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Platinum refining involves a series of steps to obtain high-purity platinum. Here's a concise overview:
- Leaching: Platinum and other metals are dissolved in a solution with strong oxidants like aqua regia and NaClO3. Silver forms a precipitate while platinum dissolves. Reaction:
3Pt+2NaClO3+18HCl→3H2PtCl6+2NaCl+6H2O
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Neutralization: Adjust the high-acidity leaching solution to pH 1 using NaOH and wash the residue with hydrochloric acid.
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Platinum Precipitation: Add ammonium chloride to the solution until no more yellow precipitate forms. Then, cool, filter, and wash the residue with 10% ammonium chloride. Reaction:
H2PtCl6+2NH4Cl→(NH4)2PtCl6↓+2HCl
- Roasting: Heat the filtered residue to decompose ammonium chloroplatinate into sponge platinum. Repeat chlorination, neutralization, and roasting until pure platinum powder is obtained.
(NH4)2PtCl6→Heating3Pt+2NH4Cl+16HCl+2N2↑
Platinum refining is critical for various industrial applications, ensuring the metal's purity and quality.