Cold sintering of strontium-adsorbed titanate adsorbents for stabilization and immobilization of secondary solid nuclear waste

The efficient immobilization of strontium-adsorbed titanates, a secondary radioactive waste from the Fukushima nuclear accident, is critical for post-accident remediation. This study presents cold sintering as a novel, one-step technique for stabilizing and immobilizing titanates for long-term disposal. In this study, sodium nonatitanate (SNT) powder was synthesized using a hydrothermal method, and the effects of transient liquid solutions, sintering temperature, uniaxial pressure, holding time on the densification of cold-sintered sodium nonatitanate (CS-SNT) were systematically investigated. The results indicate that interlayer water in sodium nonatitanate can serves as the transient solution. With optimal cold sintering conditions at 200 °C, 500 MPa, and 1 h, the relative density of Sr-SNT after cold sintering reaches 96.4 %. The sintered solidified matrix exhibited impressive mechanical properties, with a microhardness of 2.077 GPa and a compressive strength of 627 MPa. The leaching rate of the sintered solidified matrix after 14 days leaching experiments at 90 °C in deionized water was 7.1×10⁻⁷ g cm⁻² d⁻¹, showing that the solidified matrix had excellent chemical stability. The experimental results suggest that cold sintering might offers an effective, efficient, and environmentally sustainable method for Sr-SNT stabilization and solidification. This approach has the potential to advance practical technologies for managing and disposing of secondary waste from nuclear accidents.