Sodium Chloride, NaCl
Sodium chloride has been used as an ice-control chemical on
roads since early in the previous century. It is produced by three
processes:
- rock salt is mined by conventional hard rock mining equipment and techniques
- solar salt is produced by the evaporation of sea water and may contain only a small amount of impurities
- evaporated, solution or vacuum salt is a very pure form made by drying under vacuum the solution resulting from injection of water into deep underground deposits.
Most salt used for highway applications in the U.S. is rock
salt, though some solar salt is produced in several western states
and some is imported into the eastern states. Naturally occurring
rock salt is the mineral halite, which usually contains between
1 percent and 4 percent impurities, mostly gypsum, shale, dolomite
and quartz.
Brine is a solution of salt (Sodium Chloride-NaCl)
in water, which will be covered in Section 8 of this chapter.