Calcium chloride’s eutectic point is -51˚C (-60˚F.) While MgCl2 has a eutectic temperature of -33˚C (-28˚F), its melting rate drops to a low level well before it reaches this temperature.
The effectiveness of MgCl2 is often limited by the presence of magnesium sulfate as an impurity. Magnesium sulfate crystallizes between -18˚C (0˚F) and -20.5˚C (5˚F) to cause sludge in tanks and clogging of spray nozzles and transfer pumps. By contrast, a 32% CaCl2 solution, the most commonly used concentration in winter,does not form crystals within its working range.
Calcium chloride melts more ice at low temperatures. At -10˚C (14˚F), 32% CaCl2 liquid melts 27% more ice than 30% MgCl2. At -20˚C (-4˚F), 32% CaCl2 melts 94% more ice than 30% MgCl2.
The Midwest Research Institute study (based on FHWA, Strategic Highway Research Board test methods) evaluated ice penetration of calcium chloride vs magnesium chloride. The study found that at -7˚C (20˚F), CaCl2 has 22% more penetration after 10 minutes and 38% after 30 minutes than MgCl2. At -15˚C (5˚F), CaCl2 had penetrated 58% more ice after 30 minutes.
Calcium chloride has a lower application rate compared to magnesium chloride because calcium chloride has higher ice melting capacity and faster ice penetration.
Given their relative commercial strengths and active chemical purity, 50% to 100% more MgCl2 than CaCl2 is usually required to remove equal amounts of snow and ice.
Liquid CaCl2 is applied at concentrations of 25% to 35%, while that for MgCl2 normally falls between 21% and 28%. Conceptually, this means that two parts of CaCl2does more work in less time than three parts MgCl2.
Magnesium chloride is more detrimental to concrete. Testing was done by the Pittsburgh Testing Laboratory on air-entrained concrete over 500 freeze-thaw cycles. The data show that CaCl2 has the least spalling of common deicers, including MgCl2. (Concrete Spalling is when concrete chips, fragments and/or breaks away, creating large holes or craters and dangerous trip points for anyone walking on this surface.) Spalling is measured on a scale of 0 to 5 (none to severe). A 4% solution of MgCl2 showed moderate scaling and had a 3.1 rating. The same concentration of CaCl2 had a 1.6 rating, or between very slight and slight to moderate scaling.
The American Concrete Institute’s guide to Durable Concrete says calcium chloride has a “negligible” effect on concrete while MgCl2 causes a slow deterioration of concrete surfaces.
In addition, a study of concrete deterioration by deicing salts, including MgCl2 and CaCl2, at Iowa State University found that “magnesium chloride was the most destructive salt with severe deterioration produced under almost all of the experimental conditions”. Deterioration was judged by the degree of crumbling, fracturing and brownish discoloration.
The Corrosion Data Survey published by the National Association of Corrosion Engineers indicates that MgCl2 is more than twice as corrosive to 304 stainless steel as CaCl2 .
The NACE survey also indicates that MgCl2 can be 10 times more corrosive to mild steel than CaCl2.
Tiger Calcium also offers corrosion inhibitors in our winter anti-icing and de-icing products.
Although CaCl2 and MgCl2 are considered non-toxic, the Registry of Toxic Effects of Chemical Substances states that MgCl2 has nearly three times the toxicity of CaCl2 on a common measure of toxicity.
The Ministry of the Environment in British Columbia found that CaCl2 has significantly less toxicity than MgCl2 in bioassay tests on rainbow trout and the water flea daphnia. For instance, rainbow trout, which represent the high end of the food chain, were five times more sensitive to MgCl2 than to 35% CaCl2.
Both materials are used as micronutrient sources in animal feeds. CaCl2 is also a common food ingredient and is “Generally Recognized as Safe” by the US Food and Drug Administration. If anything, Magnesium Chloride is more harmful to vegetation.
Tests with calcium chloride by Quebec’s Ministry of Environment found “no definite areas of environmental problem…subject to the use of good application practices”. In addition, CaCl2 is a clean, inorganic material that does not leave an oily or powdery residue after its use.