Looking for an outdoor ice-melter that works below zero and won’t harm trees and grass, I went to a Home Depot and was pointed to magnesium chloride. On the bag, it says that magnesium chloride is even used as a fertilizer. So what’s the downside to magnesium chloride? Why would people still buy rock salt (which doesn’t melt ice below zero, and which can harm foliage once the spring rains wash it off the driveway) or calcium chloride (which apparently can harm plants and irritate skin)?
Cost?
As far as cost is concerned, there’s this list of ice melters from Ace hardware[ul]
[li]Magnesium chloride, 50 pound bag, melts down to -25 F: $18.99[/li][li]Potassium Chloride (plus sodium chloride, urea, and “MG-104”), 50 pound, melts down to 0 F: $19.99[/li][li]Calcium Chloride, 50 pound bag, melts down to -25 F: $19.99[/li][li]Rock salt, 50 pound bag: $5.99. IIRC, sodium chloride only drops the freezing point a few degrees, so probably good for 27-30 degree temperatures. Almost definitely won’t get you to zero (unless you were talking celcius).[/li][/ul] So cost may be a factor, but IMO not a major one. An extra 25 cents a pound gets you a melting temperature (assuming I’m reading those stats right) over 50 degrees lower.
Now if someone can explain why the ten pound bags are more expensive than the 50 pound bag, I’d sleep better… {although demand is probably a factor, more home users would probably find the smaller size more convenient}
Cost is a big factor. Do you have any idea how much salt municipalities go through? (I remember moving to New Brunswick and reading an article about how the mayor of Doaktown’s brother stole most of the town’s salt supply using a fleet of trucks… and even small Doaktown went through tons and tons).
The disadvantages of magnesium would seem to be road burns (due to corrosion), increased potential for fires and power outages, and so forth.
http://www.usda.gov/rus/electric/engineering/2001/magnesium_chloride.htm
It may only be 25 cents more per pound, but given that rock salt is 12cents/lb that’s over 200% more expensive.
Indeed. Salt is used in such massive amounts there are serious concerns about it poisoning the groundwater in some areas. This study came up with number of 200g per square meter per year over 104 square km in the Toronto area. That’s something like 0.44lbs/1.2 square yards over a 40 sq. mile area in old money.
And venturing into what is for me advanced maths, I make that 20,800 metric tonnes of salt per year, or nearly 23000 short tons. Thats a lot of extra quarters!