Magnesium chloride is a water-soluble salt used by city, regional, and national agencies, as well as private companies, for dealing with melting ice and dust control. Applying magnesium chloride for dust control entails using a liquid or powdered formula on unpaved or gravel roads, whereas applying it for melting ice requires spraying the formula either before or after precipitation.
When used on roads for dust control, magnesium chloride absorbs water from the air. This in turn reduces the likelihood that dust will fly up when someone drives along the road. It can also be used on tennis courts, construction sites, baseball fields, sandy floors, and inside indoor arenas, such as those used for horse riding.
This compound should be applied at a rate of 2 pounds (0.9 kilogram) per 1 square yard (0.83 square meter) on construction sites, parking lots, and unpaved roads, and then later reapplied at 50% of this rate when the surface has dried. For other surfaces, a rate of 1 pound (0.45 kilogram) per 1 square yard (0.83 square meter) should be used instead. One successful application of magnesium chloride may last between 100 to 200 days.
Use in dust and erosion control
Magnesium chloride is most commonly used for dust control, soil stabilization and wind erosion mitigation. Its second-most common use is ice control. In addition to the production of magnesium metal, magnesium chloride also is used for a variety of other applications: fertilizer, mineral supplement for animals, waste-water treatment, wallboard, artificial seawater, feed supplement, textiles, paper, fireproofing agents, cements and refrigeration brine.
When magnesium chloride is applied to roads and bare soil areas, both positive and negative performance issues occur which are related to many application factors. Water absorbing magnesium chloride (deliquescent) attributes include:
- it starts to absorb water from the air at 32% relative humidity, almost independent of temperature,
- more effective than calcium chloride solutions for increasing surface tension,
- Treated roads can be regarded and re-compacted with less concern for losing moisture and density.
However, limitations include
- a minimum humidity levels to absorb moisture from the air is required,
- it is more suitable in drier climates,
- in concentrated solutions it is very corrosive,
- it attracts moisture thereby prolonging the active period for corrosion,
- rainwater tends to leach out highly soluble chlorides,
- if high fines content in treated material then the surface may become slippery when wet,
- When less than 20% solution it has performance effectiveness similar to water.
The use of magnesium chloride on roads remains controversial.
- Cleaner air, which leads to better health as fugitive dust can cause health problems in the young, elderly and people with respiratory conditions; and
- Greater safety through improved road conditions, including increased driver visibility and decreased risks caused by loose gravel, soft spots, road roughness and flying rocks.
- It reduces foreign sediment in nearby surface waters (dust that settles in creeks and streams), helps prevent stunted crop growth caused by clogged pores in plants, and keeps vehicles and property cleaner.
- Other studies show the use of salts for road deicing or dust suppressing can contribute substantial amounts of chloride ions to runoff from surface of roads treated with the compounds.
- The salts MgCl2 (and CaCl2) are very soluble in water and will dissociate. The salts, when used on road surfaces, will dissolve during wet weather and be transported into the groundwater through infiltration and/or runoff into surface water bodies.
- Groundwater infiltration can be a problem and the chloride ion in drinking water is considered a problem when concentrations exceed 250 mg/l. It is therefore is regulated by the EPA’s drinking water standards.
The chloride concentration in the groundwater or surface water depends on several factors including: application rate, composition and type of soil, type, intensity, and amount of precipitation, the drainage of the road system.
In addition, the chloride concentration in the surface water also depends on the size or flow rate of the water body and the resulting dilution achieved. In chloride concentration studies carried out in Wisconsin during a winter deicing period, runoff from roadside drainage’s were analyzed. All studies indicated that the chloride concentration increased as a result of deicing activities the long-term effect of this exposure is not known.
Although the EPA has set the maximum chloride concentration in water for domestic use at 250 mg/l animals can tolerate higher levels. At excessively high levels, chloride is said to affect the health of animals (Heller, V.G. “Saline and Alkaline Drinking Waters.” Journal of Nutrition, 5:421-429 1932). As stated by the National Technical Advisory Committee to the Secretary of Interior (1968), “Salinity may have a two-fold effect on wildlife; a direct one affecting the body processes of the species involved and an indirect one altering the environment making living species perpetuation difficult or impossible.” One major problem associated with the use of deicing salt as far as wildlife is concerned is that wildlife are known to have “salt craving” and therefore are attracted to salted highways which can be a traffic hazard to both the animals and motorists.
Is liquid magnesium chloride lower in chloride and safer for the environment than calcium chloride?
No. The chloride content of liquid material is determined by the solution concentration, and the molecular weight of the salt. For example, a 30% solution of magnesium chloride would have about the same chloride content as a 35% calcium chloride solution. A researches report from Colorado State University “Condition of Soils and Vegetation Along Roads Treated with Magnesium Chloride for Dust Suppression, B.A. Goodrich, R.D Koski, and W.R. Jacobi, March, 2008” and the report report “Dust Palliative Selection and Application Guide, USDA Forest Service, P. Bolander and A. Yamada, November, 1999” by the U.S. Department of Agriculture Forest Service concluded that the impact of magnesium chloride is the same as other chlorides. While magnesium chloride is commercially available in 30% solutions, is typically applied at concentrations of 35% or 38% for dust control and road base stabilization applications.