With names like “boiler slag” and “bottom ash,” it’s no wonder that anyone who has ever heard of coal ash, or the coal combustion residuals (CCRs) produced from burning coal, assumes they are the basest forms of pollution. And they’re not entirely wrong; bottom ash is the burn-up matter that is too large to be carried up into the smoke stacks so it collects in the bottom of a coal furnace. Boiler slag is the glassy pellets that form in the bottom of coal stoves …
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