Salt treatment for icy streets
If you ever wonder why some trucks are spreading big rocks of salt on the streets during winter and not on food, I have to tell you that salt has more abilities than making food yummy. Salt can make ice melt. You can try it yourself if you take some salt from the kitchen and put it on some ice cubes. Soon you will see that it melts even if you keep it inside the freezer! But do you know how it works?
Water starts freezing at 0°C (32°F). But there is always a little water inside the ice. From the outside, it could look like a solid ice cube. But you can’t see that its water is continuously freezing at the same rate ice is melting. You can notice that on a warm winter day. The snow is getting moister the closer it gets to its melting point of 32°F, but it won’t melt completely. On very cold days, more water is turned into ice and the snow feels drier. Scientists say ice and water are in a state of balance.
Salt interrupts this continuous melt and freeze process because it can dissolve in water. Salty water freezes at a lower temperature than normal ice – or salted ice will continue to melt. That’s why we call it lowering the freezing point, or melting point. Once ice melts, its water will dissolve more salt, and the fresh salty water will melt the remaining ice till it’s all gone.
But salt has its limits. The colder it gets, the less water will be inside an ice crystal. Therefore, more salt is needed to keep the water from freezing. At around 0°F, there is no balance between ice and water anymore – all water is frozen. Salt (natrium chloride) won’t have any effect at this temperature. Instead, other salts are used, like calcium chloride and magnesium chloride. They are able to melt ice even in very low temperatures.
The use of salt has huge side effects on the environment. During thawing, melting ice will flush the salt into the soil. Some plants will suffer or even die if the concentration gets too high. You don't like your spaghetti either if it's too salty, right? Eventually, salt will get into the rivers and lakes and affect fish or other animals. Your cat or dog can suffer too. Their sensitive paws could have small wounds that won’t heal because salt from the streets got in there. And finally, cars and bikes will get damaged too. Did you noticed all the cars with rust holes or do you have a corroded bicycle chain like my poor bike? It’s caused by salt.
Because no one likes the side effects, some smart people invented alternatives. Salt free de-icing methods can use organic compounds like Urea. It melts ice very well and won’t have the side effects of salts. Well, but they do have other side effects, but that's another topic…