Ice is great in a beverage or on a skating rink but we don’t want it on our streets. How do we melt it? Potassium acetate, sodium chloride, calcium chloride, magnesium chloride or urea will do the job. They all interfere with the formation of ice crystals and can be used to melt ice. They do, however, differ in effectiveness, potential harm to the environment and cost.
Sodium chloride, or common salt, is cheap and can melt ice down to about -20C. At lower temperatures salt can be mixed with "beet juice" which is actually the molasses left behind when sugar is produced from sugar beets. Mixing salt with beet juice allows less salt to be used which results in a "greener" process since salt can damage soil and vegetation, contaminate surface and ground water and speed up the corrosion of concrete and metals. Corrosion of metals is a process whereby the metal react with oxygen. This requires the transfer of electrons among substances and such transfer is facilitated by the presence of ions, such as sodium and chloride. Substances that dissolve to form ions in solution are called electrolytes and speed up the rusting process. That’s why cars in Canada rust and those in Arizona do not. That is also why airplanes not in use are stored in the Arizona desert.
Not all electrolytes speed up corrosion to the same extent. Potassium acetate is much more environmentally friendly than salt but is twenty times more expensive. Calcium chloride melts snow and ice much faster than sodium chloride, is less corrosive but does damage vegetation and wildlife. It also costs more than salt. Magnesium chloride is also less corrosive, but works only down to -15C and costs five times more than salt. Urea is non-corrosive, does not damage vegetation but only melts ice down to -4C. There is yet another issue with salt. It works more effectively if the grains can be prevented from clumping. To reduce caking, small amounts of sodium ferrocyanide are added. In the presence of sunlight, this can break down and release cyanide which can be washed into waterways and damage aquatic life.
Ethlylene glycol or propylene glycol are the substances used to de-ice airplanes because they are non-corrosive. These liquids are collected and recycled but some is inevitably lost to the environment. Obviously there is no perfect way to melt ice and snow. But not using these substances would result in loss of life. As with so many scientific issues, it is a question of evaluating risk versus benefit.
