Ruthenium

Ruthenium Element

Ruthenium is a group 8 chemical element or metal in the periodic table with the symbol Ru and atomic number 44. The demand and price for ruthenium are rising due to the widespread use of metal in the electronic and chemical industries as a catalyst. In these two industries, ruthenium metal is used mainly for making electrical contacts and anode plates for chlorine production in electrochemical cells. Ruthenium metal is the rarest transition metal on the earth that imparts hardness to platinum jewelry and palladium. It is also used in solar technology for the production of electrical energy from solar energy.

Ruthenium is a hard white metal that is a member of the platinum group metals (PGMs). Ruthenium was discovered in 1844 by Russian scientist of Baltic-German ancestry Karl Ernst Claus. The name of the metal was given in honor of the country Russia.

Where is Ruthenium Found?

Ruthenium is one of the rarest metals on Earth and is generally found in ores of other platinum metals in the Ural Mountains and in North and South America. The chief source of the metal is found in South Africa, Canada, Russia, Brazil, Columbia, etc.

It is the 78th most abundant element in Earth’s crust that is found in the uncombined form in nature. Commercially, it can be extracted from the wastes of nickel refining.

The abundance of platinum metals in the earth’s crust is 0.01 ppm or less. Ruthenium is relatively rare on Earth and found in about 100 parts per trillion. Mostly, the element occurs in the minerals pentlandite and pyroxinite.

Ruthenium Isotopes

Ruthenium metal has seven naturally occurring stable isotopes. It has also 27 radioactive isotopes that have been produced by various artificial nuclear reactions. Of these 27 radioactive isotopes, the most stable are ¹⁰⁶Ru, ¹⁰³Ru, and ⁹⁷Ru. The half-lives of most of these radioactive isotopes have less than five minutes.

The primary radioactive decay mode of these isotopes is electron capture and beta emission. The primary decay products of radioisotopes are technetium and rhodium.

The concentration of ruthenium is relatively high during the fission of nuclear power reactors. Therefore, most long-lived Ru-106 may also be extracted from radioactive waste. The isotope Ru-106 is found during the nuclear fission of uranium or plutonium.

Production Process

About 30 tonnes of ruthenium are mined each year in the World. The composition of the mined platinum group metals varies widely on the geolocation. For example, the platinum group metals mined in South Africa contain on average 11% ruthenium while the platinum group metals mined in the former USSR contain only 2%.

Ruthenium is obtained commercially as a by-product from nickel, copper, and platinum metals ore refining. During the electrorefining of copper and nickel, noble metals such as silver, gold, and the platinum group metals precipitate as anode sludge.

Ruthenium Refining

The refining of ruthenium and other platinum metals from the anode sludge is given below,

Treatment of the anode slime with aqua regia removes platinum, palladium, and gold. It may form soluble salts of PtCl₆⁻², PdCl₄⁻², and AuCl₄⁻².
The residue of insoluble chlorides of osmium, ruthenium, rhodium, iridium, and silver is fused with lead carbonate followed by treatment with nitric acid. Silver is passed into the solution as silver nitrate.
After the removal of silver, the insoluble residue is fused with NaHSO₄ and leached with water. Rhodium passes into solution as Rh₂(SO₄)₃.
The insoluble residue after separating rhodium is fused with sodium peroxide and leached with water. Ru and Os pass into the solution as RuO₄⁻² and [OsO₄(OH)₂]⁻² but iridium is left as a residue of IrO₂.
Chlorine is passed into the solution containing Ru and Os. On heating the solution, OsO₄ vaporized and separated.
After removing osmium, the solution contains H₃RuCl₆. From which (NH₄)₃RuCl₆ is precipitated by NH₄Cl. The precipitate is heated with hydrogen to give ruthenium metal.

Properties

Ruthenium is a hard, brittle, silvery-white transition metal that does not react normally with acids, water, or air. It belongs to the noble metals or platinum metals family in the periodic table.

Ruthenium
Symbol	Ru
Discovery	Karl Karlovich Klaus in 1844
Name derived from	The word Ruthenia that has the Latin name for Russia
Common isotopes	₄₄Ru¹⁰¹, ₄₄Ru¹⁰², ₄₄Ru¹⁰⁴
Oxidation states	+8, +6, +4, +3, +2, 0, −2
CAS number	7440-18-8
Periodic properties
Atomic number	44
Relative atomic mass	101.07
Electron per cell	2, 8, 18, 15, 1
Electronic configuration	[Kr] 4d⁷ 5s¹
Block	d-block
Group	8
Period	5
Physical properties
State at 20 °C	Solid
Melting point	2333° C, 2606 K
Boiling point	4147 °C, 4420 K
Molar heat capacity	24.06 J mol⁻¹ K⁻¹
Crystal structure	hexagonal close-packed (hcp)
Density	12.1 g/cm³
Electrical resistivity	71 nΩ m
Atomic properties
Atomic radius (non-bonded)	2.13 Å
Covalent radius	1.36 Å
Electronegativity	2.2 (Pauling scale)
Electron affinity	101.31 kJ mol⁻¹
Ionization energy (kJ/mol)	1st	2nd	3rd
	710.18	1617.09	2746.94

