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Jewelry use of noble rhodium in products. Rhodium in jewelry

One desire appears - it should remain as beautiful, elegant and attractive even after many years. To do this, you need to put a lot of effort, and sometimes money. But usually there is not enough time even for elementary home cleaning, not to mention trips to jewelers. This is what rhodium plating was invented for.

What is the element rhodium?

Rhodium is used quite often in jewelry. He is considered a noble representative of the platinum group. It is a bright metal with an extraordinary strength. Its main feature is that rhodium is not subject to oxidation in air and the effects of acids. Outwardly, it is a light metal, very similar to silver, with a steely sheen, but in terms of hardness, other precious metals are inferior to it. When heated, it becomes plastic and interacts well with other metals; many craftsmen actively use rhodium in jewelry, creating beautiful jewelry.

The Secret of Birthing

How is rhodium used in jewelry? Let's understand what birthing is. This is a coating of any precious metal with a thin layer (from 0.1 to 1 microns) of rhodium. This procedure gives the metal high strength, immunity to oxidation and the effects of certain chemicals, as well as some other advantages:

Protection against temperature extremes (cold, heat, dry or humid air).
The decoration takes on a completely different appearance. A beautiful steel luster appears, which does not disappear over time.
There is no need for constant cleaning, because rhodium does not allow large particles of dirt to fall on the surface of the product.
A thin layer of this metal perfectly highlights precious stones against its background: diamonds, rubies, emeralds, sapphires.

How much does rhodium plated jewelry cost? The price of the product will depend, first of all, on what metal it is made of. That is, a decoration made of cheap metal can be bought for 1500-2000 rubles. Accordingly, a product made of expensive metal will cost much more.

How does the metal deposition process work?

How is rhodium used in jewelry? Is the process of applying it to the decoration difficult? The very process of coating one metal with another is not difficult, and any jeweler of the "middling hand" can carry it out, but it is necessary to trust only specialists in their field. Therefore, you should choose only proven masters.

To understand how the rhodium process is carried out, it is enough to look into the seventh grade physics textbook, but it can also be explained with a couple of sentences:

It is best to carry out rhodium plating on new jewelry, on the surface of which there are no flaws or damage. Then the rhodium layer will lie more precisely and thinner, as a conclusion: less costs, more beautiful thing.
The decoration is polished, thoroughly degreased and washed. The rhodium layer must be integral with the other precious metal and any layer of dirt or micro-dust can cause failure.
The basis of the whole process is the same physics, or rather, the phenomenon of galvanization. In with a certain solution, jewelry is lowered and an electric current is applied. Under its action, rhodium is released from the solution and covers the product with the thinnest layer. The thickness of the coating layer can be freely varied by the current strength and the duration of the process. On average, the process takes several minutes.

Disadvantages of the birth process

Rhodium plating jewelry has many advantages. But no matter how good this element of the periodic table is, it also has its drawbacks. They are insignificant, but it is better to familiarize yourself with them in advance.

The coating procedure itself does not take much time, but requires certain tools and the ability to handle them. Real jewelers who are able to work with rhodium charge a decent fee for their art. Therefore, having made the decision to cover his piece of jewelry with rhodium, the client must be ready to invest certain funds in this.
True connoisseurs of precious products believe that rhodium hides the natural beauty of metals. And if applied, it covers the true value of the jewelry.
Unfortunately, rhodium cannot be soldered. If the jewelry is deformed, the rhodium layer has to be applied again over the entire surface, repeating the original procedure. And since even the thickest layer of rhodium is erased over time, sooner or later it will have to be done.
If the owner of a rhodium-plated product is going to sell it, then this will cause some trouble in assessing. It will not be very easy for a jeweler to determine the metal from which the jewelry was originally made. What if rhodium was used in jewelry? The price of pure rhodium is quite high. But given that the top layer will have to be broken in order to find out what metal the jewelry is made of, the cost of the product can suffer significantly.

As mentioned above, close care of such products is not required, it is enough to do the following:

Wipe the jewelry every few months. As a liquid for rubbing, it is best to use an ordinary shampoo.
Under no circumstances should any chemicals be used to clean the coating from fine dirt.
Do not use materials with fine crumbs for cleaning.

The best option is to leave the choice of actions to a professional. Just take the piece to a jeweler.

