Development of Low-Cost Functional Adsorbents for Control of Mercury (Hg) Emissions from Coal Combustion

A range of environmentally advantageous low-cost carbon materials, including pulverized fuel ashes (PFA) and chars derived from different waste streams, were examined as the potential sorbents for use in mercury capture by sorbent injection. The test results demonstrated large variations in mercury retention among the fly ash samples examined, with those generated from burning bituminous coals having the best performance in general. By and large, the mercury retention capacity of fly ash appears to be mainly determined by its unburned carbon content and, to some extent, also by the chemical and morphological properties of its mineral matter. For the char samples examined, it was found that those from the gasification of paper waste materials displayed the best performance. Without any further treatment, the wastepaper-derived char materials outperformed the benchmark Norit-Darco FGD carbon by a factor of 2, in terms of mercury retention capacities. Although steam activation and KMnO4 impregnation can both be used to improve the performance in mercury retention of the samples, the one-step KMnO4 impregnation was found to be much more effective, particularly for the PFA samples where steam activation could lead to lower rather than higher mercury capacities for the fly ashes. It should be noted, however, the presence of moisture at significant levels was found to be required for the KMnO4-impregnated sorbent samples to perform efficiently in mercury capture due to the chemistry involved.