Salt-free diet for highways|
We've left out some details, but that's The Why Files's version of a new recipe for improving winter traction on roads. One thing that's conspicuously missing from the recipe is the environmentally questionable and corrosive road salt.
The recipe is being developed at Michigan Technological University in Houghton. That's in Michigan's Upper Peninsula. And you can trust us, these folks know snow and ice.
And they also know that road salt pollutes lakes by introducing chloride, a breakdown product of sodium chloride and calcium chloride, the two common kinds of road salt. University of Wisconsin-Madison researchers reported last June that chloride levels in lakes near a major highway were seven times higher than that found in lakes away from the highway. Chloride allows toxic heavy metals in the soil to enter solution where they can poison living things.
In rust we trust
But road salt is cheap -- about $30 per ton, compared to $700 per ton for CMA. Since CMA is much less corrosive than salt, it's already used at airports. (Rusty planes, presumably, are worse than rusty-but-trusty autos.)
But if CMA could be produced from locally available waste, the economics might change drastically. That's the proposition behind a research project at Michigan Tech's Institute for Materials Processing.
The work, by Allison Hein, Kip Paxton and Jim Hwang, originated in a search for uses of agricultural waste. Since most organic materials can be fermented (devoured by microbes) to make acetic acid, the researchers looked for a large demand for acetic acid.
The road salt replacement CMA was an obvious candidate for examination, since it contains an acetate group, which can be made from acetic acid. The Michigan Tech folks realized that the calcium and magnesium could be made from waste dust from some limestone quarries.
The new de-icer would also contain ground-up colored glass, which would improve traction by adding a gritty substance so tires can "grab" on ice. Green and brown glass is collected for recycling, but it's harder to use than clear glass. (Already, Hein notes, ground glass is used to improve traction on roads in Alaska and Canada.)
From these wastes, the germ of a three-way winning recipe emerged. Ferment the agricultural or food wastes. React the acetic acid with the limestone dust. That would make cheap, local CMA. Then add ground-up glass, and spread it on roads.
A few questions remain. For example:
Does it work?
Still, this is preliminary, right? You got it. Although CMA is clearly superior in terms of corrosion, its environmental record is not perfect since it does seem to reduce dissolved oxygen levels in some wetlands.
And while the recipe is promising, not all stages in the production have been demonstrated. "We're virtually certain we can make it," says Hein, a metallurgist, but the Michigan Technology group hasn't actually made it using the waste-material recipe.
The new formulation is unlikely to gain acceptance until it's almost as cheap as road salt. Yet the price of salt is only part of the cost of keeping highways clear. If the other benefits of CMA entered the equation -- better markets for recycled goods, less garbage sent to landfills, less damage to cars, bridges, and ground and surface waters -- the recycled de-icer could become the next best thing in safe winter driving.
-- Dave Tenenbaum
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