You know how. Preparation, properties and uses of lanthanum Occurrence in nature

Chemistry

The most significant thing about element No. 57, of course, is that it leads the line of 14 lanthanides - elements with extremely similar properties. Lanthanum and lanthanides are always together: in minerals, in our opinion, in metal. At the World Exhibition in Paris in 1900, samples of some believed to be pure lanthanides were demonstrated for the first time. But there is no doubt that in each sample, regardless of the label, there were also lanthanum, and cerium, and neodymium with praseodymium, and the rarest of the lanthanides - thulium, holmium, lutetium. The rarest, except for the “extinct” element No. 61-promethium, which was recreated in nuclear reactions. However, if promethium had stable isotopes, it would also be present in any sample of any rare earth element.

Only in recent decades has the development of science and technology reached the level at which humanity was able to use the individual qualities of each (or almost each) of the lanthanides, although, as before, only the metal remains one of the most widespread and cheapest rare earth products - “ a natural alloy of lanthanum and lanthanides... Therefore, it would be logical to devote only half of this story directly to element No. 57, and the other half to the rare earth “team” as a whole, of course, each of the lanthanides - as a chemical individual - deserves an independent story; here - about their “leader” and what is common to all of them.

Lanthanum without lanthanides

As sad as it is to admit, the hero of our story is a completely ordinary person. This is a metal, ordinary in appearance (silver-white, covered with a grayish oxide film) and in physical properties: melting point 920, boiling point 3469 ° C; In terms of strength, hardness, electrical conductivity and other characteristics, lanthanum metal always finds itself in the middle of the tables. Lanthanum is also common in chemical properties. It does not change in dry air - the oxide film reliably protects against oxidation in the mass. But if the air is humid (and under normal terrestrial conditions it is almost always humid), the metal lanthanum gradually oxidizes to hydroxide. La(OH) 3 is a base of medium strength, which is again characteristic of an “average” metal.

What else can be said about the chemical properties of lanthanum? In oxygen, when heated to 450°C, it burns with a bright flame (this releases quite a lot of heat). If it is ignited in a nitrogen atmosphere, black nitride is formed. In chlorine, lanthanum ignites at room temperature, but reacts with bromine and iodine only when heated. It dissolves well in mineral acids and does not react with alkali solutions. In all compounds, lanthanum exhibits a valence of 3+. In a word, a metal is like a metal - both in physical and chemical properties.
Perhaps the only distinguishing feature of lanthanum is the nature of its interaction with hydrogen. The reaction between them begins at room temperature and proceeds with the release of heat. Hydrides of variable composition are formed, since lanthanum simultaneously absorbs hydrogen - the more intensely, the higher the temperature.
Lanthanides also interact with hydrogen. One of them - cerium - is even used as a gas absorber in the electric vacuum industry and in metallurgy.
Here we come to one of the important parts of our story, to the topic “Lanthanum and cerium”, and in connection with it - to the history of lanthanum.
In terms of prevalence in nature, scale of production, and breadth of use, lanthanum is inferior to its closest analogue - the first of the lanthanides. “The ancestor” and always the second, such is the position of lanthanum in its family. And when rare earth elements began to be divided into two subgroups based on the totality of their properties, lanthanum was assigned to a subgroup whose name was given in honor of cerium... And lanthanum was discovered after cerium, as an impurity to cerium, in the mineral cerite. This is the story, the story about teachers and students.
In 1803, 24-year-old Swedish chemist Jens Jakob Berzelius, together with his teacher Hisingir, investigated the mineral now known as cerite. In this mineral, yttrium earth, discovered by Gadolin in 1794, and another rare earth, very similar to yttrium, were discovered. It was called cerium. Almost simultaneously with Berzelius, cerium earth was discovered by the famous German chemist Martin Klaproth.
Berzelius returned to work with this substance many years later, already an eminent scientist. In 1826, Karl Mozander - a student, assistant and one of Berzelius's close friends - examined cerium earth and concluded that it was heterogeneous, that, in addition to cerium, it contained one more, and perhaps more than one, new element. But to test this assumption, a lot of cerite was needed. Mozander managed to prove the complexity of cerium earth only in 1839.
It is interesting that a year earlier, a student Erdmann, unknown among chemists, found a new mineral in Norway and named it in honor of his teacher Mozander - mozanderite. Two rare earths, cerium and nova, were also isolated from this mineral.
The new element discovered in cerite and mozanderite was named lanthanum at the suggestion of Berzelius. The name is a hint: it comes from the Greek A,av0dveiv - to hide, to be forgotten. Lanthanum contained in cerite successfully hid from chemists for 36 years!
For a long time it was believed that lanthanum is divalent, that it is an analogue of calcium and other alkaline earth metals, and its atomic weight is 90-94. There was no doubt about the correctness of these figures until 1869. Mendeleev saw that there was no place for rare earth elements in group II of the periodic table and placed them in group III, assigning an atomic weight of 138-139 to lanthanum. But the legality of such a move still had to be proven. Mendeleev undertook a study of the heat capacity of lanthanum. The value he obtained directly indicated that this element should be trivalent...
Lanthanum metal, of course, far from pure, was first obtained by Mozander by heating lanthanum chloride with potassium.
Nowadays, lanthanum with a purity of more than 99% is produced on an industrial scale. Let's see how this is done, but first let's get acquainted with the main minerals of lanthanum and the first stages of the most complex process of separating rare earth elements.
It has already been mentioned that in minerals lanthanum and lanthanides invariably accompany each other. There are selective minerals in which the proportion of one or another rare earth element is greater than usual. But there are no purely lanthanum or purely cerium minerals, not to mention other lanthanides. An example of a selective lanthanum mineral is davidite, which contains up to 8.3% La2O3 and only 1.3% cerium oxide. But lanthanum is obtained mainly from monazite and bastnäsite, as well as cerium and all other elements of the cerium subgroup.
Monazite is a heavy shiny mineral, usually yellow-brown, but sometimes of other colors, since its composition does not differ in consistency. Most accurately, its composition is described by this strange formula: (REE)P04. It means that monazite is a phosphate of rare earth elements (REE). Typically, monazite contains 50-68% REE oxides and 22-31.5% Ra05. It also contains up to 7% zirconium dioxide, 10% (on average) thorium dioxide and 0.1-0.3% uranium. These figures clearly show why the paths of the rare earth and nuclear industries are so closely intertwined.
Mixed rare earth metal - mischmetal - and a mixture of their oxides began to be used at the end of the last century,
and at the beginning of this year, in connection with them, an outstanding example of international theft was / was demonstrated. German ships delivering cargo to Brazil, preparing for the return journey, filled their holds with sand from the beaches of the Atlantic coast of this country, and from certain places. The captains stated that the sand was simply ballast necessary for greater stability of the ship. In reality, they, fulfilling the orders of German industrialists, stole valuable mineral raw materials - the coastal sands of the state of Espirito Santo, rich in monazite...
Monazite placers are common along the banks of rivers, lakes and seas on all continents. At the beginning of the century (data for 1909), 92% of the world's production of rare earth raw materials, and primarily monazite, came from Brazil. Ten years later, the center of gravity moved thousands of kilometers to the east (or west, depending on how you count it) - to India. After 1950, due to the development of the nuclear industry, the United States became the hegemon among capitalist countries in the extraction and processing of rare earth raw materials.
Of course, our country and other countries had to develop their rare earth industry and find their raw materials.
Let us trace in general terms the path from monazite sand to lanthanum.
Although the sand is called monazite sand, there is not much monazite in it - a fraction of a percent. For example, in the famous monazite placers of Idaho (USA), a ton of sand contains only 330 g of monazite. Therefore, first of all, monazite concentrate is obtained.
The first stage of concentration occurs already on the dredge. The density of monazite is 4.9-5.3, and that of ordinary sand is on average 2.7 g/cm3. With such a difference in weight, gravitational separation is not particularly difficult. But, besides monazite, the same sands contain other heavy minerals. Therefore, in order to obtain monazite concentrate with a purity of 92-96%, a complex of gravitational, magnetic and electrostatic enrichment methods is used. As a result, ilmenite, rutile, zircon and other valuable concentrates are obtained along the way.
Like any mineral, monazite must be “opened.” Most often, monazite concentrate is treated with concentrated sulfuric acid. The resulting sulfates of rare earth elements and thorium are leached with ordinary water. After they go into solution, silica and the part of zircon that was not separated at previous stages remain in the sediment.
At the next stage of separation, the short-lived mesothorium (radium-228) is extracted, and then the thorium itself - sometimes together with cerium, sometimes separately. The separation of cerium from lanthanum from a mixture of lanthanides is not particularly difficult: unlike them, it is able to exhibit valency 4+ n in the form of Ce(OH) 4 hydroxide and pass into a precipitate, while its trivalent analogues remain in solution. Let us only note that the operation of cerium separation, like the previous ones, is carried out many times - in order to “squeeze out” the expensive rare earth concentrate as completely as possible.
After cerium is isolated, the solution contains the most lanthanum (in the form of nitrate La(N03h, since at one of the intermediate stages sulfuric acid was replaced by nitric acid to facilitate further separation). Lanthanum is obtained from this solution by adding ammonia, ammonium and cadmium nitrates. In the presence of Cd (N0 3) 2, the separation is more complete. With the help of these substances, all lanthanides precipitate, but only cadmium and lanthanum remain in the filtrate. Cadmium is precipitated with hydrogen sulfide, the precipitate is separated, and the lanthanum nitrate solution is separated several more times purified by fractional crystallization from lanthanide impurities.
The end result is usually lanthanum chloride LaCl 3 . Electrolysis of molten chloride produces lanthanum with a purity of up to 99.5%. Even more pure lanthanum (99.79% and higher) is obtained by the calcium-thermal method. This is the classic traditional technology.
As you can see, obtaining elemental lanthanum is a complex matter.
The separation of lanthanides - from praseodymium to lutetium - requires even more effort and money, and time, of course. Therefore, in recent decades, chemists and technologists from many countries around the world have sought to create new, more advanced methods for separating these elements. Such methods - extraction and ion exchange - were created and introduced into industry. Already in the early 60s, in installations operating on the principle of ion exchange, a 95% yield of rare earth products with a purity of up to 99.9% was achieved.
By 1965, foreign trade organizations of our country could offer buyers all lanthanides in the form of metals with a purity higher than 99%. Except for promethium, of course, although radioactive preparations of this element - products of the nuclear decay of uranium - have also become quite accessible.
Techsnabexport's catalogs also include about 300 chemically pure and highly pure compounds of lanthanum and lanthanides. This is evidence of the high level of development of the Soviet rare earth industry.
But let's return to lanthanum.

