Abstract
Alkali-activated binders (AABs), as a promising alternative to Portland cement, are now being used on a commercial scale in various applications around the world, including hazardous and radioactive waste immobilization. In this paper, the leaching resistance, strength, and nanostructural alteration of alkali-activated blast furnace slag (AABFS) doped with 2 % and 5 % cesium were investigated. The addition of cesium caused a significant increase in the compressive strength of AABFS, followed by mild strength reduction after leaching. AABFS can be considered a potentially efficient matrix for cesium immobilization, since the mean leachability index in both cases (2 % and 5 % of Cs added) was above the threshold value of 6. Both doping with Cs and leaching caused the transformation of the AABFS nanostructure. The majority of the aluminum that was released from the C-A-S-H gel due to leaching remained within the AABFS matrix, initiating gel reconstruction: the C-A-S-H gel was converted to C-S-H gel, and an additional N-(C)-A-S-H gel was also formed. Cesium was preferentially associated with the N-(C)-A-S-H gel rather than with the C-A-S-H gel. The results of this research seem to be in good agreement with the Cross-linked Substituted Tobermorite Model (CSTM).
Highlights
Immobilization of low- and intermediate-level radioactive wastes in Portland cement has been practiced for many years due to the inexpensive and readily available materials involved, and the simple and low cost processing routes
The standard leaching test was performed without any stirring within a period of 5 days, where the leachate was completely replaced by fresh leachant after cumulative leach times of 2, 7, 24, 48, 72, Table 3 activated blast furnace slag (AABFS) paste composition and setting time
The concentration of Cs leached from AABFS has reached its peak after the first 24 h of testing in the case of AABFS doped with both 2 % Cs and 5 % Cs (Fig. 1a)
Summary
Immobilization of low- and intermediate-level radioactive wastes in Portland cement has been practiced for many years due to the inexpensive and readily available materials involved, and the simple and low cost processing routes. To improve the properties of a waste-containing matrix, its resistance to leaching of radionuclides, supplementary cementitious materials such as blast furnace slag, fly ash, metakaolin, and different types of clays or zeolites are blended with Portland cement for use in waste. AABs have been frequently studied, and to some extent applied, for immobilization of hazardous, toxic and nuclear wastes, contributing significantly to the available toolkit of materials that can be applied to protect the biosphere from further contamination (Lancellotti et al, 2015; Bernal et al, 2014)
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