Origin of the name
The name of the element comes from the Latin Rhenus - the name of the river Rhine in Germany.
The existence of rhenium was predicted by D.I. Mendeleev (“tri-manganese”) in 1871, by analogy with properties of the elements in the same group of the periodic system, but the term “two-manganese” (the English “dvi-manganese”) was used more often.
The element was discovered in 1925 by the German chemists Ida and Walter Noddaks, when studying the mineral columbite by spectral analysis in the laboratory of Siemens and Halske. The fact was reported at the meeting of German chemists in Nuremberg. Next year a group of scientists extracted the first 2mg of rhenium from molybdenite. Relatively pure rhenium was obtained only in 1928. It was necessary to process more than 600kg of Norwegian molybdenite to produce 1g of rhenium.
The first industrial production of rhenium was set up in Germany in the 1930s. The capacity of the plant was 120kg per year, which fully satisfied the global demand for this metal. After processing of molybdenum concentrates the first 4.5kg of rhenium were obtained in the USA in 1943.
Rhenium was the last discovered element known for a stable isotope. All elements that were discovered later (including synthetically obtained ones) did not have stable isotopes.
Occurrence in nature
World rhenium production
The world volume of rhenium production was about 40 tons in 2006. Today the largest producer is a Chilean company Molymet. The production of rhenium is constantly growing and in 2008 it amounted to 57 tons.
Raw material sources and reserves
In terms of world rhenium reserves Chile holds the first place, the USA - the second, and Russia - the third. Today Kazakhstan, which was the main source of Re production in the USSR (a deposit near the city of Dzheskazgan), has large rhenium reserves. The reserves of rhenium in the form of rheniite on Iturup Island are estimated in 10-15 tons, in the form of volcanic gases – in about 20 tons per year. In Russia hydrogenious polyelements deposits (deposits of reservoir oxidation zones) have the largest resources potential, exceeding the potential of copper-molybdenum ores of porphyry copper deposits (the main source of rhenium in the world). Total potential rhenium reserves in deposits of this type in the territory of the Russian Federation are estimated in 2900 tons, which makes 76% of the country's Re reserves. Most of these reserves (82%) are located around Moscow and are limited to Moscow lignite, where the most studied rhenium-bearing source is Briketno-Zheltukhinskoye field in the Ryazan Region.
Total world rhenium reserves (excluding hydrogenious polyelements deposits) amount to 13,000 tons, including 3,500 tons of molybdenum raw materials and 9,500 tons of copper. With a promising level of rhenium consumption, about, 40-50 tons per year, this metal may suffice for another 250-300 years. (The number is estimated without regards to the amount of the metal recycling). In practical terms, molybdenum and copper sulphide concentrates remain the most important raw material sources for primary rhenium recovery on an industrial scale. The content of rhenium in them may reach 0.002–0.005% in mass. In total balance of rhenium production in the world they make more than 80%. The rest is recovered mainly from secondary raw materials.
During the last quarter-century, the scientists’ attention is drawn to a high-temperature rare-metal vapour-gas system of the volcano Kudriavyi on Iturup island in the Sakhalin Region of Russia, which is the first discovered rhenium source represented by a fumarole field with active sources of deep fluids. The possibility to extract rhenium and other rare metals from fumarole gases of the volcano has been proved; developed and patented technologies of ReS2 extraction from high-temperature volcanic gases have been reviewed. The composition of the first native rhenium mineral, rheniite, has been described. Emission of metals by volcanic gases may reach up to 20-36 tons a year. A conclusion has been drawn on the expediency of extraction of rhenium, indium, germanium and other metals from this unique deposit in the world, and on the fact that the fumarole vapour-gas emissions of the volcano can be considered as a new type of the unique complex mineral raw material. It has been argued that the extracted rhenium can fully meet the needs of Russia and eliminate the dependence of its industry on imports. It is planned to start rhenium production on an industrial scale by 2020. Risks of investments into the production of the rare metal concentrate from gases are considered by experts as justified. Another source of rhenium is its recycling from scrap of rhenium containing materials.
Rhenium is one of the rarest elements in the earth's crust. Its content in the earth’s crust is estimated in 7*10-8 in mass. By geochemical properties, it is similar to its far more common neighbors in the periodic system - molybdenum and tungsten. Accordingly, it is found in the minerals of these elements in the form of small impurities. The main source of rhenium is molybdenum ores of some deposits, where it is extracted as an associated component.
Rhenium occurs as a rare mineral Dzhezkazganit (CuReS4), discovered near the city of Kazakhstan Dzhezkazgan (Kaz. Zhezkazgan ). Besides, rhenium is found in columbite, pyrite, as well as in zircon and in minerals of rare-earth elements as an impurity.
The extreme diffusion of rhenium is indicated by the fact that there is only one economically beneficial rhenium deposit in the world, which is located in Russia. Its reserves are about 10-15 tons. This field was discovered in 1992 in the volcano Kudriavy on Iturup island (the Kurils). Rhenium is found here in the form of the mineral rheniite (ReS2), with a structure similar to molybdenite. The deposit in the caldera atop of the volcano is represented by a fumarole field of about 50×20m with constant springs of high-temperature deep fluids - fumaroles. This implies that the field is still actively developing: according to various estimates from 10 to 37 tons of rhenium per year are emitted into the atmosphere with gases.
Another rhenium-containing mineral, tarkianite (Cu, Fe)(Re, Mo)4S8 (53.61% Re), was discovered in a concentrate found on Hitura deposit in Finland.
Rhenium is a lustrous silvery-white metal. Rhenium powder is black or dark-gray, depending on the dispersion. It is one of the densest and solid metals (density - 21.02g/cm³). Melting point - 3459K (3186 °C). Boiling point - 5869K (5596 °C). Paramagnetic.
Rhenium has a hexagonal crystal structure a = 276.1 pm and c = 445.6 pm.
Due to a number of physical properties, rhenium is close to refractory metals of the sixth group (molybdenum, tungsten), as well as to metals of the platinum group. According to the melting point, rhenium ranks second among metals (giving way only to tungsten), and fourth in density (after osmium, iridium and platinum). According to the boiling point it takes the first place among the chemical elements (5869K, compared to 5828K of tungsten). Pure metal is ductile at room temperature, but due to its high modulus of elasticity, the hardness of rhenium increases after treatment due to its strain-hardening. It is annealed in hydrogen, inert gas, or vacuum to restore plasticity. Rhenium is resistant to repeated heating and cooling without loss in strength. Its strength at temperatures to 1200 °C is higher than that of tungsten, and considerably exceeds the strength of molybdenum. Electrical resistance of rhenium is four times higher than that of tungsten and molybdenum.
Dense rhenium is stable in air at normal temperatures. At temperatures above 300 °C metal oxidation is observed, the oxidation runs intensively at temperatures above 600 °C. Rhenium is more resistant to oxidation than tungsten, does not react directly with nitrogen and hydrogen; rhenium powder only adsorbs hydrogen. When heated, rhenium interacts with fluorine, chlorine and bromine. Rhenium is almost insoluble in hydrochloric and hydrofluoric acids and weakly reacts with sulfuric acid even when heated, but freely dissolves in nitric acid. Rhenium forms amalgam with mercury.
Rhenium interacts with aqueous solutions of hydrogen peroxide to form rhenium acid. Rhenium is the only refractory metal which does not form carbides.
Due to its low availability and high demand, rhenium is one of the most expensive metals. Its price is highly dependent on the purity of the metal. 1 kg of rhenium costs from 1,000 to 10,000 dollars.