Good Question: How Does Salt Melt Ice?

NEW BRIGHTON, MN. (WCCO) -- Until the temperature heats back up above freezing, you've likely been relying on a wintertime staple to keep your walkways clear of ice.

That made us wonder: How does salt melt ice? What other minerals do the trick? Good Question.

From your standard salt to pet-friendly mixes, and advanced mineral blends, melting ice has really become a science. There were about a dozen or more options at Beisswenger's Hardware in New Brighton.

"With our complete lineup, we have a product for everybody," said owner and manager Jim Newman.

"I don't even know what's in there, I just know it worked last year," said Rachel Kroll as she grabbed a bag to clear ice on her front steps.

How does salt melt ice? "Water normally freezes at 32°F, but when you add salt it then stays liquid down to like 15°F," said Dr. Andy Erickson, research manager at the University of Minnesota. "The salt dissolves into sodium and chloride and those are ions that are in the water."

That dissolved salt prevents water molecules from turning into ice and further melts the ice that's already formed around it, so long as it doesn't drop below 15°F.

"Below that temperature, it just can't overcome that process of solidification of the liquid water," Dr. Erickson said.

How long does salt work to continuously melt ice? As long as it stays above 15°F, it should continue to prevent ice from forming. The problem is as more ice melts, there's more liquid to dilute the salt, thus making it less effective.

If its cold stays below 15°F for several days, how can people ensure it melts? "You're gonna want to use probably the calcium chloride or the magnesium chloride, the upper-end stuff," said Newman.

Magnesium chloride is sold alongside the bags of salt at hardware stores is effective up to -10°F.

Calcium chloride goes further, working at -20°F. Those minerals are more expensive than your standard salt.

Sand and kitty litter won't melt ice, but they do provide more traction. Some municipalities will mix sand with a salt brine to treat roads.

"And what that does is it prevents the sand from freezing in the truck and also gives it kind of a sticky feel on the outside to stick to the roadway and provide grip for traffic," said Dr. Erickson.

Countries in Europe are trying a different approach to sand by heating it up with boiling water. "When it lands on the ice on the roadways, it melts into the ice a little bit and then freezes to create sandpaper on the roads," said Dr. Erickson.

Spreading salt out evenly, rather than in clumps or piles, makes it more effective at melting ice. Newman said doing so will also prevent possible damage to concrete.