GB863517A - Improvements relating to the separation of platinum from other metals - Google Patents

Abstract

Platinum is recovered as ammonium hexachloroplatinate from acid chloride solutions which also contain other precious metals, the necessary ammonium ions for the precipitation being provided by the hydrolysis of an amide in the solution. Any water-soluble hydrolysable amide may be employed, but formamide, acetamide, and especially urea, are preferred. The acknowledgement of prior art refers to the use of ammonium chloride to precipitate ammonium hexachloroplatinate from acid chloride solution. The greater the acidity and temperature of the solution, the more rapid the hydrolysis and thus the precipitation. When urea is employed it is preferred to employ 3 to 5 times the theoretical amount required and to boil for about six hours. With acetamide the precipitation may be effected at 50 DEG C., and with formamide the precipitation may be effected at room temperature or preferably below. When acetamide is employed, too large an excess should not be used as the palladium content of the precipitate will be increased by increasing excess of acetamide. The starting solution may be prepared in conventional manner by dissolving the platinum-containing material in aqua regia, and then removing nitric acid, nitro and nitrosyl compounds by treating with formic acid or evaporating to dryness with hydrochloric acid and dissolving the residue in hydrochloric acid. Gold is removed by precipitating with a reducing agent. Any iridium present should be reduced to the trivalent state to prevent its precipitation with the platinum. The ammonium hexachloroplatinate may be washed with ammonium chloride solution and then ignited to give platinum sponge, which may if desired be further refined by repeating the solution and precipitation steps described above.