sixth element is 12600 kgf/mm2. Relative elongation at break 24-30%. Tensile strength 18.5 kgf/mm2. It is noteworthy that the mechanical characteristics of palladium are not constant, which is important for technology. So after cold working, the hardness of this metal increases by 2-2.5 times, but decreases after annealing. Additives of related metals also affect the properties of palladium: the addition of 4% ruthenium and 1% rhodium doubles the tensile strength!

Like all platinum metals, palladium is paramagnetic, its magnetic susceptibility χs∙10-6 (at a temperature of 18 °C) is 5.4 electromagnetic units. The electrical resistivity at 0 °C is 10 Ohm∙cm∙10-6. Palladium has a unique ability to absorb hydrogen: in one volume of palladium, under normal conditions, more than eight hundred volumes of hydrogen are dissolved. In this case, the element retains a metallic appearance, but cracks and becomes brittle.

Chemical properties

Before describing the chemical properties of palladium, it is necessary to mention that this is the only element with an extremely filled outer electron shell: there are 18 electrons in the outer orbit of the palladium atom. What is the importance of this fact? The fact is that with such a structure, the atom simply cannot but have the highest chemical resistance. Therefore, even the all-destroying fluorine does not affect palladium under normal conditions. In compounds, palladium is divalent, trivalent, and tetravalent, most often divalent. At the same time, the forty-sixth element is the most active of the platinum metals, close in chemical properties to platinum. In air, palladium is stable up to a temperature of 300-350 °C, after which it begins to oxidize with oxygen, forming a dull film of palladium oxide PdO on the surface:

2Pd + O2 → 2PdO

Interestingly, palladium oxide PdO decomposes into metal and oxygen after “passing” the threshold of 850 °C, and at this temperature, metallic palladium becomes resistant to oxidation again.

Palladium does not react with water, dilute acids, alkalis, ammonia hydrate. This is due to the position of the forty-sixth element in the series of standard potentials, where it is located to the right of hydrogen. But palladium interacts with concentrated sulfuric and nitric acids, dissolves in aqua regia:

Pd + 2H2SO4 → PdSO4 + SO2 + 2H2O

Pd + 4HNO3 → Pd(NO3)2 + 2NO2+ 2H2O

3Pd + 4HNO3 + 18HCl → 3H2 + 4NO + 8H2O,

and also goes into solution upon anodic dissolution in hydrochloric acid. When dissolved in aqua regia, palladium forms hexachloropalladic (IV) acid H2, which decomposes upon boiling to H2 and Cl2.

At room temperature, palladium reacts with wet bromine and chlorine:

Pd + Cl2 → PdCl2

Palladium dichloride PdCl2 - red crystals, easily soluble in water and hydrochloric acid. Moreover, as a result of the last reaction, tetrachloropalladic (II) acid H2 is obtained.

At temperatures of 500 ° C and above, the forty-sixth element can interact with fluorine and other strong oxidizing agents, as well as with sulfur, selenium, tellurium, arsenic and silicon.

The interaction of palladium with hydrogen is very interesting - the metal is able to absorb a large amount of this gas (at room temperature, one volume of palladium absorbs up to 950 volumes of hydrogen) due to the formation of solid solutions with an increase in the crystal lattice parameter. Hydrogen is found in the metal in atomic form and has a high chemical activity. The absorption of a large volume of hydrogen does not pass without a trace for palladium - the metal swells, swells, and cracks. The absorbed gas is easily removed from palladium when heated to 100°C in vacuum.

In addition to absorbing hydrogen, palladium has the property of transit of this gas through itself. So, if hydrogen is pumped under pressure into a vessel made of palladium, and then the sealed container is heated, then hydrogen will “flow out” from the palladium vessel through the walls, like water through a sieve. At 240°C, 40 cubic centimeters of hydrogen pass through every square centimeter of a millimeter-thick palladium plate in one minute, and as the temperature rises, the permeability of the metal becomes even more significant.

Like all platinum metals, palladium forms many complex compounds. Complexes of bivalent palladium with amines, oximes, thiourea, and many other organic compounds have a planar square structure and this differs from the complex compounds of other platinoids. Those almost always form bulky octahedral complexes. Modern science knows more than one thousand complex compounds of palladium. Some of them are of practical use - at least in the production of palladium itself.