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45
	1 16 18 8 2
RHODIUM
102,905
4d 8 5s 1

Rhodium

A few years ago, at one of the factories, there was a one-of-a-kind mortar that weighed (together with a pestle) about 30 kg.

Outwardly, a mortar is like a mortar, but its cost is comparable, perhaps, with the cost of an entire factory, and in order to make this mortar, it was necessary to process tens of thousands of tons of ore.

This amazing mortar was made from a very rare and precious metal, rhodium, and was used to grind the same rhodium that was produced in this factory.

Production and consumption of rhodium is low; great, however, is the value and significance of this element.

Past rhodium

Element No. 45 was discovered in England in 1803 by the remarkable scientist of his time, William Hyde Wollaston. While studying native South American platinum, Wollaston drew attention to a bright pinkish-red filtrate obtained from a solution of native platinum in aqua regia. The solution acquired this color after the precipitation of platinum and palladium.

From this solution, Wollaston isolated a dark red powder, calcined it in an atmosphere of hydrogen and obtained a heavy white metal. According to the color of the solution, they named the new element: ροδοεις means "pink".

In 1819...1824. in the Urals, the richest placers of native or, as it is also called, "raw" platinum were discovered. The analysis of this platinum, carried out by Chief Bergmeister Arkhipov and Chief Probator Yakovlev, indicated the presence of rhodium in it. Already in 1828, an unheard-of amount of native platinum was mined in the Urals at that time - more than one and a half tons. For processing, it was transported to St. Petersburg, where relatively pure platinum was extracted from it.

Rhodium and other precious metals of the platinum group at that time went to waste.

In the early 1940s, having become interested in Ural platinum, professor of Kazan University K.K. Klaus discovered in the waste “not a small amount of iridium, rhodium, osmium, a few palladium”, and after that he discovered a new platinum metal, ruthenium.

According to documents, by 1843 about one and a half tons of platinum production waste had accumulated at the Mint in St. Petersburg. But they did not know how to use them and therefore they were sold abroad for almost nothing. And after the cessation of processing of raw platinum in Russia (this happened in 1867), all native platinum mined in the Urals, even without a duty, began to be exported abroad.

The price of the metal was determined only by the content of platinum, while the even rarer and more valuable metals - rhodium, iridium and osmium - were not taken into account and were actually exported free of charge.

Until the October Revolution, Russia, where almost all of the world's platinum was mined (90 ... 95% of world production), did not purify native metal and was forced to purchase rhodium and other platinum metals extracted from Russian Ural platinum for huge sums in Europe. There were no refiners in old Russia, the properties of rhodium and its “brothers” were poorly studied, and foreign firms kept secret methods for extracting and purifying platinum group metals.

After the October Revolution, the Soviet government immediately took decisive measures to create a domestic industry of precious metals, “our primordial natural wealth,” as Professor L.A. wrote about them. Chugaev.

First of all, it was necessary to develop the scientific basis for the production of platinum metals, which means that their physical and chemical properties should be well studied. That is why, already in May 1918, the Institute for the Study of Platinum and Other Noble Metals was established and began to operate, which in 1934 became part of the Institute of General and Inorganic Chemistry. N.S. Kurnakov Academy of Sciences of the USSR.

In the very first years, the Institute carried out important research in chemistry, refining and analysis of rhodium. And in 1925, the first domestic rhodium was obtained from the Ural platinum.

The credit for this belongs primarily to the outstanding chemist L.A. Chugaev and his students, later known scientists I.I. Chernyaev, V.V. Lebedinsky, N.K. Pshenitsyn.

Pink precipitate and yellow salt

The extraction of rhodium and its purification from base and noble impurities is associated with extremely complex, lengthy and labor-intensive operations. This is inevitable: rhodium is one of the rarest elements. In addition, it is scattered, does not have its own minerals. It is found along with native platinum and osmium iridium.

The technology of rhodium extraction depends primarily on the type and composition of the processed raw materials. For example, we will tell you how rhodium is extracted from native platinum.

From the mines, raw platinum enters the refinery, where precious metals are separated from base impurities and the precious metals themselves are separated. It is done like this.

