Calcium Chloride 74% vs 94%: Hydrate Form, Assay and Which One to Buy

Buyers comparing “calcium chloride 74%” and “calcium chloride 94%” are usually comparing two different things without knowing it. They are not two purity grades of one product – they are two hydrate forms, with two CAS numbers, two water contents and two sets of handling consequences. Almost every bad calcium chloride decision comes from treating 74 and 94 as points on the same purity scale.

1. Two hydrates, two CAS numbers

Property	74% flakes	94% grade
CAS	10035-04-8	10043-52-4
Formula	CaCl₂·2H₂O (dihydrate)	CaCl₂ (near-anhydrous)
Molecular weight	147.01	110.98
Theoretical CaCl₂ content	75.5%	100%
Commercial assay	74% min	94% min
Water carried	About 24% by weight	A few percent
Deliquescence	Moderate	Strong – it is a desiccant
Heat of solution	High	Higher still

The 74% figure is close to the theoretical 75.5% of the pure dihydrate, so a 74% flake is essentially “pure hydrate”. The 94% figure is far from the theoretical 100% of the anhydrous salt, so a 94% product is “near-anhydrous industrial material with the usual impurities”. Neither number is a purity ranking; both describe composition.

2. The comparison that actually decides the purchase

Step	Calculation	Example
1. Convert to delivered CaCl₂	price per tonne / assay	74% at 150/t gives about 203 per tonne of CaCl₂; 94% at 200/t gives about 213
2. Add freight per tonne of CaCl₂	freight per tonne / assay	The dihydrate ships 26% dead weight in water, so its effective freight is a third higher per unit of salt
3. Add the cost of the water in your process	Depends on the application	In a dry blend or a desiccant bed the water is a liability; in de-icing it is irrelevant
4. Add storage and handling	Deliquescence, caking, repacking	The 94% grade needs better packaging discipline and has less tolerance for half-used bags

Run those four steps and the ranking often reverses for long-distance shipments, and stays with the 74% grade for local de-icing. The headline numbers on their own tell you nothing.

3. Which one fits which application

Application	Better fit	Reason
Road de-icing, local supply	74% flakes	Cheapest per unit of melting action; the water is harmless; standard spreading equipment handles flakes
De-icing, long inland freight	Often 94%	Less water shipped; the delivered cost per tonne of salt can be lower despite a higher unit price
Dust suppression on unpaved roads	74%	Applied as a solution anyway – no benefit in paying for anhydrous material
Desiccation, gas drying	94%	Capacity per kilogram is the whole point; the dihydrate’s water is a handicap
Oilfield brine preparation	Either, depending on density target	Calculate on the brine density you need and the water balance, not on the assay
Concrete acceleration	Either, subject to chloride limits	Dosed in small quantities; the chloride restriction dominates, not the hydrate form
Food (E509)	Neither – needs a food grade	Both of these are industrial specifications with 5% NaCl permitted

4. The water question, in three applications

De-icing: the water of crystallisation is irrelevant. It dissolves anyway, and the dissolution is endothermic or exothermic depending on dilution – the salt does the work, not the water content.
Desiccation: the water is a direct loss of capacity. Buying the dihydrate for a desiccant bed means paying to ship and store water you are trying to remove from something else.
Concrete: the dihydrate adds water to the mix, which must be counted in the water/cement ratio. A 74% grade is not simply a weaker version of the 94% grade; it changes the mix design.

5. Handling differences that cost money if ignored

Issue	74% flakes	94% grade
Caking	Cakes if damp, but tolerates brief exposure	Deliquesces – an open bag becomes a fused block
Packaging condition	Moisture barrier required	Moisture barrier is critical; a split bag is a loss
Half-used bags	Recoverable if resealed	Likely to be lost
Dissolution heat	Strong	Stronger – add slowly to water, never water to solid
Dosing equipment	Flakes feed well	Prills or granules feed better than powder; check your feeder

6. What to put on the purchase order

The CAS and the hydrate form – “calcium chloride 74%” alone is ambiguous between a dihydrate and a diluted product.
Assay basis (as-received or dried), which matters for a hygroscopic salt.
NaCl limit – 5% is permitted in both these grades, and it is the impurity that matters for chloride-sensitive uses.
Physical form – flake, prill or powder, matched to your feeder.
Packaging and moisture barrier, plus a pack size you will finish in one campaign.

7. Packaging and supply

Both grades ship in 25 kg PP-woven or paper bags with an inner moisture barrier, in big bags, or in bulk. Because calcium chloride is hygroscopic and the anhydrous grade is deliquescent, the packaging is part of the specification rather than a detail – and pack size should match consumption, since a half-used bag of the 94% grade is the most common cause of a caking complaint. Every lot ships with a COA and SDS, FOB or CIF against destination.

8. The honest summary

If you are spreading salt on a road within a few hundred kilometres, the 74% flake is almost always the right purchase and the chemistry is irrelevant. If you are drying gas, making brine to a density target, or shipping a long way, work out the delivered cost per tonne of CaCl₂ and the 94% grade frequently wins. What does not work is buying on the percentage alone – the two figures describe two different materials, not two quality levels of one.