Metal Story: Manganese (Mn) – Iron’s old Companion
Those who have been to the Moscow Underground could not have missed the Mayakovskaya Station, one of the most magnificent subway palaces supported by columns finished with a beautiful pink stone along their edges. The stone is rhodonite, a mineral containing manganese. The delicate pink colour (“rhodon” in Greek means “pink”) and good workability make it an excellent finishing material which is also good to carve various articles from. Articles made from rhodonite are kept in the Hermitage and the Peter and Paul Cathedral in Leningrad and in many other museums. Large rhodonite deposits occur in the Urals (once a lump weighing 47 tons was discovered). Nowhere else in the world do such impressive accumulations of this mineral occur, neither is the Urals rhodonite surpassed in its beauty.
But the main manganese-containing mineral of industrial importance is pyrolusite or manganese dioxide, a black mineral with which man has been familiar since old times. Even Pliny the Elder, the outstanding naturalist of ancient Rome who died in the eruption of Vesuvius in the 1st century AD, mentioned the wonderful ability of the black powder (young pyrolusite) to brighten glass.
Then, in 1540, Vanoccio Biringuccio, the Italian scientist and engineer, wrote in his encyclopedic work on mining and metallurgy entitled Pyrotechnia: “… pyrolusite may be coloured dark brown; … if vitreous substances are added to it, it gives them a beautiful violet colour. The master glass-makers use it to colour glass; the master potters make violet designs on their wares with it. Furthermore, pyrolusite has one special characteristic: when alloyed with molten glass it purifies it and makes it white instead of green or yellow.”
The name “pyrolusite” was given to the mineral much later and in the Middle Ages it was called “glass soap” for its ability to decolourize glass, or “manganese” (in Greek “manganese” means “purify”). It had still other name too — “black magnesium” since pyrolusite had been mined from ancient times near the town of Magnesia in Asia Minor. It was also there that “white magnesium” (“magnesia alba” or magnesium oxide) was extracted.
The history of chemistry ascribes the discovery of manganese as a metal to the Swedish chemist, J. Gahn (1774). But there is reason to suppose that the first grains of metallic manganese were obtained by Ignatius Gottfried Kaim, who had described it in his thesis which was published in Vienna in 1770. Kaim had not completed his research and it remained unknown to most chemists of the time. But one chemical handbook does mention Kaim’s discovery: “By heating a mixture of one part of pyrolusite powder with two parts of black flux Kaim produced a bluish-white brittle metal in the form of a crystal with numerous differently-outlined lustrous facets, in which a fracture is iridescent with every tinge, from blue to yellow.”
The next attempt to find out more about manganese was made by the Swedish chemist Tornberg Bergman. “The mineral that they call ‘black magnesium’ is a new earth that should not be confused either with roasted lime nor with ‘magnesium alba’.” But still Bergman was unable to extract manganese from pyrolusite.
Bergman’s study was continued by his friend, the well-known chemist Carl Scheele. In 1774, he submitted his paper “On Manganese (i.e. pyrolusite — S.F.) and its Properties” to the Stockholm Academy of Sciences in which he reported on the discovery of a new element — gaseous chlorine, and asserted that pyrolusite contained a new metal which was different from all known at that time. But he too failed to obtain it.
Gahn succeeded in what both Bergman and Scheele had failed in the same year — 1774. He placed a mixture of ground pyrolusite and oil in a crucible the inside walls of which were covered with wet charcoal dust and put some of the dust on top. After an hour of intense heating a grain of metallic manganese was discovered in the crucible. That discovery brought Gahn world fame and the family of metals a new, fifteenth, member.
On May 16, 1774, Scheele sent Gahn purified pyrolusite with a note saying: “I’m anxiously waiting for your report on the results you will get when you apply your ‘infernal fire’ to this pure pyrolusite and I hope you will send me a small regulus of the metal as soon as possible.”
The “infernal fire” did its job and on June 27, only a month later, Sheele wrote Gahn in gratitude for the regulus of manganese: I think that the regulus obtained from pyrolusite is a semimetal different from all the semimetals and Staving a close relation to iron.”
