When a coal mine shuts down, what's left behind is not pretty: vast pools of thick, black sludge containing toxic metals such as arsenic and mercury. Rory Cutaia, CEO of GreenFields Coal, sees gold in all that sludge -- mainly because it contains tiny bits of coal. Several companies have figured out how to extract coal from slurry, but GreenFields has gone one step further: It cooks up a binding agent that holds the pieces together so they won't crumble when handled. (GreenFields's briquettes, enlarged here for detail, are actually about 4 inches long.) Last year, GreenFields purchased the rights to an abandoned coal mine in Gary, West Virginia, and in December, the company broke ground on a $25 million plant adjacent to the slurry pond. Cutaia says the site contains more than 10 million tons of coal -- enough to keep the plant humming for 20 years.