Profile of Chloride-based Dust Suppressants Used in Canada

For a full copy of this report, contact Road Salts Working Group:
Road Salts Working Group
Tel: (819) 953-6065
Fax: (819) 994-0007

1. Executive Summary

Dust from unpaved roads can be a significant source of particulate matter in the atmosphere, and can have numerous environmental and socio-economic implications such as air pollution, impairment of driver vision, health impacts, and impacts to aesthetics. Road deterioration can increase because of loss of fines (i.e., <0.075 mm), since they act as road surface binders. This can lead to road safety issues, increased economic cost to vehicles and increased road maintenance needs. The use of dust suppressants has been shown to lower road maintenance requirements and associated costs as well as mitigate the environmental and health impacts associated with road dust.

There are numerous products/techniques that can be used for dust suppression. Various road salts make up the main chemical-based dust suppressants currently used in Canada. However, in 1995 road salts were placed on the Federal Government's Priority Substances List 2 for assessment to determine its toxicity under the Canadian Environmental Protection Act (CEPA). The science assessment concluded that because of the high releases around storage and snow disposal sites and through run-off and splash from roadways into soils, streams and rivers, road salts pose a serious threat to the aquatic environment, plants and animals.

There are several road salts that could be used as dust suppressants in Canada, for instance calcium chloride, magnesium chloride, potassium chloride and sodium chloride. The purpose of this report is to provide an overview of economic and environmental issues that relate to the production and use of calcium chloride as a dust suppressant. The focus of this study is on calcium chloride. However, economic and environmental data on other relevant chloride-based dust suppressants (i.e. magnesium chloride, sodium chloride, potassium chloride) is also provided where relevant data has been identified.

The main use of dust suppression products is to minimize dust emissions from unpaved roads and unpaved shoulders of paved roads. Loss of aggregate and subsequent road surface deterioration (e.g. ruts, potholes, and corrugations) with the loss of road surface fines results in dust generation. There are two major alternatives employed to achieve desired dust control results. The first general method to control dust generation is to apply good construction and maintenance practices on unpaved roads. The second general method is the application of chemical methods of dust suppression. Other methods of dust suppression include changes to speed limits, encouraging the use of alternative routes, restricting heavy traffic, paving roads, or changing the timing of road construction and maintenance activities (i.e., to occur during wet weather).

Seven categories of chemical dust suppressants have been identified and described in the report, specifically:

1. Chloride (e.g. calcium chloride and magnesium chloride) salts and brines. These chemicals are either mixed in place with the top few centimeters of surface material, or they are topically sprayed. Water-attracting chemical dust suppressants are recognized for providing the best combination of application ease, durability, cost, and dust control for semi-arid, semi-humid, and humid climates. They can have significant impacts on the reduction of dust (e.g. 30 to 80%) but require frequent re-application to maintain long-term dust suppression performance. Environmental impacts of chlorides include metal corrosion, degradation to nearby vegetation, surface water, groundwater and aquatic species.
   
   
2. Organic non-bituminous chemicals (which include lignosulfonates, sulphite pulp mill liquors, tall oil pitch, pine tar, vegetable oils, and molasses) adhere to the soil particles or physically bind the soil particles together to increase particle mass and cohesion. They tend to require frequent application. Environmental impacts include being sticky, odorous and visually unappealing. They are also slow to biodegrade, may contribute to deoxygenation of surface water (i.e., from spills) and may cause the road to becomes slippery when wet.
   
   
3. Petroleum-based binders and waste oils are insoluble and create a sealed surface on the road. They can be very effective. However, there may be significant sealed surface leakages associated with hazardous components that may contaminate surface and groundwater.
   
   
4. Electro-chemical stabilizers attract positively charged fine dust particles and bind ionically to them. They also expel adsorbed water from the soil and increase compaction. These stabilizers are considered environmentally acceptable, but vegetation does not easily establish on compacted sites where sulphonated petroleum products have been used.
   
   
5. Polymers, most effective in lightly trafficked surfaces, are composed of long-chained molecular structures. These dust suppressants can stick to more particles and bridge greater gaps between particles.
   
   
6. Enzyme slurries promote compaction, which reduces dust generation. They have been effective under highly specific trafficked surface and aggregate conditions.
   
