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Element Platinum, Pt, Transition Metal

History

Platinum and its alloys have been known for a long time. First it was described in 1557 by the Italian humanist Julius Caesar Scaliger, as a metal (transitional metal), which cannot be melted by any fire nor by any Spanish technique. It reflects somewhat diminishing attitude, negligence towards platinum as something useless, which cannot be treated. The word "platinum" comes from the Spanish word platina, meaning "little silver".

Occurrence

Transition metal Platinum is one of the rarest elements. Its crustal abundance is 5x10-7 mass %. Platinum occurs as native metal as well as in compounds. Most important platinum-bearing minerals are polyxene which contains 6-10% iron, as well as palladic platinum, (60-90% platinum, 7-39% palladium), ferroplatinum (contains 12-20% iron), iridioplatinum (55-60% platinum and up to 30% iridium), sperrylite PtAs2, cooperate with general formula (Pt,Pd,Ni)S and braggite (Pt, Pd, Ni)S. Commercially most important deposits are located in South Africa, Russia, and Canada.

Two varieties of native platinum are known, namely:
  1. Non-magnetic. - This is the more usual form, and has the greater density, namely, 16.5 to 18.
  2. 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 no way exists. Some specimens of native platinum from the Urals, indeed, are said to attract iron filings even more powerfully than an ordinary magnet.


Platinum was probably first discovered in the alluvial deposits of the River Pinto in the province of Choco, Columbia (S. America). It was first brought to Europe in 1735, and received its name from the Spanish plata, silver, in consequence of its white appearance.

Native platinum has also been found in Brazil along with gold in syenite; in alluvial material amongst the Urals; 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, New South Wales, California, British Columbia and the Yukon River, and in Spain.

The mining of platinum in British Columbia dates from 1885. Much of the ore is coarse and has the rough, unworn appearance of nuggets that have not travelled far from their original source. The nuggets are rarely large, and seldom exceed half an ounce (14 grams) in weight. Most of the metal occurs in small grains which can be separated into magnetic and non-magnetic, the latter forming the greater proportion of the total.

The largest nugget of platinum ever yet found weighed 21 lb. troy, or 7837 grams, and was deposited in the Demidoff Museum at Petrograd.

Native platinum frequently contains traces of nickel, as evidenced by the spectrochemical examination of specimens from Russia, Spain, and America. A sample from Kitlim, for example, contained 0.1 per cent, of nickel or more. 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.

Platinum is found in combination with arsenic as the rare mineral sperrylite, PtAs2, at Vermillion Mine in Ontario, Canada. It was first discovered by Sperry (whence its name) in 1887 along with copper and iron pyrites in contact with gold ore. It crystallises in cubes or, less frequently, in octahedra; hardness, 6.7; specific gravity, 10.602 at 20° C. It is tin-white in colour, possessed of metallic lustre, and contains traces of rhodium and antimony.

Sperrylite occurs in small quantities in the nickel ores of Sudbury, Ontario, the actual percentage of platinum being directly proportional to the copper content of the ore, that is, proportional to the amount of copper pyrites. It occurs in small crystalline fragments disseminated throughout the mass of the ore.

Platinum has also been detected in meteoric iron.

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