锇 refining

The most effective technique for separating hydrazine is oxidative distillation-alkali absorption, so the hydrazine refining is based on hydrazine absorbing liquid. There are methods such as pressurized hydrogen reduction, sodium sulfide precipitation, ammonium chloride precipitation, and formic acid reduction.
1. Pressurized hydrogen reduction method: A solution containing about 1g/L of sodium citrate (Na ₂ OSO ₄ ), neutralized with sulfuric acid to pH 8~9, then passed SO ₂ to pH=6 and heated to a slight boiling, static After standing overnight, the brown sodium salt was precipitated and the reaction was:
2OsO ₄ +12NaOH+8SO ₂ +4H ₂ O=====2[(Na ₂ O) ₃ OsO ₃ (SO ₂ ) ₄ ·5H ₂ O]↓+O ₂
The filtered sodium sulphate precipitate was re-introduced into the distiller, dissolved by heating with 1:1H ₂ SO ₄ , and reoxidized by adding 40% NaCIO ₃ solution at 90 ° C, and the sodium hydroxide solution was absorbed. A small amount of methanol was added to the first-stage absorption liquid containing bismuth 15-35 g/L, and Ru(OH) _{4 was} precipitated by standing at 40 ° C overnight, and purple K ₂ OsO _{4 was} precipitated by adding KOH to the pure sodium citrate solution after filtration separation. The response is:
2Na ₂ OsO ₄ +4KOH=====2K ₂ OsO ₄ ↓+4NaOH
The precipitate of potassium citrate obtained after filtration is further slurried with 1:1 HCl, placed in an autoclave, and reduced to 1-2 hours by hydrogen (hydrogen pressure 3-4 kPa) at 125 ° C to obtain a sponge mash. The reaction is:
K ₂ OsO ₄ +2HCl+H ₂ =====Os↓+2KCl+4H ₂ O
Osmium metal powder promptly filtered and washed with ethanol, re-placed in a tube furnace, hydrogen or nitrogen through the low temperature drying, slowly warmed to 900 deg.] C reduction with hydrogen IH, cooled to room temperature to obtain a metal powder osmium.
2. Sodium sulfide precipitation method Low concentration bismuth absorbing solution is added with sodium sulfide at room temperature to precipitate OsS ₂ , dried at 80 ° C after filtration, and calcined at 700 ° C in a hydrogen stream to obtain bismuth powder:

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3. Ammonium chloride precipitation method Pure saponin absorbing solution is added with a small amount of methanol or ethanol to make hydrazine in the presence of stable Na ₂ OsO ₄ . Ammonium chloride is added quantitatively at room temperature to precipitate yellow [OsO ₂ (NH ₃ ) ₄ ]Cl ₂ , the response is:
Na ₂ OsO ₄ +4NH ₄ Cl=====[OsO ₂ (NH ₃ ) ₄ ]Cl ₂ ↓+2NaCl+2H ₂ O
Immediately filtration, the sodium salt in the precipitate was washed away with dilute hydrochloric acid, dried at 80 ° C, and calcined at 800 ° C in a hydrogen stream to obtain a tantalum powder.
If osmium tetroxide is saturated with 1:1 HCl absorption of SO ₂ during oxidative distillation, the ruthenium in the solution is in the state of H ₂ OsCl ₆ , slowly concentrated to a cerium content greater than 20 g/L, and ammonium chloride is added at room temperature to form (NH ₄ ) _{2 .} OsCl ₆ precipitates and the reaction is:
H ₂ OsCl6+2NH ₄ Cl=====(NH ₄ ) ₂ OsCl ₆ ↓+2HCl
After filtration, the precipitate is washed with ethanol, dried in a hydrogen stream, and reduced at 900 ° C to obtain a powder:

4. Formic acid reduction method Pure sodium citrate alkali absorption solution is neutralized with hydrochloric acid to pH 6-7, and formic acid or hydrazine hydrate is added at 80 ° C to reduce Na ₂ OsO ₄ to OsO ₂ ·nH ₂ O. The reaction is:
Na ₂ OsO ₄ +HCOOH=====OsO ₂ ·H ₂ O↓+Na ₂ CO ₃
It is dried in a hydrogen stream and reduced in a hydrogen stream at 900 ° C to obtain a tantalum powder.
All the calcined powder obtained osmium and cooled down process, are required in the stream of hydrogen, the obtained powders need to immediately transferred to a sealed osmium dryer, because oxygen in the air and carbon dioxide gas can cause spontaneous combustion osmium oxide, generating four Oxide is volatilized.
5. Product standards for metal bismuth The enterprise standards of the Kunming Institute of Precious Metals in China are listed in the table.