# Removal of Cesium from Radioactive Waste Liquids Using Geomaterials
## 3 Results and Discussion
### Characterization of Geomeraterials  
The influence of the doped Cs on the crystal structure of the adhesive was investigated by XRD, and the results are shown in Figure 4. In the Portland cement binder, the addition of Cs did not cause the formation of a crystalline phase but led to the formation of [PERSON]'s salt, which was due to the sulfate ion in monosulfate (AFm) or ettringite (AFt) being replaced by a chloride ion. This indicates that the chloride ions from cesium chloride resulted in the formation of Friedel's salt [37; 38]. In the fly ash-based geomeraterials, the crystalline phases were mullite, quartz, coesite, hematite, and magnetite, that is, the non-reactive crystalline phase present in the original fly ash. The crystalline phase in the slag-based geomeraterials was similar to the fly ash-based geomeraterials, and the peak corresponding to C-S-H increased with increasing the slag content. No cesium-containing  
Figure 2: Effect of sorbent dosage on the adsorption of Cs by fly ash-based geomeraterials and slag-based geomeraterials.  
crystalline phase was observed, which is similar to the results of the Portland cement and the fly ash-based geomaterials.  
The SEM and element mapping of the geomaterial matrices are shown in Figure 5. From the SEM images, we can see the flocculated substance and crystal, among which the flocculated substance is amorphous silicon aluminate. The SEM images of the Portland cement and slag-based geomaterials show that the whole material structure is relatively compact, and the pores are small. The morphological characteristics of fly ash-based geomaterials is similar to that of [PERSON] [39], who used alkali slag-modified alkali to stimulate fly ash-based geopolymer gels, but the pores of the fly ash-based geomaterials are larger. The white sediment in the geomaterials may be formed by Cs, which is evenly distributed, and the location is not concentrated. It is important to note a negative correlation between  
Figure 4: XRD of some geomaterials before and after the incorporation of Cs. P: portlandite, H: hematite, Ma: magnetite, C: C–S–H, M: mullite, Q: quartz, Co: coesite, T: tricalcium silicate, D: dicalcium silicate.  
Figure 3: Adsorption capacity of fly ash-based geomaterials and slag-based geomaterials for Cs adsorption.  
Cs and Na can be found in the element mapping image. This correlation could be the evidence of the typical cation exchange reactions that occur in geotechnical materials, in which sodium zeolite or its precursor exchanges its charge-balanced cations. Specifically, molecular sieves or their precursors serve as adsorption sites where sodium is replaced by cesium [40; 41].  
Figure 5: _Cont._  
Figure 5: _Cont_.  
The specific surface areas of ordinary Portland cement, fly ash-based geomaterials, and slag-based geomaterials were measured by N\({}_{2}\) adsorption. The pore characteristics of the powder binder determined by the BET method are summarized in Table 2. These results indicate that the fly ash-based geomaterials had the highest surface area and micropore volume and that the pore characteristics of the fly ash-based geomaterials were the most suitable for the adsorption of Cs, which is consistent with the SEM results. This also indicates that fly ash-based geomaterials may be the most effective in terms of chemical barriers to prevent the release of cesium.  
Figure 5: SEM and element mapping images of the geomaterial matrices. (**A**) Portland cement, (**B**) fly ash, (**C**) slag.