Briefly about the use of lanthanum and its compounds

Pure lanthanum is almost never used as an alloying metal, using cheaper and more accessible cerium or mischmetal - the alloying effect of lanthanum and lanthanides is almost the same.
It was mentioned above that sometimes lanthanum is extracted from a mixture by extraction using the different solubility of certain (mainly complex) compounds of rare earth elements in organic solvents. But it happens that element No. 57 itself is used as an extractant. Plutonium is extracted from liquid uranium with molten lanthanum. Here is another point of contact between the nuclear and rare earth industries.
Lanthanum oxide La 2 0 3 is used much more widely. This white amorphous powder, insoluble in water but soluble in acids, has become an important component of optical glasses. Photographic lenses from the famous Kodak company contain from 20 to 40% La203. Thanks to lanthanum additives, it was possible to reduce the size of the lens at the same aperture ratio and greatly improve the quality of color photography. It is known that during the Second World War, lanthanum glasses were used in field optical instruments. The best domestic photographic lenses, for example "Industar-61LZ", are also made of lanthanum glass, and one of our best amateur film cameras is called "Lanthan"... Recently, lanthanum glass is also used in the manufacture of laboratory glassware. Lanthanum oxide gives glass not only valuable optical properties, but also greater heat resistance and acid resistance.
This is, perhaps, all the main thing that can be said about lanthanum without lanthanides, although in some places it was impossible not to deviate from the “without” principle...

Lantan and his team

Comparing lanthanum and lanthanides to a sports team may seem far-fetched to some. However, this comparison is no more seditious than such well-known definitions as “lanthanide family” or “chemical twins”. Judge for yourself: Lantan and his team have a single uniform (silver-white) and, like hockey players, they all have protective equipment (made of oxide films). All of them are endowed with approximately equal amounts by nature (the similarities are extremely great), but, as in sports, for various reasons, “abilities” are not realized to the same extent: some “play” better, others worse... And of course, each member of this teams their favorite “feints” and “techniques” - gadolinium ferromagnetism, for example.

And in terms of chemical properties, the lanthanides are still not twins - otherwise it would not have been possible to separate them. Like a good sports team, they are united in the main things and individual in the particulars. As for the number of participants, different games have different numbers of players, 14 is within the normal range...
True, there was a time when almost fifty candidates were recommended for this “team”. The number of discovered lanthanum-like elements grew with catastrophic speed. In the list of falsely discovered elements compiled by Professor N.A. Figurovsky, the majority are false lanthanides. Even major scientists did not avoid mistakes - Mozander, Lecoq de Boisbaudran, Auer von Welsbach, Crookes, Urbain.
The non-periodic properties of lanthanum and its team, falling out of the strict sequence of the periodic system, caused trouble for Mendeleev. But with change everything was resolved. It was Boguslav Franzevich Brauner, a professor at the University of Prague, who was the first to suggest moving the lanthanides outside the main part of the table.
“You have to be such an expert on “rare earths” as F. Brauner is in order to understand this complex, difficult and still hardly any completed subject, in which verification is complicated not only by the originality and similarity of many initial relations, but also by the difficulties in obtaining the most natural material,” Mendeleev wrote in 1902.
“As for the systematics of the rare earth elements and their place in the periodic table, at present we can confidently assume that scandium, yttrium and lanthanum are in the even rows of group III, as follows from their atomic weights and the volume of their oxides... Other rare earth elements probably form an interperiodic group or node in the system, where they follow each other in atomic weights.” These are Brauner’s words from the article “Elements of Rare Earths,” written for the penultimate (1903) lifetime edition of Mendeleev’s “Fundamentals of Chemistry.”
It was finally possible to unravel the “knot in the system” only after the periodic table was based on a new, physically more accurate criterion - the charge of the atomic nucleus. Then it became clear that only 15 elements could fit between lanthanum and tantalum, and the latter should be an analogue of zirconium. This element, hafnium, was discovered by Coster and Hsvesi in 1923.
The last (by atomic number) lanthanide, lutetium, was discovered earlier - in 1907.
It is natural to look for the reasons for the common properties of lanthanum and lanthanides in the structure of the electronic shells of their atoms.
According to the laws of quantum mechanics, electrons cannot rotate around nuclei in any orbit. They seem to be distributed into layers - shells. The capacity of these shells, the maximum number of electrons in them, is determined by the formula ne = 2A/2, where ne is the number of electrons, and N is the number of the shell, counting from the nucleus. It follows that the first shell can have only two electrons, the second - eight, the third - eighteen, the fourth - thirty-two, etc.
Already in the fourth period of the periodic table, starting with scandium, the “sequential” electrons fall not into the outer fourth layer, but into the previous one. This is why the difference in properties of elements with atomic numbers from 12 to 30 is not as dramatic as that of lighter elements. A similar picture is observed in the fifth period. And here, starting with yttrium, new electrons fill not the fifth, but the penultimate, fourth shell - another row of so-called transition metals is formed.
Transferring this analogy to the sixth period, it would be logical to assume that, starting with lanthanum (it is an analogue of scandium and yttrium), the same thing will happen here. Electrons, however, regardless of our logic, fill not the penultimate shell here, but the third one from the outside, since there are vacancies on it. According to the formula ne = 2A2, this shell - the fourth from the nucleus - can have 32 electrons. With rare exceptions, this is where the “new” electrons of the next lanthanides end up. And since the chemical properties of an element are determined primarily by the structure of the outer electron shells, the properties of lanthanides turn out to be even closer than the properties of transition metals.
As befits group III elements, lanthanides are usually trivalent. But some of them may exhibit a different valence: cerium, praseodymium and terbium - 4 +; samarium, europium and ytterbium - 2 +.
The anomalous valencies of lanthanides were studied and explained by the German chemist Wilhelm Klemm. Using X-ray spectra, he determined the main parameters of their crystals and atomic volumes. The atomic volume curve clearly shows maxima (europium, ytterbium) and less pronounced minima (cerium, terbium). Praseodymium and samarium also fall out, although not so much, from the series defined by a smoothly descending curve. Therefore, the first one “gravitates” towards small-volume cerium and terbium, while the author - towards large-volume europium and ytterbium. Elements with larger atomic volumes hold electrons more tightly, and therefore are only trivalent or even divalent. In “low-volume” atoms, on the contrary, one of the “internal” electrons is not tightly enclosed in the shell - therefore, the atoms of cerium, praseodymium and terbium can be tetravalent.
Klemm's works also provide a physical basis for the long-established division of rare earth elements into two subgroups - cerium and yttrium. The first includes lanthanum and lanthanides from cerium to gadolinium, the second includes yttrium and lanthanides from terbium to lutetium. The difference between the elements of these two groups is the direction of the spins of the electrons filling the fourth shell, the main one for the lanthanides.
The spins - the proper angular momentum of the electrons - have the same sign for the former; in the latter, half of the electrons have spins of one sign, and half - of another.
But enough about anomalies that can only be explained with the help of quantum mechanics, let’s get back to the laws.
When it comes to lanthanides, the patterns also sometimes seem illogical. An example of this is lanthanide compression.
Lanthanide compression is the name given to the natural decrease in the size of the trivalent ion of rare earth elements, discovered by the Norwegian geochemist Goldschmidt, from lanthanum to lutetium. It would seem that everything should be the other way around: in the nucleus of a cerium atom there is one more proton than in the nucleus of a lanthanum atom; the praseodymium nucleus is larger than the cerium nucleus, and so on. Accordingly, the number of electrons rotating around the nucleus increases. And if we imagine the atom as it is usually drawn on diagrams - in the form of a small disk surrounded by elongated orbits of invisible electrons, orbits of different sizes, then obviously the profit of electrons should increase the size of the atom as a whole. Or, if we discard the outer electrons, the number of which may not be the same, the same pattern should be observed in the sizes of trivalent lanthanum ions and its team.
The true state of affairs is illustrated by the lanthanide compression diagram. The radius of the trivalent lanthanum ion is 1.22 A, and the same lutetium ion is only 0.99 A. Everything is not logical, but just the opposite. However, it is not difficult to get to the bottom of the physical meaning of the phenomenon of lanthanide compression even without quantum mechanics; you just need to remember the basic laws of electromagnetism.
The charge of the nucleus and the number of electrons around it grow in parallel. The force of attraction between unlike charges also increases: a heavier nucleus attracts electrons more strongly, shortening their orbits. And since the deep orbits in lanthanide atoms are most saturated with electrons, electrical attraction has an even stronger effect.
The proximity of ionic radii and common chemical properties are the main reasons for the joint presence of lanthanides in minerals.

