Hydrothermal synthesis and sorption performance to Cs(I) and Sr(II) of zirconia-analcime composites derived from coal fly ash cenospheres published by Ural Federal University eISSN 2411-1414; chimicatechnoacta.ru ARTICLE 2022, vol. 9(4), No. 20229418 DOI: 10.15826/chimtech.2022.9.4.18 1 of 9 Hydrothermal synthesis and sorption performance to Cs(I) and Sr(II) of zirconia-analcime composites derived from coal fly ash cenospheres Tatiana A. Vereshchagina a* , Ekaterina A. Kutikhina a , Olga V. Buyko b , Alexander G. Anshits a,с a: Institute of Chemistry and Chemical Technology, Federal Research Center “Krasnoyarsk Science Center of Siberian Branch of the Russian Academy of Sciences”, Krasnoyarsk 660036, Russia b: Research Department, Siberian Federal University, Krasnoyarsk 660041, Russia c: Department of Chemistry, Siberian Federal University, Krasnoyarsk 660041, Russia * Corresponding author: vereschagina.ta@icct.krasn.ru This paper belongs to a Regular Issue. © 2022, the Authors. This article is published in open access under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract The paper is concerned with (i) the hydrothermal synthesis of hydrous zirconium dioxide (HZD) bearing analcime (HZD–ANA, zirconia-anal- cime) and (ii) its sorption properties with respect to Cs+ and Sr2+. The HZD–ANA particles were synthesized from coal fly ash cenospheres composed of aluminosilicate glass with (SiO2/Al2O3)wt.=3.1 and char- acterized by PXRD, SEM-EDS, STA, and low-temperature N2 adsorp- tion. The non-radioactive simulant solutions of different acidity (pH = 2–10) and Cs+/Sr2+ content (0.5–50.0 mg/L) were used in the work. The effect of synthesis conditions on the HZD–ANA particle size, zirconia content and localization as well as the sorption behavior with respect to Cs+ and Sr2+ (capacity, KD) were clarified. It was found that the small-sized HZD–ANA composites surpasses the Zr-free analcime and large-sized HZD–ANA material in the Cs+ and Sr2+ sorption param- eters (KD ~ 104–106 mL/g). The conditions to synthesize the zirconia- analcime composite of the highly enhanced sorption ability with re- spect to Sr2+ (KD ~ 106 mL/g) were determined. The high-temperature solid-phase re-crystallization of Cs+/Sr2+-exchanged HZD–ANA com- posites was shown to occur at 1000 °C, resulting in a polyphase sys- tem based on nepheline, tetragonal ZrO2, and glass phase. Keywords cenospheres hydrothermal synthesis zirconia-analcime composite Cs(I) and Sr(II) sorption radioactive waste Received: 10.10.22 Revised: 04.11.22 Accepted: 05.11.22 Available online: 10.11.22 1. Introduction The increased role of inorganic ion exchangers for treat- ment of radioactive waste solutions, both in nuclear power production and fuel reprocessing plants, is widely recog- nized [1, 2]. The sorption technologies being developed are aimed, first of all, at separation of heat-emitting fission products, such as 137Cs (T1/2 ~ 30 years) and 90Sr (T1/2 ~ 29 years) [3, 4], and long-lived actinides, e.g., Am (III), Cm (III), U (IV), Pu (IV) [5, 6]. In the context of the ultimate disposal of radioactive waste, the thermally treated inorganic ion exchangers loaded with radionuclides can function as primary mineral-like containment media in a multibarrier geological disposal system [1, 7]. From the point of view of radioactive waste minimiza- tion and reduction of a number of separation stages uti- lized, sorption technologies that simultaneously separate two or more radionuclides are of the greatest interest as compared with technologies that separate only one ele- ment. The management of different radionuclides together results in a single product, in which sorbed cations can ac- commodate in the only phase [8, 9] or be partitioned be- tween several phases [10]. The last immobilization option can be implemented us- ing composite sorbents based on the components differen- tiated by the affinity to certain radionuclides. Some compo- site sorbents for co-sorption of different cations, for exam- ple, alginate-encapsulated graphene oxide-layered double hydroxide beads [11], Al2O3–ZrO2–CeO2 composite material [12], poly-condensed feldspar and perlite-based sorbents [13], nickel-potassium ferrocyanide supported by hydrated titanium and zirconium dioxides [14], silica/ferrocyanide composite [15], synthetic nanocopper ferrocyanide-SiO2 materials [16], nano composite materials from biomass waste [17] were reported. http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2022.9.4.18 mailto:vereschagina.ta@icct.krasn.ru http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0003-4538-8902 https://orcid.org/0000-0002-8730-129X https://orcid.org/0000-0003-4671-4909 https://orcid.org/0000-0002-5259-0319 https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2022.9.4.18&domain=pdf&date_stamp=2022-11-10 Chimica Techno Acta 2022, vol. 9(4), No. 20229418 ARTICLE 2 of 9 Great capabilities for selective separation of metal cati- ons are inherent to zeolites, which are framework alumino- silicates with an open microporosity [18, 19]. The size of pore entrances imparts a molecular/ion sieve property to zeolites. In particular, analcime (ANA) having the minimal pore en- trances (d = 2.6 Å) compared to other zeolites displays an af- finity towards well-proportioned cations of actinides, lantha- nides, and heavy metals [20–22]. At the same time, due to the ion sieving effect, analcime has a