Recycling of coal fly ash by ceramic processing

Coal fly ash was used as raw material for the preparation of ceramic materials by aconventional powder technology route. Powder compacts were made from as-received fly ash,from calcined fly ash and from powder mixtures having 90% of calcined fly ash plus a low-costmineral as additive (dolomite, CaCO3.MgCO3). The compacts were sintered in air attemperatures between 900 and 1300ºC for 2h.The effects of the processing parameters on the densification, microstructural developmentand properties of the ceramic bodies were investigated. The unburned carbon present in theas-received fly ash inhibited densification due to gas formation during firing, resulting in anincreased porosity. A maximum density of ~2.6 g cm -3 was achieved at a sinteringtemperature 1050-1100ºC, either for compacts prepared from 100 % calcined fly ash or forcompacts containing 10 wt% dolomite. The addition of dolomite caused the formation of anincreased amount of anorthite and of liquid phase. The density, thermal expansion coefficientand the modulus of rupture of the densest fly ash-based ceramic materials are identical tothose exhibited by some traditional ceramics used in civil construction.The present results indicate a convenient way to treat coal fly ash, transforming it intouseful ceramic products via a simple and cost effective powder technology and sinteringroute.