DEFINITION

Palladium located in the fifth period of the VIII group of the secondary (B) subgroup of the Periodic Table.

Relates to elements d-families. Metal. Designation - Pd. Ordinal number - 46. Relative atomic mass - 106.4 a.m.u.

Electronic structure of the palladium atom

The palladium atom consists of a positively charged nucleus (+46), inside which there are 46 protons and 60 neutrons, and 46 electrons move around in five orbits.

Fig.1. Schematic structure of the palladium atom.

The distribution of electrons in orbitals is as follows:

46Pd) 2) 8) 18) 18) 0 ;

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 0 .

The valence electrons of the palladium atom are those located on 4 d- and 5 s-orbitals. The energy diagram of the ground state takes the following form:

The valence electrons of a palladium atom can be characterized by a set of four quantum numbers: n(chief quantum), l(orbital), m l(magnetic) and s(spin):

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

PALLADIUM (chemical element)

PALLADIUM (lat. Palladium, after the name of one of the largest asteroids Pallas), Pd (read "palladium"), a chemical element with atomic number 46, atomic mass 106.42. Natural palladium consists of six stable isotopes 102Pd (1.00%), 104Pd (11.14%), 105Pd (22.33%), 106Pd (27.33%), 108Pd (26.46% ) and 110 Pd (11.72%). The longest-lived is the artificial radioactive isotope 107 Pd ( T 1/2 7 million years). Numerous isotopes of palladium are formed during the fission of U and Pu nuclei. In modern nuclear reactors, 1.5 kg of Pd is formed per 1 ton of fuel at 3% burnup.
Configuration of the two outer electron layers 4s 2 p 6 d 10 5s 0 . It is located in the VIIIB group of the 5th period of the Periodic Table of the Elements. Together with ruthenium (cm. RUTHENIUM) and rhodium (cm. RHODIUM) forms a triad of elements. Refers to platinum metals (cm. PLATINUM METALS).
Oxidation states 0, +1, +2 (most common), +3, +4 (often), +5, +6 (very rare).
Atomic radius 0.137 nm, Pd 2+ ionic radius 0.078 (coordination number 4), 0.100 (6), Pd 4+ 0.064 (6). Sequential ionization energies 8.336, 19.428, 32.95 eV. Electronegativity according to Pauling (cm. PAULING Linus) 2,2.
Discovery history
Palladium was discovered in 1803 by W. H. Wollaston (cm. WOLLASTON William Hyde) when studying native platinum.
Being in nature
Palladium is one of the rarest elements. The content in the earth's crust is 1 10 -6% by weight. It occurs in native form, in the form of alloys (palladium platinum, up to 39% Pd) and compounds (allopalladium contains impurities of Cu, Hg, Pt, Ru), in the form of alloys. About 30 minerals containing Pd are known: palladite PdO, stannopalladite Pd 3 Sn 2 , stibiopalladite Sb 3 Pd, breggite (Pd,Pt,Ni)S.
Receipt
The extraction of palladium begins with the isolation and separation of the platinum metals. From the resulting concentrated solution of platinum metal compounds, gold is first precipitated (cm. GOLD (chemical element)) and platinum, then Pd(NH 3) 2 Cl 2 . Next, palladium in the form of Pd(NH 3) 2 Cl 2 is purified from impurities of other metals by recrystallization from a solution of NH 4 Cl. The resulting salt is calcined in a reducing atmosphere:
Pd (NH 3) 2 Cl 2 \u003d Pd + N 2 + 2HCl + 2H 2.
The prepared palladium powder is smelted into ingots. By reducing solutions of palladium salts, fine-crystalline Pd - palladium black is obtained.
Physical and chemical properties
Palladium is a silvery-white metal with a face-centered cubic lattice of the Cu type, a= 0.38902 nm. Melting point 1554°C, boiling point 2940°C density 12.02 g/cm 3 . Displays the properties of a paramagnet.
In terms of chemical behavior, Pd is close to platinum. It has a unique ability to dissolve hydrogen: 800 volumes of H 2 are dissolved in 1 volume of Pd under normal conditions. If Pd, which has absorbed H 2 , is taken out into the air, then it will lose all H 2 .
Palladium is plastic, nickel microadditives (cm. NICKEL) or ruthenium improve the mechanical properties of Pd.
In a series of standard potentials, palladium is located to the right of hydrogen and does not react with non-oxidizing acids and water. It is the most active platinum metal.
Pd is resistant to oxidation when heated in air up to 300°C. At 350-800°C, Pd is oxidized to form PdO oxide:
2Pd + O 2 = 2PdO
Above 850°C palladium oxide PdO decomposes into metal and oxygen (cm. OXYGEN), and at these temperatures Pd is resistant to oxidation.
Palladium dissolves in aqua regia (cm. AQUA REGIA):
3Pd + 4HNO 3 + 18HCl = 3H 2 + 4NO + 8H 2 O
Unlike other platinum metals, palladium dissolves in hot nitric and sulfuric acids:
Pd + 4HNO 3 \u003d Pd (NO 3) 2 + 2NO 2 + 2H 2 O
Pd + 2H 2 SO 4 \u003d PdSO 4 + SO 2 + 2H 2 O.
At room temperature, it reacts with wet Cl 2 and Br 2:
Pd + Cl 2 = PdCl 2
Crystalline PdCl 2 has a chain structure, each palladium atom in it is located in the center of a square, the vertices of which are formed by chlorine atoms:
In the presence of chlorides, Pd forms complexes:
Pd + 2Cl 2 + 2NaCl \u003d Na 2 PdCl 6.
When heated, Pd reacts with fluorine (cm. FLUORINE), gray (cm. SULFUR), selenium (cm. SELENIUM), tellurium (cm. TELLURIUM), arsenic (cm. ARSENIC) and silicon (cm. SILICON).
Hydrolysis of palladium (II, III, IV) salts yielded black hydroxide Pd(OH) 2 , chocolate-black Pd 2 O 3 ·nH 2 O, and dark red PdO 2 .
Na 2 PdCl 4 + 2NaOH \u003d Pd (OH) 2 + 4NaCl
All these compounds exhibit strong oxidizing properties.
Palladium (III) and (IV) oxides, when heated, lose oxygen and turn into PdO:
2Pd 2 O 3 \u003d 4PdO + O 2,
2PdO 2 \u003d 2PdO + O 2.
Palladium(II) hydroxide exhibits amphoteric (cm. AMPHOTERICITY) properties:
Pd (OH) 2 + 4HCl \u003d H 2 PdCl 4 + 2H 2 O
Pd (OH) 2 + 2KOH \u003d K 2 Pd (OH) 4.
Intensely colored ammonia complexes 2+ and complex compounds are known, in which Pd is an anion - .
Due to their square structure, many Pd(II) complexes have optical isomerism (cm. ISOMERISM OF MOLECULES).
Application
Palladium is used for the manufacture of special chemical glassware, corrosion-resistant parts of high-precision measuring instruments. Medical instruments, parts of pacemakers, dentures, and some medicines are made from Pd and its alloys. Palladium is used for deep purification of hydrogen, in electronics.
Palladium and its compounds are catalysts for chemical processes.