About rare earth minerals

The main one - monazite - is described above. The second most important rare earth mineral, bastnäsite, is similar in many ways. Bastnaesite is also heavy, also shiny, and also not constant in color (most often light yellow). But chemically it is similar to monazite only by its high content of lanthanum and lanthanides. If monazite is a phosphate, then bastnäsite is a rare earth fluorocarbonate, its composition is usually written as follows: (La, Ce)FC0 3. But, as often happens, the formula of a mineral does not fully reflect its composition. In this case, it indicates only the main components: bastnaesite contains 36.9-40.5% cerium oxide and almost the same amount (in total) oxides of lanthanum, praseodymium and neodymium. But, of course, it also contains other lanthanides.
In addition to bastnäsite and monazite, several more rare earth minerals are practically used, albeit to a limited extent, in particular gadolinite, in which there are up to 32% of rare earth oxides of the cerium subgroup and 22-50% of ittuium. In some countries, rare earth metals are extracted through complex processing of loparite and apatite.
In total, about 70 rare earth minerals themselves are known and about 200 more minerals in which these elements are included as impurities. This suggests that the “rare” earths are not so rare after all, and that this old common name for scandium, yttrium and lanthanum with the lanthanides is nothing more than a tribute to the past. They are not rare - there is more cerium in the earth than lead, and the rarest of the rare earths are much more common in the earth's crust than . It's all about the dispersion of these elements and the difficulty of separating them from one another. But, of course, lanthanides are not equally distributed in nature. Elements with even atomic numbers are much more common than their odd neighbors. This circumstance naturally affects the scale of production and prices for rare earth metals. The most difficult to obtain lanthanides - terbium, thulium, lutetium (note that these are all lanthanides with odd atomic numbers) - are more expensive than gold and platinum. And the price of cerium of more than 99% purity is only 55 rubles per kilogram (data from 1970). For comparison, we point out that a kilogram of mischmetal costs 6-7 rubles, and ferrocerium (10% iron, 90% rare earth elements, mainly cerium) costs only five. The scale of use of rare earth elements is usually proportional to prices...

Lanthanides in practice

In the fall of 1970, the Scientific Council of the Institute of Mineralogy, Geochemistry and Crystal Chemistry of Rare Elements of the USSR Academy of Sciences met for an extended meeting with a rather unusual agenda. The possibilities of rare earth elements "in the light of agricultural problems" were discussed.
The question of the influence of these elements on living organisms did not arise by chance. On the one hand, it is known that rare earths are often included as an admixture in the composition of the most important minerals for agrochemistry - phosphorites and apatite. On the other hand, plants have been identified that can serve as biochemical indicators of lanthanum and its analogues. For example, the ash of southern hickory leaves contains up to 2.5% rare earth elements. Increased concentrations of these elements were also found in sugar beets and lupine. The content of rare earth elements in tundra soil reaches almost 0.5%.
It is unlikely that these common elements did not influence the development of plants, and possibly organisms at other levels of the evolutionary ladder. Back in the mid-30s, the Soviet scientist A. A. Drobkov studied the influence of rare earths on various plants. He experimented with peas, turnips and other crops, introducing rare earths with or without boron, manganese. The results of the experiments said that rare earths are needed for the normal development of plants... But a quarter of a century passed before these elements became relatively accessible. A final answer to the question of the biological role of lanthanum and its team has yet to be given.
Metallurgists in this sense are significantly ahead of agrochemists. One of the most significant events of recent decades in the ferrous metallurgy is associated with lanthanum and his team.
Ductile iron was usually obtained by modifying it with magnesium. The physical meaning of this additive will become clear if we remember that cast iron contains 2-4.5% carbon in the form of flake graphite, which gives cast iron its main technical disadvantage - fragility. The addition of magnesium causes graphite to transform into a more evenly distributed spherical or globular shape in the metal. As a result, the structure and with it the mechanical properties of cast iron are significantly improved. However, alloying cast iron with magnesium requires additional costs: the reaction is very violent, molten metal splashes in all directions, and therefore special chambers had to be built for this process.
Rare earth metals act on cast iron in a similar way: they “remove” oxide impurities, bind and remove sulfur, and promote the transition of graphite into a globular form. And at the same time they do not require special chambers - the reaction proceeds calmly. And the result?
Only 4 kg (0.4%) of ferrocerium alloy with magnesium is added per ton of cast iron, and the strength of cast iron doubles! In many cases, such cast iron can be used instead of steel, in particular in the manufacture of crankshafts. Not only is high-strength cast iron 20-25% cheaper than steel castings and 3-4 times cheaper than steel forgings. The abrasion resistance of cast iron shaft journals turned out to be 2-3 times higher than that of steel ones. Ductile iron crankshafts are already used in diesel locomotives and other heavy machinery.

Rare earth elements (in the form of mischmetal and ferrocerium) are also added to different grades of steel. In all cases, this additive works as a strong deoxidizer, an excellent degasser and desulfator. In some cases, rare earths are alloyed... alloy steel. Chromium-nickel steels are difficult to roll - only 0.03% misch metal introduced into such steel greatly increases its ductility. This facilitates rolling, making forgings, and metal cutting.
Rare earth elements are also introduced into the composition of light alloys. For example, a heat-resistant aluminum alloy with 11% misch metal is known. Additions of lanthanum, cerium, neodymium and praseodymium made it possible to increase the softening temperature of magnesium alloys by more than three times and at the same time increase their corrosion resistance. After this, magnesium alloys with rare earth elements began to be used for the manufacture of parts for supersonic aircraft and shells of artificial Earth satellites.
Rare earth additives improve the properties of other important metals - copper, chromium, vanadium, titanium... It is not surprising that metallurgists are using rare earth metals more and more every year.
Lanthanum and its analogs have found application in other areas of modern technology. In the chemical and petroleum industries, they (and their compounds) act as effective catalysts, in the glass industry - as dyes and as substances that impart specific properties to glass. The use of lanthanides in nuclear technology and related industries is varied. But more on this later, in the sections devoted to each of the lanthanides. Let us only point out that even artificially created promethium has found application: the decay energy of promethium-147 is used in atomic electric batteries. In a word, the time of unemployment of rare earth elements ended long ago and irrevocably.
One should not assume, however, that all problems associated with the “node” in the periodic table have already been resolved. Nowadays, the words of Dmitry Ivanovich Mendeleev about “rare earths” are especially relevant: “A lot of new things have accumulated here in recent years”... However, only amateurs can assume that everything and everyone is known, that the rare earth topic has exhausted itself. Experts, on the contrary, are confident that knowledge of lanthanum and its team is just beginning, that these elements will surprise the scientific world more than once. Or maybe - not only scientific.
REACTOR POISON. Natural lanthanum consists of two isotopes with mass numbers 138 and 139, and the first (its share is only 0.089%) is radioactive. It decays by K-capture with a half-life of 3.2-10 years. The isotope lantai-139 is stable. By the way, it is formed in nuclear reactors during the decay of uranium (6.3% of the mass of all fragments). This isotope is considered a reactor poison, since it quite actively captures thermal neutrons, which is also typical for lanthanides. Of the artificial isotopes of lanthanum, the most interesting is lanthanum-140 with a half-life of 40.22 hours. This isotope is used as a radioactive tracer in studying the processes of separation of lanthanum and lanthanides.
WHICH OF THE THREE? The elements following lanthanum are called rare earths, or lanthanides, or lanthanides. Which of these names is most justified? The term “rare earths” appeared in the 18th century. Now it is classified as the oxides of scandium, yttrium, lanthanum and its analogues; Initially, this term had a broader meaning. “Earths” generally meant all refractory metal oxides. This is true for elements with atomic numbers from 57 to 71: the melting point of Na33 is about 2600° C. In their pure form, many of these “earths” are rare to this day. But there is no longer any need to talk about the rarity of rare earth elements in the earth’s crust...
The term "lanthanides" was introduced to show that the next fourteen elements come after lanthanum. But then, with equal success, fluorine can be called an oxygenide (or oxide) - it follows oxygen, and chlorine - a sulfide... But chemistry has long been invested in the concepts of “sulfide”, “phosphide”, “hydride”, chloride” and so on different meaning. Therefore, most scientists consider the term “lanthanides” to be unsuccessful and use it less and less.
“Lanthanoids” is more justified. The ending "oid" indicates similarity. “Lanthanoids” means “lanthanum-like”. Apparently, this term should be used to designate 14 elements - analogues of lanthanum.

