Impact of oxidation and carbonation on the release rates of iodine, selenium, technetium, and nitrogen from a cementitious waste form

Recyclable Robust Plastic Scintillation Resin Achieving the Exceptional Separation and Detection of Technetium-99

Rapid detection and absorption of 99TcO4 ⁻ contamination in the environment are critical due to its high radioactivity, long half-life, and significant environmental mobility. Resins have been demonstrated effective bifunctional properties for both the detection and separation of 99TcO4 ⁻. However, the poor stability of these compounds limits their practical application. Here, a chemical grafting strategy is presented to synthesize ultra-stable plastic scintillation resin, in which 4-vinylpyridine and divinylbenzene are cross-linked as matrix polymer to withstand extreme conditions and a fluorophore "shield" to convert beta radiation into detectable signals. As expected, the as-obtained resin exhibits a high adsorption capacity of 549.2 mg g⁻¹ for 99TcO4 ⁻ with a rapid kinetic response of just 10 min as well as superior selectivity at 1000 times excess of interfering ions and full reusability. Moreover, it showed remarkable stability under 800 kGy, 3.0 mol L-1 HNO3 or 2.5 L solution continuous leaching, consistently maintaining high separation and detection efficiency after recycling 10 times. This strategy paves a new way to develop stable resin for the rapid capture and accurate measurement of 99TcO4 ⁻, which owns great potential for practical application.

Evaluating the impact of drying on leaching from a solidified/stabilized waste using a monolithic diffusion model

The release rates of constituents of potential concern from solidified/stabilized cementitious waste forms are potentially impacted by drying, which, however, is not well understood. This study aimed to identify the impacts of drying on subsequent leaching from Cast Stone as an example of a solidified cementitious waste form. The release fluxes of constituents from monoliths after aging under 100, 68, 40, and 15 % relative humidity for 16, 32, and 48 weeks, respectively, were derived from mass transfer tank leaching tests following EPA Method 1315. A monolithic diffusion model was calibrated based on the leaching test results to simulate the leaching of major and redox-sensitive constituents from monoliths after drying. The reduction in physical retention of constituents (tortuosity-factor) in the unsaturated zone was identified as the primary impact from drying on subsequent leaching. Fluxes of both major (i.e., OH^-, Na, K, Ca, Si, and Al) and redox-sensitive constituents (i.e., Tc, Cr, Fe, and S) from monoliths during leaching were well described by the model. The drying-induced reduction of tortuosity-factor and concomitant changes in porewater pH and redox conditions can significantly change the subsequent release fluxes of pH- and redox- sensitive constituents.