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Difference between revisions of "How salt works and overview of deicing chemicals"

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===Carbohydrates===
 
===Carbohydrates===
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Carbohydrate-based deicers are often made from the fermentation of grains or the processing of sugars such as cane or beet sugar (Rubin et al., 2010). Small quantities of carbohydrates are sometimes used with other deicers. Alone carbohydrates do not aid in melting ice or snow; however, their use can help reduce the freezing point of ice further than salt and can help salt stick better to the road surface (Fortin et al, 2014; Rhodan and Sanburn, 2014).
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Carbohydrate-based deicers are often made from the fermentation of grains or the processing of sugars such as cane or beet sugar (Rubin et al., 2010). Small quantities of carbohydrates are sometimes used with other deicers. Alone, carbohydrates do not aid in melting ice or snow; however, their use can help reduce the freezing point of ice further than salt and can help salt stick better to the road surface (Fortin et al, 2014; Rhodan and Sanburn, 2014).
 
Carbohydrates are not corrosive to steel, and at high concentrations, carbohydrates can act as a corrosion inhibitor for salt brines.  
 
Carbohydrates are not corrosive to steel, and at high concentrations, carbohydrates can act as a corrosion inhibitor for salt brines.  
  

Revision as of 16:52, 10 March 2016

File:Ice melting from road salt.png
Deicers lower the freezing point of water, resulting in melting of ice when weather conditions are favorable.

Winter weather conditions in Minnesota can cause icy roads and walkways, leading to dangerous conditions for drivers and pedestrians. In order to combat this situation, municipalities, businesses, and individuals often employ the use of deicers. A deicer is a substance that melts or prevents the formation of ice, and does so by lowering the freezing point of water and preventing a bond between ice and paved surfaces. Sodium chloride for example, which is one of the most commonly used deicing agents, can be used to reduce the freezing point of water to 15°F (Local Road Research Board, 2012). A study by Marquette University found that deicing roads with salt reduces accidents by 88 percent and injuries by 85 percent (Kuemmel and Hanbali, 1992).

While deicers have the ability to greatly improve road and walkway safety, they can also have negative effects on the environment and surrounding infrastructure. Once applied, deicers dissolved in the melting snow and ice are carried away with runoff to surface and/or groundwater. In addition, some deicers are corrosive and will negatively impact roads, bridges, and other structures, as well as automobiles. Efforts are underway to minimize these environmental and infrastructure impacts, including optimizing deicer application and using of alternative deicing chemicals. Despite these negative effects, the benefits of deicers to public safety ensures they will be utilized for years to come.

The Iowa Department of Transportation prepared a winter maintenance training series that includes a video titled How Deicing Chemicals Work.

Overview of Deicing Chemicals

Several different types of deicing chemicals exist. Those covered in this section include chloride-based deicers, acetate-based deicers, and carbohydrates. A list of the chemicals approved for use by the MNDOT can be found here.

Chlorides

The chloride-based deicers discussed in this section are sodium chloride (NaCl), magnesium chloride (MgCl2), and calcium chloride (CaCl2). In general, chloride-based deicers are the least expensive deicers on the market.

Sodium Chloride. Sodium chloride is the most common deicer used in Minnesota and across the U.S. (Sleeper, 2013). In the Twin Cities Metro Area (TCMA) alone, it is estimated that 349,000 tons of sodium chloride is used each year (Sander et al., 2007). Sodium chloride is usually sold as a solid, though it can be purchased as a pre-wetted or brine solution. The lowest practical melting temperature is 15°F (Local Road Research Board, 2012).
Magnesium Chloride. Magnesium chloride can be purchased as either flakes, pellets, or a liquid, and is often wetted and added to sodium chloride to help improve deicing performance. Magnesium chloride’s lowest practical melting temperature is -10°F.
Calcium Chloride. Calcium chloride can be purchased as either flakes, pellets, or as a liquid, and is often wetted and added to sodium chloride to improve deicing performance. Its lowest practical melting temperature is -20°F (Local Road Research Board, 2012). Calcium chloride is also corrosive.

Acetates

Acetate-based deicers are often used in areas where the use of chloride-based deicers is limited. Acetate-based deicers include calcium-magnesium acetate (CMA), potassium acetate (KAc), and sodium acetate (NaAc). Much of the information provided here is based on studies and experiences using CMA.

Advantages of acetates include the following.

  • Marginally corrosive to steel (Fortin, et al 2014).
  • Biodegradable (Local Road Research Board, 2012)

Disadvantages of acetates include the following.

  • Reacts with and corrodes zinc so it would affect galvanized steel (Fortin, et al 2014).
  • Potentially results in anoxic conditions as they break down (Levelton Consultants Ltd., 2008).
  • Requires more material relative to salt to get comparable ice melting. An extra 20 to 70 percent more by weight is estimated to be needed (NRC, 1991).
  • Does not perform as well as chloride based deicers at temperatures below -5°C during heavy snowfall and freezing rain events (NRC, 1991).

Acetates include the following.

