In natural minerals niobium and tantalum always meet together and their separation - one of the most complicated problems of chemical technology.

Metal niobium and tantalum on appearance remind platinum. Niobium – the metal of light grey color. Tantalum is darker, with a bluish shade. Niobium is more distributed in the earth's crust, than tantalum.

Pure metals are plastic, are easily given to processing by pressure at room temperature, are well welded. Mechanical properties, especially plasticity, in a strong degree depend on the content of gas impurities. On air at normal conditions both metals are steady, niobium is oxidized above 200⁰С, tantalum - above 280⁰С. For protection of niobium and its alloys from oxidation the coverings from zinc and chemically steady oxides and nitrides of metals are used. As a result of it niobium and alloys on its basis are not oxidized even at temperature 1200⁰С.

Ta and Nb possess the ability to absorb and keep gases (H₂, N₂, O₂) at the high temperature. Ta and Nb are the very stable to action of acids and many other aggressive mediums. Ta and Nb form with each other the continuous line of homogeneous solid solutions. Alloys of these metals are plastic, chemically stable and possess all valuable properties of pure metals. It has the big practical value as allows to replace pure tantalum with tantalum-niobium alloys.

From chemical compounds Ta and Nb compounds of V-valent metals are steadiest and practically important. At the same time compounds with valency IV, III, II and even I are known.

For separation Ta and Nb in the quantitative chemical analysis the great value has their ability to form with tannin (complex ether of glucose and digallic acid) the adsorption complexes differing on the properties. The tantalic complex of citreous color drops out after boiling at pH = 3-4, the niobium complex of orange color drops out at pH = 6-7.

Application of Ta, Nb and their alloys.

- Nb - the universal alloying element for chromium-nickel stainless, chromic, chromium-manganese steels. It is used basically as ferroniobium and ferro-tantalum-niobium. Stainless steels with the niobium content serve for manufacture of the chemical and oil refining equipment. Tantalum operates on steel similarly, but because of deficiency it is applied much less;

- Nb (alongside with W, Mo, Ta) - one of the major components of the heat resistance alloys used at high temperatures. Heat resistance steels (more than 1,5 % Nb) serve for manufacturing jet engines, details of planes, gas turbines;

- Due to a low level of the induced radio-activity and high corrosion stability the important scope of niobium is the atomic engineering. In the field of atomic engineering Nb is used as a constructional and alloying material which is used for manufacture of shells for uranium elements in nuclear reactors (alloying of uranium by niobium increases the service life of heat-producing elements), installations for radioactive waste products;

- Ta and Nb are the best compactors of metals. Properties Al, Cu, Mo, Ti, Zr and their alloys sharply improve at alloying by niobium and tantalum;

- Carbides of Ta and Nb are applied in manufacture of hard alloys and in high-temperature technics;

- In electrovacuum technics Ta is applied to manufacturing details of the radio engineering, radar-tracking and x-ray equipment;

- Ta and Nb are used as the electrolytic condensers since these metals are capable to form steady anodi oxide films, and also for manufacturing rectifiers of an alternating current, safety cutoffs;

- Chemical mechanical engineering: heaters, condensers, adsorbers, reactors, pipelines and other details of the equipment for manufacture of chemically aggressive substances (HCl, H₂SO₄, HNO₃, CH₃COOH, etc.). Rather high cost of the equipment pays off practically unlimited service life;

- The chemical industry: crucibles from tantalum are used at reduction and melting of rare-earth elements. Ta and Nb are used in electrochemistry (electrodes), analytical chemistry (reference calibrated weight from tantalum), as catalysts by manufacture of synthetic rubber and other compounds;

- Medicine;

- Manufacture of optical glasses.

Ores and concentrates of niobium and tantalum. The affinity of chemical properties causes joint presence Ta and Nb in the same minerals. Except for own minerals Ta and Nb are also as impurity in minerals Ti, Zr, Sn, W and other metals.

The basic method of tantalum-niobium ores concentration - gravitation. Received crude concentrate is subjected to flotation, electromagnetic separation and other operations, and in result a standard concentrate is received. The content Nb₂O₅ - 40-60 %, Ta₂O₅- 40-65 %.

By manufacture of Ta and Nb the technology of concentrates processing includes the following stages:

1. Opening of concentrate with preparation of the technical product concentrating both elements;

2. Separation Ta and Nb with preparation of pure compounds;

3. Production and refining of each of metals.

Zirconium Zr and hafnium Hf. Metals characterized the high durability of a crystal lattice that defines the raised hardness, high temperature of fusion, corrosion resistance. The affinity of properties of similar Zr and Hf compounds is completely exclusive. The basic valency - IV, but compounds with valency II, III are known. These compounds are unstable and they are the strong reducers.

