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Isolation
Here is a brief summary of the isolation of rhodium.
It would not normally be necessary to make a sample of rhodium in
the laboratory as the metal is available, at a price, commercially.
The industrial extraction of rhodium is complex as the metal occurs
in ores mixed with other metals such as palladium, silver, platinum,
and gold. Sometimes extraction of the precious metals such as
rhodium, platinum and palladium is the main focus of a partiular
industrial operation while in other cases it is a byproduct. The
extraction is complex because of the other metals present and only
worthwhile since rhodium is the basis of very important catalysts in
industry.
Preliminary treatment of the ore or base metal byproduct is required
to remove silver, gold, palladium, and platinum. The resulting
residue is melted with sodium bisulphate (NaHSO4) and the resulting
mixture extracted water to give a solution containing rhodium
sulphate, Rh2(SO4)3. The rhodium is precipitated out as the
hydroxide by addition of sodium hydroxide, NaOH, and redissolved in
hydrochloric acid, HCl, to give H3RhCl6. This is treated with NaNO2
and NH4Cl to form a precipitate of the rhodium complex
(NH4)3[Rh(NO2)6]. Dissolution of the precipitate in HCl gives a
solution of pure (NH4)3RhCl6. Evaporation to dryness and burning
under hydrogen gas gives pure rhodium.
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