Raw, platinum is loaded into porcelain cauldrons and treated with aqua regia. The process goes on heating during the day. Rhodium, and with it almost all platinum, palladium, base metals (iron, copper and others), partly ruthenium and iridium go into solution, and osmium iridium, quartz, chromium iron ore and other mineral impurities remain in the sediment.

Since our story is about rhodium, we will leave the precipitate alone, and follow the solution. First, it is treated with ammonium chloride to precipitate and separate the platinum. The remaining solution is evaporated: a precipitate is formed, which consists of several salts. It contains up to 6% rhodium; there are also palladium, ruthenium, iridium, platinum (all of it cannot be separated with NH 4 Cl) and base metals. This precipitate is dissolved in water and the platinum is separated again in the same way. And the solution, in which rhodium, ruthenium and palladium remained, is sent for purification and separation as it accumulates.

Rhodium is extracted in various ways. For example, according to the method proposed by the Soviet scientist V.V. Lebedinsky in 1932, first, sodium nitrite NaNO 2 is precipitated and the precipitate of base metal hydroxides is separated from the solution; rhodium remains in solution in the form of Na 3 . After that, with the help of NH 4 Cl, rhodium is isolated from the solution in the cold; it leaves in the form of a sparingly soluble complex (NH 4) 2 Na. However, along with rhodium, iridium also precipitates; the other platinum metals ruthenium, palladium and platinum residues remain in solution. So, rhodium is in the sediment, and now we are only interested in this sediment. What happens to him next?

The precipitate is dissolved in dilute sodium hydroxide and rhodium is again precipitated from this solution by the action of ammonia and NH 4 Cl, now in the form of another complex compound. The precipitate is separated and washed thoroughly with ammonium chloride solution.

This is not the end of the rhodium purification. The precipitate is again loaded into a boiler with hydrochloric acid and heated for several hours. There is a reaction:

2 + 6HCl → 2 + 3NO 2 + 3NO + 3H 2 O

with the formation of a new bright yellow rhodium complex compound. This is rhodium triamine trichloride. It is thoroughly washed with water and only after that they begin to isolate metallic rhodium.

Salt is loaded into the furnace and calcined for several hours at 800...900°C. The complex compound decomposes and a powdery product of a mixture of rhodium with its oxides is formed. After cooling, the powder is again thoroughly washed with diluted aqua regia to remove the remaining insignificant amount of base impurities, and then it is again loaded into the furnace and reduced to metal by calcining in a hydrogen atmosphere.

This is the long and complicated process by which pure rhodium is obtained.

It should be borne in mind that in our story this path is still simplified and shortened: secondary stages that do not carry an independent “chemical load” are omitted. But in reality, there are no “little things” at all stages of rhodium production. Temperature conditions, concentration of reagents, duration of operations, equipment materials everything is important. Managing all processes requires great knowledge and vast experience.

Now rhodium, along with other platinum metals, is also mined from copper-nickel sulfide ores. The content of element No. 45 in these ores is calculated in milligrams per ton of ore. Therefore, the actual refining of rhodium is preceded by complex technological operations for separating the main amounts of non-ferrous metals and obtaining a concentrate of precious metals. And then approximately as described above.

Rhodium through the eyes of a chemist

In appearance, compact rhodium is a beautiful silvery metal with a bluish tint. It melts at about 1960°C and is slightly volatile up to 2500°C. Unlike gold and platinum, rhodium is difficult to machine. Therefore, it can be rolled or stretched into a wire only at 800...900°C.

Element #45 easily forms alloys with platinum, palladium, copper and other metals.

Rhodium is classified as a noble metal not only for its spectacular appearance: as it should be for an “aristocratic” metal, it has a very high chemical resistance. Compact rhodium is not affected by acids or alkalis. Only finely crushed rhodium slowly dissolves in hot aqua regia or concentrated sulfuric acid. Rhodium is also very resistant to the action of halogens: it reacts with chlorine, bromine and even fluorine only after prolonged heating. In this case, depending on the reaction temperature, halides of various compositions are obtained. In particular, one-, two- and trivalent rhodium chlorides RhCl, RhCl 2 , RhCl 3 are formed with chlorine. At high temperatures, rhodium slowly reacts with sulfur, turning into sulfides RhS, RhS 2 , Rh 2 S 5 .

