Novel calcium silicate from fly ash for simulated seawater Sr²⁺ decontamination: efficient removal and stable...

In this study, a series of calcium silicate adsorbents were prepared using fly ash as the raw material via a dynamic hydrothermal process. These adsorbents were employed to address radioactive contamination caused by ⁹⁰Sr, a typical fission product resulting from nuclear leaks, and a comprehensive technical solution was developed that covers the entire process from radionuclide capture to safe disposal. The material structure was systematically analyzed through XRD, XPS, FT-IR, TEM, and N₂ adsorption-desorption characterization. Results revealed that as the Ca/Si molar ratio increased, the material gradually transformed from chain-like tobermorite to a layered intermediate phase, ultimately forming a disordered flocculent structure. This structural evolution was accompanied by a transition in adsorption mechanisms, shifting from predominantly surface complexation to interlayer ion exchange and ultimately to bulk coprecipitation. The adsorption mechanism primarily involves Ca²⁺-Sr²⁺ ion exchange, Sr²⁺ intercalation within the Si-O framework, and coordination with oxygen-containing functional groups (-C=O, C-O). The adsorption kinetics were well-described by the pseudo-second-order and intra-particle diffusion models, suggesting a chemisorption-controlled process. Immobilization experiments and permeability tests demonstrate the material's excellent long-term stable Immobilization capacity for Sr²⁺. All indicators meet environmental safety standards, showing promising application prospects in the remediation of seawater contaminated with radioactive strontium.