Making cement from a different type of rock could clean up emissions

Cement production alone currently accounts for about 8 percent of global CO 2 emissions, so considerable effort is going into lowering that number. Efficiency can be increased, and energy sources can be swapped for cleaner ones, but a stubborn reality remains: The byproduct of turning limestone into lime during cement production releases CO 2 gas. These “direct process emissions” are actually slightly larger than the emissions from burning fuel to heat the kilns and drive this process.