poor Cs+ and Sr2+ sorp- tion capacity at 25 °C [23] but is capable to trap these cations under hydrothermal conditions at 250–300 °C [24]. The prospective single-phase ceramics proposed for ‘‘minor’’ actinide isolation are based on Zr-bearing mineral- like host phases including zircon, zirconia, zirconates, etc. [25, 26]. To implement the sorption approach to actinide immobilization, the Zr-based ion exchangers as precursors of Zr-bearing phases are to be used. The sorbent-precursor must be thermodynamically metastable to undergo the phase transformation in relatively mild conditions. High sorption ability and a developed porosity also facilitate crystallization of the sorbent due to the homogeneous dis- tribution of target radionuclides in the sorbent structure. These properties are inherent to the microporous/layered ion exchange materials synthesized under mild hydrother- mal treatment at 100–200 °C and autogenic pressure [27, 28]. The methods to synthesize hydrothermally nano-zirco- nia, zirconium incorporated micro/mesoporous silica, and zirconia-based nanocomposites were also reported [29−31]. Recently, the analcime based composite materials with hydrous zirconium dioxide (HZD) species embedded in a ze- olite analcime body (HZD-ANA) were synthesized hydrother- mally in an alkaline media using coal fly ash cenospheres as a Si and Al source and zirconium citrate, ammonium com- plex, as a Zr source [22, 32]. Variation of the synthesis con- ditions enables producing small-sized and large-sized ZrO2- analcime crystals of narrow size distributions with maxima at about 6 μm [22] and 40 μm [32], respectively. The thermal treatment of ZrO2-bearing analcime up to 1000 °C resulted in a powdered zirconia/nepheline/glass composite material [32] having a potential as a precursor of the chemically – mechanically –, and radiation – re- sistant nuclear waste form, in which sorbed actinides can accommodate in a tetragonal zirconia-based phase, and retained Cs+ and Sr2+ can be hosted by aluminosilicate- based or vitreous phases [33, 34]. Evaluation of sorption properties of the small-sized HZD–ANA particles with respect to Nd3+, taken as an imita- tor of actinides (III), demonstrated that the material traps Nd3+ cations from diluted solutions with a distribution co- efficient of about 105 mL/g and efficiency of up to 99.6% [22]. The Nd3+ sorption parameters obtained for HZD–ANA are comparable with ones determined for pure analcime. This fact testifies that, for the most part, analcime but not zirconia is responsible for Nd3+ sorption on the HZD– ANA composite. As for the Zr-bearing component, zirconia in a hydrous form is an effective ion exchanger with respect to both anions and cations, including cesium and strontium [2, 35–37]. So, the HZD–ANA material is expected to display the sorption properties also towards the Cs+ and Sr2+ cations. The present paper is aimed at (i) the hydrothermal synthe- sis of hydrous zirconia bearing analcime under varied condi- tions, (ii) the evaluation of its sorption properties with respect to Cs+ and Sr2+ as imitators of radionuclides 137Cs and 90Sr, and (iii) the demonstration of possibility to immobilize the sorbed cations of different nature in a single solid. The non-radioac- tive simulant solutions of different acidity (pH = 2–10) and Cs+/Sr2+ contents being close to the compositions of the actual radioactive wastewater were used in the work. 2. Experimental 2.1 Chemicals and materials The chemicals (sodium hydroxide; zirconium citrate, ammo- nium complex) used in this work were of reagent grade qual- ity. They were obtained from the commercial supplier (OOO “Reactiv”, Russia) and used without further purification. The cenosphere material (marked further as (SiO2–Al2O3)glass) was a product of separation of a coal fly ash cenosphere concentrate resulted from combustion of Kuznetsk coal (Russia) [38, 39]. The chemical and phase compositions (wt.%) of the initial cenosphere fraction were as follows: SiO2 – 67.6, Al2O3 – 21.0, Fe2O3 – 3.2, CaO+MgO+Na2O+K2O – 7.7; quartz – 3.4, mullite – 0.8, cal- cite – 0.5, glass phase – 95.4; (SiO2/Al2O3)glass – 3.1. The mi- crographs of the cenosphere globules are given in Figure 1. 2.2 Synthetic procedures The small-sized zirconia bearing analcime was synthesized in the ZrC6H7O7NH4–NaOH–H2O–(SiO2–Al2O3)glass system of the 1.0 SiO2/0.18 Al2O3/0.89 Na2O/0.15 ZrO2/65 H2O molar composition using zirconium-ammonium citrate as a Zr source and cenospheres as a Si and Al source. The reaction mixture was hydrothermally treated in a Teflon-lined stain- less-steel autoclave (“Beluga”, Premex AG Switzerland) at 150 °C and autogenoius pressure for 48–96 h applying two stirring modes. The first one is based on the permanent stir- ring of the reaction mixture in the horizontal plane at a rate of 50 rpm for 48 h (the sample is denoted as SS-HZD-ANA- 50). Another option is the alternate stirring in the horizon- tal plane at a rate of 30 rpm, under which the agitation for 30 min alternated with the two-hour non-stirring regime for 96 h (the sample is denoted as SS–HZD–ANA–30). The solid products were separated by filtration and washed with distilled water, followed by centrifuging the suspension, separation of a sediment, and drying at 65 °C. The subsequent separation of the sediment by par- ticle sizes was done using a sieve with an aperture of 36 μm. To remove free zirconium