Ice Melters – How Salt Granules Work
The most familiar ice melter is rock salt because it is used to make our highway safe during winter storms. Many buyers know little about the many other ice melters that are used to make our sidewalks, driveways and parking lots safe. This article uses simple/non-technical language to explain how all these ice melters work.
All traditional ice melters are formulations of four basic salts and/or fertilizers. In addition, other ingredients are sometimes added to make the products stick, spread, pour better and/or more visible. The word salt is used to describe a compound containing the basic element called “chloride”. Rock salt is the compound Sodium Chloride mined naturally from under the ground. The four salts are:
1) Sodium Chloride — The rock salt (natural sodium chloride) granules work by absorbing heat. When these granules are spread on pavement containing water and/or ice, two things happen:
o The granules mix into solution with the water and/or ice.
o The granules absorb heat from the sun, car tires, crushing force, etc. raising the temperature of the solution.
This rise in temperature of the solution causes ice to melt even though the outside air temperature is between +20F and the freezing point of water, 32F. Rock salt has a minimum effective temperature (MET) of +20F. This means that when the outside temperature is below +20F ice can still form under normal application rates.
2) Calcium chloride — The granules of this compound give off lots of heat when allowed to contact water/ice in contrast to the rock salt that absorbed heat. Calcium chloride has a MET of -25F.
3) Magnesium chloride — The granules of this compound also give off heat. However, it has a MET of only zero F. This is because the granules contain about 50% water and 50% magnesium chloride making it only half as effective when mixed with water/ice. Because of the water content, the application rate must be significantly increased to get the same amount of melting compared to calcium chloride.
4) Potassium chloride — The granules of this compound work similar to rock salt by absorbing heat. Therefore, Potassium chloride is less effective than the previous two salts. Potassium chloride has a MET of +25F. Potassium chloride is also a commonly used as a fertilizer.
Now that it is known that the above four salts work by either absorbing heat or giving off heat, what determines the actual performance of ice melters? By varying the proportions of the above four salts in a product, the manufacturer can adjust the many characteristics of ice melters such as MET’s, melting speed, melting durations, and environment impact (vegetation, animal life, concrete, floor covering, etc.).
The performance of a specific ice melter is determined by the predominant salt in the ice melter because there is very little interaction between the different salts when mixed. Adding a salt with a weaker characteristic, such as MET, weakens the resulting product according to the proportions used in the product. The same is true for adding a small amount of a salt with a stronger characteristic. The resulting product is only strengthened for the specific characteristic according to the proportions used in the product.
Finally, non-corrosive/non-salt additives such as urea and CMA can also play an important role in how the granules of an ice melt product work.
o Urea (a common form of nitrogen found in fertilizer) is sometimes mixed with the above salts but is not very effective as an ice melter. Too much urea can significantly weaken the products performance. While products with urea may appear to be friendlier to the environment, they can actually be worse for the environment because of the high rate of usage required to melt ice.
o CMA (calcium magnesium acetate) is a key ingredient added to many ice melters to increase melting speed and make it less corrosive. Pure CMA is no more corrosive than water. CMA is quite expensive. The CMA additive is biodegradable. This means that it decomposes to compounds normally found in nature. Products with the CMA additive are often advertized as being friendlier to the environment.
Both urea and CMA are use at airports to clean runways and/or aircraft because they are lest corrosive than the salts.