## 3 Results and Discussion  
### Characterization of the Synthesized Compounds Containing Chlorides  
The obtained X-ray diffraction patterns of the samples after solidification of spent electrolyte imitator are shown in Figure 1. It was found (Figure 1a) that the main crystalline phase of the MPP compound is the target matrix phase of the composition MgKPO\({}_{4}\cdot\)6H\({}_{2}\)O-K-struvite analog (Phase #1, main reflexes at 4.25 and 4.13 A). The MgO phase (Phase #2, periclase, main reflexes at 2.11 and 2.43 A), which is associated with an excess of used MgO relative to the stoichiometry of the reaction of the formation of MPP matrix [28], and the MgHPO\({}_{4}\cdot\)3H\({}_{2}\)O phase (Phase #3, newberyite, main reflexes at 3.04 and 3.46 A), which is formed in the reaction of Mg(H\({}_{2}\)PO\({}_{4}\))\({}_{2}\) with MgO in water solution [29], are also present in the MPP compound. It was shown that lithium and cesium are present in the compound as components of low-soluble phosphates, for example, cesium-MgCsPO\({}_{4}\cdot\)6H\({}_{2}\)O (Phase #4, main reflexes at 5.40 and 3.44 A), indicating the replacement of potassium ions with cesium in the matrix structure, while lithium-Li\({}_{3}\)PO\({}_{4}\) (Phase #5, lithiophosphosphate, main reflexes at 3.99 and 3.82 A). This is confirmed by the presence of the KCl phase (Phase #6, sylvitle, main reflexes at 3.15 and 2.23 A) in the compound, which was also noted earlier in the immobilization of CsCl in the MPP compound [18]. It was found that the NAFP glass samples are homogeneous and amorphous (Figure 1b), which indicates a high resistance of this glass composition to crystallization. Ceramics based on bentonite clay represent polyphase materials with the following main observed phases (Figure 1c): KAlSi\({}_{3}\)O\({}_{8}\) (Phase #7, orthoclase, main peaks at 3.31 and 3.77 A), LiAlSi\({}_{3}\)O\({}_{8}\) (Phase #8, main peaks at 3.47 and 3.89 A), SrAl\({}_{2}\)Si\({}_{2}\)O\({}_{8}\) (Phase #9, main peaks at 3.27 and 3.22 A). Additionally, some minor phases ((Na,K)AlSi\({}_{3}\)O\({}_{8}\), CsAlSiO\({}_{4}\), CsAlSi\({}_{2}\)O\({}_{6}\)) can present in the samples as it was shown in [17]. Thus, it can be suggested that fission products (primarily cesium and strontium) enter the crystal lattice of ceramics based on bentonite clay, that improves the immobilization (fixation) of RW in the samples. SEM micrographs of the surface of the obtained materials containing spent electrolyte imitators are shown in Figure 2. It was noted that the MPP compound consists of several phases, in which elemental composition based on the results of EDS analysis is presented in Table 1. It was found that the main phase consists of the main matrix components Mg, K, and P (Phase #1, Figure 2a, Table 1). Light inclusions contain cesium up to 2.5 at% (Phase #2, Figure 2a, Table 1), which partially replaced potassium in the matrix. The KCl phase (Phase #3, Figure 2a, Table 1) was detected in the sample, which confirms the XRD results (Phase #6, Figure 1a). It was found that the fission products form low soluble phosphate compounds, and there are some particles containing significant amounts of phosphorus and lanthanum of about 21.4 and 10.9 at%, respectively (Phase #4, Figure 2a,b, Table 1). Crystalline phase formation was not detected on the surface of NAFP glass (Figure 2c), which confirms the XRD results of the glass homogeneity and amorphousness (Figure 1b). The data on the elemental composition of the studied samples are presented in Table 2. It was found that the quenched samples are represented by a glass phase that coincides in composition with the calculated content in terms of the main structure-forming components. The inclusion of silicon oxide up to 1.2 wt% in the composition of the obtained samples was found, which is due to the synthesis of glasses in quartz crucibles. The elemental composition and the degree of chloride inclusion in glasses were confirmed by XRF. It is shown that about 35% of the introduced amount of chlorides is included in the glass composition.