Platinum group

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Platinum group metals (PGM) in the periodic table
H   He
Li Be   B C N O F Ne
Na Mg   Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba * Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra ** Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Fl Uup Lv Uus Uuo
 * La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb
** Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No
   Platinum group metals

The platinum-group metals (abbreviated as the PGMs; alternatively, the platinoids, platinides, platidises, platinum group, platinum metals, platinum family or platinum-group elements (PGEs)) is a term used sometimes to collectively refer to six metallic elements clustered together in the periodic table. These elements are all transition metals, 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.[1] However they can be further subdivided into the iridium-group platinum-group elements (IPGEs: Os, Ir, Ru) and the palladium-group platinum-group elements (PPGEs: Rh, Pt, Pd) based on their behaviour in geological systems. [2]

History[edit]

Naturally occurring platinum and platinum-rich alloys have been known by pre-Columbian Americans for many years.[3] 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").[3]

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.[3][4]

Properties[edit]

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 electrical properties. All these properties have been exploited for industrial applications.[5]

Sources[edit]

Platinum[edit]

Sperrylite (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.[6][7] Platinum and palladium are also mined commercially from the Stillwater igneous complex in Montana, USA.

Osmium[edit]

Iridiosmium is a naturally occurring alloy of iridium and osmium found in platinum-bearing river sands in the Ural Mountains and in North 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.[7][8]

Iridium[edit]

Metallic iridium is found with platinum and other platinum group metals in alluvial deposits. Naturally occurring iridium alloys include osmiridium and iridiosmium, both of which are mixtures of iridium and osmium. It is recovered commercially as a by-product from nickel mining and processing.[7]

Ruthenium[edit]

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 pentlandite extracted from Sudbury, Ontario and in pyroxenite deposits in South Africa.[7]

Rhodium[edit]

The industrial extraction of rhodium is complex as the metal occurs in ores mixed with other metals such as palladium, silver, 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 tons and there are very few rhodium minerals.[9]

Palladium[edit]

Palladium is found as a free metal and alloyed with platinum and gold with platinum group metals in placer 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.[9][dead link]

Production[edit]

Process flow diagram for the separation of the platinum group metals.

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 (other fast refining methods used today), copper or nickel production. The differences in chemical reactivity and solubility of several compounds of the metals under extraction are used to separate them.[5]

A first step is to dissolve all the metals in aqua regia forming their respective Cl-complexes. If silver is 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 tetroxides. All of these metals' final chemical compounds can ultimately be reduced to the elemental metal using hydrogen.[5]

Production in nuclear reactors[edit]

Significant quantities of the three light platinum group metals—ruthenium, rhodium and palladium—are formed as fission products in nuclear reactors.[10] With escalating prices and increasing global demand, reactor-produced noble metals are emerging as an alternative source. Various reports are available on the possibility of recovering fission noble metals from spent nuclear fuel.[11][12][13]

Recently[when?] 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,[14][15] using room temperature ionic liquids (RTILs) as electrolyte for nuclear fuel dissolution and recovery,[16] solvent extraction, ion exchange, etc. Room temperature ionic liquids have been employed to recover rhodium,[17] and ruthenium [18] also recently.

See also[edit]

Notes[edit]

  1. ^ Harris, D. C.; Cabri L. J. (1991). "Nomenclature of platinum-group-element alloys; review and revision". The Canadian Mineralogist 29 (2): 231–237. 
  2. ^ Rollinson, Hugh (1993). Using Geochemical Data: Evaluation, Presentation, Interpretation. Longman Scientific and Technical. ISBN 0-582-06701-4. 
  3. ^ a b c Weeks, M. E. (1968). Discovery of the Elements (7 ed.). Journal of Chemical Education. pp. 385–407. ISBN 0-8486-8579-2. OCLC 23991202. 
  4. ^ Woods, Ian (2004). The Elements: Platinum. Benchmark Books. ISBN 978-0-7614-1550-3. 
  5. ^ a b c Hunt, L. B.; Lever, F. M. (1969). "Platinum Metals: A Survey of Productive Resources to industrial Uses". Platinum Metals Review 13 (4): 126–138. Retrieved 2009-10-02. 
  6. ^ Xiao, Z.; Laplante, A. R. (2004). "Characterizing and recovering the platinum group minerals—a review". Minerals Engineering 17 (9–10): 961–979. doi:10.1016/j.mineng.2004.04.001. 
  7. ^ a b c d "Platinum–Group Metals" (PDF). U.S. Geological Survey, Mineral Commodity Summaries. January 2007. Retrieved 2008-09-09. 
  8. ^ Emsley, J. (2003). "Iridium". Nature's Building Blocks: An A-Z Guide to the Elements. Oxford, England, UK: Oxford University Press. pp. 201–204. ISBN 0-19-850340-7. 
  9. ^ a b Chevalier, Patrick. "Mineral Yearbook: Platinum Group Metals". Natural Resources Canada. Retrieved 2008-10-17. 
  10. ^ R. J. Newman, F. J. Smith (1970). "Platinum Metals from Nuclear Fission – an evaluation of their possible use by the industry". Platinum Metals Review 14 (3): 88. 
  11. ^ Zdenek Kolarik, Edouard V. Renard (2003). "Recovery of Value Fission Platinoids from Spent Nuclear Fuel; PART I: general considerations and basic chemistry". Platinum Metals Review 47 (2): 74. 
  12. ^ Kolarik, Zdenek; Renard, Edouard V. (2005). "Potential Applications of Fission Platinoids in Industry". Platinum Metals Review 49 (2): 79. doi:10.1595/147106705X35263. 
  13. ^ Zdenek Kolarik, Edouard V. Renard (2003). "Recovery of Value Fission Platinoids from Spent Nuclear Fuel; PART II: Separation process". Platinum Metals Review 47 (3): 123. 
  14. ^ Jayakumar, M; Venkatesan, K; Srinivasan, T; Rao, P (2009). "Studies on the feasibility of electrochemical recovery of palladium from high-level liquid waste". Electrochimica Acta 54 (3): 1083. doi:10.1016/j.electacta.2008.08.034. 
  15. ^ Pokhitonov, Yu. A.; Romanovskii, V. N. (2005). "Palladium in Irradiated Fuel. Are There Any Prospects for Recovery and Application?". Radiochemistry 47: 1. doi:10.1007/s11137-005-0040-7. 
  16. ^ Jayakumar, M; Venkatesan, K; Srinivasan, T (2007). "Electrochemical behavior of fission palladium in 1-butyl-3-methylimidazolium chloride". Electrochimica Acta 52 (24): 7121. doi:10.1016/j.electacta.2007.05.049. 
  17. ^ Jayakumar, M; Venkatesan, K; Srinivasan, T (2008). "Electrochemical behavior of rhodium(III) in 1-butyl-3-methylimidazolium chloride ionic liquid". Electrochimica Acta 53 (6): 2794. doi:10.1016/j.electacta.2007.10.056. 
  18. ^ Jayakumar, M; Venkatesan, K.A.; Srinivasan, T.G.; Vasudeva Rao, P.R. (2008). "Electrochemical behavior of ruthenium (III), rhodium (III) and palladium (II) in 1-butyl-3-methylimidazolium chloride ionic liquid". Electrochimica Acta 54 (26): 2747. doi:10.1016/j.electacta.2009.06.043. 

External links[edit]