dioxide, the product fractions <36 μm were put into water and treated by an ultrasonic source (Cole-Parmer Instruments CPX-750, USA) for 30 min. The sediments were separated by de- cantation and dried at 65 °C. Chimica Techno Acta 2022, vol. 9(4), No. 20229418 ARTICLE 3 of 9 Figure 1 SEM images of initial cenospheres: total view (a); broken globule (b). The large-sized (~40 µm) zirconia bearing analcime was prepared as described in [32] applying the agitation proce- dure based on rotation of the autoclave in a vertical plane at a rate of 30 rpm (the sample is denoted as LS–HZD–ANA–30). Small-sized Zr free analcime was synthesized in the NaOH–H2O–(SiO2–Al2O3)glass system of the 1.0 SiO2/0.18 Al2O3/0.89 Na2O/65 molar composition under the same hy- drothermal conditions (150 °C, 48 h) applying the permanent stirring of the reaction mixture in the horizontal plane at a rate of 50 rpm as described in [40] (the sample is denoted as SS–ANA–50). The solid product was washed with distilled water followed by filtration and drying at 80 °C. 2.3 Sorption experiments Batch sorption experiments were performed upon contact- ing the specimen (0.0500±0.0005 g) with CsNO3 or Sr(NO3)2 solution of 0.5–50.0 mg/L Cs+/Sr2+ at agitation and ambient temperature (V = 40 mL; τ = 24 h). Then the solid and liquid phases were separated by filtration and Cs+/Sr2+ equilibrium concentrations in the filtrate solutions were measured by flame atomic absorption spectroscopy (AAS) (AAS-30, Carl Zeiss, Germany) and, in the case of the metal content being below an AAS detection limit, induc- tively coupled plasma mass spectrometry (ICP-MS) (XSeries II, Thermo Scientific, USA). The equilibrium Cs+/Sr2+ concentrations in the solid phase (Qe, mg/g) were determined as Qe = (Co–Ce)∙V/m, where Co is the initial metal concentration in the liquid phase, mg/L; Ce is the equilibrium Cs+/Sr2+ concentration in the liquid phase, mg/L; V is the volume of solution, L; m is the mass of the sample, g. The experimental sorption data were plotted as Qe = f(Сe) and fitted by the Langmuir equation: 𝑄𝑒 = 𝑎𝑚 ∙ 𝑏 ∙ 𝐶𝑒 (1 + 𝐶𝑒) , (1) where am is the maximum sorption capacity of the solid, mg/g; b is the Langmuir constant, L/mg; Ce is the Cs+/Sr2+ equilibrium solution concentration, mg/L. The distribution coefficient values (KD = Qe/Ce, mL/g) were determined for the region of low equilibrium concen- trations (Ce < 1 mg/L). 2.4 Characterization techniques Chemical composition of the cenosphere fraction was deter- mined according to State Standard (GOST) No. 5382-2019 [41]. Powder X-ray diffraction (PXRD) data were collected on a DRON-3 (Russia) and a PANalytical X’Pert PRO (Nether- lands) diffractometers using the Cu Kα radiation over the 2θ range of 12–120 °. The samples were prepared by grind- ing with octane in an agate mortar and packed into a flat sample holder for the PXRD measurements in the Bragg- Brentano geometry. The crystallographic data base JCPDS- ICDD PDF-2 Release 2004 and the software PhasanX 2.0 were used to process the PXRD patterns. The morphologies of materials under study were identi- fied by the scanning electron microscopy (SEM) using a ТМ- 3000 and a TM-4000 (Hitachi, Japan) instruments. To iden- tify the elemental composition of sample materials, energy dispersive X-ray spectroscopy (EDS or EDX) analysis was performed using the TM-3000 microscope equipped with the Bruker microanalysis system including an energy-dis- persive X-ray spectrometer with an XFlash 430 H detector and QUANTAX 70 software. The analysis was carried out at an accelerating voltage of 15 kV in a mapping mode. The data accumulation time was 10 min. The synchronic thermal analysis (STA) was performed on a STA Jupiter 449C device (Netzsch, Germany) under a dynamic argon-oxygen atmosphere (20% O2, 50 ml/min to- tal flow rate). Platinum crucibles with perforated lids were used. The measurement procedure consisted of a tempera- ture stabilization segment (30 min at 40 oC) and a dynamic segment at a heating rate of 10 o/min. Qualitative composi- tion of a gas phase was evaluated on the basis of the ion intensity change with m/z = 18 (H2O). The specific surface area (SSA, m2/g) of the ANA-based materials was evaluated by the Brunauer-Emmett-Teller (BET) method [42] on the basis of nitrogen adsorption iso- therm measurements at 77 K using a Nova 3200e analyzer (Quantachrome Instruments, USA) and NovaWin soft- ware. Chimica Techno Acta 2022, vol. 9(4), No. 20229418 ARTICLE 4 of 9 3. Results and discussion 3.1 Morphology and composition of solid products As it follows from Table 1, the single crystal phase identified by PXRD in all the solid products is cubic analcime (ANA), NaAlSi2O6∙H2O (ICDD #01–070–1575). The PXRD peaks of zirconium phases were not observed for the Zr bearing sys- tems. This fact gives reason to assume that Zr-containing matter is essentially amorphous in the sample. By the SEM data (Figure 2–6), crystals of an icositetra- hedron habit typical of analcime [43] are visualized on all images. However, some differences in the particle mor- phology and analcime crystal sizes are clearly evident for solids resulted from the Zr-free and Zr-containing reac- tion mixtures. So, in the Na2O–H2O–(SiO2–Al2O3)glass sys- tem the analcime crystals of 3–10 µm in size are attached to an unconverted glass support, forming the hollow pol- ycrystalline analcime microspheres (Figure 2). In the presence of zirconium, the loose analcime crystals of a narrow size distribution (5–10 µm) are formed (Figure 3, 4), the analcime-like particles being the only product in the reaction mixtures. The effect of the synthesis operation (autoclave type, ag- itation mode) was manifested to the greatest extent in the size of the formed particles. Figure 3 shows the large-sized zirconium-bearing analcime crystals with the size distribu- tion maximum of about 40 µm (Figure 3a, Table 1), which were produced under rotation of the autoclave in a vertical plane and described in detail in the earlier work [32]. The zirconia inclusions in the bulk of analcime crystals with an average Zr content of 4.8 wt.