High Purity Selenium Purification Processes

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High Purity Selenium Purification Processes

The purification of high-purity selenium (≥99.999%) involves a combination of physical and chemical methods to remove impurities such as Te, Pb, Fe, and As. The following are key processes and parameters:

 硒块

 1. Vacuum Distillation

Process Flow:

1. Place crude selenium (≥99.9%) in a quartz crucible within a vacuum distillation furnace.

2. Heat to 300-500°C under vacuum (1-100 Pa) for 60-180 minutes.

3. Selenium vapor condenses in a two-stage condenser (lower stage with Pb/Cu particles, upper stage for selenium collection).

4. Collect selenium from the upper condenser;碲(Te) and other high-boiling impurities remain in the lower stage.

 

Parameters:

- Temperature: 300-500°C

- Pressure: 1-100 Pa

- Condenser material: Quartz or stainless steel .

 

2. Chemical Purification + Vacuum Distillation

Process Flow:

1. Oxidation Combustion: React crude selenium (99.9%) with O₂ at 500°C to form SeO₂ and TeO₂ gases.

2. Solvent Extraction: Dissolve SeO₂ in an ethanol-water solution, filter out TeO₂ precipitate.

3. Reduction: Use hydrazine (N₂H₄) to reduce SeO₂ to elemental selenium.

4. Deep De-Te: Oxidize selenium again to SeO₄²⁻, then extract Te using solvent extraction.

5. Final Vacuum Distillation: Purify selenium at 300-500°C and 1-100 Pa to achieve 6N (99.9999%) purity.

 

Parameters:

- Oxidation temperature: 500°C

- Hydrazine dosage: Excess to ensure complete reduction .

 

3. Electrolytic Purification

Process Flow:

1. Use an electrolyte (e.g., selenous acid) with a current density of 5-10 A/dm².

2. Selenium deposits on the cathode, while selenium oxides volatilize at the anode.

 

Parameters:

- Current density: 5-10 A/dm²

- Electrolyte: Selenous acid or selenate solution .

 

4. Solvent Extraction

Process Flow:

1. Extract Se⁴⁺ from the solution using TBP (tributyl phosphate) or TOA (trioctylamine) in hydrochloric or sulfuric acid media.

2. Strip and precipitate selenium, then recrystallize.

 

Parameters:

- Extractant: TBP (HCl medium) or TOA (H₂SO₄ medium)

- Number of stages: 2-3 .

 

5. Zone Melting

Process Flow:

1. Repeatedly zone-melt selenium ingots to remove trace impurities.

2. Suitable for achieving >5N purity from high-purity starting materials.

 

Note: Requires specialized equipment and is energy-intensive .

 

Figure Suggestion

For visual reference, refer to the following figures from literature:

- Vacuum Distillation Setup: Schematic of a two-stage condenser system .

- Se-Te Phase Diagram: Illustrates separation challenges due to close boiling points .

 

References

- Vacuum distillation and chemical methods:

- Electrolytic and solvent extraction:

- Advanced techniques and challenges:


Post time: Mar-21-2025