Caustic soda: Characteristics
Why rayon and battery makers check salt and iron
What this tab covers The physical and chemical properties that set its grade, price and uses, with the commercial grades and the standards that define them.Caustic is traded on a dry metric tonne (dmt, 100% NaOH) basis whether sold as 32%, 50% solution or 98% flake. Salt, chlorate and iron content matter to rayon, food, pharmaceutical and battery users. Membrane-grade caustic commands a small premium over diaphragm-grade.
Properties that matter commercially
| Property | Value / specification | Why it matters | Source |
|---|---|---|---|
| Concentration | liquid 48-50% or 32%; flakes 98-99% | sets freight cost and handling | IS 252 (indicative) |
| Sodium chloride | membrane grade below about 0.01%; diaphragm grade about 1% | chloride corrodes equipment and spoils rayon and battery uses | indicative |
| Freezing point | about 12 C for 50% solution | requires heated storage and tanks | standard property |
Commercial grades
- Rayon grade (low salt, low iron) for viscose
- Membrane grade 50% lye
- Diaphragm grade 50% lye
- Flakes and prills 98-99%
- Food and pharma grade