Platinum group
Encyclopedia
The platinum group metals (abbreviated as the PGMs; alternatively, the platinoids, platidises, platinum group or platinum metals) is a term used sometimes to collectively refer to six metal
lic elements
clustered together in the periodic table
.
These elements are all transition metal
s, lying in the d-block
(groups 8
, 9
, and 10
, periods 5
and 6
).
The six platinum group metals are ruthenium
, rhodium
, palladium
, osmium
, iridium
, and platinum
. They have similar physical and chemical properties, and tend to occur together in the same mineral deposits.
Americans for a long time. Though the metal was used by pre-Columbian peoples, the first European reference to platinum appears in 1557 in the writings of the Italian humanist Julius Caesar Scaliger
(1484–1558) as a description of a mysterious metal found in Central American mines between Darién (Panama) and Mexico ("up until now impossible to melt by any of the Spanish arts").
The Spaniards named the metal platina ("little silver") when they first encountered it in Colombia
. They regarded platinum as an unwanted impurity in the silver they were mining.
properties. All these properties have been exploited for industrial applications.
(platinum arsenide
, PtAs2) ore
is a major source of this metal. A naturally occurring platinum-iridium alloy, platiniridium, is found in the mineral
cooperite
(platinum sulfide
, PtS). Platinum in a native state, often accompanied by small amounts of other platinum metals, is found in alluvial
and placer deposits in Colombia
, Ontario
, the Ural Mountains
, and in certain western American
states. Platinum is also produced commercially as a by-product of nickel
ore processing. The huge quantities of nickel ore processed makes up for the fact that platinum makes up only two parts per million of the ore. South Africa
, with vast platinum ore deposits in the Merensky Reef
of the Bushveld complex
, is the world's largest producer of platinum, followed by Russia
. Platinum and palladium are also mined commercially from the Stillwater igneous complex
in Montana, USA.
and South America
. Trace amounts of osmium also exist in nickel-bearing ores found in the Sudbury, Ontario
region along with other platinum group metals. Even though the quantity of platinum metals found in these ores is small, the large volume of nickel ores processed makes commercial recovery possible.
and iridiosmium, both of which are mixtures of iridium and osmium. It is recovered commercially as a by-product from nickel mining and processing.
extracted from Sudbury, Ontario and in pyroxenite
deposits in South Africa.
, platinum, and gold
. It is found in platinum ores and obtained free as a white inert metal which is very difficult to fuse. Principal sources of this element are located in river sands of the Ural Mountains, in North and South America and also in the copper-nickel sulfide mining area of the Sudbury Basin
region. Although the quantity at Sudbury is very small, the large amount of nickel ore processed makes rhodium recovery cost effective. However, the annual world production in 2003 of this element is only 7 or 8 ton
s and there are very few rhodium minerals.
deposits of the Ural Mountains
of Eurasia
, Australia
, Ethiopia
, South and North America
. However it is commercially produced from nickel-copper
deposits found in South Africa
and Ontario, Canada. The huge volume of nickel-copper ore processed makes this extraction profitable in spite of its low concentration in these ores.
A first step is to dissolve all the metals in aqua regia
forming their respective nitrates. If silver is still present, this is then separated by forming insoluble silver chloride
. Rhodium sulfate is separated after the salts have been melted together with sodium bisulfate
and leached with water. The residue is then melted together with sodium peroxide
, which dissolves all the metals and leaves the iridium. The two remaining metals, ruthenium and osmium, form ruthenium and osmium tetroxides after chlorine
has been added to solution. The osmium tetroxide is then dissolved in alcoholic sodium hydroxide and separated from the ruthenium tetroxide
s. All of these metals' final chemical compounds can ultimately be reduced to the elemental metal using hydrogen
.
s are emerging as an alternative source. Various reports are available on the possibility of recovering fission noble metals from spent nuclear fuel.
Recently there is an upsurge in the recovery of valuable fission products which reflects in the form of articles in leading scientific journals. Palladium has been of special interest due to its less complex behavior when compared to rhodium and ruthenium. The special interest in palladium may be also due to its widespread application in chemical catalysis and the electronics industry. Several research groups are exploring the possibility of recovering palladium by various methods like direct electrolysis of high-level liquid waste, using room temperature ionic liquids (RTILs) as electrolyte
for nuclear fuel dissolution and recovery, solvent extraction, ion exchange
, etc. Room temperature ionic liquids have been employed to recover rhodium, and ruthenium also recently.