One of the important features of rhodium is the nature of its interaction with oxygen at high temperatures. When rhodium is heated in oxygen, the oxide Rh 2 O 3 is formed. But the process is very slow. In order to oxidize tenths of a gram of finely dispersed rhodium in air, it must be kept continuously for many hours in an oven at a temperature of the order of 1000°C.

Since rhodium is in Group VIII of the Periodic Table, it should be a typical complexing metal. Indeed, the chemistry of rhodium is the chemistry of its complex compounds.

The initial compounds for the synthesis of many hundreds of complex compounds of rhodium are usually its chloro complexes. To obtain them, metallic rhodium is preliminarily sintered with barium peroxide or sodium peroxide at 700...1000°C, and then the resulting products are treated with hydrochloric acid. In this case, element No. 45 passes into solution in the form of easily hydrolyzed complex ions 3. Complex rhodium chlorides are also obtained by chlorinating a mixture of metallic rhodium with common salt at high temperature, followed by dissolution of the resulting substance in hydrochloric acid. The same happens with the electrolytic dissolution of the metal in HCl.

In complex compounds, rhodium is usually trivalent, and their molecules have an octahedral structure. The rhodium atom is located in the center, and the ligands associated with it by chemical bond are located at the corners of the octahedron. Ligands can be various acid residues and neutral molecules (Сl , Br , NO 2 , CN , NH 3, H 2 O, pyridine, amines and many other organic substances). The physicochemical properties of these compounds are largely determined by the nature and number of ligands, their mutual arrangement in space.

Certain complex compounds, as we have seen, find use in the extraction and purification of rhodium itself.

What is the value of rhodium?

The high resistance of rhodium to the action of aggressive media and elevated temperatures allows it to be used in a wide variety of industries.

Rhodium is one of the most expensive metals, yet the demand for it outstrips production. Naturally, in such a situation, rhodium enters only where it cannot be replaced by any other metals.

The most important consumer of rhodium is the chemical industry. Platinum-rhodium alloy is used to make catalyst gauzes, on which, at a temperature of 800...900°C, ammonia is oxidized to nitrogen oxides - the main stage in the process of obtaining nitric acid. An additive of 5...10% rhodium greatly increases the strength of the mesh, and the loss of platinum during the production process is reduced by one and a half two times. Moreover, this additive increases the catalytic activity. The production of nitric acid on platinum-rhodium grids now amounts to tens of millions of tons per year and requires annually several hundred kilograms of rhodium.

Another major consumer of rhodium is the glass industry. An alloy of rhodium and platinum (usually 7% Rh) is used to make vessels for melting glass mass and obtaining the finest glass and quartz filaments. And in this case, rhodium sharply increases the chemical and mechanical resistance of platinum and, in addition, significantly increases its melting point. Here, rhodium is also almost indispensable.

Platinum alloys with 1...3% rhodium are used for the manufacture of laboratory chemical glassware, which require high chemical and thermal resistance and the ability not to change its weight even during prolonged calcination. Such utensils are used in the most responsible and accurate analytical studies.

The stability of thermoelectric properties and high refractoriness have long made rhodium an extremely important material for thermocouples in high temperature measurement technology. For example, a thermocouple made of platinum-rhodium wire (1...40% Rh) can measure temperatures up to 1800°C.

The surface of rhodium has a high reflectivity (80%) for the visible part of the spectrum. The reflectivity of rhodium is less than that of silver (95%), but its resistance to corrosive gases and high temperatures is much greater. Rhodium-plated surfaces do not fade even in the atmosphere of a voltaic arc. That is why rhodium is used to cover projector reflectors and technical mirrors of precision measuring instruments of various purposes. Rhodium plating gives jewelry a special shine and beauty. However, the great technical value of rhodium, the difficulty of obtaining it and the scarcity of its reserves in nature limit the use of this metal for the manufacture of luxury goods.

Finishing the story about rhodium, we want to emphasize that the properties of this element very rare and very valuable are far from being fully studied. The knowledge of these properties continues and, one must think, further research on rhodium will give science a lot of interesting things, and industry useful.

Opportunities and needs

Rhodium deposits in our country are located in the Urals and in the Arctic, and abroad the largest in the Republic of South Africa. Canada and Colombia. Over the past 20 years, the demand for rhodium has grown 10-13 times and continues to grow by about 20% annually.

