Sodium Sulphate: Anhydrous vs Decahydrate, and Why the Difference Costs You Money

Two products, one name

Sodium sulphate is sold as the anhydrous salt (Na₂SO₄) and as the decahydrate (Glauber's salt, Na₂SO₄·10H₂O). The decahydrate carries a large proportion of water of crystallisation, so a tonne of it contains far less Na₂SO₄ than a tonne of the anhydrous material.

If a price looks unusually low, the first thing to check is whether the offer is for the anhydrous salt at all.

Why moisture control matters downstream

Anhydrous sodium sulphate is hygroscopic and can cake if it takes up moisture in transit or in storage — which is why delivered moisture content and packing quality matter as much as the headline assay figure. In detergent production, glass batching and textile processing, an inconsistent feed changes dosing and can affect the finished product.

For buyers, the practical controls are: specify delivered moisture, specify water insoluble matter, and ask how the material is packed and lined. A jumbo bag with an inner liner behaves differently in a humid port than a plain woven bag.

Points worth specifying

Include these on your enquiry so offers are comparable:

• Anhydrous or decahydrate — stated explicitly
• Na₂SO₄ content and the basis on which it is measured
• Delivered moisture limit
• Water insoluble matter limit
• Powder or granular form, and particle size if your process needs it
• Packaging with the liner type, and whether palletisation is required

One more thing: whiteness and iron

For glass and for some textile applications, iron content and whiteness matter as much as the assay. They are usually available on request — ask before you buy rather than discovering it in the batch analysis.