Platinum Refining Process

The refining technology for platinum within the platinum group metals (PGMs) is well-established, seamlessly integrating with precious metal separation processes. Refining feedstocks include crude platinum with a grade >90%, platinum-containing solutions, or stripping solutions obtained via solvent extraction. The primary refining methods are the repeated ammonium chloride precipitation method and the oxidative hydrolysis method, both leveraging two unique properties of platinum compounds:

Formation of insoluble（NH4）2PtCl6 precipitate in acidic media, enabling separation from non-precipitating base metals and low-valence soluble chloroammonium salts of other PGMs.
Formation of soluble NaPt（OH）6 in alkaline media, facilitating separation from hydrolyzed precipitates of other precious and base metals.
Subsequent calcination of（NH4）2PtCl6 yields metallic platinum, producing products with purities ranging from 9% to 99.999%.

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Repeated Ammonium Chloride Precipitation Method

Solution Adjustment: The platinum concentration in the solution is adjusted to Pt50-80g/L. While stirring, NH₄Cl is added to the heated solution to form yellow （NH4）2PtCl6 precipitate:
H2PtCl6+2NH4Cl=(NH4)2PtCl↓+2HCI
Excess NH₄Cl is added to maintain a free NH₄Cl concentration of 5–10% in the solution. After cooling, the ammonium chloroplatinate salt is filtered out, leaving soluble chloride salts of base metals and low-valence chloroammonium salts of gold, palladium, and iridium in the solution.
Washing and Purity Check: The platinum ammonium salt is washed with a 5% NH4Cl solution (acidified with HCl to pH = 1). A small sample is calcined to spongy platinum for spectral analysis. If purity is insufficient, the entire batch can be recycled as crude platinum for re-dissolution, or alternatively, the following simplified method can be applied:
√ After filtering out minor insolubles, hydrazine hydrate is used to reduce platinum black from the solution at room temperature.
√ The platinum black is then dissolved using HCl + H₂O₂, followed by re-precipitation as pure platinum ammonium salt with NH₄Cl.
Final Refining: For crude platinum with an initial grade of 90%, three cycles of dissolution → ammonium chloride precipitation typically yield pure (NH4)2PtCI6. Calcination at 800°C produces spongy platinum with a purity of 99.99%.