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
lic elements
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
clustered together in the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
.
These elements are all transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
s, lying in the d-block
D-block
The d-block is the portion of the periodic table that contains the element groups 3-12. These groups correspond to the filling of the atomic d-orbital subshell, with electron configurations ranging from s2d1 to s2d10...
(groups 8
Group 8 element
A Group 8 element is one in the series of elements in group 8 in the periodic table, which consists of the transition metals iron , ruthenium , osmium and hassium ....
, 9
Group 9 element
In modern IUPAC nomenclature, Group 9 of the periodic table contains the elements cobalt , rhodium , iridium , and meitnerium . These are all d-block transition metals...
, and 10
Group 10 element
A Group 10 element is one in the series of elements in group 10 in the periodic table, which consists of the transition metals nickel , palladium , platinum , and darmstadtium ....
, periods 5
Period 5 element
A period 5 element is one of the chemical elements in the fifth row of the periodic table of the elements. The periodic table is laid out in rows to illustrate recurring trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour...
and 6
Period 6 element
A period 6 element is one of the chemical elements in the sixth row of the periodic table of the elements, including the lanthanides...
).
The six platinum group metals are ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
, rhodium
Rhodium
Rhodium is a chemical element that is a rare, silvery-white, hard and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one isotope, 103Rh. Naturally occurring rhodium is found as the free metal, alloyed...
, palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...
, osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
, iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
, and platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
. They have similar physical and chemical properties, and tend to occur together in the same mineral deposits.
History
Naturally occurring platinum and platinum-rich alloys have been known by pre-ColumbianPre-Columbian
The pre-Columbian era incorporates all period subdivisions in the history and prehistory of the Americas before the appearance of significant European influences on the American continents, spanning the time of the original settlement in the Upper Paleolithic period to European colonization during...
Americans for a long time. Though the metal was used by pre-Columbian peoples, the first European reference to platinum appears in 1557 in the writings of the Italian humanist Julius Caesar Scaliger
Julius Caesar Scaliger
Julius Caesar Scaliger was an Italian scholar and physician who spent a major part of his career in France. He employed the techniques and discoveries of Renaissance humanism to defend Aristotelianism against the new learning...
(1484–1558) as a description of a mysterious metal found in Central American mines between Darién (Panama) and Mexico ("up until now impossible to melt by any of the Spanish arts").
The Spaniards named the metal platina ("little silver") when they first encountered it in Colombia
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
. They regarded platinum as an unwanted impurity in the silver they were mining.
Properties
The platinum metals have outstanding catalytic properties. They are highly resistant to wear and tarnish, making platinum, in particular, well suited for fine jewelry. Other distinctive properties include resistance to chemical attack, excellent high-temperature characteristics, and stable electricalElectricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
properties. All these properties have been exploited for industrial applications.
Platinum
SperryliteSperrylite
Sperrylite is a platinum arsenide mineral with formula: PtAs2 and is an opaque metallic tin white mineral which crystallizes in the isometric system with the pyrite group structure. It forms cubic, octahedral or pyritohedral crystals in addition to massive and reniform habits...
(platinum arsenide
Arsenide
Arsenide is an arsenic anion with the charge −3. The trianion is formed by the reduction of arsenic by three electrons. For example heating arsenic powder with excess sodium gives sodium arsenide . The anions have no existence in solution since they are extremely basic...
, PtAs2) ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....
is a major source of this metal. A naturally occurring platinum-iridium alloy, platiniridium, is found in the mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
cooperite
Cooperite
Cooperite is a grey mineral consisting of platinum sulfide , generally in combinations with sulfides of other elements such as palladium and nickel . Its general formula is S. It is a dimorph of braggite....
(platinum sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
, PtS). Platinum in a native state, often accompanied by small amounts of other platinum metals, is found in alluvial
Alluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...
and placer deposits in Colombia
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, the Ural Mountains
Ural Mountains
The Ural Mountains , or simply the Urals, are a mountain range that runs approximately from north to south through western Russia, from the coast of the Arctic Ocean to the Ural River and northwestern Kazakhstan. Their eastern side is usually considered the natural boundary between Europe and Asia...