"NEW STORY". In the history of lanthanum and lanthanides, two periods of time can be distinguished, especially rich in discoveries and disputes. The first of these dates back to the end of the 19th century, when lanthanides were discovered and “closed” so often that eventually
it became not even interesting... The second turbulent period was the 50s of the 20th century, when the development of nuclear technology helped obtain large quantities of rare earth raw materials and stimulated new research in this area. It was then that a tendency emerged to obtain and use rare earth elements not in a mixture, but each separately, using their specific properties. It is no coincidence that over 15 years (from 1944 to 1958) the number of scientific publications devoted to lanthanides increased by 7.6 times, and for some individual elements even more: for holmium, for example, by 24, and for thulium, by 45 times!
MASKING AS STARCH. One of lanthanum's compounds, its basic acetate, behaves like starch when iodine is added to it. The white gel takes on a bright blue color. Analysts sometimes use this property to discover lanthanum in mixtures and solutions.
BIVALENT IS ONLY FORMAL. It has been established that in all compounds lanthanum exhibits the same valency - 3+. But how then can we explain the existence of the gray-black dihydride LaH2 and the yellow sulfide LaS? It has been established that LaH 2 is a relatively stable intermediate product of the reaction of formation of LaH3 and that in both hydrides lanthanum is trivalent. The dihydride molecule contains a metallic La - La bond. With sulfide everything is explained even simpler. This substance has high electrical conductivity, which suggests the presence of La3+ ions and free electrons in it. By the way, La I 2 also conducts current well, while LaH3 is a semiconductor.

The most significant thing about element 57, of course, is that it leads a line of 14 lanthanides - elements with extremely similar properties. Lanthanum and lanthanides are always together: in minerals, in our opinion, in metal. At the World Exhibition in Paris in 1900, samples of some believed to be pure lanthanides were demonstrated for the first time. But there is no doubt that each sample, regardless of the label, contained lanthanum, cerium, neodymium and praseodymium, and the rarest of the lanthanides - thulium, holmium, lutetium. The rarest, except for the “extinct” and recreated in nuclear reactions element No. 61 - promethium. However, if promethium had stable isotopes, it would also be present in any sample of any rare earth element.

Only in recent decades has the development of science and technology reached the level at which humanity was able to take advantage of the individual qualities of each (or almost each) of the lanthanides, although, as before, mischmetal - “natural an alloy of lanthanum and lanthanides... Therefore, it would be logical to devote only half of this story directly to element No. 57, and the other half to the rare earth “team” as a whole*. Of course, each of the lanthanides - as a chemical individual - deserves an independent story; here - about their “leader” and what is common to all of them.

* In addition to lanthanum and lanthanides, rare earth elements include scandium and yttrium.

Lanthanum without lanthanides

As sad as it is to admit, the hero of our story is a completely ordinary person. This is a metal, ordinary in appearance (silver-white, covered with a grayish oxide film) and in physical properties: melting point 920, boiling point 3469 ° C; In terms of strength, hardness, electrical conductivity and other characteristics, lanthanum metal always finds itself in the middle of the tables. Lanthanum is also common in chemical properties. It does not change in dry air - the oxide film reliably protects against oxidation in the mass. But if the air is humid (and under normal terrestrial conditions it is almost always humid), the metal lanthanum gradually oxidizes to hydroxide. La(OH) 3 is a base of medium strength, which is again characteristic of an “average” metal.

What else can be said about the chemical properties of lanthanum? In oxygen, when heated to 450°C, it burns with a bright flame (and quite a lot of heat is released). If it is ignited in a nitrogen atmosphere, black nitride is formed. In chlorine, lanthanum ignites at room temperature, but reacts with bromine and iodine only when heated. It dissolves well in mineral acids and does not react with alkali solutions. In all compounds, lanthanum exhibits a valence of 3+. In a word, a metal is like a metal – both in physical and chemical properties.

Perhaps the only distinguishing feature of lanthanum is the nature of its interaction with hydrogen. The reaction between them begins at room temperature and proceeds with the release of heat. Hydrides of variable composition are formed, since lanthanum simultaneously absorbs hydrogen - the more intensely, the higher the temperature.

Lanthanides also interact with hydrogen. One of them, cerium, is even used as a gas absorber in the electric vacuum industry and metallurgy.

Here we come to one of the important parts of our story, to the topic “Lanthanum and cerium”, and in connection with it - to the history of lanthanum.

In terms of prevalence in nature, scale of production, and breadth of use, lanthanum is inferior to its closest analogue - the first of the lanthanides. “The ancestor” and always the second, such is the position of lanthanum in its family. And when rare earth elements began to be divided into two subgroups based on the totality of their properties, lanthanum was assigned to a subgroup whose name was given in honor of cerium... And lanthanum was discovered after cerium, as an impurity to cerium, in the mineral cerite. This is the story, the story about teachers and students.

In 1803, 24-year-old Swedish chemist Jene Jakob Berzelius, together with his teacher Hisinger, investigated the mineral now known as cerite. In this mineral, yttrium earth, discovered by Gadolin in 1794, and another rare earth, very similar to yttrium, were discovered. It was called cerium. Almost simultaneously with Berzelius, cerium earth was discovered by the famous German chemist Martin Klaproth.

Berzelius returned to work with this substance many years later, already an eminent scientist. In 1826, Karl Mozander, a student, assistant and one of Berzelius’s close friends, examined cerium earth and concluded that it was heterogeneous, that, in addition to cerium, it contained one more, and perhaps more than one, new element. But to test this assumption, a lot of cerite was needed. Mozander managed to prove the complexity of cerium earth only in 1839.

Interestingly, a year earlier, a student Erdmann, unknown among chemists, found a new mineral in Norway and named it in honor of his teacher Mozander - mozanderite. Two rare earths, cerium and nova, were also isolated from this mineral.

The new element discovered in cerite and mozanderite was named lanthanum at the suggestion of Berzelius. The name is a hint: it comes from the Greek λανθανειν - to hide, to be forgotten. Lanthanum contained in cerite successfully hid from chemists for 36 years!

For a long time it was believed that lanthanum is divalent, that it is an analogue of calcium and other alkaline earth metals, and its atomic weight is 90...94. There was no doubt about the correctness of these figures until 1869. Mendeleev saw that there was no place for rare earth elements in group II of the periodic table and placed them in group III, assigning an atomic weight of 138...139 to lanthanum. But the legality of such a move still had to be proven. Mendeleev undertook a study of the heat capacity of lanthanum. The value he obtained directly indicated that this element should be trivalent...

Lanthanum metal, of course, far from pure, was first obtained by Mozander by heating lanthanum chloride with potassium.

Nowadays, lanthanum with a purity of more than 99% is produced on an industrial scale. Let's see how this is done, but first let's get acquainted with the main minerals of lanthanum and the first stages of the most complex process of separating rare earth elements.

It has already been mentioned that in minerals lanthanum and lanthanides invariably accompany each other. There are selective minerals in which the proportion of one or another rare earth element is greater than usual. But there are no purely lanthanum or purely cerium minerals, not to mention other lanthanides. An example of a selective lanthanum mineral is davidite, which contains up to 8.3% La 2 O 3 and only 1.3% cerium oxide. But lanthanum is obtained mainly from monazite and bastnäsite, as well as cerium and all other elements of the cerium subgroup.

