What is the difference between calcium chloride and calcium chloride dihydrate?

Calcium chloride (anhydrous): purity is usually ≥94%, allowed to contain magnesium, iron, alkali metal salts and other impurities (the total amount of ≤5%), mainly used for road snowmelt, drilling fluids, concrete antifreeze and other scenarios with lower purity requirements.

Purity and Impurity Control Differences

Industrial grade products

Calcium chloride (anhydrous): purity is usually ≥94%, allowed to contain magnesium, iron, alkali metal salts and other impurities (the total amount of ≤5%), mainly used for road snowmelt, drilling fluids, concrete antifreeze and other scenarios with lower purity requirements.

Calcium chloride dihydrate: purity ≥74% (in CaCl₂), slightly higher impurities (such as magnesium salts ≤2%), commonly used in water treatment, soil improvement, refrigeration fluid preparation and so on.

Food / Pharmaceutical Grade Products

Calcium chloride (anhydrous): purity ≥99%, need to strictly control heavy metals (As ≤ 3 mg/kg, Pb ≤ 2 mg/kg), fluoride (≤ 50 mg/kg), mainly used as calcium supplements for pharmaceutical injections (need to comply with USP/NF standards).

Calcium chloride dihydrate: food-grade purity ≥ 97% (GB 1886.45), stable water of crystallization, more suitable for food additives (e.g., soybean products coagulation, electrolyte drinks), due to the presence of water of crystallization, measurement of the active ingredient needs to be converted (1g dihydrate ≈ 0.75g anhydrous).

Core differences in functional application scenarios

Industrial field

Anhydrous calcium chloride:

Drying and dehydration: used to dry industrial gases such as nitrogen and oxygen, or as laboratory desiccant (cannot dry ammonia, because it will form complex CaCl₂・8NH₃).

Snow-melting agent: Because of strong moisture absorption and low freezing point (freezing point of aqueous solution - 55℃), it is often used to melt snow on roads in cold areas, but it is corrosive to reinforced concrete.

Calcium chloride dihydrate:

Refrigeration medium: Preparation of low-temperature brine (e.g. - 20 ℃ coolant), due to the presence of crystalline water, dissolution heat effect is small, the operation is safer.

Building additives: add 0.5%-1% in concrete, accelerate hardening, improve early strength, but need to control the dosage to prevent cracking (due to the risk of corrosion of CaCl₂ on the steel reinforcement, has been gradually replaced by non-chlorine early strength agent).