Assessment of structural stability and leaching characteristics of phosphate-based geopolymer waste form containing radioactive spent ion exchange resins

Abstract

The use of hydrated waste forms, such as cement, for immobilizing radioactive spent ion-exchange resins (IERs) is unsuitable due to low waste loading, high leaching of radionuclides, and poor durability. Here, simulant spent IERs were immobilized by a phosphate-based geopolymer (P-GP) for the first time. The 7-day compressive strength of the P-GP waste form was inversely proportional to waste loading because the pore size of the P-GP waste form increased with increasing waste loading. The P-GP waste forms with 40 wt% spent IERs satisfied all of South Korea's waste acceptance criteria for compressive strength, thermal cycling, water immersion, and gamma irradiation tests. The leaching behaviors of Co, Cs, and Sr differed from those of alkali-activated materials, but the leaching index exceeded the criterion value of 6.0. The leaching mechanism was governed by the combination of surface wash-off and diffusion or solely diffusion. The P-GP waste form could play as a primary physical barrier against releasing radionuclides. In addition, the geopolymer waste form did not undergo significant structural changes after waste acceptance criteria tests, indicating that it can efficiently immobilize spent IERs. Our findings can contribute new insights into efficient waste form materials for immobilizing radioactive spent IERs.