Monazite is a heavy shiny mineral, usually yellow-brown, but sometimes of other colors, since its composition does not differ in consistency. Most accurately, its composition is described by this strange formula: (REE)PO 4. It means that monazite is a phosphate of rare earth elements (REE). Typically, monazite contains 50...68% REE oxides and 22...31.5% P 2 O 5. It also contains up to 7% zirconium dioxide, 10% (on average) thorium dioxide and 0.1...0.3% uranium. These figures clearly show why the paths of the rare earth and nuclear industries are so closely intertwined.

Mixed rare earth metal - mischmetal - and a mixture of their oxides began to be used at the end of the last century, and at the beginning of this century an outstanding example of international theft was demonstrated in connection with them. German ships delivering cargo to Brazil, preparing for the return journey, filled their holds with sand from the beaches of the Atlantic coast of this country, and from certain places. The captains stated that the sand was simply ballast necessary for greater stability of the ship. In reality, they, fulfilling the orders of German industrialists, stole valuable mineral raw materials - the coastal sands of the state of Espirito Santo, rich in monazite...

Monazite placers are common along the banks of rivers, lakes and seas on all continents. At the beginning of the century (data for 1909), 92% of the world's production of rare earth raw materials, and primarily monazite, came from Brazil. Ten years later, the center of gravity moved thousands of kilometers to the east (or west, depending on how you count it) - to India. After 1950, due to the development of the nuclear industry, the United States became the hegemon among capitalist countries in the extraction and processing of rare earth raw materials.

Of course, our country and other countries of the socialist community had to develop their rare earth industry and find their raw materials.

Let us trace in general terms the path from monazite sand to lanthanum.

Although the sand is called monazite sand, there is not much monazite in it - a fraction of a percent. For example, in the famous monazite placers of Idaho (USA), a ton of sand contains only 330 g of monazite. Therefore, first of all, monazite concentrate is obtained.

The first stage of concentration occurs already on the dredge. The density of monazite is 4.9...5.3, and that of ordinary sand is on average 2.7 g/cm3. With such a difference in weight, gravitational separation is not particularly difficult. But, besides monazite, the same sands contain other heavy minerals. Therefore, in order to obtain monazite concentrate with a purity of 92...96%, a complex of gravitational, magnetic and electrostatic enrichment methods is used. As a result, ilmenite, rutile, zircon and other valuable concentrates are obtained along the way.

Like any mineral, monazite must be “opened.” Most often, monazite concentrate is treated with concentrated sulfuric acid*. The resulting sulfates of rare earth elements and thorium are leached with ordinary water. After they go into solution, silica and the part of zircon that was not separated at previous stages remain in the sediment.

* The alkaline method of opening monazite is also common.

At the next stage of separation, the short-lived mesothorium (radium-228) is extracted, and then the thorium itself - sometimes together with cerium, sometimes separately. The separation of cerium from lanthanum and a mixture of lanthanides is not particularly difficult: unlike them, it is capable of exhibiting valency 4+ and precipitating in the form of hydroxide Ce(OH) 4, while its trivalent analogues remain in solution. Let us only note that the operation of cerium separation, like the previous ones, is carried out many times - in order to “squeeze out” the expensive rare earth concentrate as completely as possible.

After cerium is isolated, the solution contains the most lanthanum (in the form of La(NO 3) 3 nitrate, since at one of the intermediate stages sulfuric acid was replaced by nitric acid to facilitate further separation). Lanthanum is obtained from this solution by adding ammonia, ammonium and cadmium nitrates. In the presence of Cd(NO 3) 2 the separation is more complete. With the help of these substances, all lanthanides precipitate, leaving only cadmium and lanthanum in the filtrate. Cadmium is precipitated with hydrogen sulfide, the precipitate is separated, and the lanthanum nitrate solution is purified several more times by fractional crystallization to remove lanthanide impurities.

The end result is usually lanthanum chloride LaCl 3 . Electrolysis of molten chloride produces lanthanum with a purity of up to 99.5%. Even more pure lanthanum (99.79% and higher) is obtained by the calcium-thermal method. This is the classic traditional technology.

As you can see, obtaining elemental lanthanum is a complex matter.

The separation of lanthanides - from praseodymium to lutetium - requires even more effort and money, and time, of course. Therefore, in recent decades, chemists and technologists from many countries around the world have sought to create new, more advanced methods for separating these elements. Such methods - extraction and ion exchange - were created and introduced into industry. Already in the early 60s, in installations operating on the principle of ion exchange, a 95% yield of rare earth products with a purity of up to 99.9% was achieved.

By 1965, foreign trade organizations of our country could offer buyers all lanthanides in the form of metals with a purity higher than 99%. In addition to promethium, of course, although radioactive preparations of this element - products of the nuclear decay of uranium - have also become quite accessible.

Techsnabexport's catalogs also include about 300 chemically pure and highly pure compounds of lanthanum and lanthanides. This is evidence of the high level of development of the Soviet rare earth industry.

But let's return to lanthanum.

Briefly about the use of lanthanum and its compounds

Pure lanthanum is almost never used as an alloying metal, using cheaper and more accessible cerium or mischmetal - the alloying effect of lanthanum and lanthanides is almost the same.

It was mentioned above that sometimes lanthanum is extracted from a mixture by extraction, using the different solubility of certain (mainly complex) compounds of rare earth elements in organic solvents. But it happens that element No. 57 itself is used as an extractant. Molten lanthanum is used to extract plutonium from liquid uranium. Here is another point of contact between the nuclear and rare earth industries.

Lanthanum oxide La 2 O 3 is used much more widely. This white amorphous powder, insoluble in water but soluble in acids, became an important component of optical glasses. Photographic lenses from the famous Kodak company contain from 20 to 40% La 2 O 3. Thanks to lanthanum additives, it was possible to reduce the size of the lens at the same aperture ratio and greatly improve the quality of color photography. It is known that during the Second World War, lanthanum glasses were used in field optical instruments. The best domestic photographic lenses, for example "Industar-61LZ", are also made of lanthanum glass, and one of our best amateur film cameras is called "Lanthan"... Recently, lanthanum glass is also used in the manufacture of laboratory glassware. Lanthanum oxide gives glass not only valuable optical properties, but also greater heat resistance and acid resistance.

This is, perhaps, all the main thing that can be said about lanthanum without lanthanides, although in some places it was impossible not to deviate from the “without” principle...

Lantan and his team

Comparing lanthanum and lanthanides to a sports team may seem far-fetched to some. However, this comparison is no more seditious than such well-known definitions as “lanthanide family” or “chemical twins”. Judge for yourself: Lantan and his team have a single uniform (silver-white) and, like hockey players, they all have protective equipment (made of oxide films). All of them are endowed with approximately equal amounts by nature (the similarities are extremely great), but, as in sports, for various reasons, “abilities” are not realized to the same extent: some “play” better, others worse... And of course, each member of this teams their favorite “feints” and “techniques” - gadolinium ferromagnetism, for example.

And in terms of chemical properties, the lanthanides are still not twins - otherwise it would not have been possible to separate them. Like a good sports team, they are united in the main things and individual in the particulars. As for the number of participants, different games have different numbers of players, 14 is within the normal range...

True, there was a time when almost fifty candidates were recommended for this “team”. The number of discovered lanthanum-like elements grew with catastrophic speed. Compiled by Professor N.A. Figurov's list of falsely discovered elements contains the largest number of false lanthanides. Even major scientists did not avoid mistakes - Mozander, Lecoq de Boisbaudran, Auer von Welsbach, Crookes, Urbain.

The non-periodic properties of lanthanum and its team, falling out of the strict sequence of the periodic system, caused trouble for Mendeleev. But over time everything was resolved. It was Boguslav Franzevich Brauner, a professor at the University of Prague, who was the first to suggest moving the lanthanides outside the main part of the table.

“You have to be such an expert on “rare earths” as B.F. Brauner, in order to understand this complex, difficult and still hardly any completed subject, in which verification is complicated not only by the originality and similarity of many initial relationships, but also by the difficulties in obtaining the natural material itself,” Mendeleev wrote in 1902.

“As for the systematics of the rare earth elements and their place in the periodic table, at present we can confidently assume that scandium, yttrium and lanthanum are in the even rows of group III, as follows from their atomic weights and the volume of their oxides... Other rare earth elements probably form an interperiodic group or node in the system, where they follow each other in atomic weights.” These are Brauner’s words from the article “Elements of Rare Earths,” written for the penultimate (1903) lifetime edition of Mendeleev’s “Fundamentals of Chemistry.”

It was finally possible to unravel the “knot in the system” only after the periodic table was based on a new, physically more accurate criterion - the charge of the atomic nucleus. Then it became clear that only 15 elements could fit between lanthanum and tantalum, and the latter should be an analogue of zirconium. This element, hafnium, was discovered by Coster and Hevosi in 1923.

The last (by atomic number) lanthanide, lutetium, was discovered earlier - in 1907.

It is natural to look for the reasons for the common properties of lanthanum and lanthanides in the structure of the electronic shells of their atoms.

