Influence of fly ash fineness on cesium immobilization in geopolymers

The influence of fly ash (FA) fineness on cesium (Cs) immobilization in geopolymers was investigated by comparing samples synthesized in this study with those reported previously, as all samples were prepared at 95 °C with Cs contents of 2 and 5 wt.%. The effect of FA particle size distribution on physico-mechanical properties, gel structure development, and Cs leaching behavior was evaluated. Results show that FA fineness significantly affects the kinetics of geopolymerization and the development of mechanical properties. In general, Cs addition prolongs the setting time in G-FA, with longer setting times observed in G-FA based on coarser FA sample. These samples also showed lower compressive strengths, indicating that finer FA particles promote faster dissolution of aluminosilicate species and more rapid formation of the geopolymeric gel. Leaching behavior revealed that Cs release is diffusion-controlled regardless of FA fineness and Cs content, but the mean leachability index (Lmean) was lower in samples based on coarser FA particles, although in all cases it was higher than 9, which indicates effective Cs immobilization and satisfactory long-term stability of the material. Overall, FA fineness influences geopolymer reactivity, gel structure, and thus mechanical performance and effectiveness of Cs immobilization