Stocks and prices

World reserves of rhodium (without the USSR) are estimated at only a few tons, and the annual production is estimated at hundreds of kilograms. Rhodium is several times more expensive than gold. On the world market, a gram of rhodium costs about $9.

Explosive rhodium

Compact rhodium is exceptionally resistant to any chemical attack. However, if you take an alloy of rhodium with zinc or cadmium and dissolve it in hydrochloric acid, and then filter it, you will get a precipitate of finely dispersed rhodium that can explode in air.

According to most of our contemporaries, Professor Lebedinsky is a man who sang intelligibly about the treacherous moods among the boatmen. The world scientific community knows another Professor Lebedinsky - a remarkable scientist of the last century, the author of a method for obtaining rhodium from ore residue.

The point is that in nature rhodium is found in minerals rich in several platinoids at once. The isolation of rhodium, especially on an industrial scale, is an intractable problem.

William Wollaston, the discoverer of rhodium, synthesized the sodium hydroxide salt of rhodium quite easily - and then heated the pink-red powder in a jet of hydrogen flame for a long time to get a few drops of pure metal.

Professor V. V. Lebedinsky contrasted the tradition of calcination with the power of cold. Cooling a complex solution of platinum salts, he achieved the precipitation of a mixture of rhodium and iridium compounds. Today, using the Lebedinsky method, about 30 tons of pure rhodium is annually released from associated rocks.

Rhodium means pink?

"Rodon" in Greek means "rose". As the name suggests, rhodium should be like a blooming flower. However, red tones are inherent only in rhodium compounds; the metal itself is unpainted, and its brilliance is similar to brilliance - although not so bright.

Polished rhodium reflects about 80% of the light falling on its surface - while silver absorbs only 5%, and returns 95% of the light flux. However, many technical mirrors are plated with rhodium rather than silver. The reason is that the platinum metal is refractory and is able to work in conditions of extremely high density of electromagnetic radiation - including the infrared range. Where, due to overheating, silver does not withstand even a day, rhodium plating lasts for years.

The lion's share of mined rhodium is consumed by the automotive industry. The excellent catalytic properties of the metal make it possible to produce exhaust gas converters from its alloys. A significant part of rhodium is used to make catalysts for the chemical industry. An alloy of rhodium and platinum has been an indispensable tool for the production of nitric acid for several decades.

Rhodium is needed everywhere!

The hardness, strength and wear resistance of the platinum and rhodium alloy appealed to glassmakers. Through platinum-rhodium dies stretch optical fiber, technical glass fiber, flat glass for monitors.

Scientists order platinum-rhodium containers for growing crystals. The diffraction gratings of modern spectrometers are also made of a noble metal alloy. Electronics, for which spark discharges are destructive, use rhodium to cover especially critical contacts. Thermocouples made of rhodium and iridium are used in high-temperature - up to 2200°C - thermometers.

Rhodium plating protects various materials from corrosion.

Jewelry rhodium

Techniques were the first to use childbirth. The jewelry industry for a long time did not find it necessary to use the unique properties of rhodium. However, the increasing popularity of silver jewelry and the high demand for white gold forced craftsmen to look for methods to prevent abrasive wear of products and increase the aesthetic potential of products.

Silver, among other things, is prone to tarnishing, and the available methods of cleaning products do not always allow preserving the artistic expressiveness of precious metals. White gold visibly yellows, which interferes with the perception of beauty.

Electroplated rhodium plating solves the problem. Jewelry made of rhodium-plated silver looks extremely aristocratic. The light coloration inherent in jewelry silver of not the highest standard, which occurs due to the introduction of copper into the composition of the ligature, is leveled by rhodium.

In addition, rhodium deposited on silver eliminates the possibility of an oxide film on the metal. Rodized products do not need to be cleaned, they retain their ceremonial shine for a long time, they are perfectly cleaned with mild detergents.

Durability rhodium plating

Rhodium plating does not last forever, but its lifespan depends on several factors. The first is thickness. Rhodium plating, carried out solely for decorative purposes, may be associated with the application of a layer of platinoid to a thickness of one ten-thousandth of a millimeter on the product! A similar effect is used to harden the upper layer of the product (the hardness and strength of rhodium is comparable to the parameters of steel).

