Native platinum

Impure, native platinum seems to have been used unwittingly by ancient Egyptian craftsmen in place of silver, and was certainly used to make small items of jewellery by the Indians of Ecuador before the Spanish conquest. The introduction of the metal to Europe is a complex and intriguing story. In 1736 A. de Ulloa, a Spanish astronomer and naval officer, observed an unworkable metal, platina (Spanish, little... 

Sobolcvsky A process for converting native platinum to malleable platinum by pressing and heating. Developed by P. G. Sobolevsky in Russia in the 1820s. 

Iridium occurs in small amounts in native platinum or platinum metal alloys. Iridium and osmium together constitute osmiridium, which is resistant to chemical attack and is a byproduct of platinum extraction. 

Palladium was discovered in 1803 by W.H. Wollaston during refining and purification oP platinum metal. This new metal was found in the aqua regia extract of native platinum and was detected in solution after platinum was precipitated. It was removed as ammonium chloroplatinate. Treating this solution with mercurous cyanide precipitated a yellow palladium complex salt. The precipitate was washed and ignited to form palladium metal. Wollaston named the element palladium after the newly discovered asteroid Pallas. 

Ruthenium was recognized as a new element hy G.W. Osann in 1828. He found it in insoluhle residues from aqua regia extract of native platinum from alluvial deposits in the Ural mountains of Russia. He named it Ruthen after the Latin name Ruthenia for Russia. The discovery of this element, however, is credited to Klaus who in 1844 found that Osann s ruthenium oxide was very impure and isolated pure Ru metal from crude platinum residues insoluhle in aqua regia. 

In 1809 Wollaston demonstrated the presence of grains of native palladium and native platinum in a Brazilian alluvial gold ore presented to him by the Portuguese ambassador, H. E. Chev. de Souza Coutinho. Wollaston was led to this discovery by the observation that some of the grains, although they looked like platinum, dissolved faster in aqua regia (44, 122, 123). In 1825 Alexander von Humboldt also reported the occurrence of native palladium in Brazil (109). 

These metals occur in both primary and secondary deposits. The primary deposits are generally associated with Ni-Cu sulfide ores. The Sudbury ores of Canada and the deposits of the Bushveld complex of South Africa are of this type. Native platinum occurs as a primary deposit in the Ural Mountains of the former U.S.S.R. and also in the Choco district of Colombia. Weathering and erosion of these deposits have resulted in the formation of secondary, or placer, deposits of native Pt in riverbeds and streams. One nugget of Pt found in Ihe Urals weighed over 25 pounds (11.3 kilograms). Most of the world s platinum comes from Canada, the former... 

Magnetic.—Density circa 14. The magnetic property appears to bear some relation to the percentage of iron contained in the alloy, but strict proportionality in n way exists.1 Some specimens of native platinum from the Urals, indeed, are said to attract iron filings even more powerfully than an ordinary magnet. 

Native platinum has also been found in Brazil along with gold in syenite 2 in alluvial material amongst the Urals 3 in sand from the Ivalo River, N. Lapland, associated with the diamond as well as in Borneo, in the sands of the Rhine in County Wicklow, Ireland in New Zealand,4 New South Wales, California, British Columbia and the Yukon River, and in Spain.5... 

Native platinum frequently contains traces of nickel, as evidenced by the spectrochemical examination of specimens from Russia, Spain, and America. A sample from Kitlim,1 for example, contained 0-1 per cent, of nickel or more.8 Only one previous analysis of platinum appears to have been recorded, containing nickel, namely, a magnetic platinum from Nizhne-Tagilsk, in which 0-75 per cent, of nickel was present. Platinum ores rich in iron yield the most intense nickel spectrum. 

In the following table 3 are given the mean analyses of native platinum obtained from various mines in the Urals ... 

The table on page 258 gives analyses of native platinum found in various other parts of the world, and from it the reader will obtain a fair idea of the variations in composition usually encountered. 

The density of native platinum varies from 14 to 19, the variation being mainly due to impurities such as iron which may range from 5 to 16 per cent., and to smaller quantities of copper, iridium, osmium, rhodium, and palladium. 

Iridium is a third-row d-block metal and is the heaviest element in group 9. It is a hard, lustrous, silvery metal, discovered by Tennant in 1803 the name iridium derives from the Latin iris (rainbow). The element occurs as a native platinum alloy and in osmiridium (a native alloy of osmium, 15-40%, and iridium, 50-80%). Selected physical and chemical properties of Ir are given in Table 1. It is considered both as a platinum metal and as a precious metal. At room temperature, Ir is particularly resistant to corrosion. 

Occurrence in earth s crust about 0.001 ppm. Discovered in 1804 by Tennant. Occurs in nature in the metallic state, usually as a natural alloy with osmium (osmiridium) found in small quantities alloyed with native platinum (platinum mineral) or with native gold. Recovery and purification from osmiridium Deville, De-bray, Ann, Chim. phys. 61, 84 (1861) from the platinum mineral Wichers, J. Res. Nat. Bur. Stand. 10, 819 (1933). Reviews of prepn, properties and chemistry of iridium and other platinum metals Gilchrist, Chem. Rev. 32, 277-372 (1943) W p. Griffith, The Chemistry of the Rare Platinum Metals (John Wiley, New York, 1967) pp 1-41, 227-312 Livingstone in Comprehensive Inorganic Chemistry vol. 3, J. C. Bailar Jr. et at, Eds. (Pergamoti Press, Oxford, 1973) pp 1163-1189, 1254-1274. 

The story now returns to South America. In 1735, Don Antonio de Ulloa was one of two officers selected by the French and Spanish Governments to take charge of a scientific expedition to Peru. Whilst out there, Ulloa came across native platinum and included... 

Following up his discovery of palladium, Wollaston dissolved some native platinum in aqua regia, removed platinum as ammonium hexachlorplatinate and palladium as cyanide. Evaporation of the filtrate with acid effected the decomposition of excess of the... 

The platinum-group metals (Ru, Os, Rh, Ir, Pd and Pt) are rare (Figure 23.1) and expensive, and occur together either native or in sulfide ores of Cu and Ni. Three sites of mineral deposits in the former Soviet Union, Canada and South Africa hold the world s reserves. The main source of ruthenium is from wastes from Ni refining, e.g. from pentlandite, (Fe,Ni)S. Osmium and iridium occur in osmiridium, a native alloy with variable composition 15-40% osmium and 80-50% iridium. Rhodium occurs in native platinum and in pyrrhotite ores (Fei S, n = 0-0.2, often with <5% Ni). Native platinum is of variable composition but may contain as much as 86% Pt, other... 

Osann investigated the part of Russian native platinum insoluble in aqua regia, and in 1827 claimed to have discovered three new metals ruthenium, polinium, and pluranium. He sent a specimen to Berzelius (with whom he had worked), but since Berzelius found nothing new in it, Osann withdrew his claim in 1829. "The platinum residues were re-investigated by Claus, who by working up 15 lb. in a research begun in 1840, discovered in them in 1844 new metal for which he retained Osann s name ruthenium. ... 

Specimens of native platinum were brought from Carthagena to Europe in 1741 by Charles Wood the Spaniards called it platina de pinto. Experiments with it were made by Brownrigg and by Lewis, but Scheffer s was the first accurate examination of the metal. 

Fourcroy and Vauquelin investigated the properties of nitrous oxide, confirming many of Davy s results. In 1803-4 they described the residue from the action of aqua regia on native platinum as a new metal it was shown to con-... 

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