, and in certain western American
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
states. Platinum is also produced commercially as a by-product of nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
ore processing. The huge quantities of nickel ore processed makes up for the fact that platinum makes up only two parts per million of the ore. South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, with vast platinum ore deposits in the Merensky Reef
Merensky Reef
The Merensky Reef, is a layer of igneous rock in the Bushveld Igneous Complex in the Transvaal which together with an underlying layer, the Upper Group 2 Reef , contains most of the world's known reserves of platinum group metals or platinum group elements - platinum, palladium, rhodium,...
of the Bushveld complex
Bushveld igneous complex
The Bushveld Igneous Complex is a large layered igneous intrusion within the Earth's crust which has been tilted and eroded and now outcrops around what appears to be the edge of a great geological basin, the Transvaal Basin. Located in South Africa, the BIC contains some of the richest ore...
, is the world's largest producer of platinum, followed by Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. Platinum and palladium are also mined commercially from the Stillwater igneous complex
Stillwater igneous complex
The Stillwater igneous complex is a large layered intrusion located in southern Montana in Stillwater, Sweet Grass and Park Counties. The complex is exposed across 30 miles of the north flank of the Beartooth Mountain Range. The complex has extensive reserves of chromium ore and has a history of...
in Montana, USA.
Osmium
Iridiosmium is a naturally occurring alloy of iridium and osmium found in platinum-bearing river sands in the Ural Mountains and in NorthNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. Trace amounts of osmium also exist in nickel-bearing ores found in the Sudbury, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
region along with other platinum group metals. Even though the quantity of platinum metals found in these ores is small, the large volume of nickel ores processed makes commercial recovery possible.
Iridium
Metallic iridium is found with platinum and other platinum group metals in alluvial deposits. Naturally occurring iridium alloys include osmiridiumOsmiridium
Osmiridium, are names given to natural alloys of osmium and iridium, with traces of other platinum group metals. Osmiridium has been defined as containing a higher proportion of iridium, while iridosmine contains more osmium...
and iridiosmium, both of which are mixtures of iridium and osmium. It is recovered commercially as a by-product from nickel mining and processing.
Ruthenium
Ruthenium is generally found in ores with the other platinum group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlanditePentlandite
Pentlandite is an iron-nickel sulfide, 9S8. Pentlandite usually has a Ni:Fe ratio of close to 1:1. It also contains minor cobalt.Pentlandite forms isometric crystals, but is normally found in massive granular aggregates. It is brittle with a hardness of 3.5 - 4 and specific gravity of 4.6 - 5.0 and...
extracted from Sudbury, Ontario and in pyroxenite
Pyroxenite
Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite and diopside, hypersthene, bronzite or enstatite. They are classified into clinopyroxenites, orthopyroxenites, and the websterites which contain both pyroxenes...
deposits in South Africa.
Rhodium
The industrial extraction of rhodium is complex as the metal occurs in ores mixed with other metals such as palladium, silverSilver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
, platinum, and gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
. It is found in platinum ores and obtained free as a white inert metal which is very difficult to fuse. Principal sources of this element are located in river sands of the Ural Mountains, in North and South America and also in the copper-nickel sulfide mining area of the Sudbury Basin
Sudbury Basin
The Sudbury Basin, also known as Sudbury Structure or the Sudbury Nickel Irruptive, is a major geologic structure in Ontario, Canada. It is the second-largest known impact crater or astrobleme on Earth, as well as one of the oldest....
region. Although the quantity at Sudbury is very small, the large amount of nickel ore processed makes rhodium recovery cost effective. However, the annual world production in 2003 of this element is only 7 or 8 ton
Ton
The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of weight, and as a unit of volume. It can also be used as a measure of energy, for truck classification, or as a colloquial term.It is derived from...
s and there are very few rhodium minerals.
