This new technique could cut cement GHG emissions by 30%

Scientists at the Rice Lab have created a new method that could instantly cut the GHG emissions from cement production significantly.
Christopher McFadden
The new technique could dramatically reduce cement production's impact on the environment.


A new study has found a way to make cement production more sustainable by reducing its associated greenhouse gas emissions. This is important because the cement industry accounts for about 8 percent of the world's carbon dioxide emissions. To this end, James Tour, a chemist at the Rice lab, created a technique to remove hazardous heavy metals from coal fly ash, a byproduct of coal-based power plants used in concrete mixtures. Purified coal fly ash reduces the amount of cement required and enhances concrete quality.

The study showed that replacing 30 percent of the cement in concrete with clean coal fly ash made it 51 percent more robust and 28% more flexible. Moreover, it reduced greenhouse gas emissions by 30 percent and heavy metal emissions by 41 percent. The researchers utilized "flash joule heating," a rapid and water-free process, to remove up to 90 percent of heavy metals in coal fly ash, making it more suitable for infrastructure applications.

The process involves mixing fly ash with carbon black, which makes the mixture conductive, placing it between two electrodes, and supplying a short current pulse. This raises the temperature to about 5,432 °F (3,000 °C), which makes the heavy metals evaporate and be caught. The removal efficiency for various heavy metals ranges between 70 percent and 90 percent in just one second.

Flash joule heating works on different coal fly ash compositions, regardless of the coal's geographical origin. The method is effective for Class C and Class F coal fly ash and other hazardous wastes like red mud or bauxite residue, suggesting potential for large-scale industrial solid waste decontamination.

Clean coal fly ash is good for the environment and makes concrete more robust and durable. When 30 percent of the cement in concrete is replaced with clean coal fly ash, the material's compressive strength and elastic modulus go up a lot. This is important for structural engineering and the construction industry, as more robust structures can be built using less cement.

The process also lets heavy metals that have evaporated be put in a vacuum chamber to keep them from entering the environment. Additionally, the energy consumed during the process is relatively low, at about 532 kilowatts per ton. The life cycle analysis indicates that value can be extracted from waste materials.

The research is a big win for the environment because it cuts down on pollution without releasing heavy metals. You can read the study for yourself in the journal Communications Engineering.

Study abstract:

"Development of cementitious materials with low carbon footprint is critical for greenhouse gas mitigation. Coal fly ash (CFA) is an attractive diluent additive in cement due to its widespread availability and ultralow cost, but the heavy metals in CFA could leach out over time. Traditional acid washing processes for heavy metal removal suffer from high chemical consumption and high-volume wastewater streams. Here, we report a rapid and water-free process based on flash Joule heating (FJH) for heavy metals removal from CFA. The FJH process ramps the temperature to ~3000 °C within one second by an electric pulse, enabling the evaporative removal of heavy metals with efficiencies of 70–90% for arsenic, cadmium, cobalt, nickel, and lead. The purified CFA is partially substituted in Portland cement, showing enhanced strength and less heavy metal leakage under acid leaching. Techno-economic analysis shows that the process is energy-efficient with the cost of ~$21 ton−1 in electrical energy. Life cycle analysis reveals the reuse of CFA in cement reduces greenhouse gas emissions by ~30% and heavy metal emissions by ~41%, while the energy consumption is balanced, when compared to landfilling. The FJH strategy also works for decontamination of other industrial wastes such as bauxite residue."

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