Such a thin layer of rhodium almost does not change the color of the product and is therefore widely used in the manufacture of jewelry from colored - often very fragile -.

The opaque layer of rhodium can reach a thickness of 25 thousandths of a millimeter. This is how products designed for everyday wear are born. An engagement ring coated with a 25 micron rhodium layer retains its external merits for at least ten years!

According to the experience of use, the renewal of the rhodium layer on rings, earrings, chains is required every five years and less often, depending on the intensity of use of the product. In many cases, high-quality rhodium plating adorns the metal for decades.

Rhodium is not that expensive

Today's the price of rhodium is quite democratic. Rhodium is about one and a half times cheaper than gold - although there are no guarantees that this ratio will remain forever. Rhodium plating of one item in a jewelry workshop costs 15-20 dollars. The need to pre-disassemble the jewelry increases the cost of the procedure.

Origin and properties of rhodium

Russia has been purchasing rhodium abroad until the 1920s. This is despite the fact that the element was discovered by the Englishman William Hyde back in 1803. Yes and rhodium reserves Russia is one of the largest in the world.

The fact is that the rare metal is found only in native platinum, and then only in hundredths of a percent. To get a kilogram of rhodium, you need to process tons, and just before the first quarter of the 20th century, our country did not know how to purify it from impurities.

European scientists were in no hurry to share with the Russians the technology for extracting rhodium, palladium and other valuable additives contained in native platinum.

So the authorities of the Soviets had to create a domestic center for the study of platinum in 1918. First mined rhodium the Russians extracted from it only in 1925. The importance of what happened can be understood if you remember how much an ounce of a rare metal costs now. The English measure of weight is 28 grams, and they ask for at least 7 thousand dollars for it.

Application of rhodium

Rhodium price high not only because the element is precious, but also because there are more industries where it is needed than the metal itself. If its reserves were more impressive, then rhodium would be useful in obtaining pure graphite. It is used in reactors of nuclear power plants. It has an expensive element and disinfecting properties, for example, it purifies water.

But, use rhodium only where there is no cheaper and more common alternative. Every year, several hundred kilograms of metal is spent on the production of nitric acid. Without meshes of rhodium with platinum, the substance cannot be obtained. The metal base serves as a catalyst in a chemical reaction.

Without rhodium metal does not manage the production of glassware for chemical laboratories. The precious element does not react with almost any elements. In flasks and test tubes made of rhodium, you can mix any substance.

Without the metal placed under the 45th number in , it is impossible to measure high temperatures. Rhodium is so resistant to heat that it is used to make thermocouples. These are temperature sensors from two connected conductors. Rhodium parts able to fix, without melting at the same time, a temperature of 1800 degrees Celsius.

The 45th element is needed in the manufacture of car exhaust systems. In them, the metal acts as a catalyst. Rhodium is coated with measuring equipment mirrors. A rare element is slightly inferior in reflective properties, but it is resistant to gases that can cause corrosion of elements.

Of precious substance and filters of liquid crystal monitors. The need for them is growing every year. More and more rhodium is required for this industry. There are precious minerals that grow under artificial conditions only on filters made from an alloy of platinum and rhodium.

#45 metal plating is required for some fine jewelry. A film of rare metal makes products sparkling. Rhodium reflects 80% of the rays of the visible spectrum. Jewelry with rhodium do not lose their luster for many years. By the way, it's cold. shine of rhodium perfectly emphasizes the play of diamonds and cubic zirkonia. They try to cover with rare metal.

It often contains, which in 20% of people causes allergies, redness and itching of the skin. Rhodium plating keeps the hazardous metal from coming into contact with the body. In addition, products with element No. 45 do not scratch, do not oxidize, and are resistant to temperatures. Products with a rare metal are called rhodium-plated.

And yet, whenever possible, jewelers try to replace rhodium with other precious metals, for example. It is slightly inferior in characteristics to element No. 45, but more accessible. Geologists estimate world reserves of rhodium at only a few tons. Every year, humanity spends about half a ton.

Deposits and mining of rhodium

Previously, the main deposits were located in Russia. Impressive reserves of native platinum were found in the Urals. But, now, they have already been developed. Today, Mexico is the leader in rhodium mining and reserves. It is followed by South Africa and Colombia. There is a precious metal content in the US gold sands. The rest of the countries are content with crumbs.

