Thermochemical treatment of fly ash for synthesis of mesoporous activated carbon

A mesoporous activated carbon is produced from oil fly ash (OFA) using chemical and thermal treatments at different activation conditions. The ash samples were refluxed with a range of compositions of sulfuric, nitric, and phosphoric acids followed by thermal activation in a tubular reactor. The composition of the acids and the reaction temperature were optimized to yield mesoporous activated carbon with a high surface area and yield. Several characterization methods were used to study the surface characteristics, morphology, functional groups, phase transition, and adsorption. FTIR spectra show the existence of carboxylic and amine functional groups, which increase with increasing percentage of nitric acid. SEM spot analysis and EDX demonstrate that the carbon content increases from 77.4 to 95.7 % upon chemical treatment. Specimens treated with a mixture comprises of 3.6 mol L^-1 H₂SO₄, 6.4 mol L^-1 HNO₃ and 5.9 mol L^-1 H₃PO₄ and activated at 990 °C have a BET surface area of 375.7 m² g^-1 when compared to 4 m² g^-1 for the original OFA. The BJH adsorption pore distribution indicates an average pore size of 50 Å with a total mesopore volume of 0.2211 cm³ g^-1 (73.6 % of the total pore volume). Thus, waste OFA is a suitable raw material for the production of activated carbon.