encyclopedic Dictionary. 2009 .

See what "PALLADIUM (chemical element)" is in other dictionaries:

- [chem. Palladium, Pd \u003d 106 [According to new definitions (1894, E. N. Keiser, M. B. Breed) Pd \u003d 106.2 106.3] one of the light members of the platinum group of metals, discovered (1803) by Wollaston in platinum ore from Colombia. This metal is found in almost... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

Palladium (lat. Palladium; named after the discovery of the minor planet Pallas), Pd, a chemical element of group VIII of the Mendeleev periodic system; atomic number 46, atomic mass 106.4; heavy refractory metal (see Platinum metals) ... Great Soviet Encyclopedia

Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

- (Platine French, Platina or um English, Platin German; Pt = 194.83, if O = 16 according to K. Seibert). P. is usually accompanied by other metals, and those of these metals that are adjacent to it in terms of their chemical properties are called ... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

Palladium- - a chemical element, a silver-white precious metal, which is an exchange commodity. Denoted by the symbol Pd. It is believed that the name comes from the asteroid Pallas, discovered shortly before the chemical element. In its turn,… … Banking encyclopedia Dictionary of foreign words of the Russian language

- (Palladium), Pd, chemical element of group VIII of the periodic system, atomic number 46, atomic mass 106.42; refers to platinum metals, mp 1554 shC. Palladium and its alloys are used to make medical instruments, dentures, crucibles for ... ... Modern Encyclopedia