Topics: Water, Sodium chloride, Salt Pages: 7 (2553 words) Published: May 22, 2013
“Road salt” is a common term used for some chloride salts, including sodium chloride (NaCl), which are used as de-icing agents on roads. The application of these de-icers on roads and other impervious surfaces in North America during winter months was in practice since the 1960s. The amount of snow fall is so high in these areas that snow and ice management becomes very essential to prevent road accidents, to maintain a continuous flow of traffic and to ensure safe pedestrian travel during winter months. Sodium chloride is the most commonly used de-icing agent (Road salting). Sometimes, it can be used along with some anti-caking agents like sodium hexacyanoferrate (II) or sand and grits. These elements like sodium, chloride, ferrocyanide and other impurities seep into our environment when the snow or ice melts, and poses a threat to water bodies, soil, vegetation and large number of species sustaining on them (Environmental, Health and Economic Impacts of Road Salt). De-icing of the roads is, beyond a doubt, very essential, as it saves lives by preventing accidents, but there are more alternatives other than the use of road salt which I will also explain. This research paper explains how road salt acts as a de-icing agent and what factors promote its widespread use. The primary aim of this paper is to give an elaborate idea about how road salt damages our environment. It also provides a list of some safer alternatives which can be used for de-icing. Road salt does not allow the ice or snow to adhere to the pavement and form a hard pack. Sodium chloride can readily depress the freezing point of ice, so that the ice starts melting. Salt crystals can pull water molecules from ice crystals to form brine. The formation of brine facilitates the process of meting of ice. However, the rate of melting depends upon the temperature at that time. At temperatures below 15° F, sodium chloride cannot form solution efficiently; hence its efficiency is reduced. In fact, even if sodium chloride is applied at high rates at these temperatures, it cannot melt snow or ice effectively. Hence, people involved in road management should acquire knowledge about the current and expected temperatures (Road Salt and Water Quality, 1). Sodium chloride also prevents the formation of ice on roads. Depending upon the conditions, road salt is applied as either liquid or solid medium. When compared with other salts, sodium chloride is less expensive with an average cost of $50 - $60 per ton. Some other characteristics like easy availability and ease in handling and storage make it a more commonly used de-icing agent. Salt as such is non-hazardous to the environment and does not degrade to produce harmful substances. Problem of bio-accumulation is also not associated with sodium chloride. Addition of an anti-caking agent like sodium hexacyanoferrate (II) in low levels (below 100mg/kg), prevents the salt from caking, and makes it readily usable during the winter months (Road Salt and Water Quality, 1) (De-Icing & the Environment). When dissolved in melting ice or snow, road salt gets dissociated into 40 percent sodium ions (Na+) and 60 percent chloride ions (Cl-). Chloride settles down in the bottom of the water bodies because of its density and increased mobility. Chloride is completely soluble and mobile. At a concentration of 230 mg/l and above, chloride is toxic to aquatic life and affects vegetation and wild life. Chloride gets accumulated in the long run as no natural process can break it down or metabolize it. Chloride cannot be absorbed by the vegetation. Gradual accumulation of chloride has damaged many water bodies, by changing the taste of the water. On the other hand, sodium (Na+) ions are subjected to ion exchange. These ions can either bind to the negatively charged soil particles, hence altering the soil chemistry, or be taken up in biological processes. They promote the release of nutrients into the groundwater and surface water, hence affecting...
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