(585c) Preparation of Geopolymers from Wastes
Geopolymers, an inorganic polymer composed of alumina and silica network with alkali metal ions, were prepared from wastes, such as incinerated ash of sewage sludge or fly ash from power plants. We have examined the effect of the initial compositions of the raw materials controlling the ratio of alumina, silica, and alkali in addition to the solid / liquid (water) ratios on the polymerization reactions of the geopolymer. In some cases, meta-kaolin and silica powder were added to adjust the target composition. We demonstrated the region where geopolymer is formed in a ternary diagram of which the three axes are fraction of silica, alumina, and alkali under a fixed solid /water ratio. The formation of geopolymers was confirmed by checking the hardening of the mixtures, and the solid product was characterized with XRD and BET measurements in addition to the strength tests. The surface area and the pore size distribution of the geopolymers greatly depended on the initial composition of the raw materials. In some cases, zeolites are formed: under the ambient temperature and pressure conditions. The surface area varied in the range of about 8.6 m2/g to 460 m2/g. We have found the surface areas of the geopolymers can be well correlated with the two ratios of silica / alkali and alumina / alkali.