Physical barrier effect of geopolymeric waste form on diffusivity of cesium and strontium

Cesium and Strontium Retentions Governed by Aluminosilicate Gel in Alkali-Activated Cements

“…Previous studies dealing with the leaching behavior of cesium and strontium from alkali-activated cements commonly reported significantly higher leaching resistance in comparison with Portland cement-based matrix [21,22,24,25]. A recent study conducted by the authors showed that the higher leaching resistance of cesium or strontium was found to be attributed to the physical barrier effect of alkali-activated fly ash to some extent, while the chemical aspect may govern the immobilization capacity [24].…”

“…A recent study conducted by the authors showed that the higher leaching resistance of cesium or strontium was found to be attributed to the physical barrier effect of alkali-activated fly ash to some extent, while the chemical aspect may govern the immobilization capacity [24]. In the present study, the performance of the fly ash-based binder (S0) during the immobilization of cesium was the most outstanding, while that of the fly ash/slag blended binder was middling among the three binder systems.…”

“…The alkali-activator used for the fly ash/slag blended binder was composed with a mixture of a 4 M NaOH solution and a sodium silicate solution at a weight ratio of 2:1. The activators used in this study were determined from a former work conducted by the authors, considering reaction degree and mechanical properties of the materials [24]. …”

“…Initial works on the application of alkali-activated cements for the immobilization of radioactive waste reported promising results [20,21]. Further research has thereafter pioneered to correlate the characteristics of alkali-activated cements with its performance in the immobilization of radionuclides [22,23,24,25]. Previous studies focusing on the leaching behavior of various cationic contaminants from alkali-activated cements based on fly ash or metakaolin validated the effectiveness of alkali-activation to immobilize various radionuclides such as Ba, Sr, As and Se [23].…”

“…Shi and Fernández-Jiménez [25] reported that the immobilization mechanism of alkali metals such as Li, Na, K, Rb and Cs is that these metals balance the charge in the alkali-activated cement. Similarly, a recent study conducted by the authors showed that the diffusivity of cesium and strontium was significantly lower in alkali-activated fly ash-based waste forms than that in a Portland cement-based waste form [24]. However, previous studies are particularly lacking in a clear understanding of the retention mechanism of alkali-activated cements, especially in chemical aspects.…”