The rose is the queen of flowers, and rhodium, apparently, is the king of metals. The name of the element in translation from ancient Greek means exactly “rose”. True, when a rare metal was called, it had not yet been used, and therefore they did not suspect the importance of his person. Rhodium gets its name from the color of its typical compounds, which are red, like roses.

Lose this metal, humanity can not. Therefore, technology is being developed rhodium mining from radioactive waste. Metal #45 accumulates in them. There are up to 180 grams of the element per ton of fragments.

Nuclear power is so developed that the extraction of rhodium from the waste of its production in terms of volume should exceed the amount of metal extracted from the ores of the earth's crust. Physicists are also working on the schemes of new reactors, which will accumulate even more metal No. 45.

You can lose all the rhodium if you dissolve its alloy with hydrochloric acid, and then filter it. The reaction will give rhodium precipitate called finely dispersed. It explodes in the air.

So, the reserves of the king of precious metals and, perhaps, the land surrounding the point of explosion will disappear at once. The finely dispersed state of the metal is the only one in which it is not stable. Compact element No. 45, as already mentioned, does not respond to any "irritants".

Rhodium (lat. Rhodium; denoted by the symbol Rh) - an element of a side subgroup of the eighth group of the fifth period of the periodic system of chemical elements of D. I. Mendeleev, atomic number 45. This is the brightest and hardest metal of the entire platinum group.

Atomic number - 45

Atomic mass - 102.91

Density, kg/m³ - 12400

Melting point, °С - 1966

Heat capacity, kJ / (kg ° С) - 0.247

Electronegativity - 2.2

Covalent radius, Å - 1.25

1st ionization potential, ev - 7.46

The history of the discovery of rhodium

Rhodium and other precious metals of the platinum group at that time went to waste.

In the very first years, the Institute carried out important research in chemistry, refining and analysis of rhodium. And in 1925, the first domestic rhodium was obtained from the Ural platinum.

The credit for this belongs primarily to the outstanding chemist L.A. Chugaev and his students, later known scientists I.I. Chernyaev, V.V. Lebedinsky, N.K. Pshenitsyn.

The content of rhodium in nature

Rhodium is found in platinum ores, in some of the golden sands of South America. Up to 43% rhodium is found in Mexican gold.

Getting rhodium

The technology of rhodium extraction depends primarily on the type and composition of the processed raw materials. For example, we will tell you how rhodium is extracted from native platinum.

From the mines, raw platinum enters the refinery, where precious metals are separated from base impurities and the precious metals themselves are separated. It is done like this.

First, the solution is treated with ammonium chloride to precipitate and separate the platinum. The remaining solution is evaporated: a precipitate is formed, which consists of several salts. It contains up to 6% rhodium; there are also palladium, ruthenium, iridium, platinum (all of it cannot be separated with NH 4 Cl) and base metals. This precipitate is dissolved in water and the platinum is separated again in the same way. And the solution, in which rhodium, ruthenium and palladium remained, is sent for purification and separation as it accumulates.

Rhodium is extracted in various ways. For example, according to the method proposed by the Soviet scientist V.V. Lebedinsky in 1932, first, sodium nitrite NaNO 2 is precipitated and the precipitate of base metal hydroxides is separated from the solution; rhodium remains in solution in the form of Na 3 . After that, with the help of NH 4 Cl, rhodium is isolated from the solution in the cold; it leaves in the form of a sparingly soluble complex (NH 4) 2 Na. However, along with rhodium, iridium also precipitates; other platinum metals - ruthenium, palladium and platinum residues - remain in solution. So, rhodium is in the sediment, and now we are only interested in this sediment. What happens to him next?

The precipitate is dissolved in dilute sodium hydroxide and rhodium is again precipitated from this solution by the action of ammonia and NH 4 Cl - now in the form of another complex compound. The precipitate is separated and washed thoroughly with ammonium chloride solution.

This is not the end of the rhodium purification. The precipitate is again loaded into a boiler with hydrochloric acid and heated for several hours. There is a reaction:

2 + 6HCl → 2 + 3NO 2 + 3NO + 3H 2 O

This is the long and complicated process by which pure rhodium is obtained.