% was supported in [32] by the SEM-EDS measurements over analcime crystal cross-sections and X-ray photoelectron spectroscopy. Zirconia species are also visible as contrast white spots on facets of analcime icositetrahedra (Figure 3b, 3c) giving the Zr content of about 5 wt.% (Figure 3d). The most prob- able state of zirconium occurred in Zr-bearing analcime is amorphous zirconia. There is no free zirconia matter on the crystal surfaces and between analcime particles (Figure 3a). The absence of an unbound porous material mixed with analcime is supported by the measurements of the low-tem- perature N2 adsorption, which was extremely small due to the inaccessibility of the analcime microporous structure (D = 0.26 nm) for penetration of nitrogen molecules with a kinetic diameter of 0.37 nm [18]. As for the small-sized Zr-analcimes synthesized in the autoclave applying the stirring in a horizontal plane, the ag- gregated zirconia species cover the crystal surfaces as a free porous matter (Figure 4) providing the rather high spe- cific surface area – 30–40 m2∙g–1 (Table 1). The enhanced SSA of the Zr-free SS-ANA-50 is likely to be due to the porosity of residual leached glass and mi- cro/meso-sized voids between analcime crystals fixed on glass. The main difference between two small-sized Zr- analcimes is revealed in the Zr content on the crystal sur- face (Figure 4e, 4f). The analcime particles synthesized at the alternate stirring are characterized by the greater Zr content than zirconia-analcime resulted from the synthesis at the permanent agitation. One can see in Figure 5 that the analcime particles en- tering the SS–HZD–ANA–30 display the inhomogenious zir- conia covering with variation of the Zr content in the range of 8–14 wt.%. Additional agglomerates of an irregular form containing Zr species together with glass residues are also a part of this solid product. Table 1 Composition, specific surface area and crystal size of the solid products. Sample Main crystal phase SSA, m2g–1 Zr content, wt.% Crystal size, µm SS–ANA– 50* Cubic (Ia–3d) analcime NaAlSi2O6∙H2O 36 – 2−7 SS–HZD– ANA–50 30 4−5 5−10 SS–HZD– ANA–30 39 8−13 7−10 LS–HZD– ANA–30 n.d.** 5−7 20−50/41 *** *glass-supported analcime; ** not determined; *** crystal size distribution maximum. Figure 2 SEM images of Zr-free devitrified cenospheres resulted from the NaOH–H2O–(SiO2–Al2O3)glass system: total view of the mi- crosphere product (a); glass-supported analcime (b). Chimica Techno Acta 2022, vol. 9(4), No. 20229418 ARTICLE 5 of 9 In turn, the synthesis carried out at the permanent agi- tation resulted in predominantly pure zirconia-analcime with the lower content of zirconia deposition (4–7 wt.% Zr) (Figure 6). The SSA value for SS–HZD–ANA–50 is, reasona- bly, by one and a half time lower than the SSA for the SS– HZD–ANA–30 sample (Table 1). Thus, the revealed features of particle morphology, zir- conia occurrence form and content in the solid products are expected to affect their retention ability with respect to Cs+ and Sr2+. 3.2 Sorption behavior to Cs(I) and Sr(II) of the zirconia-analcime composites The sorption ability of the zirconia-analcime composites with respect to Cs+ and Sr2+ was evaluated by measuring the equilibrium sorption capacity at different concentra- tions of metal cations in solutions and pH. Figure 7 show the experimental values of Cs+ and Sr2+ sorption at pH = 6 as well as the Cs+ and Sr2+ sorption isotherms based on the Langmuir model for SS–ANA–50 (Figure 7a) and LS–HZD– ANA–30 (Figure 7b). It was revealed that the Zr-free analcime bearing solid exhibits the expected poor Cs+ and Sr2+ sorption capacities (Figure 7a, Table 2) because of the ion-sieve effect [18]. Figure 3 SEM (a) and BSE (b, c) images of LS-HZD-ANA-30 parti- cles; EDX spectrum (d) of the marked crystal part (b) and associ- ated Zr distribution map (c). Figure 4 SEM images of small-sized HZD-analcime crystals pre- pared at different agitation regimes: SS–HZD–ANA–30 (a, c, e); SS– HZD–ANA–50 (b, d, f). Figure 5 The Zr distribution map for SS–HZD–ANA–30 particles of the following Zr content (wt.