Microwave vitrification of simulated radioactively contaminated soil: Mechanism and performance

To explore the immobilization mechanism and effect of tetravalent actinides (one of the main sources of pollution) in the heavily contaminated soil, soil with different content of CeO2 (surrogate of An4+) were rapidly vitrified by microwave sintering. The phase, microstructure, element distribution, bonding state, density and chemical stability of the sintered matrix were studied. As the solution of CeO2 below 14 ​wt %, the samples exhibited a single amorphous phase and the distribution of Ce elements is relatively uniform. Si and Al mainly exist in the form of four coordination and this resulted in a huge spatial network structure. Moreover, the density of sintered matrix gradually increased with increased CeO2 content and the average leaching rate of Ce4+ was below 0.9 ​× ​10−5 ​g m−2 d−1 after 42 days. Soil with different content of CeO2 (surrogate of An4+) were rapidly vitrified by microwave sintering at 1300 ​°C in 30 ​min. Si and Al mainly exist in the form of four coordination and this resulted in a huge spatial network structure. Ce4+ were contained in this network structure. Moreover, 14 ​wt % of CeO2 can be loaded in the vitrified samples in a single amorphous phase and the average leaching rate of Ce4+ was below 0.9 ​× ​10−5 ​g m−2 d−1 after 42 days. [Display omitted] •Simulated radioactively contaminated soil is treated by microwave sintering.•Crystallization occurs in the solid matrix as CeO2 beyond 14 ​wt %.•Ce4+ is contained in a three-dimensional network structure of glass.•The vitrified soil matrix performs reliable chemical durability.