Removing heavy metals in fly ash successfully

Flash joule heating can remove toxic heavy metals from fly ash so the amount of cement is reduced in concrete whilst improving its strength and elasticity.

Researchers at Rice University in the US have published a paper in Communications Engineering explaining their research. The experiment replaced 30% of cement used to make a batch of concrete with purified coal fly ash. It is reported that the strength of the concrete and elasticity were improved by 51% and 28% respectively.

And greenhouse gas and heavy metal emissions were decreased by 30% and 41% respectively. And lead author Bing Deng told the process could remove up to 90% of heavy metals without using water.

“We mix the fly ash with carbon black, because fly ash does not conduct electricity, and the carbon black makes the mixture conductive,” he explained. “Next, we place the mixture between two graphite or copper electrodes and use a capacitor to supply a short current pulse to the sample … [bringing] the sample temperature up to about 3000 degrees Celsius.”

The high temperature makes the heavy metals evaporate into a volatile stream that is captured. The method is highly efficient, according to the study’s authors, and for different metals like arsenic, cadmium, cobalt, nickel or lead, their removal was registered between 70% and 90% in one second.

Flash joule heating also worked on different coal fly ash compositions from various locations. Civil engineers tested the new concrete and found the compressive strength and elastic modulus of the composite increased significantly.

Image: (L-R): Wei Meng, Bing Deng, James Tour and Satish Nagarajaiah.

About the author

Desi Corbett

Desi is the Editor of Concrete in Australia and at the helm of our magazine for 8 years. She was behind the Institute's weekly news bulletins from 2016-2021 and is now writing our focused news items. Desi has been an engineering news and features journalist/editor across all disciplines since 2013 - part of a 30-year career writing for a wide range of industries.