Reading a Calcium Chloride Specification: NaCl, Alkalinity and Insolubles

A calcium chloride certificate looks simple: nine lines, one of which is the assay. But six of the other eight lines decide whether the material works in your application, and the assay – the number everyone compares – is the least informative of the lot. This article goes through each line and says what it actually means.

1. The sheet, in order

Item	74% flakes	94% grade	What it is
Purity as CaCl₂	74% min	94% min	Salt content, on the hydrate basis
Alkalinity as Ca(OH)₂	0.2% max	0.25% max	Free lime
Total alkali chloride as NaCl	5.0% max	5.0% max	Sodium chloride from raw material and process
Water insoluble	0.15% max	0.25% max	Grit, sludge, undissolved matter
Iron as Fe	0.006% max	0.006% max	Metallic impurity, colour and staining
pH	7.5 – 11.0	7.5 – 11.0	Solution acidity/alkalinity
Total magnesium as MgCl₂	0.5% max	0.5% max	From the raw mineral
Sulphate as CaSO₄	0.05% max	0.05% max	Low-solubility salt

2. Assay: the number that needs a basis

“74% as CaCl₂” and “94% as CaCl₂” are compositions of two different hydrates, not two purity levels. For a material that absorbs water from the air, the assay also needs a stated basis: as-received or dried. A hygroscopic salt can assay 94% on a dried basis and deliver considerably less in the bag after a humid week.

Practical rule: for a technical salt, ask for the assay and the water content together, and treat the sum with suspicion if it does not make sense.

3. NaCl at 5% – the biggest impurity by far

Application	Does 5% NaCl matter?	Why
De-icing	No	Both salts melt ice; the mixture works fine
Concrete	Yes	Adds chloride to a mix that is already chloride-limited
Desiccation	Marginally	Reduces capacity per kilogram; NaCl is also hygroscopic so the effect is small
Oilfield brine	Depends on the target	Changes the density calculation and adds a second salt to the water balance
Food	Yes	Affects taste and is limited far below 5% in food-grade specifications
Chemical manufacture	Often yes	If you are making a downstream calcium product, NaCl is a contaminant you must remove

Five percent is a large allowance – a tonne of this material can contain 50 kg of sodium chloride. If your process cannot tolerate it, you need a lower-NaCl grade, not a higher-assay one; the 94% product carries the same 5% allowance.

4. Alkalinity as Ca(OH)₂

Free lime left from the manufacturing route. It matters for three reasons:

pH: it is what makes the solution pH sit between 7.5 and 11 rather than at neutral.
Reactions: a free base can react with acidic components in a formulation, generating heat or gas.
Corrosion and scaling: in brines and water circuits, alkalinity drives carbonate scaling and affects corrosion inhibitor selection.

A 0.2% figure is a normal technical-grade allowance. If you need a neutral calcium chloride solution, you neutralise it yourself – the specification will not do it for you.

5. Water insolubles

Level	Where it hurts
0.15% (74% grade) and 0.25% (94% grade)	In a brine circuit: settles in tanks, abrades pumps, blocks filters. In a spray system: plugs nozzles. In a desiccant bed: channels the gas flow and eventually blinds the bed. In food or pharmaceutical preparation: visible haze and failed clarity tests

Insolubles are the impurity most likely to cause an operational problem that looks like an equipment fault. If your brine is going through a filter, the filter loading is a design parameter worth calculating from this figure.

6. Iron at 60 ppm

Low enough to be irrelevant in de-icing, and important in three places: textile and paper processing (iron stains), white or light-coloured products, and any application where the calcium chloride solution must remain water-clear. Iron also accelerates the oxidation of some organic additives.

7. pH 7.5 – 11.0

A wide range, and it should be read as such. It tells you the material is basic and that the manufacturer is not controlling pH closely. If your process needs a specific pH, you will be adjusting it – do not expect the incoming material to arrive in a narrow window.

8. Magnesium and sulphate

Magnesium as MgCl₂, 0.5% max: comes with the raw mineral. It changes brine density and, in a downstream process making a pure calcium salt, it is the first thing you have to remove.
Sulphate as CaSO₄, 0.05% max: calcium sulphate has low solubility, so sulphate can precipitate as gypsum in a brine circuit – scale on heat exchangers, haze in a completion fluid. The limit is tight for a reason.

9. What to test on arrival

Check	Method	Why
Assay	EDTA titration or gravimetric	Confirm the hydrate form and the delivered content
Water content	Karl Fischer or loss on drying	Distinguishes a properly packed anhydrous lot from one that has picked up moisture
Appearance / insolubles	Visual, and a solution clarity test	The fastest operational check; haze means the material is not what the sheet says
Caking / flow	Visual on opening	Deliquescence shows here first
NaCl (where it matters)	Chloride balance or ion chromatography	The 5% allowance is large; verify if your process is sensitive

10. Packaging and supply

Both grades ship in 25 kg bags with a moisture barrier, in big bags or in bulk. The specification is only meaningful if the packaging preserves it: a hygroscopic salt in a split bag no longer assays what the certificate says. Every lot ships with a COA and SDS, FOB or CIF against destination.