Recovering and Recycling Landfill Fly Ash

Coal-fired power plants in the United States generate about 75 million tons of coal ash annually. Compared with the 267 million tons of trash that Americans generate per year, it makes sense to find alternative uses for coal ash to keep landfills from being overwhelmed with this residual matter.

On the plus side, approximately fifty-eight percent of the coal ash generated in 2018 was recycled. One way to do that is to use it in the production of concrete. Long before portland cement was invented, the Romans used a mixture of volcanic ash mixed with lime to create a very effective kind of concrete. Using fly ash from coal-fired power plants creates a similar chemical reaction when used in the production of concrete, which makes it a suitable substitute for cement substitution. The significance in keeping fly ash out of landfills is huge, but there’s more to the environmental equation.

When portland cement cures, it leaves behind some of the hydrated lime that is added with water to create a binding agent. When fly ash is used in place of cement, it allows the lime to cure as well, contributing to added strength and durability of hardened concrete in comparison to cement alone.

More importantly, it significantly reduces the amount of energy needed to produce portland cement. Nearly a ton of carbon dioxide is emitted in the production of a ton of portland cement, while fly ash is already combusted and therefore does not release additional CO2 upon being used in concrete. For each ton of cement replaced by fly ash in a concrete mixture, a ton of carbon dioxide emissions is avoided.

So, not only does recycling fly ash help to keep landfills from being overburdened, it also reduces the amount of energy needed to produce concrete as well as the amount of carbon dioxide released into the atmosphere during the concrete production process.

The key to the strength and durability of building products made with fly ash is to reduce its carbon content and control its quality. The ST Equipment & Technology’s triboelectrostatic belt separator can remove residual carbon coal char and generate a high quality consistent processed fly ash product, ProAsh®, a valuable material for concrete producers.