Calcium Chloride

Calcium Chloride vs. Magnesium Chloride

Calcium chloride works well down to this temperature, while the melting action is impractically slow at this point. Melting temperature is a confusing area. Many suppliers quote the lowest temperature at which their product melts ice in a laboratory (the eutectic point), rather than what is practical in the field.
While MgCl₂ has a eutectic of -33 C (-28 F), its melting rate drops to a low level well before it reaches this temperature. CaCl₂, with a eutectic point of -51 C (-60), still has substantial ice melting ability between between -23 and -32 C (-10 and -25 F).

Magnesium Chloride can clog equipment as temperature drops.
The effectiveness of MgCl₂ is often limited by the presence of magnesium sulphate as an impurity. Magnesium sulphate 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 (down to -29 C or -20 F).

Calcium Chloride actually melts more ice between -18 c and -1 C (0F and 30 F.
This was clearly shown in a Midwest Research Institute study (based on FHWA, Strategic Highway Research Board test methods). The study found that at -7 C (20 F), CaCl₂ flake melted 29% more ice after 10 minutes and 42% more ice after 30 minutes than did MgCl₂ flake. At -15 C (5 F), the difference was 25% after 30 minutes.
The results were even more dramatic in a study by SGS Testing Services. At -18 C (0 F), CaCl₂ flake melted 40 % more ice than MgCl₂ flake 5 minutes after application. This increased to 75% after 30 minutes. At -1 C (30 F), CaCl₂ was 50% better after 5 Minutes and 132% better after 30 minutes.

Calcium chloride penetrates ice faster than magnesium chloride.
The Midwest Research Institute study also evaluated ice penetration. This factor is critical, because ice melters must punch through ice and packed snow to break their bond with the pavement so plows can remove them. 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.
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 32% to 38%, while that for MgCl₂ normally falls between 21% and 28%. similarly, dry CaCl₂ flake contains a minimum 77% active chemical versus dry MgCl₂ which is at 45% to 48%. Conceptually, this means that two parts of CaCl₂ does more work in less time than three parts MgCl₂.

Magnesium chloride is more detrimental to concrete.
MgCl₂ suppliers claim less spalling than other de-icers based on a test developed by SHRP. This method, which was designed to screen de-icers quickly does not correlate to the real world because it uses substandard, non air-entrained concrete and only 15 freeze-thaw cycles. The test sacrifices accuracy for speed. SHRP recognized this, and in the manual that discusses this laboratory test, it notes that "field testing is ultimately required to determine acceptable de-icer performance and compatibility."
More realistic testing was done by the Pittsburgh Testing Laboratory on air-entrained concrete (prepared according to ASTM C 672-91) over 500 freeze-thaw cycles. The data show that CaCl₂ has the least spalling of common de-icers, including MgCl₂. 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.
This is borne out in American Concrete Institute's guide to Durable Concrete, that says CaCl₂ has a "negligible" effect on concrete while MgCl₂ causes a slow deterioration of concrete surfaces.
In addition, a study of concrete deterioration by de-icing 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.

Magnesium chloride is more corrosive to the metals found on roadways.
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 than CaCl₂. The NACE survey also indicates that MgCl₂ can be 10 times more corrosive to mild steel than CaCl₂.
In addition, Pollard offers additives that provide even greater protection for concrete reinforcements, bridge decks, metal rebar in parking structures and metal highway components. These can reduce corrosion by more than 70% when compared to standard road salt.

Magnesium Chloride is more toxic.
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. It is found in such foods as beer, cheese, canned tomatoes, olives, cherries and pickles.

If anything, Magnesium Chloride is more harmful to vegetation.
Both materials are used in fertilizers. Beyond this, CaCl₂ is sprayed on fruit trees and vegetables to provide calcium uptake. In fruit trees, for instance, this improves cold hardiness, reduces fruit disorders and boosts yields. And, an evaluation of how de-icing salts affect spruce trees found that CaCl₂ aids beneficial potassium uptake, while chloride levels increased with MgCl₂.
After the first year of a two year study on how dicers affect turf grass at Iowa State university, MgCl₂ was found to be more detrimental than all other de-icers except urea.

Magnesium Chloride appears to be more harmful to the environment
Chloride ions (not the element chlorine) are generally considered when looking at adverse effects on the environment. When the two materials are compared equally (on a dry weight basis that removes all water), MgCl₂ has a 74% chloride while CaCl₂ has a 64% chloride. When the two compounds are used in equal amounts, MgCl₂ thus adds about 15% more chloride to the environment than CaCl₂.
Also, since MgCl₂ is a less effective ice melter than CaCl₂, MgCl₂ adds even more chloride to the environment because more must be used to achieve the same degree of ice control as a given amount of CaCl₂.
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.