Microstructural and sorption properties evolution on leached geopolymers for strontium decontamination

Geopolymers are promising materials to be used as strontium adsorbent in fixed-bed processes for nuclear wastewater decontamination. Nevertheless, geopolymer formulation parameters – SiO 2 /M 2 O, H 2 O/M 2 O molar ratios – influence microstructure and strontium sorption property evolution under water leaching. Increasing the SiO 2 /M 2 O ratio increases the geopolymer’s compressive strength (16 MPa to 35 MPa) and reduces silicon leaching in water (1.31 mmol.g −1 to 0.26 mmol.g −1 ). This resistance to leaching results from a silicon-richer structure, reinforcing hydrolysis resistance. An increase in H 2 O/M 2 O ratio reduces the material’s strength (59 MPa to 28 MPa), and increases leaching due to greater porosity. Then, water leaching lowers sorption properties of the geopolymers by releasing Al I V , which are exchange sites for cations. Nonetheless, the composition with the lowest Al I V concentration achieved the highest distribution coefficient (K D ) and fastest kinetics. This highlights the critical role of the silicon environment for optimal cation trapping, outmatch the total concentration of Al I V sites. • Increasing Si/Al ratio enhances strength and limits leaching due to more Si-O-Si. • High H 2 O/M 2 O ratio increases porosity, lowers strength, and raises leaching. • Leaching increases pore volume and reduces Al I V concentration. • Sorption capacity relies on optimal silicon environment, not just Al I V concentration. • Geopolymer with the lowest Al I V concentration exhibits greatest sorption properties.