h i g h l i g h t sFly-ash acts as a blocking barrier for radionuclide cations diffusion. Fixation of the radionuclides is via -AlO 2 À /-SiO 3 À anions at the fly ash surface.A novel Sr 90 fixation mode via precipitation and adsorption to the fly ash is found.a r t i c l e i n f o a b s t r a c tIsrael produces $1.3 Mt/year of fly ash (FA), a byproduct of its coal-fired power plants. Due to increasing environmental regulations, these imported coals are processed to reduce the sulfur concentration ($0.6%). These processing methods result in a material that has an enriched alkali/alkali earth component with pozzolanic and basic properties (pH > 10.5). FAs are utilized worldwide, mainly as a cement additive for the construction industry. Recently, it was demonstrated that Class F FA can act as an excellent fixation reagent for acidic wastes from the phosphate or the oil regeneration industries. In the current work the potential utilization of Class F FAs as fixation reagents for low-activity radioactive waste from the nuclear industry was examined. Aqueous solutions containing radionuclide simulants: cesium (Cs + ), strontium, (Sr 2+ ), and cerium (Ce 3+, Ce 4+ ) were used as case studies with promising results. It is suggested that the primary fixation mechanism involves the aluminate/silicate anions at the FA surface. A novel experimental fixation approach utilizing the formation of carbonates is demonstrated and a new interaction mechanism is suggested based on the electrostatic interactions of the positively charged fine precipitates with the negatively charged FA surface.