Zr and Hf have both metal, and nonmetallic properties. With halogens they can form compounds such as MeX_n, and at the same time – the insoluble in water hafnates and zirconates of alkaline metals such as Me₂MeO₃.

On chemical stability Zr and Hf surpass titan and are close to niobium and tantalum. Pure Zr and Hf possess the high plasticity, but the content of impurity (especially gases) strongly influences on their properties.

Zr application:

- The high melt temperature causes zirconium application in nuclear reactors and nuclear engines; in rocket technics, as ceramic and fused refractory materials, melting crucibles, etc.;

- As deoxidizer and deaerator of steels;

- As alloying additive to steels;

- In manufacture of ferroalloys;

- As enamels;

- The additive to the optical glasses used in atomic engineering;

- Protective ceramic coverings (in rocket technical equipment, in manufacture of guided missiles, etc.): 98 % ZrO₂ - Тmelt = 2460⁰С,

65 % ZrO₂ + 34 % SiO₂ - Тmelt = 1630⁰C.

Hf application:

1. Nuclear technics. Hafnium has the high corrosion resistance, high temperature of fusion, high section of thermal neutrons capture. Owing to these properties in complex hafnium is the irreplaceable material in nuclear technics in quality of moderator in regulating devices of nuclear reactors, nuclear engines of sea vessels and planes.

2. The component of superhigh-temperature alloys for space vehicles and other branches of technics. Alloys on Nb, Ta, Mo, Ti, W basis, containing Hf are known. For example, the steel containing 90 % Nb, 8 % W and 2 % Hf keeps the high durability not only up to temperature 1930⁰С, but also at cooling up to absolute zero. The alloy is easily rolled at room temperature. Oxide, boride, carbide and silicide of hafnium occupy the first place among high refractory compounds. Carbide of hafnium and tantalum (1:4) is considered the most refractory compound (Тmelt = 3930⁰C). The compositions, containing such compounds, is possible to apply as protective coverings of high-temperature and superhigh-temperature alloys used for manufacturing of details of superfast planes, rockets and spacecrafts.

3. The component of superhard alloys for cutting tools.

Minerals of zirconium and hafnium.

Zircon ZrSiO₄ - the basic mineral containing 49,5 % Zr; baddeleyite ZrO₂; evdialite, containing Zr in 5-7 times less. In placer deposits minerals Zr accompany to magnetite, ilmenite, rutile.

The hafnium content in the earth's crust is in 150 times less, than the zirconium content. Hafnium does not form independent minerals, but always accompanies zirconium as an impurity. So, zircon contains 0,6-8 % HfO₂, baddeleyite - 0,1-3,5 % HfO₂, evdialite - 0,1-1 % HfO₂. Manufacture of hafnium can be organized only at complex use of Zr-Hf ores.

Processing of ore raw material.

I. Mechanical concentration.

II. Opening of concentrates.

For this purpose many methods are used, for example, chlorination – sublimation – condensation, i.e. chlorination of Zr and Hf carbonitrides by gaseous chlorine and fractional condensation of Zr and Hf chlorides without their separation:

0,5ZrO₂(solid) + Cl₂(gas) = 0,5ZrCl₄(gas) + 0,5O₂(gas)

III. Clearing of chlorides from impurity and separation of Zr and Hf by selective extraction; Zr oxide and Hf oxide are separately received.

IV. Oxides are chlorinated, received chlorides are cleared from impurity and subjected to metallothermic reduction:

MeCl₄(solid, gas) + 2Mg(solid, liquid, gas) = Me(solid) + 2MgCl₂(solid, liquid)

Received Zr or Hf sponge is subjected to melting with obtaining of compact metal or to sintering by methods of powder metallurgy.

Rhenium Rh was opened in 1925 by German scientists Н. and V. Noddak in platinum ores. On melting point rhenium occupies the second place, conceding only tungsten. Specific electroresistance of rhenium is higher in 4 times, than at tungsten and molybdenum. On density rhenium stands on 4th place after Os, Ir, Pt. As against tungsten rhenium is plastic and it is deformed on a cold.

Metal rhenium is the light grey metal, stable on air at usual temperature. At temperature higher 300⁰С oxidation of metal is observed which intensively proceeds above 600⁰С. Rhenium is more stable against oxidation, than tungsten; does not react directly with nitrogen and hydrogen and does not form chemical compounds with them. At heating rhenium reacts with fluorine, chlorine and sulfur; with bromine and iodine practically does not cooperate. As against other refractory metals rhenium does not form carbides. Rhenium is stable against action of fused metals. Rhenium corroded in hydrochloric and fluoric acids on a cold and at heating. In nitric acid, the hot concentrated sulfuric acid, hydrogen peroxide rhenium is dissolved with formation of rhenium acid HreO₄. Oxides: Re₂O, ReO, Re₂O₃, ReO₂, Re₂O₇.