%): 1 – 8.8; 2 – 8.5; 3 – 13.0; 4 – 8.8; 5 – 13.6; 6 – 11.2; 7 – 12.2. Figure 6 BSE images of a SS–HZD–ANA–50 crystal (a, b); EDX spec- trum (c) of the marked crystal part (a) and associated Zr distribu- tion map (b). Chimica Techno Acta 2022, vol. 9(4), No. 20229418 ARTICLE 6 of 9 The sorption behavior of the large-sized zirconia-anal- cime composite is slightly better (Figure 7 b, Table 2), which is most likely due to embedded zirconia being par- tially available on the particle surface. It is notable that the Qe = f(Сe) dependences for Sr2+ sorp- tion on SS–HZD–ANA–30 are linear in the whole region of applied Sr2+ concentrations and pH, giving the KD of up to 106 mL/g (Figure 8a–c). Such high Sr2+ sorption parameters of the small-sized zirconia-analcime composites are compa- rable with those for the known specific Sr2+ sorbents, such as hydrated antimony pentoxide [44, 45], titano- and zircono- silicates [46, 47]. A number of distribution coefficients for Cs+ and Sr2+ sorption for different inorganic sorbents pro- duced in Russia [48] are given in Table 3. It can be seen that in near neutral solutions hydrated zirconium dioxide (Termoxide 3K) displays the higher KD value (3.5104 mL/g) for the Sr2+ sorption than KD for the Cs+ sorption. The lower KD for the Cs+ sorption is observed also in the case of SS–HZD–ANA–30 (Tables 2, 3). The enhanced KD at pH ≥ 6 is the characteristic feature of amphoteric oxides, such as hydrated zirconia, operating as a cation exchanger in alkaline and neutral solutions [49]. This is also in good agreement with the zirconia content and ac- cessibility on the analcime surface in both samples, sup- porting the determining role of hydrated zirconia in the Cs+ and Sr2+ sorption behavior of the zirconia-analcime composites. At the same time, due to the dissolution of ce- nosphere’s aluminosilicate glass in the alkaline reaction medium, the formation of zirconium silicate cannot be ex- cluded. Therefore, the marked Cs+ and Sr2+ sorption in acid media (Figure 8a, d) can be associated with the exist- ence of additional binding centers, such as zirconium sili- cate reported as a cation exchanger [50]. Table 2 Parameters of the Langmuir equation and distribution co- efficients for Cs+ and Sr2+ sorption on Zr-free and Zr-bearing anal- cime solids. Sample pH Cation am, mg/g b, L/mg KD, mL/g SS–ANA–50 6 Cs+ 24.3 0.03 9.0∙103 Sr2+ 15.7 0.17 4.7∙103 LS–HZD– ANA–30 6 Cs+ 30.5 0.06 7.0∙103 Sr2+ 15.9 0.77 5.0∙104 SS–HZD– ANA–30 2 Cs+ 66.5 0.05 4.8∙103 Sr2+ n.d. n.d. 2.8∙103 6 Cs+ 39.7 0.69 8.1∙104 Sr2+ n.d. n.d. 1.3∙106 10 Cs+ 36.0 0.48 5.2∙104 Sr2+ n.d. n.d. 2.5∙106 SS–HZD– ANA–50 2 Cs+ 26.9 0.11 2.5∙103 Sr2+ n.d. n.d. 3.0∙103 6 Cs+ 12.9 0.28 3.6∙104 Sr2+ 9.3 4.2 6.0∙104 10 Cs+ 31.5 0.43 2.7∙104 Sr2+ 36.4 0.75 2.7∙105 Figure 7 The Cs+ and Sr2+ sorption isotherms for SS–ANA–50 (a) and LS–HZD–ANA–30 (b) at pH = 6: (points – experiment, lines – Langmuir model). Figure 8 The Cs+ and Sr2+ sorption isotherms for ZrO2-analcime composites at different pH: SS–HZD–ANA–30 (a–c), SS–HZD–ANA– 50 (d–f): (points – experiment, solid lines – Langmuir model, dashed lines – linear approximations of experimental points as a guide toeyes). Table 3 Distribution coefficients (KD) for Cs + and Sr2+ sorption on different inorganic sorbents in 0.1 mol/L NaNO3, pH = 5−6 [48]. Sorbent KD, mL/g Cs+ Sr2+ Natural zeolite clinoptilolite 1800 310 Bentonite clay 1.9104 110 Synthetic zeolite NaA 8900 8.5104 Synthetic zeolite NaX 1800 7900 Hydrated zirconium dioxide (Termoxide 3K) 150 3.5104 Zirconium phosphate (Termoxide 3A) 1800 326 Sodium titanosilicate (TiSi) 1.9105 3.0104 Nickel ferrocyanide/Hydrated zirconium dioxide (Termoxide 35) 1.2105 – Nickel ferrocyanide/Silica gel 8.4104 – Hydrated zirconium dioxide/Analcime (SS–HZD–ANA–30) (this work)* 8.1∙104 1.3∙106 * pH = 6, no added NaNO3 0 10 20 30 40 0 10 20 30 40 50 a Cs+ Sr2+ Q e , m g /g Ce, mg/L 0 10 20 30 40 0 10 20 30 40 50 b Q e , m g /g Ce, mg/L Cs+ Sr2+ Chimica Techno Acta 2022, vol. 9(4), No. 20229418 ARTICLE 7 of 9 3.3 Thermochemical conversion of zirconia-anal- cime composites loaded with Cs(I) and Sr(II) The thermochemical conversion of the zirconia-analcime composites studied by example of the SS–HZD–ANA–30 sample loaded with Cs+ and Sr2+ includes two stages (Figure 9). The first broad endothermic DSC peak with the substan- tial mass loss is situated at 100–400 °C and is accompanied by the simultaneous increase of intensity of m/z=18 (H2O) ion due to the elimination of structural water from the anal- cime structure [32]. There are two pronounced exothermic peaks at 800–950 °C. The absence of mass change in this temperature interval suggests that the exo-effects are caused by the solid-state transformation (re-crystallization) of anal- cime and amorphous zirconia [51, 52]. The PXRD analysis of the zirconia-analcime composite calcined at 1000 °C revealed tetragonal zirconia (ICDD #04-005-4479) and hexagonal nepheline (ICDD #01-079- 992) phases in the calcination product (Figure 1b, c), so the observed broad double peak at 800–950 °C can be assigned to the HZD and analcime (Figure 10a) phase transfor- mation. Figure 9 The TG and DSC curves for thermal conversion of the SS– HZD–ANA–30 material loaded with Cs+ (a) and Sr2+ (b). Figure 10 Powder X-ray diffraction patterns for the SS–HZD–ANA– 30 (a) and solids resulted from calcination of the SS–HZD–ANA–30 loaded with sorbed Cs+ (b) and Sr2+ (c) at 1000 °C: A – c-analcime (ICDD #01-070-1575), N – h-nepheline (ICDD #01- 079-992), Z – t-zirconia (ICDD #04-005-4479). The formation of tetragonal zirconia under heating is an additional evidence of the fact that amorphous zirconia that resulted from the hydrothermal synthesis is the dominant Zr-bearing matter covering the analcime surface. Thus, the obtained data for the small-sized HZD-analcime composites loaded with Cs+ and Sr2+ are in agreement with the previous STA results [32], making it possible to consider this material as the efficient Cs+ and Sr2+ sorbent with a potential to be a precursor of a Zr-aluminosilicate mineral-like matrix hosting the trapped cations. 