Physical properties of rhodium

Rhodium - metal, silver-gray color. It has a high reflection coefficient of electromagnetic rays in the visible part of the spectrum, therefore it is widely used for the manufacture of "surface" mirrors.

Rhodium is a metal that is extremely resistant to many substances. It is insoluble not only in ordinary acids, but also in aqua regia. The melting point of rhodium is about two thousand degrees (1966°C). In the liquid state, rhodium dissolves up to seven percent of carbon, and when cooled, it releases dissolved carbon in the form of graphite.

Rhodium is malleable enough to be rolled into foil (although this will require several intermediate annealings to recrystallize). This metal has a somewhat peculiar behavior when heated in air. It is stable up to a temperature of 800 degrees, and then a film of oxide Rh2O3 appears on the surface of rhodium, which, with a further increase in temperature to 1000 degrees, again decomposes to metal.

Chemical properties of rhodium

All satellites of platinum are known to be good catalysts, especially in a state of great grinding, as chemists say, in the form of "niello".

Most metals in a compact state have a specific, so-called metallic luster and "white", "light" color. The exceptions are copper, gold and a few other non-ferrous metals, which retain their characteristic color even when crushed. However, fine powders of other metals are gray in color, and the finest powder is black or almost black. Hence the chemical, and then the technical name - "niello".

Rhodium "black" is soluble in acids, while rhodium ingot, as already mentioned, is insoluble even in aqua regia. The catalytic activity of rhodium "niello" is so great that wine alcohol quickly turns into acetic acid in its presence. By the way, the rhodium catalyst is resistant to poisons that poison catalysts.

Rhodium is a noble metal that surpasses platinum in chemical resistance in most corrosive environments.

Metallic rhodium dissolves in aqua regia during boiling, as well as electrochemically, anodic - in a mixture of hydrogen peroxide and sulfuric acid.

Rhodium is characterized by high chemical resistance. It interacts with non-metals only at a temperature of red heat. Finely ground rhodium only slowly oxidizes at temperatures above 600 °C:

4Rh + 3O 2 \u003d 2Rh 2 O 3.

When heated, rhodium reacts slowly with concentrated sulfuric acid, sodium hypochlorite solution and hydrogen bromide. During sintering, it reacts with melts of potassium hydrogen sulfate KHSO 4 , sodium peroxide Na 2 O 2 and barium peroxide BaO 2:

2Rh + 6KHSO 4 \u003d 2K 3 Rh (SO 4) 3 + 3H 2,

2Rh + 3BaO 2 = Rh 2 O 3 + 3BaO.

In the presence of alkali metal chlorides, when it is possible to form 3- complexes, rhodium interacts with chlorine, for example:

2Rh + 6NaCl + Cl 2 \u003d 2Na 3.

When exposed to aqueous solutions of salts and complexes of rhodium (III) with alkalis, a precipitate of rhodium hydroxide Rh (OH) 3 is formed:

Na 3 + 3NaOH \u003d Rh (OH) 3 ↓ + 6NaCl.

Hydroxide and oxide of rhodium (III) exhibit basic properties and interact with acids to form Rh (III) complexes:

Rh 2 O 3 + 12HCl = 2H 3 RhCl 6 + 3H 2 O,

Rh(OH) 3 + 6HCl = H 3 RhCl 6 + 3H 2 O.

Rhodium exhibits the highest oxidation state +6 in RhF 6 hexafluoride, which is formed by direct combustion of rhodium in fluorine. The connection is unstable. In the absence of water vapor, hexafluoride oxidizes free chlorine or nitric oxide (II) NO:

2RhF 6 + 3Cl 2 = 2RhF 3 + 6ClF.

In the lower oxidation states +1 and +2, rhodium forms complex compounds.

Application of rhodium

If rhodium were a more accessible metal, it could be used to obtain the purest graphite, so necessary in many branches of modern technology. Rhodium disinfects water

The biological role of rhodium and its physiological effects

Rhodium plays no biological role.

Rhodium compounds are quite rare in everyday life and their effects on the human body are not fully understood. Despite this, they are highly toxic and carcinogenic substances. LD 50 of rhodium chloride for rats - 12.6 mg/kg. Rhodium salts can strongly stain human skin.

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