Bromate hydrolysis

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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.

Reaction

The reaction centers around.

IrCl4 + 4H2O -> Ir(OH)4 + 4HCl
RhCl4 + 4H2O -> Rh(OH)4 + 4HCl (needs verification)

The HCl created is removed by reacting it with sodium bromide and sodium bromate

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.

Alternative chemicals

If there is problems to acquire sodium bromate, it can be made from sodium bromide. As an alternative sodium hypochlorite can be used, but "doesn't work as well" according to Lou.

References

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