Understanding and mastering coal fired ashes geopolymerisation process in order to turn potential into profit (GEOASH)

The EU regulations are restrictive with regard to solid residues and waste management. Research efforts to develop satisfying solutions are thus necessary. The GEOASH project aims, on one hand, at producing new geopolymeric matrixes using the advantageous properties of fine particles extracted from (co)-combustion fly ashes for the long-term stabilisation of inorganic hazardous wastes and, on the other, at predicting technologies for the recycling of coal ashes into added-value products which could be integrated in manufacture processes, allowing a reduction of primary resources consumption. The new geopolymer matrixes produced at room temperature in moderate alkaline conditions display a compressive strength of 60-80 MPa that is not affected by the particle size of the starting fly ashes. High content of unburned carbon (10 %) in the fly ash inhibits the reactions. The higher the amorphous phases content in fly ashes the higher the polymerisation degree typical of the geopolymer framework. Additionally, fly ashes with a high SiO{sub 2}/Al{sub 2}O{sub 3} ratio require less chemical reagents to reach high compressive strength, reducing significantly the cost of the geopolymerisation. Considering the pilot plant tests performed with a semi-industrial mixer, it appears that the amounts of water and chemical reagents may be reduced at pilot plant scale without an appreciable sacrifice in the properties of the geopolymer solids. Despite the rather satisfying results obtained by the leaching tests applied to two multimetal wastes that are difficult to stabilise, such as the MSWI residues and arc furnace dust solidified/stabilised in fly ash-based geopolymer matrixes, further research is still needed. 43 refs., 44 figs., 49 tabs.