Application of fly ash-based materials for stabilization/solidification of cesium and strontium

Coal fly ash, as a solid waste produced from coal-fired power plants, was recycled for synthesis of zeolite A and geopolymer which were used for stabilization/solidification of Cs⁺ and Sr²⁺ from aqueous solutions. Specifically, the sorption data was successfully fitted by kinetic and thermodynamic models. The microstructure changes of zeolite A after loading Cs⁺ and Sr²⁺ were explored using XRD, FTIR, Raman, TG-DTA, and N₂ adsorption/desorption isotherm. The solidification of the spent zeolites using geopolymer was conducted and evaluated. It was found that pseudo-second sorption mechanism was predominant and, according to the Boyd equation, film diffusion seemed to govern the sorption process. The maximum sorption capacities on Cs⁺ and Sr²⁺ based on Langmuir model were 2.12 and 1.93 mmol/g, respectively. During ion exchange with Cs⁺ and Sr²⁺, Cs⁺ was inclined to go through the window to occupy the position of eight-member ring, while the Sr²⁺ was more likely to replace the Na⁺ in the six-member ring, thereby easily leading to the different changes of zeolite structure. In addition, geopolymer could be a promising matrix for the treatment of radioactive waste because the leaching fraction greatly decreased after solidification by geopolymer. Therefore, the recycling of coal fly ash for radioactive waste disposal could achieve the concept of disposal waste with waste and recycling, which could greatly contribute to the sustainable development of society.