Manganese began to be produced in Russia in the first quarter of the 19th century as an alloy with iron— ferromanganese. The Mining Journal mentioned steel smelting with the introduction of manganese in 1825. Since then the fate of this element has been inseparably linked with metallurgy. Today too it remains the main consumer (95 per cent) of manganese ore.
In the now classical work On Damask Steels published in 1841, the outstanding Russian metallurgist P. P. Anosov describe ed the results of his study of steels with different manganese content. For introduction into steel Anosov used the ferromanganese obtained in crucibles. From 1876 industrial smelting of ferromanganese began at the Nizhni- Tagil plant.
The year 1882 became a landmark in the history of manganese — the British metallurgist Robert Hadfield produced steel with a 13-per-cent manganese content. It was in 1878 that the 19-year-old metallurgist of Sheffield began studying alloys of iron with other elements, and particularly, with manganese. Four years later Hadfield made the following entry in his log-book: “I started these experiments intending to make steel that would be hard and at the same time malleable. The experiments have yielded some curious results, quite important and capable of changing metallurgists’ current views on the alloys of iron.”
In 1883 Hadfield was issued the first British patent for manganese steel prepared on the basis of a rich ferromanganese addition to iron. He continued studying problems of manganese steel and published his findings in several books dealing with the application of manganese in metallurgy, with some newly-discovered properties of iron and manganese and with manganous steel. He established that water quenching gave steel new wonderful properties. He obtained several more patents concerned with the thermal treatment of manganous steel and in 1901 patented his design of a furnace intended for heating this steel before hardening.
Hadfield’s steel soon won the recognition of metallurgists and engineers. Owing to its high wear-resistance, it began to be used for parts subject to excessive wear under high pressure — rail frogs, crusher jaws, tumbling balls, caterpillar tracks, etc. But the most amazing fact was that under the effect of load the steel from which those components were made became increasingly harder. The lollowing explanation was found. After casting, extra carbides settle on the grain boundaries of steel reducing its strength. These carbides are dissolved in the metal by means of hardening. During service carbon is released in the surface layer as a result of work hardening (under the effect of load) and’ steel becomes stronger.
Small wonder, therefore, that Hadfield’s steel aroused the liveliest interest of firms manufacturing safes and locks.
Manganese iron is also characterized by the self-hardening property. Excavators with bearings made from this iron were in service without repairs twice as long as their “fellows” with bronze bearings.
Manganese is extensively used in metallurgy for deoxidation and desulphurization of steel. It is used as an alloy element in spring steels, steels for oil and gas pipelines and in non-magnetic steels. As a matter of fact, there is hardly any need to enumerate the manganese-containing steels: the element discovered by Gahn is present in a certain quantity in literally all the steels and irons. It is for good reason that it is called iron’s eternal companion. In the Periodic Table manganese and iron occupy neighbouring “cells” (Nos. 25 and 26). (Together with iron, manganese even finds its way into sharks’ teeth, but more about it later.)
After the Russian scientists S. F. Zhemchuzhny and V. K, Petrashevich discovered in 1917 that even small additions of copper (about 3.5 per cent) make manganese more ductile, metallurgists became interested in manganese alloys as well.
Modern technology applies a large number of manganins, that is, alloys of manganese, copper and nickel, characterized by high elfectrical resistivity which is practically independent of temperature. The work of electric manometers is based on the ability of manganin to change resistance under pressure. A common manometer cannot be used when it is necessary to measure a pressure of several scores of thousands of atmospheres: the liquid or gas inside the manometer tube breaks through its walls, no matter how strong the material from which it is made. This task is successfully coped with by the electric manometer: measuring the electrical resistivity of manganin under definite pressure it is possible to calculate pressure 1 to any degree of accuracy on the basis of a definite formula.
Manganins are characterized by another valuable property: damping, that is, the ability to absorb the energy of oscillations. Had it occurred to anyone to cast a bell from manganin, it would hardly be possible to use it at all: instead of the resounding boom the manganin bell would produce short thumps.
