Platinum refining

The main chemical refining method, a first step to give pure Compound ₂ PtCl _{6 (4} NH) or pure solution of Na ₂ PtCl _6, the second step is calcined hydrazine or metal, can produce different 99.9% -99.999% purity The product.
1. Ammonium chloride multiple precipitation method A solution containing platinum 50-80 g/L is boiled, and NH ₄ Cl is added with stirring to form a yellow (NH ₄ ) ₂ PtCl ₆ precipitate:
H ₂ PtCl ₆ +2NH ₄ Cl====(NH ₄ ) ₂ PtCI ₆ ↓+2HCl
The concentration of free NH ₄ Cl in the solution was maintained at 5% to 10% during precipitation. After filtration, the precipitate is washed with ammonium chloride of pH=1. If the purity of the ammonium salt is unqualified by spectroscopic analysis, the ammonium chloroplatinate can be directly boiled and re-dissolved with aqua regia, or the crude platinum metal after the platinum ammonium salt is calcined, and the solution is obtained. Concentrate to a paste, add concentrated hydrochloric acid to the near-drying several times to destroy the insoluble platinum compound, and finally dissolve it with dilute hydrochloric acid to obtain a platinum-containing solution. After filtering, add ammonium chloride to precipitate platinum ammonium salt. After analysis, calcination is carried out after passing the analysis. Sponge platinum product; can also directly reduce the suspension of ammonium chloroplatinate in solution by using SO ₂ or hydrazine hydrate to form soluble ammonium chloroplatinate:
(NH ₄ ) ₂ PtCI ₆ +2H ₂ O+SO ₂ =====(NH ₄ ) ₂ PtCl ₄ +H ₂ SO ₄ +2HCl
The insoluble matter was filtered off, and the obtained solution was dark red. The solution was purged with chlorine gas or hydrogen peroxide (NH ₄ ) ₂ PtCI _{6 was} added thereto, and the ammonium salt was calcined to a sponge metal platinum product at 800 ° C after passing the spectrum analysis.
2. Sodium Bromate Hydrolysis An important method for the production of high purity platinum is particularly effective for separating cerium , lanthanum and cerium metal impurities. 50g / L concentration of platinum solution boiled, slowly added 20% NaOH with stirring, neutralized to pH ≈ 2.5, 10% of the amount of platinum in the ammonium solution was added to the sodium bromate oxidation, the first time added 70% of the total amount of sodium bromate ( 10% concentration solution), after boiling, adjust pH ≈5 with 10% NaOH or NaHCO ₃ , and then add the remaining sodium bromate solution to adjust pH 7.5-8. NaBrO ₃ decomposes to release new ecological oxygen and new ecological chlorine, so that the noble and bismuth metals in the solution are oxidized to a high price state, and the solution is neutralized with alkali to convert the platinum into soluble Na ₂ Pt(OH) ₆ :
H ₂ PtCl ₆ +8 NaOH=====Na ₂ Pt(OH) ₆ +6NaCl+2H ₂ O
Other noble and base metal impurities are hydrolyzed into hydroxide precipitates, boiled and rapidly cooled to room temperature, left to stand still, filtered, and the precipitate is washed with pure water of pH ≈8. The platinum-containing filtrate and the washing water were combined, acidified to pH ≈O.5 with hydrochloric acid, boiled and bromine added, and ammonium chloride was precipitated to precipitate a platinum ammonium salt. One-time oxidative hydrolysis and one ammonium chloride precipitation can purify 90%-95% of the crude platinum containing platinum to 99.99%. The disadvantage is that the operation is complicated, the bromine time is long, the oxidant is expensive, and the bromine pollutes the environment. [next]
3. Carrier hydrolysis method It is suitable for the case where the impurity content in the platinum solution is not high, and high purity platinum is obtained and the direct yield is allowed to be low. Platinum solution plus NaCl is converted to Na ₂ PtCl ₆ , ammonium is added with 50g FeCl ₃ per kilogram of platinum as carrier, hydrogen peroxide or bubbling air is oxidized and boiled, and ammonium is hydrolyzed to form a large amount of ammonium hydroxide precipitate, which aggregates and strengthens the hydrolysis of other impurity elements. precipitation. After the precipitated platinum-containing solution is acidified with hydrochloric acid, the pure ammonium chloroplatinate can be precipitated with ammonium chloride.
4. Cation exchange method The Na ₂ PtCl ₆ solution containing ruthenium metal is adjusted to pH ≈ 1.5 to keep the ruthenium metal in a cationic state, and slowly flow through the cation resin exchange column to adsorb the ruthenium metal cation by the resin, and then adjust the pH to 2~3 and then pass another A cation exchange column. Repeat the operation to remove the ruthenium metal until the effluent anion-containing PtCl ₆ ^2- solution reaches the desired purity and then precipitate the platinum ammonium salt with ammonium chloride.
5. Metal Preparation and Product Standards There are two methods for the final preparation of metallic platinum - reduction and calcination.
(1) Reduction method The obtained Na ₂ PtCl ₆ or H ₂ PtCl ₆ solution is refined, pH 3-4 is adjusted, and phosphine phosphine is added to reduce sponge platinum, and the reaction is:
Na ₂ PtCl ₆ +4[N ₂ H ₄ ·H ₂ O]====Pt+2NaCl+4NH ₄ Cl+2N ₂ +4H ₂ O
(2) Calcination method Purified pure (NH ₄ ) ₂ PtCl ₆ precipitate, transferred to a special clean porcelain crucible and capped, placed in a special muffle furnace, slowly dried at low temperature, and then heated to 350 ° C to maintain A few hours until the white smoke is reduced, and then heated to 750-800 ° C satin burning 1-3h to obtain a sponge platinum product. The reaction by calcination decomposition is:

China Metal Platinum Product Standard (GB1419-89) is shown in the table.