Forty-seven tons of mercury is emitted from coal combustion systems in the U.S. each year. Current technologies of remediating the flue gases are not able to economically capture much of the mercury because it is in an elemental form that is not readily removed by existing wet scrubbers or particulate matter systems. Prior work investigated gas phase interactions between chlorine and mercury and found that the reactions to form water soluble chlorine compounds with mercury were too slow to lead to oxidized forms that could be removed easily.

This mercury work builds on that previous work by investigating mercury-surface interactions for adsorption technologies to capture mercury at higher temperatures using a sorbent derived from paper waste. This work explores how Hg, HgCl, and HgCl₂ interact with the principle components of the novel sorbent: SiO₂, Al₂O₃, and CaO. Geometry optimizations were primarily done using the Harris approximation combined with the LDA, while higher level energies were computed with the GGA. Comparisons to the limited geometry data for representative surfaces shows good agreement between our calculations and those values. However, adsorption energies are nonexistent for the mercury species on these surfaces.

We find that mercury atom is adsorbed onto all three surfaces, but is generally physisorption. Much stronger bonds are formed to the surface when chlorine is present for all three surfaces. We also find that the mercury adsorption was reduced at elevated temperature, as one expects for exothermic phenomena. Throughout the work, we explored the importance of surface cluster models for predicting adsorption phenomena, specifically the cluster size and morphology, and those results show some non-intuitive trends. A particular challenge has been the treatment of amorphous surface systems reliably while keeping computational costs to a reasonable level. This challenge will intensify in our next work as an aggregate surface is constructed from the individual surfaces to simulate the complexities of the paper waste derived sorbent system.