Element Rhodium, Rh, Transition Metal

Rhodium was discovered in 1803 by William Hyde Wollaston, soon after his discovery of palladium. Wollaston dissolved raw platinum in aqua regia. The acid surplus was neutralized by caustic soda. He then precipitated the platinum by adding ammonium chloride, NH₄Cl; palladium was removed as palladium cyanide after treating the solution with mercuric cyanide. The material that remained was a red powder double (rhodium) chloride. Rhodium metal was isolated by roasting via reduction with hydrogen gas. Rhodium derived from Greek rhodon meaning "rose", because of the color of rhodium chloride solution.

Rhodium crustal abundance is 1x10^-7% by mass. It makes solid solutions with platinum group of metals; it is also contained in native platinum and osmium-iridium minerals. Rhodium may be also found in sulphuric, arsenic and antimonous platinum compounds, which accompany copper-nickel ores. Rhodium abundance in raw material varies from 0.2% in nickel minerals to 11.3% in Rhodium nevyanskite.

Rhodium is a very rare transition metal, only several tons. Principal sources of this element are located in South Africa, in river sands of the Ural Mountains, in North and South America and also in the copper-nickel sulfide mining area of the Sudbury, Ontario region. Demand for rhodium increases on 20% annually.