According to the laws of quantum mechanics, electrons cannot rotate around nuclei in any orbit. They seem to be distributed among layers - shells. The capacity of these shells, the maximum number of electrons in them, is determined by the formula n e = 2N 2 where n e– number of electrons, a N– shell number, counting from the core. It follows that the first shell can have only two electrons, the second - eight, the third - eighteen, the fourth - thirty-two, etc.

Already in the fourth period of the periodic table, starting with scandium, the “sequential” electrons fall not into the outer fourth layer, but into the previous one. This is why the difference in properties of elements with atomic numbers from 12 to 30 is not as dramatic as that of lighter elements. A similar picture is observed in the fifth period. And here, starting with yttrium, new electrons fill not the fifth, but the penultimate, fourth shell - another row of so-called transition metals is formed.

Rice. 3. Atomic volume curve of rare earth elements. It has two maxima formed by elements exhibiting valency 2+; in contrast, elements that can be tetravalent have minimal atomic volumes

Transferring this analogy to the sixth period, it would be logical to assume that, starting with lanthanum (it is an analogue of scandium and yttrium), the same thing will happen here. Electrons, however, regardless of our logic, fill not the penultimate shell here, but the third one from the outside, since there are vacancies on it. According to the formula n e = 2N 2, this shell - the fourth from the nucleus - can have 32 electrons. With rare exceptions, this is where the “new” electrons of the next lanthanides end up. And since the chemical properties of an element are determined primarily by the structure of the outer electron shells, the properties of lanthanides turn out to be even closer than the properties of transition metals.

As befits group III elements, lanthanides are usually trivalent. But some of them may exhibit a different valency: cerium, praseodymium and terbium - 4+; samarium, europium and ytterbium – 2+.

The anomalous valencies of lanthanides were studied and explained by the German chemist Wilhelm Klemm. Using X-ray spectra, he determined the main parameters of their crystals and atomic volumes. The atomic volume curve shows clearly pronounced maxima (europium, ytterbium) and less pronounced minima (cerium, terbium). Praseodymium and samarium also fall out, although not so much, from the series defined by a smoothly descending curve. Therefore, the first “gravitates” towards low-volume cerium and terbium, and the second – towards large europium and ytterbium. Elements with larger atomic volumes hold electrons more tightly, and therefore are only trivalent or even divalent. In “low-volume” atoms, on the contrary, one of the “internal” electrons is not tightly enclosed in the shell - therefore, the atoms of cerium, praseodymium and terbium can be tetravalent.

Klemm's works also provide a physical basis for the long-established division of rare earth elements into two subgroups - cerium and yttrium. The first includes lanthanum and lanthanides from cerium to gadolinium, the second includes yttrium and lanthanides from terbium to lutetium. The difference between the elements of these two groups is the direction of the spins of the electrons that fill the fourth shell, the main one for the lanthanides.

The spins - the proper angular momentum of the electrons - have the same sign for the former; in the latter, half of the electrons have spins of one sign, and half have spins of another.

But enough about anomalies that can only be explained using quantum mechanics, let’s get back to the patterns.

When it comes to lanthanides, the patterns also sometimes seem illogical. An example of this is lanthanide compression.

Lanthanide compression is the name given to the natural decrease in the size of the trivalent ion of rare earth elements, discovered by the Norwegian geochemist Goldschmidt, from lanthanum to lutetium. It would seem that everything should be the other way around: in the nucleus of a cerium atom there is one more proton than in the nucleus of a lanthanum atom; the praseodymium nucleus is larger than the cerium nucleus, and so on. Accordingly, the number of electrons rotating around the nucleus increases. And if you imagine the atom as it is usually drawn on diagrams - in the form of a small disk surrounded by elongated orbits of invisible electrons, orbits of different sizes, then obviously the profit of electrons should increase the size of the atom as a whole. Or, if we discard the outer electrons, the number of which may not be the same, the same pattern should be observed in the sizes of trivalent lanthanum ions and its team.

The true state of affairs is illustrated by the lanthanide compression diagram. The radius of the trivalent lanthanum ion is 1.22 Å, and the same lutetium ion is only 0.99 Å. Everything is not logical, but just the opposite. However, it is not difficult to get to the bottom of the physical meaning of the phenomenon of lanthanide compression even without quantum mechanics; you just need to remember the basic laws of electromagnetism.

The charge of the nucleus and the number of electrons around it grow in parallel. The force of attraction between unlike charges also increases; a heavier nucleus attracts electrons more strongly and shortens their orbits. And since the deep orbits in lanthanide atoms are most saturated with electrons, electrical attraction has an even stronger effect.

The proximity of ionic radii and common chemical properties are the main reasons for the joint presence of lanthanides in minerals.

About rare earth minerals

The main one, monazite, is described above. The second most important rare earth mineral, bastnäsite, is similar in many ways. Bastnaesite is also heavy, also shiny, and also not constant in color (most often light yellow). But chemically it is similar to monazite only by its high content of lanthanum and lanthanides. If monazite is a phosphate, then bastnäsite is a rare earth fluorocarbonate, its composition is usually written as follows: (La, Ce)FCO 3. But, as often happens, the formula of a mineral does not fully reflect its composition. In this case, it indicates only the main components: bastnaesite contains 36.9...40.5% cerium oxide and almost the same amount (in total) oxides of lanthanum, praseodymium and neodymium. But, of course, it also contains other lanthanides.

In addition to bastnäsite and monazite, several more rare earth minerals are practically used, albeit to a limited extent, in particular gadolinite, which contains up to 32% of rare earth oxides of the cerium subgroup and 22...50% of yttrium. In some countries, rare earth metals are extracted through complex processing of loparite and apatite.

Rice. 4. Relative content of lanthanides in the earth's crust. Pattern: Even numbers are more common than odd numbers.

In total, about 70 rare earth minerals themselves are known and about 200 more minerals in which these elements are included as impurities. This indicates that the “rare” earths are not so rare after all, and that this old common name for scandium, yttrium and lanthanum with lanthanides is nothing more than a tribute to the past. They are not rare - there is more cerium in the earth than lead, and the rarest of the rare earths are much more widespread in the earth's crust than mercury. It's all about the dispersion of these elements and the difficulty of separating them from one another. But, of course, lanthanides are not equally distributed in nature. Elements with even atomic numbers are much more common than their odd neighbors. This circumstance naturally affects the scale of production and prices for rare earth metals. The most difficult to obtain lanthanides - terbium, thulium, lutetium (note that these are all lanthanides with odd atomic numbers) - are more expensive than gold and platinum. And the price of cerium of more than 99% purity is only 55 rubles per kilogram (data from 1970). For comparison, we point out that a kilogram of mischmetal costs 6...7 rubles, and ferrocerium (10% iron, 90% rare earth elements, mainly cerium) costs only five. The scale of use of rare earth elements is usually proportional to prices...

Lanthanides in practice

In the fall of 1970, the Scientific Council of the Institute of Mineralogy, Geochemistry and Crystal Chemistry of Rare Elements of the USSR Academy of Sciences met for an extended meeting with a rather unusual agenda. The possibilities of rare earth elements "in the light of agricultural problems" were discussed.

The question of the influence of these elements on living organisms did not arise by chance. On the one hand, it is known that rare earths are often included as an admixture in the composition of the most important minerals for agrochemistry - phosphorites and apatite. On the other hand, plants have been identified that can serve as biochemical indicators of lanthanum and its analogues. For example, the ash of southern hickory leaves contains up to 2.5% rare earth elements. Increased concentrations of these elements were also found in sugar beets and lupine. The content of rare earth elements in tundra soil reaches almost 0.5%.

It is unlikely that these common elements did not influence the development of plants, and perhaps organisms at other levels of the evolutionary ladder. Back in the mid-30s, Soviet scientist A.A. Drobkov studied the influence of rare earths on various plants. He experimented with peas, turnips and other crops, introducing rare earths with or without boron, manganese. The results of the experiments said that rare earths are needed for the normal development of plants... But a quarter of a century passed before these elements became relatively accessible. A final answer to the question of the biological role of lanthanum and its team has yet to be given.

Metallurgists in this sense are significantly ahead of agrochemists. One of the most significant events of recent decades in the ferrous metallurgy is associated with lanthanum and his team.

Ductile iron was usually obtained by modifying it with magnesium. The physical meaning of this additive will become clear if we remember that cast iron contains 2...4.5% carbon in the form of flake graphite, which gives cast iron its main technical disadvantage - fragility. The addition of magnesium causes graphite to transform into a more evenly distributed spherical or globular shape in the metal. As a result, the structure and with it the mechanical properties of cast iron are significantly improved. However, alloying cast iron with magnesium requires additional costs: the reaction is very violent, molten metal splashes in all directions, and therefore special chambers had to be built for this process.