Palladium
Palladium is found as a free metal and alloyed with platinum and gold with platinum group metals in placerPlacer mining
Placer mining is the mining of alluvial deposits for minerals. This may be done by open-pit or by various surface excavating equipment or tunneling equipment....
deposits of the Ural Mountains
Ural Mountains
The Ural Mountains , or simply the Urals, are a mountain range that runs approximately from north to south through western Russia, from the coast of the Arctic Ocean to the Ural River and northwestern Kazakhstan. Their eastern side is usually considered the natural boundary between Europe and Asia...
of Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Ethiopia
Ethiopia
Ethiopia , officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is the second-most populous nation in Africa, with over 82 million inhabitants, and the tenth-largest by area, occupying 1,100,000 km2...
, South and North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. However it is commercially produced from nickel-copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
deposits found in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
and Ontario, Canada. The huge volume of nickel-copper ore processed makes this extraction profitable in spite of its low concentration in these ores.
Production
The production of pure platinum group metals normally starts from residues of the production of other metals with a mixture of several of those metals. One typical starting product is the anode residue of gold or nickel production. The differences in chemical reactivity and solubility of several compounds of the metals under extraction are used to separate them.A first step is to dissolve all the metals in aqua regia
Aqua regia
Aqua regia or aqua regis is a highly corrosive mixture of acids, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and hydrochloric acid, usually in a volume ratio of 1:3, respectively...
forming their respective nitrates. If silver is still present, this is then separated by forming insoluble silver chloride
Silver chloride
Silver chloride is a chemical compound with the chemical formula AgCl. This white crystalline solid is well known for its low solubility in water . Upon illumination or heating, silver chloride converts to silver , which is signalled by greyish or purplish coloration to some samples...
. Rhodium sulfate is separated after the salts have been melted together with sodium bisulfate
Sodium bisulfate
Sodium bisulfate, also known as sodium hydrogen sulfate , is an acid salt. It is a dry granular product that can be safely shipped and stored. The anhydrous form is hygroscopic. Solutions of sodium bisulfate are acidic, with a 1M solution having a pH of Sodium bisulfate, also known as sodium...
and leached with water. The residue is then melted together with sodium peroxide
Sodium peroxide
Sodium peroxide is the inorganic compound with the formula Na2O2. This solid is the product when sodium is burned with oxygen. It is a strong base and a potent oxidizing agent. It exists in several hydrates and peroxyhydrates including Na2O2·2H2O2·4H2O, Na2O2·2H2O, Na2O2·2H2O2, and...
, which dissolves all the metals and leaves the iridium. The two remaining metals, ruthenium and osmium, form ruthenium and osmium tetroxides after chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
has been added to solution. The osmium tetroxide is then dissolved in alcoholic sodium hydroxide and separated from the ruthenium tetroxide
Ruthenium tetroxide
Ruthenium tetroxide is a diamagnetic tetrahedral ruthenium compound. As expected for a charge-neutral symmetrical oxide, it is quite volatile. The analogous OsO4 is more widely used and better known...
s. All of these metals' final chemical compounds can ultimately be reduced to the elemental metal using hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
.
Production in nuclear reactors
Significant quantities of the three light platinum group metals — Ruthenium, Rhodium and Palladium — are formed as fission products in nuclear reactors. With escalating prices and increasing global demand, reactor-produced noble metalNoble metal
Noble metals are metals that are resistant to corrosion and oxidation in moist air, unlike most base metals. They tend to be precious, often due to their rarity in the Earth's crust...
s are emerging as an alternative source. Various reports are available on the possibility of recovering fission noble metals from spent nuclear fuel.
Recently there is an upsurge in the recovery of valuable fission products which reflects in the form of articles in leading scientific journals. Palladium has been of special interest due to its less complex behavior when compared to rhodium and ruthenium. The special interest in palladium may be also due to its widespread application in chemical catalysis and the electronics industry. Several research groups are exploring the possibility of recovering palladium by various methods like direct electrolysis of high-level liquid waste, using room temperature ionic liquids (RTILs) as electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
for nuclear fuel dissolution and recovery, solvent extraction, ion exchange
Ion exchange
Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...
, etc. Room temperature ionic liquids have been employed to recover rhodium, and ruthenium also recently.
External links
- Platinum Today: The world's leading authority on platinum group metals
- Platinum Group Spot Prices
- USGS page on PGM's
- Platinum Metals Review: A free, quarterly journal of research on the science and technology of the platinum group metals and developments in their application in industry
- The PGM Database: Data defining the physical properties and characteristics of the platinum group metals and their alloys