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Functional forms of the unburned carbon present in six kinds of coal fly ashes have been examined mainly by the temperature-programmed desorption (TPD)/temperature-programmed oxidation (TPO) and laser Raman spectroscopy (LRS) methods. The carbon contents of the ash samples range from 0.4 to 4.1 mass%. The LRS analysis shows that the C consists of both amorphous and crystallized forms, and the proportion of the former is as large as 50-65 C%. Further, the TPD measurement exhibits that the C contains several types of surface oxygen species, such as carboxyl and lactone/acid anhydride groups, which can readily be decomposed into CO2 up to 700 °C to provide active carbon sites. The results of the TPD also indicate that the ashes have surface CaCO3, and most of this species can be converted to CaO and CO2 around 600-700 °C. Interestingly, there is a significant correlation between organic fluorine concentrations and carboxyl/lactone/acid anhydride groups or surface CaCO3 contents in the ash samples. It might thus be possible that the formation of organic F forms proceeds through gas-solid-solid interactions among HF (and/or F2) in flue gas, active carbon sites and surface Ca species produced around 600-700 °C downstream of coal-fired boilers.

We prepared a carbonaceous sorbent for Cr(VI) from the culm of Sasa kurilensis by dehydration with concentrated H 2 SO 4 . The removal of Cr(VI) by the sorbent was highly solution pH dependent and mainly governed by physicochemical sorption. The equilibrium data fit well in the Langmuir isotherm model and indicate the endothermic nature of the Cr(VI) sorption. The desorption experiments suggest that the Cr(VI) sorption is generally irreversible, owing to strong interaction of HCrO 4 -with the active sites of the sorbent.

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