Rare earth metals act on cast iron in a similar way: they “remove” oxide impurities, bind and remove sulfur, and promote the transition of graphite into a globular form. And at the same time they do not require special chambers - the reaction proceeds calmly. And the result?

Only 4 kg (0.4%) of ferrocerium alloy with magnesium is added per ton of cast iron, and the strength of cast iron doubles! In many cases, such cast iron can be used instead of steel, in particular in the manufacture of crankshafts. Not only is high-strength cast iron 20...25% cheaper than steel castings and 3...4 times cheaper than steel forgings. The abrasion resistance of cast iron shaft journals turned out to be 2...3 times higher than that of steel ones. Ductile iron crankshafts are already used in diesel locomotives and other heavy machinery.

Rare earth elements (in the form of mischmetal and ferrocerium) are also added to different grades of steel. In all cases, this additive works as a strong deoxidizer, an excellent degasser and desulfator. In some cases, rare earths are alloyed... alloy steel. Chromium-nickel steels are difficult to roll - only 0.03% misch metal introduced into such steel greatly increases its ductility. This facilitates rolling, making forgings, and metal cutting.

Rare earth elements are also introduced into the composition of light alloys. For example, a heat-resistant aluminum alloy with 11% misch metal is known. Additions of lanthanum, cerium, neodymium and praseodymium made it possible to increase the softening temperature of magnesium alloys by more than three times and at the same time increase their corrosion resistance. After this, magnesium alloys with rare earth elements began to be used for the manufacture of parts for supersonic aircraft and shells of artificial Earth satellites.

Rare earth additives improve the properties of other important metals - copper, chromium, vanadium, titanium... It is not surprising that metallurgists are using rare earth metals more and more every year.

Lanthanum and its analogs have found application in other areas of modern technology. In the chemical and petroleum industries, they (and their compounds) act as effective catalysts, in the glass industry - as dyes and as substances that impart specific properties to glass. The use of lanthanides in nuclear technology and related industries is varied. But more on this later, in the sections devoted to each of the lanthanides. Let us only point out that even artificially created promethium has found application: the decay energy of promethium-147 is used in atomic electric batteries. In a word, the time of unemployment of rare earth elements ended long ago and irrevocably.

One should not assume, however, that all problems associated with the “node” in the periodic table have already been resolved. Nowadays, the words of Dmitry Ivanovich Mendeleev about “rare earths” are especially relevant: “A lot of new things have accumulated here in recent years”... However, only amateurs can assume that everything and everyone is known, that the rare earth topic has exhausted itself. Experts, on the contrary, are confident that knowledge of lanthanum and its team is just beginning, that these elements will surprise the scientific world more than once. Or maybe – not only scientific.

Reactor poison

Natural lanthanum consists of two isotopes with mass numbers 138 and 139, and the first (its share is only 0.089%) is radioactive. It decays by K-capture with a half-life of 3.2·10 11 years. The isotope lanthanum-139 is stable. By the way, it is formed in nuclear reactors during the decay of uranium (6.3% of the mass of all fragments). This isotope is considered a reactor poison, since it quite actively captures thermal neutrons, which is also typical for lanthanides. Of the artificial isotopes of lanthanum, the most interesting is lanthanum-140 with a half-life of 40.22 hours. This isotope is used as a radioactive tracer in studying the processes of separation of lanthanum and lanthanides.

Which of the three?

The elements following lanthanum are called rare earths, or lanthanides, or lanthanides. Which of these names is most justified? The term “rare earths” appeared in the 18th century. Now it is classified as the oxides of scandium, yttrium, lanthanum and its analogues; Initially, this term had a broader meaning. “Earths” generally meant all refractory metal oxides. This is true for elements with atomic numbers from 57 to 71: the melting point of La 2 O 3 is about 2600°C. In their pure form, many of these “lands” are rare to this day. But there is no longer any need to talk about the rarity of rare earth elements in the earth’s crust...

The term "lanthanides" was introduced to show that the next fourteen elements come after lanthanum. But then, with equal success, fluorine can be called an oxygenide (or oxide) - it follows oxygen, and chlorine - a sulfide... But chemistry has long been invested in the concepts of “sulfide”, “phosphide”, “hydride”, chloride” and so on different meaning. Therefore, most scientists consider the term “lanthanides” to be unsuccessful and use it less and less.

“Lanthanoids” is more justified. The ending "oid" indicates similarity. “Lanthanoids” means “lanthanum-like”. Apparently, this term should be used to designate 14 elements - analogues of lanthanum.

"New story"

In the history of lanthanum and lanthanides, two periods of time can be distinguished, especially rich in discoveries and disputes. The first of them dates back to the end of the 19th century, when lanthanides were discovered and “closed” so often that in the end it became not even interesting... The second turbulent period is the 50s of the 20th century, when the development of atomic technology helped to obtain large quantities of rare earth raw materials and stimulated new research in this area. It was then that a tendency emerged to obtain and use rare earth elements not in a mixture, but each separately, using their specific properties. It is no coincidence that over 15 years (from 1944 to 1958) the number of scientific publications devoted to lanthanides increased by 7.6 times, and for some individual elements even more: for holmium, for example, by 24, and for thulium, by 45 times!

Masquerading as starch

One of the lanthanum compounds, its basic acetate, behaves like starch when iodine is added to it. The white gel takes on a bright blue color. Analysts sometimes use this property to discover lanthanum in mixtures and solutions.

Bivalent only formally

It has been established that in all compounds lanthanum exhibits the same valence – 3+. But how then can we explain the existence of the gray-black dihydride LaH 2 and the yellow sulfide LaS? It has been established that LaH 2 is a relatively stable intermediate product of the formation of LaH 3 and that lanthanum is trivalent in both hydrides. The dihydride molecule contains a metallic La–La bond. With sulfide everything is explained even simpler. This substance has high electrical conductivity, which suggests the presence of La 3+ ions and free electrons in it. By the way, LaH 2 also conducts current well, while LaH 3 is a semiconductor.

Lanthanum, as a chemical element, could not be discovered for 36 years. In 1803, 24-year-old Swedish chemist Jons Jakob Berzelius investigated the mineral now known as cerite. Yttrium earth and another rare earth very similar to yttrium were discovered in this mineral. It was called cerium. In 1826, Karl Mozander examined cerium earth and concluded that it was heterogeneous and that, in addition to cerium, it contained another new element. Mozander managed to prove the complexity of cerium earth only in 1839. He was able to isolate a new element when he had a larger amount of cerite at his disposal.

origin of name

The new element discovered in cerite and mozanderite was named lanthanum at the suggestion of Berzelius. It was given in honor of the history of its discovery and comes from ancient Greek. λανθάνω - “hiding”, “hiding”.

Being in nature

For more information on this topic, see: Rare earth elements.
Lanthanum, along with cerium and neodymium, is one of the most common rare earth elements. The lanthanum content in the earth's crust is about 2.9·10−3% by mass, in sea water - about 2.9·10−6 mg/l. The main industrial lanthanum minerals are monazite, bastnäsite, apatite and loparite. These minerals also contain other rare earths.

Receipt

The production of lanthanum involves the separation of the feedstock into fractions. Lanthanum is concentrated together with cerium, praseodymium and neodymium. First, cerium is separated from the mixture, then the remaining elements are separated by extraction.

Physical properties

Lanthanum is a shiny silvery-white metal, malleable and malleable in its pure state. Weakly paramagnetic. The crystal structure is close-packed, like the closest hexagonal packing.

It exists in three crystalline modifications: α-La with a hexagonal lattice (a=0.3772 nm, c=1.2144 nm, z=4, space group P63/tts), β-La with a cubic copper-type lattice (a=0 ,5296 nm, z=4, space group Fm3m), γ-La with a body-centered cubic lattice of the α-Fe type (a=0.426 nm, z=2, space group Im3m, stable up to 920 °C) transition temperatures α↔β 277 °C and β↔γ 861 °C. DH° polymorphic transitions: α:β - 0.36 kJ/mol, β:γ - 3.12 kJ/mol. When moving from one modification to another, the density of lanthanum changes: α-La has a density of 6.162-6.18 g/cm3, β-La - 6.19 g/cm3, γ-La - 5.97 g/cm3.

Alloys with zinc, magnesium, calcium, thallium, tin, lead, nickel, cobalt, manganese, mercury, silver, aluminum, copper and cadmium. Lanthanum forms a pyrophoric alloy with iron.

author unknown

Lanthanum (Lanthanum, La) chemical element number 57 in the periodic table.

This “family” occupies a special place among chemical elements, connected by exceptional similarity of properties. Their outdated name is rare earth elements (REE). Interest in them increased significantly after the first nuclear reactors were launched, during the operation of which these elements are formed as by-products.

