Computational and experimental studies of mercury adsorption on unburned carbon present in fly ash

Unburned carbon (UBC) present in fly ash has been shown to adsorb mercury. In this work mercury adsorption onto the surface of UBC particles was investigated by using both computational and experimental methods. The UBC surfaces were assumed to be similar to that of graphene (single-layer graphite). The theoretical predictions using the Hartree–Fock method found that the zigzag edge of the carbonaceous cluster (C25H9) used provides stronger forces to attract mercury compared to the armchair edge (C24H8), probably resulting in greater mercury removal from flue gases. The adsorption of mercury on the simulated UBC surface (C25H9) was found to be a chemical process, with the predicated adsorption energy of 288.632 kJ/mol at room temperature. Furthermore, as temperature increases the adsorption energy slightly raises. The experimental studies showed that decreasing the particle size of UBC particles resulted in higher mercury uptake. Increasing the bed length resulted in higher mercury uptakes. Particle size can affect the sorbent capacity, and in this study UBC particles with size ranging between 125 and 250 μm seem to be more effective for mercury adsorption.