4. Conclusions For the first time, the hydrous zirconia bearing analcime composite which demonstrated the high sorption ability to trap Cs+ and Sr2+ from diluted CsNO3 and Sr(NO3)2 solutions of pH = 2–10, in terms of retention capacity and distribu- tion coefficient, was prepared under selected hydrothermal conditions starting from coal fly ash cenospheres with the (SiO2/Al2O3)glass = 3.1. It was established that the defining role in the sorption performance to Cs+ and Sr2+ belongs to the parameters such as the zirconia occurrence form, its content and the localization in the HZD–ANA particle as well as the particle size. The conditions for the synthesis of the zirconia-analcime with a highly enhanced sorption abil- ity regarding Sr2+ (KD ~106 mL/g) were determined. Based on the previous knowledge together with the data obtained, the HZD-analcime composite can be considered as a sorbent targeted at both Cs+/Sr2+ (due to HZD) and Ln3+ (due to analcime), which can simultaneously immobilize two or more radionuclides in the single product under heat- ing with partitioning the sorbed cations between several phases – Cs+/Sr2+ in the aluminosilicate phases (e.g., neph- eline) and Ln3+/An3+ in the Zr-phases (in this case, zirco- nia). The further testing of the sorbent on simulant waste solutions and real radioactive waste is a necessary step to confirm its effectiveness. Supplementary materials No supplementary materials are available. Funding This research was funded by Ministry of Science and Higher Education of the Russian Federation (Budget Project No. 0287-2021-0013 for the Institute of Chemistry and Chemi- cal Technology SB RAS). The reported study was conducted by using the equipment of Krasnoyarsk Regional Research Equipment Centre of SB RAS for SEM-EDS, PXRD and AAS analyses and Siberian Federal University for STA, PXRD and ICP-MS analyses. Acknowledgments The authors acknowledge G.N. Bondarenko and L.A. Solo- vyov for performing the PXRD, S.N. Vereshchagin for the 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 1800 a b c ZZZ N Z NNN N 1 .5 8 1 .8 2 2 .3 4 2 .5 9 2 .9 6 3 .2 6 3 .8 4 4 .1 7 8 .5 9 In te n s it y 1 /2 ( a rb . u n it s ) 2 Theta (degrees) AA A A A A 1 .7 4 6 2 .6 9 8 2 .9 3 7 3 .4 4 3 4 ,8 8 5 .6 3 Chimica Techno Acta 2022, vol. 9(4), No. 20229418 ARTICLE 8 of 9 STA, E.V. Mazurova for the SEM-EDS, O.A. Levitskaya and V.R. Kuzik for the AAS analysis. Author contributions Conceptualization: V.T.A., A.A.G. Data curation: K.E.A. Formal Analysis: K.E.A., B.O.V. Funding acquisition: V.T.A., A.A.G. Investigation: K.E.A., B.O.V. Methodology: V.T.A., A.A.G. Project administration: A.A.G. Resources: K.E.A., B.O.V. Software: K.E.A., B.O.V. Supervision: A.A.G. Writing – original draft: V.T.A. Writing – review & editing: V.T.A. Conflict of interest The authors declare no conflict of interest. Additional information Author IDs: Tatiana A. Vereshchagina, Scopus ID 670142870; Ekaterina A. Kutikhina, Scopus ID 24399263000; Olga V. Buyko, Scopus ID 26026599100; Alexander G. Anshits, Scopus ID 57200009289. Websites: Institute of Chemistry and Chemical Technology SB RAS, Federal Research Center "Krasnoyarsk Science Center SB RAS", https://ksc.krasn.ru; Siberian Federal University, https://www.sfu-kras.ru. References 1. International Atomic Energy Agency, Application of Ion Ex- change Processes for the Treatment of Radioactive Waste and Management of Spent Ion Exchangers. Tech. Rep. Ser. No. 408. Vienna: IAEA; 2002. 124 p. 2. Clearfield A. Inorganic ion exchangers, past, present, and fu- ture. Solvent Extr Ion Exch. 2000;18:655–678. doi:10.1080/07366290008934702 3. El-Kamash AM. Evaluation of zeolite A for the sorptive re- moval of Cs+ and Sr2+ ions from aqueous solutions using batch and fixed bed column operations. J Hazard Mater. 2008;151:432–445. doi:10.1016/j.jhazmat.2007.06.009 4. Figueiredo BR, Cardoso SP, Portugal I, Rocha J, Silva CM, Inor- ganic ion exchangers for cesium removal from radioactive wastewater. Separ Purif Rev. 2018;47:306–336. doi:10.1080/15422119.2017.1392974 5. Peters TB, Barnes MJ, Hobbs DT, Walker DD, Fondeur FF, Norato MA, Fink SD, Pulmano RL. Strontium and actinide sep- arations from high level nuclear waste solutions using mono- sodium titanate 2. Actual Waste Testing. Separ Sci Technol. 2006;41:2409–2427. doi:10.1080/01496390600742963 6. Pichot E, Dacheux N, Brandel V, Genet M. Investigation of 137Cs+, 85Sr2+ and 241Am3+ ion exchange on thorium phosphate hydrogenphosphate and their immobilization in the thorium phosphate diphosphate. New J Chem. 2000;24:1017–1023. doi:10.1039/B006022O 7. Saeb S, Patchet SJ. Radioactive Waste Disposal (Geology). Edi- tor(s): Robert A. Meyers, Encyclopedia of Physical Science and Technology (3nd ed.). Moscow: Academic Press; 2003. P. 633– 641. doi:10.1016/B0-12-227410-5/00641-4 8. Vereshchagina TA, Fomenko EV, Vasilieva NG, Solovyov LA, Vereshchagin SN, Bazarova ZG, Anshits AG. A novel layered zirconium molybdate as a precursor to a ceramic zirconomo- lybdate host for lanthanide bearing radioactive waste. J. Ma- ter. Chem. 2011;21:12001–12007. doi:10.1039/C1JM11202C 9. Mimura H, Akiba K, Ozawa M. Preparation of ceramic solid forms immobilizing cesium and/or strontium and evaluation of their physical and chemical properties. In: Proc. Inter. Conf. Nuclear Energy for New Europe; 2002 Sep 9–12; Kranjska Gora, Slovenia. p. 62640. 