Immobilisation of simulant nuclear-grade spent ion-exchange resins in alkali-activated cement: Fresh state properties of the cement matrix

This study evaluates the fresh-state properties of alkali-activated cements (AACs) for the solidification of nuclear-grade spent ion-exchange resins (SIERs), a challenging waste stream in the nuclear industry. The formulations assessed use blast furnace slag and fly ash as precursors and Na₂SiO₃ and Na₂CO₃ as alkaline activators, for the immobilisation of SIERs. Setting time, workability, rheology, and reaction kinetics are assessed to optimise the cementitious matrix for effective waste encapsulation.

The incorporation of higher ash content slows reaction kinetics of the cement, delays setting, and reduces viscosity and yield stress, while slag accelerates polymerisation, increasing viscosity. Na₂CO₃ activation promotes early calcium carbonate precipitation, leading to faster setting and higher viscosity, whereas Na₂SiO₃ maintains fluidity over time. Resin incorporation is the dominant factor affecting fresh-state properties, significantly delaying reaction kinetics and reducing viscosity and yield stress, attributed to chemical interactions between Ca²⁺ from the pore solution and boron compounds released from the resin. Maintaining a setting time below 24 h, AACs with >85% slag allow more resin content than Portland cement. Slower kinetics may improve the stability of the resin encapsulation by allowing it to adapt to deformations.