Sodium Dithionite (Sodium Hydrosulfite)
CAS Number: 7775-14-6
Sodium dithionite (sodium hydrosulfite) is a powerful reductive bleaching agent used primarily for brightening mechanical pulps such as groundwood, thermomechanical pulp (TMP), and chemithermomechanical pulp (CTMP). It selectively reduces chromophoric groups in lignin without significant fiber degradation, providing rapid and effective brightness gain. It is also used in recycled fiber deinking and newsprint brightening.
Technical Specifications
| appearance | White to light yellow powder |
| iron content (ppm) | ≤ 20 |
| moisture content (%) | ≤ 2.0 |
| sodium dithionite content (%) | ≥ 85 |
Applications
- Reductive brightening of TMP and CTMP mechanical pulps
- Groundwood pulp brightness improvement for newsprint
- Recycled fiber (deinked pulp) reductive stage
- Bleaching of cotton and flax specialty pulps
- Complementary reductive stage in multi-stage bleaching
Key Features
- Effective reductive bleaching without fiber strength loss
- Rapid dissolution and reaction for inline mill application
- Complementary to peroxide for dual-stage brightening systems
- Low effluent impact compared to chlorine-based bleaching
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