10. Dosch RG. Ceramic from ion exchangers: an approach to nu- clear waste solidification. Trans Amer Nucl. Soc. 1975;22:355– 357. 11. Guo B, Kamura Y, Koilraj P, Sasaki K. Co-sorption of Sr2+ and SeO4 2− as the surrogate of radionuclide by alginate-encapsu- lated graphene oxide-layered double hydroxide beads. Envi- ron. Res. 2020;187:109712. doi:10.1016/j.envres.2020.109712 12. Attallah MF, Hassan HS, Youssef MA. Synthesis and sorption potential study of Al2O3–ZrO2–CeO2 composite material for re- moval of some radionuclides from radioactive waste effluent. Appl Radiat Isot. 2019;147:40–47. doi:10.1515/ract-2019-3221 13. Youssef MA, El-Naggar MR, Ahmed IM, Attallah MF. Batch ki- netics of 134Cs and 152+154Eu radionuclides onto poly-condensed feldspar and perlite based sorbents. J. Hazard Mater. 2021;403:123945. doi:10.1016/j.jhazmat.2020.123945 14. Voronina AV, Noskova AYu, Semenishchev VS, Gupta DK. De- contamination of seawater from 137Cs and 90Sr radionuclides using inorganic sorbents. J Environ Radioact. 2020;217:106210. doi:10.1016/j.jenvrad.2020.106210 15. Mahmoud MR, Seliman AF. Evaluation of silica/ferrocyanide composite as a dual-function material for simultaneous removal of 137Cs+ and 99TcO4 − from aqueous solutions. Appl Radiat Isot. 2014;91:141–154. doi:10.1016/j.apradiso.2014.05.021 16. Nayl AA, Ahmed IM, Abd-Elhamid AI, Aly HF, Attallah MF. Se- lective sorption of 134Cs and 60Co radioisotopes using syn- thetic nanocopper ferrocyanide-SiO2 materials. Sep Purif Technol. 2020;234:116060. doi:10.1016/j.seppur.2019.116060 17. Attallah MF, Youssef MA, Imam DM. Preparation of novel nano composite materials from biomass waste and their sorptive characteristics for certain radionuclides. Radiochim Acta. 2020;108:137−149. doi:10.1515/ract-2019-3108 18. Breck DW. Zeolite Molecular Sieves: Structure, Chemistry, and Use. New York: John Wiley & Sons; 1974. 771 p. 19. Jiménez-Reyes M, Almazán-Sánchez PT, Solache-Ríosa M. Ra- dioactive waste treatments by using zeolites. A short review. J Environ Radioact. 2021;233:106610. doi:10.1016/j.jenvrad.2021.106610 20. Rachkova NG, Taskaev AI. Immobilization of U, Ra, and Th com- pounds with analcime-containing rock and hydrolysis lignin. Ra- diochem. 2011;53:314–321. doi:10.1134/S1066362211030155 21. Hegazy EZ, Abd El Maksod IH, Abo El Enin RMM. Preparation and characterization of Ti and V modified analcime from local kaolin. Appl Clay Sci. 2010;49:149–155. doi:10.1016/j.clay.2010.04.019 22. Vereshchagina TA, Kutikhina EA, Chernykh YaYu, Fomenko EV, Mazurova EV, Vereshchagin SN, Bondarenko GN. Prepara- tion and properties of Zr-bearing sorption materials based on coal fly ash microspheres. J Sib Fed Univ Chem. 2019;12:347– 363. doi:10.17516/1998-2836-0132 23. Ames LL. Cation exchange properties of wairakite and anal- cime. Amer Miner. 1966;51:903–909. 24. Redkin AF, Hemley JJ. Experimental Cs and Sr sorption on analcime in rock-buffered systems at 250–300 °C and Psat and the thermodynamic evaluation of mineral solubilities and https://www.scopus.com/authid/detail.uri?authorId=670142870 https://www.scopus.com/authid/detail.uri?authorId=24399263000 https://www.scopus.com/authid/detail.uri?authorId=26026599100 https://www.scopus.com/authid/detail.uri?authorId=57200009289 https://ksc.krasn.ru/ https://www.sfu-kras.ru/ https://doi.org/10.1080/07366290008934702 https://doi.org/10.1016/j.jhazmat.2007.06.009 https://doi.org/10.1080/15422119.2017.1392974 https://doi.org/10.1080/01496390600742963 https://doi.org/10.1039/B006022O https://doi.org/10.1016/B0-12-227410-5/00641-4 https://doi.org/10.1039/C1JM11202C https://doi.org/10.1016/j.envres.2020.109712 https://doi.org/10.1515/ract-2019-3221 https://doi.org/10.1016/j.jhazmat.2020.123945 https://doi.org/10.1016/j.jenvrad.2020.106210 https://doi.org/10.1016/j.apradiso.2014.05.021 https://doi.org/10.1016/j.seppur.2019.116060 https://www.scopus.com/sourceid/27037?origin=resultslist https://www.scopus.com/sourceid/27037?origin=resultslist https://doi.org/10.1515/ract-2019-3108 https://doi.org/10.1016/j.jenvrad.2021.106610 https://doi.org/10.1134/S1066362211030155 https://doi.org/10.1016/j.clay.2010.04.019 https://doi.org/10.17516/1998-2836-0132 Chimica Techno Acta 2022, vol. 9(4), No. 20229418 ARTICLE 9 of 9 phase relations. Eur J Mineral. 2000;12:999–1014. doi:10.1127/0935-1221/2000/0012-0999 25. Trachenko K, Understanding resistance to amorphization by radiation damage. J Phys Condens Matter. 2004;16:R1491– R1515. doi:10.1088/0953-8984/16/49/R03 26. Lee WE, Ojovan MI, Stennett MC, Hyatt NC. Immobilisation of radioactive waste in glasses, glass composite materials and ceramics. Adv Appl Ceram. 2006;105:3–12. doi:10.1179/174367606X81669 27. Luca V, Griffith CS, Drabarek E, Chronis H. Tungsten bronze- based nuclear waste form ceramics. Part 1. Conversion of mi- croporous tungstates to leach resistant ceramics. J Nucl Ma- ter. 2006;358:139–150. doi:10.1016/j.jnucmat.2006.06.017 28. Borade RB, Clearfield A. Hydrothermal synthesis of an iron sil- icate with layered structure. Chem Commun. 