This element was hidden from inquisitive chemists for a very long time, for which it received the name lanthanum (“lantano” in Greek “I hide”, “I hide”). It was discovered by the Swedish chemist Mozander in 1839. For more than a hundred years, lanthanum was an element difficult to obtain not only for industry, but also for the chemical laboratory. In its pure form, lanthanum (and its compounds) was obtained only after the so-called chromatographic analysis, developed by the Russian scientist M. S. Tsvet in 1903, became firmly established in the practice of laboratories and industrial enterprises.

The essence of this method in the most general terms is as follows. The test solution is passed through a tube filled with an uncolored powdery or fine-grained substance that has the ability to retain (adsorb) particles of other substances on its surface.

The substances included in the mixture, depending on the degree of their adsorption on the surface of the absorber (adsorbent), will be located at different levels of its height in the tube (column). If a solution consists of a mixture of colored substances (MS Tsvet worked with such solutions in his time), then, due to their different adsorbability, they are retained in different parts of the adsorbent, coloring it in the color appropriate for the given substance.

Thus, the components of the mixture are separated. The mass of the adsorbent along its entire length in the tube, in accordance with the color of the retained substance, will have different colors or different shades of the same color (depending on the colors of the components of the mixture). The resulting column of colored adsorbent is called a chromatogram (from the Greek “chrome” - paint, color and “grapho” - write). To isolate the components of the mixture, the adsorbent column is carefully removed from the tube and divided into color zones. The composition of each colored zone is determined by conventional methods of chemical analysis. It is quite clear that the analysis does not present difficulties when only one substance is present in each zone. However, in most cases, the zones of the colored adsorbent are not so sharply different from each other that they can be easily separated mechanically. Usually the zones are combined and gradually transform into one another. In these cases, the tube containing the adsorbent with the substances retained on it is washed with a specially selected solvent, which relates differently to the adsorbed components of the mixture. This method of extracting an adsorbed substance from an adsorbent is called elution (from the Latin “elucio” - washing). Elution makes it possible to use not only the difference in the adsorbability of the components of the mixture, but also in their solubility.

Lanthanum and its compounds show very strong similarities with a number of other elements very similar to lanthanum.

The number of "relatives" of lanthanum is known. There are 14 of them. From lanthanum, as the most well studied, they are all combined into one group, into one cell of the periodic system under the name of the lanthanide family.

The great similarity of the chemical properties of the lanthanides is associated with the special structure of the electron shells of the atoms of these elements, starting from lanthanum to lutetium inclusive. This special structure leads to the fact that as the atomic number of an element increases, the radius of the atoms does not increase (lanthanide compression). This phenomenon explains such a great chemical similarity of all lanthanides.

Once pure lanthanum salts were isolated, obtaining lanthanum itself was no longer difficult. For example, by electrolysis of lanthanum chloride, the metal lanthanum was obtained, which in its chemical behavior resembles the metal calcium. Lanthanum is similar in hardness to tin (density 6.2), its melting point is only 915-925°C, but its boiling point is surprisingly high (4515°C). Like many active metals, it decomposes water, reacts well with acids, and when heated vigorously - with chlorine, sulfur and other metalloids, i.e. it exhibits the properties of a typical metal.

Lanthanum is a “self-protecting” metal: in dry air it becomes covered with a thin film of oxide, which protects it from further oxidation. But such “protection” occurs only in dry air; moisture combines with this film and forms a strong base.

We have repeatedly mentioned such an important metal as aluminum, and pointed out, in particular, its ability to burn with the release of a large amount of heat. Many different processes are based on this reaction. Lanthanum has an even greater heat of reaction with oxygen. As soon as they learned to produce lanthanum in large quantities, it began to compete with aluminum in metallurgy. To remove oxygen from liquid steel, lanthanum, rather than aluminum, is often introduced into it. For a ton of steel, only one kilogram of this “deoxidizer” is needed, as substances that free steel from oxygen are called in technology. Millions of tons of steel have already been processed in this way and it is claimed that this is an excellent method of improving its quality.

Lanthanum was obtained in a mixture with cerium, another member of the lanthanide family, in an approximately 1:1 ratio. By fusing a mixture of these metals with iron, they got... “flint”, which was widely used in pocket lighters. Of course, iron-cerium-lanthanum "flint" has nothing in common with the natural stone flint - a silicon compound. This name was given to the alloy for its ability to “spark” when a jagged steel wheel is rubbed against it. This ability was used not only in harmless lighters, but also in artillery shells. Having equipped the projectile with a nozzle made of this “mixed metal”, we were able to observe the projectile in flight. "Mixed metal" sparks when flying in the air. In this case, the role of the lighter wheel is played by the air itself, rubbing against the metal.

Lanthanum compounds are used in the manufacture of glass for the best camera lenses and special safety glasses. When alloyed with magnesium, lanthanum is used to make aircraft engine parts.

It is curious that the familiar “deposits” of lanthanum are the familiar blueberry plant, the ash of which contains up to 0.17% lanthanum oxide. There is a lot of lanthanum in the ash of low-growing Karelian birches.

In 1826, Karl Mozander, a student, assistant and one of Berzelius’s close friends, examined cerium earth and concluded that it was heterogeneous, that, in addition to cerium, it contained one more, and perhaps more than one, new element. Mozander managed to prove this only in 1839. The new element discovered in cerite, at the suggestion of Berzelius, was called lanthanum (from the Greek lanqanein- hide, forget). Lanthanum contained in cerite successfully hid from chemists for 36 years!
And then lanthanum continued to live up to its name. For a long time it was believed that it is an analogue of calcium and other alkaline earth metals, its valency is two, and its atomic weight is 90...94. Only in 1869 did Mendeleev see that there was no place for rare earth elements in group II of the periodic table and placed them in group III, assigning an atomic weight of 138...139 to lanthanum. Mendeleev's study of the heat capacity of lanthanum proved that lanthanum must be trivalent.

Receipt:

Lanthanum metal, of course, far from pure, was first obtained by Mozander by heating lanthanum chloride with potassium.
Currently, lanthanum is obtained mainly from monazite and bastnaesite ((La, Ce)FCO 3), like all other metals of the cerium subgroup. Monazite concentrate (LnPO 4 + 7% zirconium dioxide, 10% thorium dioxide and 0.1...0.3% uranium) is treated with concentrated sulfuric acid, the resulting sulfates of rare earth elements and thorium are leached with ordinary water. By successively separating thorium, cerium, and other rare earth elements, lanthanum chloride LaCl 3 is usually obtained. Electrolysis of molten chloride produces lanthanum with a purity of up to 99.5%. Even more pure lanthanum (99.79% and higher) is obtained by the calcium-thermal method.
It is much easier and cheaper to obtain mischmetal - mixed rare earth metal.

Physical properties:

Silver-white metal. Lanthanum is similar in hardness to tin (density 6.2), its melting point is only 915-925°C, but its boiling point is surprisingly high (4515°C).

Chemical properties:

Lanthanum in dry air becomes covered with a thin film of oxide, which protects it from further oxidation. But such “protection” occurs only in dry air.
In its chemical behavior, lanthanum resembles calcium. Like many active metals, it decomposes water, reacts well with acids, and when heated vigorously - with chlorine, sulfur and other metalloids, i.e. it exhibits the properties of a typical metal.
In compounds it exhibits an oxidation state of +3.

The most important connections:

Lanthanum oxide, La 2 O 3 , a white amorphous powder, insoluble in water but soluble in acids. Interacting with CO 2 it turns into carbonate.
Lanthanum hydroxide La(OH) 3, a gelatinous white precipitate, is formed by the interaction of lanthanum with water, lanthanum salts with alkali solutions. Interacting with CO 2 it turns into carbonate.
Lanthanum salts colorless crystals substances. Soluble salts - nitrate, halides, sulfate; insoluble - fluoride, phosphate, carbonate. Nitrate and carbonate decompose when heated to form lanthanum oxide. Basic lanthanum acetate behaves like starch when iodine is added to it. The white gel takes on a bright blue color. This property is sometimes used to discover lanthanum in mixtures and solutions.

Application:

Pure lanthanum is almost never used as an alloying metal, using cheaper and more accessible misch metal. This additive to cast iron and steel works as a strong deoxidizing agent, an excellent degasser and desulfator. Additions of rare earth elements to light alloys (magnesium, aluminum) increase their heat resistance and corrosion resistance. REE are also used to improve the properties of alloys of copper, chromium, vanadium, titanium...
Molten lanthanum is used to extract plutonium from liquid uranium.
Iron-cerium-lanthanum "flint" is used in pocket lighters and tracer artillery shells.
Lanthanum oxide La 2 O 3 is an important component of optical glasses (Kodak photographic lenses contain from 20 to 40% La 2 O 3, the best domestic photographic lenses are also made of lanthanum glass). Lanthanum glass is also used in the manufacture of laboratory glassware (heat resistance and acid resistance) . See also:
Popular library of chemical elements Nauka Publishing House, 1977.