De-icing chemicals: Alternatives to common road salt
By Dawn Pettinelli - UConn Home & Garden Education Center
Featured Article - posted Thu., Dec. 26, 2013
Snow and ice can be lovely to look at but treacherous to travel across, either by foot or vehicle. Shovels, snowblowers and plows best accomplish removal of snow and ice, but sometimes mechanical means are not sufficient to address safety concerns, and chemical de-icing compounds need to be employed.
Sodium chloride has been used as a de-icing agent since the 1940s. It is especially effective on roadways because there is heat generated by the friction of moving traffic. Sodium chloride loses much of its de-icing effectiveness at temperatures below 16 to 20 degrees F.
Chemical de-icers work on the principal that solutions containing a salt compound freeze at lower temperatures than pure water. So while pure water will freeze at 32 degrees F, water with a salt dissolved in it will not freeze until temperatures fall below 32 degrees F. How much below depends on the particular salt used.
When chemical de-icing compounds come in contact with moisture, they form a liquid brine or salt solution. Since this brine has a lower freezing temperature than water, any snow or ice particles will dissolve upon contact. This melting process continues until either all the snow and ice has melted, or the melt water dilutes the brine enough to allow it to refreeze.
While sodium chloride is readily available and inexpensive to purchase, its effects on plants, water quality, cars, roads and other structures is generally unfavorable. Plants can be damaged by the salt-laden slush splashed on them by plows and other vehicles.
Evergreen plants near roadways are especially vulnerable to salt spray damage. Melt water containing salts can leach into nearby soil where plants can take up the sodium and chloride ions as they resume growth in the spring. This uptake may cause stunted growth, desiccation and dieback. The accumulation of salt in soil over successive years may result in progressive plant decline and eventual death.
Sodium chloride that leaches into the soil may contaminate nearby wells or groundwater supplies. Runoff may enter surface waters. Also, sodium chloride is highly corrosive to cars, buildings and some paved surfaces.
Alternatives to common road salt are being explored. No one magical chemical exists, but several options offer a more environmentally-friendly approach to eliminating slippery conditions. The pros and cons of any chemical should be weighed before use. Some of these compounds may not be available locally, but by requesting them, your options may be widened in future years.
Calcium chloride is safer for both plants and the environment. It works well to -25 degrees F. This is because it gives off heat as it dissolves. It also has a greater capacity to absorb water from either the air or its surroundings. This means it will dissolve quicker than sodium chloride so it will start melting ice and snow faster. Unfortunately, this hygroscopic (water-absorbing) quality also make for more difficult storage and handling techniques, which is one reason it is not widely used on roadways.
Calcium chloride costs about three times as much as sodium chloride. It would be a good alternative for homeowners who are concerned about vegetation along walkways and sidewalks. Calcium chloride is available as pellets and also as a liquid that can be sprayed on paved surfaces before icy precipitation begins for easier removal.
Magnesium chloride has properties similar to calcium chloride, but only works effectively to about -13 degrees F. One company has manufactured a liquid magnesium chloride compound that also contains anti-corrosives and a sticker-spreader derived from corn to better bind their product to paved surfaces and reduce residue tracked into buildings. Both calcium and magnesium chlorides will damage the finishes on flooring unless promptly removed.
Salts of potassium and nitrogen have also been suggested by some sources as alternatives to sodium chlorides. Potassium chloride is generally not practical, as it is not very effective at low temperatures. Nitrogen compounds are not advisable because of their potential for ground and surface water pollution.
Two organically-based de-icing salt alternatives are calcium magnesium acetate (CMA) and potassium acetate. These substances are improvements over salt in terms of negative environmental effects and corrosiveness. They are biodegradable and generally not harmful to vegetation if used as directed. They can, however, reduce oxygen levels in surface waters if they enter via runoff.
CMA is a relatively new salt-free de-icing compound derived from dolomitic limestone and acetic acid. Major drawbacks to using these two products are cost (eight to 20 times as much as sodium chloride) and they may cause some slickness on paved surfaces. CMA is only effective to about 25 degrees F, while potassium acetate works to -75 degrees F.
Other new products combine de-icing agents to increase their effectiveness. Often corrosive-inhibiting compounds are added to lessen the effects of chloride containing salts.
Non-toxic abrasive substances like sand, small gravel, sawdust and cat litter can be used to improve traction. Place a sturdy doormat to catch the scratchy residue near entrances. Salts can also be mixed with coarse sand to reduce the amount of chemical de-icer needed. As a general rule of thumb, 1 pound of salt can be mixed with about 50 pounds of sand.
When selecting materials to apply to icy stairs and walkways, don’t just consider their dollar cost. Take into account their effectiveness and also their potential for harmful effects to your landscape and the environment. Often it is not what you spend that counts, but what you save.
If you have questions about de-icing chemicals or on other indoor or outdoor gardening topics, call the UConn Home & Garden Education Center, toll-free, at 877-486-6271, visit www.ladybug.uconn.edu, or contact your local Cooperative Extension Center.