1997:277–278. doi:10.1039/A606343H 29. Liu L, Wang S, Zhang B, Jiang G, Yang J. Supercritical hydro- thermal synthesis of nano-ZrO2: Influence of technological parameters and mechanism. J Alloys Comp. 2022;898:162878. doi:10.1016/j.jallcom.2021.162878 30. Zhang M, Sheng X, Zhang Y, Zhou Y, Zhao S, Fu X, Zhang H. Zirconium incorporated micro/mesoporous silica solid acid catalysts for alkylation of o-xylene with styrene. J Porous Ma- ter. 2017;24:109–120. doi:10.1007/s10934-016-0243-7 31. Luo X, Wang X, Bao S, Liu X, Zhang W, Fang T. Adsorption of phosphate in water using one-step synthesized zirconium- loaded reduced graphene oxide. Sci Rep. 2016;6:39108. doi:10.1038/srep39108 32. Vereshchagina TA, Kutikhina EA, Solovyov LA, Vereshchagin SN, Mazurova EV, Chernykh YaYu, Anshits AG. Synthesis and structure of analcime and analcime-zirconia composite de- rived from coal fly ash cenospheres. Microporous Mesoporous Mater. 2018;258:228–235. doi:10.1016/j.micromeso.2017.09.011 33. Orlova AI, Ojovan MI. Ceramic mineral waste-forms for nu- clear waste immobilization. Mater. 2019;12:2638. doi:10.3390/ma12162638 34. The National Academies Press. Waste Forms Technology and Performance: Final Report. Committee on Waste Forms Tech- nology and Performance. National Research Council: Washing- ton, DC, USA. 2011. 308 p. doi:10.17226/13100 35. Hamoud MA, Allan KF, Sanad WA, El-Hamouly SH, Ayoub RR. Gamma irradiation induced preparation of poly(acrylamide-it- aconic acid)/zirconium hydrous oxide for removal of Cs-134 radionuclide and methylene blue. J Radioanal Nucl Chem. 2014;302:169–178. doi:10.1007/s10967-014-3206-y 36. Tel H, Altas Y, Gur F, Ugur A. Sorption kinetics of cesium on ZrO2 and ZrO2–SiO2–TiO2 microspheres. Radiochim Acta. 2010;98:215–219. doi:10.1524/ract.2010.1707 37. Venkatesan KA, Selvam GP, Rao PRV. Sorption of strontium on hydrous zirconium oxide. Sep Sci Technol. 2000;35:2343– 2357. doi:10.1081/SS-100102106 38. Anshits NN, Mikhailova OA, Salanov AN, Anshits AG. Chemical composition and structure of the shell of fly ash non- perforated cenospheres produced from the combustion of the Kuznetsk coal (Russia). Fuel. 2010; 89: 1849−1862. doi:10.1016/j.fuel.2010.03.049 39. Fomenko EV, Anshits NN, Solovyov LA, Mikhaylova OA, An- shits AG. Composition and morphology of fly ash cenospheres produced from the combustion of Kuznetsk coal. Energy Fuels. 2013; 27: 5440–5448. doi:10.1021/ef400754c 40. Vereshchagina TA, Kutikhina EA, Chernykh YaYu, Solovyov LA, Zhizhaev AM, Vereshchagin SN, Anshits AG. One-step immobi- lization of cesium and strontium from alkaline solutions via a facile hydrothermal route. J Nucl Mater. 2018;510:243–255. doi:10.1016/j.jnucmat.2018.08.015 41. Cements and materials for cement production. Chemical anal- ysis methods. State Standard (GOST) No. 5382–2019. Moscow: IPK, Izdatel’stvo standartov; 2002. 70 p. 42. Greg SJ, Singh KSW. Adsorption, Surface Area, and Porosity. London: Academic Press; 1982. 304 p. 43. Wise WS. Handbook of Natural Zeolites. ed. C. Colella. Inter- national Zeolite Association. Napoli, Italy, A. De Frede Edotore: Natural Zeolites Commission; 2013. 126 p. 44. Mu W, Zhang R, Li X, Xie X, Yu Q, Lv K, Wei H, Jian Y. Pyro- chlore Ta-doped antimony oxide as a novel adsorbent for effi- cient strontium removal. RSC Adv. 2015;5:10378–10385. doi:10.1039/C4RA13992E 45. Shavinsky BM, Levchenko LM, Mitkin VN. Obtaining hydrated antimony pentoxide for the sorption of cesium and strontium ions. Chem Sustain Develop. 2010;18:663–667. 46. Popa K, Pavela CC. Radioactive wastewaters purification using titanosilicates materials: State of the art and perspectives. De- salination. 2012;293:78–86. doi:10.1016/j.desal.2012.02.027 47. Bortun AI, Bortun LN, Clearfield A. Hydrothermal synthesis of so- dium zirconium silicates and characterization of their properties. Chem Mater. 1997;9:1854–1864. doi:10.1021/cm9701419 48. Milyutin VV, Nekrasova NA, Kaptakov VO. Modern sorption materials for cesium and strontium radionuclide extraction from liquid radioactive waste radioactive waste. Radioact Waste. 2020;4(13):80—89 (In Russian). doi:10 25283/2587-9707-2020-4-80-89 49. Misak NZ. Outlines of the ion exchange characteristics of hy- drous oxides. Adv Colloid Interface Sci. 1994;51:29–135. doi:10.1016/0001-8686(94)80034-0 50. Amphlett CB. Inorganic Ion exchangers. New York, London: Elsevier Pub. Co; 1964. 141 p. 51. Suvorova VA, Kotel’nikov AR, Akhmedzhanova GM. Phase Transformation of Zeolites Saturated with Alkali and Alkaline- Earth Elements into Ceramic. Vestn Ross Akad Nauk Ser Earth Sci. 2002;1:20. 52. Kotel’nikov AR, Bychkov AM, Zyryanov VN, Akhmedzhanova GM, Gavlina OT. Phase Transformation of Zeolites into Feld- spar as a Method for Preparing Aluminosilicate Matrices for Radionuclide Fixation. Geokhimiya. 1995;10:1527–1532. https://doi.org/10.1127/0935-1221/2000/0012-0999 https://doi.org/10.1088/0953-8984/16/49/R03 https://doi.org/10.1179/174367606X81669 https://doi.org/10.1016/j.jnucmat.2006.06.017 https://doi.org/:10.1039/A606343H https://doi.org/10.1016/j.jallcom.2021.162878 https://doi.org/10.1007/s10934-016-0243-7 https://doi.org/10.1038/srep39108 https://doi.org/10.1016/j.micromeso.2017.09.011 https://doi.org/10.3390/ma12162638 https://doi.org/10.17226/13100 https://doi.org/10.1007/s10967-014-3206-y https://doi.org/10.1524/ract.2010.1707 https://doi.org/10.1081/SS-100102106 https://doi.org/10.1016/j.fuel.2010.03.049 https://doi.org/10.1021/ef400754c https://doi.org/10.1016/j.jnucmat.2018.08.015 https://doi.org/10.1039/C4RA13992E https://doi.org/10.1016/j.desal.2012.02.027 https://doi.org/10.1021/cm9701419 https://doi.org/10%2025283/2587-9707-2020-4-80-89 https://doi.org/10.1016/0001-8686(94)80034-0