General characteristics of coal combustion residuals
Coal combustion residuals – also known as coal ash – are a byproduct of the coal combustion process that comes from left-over dirt from the coal mining process. Coal ash typically contains 55 percent silica, or sand, as well as calcium, iron, potassium and aluminum oxides and trace metal oxides.
In general, the elements that make up coal ash are very similar to the elements that make up Kentucky’s soils. The composition of coal ash can vary, depending on where it was mined and how deep it was located beneath the ground’s surface.