   
7. Cementitious binders work by chemically and permanently binding soil particles together.

Total consumption of chloride-based dust suppressants in Canada is estimated at approximately 103 kt in 2000 (on a 100% basis). The majority of this consumption is calcium chloride, which is used across Canada. Smaller amounts of magnesium chloride are used as a dust suppressant, primarily in western Canada (i.e. 3 U.S. manufacturers of magnesium chloride are located in the western U.S.). Historically, liquid solutions of calcium chloride have generally been used as a dust suppressant. These liquid solutions typically contain 38% calcium chloride. Recently, the flaked form of calcium chloride has seen increased usage for dust control. The flaked form generally contains 78% calcium chloride (the rest moisture). Magnesium chloride is applied as a liquid, which contains approximately 28% magnesium chloride (the rest mostly water). Research conducted for this study did not identify the use of potassium chloride or sodium chloride as dust suppressants in Canada.

Source: Industry interviews, Statistics Canada, Cheminfo estimates.

There are three manufacturers of calcium chloride in Canada operating a total of 5 production facilities, namely: (i) General Chemical (2 facilities); (ii) Tiger Calcium (2 facilities); and (iii) Ward Chemical. Total annual capacity of these 5 production facilities is estimated at 480,000 flaked equivalent tonnes (480 kt) of calcium chloride, while annual production is estimated at 290,000 flaked equivalent tonnes (290 kt).

Source: Interviews with calcium chloride manufacturers.

The overall Year 2000 demand for calcium chloride in Canada is estimated at approximately 228 kt (on a flaked equivalent basis). Based upon discussion with industry sources, General Chemical's production is distributed 1/3^rd into dust suppression and 2/3^rds into road de-icing (and other uses). It should be noted that this allocation is highly variable and can change quite significantly from year to year, based upon weather conditions in the summer and winter. Ward Chemical on the other hand has estimated that in western Canada, there is 10 times the use of calcium chloride as a dust suppressant vs. its use for road de-icing.

Based upon this information, the demand for calcium chloride (on a flaked equivalent basis) as a dust suppressant in 2000 has been estimated at approximately 125 kt. On a 100% calcium chloride basis, it is estimated that 98 kt were used as a dust suppressant in 2000.

Note: Statistics Canada reports imports and exports in dry and solution form. Based upon input from industry sources, the quantity of solution was converted to dry form by applying a conversion factor of 0.38.
Source: Statistics Canada, Industry interviews.

In terms of magnesium chloride, Year 2000 domestic demand has been estimated at approximately 5.9 kt (on a 100% basis), which is somewhat lower than was experienced during the rest of the 1990's. The two largest end-uses for magnesium chloride are for dust suppression/ice control and as a chemical intermediate. Based upon research conducted for this study, it is estimated that 90% of Canadian consumption of magnesium chloride is for use as a dust suppressant (remainder is mostly consumed for ice control). Demand over the next decade is expected to remained largely unchanged.

Source: Statistics Canada, Industry interviews.

Calcium chloride dust suppressants are consumed across Canada, with the majority of consumption concentrated in central Canada. Ontario and Quebec are estimated to represent approximately 60% of the annual demand for these dust suppressants. The remainder is distributed among the Provinces/Territories, with B.C. consuming the next largest quantity. Magnesium chloride is only produced at three sites in the U.S. (no production in Canada), each of which is in the west. As a result, the small amount of magnesium chloride consumed as a dust suppressant in Canada is concentrated in the western Provinces. Most magnesium chloride is consumed in B.C. and Manitoba.

Note: quantity of calcium chloride and magnesium chloride is on 100% basis. Greater quantities are applied, which contain water and other ingredients.
Research conducted for this study did not identify the use of sodium chloride or potassium chloride in Canada for dust suppression. Source: Industry interviews, Cheminfo estimates.

There were no identified prohibitions on the use of chloride-based dust suppressants in Canada, the U.S. or Europe. Some individual jurisdictions have developed some minor restrictions with respect to the application of chloride-based dust suppressants. Ontario and Quebec are the dominant users of chloride-based dust suppressants in Canada. Currently, Ontario has prohibited only one dust suppressant, namely used oil, with another dust suppressant (Dombind - a lignosulfonate-based dust suppressant) scheduled to be prohibited later in 2002. Quebec has banned used oil as well as calcium lignosulfonate for use as a dust suppressant in the Province.