Strontium immobilization in alkali-borosilicate matrices prepared from industrial waste glass grit: Insights into hydraulic durability and microstructural alterations.

Strontium (Sr) was selected as a non-radioactive surrogate for the high-risk radionuclide Sr due to their environmental and chemical similarities, enabling the safe evaluation of long-term immobilization strategies. This study investigates the potential of alkali-borosilicate glasses (ABS) synthesized from industrial waste glass grit as a sustainable and durable waste form for Sr immobilization. The structural integrity and degradation behavior of Sr-loaded ABS glass samples were examined under short-term leaching and harsh conditions. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) revealed uniform surface morphology without microcracks and a homogeneous elemental distribution in both ABS and Sr-ABS samples. Sr incorporation resulted in increased non-bridging oxygen (NBO) sites, as identified through Fourier-transform infrared spectroscopy (FTIR), indicating enhanced structural disorder and effective immobilization within the glass network. X-ray diffraction (XRD) confirmed the amorphous nature of the materials. Thermal analyses showed increased glass transition and crystallization temperatures upon Sr addition, attributed to stronger Sr-O bonds replacing Si-O linkages, enhancing network rigidity. Radiological assessments demonstrated high structural stability under gamma irradiation, with ESR spectroscopy detecting limited defect formation. Sr addition mitigated the formation of radiation-induced defects such as elemental Na, thereby improving radiological resistance. Leaching experiments revealed partial elemental depletion and alteration layer formation on Sr-ABS particles, with FTIR indicating localized structural changes post-leaching. The cumulative leaching fractions of Sr, B, and Na were quantified, and the dominant leaching mechanism for each element was identified. A multivariate procedure was used to gain insight into the effect of the leaching temperature, initial pH and leaching time on the final pH of the synthesized simulant waste matrix and the concentration and normalized leaching fraction of the Sr and Na elements. The normalized leaching rate of Sr under optimal leaching conditions (pH 4, 25 °C, ∼23 h) was as low as 1.0 × 10 g m d, indicating effective retention of Sr within the alkali-borosilicate (ABS) glass matrix. For the simulated Sr-ABS matrix, Sr is leached via dissolution and a first-order reaction, while B and structural alkali Na are mainly leached via a first-order reaction. By repurposing industrial waste to create resilient glass matrices capable of immobilizing hazardous radionuclides, this research offers a low-cost, scalable, and environmentally responsible solution for reducing risks associated with radioactive waste. The findings contribute to disaster risk reduction efforts by enhancing the safety, durability, and sustainability of waste containment materials used in nuclear and environmental waste management.