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Bromate hydrolysis is a step in refining platinum group metals, it more exactly is used to separate palladium, iridium and rhodium from platinum by precipitating Ir, Rh, and Pd as their hydroxides. Iridium is the most difficult of the metals to remove. This procedure is usually used on nearly pure (>99% wt. basis) platinum that was made from a preliminary precipitation as a halogenoplatinate (i.e. ammonium hexachloroplatinate). The reason for this is due to the level of entrainment/ absorption of valuable platinum liquor if applied to materials containing high levels of base metals. Normally palladium is removed in other ways today so it will not be covered here yet but is precipitated from the solution in the same way.
The reaction centers around.
IrCl4 + 4H2O -> Ir(OH)4 + 4HCl RhCl4 + 4H2O -> Rh(OH)4 + 4HCl (needs verification)
5NaBr + NaBrO3 + 6HCl -> 3Br2 + 6NaCl + 3H2O
The elemental bromine created is removed by boiling so the reaction is driven to completion.
At pH 6 this reaction will precipitate solids of the three PGM:s while platinum remains in solution. The solids are easy to filter and can be washed with water at pH 6.
- GRF : Freechemist on bromate hydrolysis
- Raleigh Gilchrist : METHODS FOR THE SEPARATION OF PLATINUM, PALLADIUM, RHODIUM, AND IRIDIUM FROM ONE ANOTHER AND FOR THEIR GRAVIMETRIC DETERMINATION, U.S. Department of Commerce, Bureau of Standards, 1934
- GRF : Lou on alternatives for sodium bromate
- GRF : Lou on separating Pt and Ir
- Wikipedia : Sodium bromate