Electron Configuration

The 44 electrons in the ruthenium atom are distributed in different energy levels to show the following electron configuration given below the picture,

Ruthenium in the Periodic Table

Ruthenium is placed in group 8 and period 5 in the periodic table. It is a d-block element or transition metal that lies between technetium and rhodium.

Chemical Compounds

The platinum or noble metal ruthenium is quite unreactive. The metal shows the highest observed oxidation state VIII but the VI and IV states of metal are also very stable.

It forms a wide range of chemical compounds in various oxidation states. The most common oxides, fluorides, and complexes of ruthenium in +4 and +6 oxidation states are given below,

Ruthenium Oxides

The oxidation states IV and VI of Ru are quite stable. It burns in the air directly to form blue-black ruthenium dioxide with the chemical formula RuO₂. The dioxide is a stable solid with a rutile structure and is insoluble in water.

The volatile orange-yellow tetroxide (RuO₄) is formed by oxidation of Ru (VI) in an acid solution with KBrO₃, KMnO₄, Cl₂, etc. The molecule contains a regular tetrahedral structure with an ozone-like odor. It is a strong oxidizing agent that dissolves in alkali by evolving oxygen gas.

Ruthenium Fluorides

The hexafluoride and tetrafluoride form of Ru is common. The brown colour hexafluoride (RuF₆) is obtained by the reaction of Ru with fluorine under pressure and quenching the vapour.

It formed yellow RuF₄ when RuF₅ is reduced by iodine. RuF₅ is a normal product of the reaction between Ru and fluorine. Probably the tetrafluoride compound is polymeric in nature.

Coordination Complexes

In lower oxidation states the metal forms a variety of coordination complexes. There are a few simple compounds observed in the +2 state of the metal. It formed numerous complexes with amine and arsine. These complexes are formed by the reduction of ruthenium metal in the presence of ligands.

Reduction of RuCl₃ with hydrazine or zinc amalgam in the presence of ammonia gives dinitrogen complex [Ru(NH₃)₅N₂]⁺. It is the first compound reported to contain a coordinated nitrogen molecule.

Facts About Ruthenium

Ruthenium was the last discovered platinum group of metals that was discovered by Russian-born scientist of Baltic-German ancestry Karl Ernst Claus in 1844.
The name of the element comes from the Latin word Ruthenia means Russia. It refers to the Ural Mountains of Russia, the original source of ores of platinum metals.
It is the only group 8 element that does not contain 2 electrons in its outer quantum shell.
It shows a wide range of oxidation numbers or states. The most commonly found oxidation states of metal are +8, +6, and +4.
Like other platinum metals, it forms a wide variety of binary compounds like oxides, sulfides, and especially halides.
It is a versatile catalyst that is used in the removal of hydrogen sulfide from oil refineries and other industrial processes. The ruthenium catalyst is also used for the production of ammonia and acetic acid.
It is toxic to humans that believed to have carcinogenic properties. The tetroxide (RuO₄) is particularly dangerous for humans.

Uses of Ruthenium

Ruthenium is an important alloying material to impart hardness in platinum and palladium.
It is also used as a chemical catalyst for the production of ammonia from natural gas and acetic acid from methanol.
Ruthenium is used in the electronics industry for making resistors and electrical contacts.
In the chlorine production process, ruthenium oxide is used to coat the anodes of electrochemical cells.
It is added to titanium alloys to improve the corrosion resistance properties of titanium alloys.
It is also used for alloying cobalt, molybdenum, nickel, tungsten, and other metals.
Ruthenium compounds can be used in solar cells for the production of solar renewable energy.
It is alloyed with platinum for the production of some jewelry.
The beta-decaying isotope ruthenium 106 is used in radiotherapy to treat eye tumors and malignant melanoma of the uvea.

Ruthenium Price

It is used widely in the electrical industry because the properties of ruthenium are similar to that of rhodium but the price of the Ru is lower than rhodium.

The ruthenium plate is used in electrical contact and electrode base metal electroplating or sputtering. The average price of pure ruthenium metal is around $1400 per 100 grams.