But it must be said that while “dumbness” is clearly a shortcoming in a bell, it is fine in such “sonorous” parts as tram wheels, rail joints and many other things that can produce unnecessary rumbling. “Mute” alloys can considerably lower the harmful noise level in forging and stamping shops. The greatest ability to “keep quiet” is displayed by alloys consisting of 70 per cent of manganese and 30 per cent of copper. Some of them are not inferior to steel in strength.
Interestingly enough, manganese bronze — an alloy of manganese with copper — can be magnetized even though neither of the components have magnetic properties.
Alloys possessing “memory” have become rather well-known during the last few years (you will read about the best-known of them, nitinol, in the chapter entitled “The Copper Devil”). The number of such alloys has been growing steadily. Recently a group of researchers under Ye. M. Savitsky, Corresponding Member of the USSR Academy of Sciences at the A. A. Baikov Institute of Metallurgy, developed an alloy on the basis of manganese (with an addition of copper) which even exceeds the famous nitinol in its ability “to remember” its former shape. It is easily manufactured and machined and will doubtlessly find quite a number of fascinating spheres of application.
For a long time expensive metals, such as palladium and platinum, had been used as catalysts in the production of superpure nitrogen. The Inorganic Chemistry and Electrochemistry Institute of the Georgian Academy of Sciences has developed a process in which manganese acts as the catalyst. The first industrial facility for the production of ideal nitrogen from the air, essential for the manufacture of kapron, has been built at the Rustavi Synthetic Fibre Plant.
We are all familiar with one manganese compound — potassium permanganate. It is the solution used as a disinfectant to bathe a wound, rinse a sore throat or treat a burn. It is also widely applied in chemical laboratories for manganometry, i.e. quantitative analysis.
Just as many other elements, manganese is absolutely essential for the normal development of animals and plants.
Generally, the content of this element in the living organism is not more than several thousandths of one per cent, but some flora and fauna species show a special interest in it. For example, red ants contain 0.05 per cent of manganese; up to one per cent of manganese is contained in rust fungi, sea weed and water nut. In certain bacteria the manganese content may be as high as several per cent. The human organism needs daily from 3 to 5 milligrams of manganese, the blood containing 0.002-0.003 per cent of it.
A few words about the shark we have mentioned, while we are on the subject of plants and animals. Scientists who studied the tooth of this marine carnivore which had lain on the ocean floor for several thousand years found that the tooth was still in a good state except that it had become covered with iron and manganese compounds. How had these elements managed to end up there?
Some hundred years ago, in 1876 to be more exact, the Challenger, a British threemast sailer which had been on a scientific expedition, plying the seas and oceans for more than three years, brought to Britain, together with her other “spoils”, some mysterious dark cone-shaped lumps which had been lifted from different regions of the ocean floor. Since manganese was the principal component of the “cones” they came to be known as “manganese nodules”, or iron-manganese concretions in more scientific terms. Later expeditions revealed that there are tremendous accumulations of “manganese nodules” in many parts of the ocean floor. But no particular interest was shown in them up to the middle of this century. And it is only in recent years and owing to the comparatively insufficient reserves of manganese ore in the world, that the underwater treasure has aroused scientific interest.
The regions of accumulations have been carefully studied, revealing startling results. According to preliminary (and it can definitely be said, modest) calculations, nearly 100 thousand million (!) tons of excellent iron-manganese ore has accumulated in the Pacific alone. And the word “ore” is no slip of the tongue: the concentration of manganese in it comes to 50 per cent and of iron, to 27 per cent. (In some concretions the content of manganese dioxide is 98 per cent and it can be used without preliminary processing in the manufacture of electric batteries, for instance.)
As wealthy is the Atlantic, and as far as the Indian Ocean is concerned, the Soviet expedition on the Vityaz has discovered iron-manganese concretions on the bottom of this ocean too. Calculations show that the reserves in the Indian Ocean are at least as big as in the other oceans.
Oceanographers believe that the concretions are a result of concentration around a body of minerals dissolved in water solutions. Some scientists maintain that a certain part in this process is played by marine bacteria, those microscopic “ore-dressers” of the sea. Biologists in Leningrad have discovered hitherto unknown species of so-called “metallogenic” bacteria capable of extracting manganese from water and concentrating it. In a laboratory experiment the “underwater metallurgists” demonstrated enviable efficiency: they created manganese concretions the size of a match-head within two or three weeks. Amazing productivity, considering that the “toilers” themselves are hardly discernible under the microscope.
