Salt can be obtained from the earth or from naturally occurring saltwater.
Solution mining involves digging a well deep into an underground salt deposit, pumping in water to dissolve the salt crystals, and then drawing the brine back up to the surface. The process doesn’t produce much noise, airborne pollutants, or groundwater contamination. (The worst-case scenario would be a cave-in, although that’s highly uncommon.) The processing method —known as vacuum pan refining—is the most costly and energy-intensive way to make salt, but it creates a very pure product that’s nearly 100 percent sodium chloride.
Most of the salt for highway ice removal is instead obtained by physically mining it out of the earth in its mineral form.
Salt can also be obtained by solar evaporation, in which seawater (or briny lake water) is pumped into a series of large, shallow ponds and left to evaporate naturally. The process is very slow—it can take years—but it requires very little fossil-fuel input. With large-scale operations, wildlife issues may come into play, while ponds can provide sanctuary for certain wetland species, like flamingos and other birds. The liquid that remains after the solar evaporation process—known as bitterns— in large, concentrated amounts can be harmful to fish and other aquatic organisms. Washing and refining can be as energy-intensive as vacuum pan refining. But most gourmet sea salts are harvested from the evaporation ponds—sometimes with hand tools—and then treated very minimally before they’re packaged and sold. Friend of the Sea has developed Sustainable Sea Salt standards and it is in the process of developing standards for Sustainable Salt from solution mining.