  • Calcium-magnesium acetate (CMA). CMA is probably the most common acetate-based deicer. It can be purchased as either a powder, crystals, pellets, or liquids. CMA has a lowest practical melting temperature of 20°F (Local Road Research Board, 2012).
  • Potassium Acetate (KAc). KAc is usually purchased as a liquid and has a lowest practical melting temperature of -15°F (Local Road Research Board, 2012).

Carbohydrates

Carbohydrate-based deicers are often made from the fermentation of grains or the processing of sugars such as cane or beet sugar (Rubin et al., 2010). Small quantities of carbohydrates are sometimes used with other deicers. Alone, carbohydrates do not aid in melting ice or snow; however, their use can help reduce the freezing point of ice further than salt and can help salt stick better to the road surface (Fortin et al, 2014; Rhodan and Sanburn, 2014). Carbohydrates are not corrosive to steel, and at high concentrations, carbohydrates can act as a corrosion inhibitor for salt brines.

There is evidence that the use of carbohydrates in the United States is increasing. For example, sales of a beet based product called Beet Heet were around 900,000 gallons at the end of the winter season in 2013. By February of 2014, 1.5 million gallons of Beet Heet had been sold. The Morton Arboretum in Lisle, Il uses beet juice in their deicers. The beet juice additive has minimal environmental affects, and helps the salt stick where applied. With the addition of beet juice, the arboretum is using nine times less salt, and saving an estimated $14,000 in material costs (The Morton Arboretum, 2014). Another unconventional additive that has been used is cheese brine. Wisconsin has used a cheese brine in at least six counties in the state (Rodan and Sanburn, 2014).

Fu et al. (2012) looked at two beet molasses-based deicers in comparison with a salt brine deicer. When used as a prewetting material, there was no statistically significant difference between any of the chemicals. When used as an anti-icing material, the organic material performed 30% better.

Summary

Table summarizing of properties of deicing agents. Adapted from Local Road Research Board, 2012, Ketcham et al., 1996 and Levelton Consultants Ltd., 2008.
Link to this table

Category Type Lowest Practical Melting Pavement Temperature Potential for corrosion impairment3 Environmental Impact
Atmospheric Corrosion to Metals Concrete Matrix Concrete Reinforcing Water Quality/Aquatic Life Air Quality Soils Vegetation
Chloride Based Deicers Sodium Chloride 15°F High; will initiate and accelerate corrosion Low/moderate; Will exacerbate scaling; low risk of paste attack High: Will initiate corrosion of rebar Moderate: Excessive chloride loading/metals contaminants; ferrocyanide additives Low: Leads to reduced abrasives use Moderate/High: Sodium accumulation breaks down soil structure and decreases permeability and soil stability; potential for metals to mobilize High: Spray causes foliage damage; osmotic stress harms roots, chloride toxicosis
Calcium Chloride -20°F High; Will initiate and accelerate corrosion; higher potential for corrosion related to hydroscopic properties Low/moderate; Will exacerbate scaling; low risk of paste attack High: Will initiate corrosion of rebar Moderate: Excessive chloride loading; heavy metal contamination Low: Leads to reduced abrasives use Low/Moderate: Improves soil structure; increases permeability; potential for metals to mobilize High: Spray causes foliage damage; osmotic stress harms roots, chloride toxicosis
Magnesium Chloride -10°F High; Will initiate and accelerate corrosion; higher potential for corrosion related to hydroscopic properties Moderate/high: Will exacerbate scaling; risk of paste deterioration from magnesium High: Will initiate corrosion of rebar, evidence suggest MgCl2 has the highest potential for corrosion of chloride produces Moderate: Excessive chloride loading; heavy metal contamination Low: Leads to reduced abrasives Low/Moderate: Improves soil structure; increases permeability; potential for metals to mobilize High: Spray causes foliage damage; osmotic stress harms roots, chloride toxicosis
Acetate Based Deicers Calcium Magnesium Acetate 20°F [1] Low/moderate; Potential to initiate and accelerate corrosion due to elevated conductivity Moderate/high: Will exacerbate scaling; risk of pate deterioration from magnesium reactions Low; probably little or no effect High: Organic content leading to oxygen demand Low: Leads to reduced abrasives use Low/Moderate: Improves soil structure; increases permeability; potential for metals to mobilize Low: Little or no adverse effect; osmotic stress at high levels
Potassium Acetate -26°F [2] Low/moderate; Potential to initiate and accelerate corrosion due to elevated conductivity [3] Low; probably little or no effect [4] High: Organic content leading to oxygen demand Low: Leads to reduced abrasives use
Sodium Acetate 0°F [5] Relative aquatic toxicity: high
Carbohydrates Beet Juice NA Low; Potential to initiate and accelerate corrosion due to elevated conductivity clams of mitigation of corrosion require further evaluation Low; Probably little or no effect Low; Probably little or no effect; claims of mitigation of corrosion require further evaluation High Organic matter leading to oxygen demand; nutrient enrichment by phosphorus and nitrogen; heavy metals Low: Leads to reduced abrasive use Low: Probably little or no effect; limited information available Low: Probably little or no effect
Molasses NA
Corn Syrup NA



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