The oceanic concretions are not unlike potato tubers and their colouring ranges between brown and black, depending on whether it is iron or manganese that predominates in the composition. If the content of manganese is high, the colour is absolutely black.
The size of the concretions varies from fractions of a millimetre to 15 centimetres. But considerably larger accumulations are also found. The collection of the Scripps Oceanographic Society has a 57-kg concretion which was found in the vicinity of the Hawaii. A still larger concretion, one weighing 136 kilograms, was discovered stranded in the loops of the underwater telegraph cable when it was being hoisted for repairs. But that unique specimen was not destined to become a museum exhibit; after it had been studied and a drawing of it made, it was thrown overboard because of a misunderstanding. But even that record was broken when the Vityaz expedition in the Pacific fished out a lump one and a half metres long: it weighed almost a ton.
Many countries have now really become interested in the development of underwater resources. Scientists and engineers, naturally, will yet have to find answers to the most complex technological problems involved in underwater mining. Under construction today are special submarines, amphibious tractors, excavators on pontoons and other such facilities intended for the extraction of the treasure stored in the underwater abyss. “Ocean mining” will have an indisputable advantage over the mining industry as we know it today: it will not need the laying of roads and other communications which would be indispensable on the surface. Boats will take people and equipment to any part of the ocean and will ship the minerals extracted to any destination. Dutch engineers have designed an underwater caterpillar automatic excavator intended to collect manganese and other ores on the seabed. This automatic “miner” will be able to work at a depth of up to five kilometers. It will be electrically-driven and remote-controlled by a TV camera operator on board the ocean ore carrier. The spiral rotor of the excavator will pick up a certain amount of ore and empty it into its hull. Scientists and engineers in Japan are now developing a bathyscaphe to carry out underwater prospecting for oil and manganese and do other survey work. A 30-ton displacement bathyscaphe intended for three people will be able to submerge to a depth of up to two kilometres, move at considerable speed, have good manoeuvrability, and stay underwater for more than three days and nights without surfacing. Their next project which will be launched at the beginning of the 1980s is an oceanographic submarine to carry out geological survey and study fish reserves of the ocean at a depth of up to 6 kilometres.
Important work designed to put the wealth of the oceans to use is under way in the Soviet Union as well. Hundreds of expeditions every year go out to the seas and oceans that cover more than 70 per cent of the earth’s surface. The time is not far off when industrial exploitation of the world ocean resources will begin but right now geologists and miners have enough to do exploring the earth’s depths.
In content in the earth’s crust manganese is in 15th place (0.09 per cent). According to geologists, almost all manganese deposits are more or less “coevals”. This has given scientists reason to hypothesize a cosmic origin of the manganese accumulations. Their theory is that some two thousand million years ago meteoritic dust rich in manganese had precipitated on the earth surface, forming the manganese deposits found today in the ground and on the sea and ocean floor.
Manganese ores occur in India, Ghana, the South African Republic, Morocco and Brazil. But not one of these countries can compete with the Soviet Union in this respect. The Chiatura manganese deposit situated in Soviet Georgia is the world’s biggest. It is a curious fact that the small river Rioni flowing in these parts dumps more than 100 000 tons of manganese into the Black Sea every year.
The production of manganese at Chiatura was started as early as 1879, and in 1886 another big deposit began to be developed near Nikopol. Tsarist Russia, however, “had no need” for manganese: 1 195 thousand tons of the 1 245 thousand it had produced in 1913 was exported to other countries. During the Great Patriotic War intensive development of manganese deposits began in the Urals, Kazakhstan and Siberia. Today the Soviet Union leads the world in the production of this valuable mineral.
Ferroalloy plants are the main consumers of manganese ores. The processes introduced there yield alloys of manganese with iron or silicon, or the pure metal. From there manganese is shipped to steel-making shops.
Source: Tales About Metals, S. Venetsky