Synthesis and Application of MnO-Fe 2 O 3 Nanocomposites for the Removal of 137 Cs and 60 Co Radionuclides from Artiﬁcial Radioactive Aqueous Waste

: For innovative application in wastewater treatment techniques, MnO-Fe 2 O 3 nanocomposites were successfully synthesized using the sol–gel auto-combustion method at different temperatures for the adsorption of 137 Cs and 60 Co radionuclides from aqueous solution. The characterization of these nanocomposites was carried out through FT-IR, SEM-EDX, and X-ray diffraction. These nanocomposites were employed as adsorbent materials for the removal of 137 Cs and 60 Co radionuclides from simulated radioactive waste solutions. The study involved a series of experiments aiming to demonstrate the MnO-Fe 2 O 3 nanoparticles’ exceptional adsorption potential concerning 137 Cs and 60 Co. Additionally, the investigation delved into how variations in temperature, dose amount, contact time, and pH value inﬂuence the adsorption dynamics. Due to their high speciﬁc surface area, the synthesized MnO-Fe 2 O 3 nanoparticles had high adsorption capacity of more than 60% and 90% for 137 Cs and 60 Co, respectively. By investigation of kinetics and adsorption isotherms, pseudo-second-order reaction and the Langmuir model turned out to ﬁt well for the adsorption of 137 Cs and 60 Co onto the MnO-Fe 2 O 3 nanocomposites. Moreover, a thermodynamic analysis revealed that the adsorption process was spontaneous for both target metals and the adsorption of 60 Co was endothermic, whereas the adsorption of 137 Cs was exothermic.


Introduction
Nowadays, the development of contemporary and advanced methods for wastewater treatment is of significant relevance and a hot issue of current scientific research all over the world in order to deal with steadily increasing environmental concerns [1].In recent years, there has been increased interest in using magnetic particles to alleviate various environmental challenges.Radioactive waste and nuclear pollution primarily originate from nuclear fuel-based electricity generation, nuclear weaponry testing, fuel reprocessing, and nuclear incidents [2], as well as the use of radionuclides in medicine, agriculture, industry, and research.This radioactive waste has a negative impact on human health and the environment [3].Furthermore, the extensive distribution of radionuclides in the environment has led to the inclusion of liquid radioactive waste from diverse civil nuclear applications and nuclear facilities among hazardous materials [4].
The most significant procedure in the management of radioactive waste is treatment, which tries to concentrate and reduce waste produced in order to ensure safety and to lower the costs of following management schemes.Liquid radioactive waste is regarded as having a highly hazardous effect on humans and the environment, highlighting the critical need for evaluating and improving its treatment around the world [5].The choice of its many management alternatives is due to the need for shielding, the radioactivity level in the waste influences.Therefore, the current, widely accepted classification system is based on the amount of activity and half-life.
Several alternative approaches to the elimination of heavy metals and radionuclides from contaminated aqueous systems have been investigated.Coagulation, chemical precipitation, ion exchange, adsorption, solvent extraction, membrane filtration, phytoremediation, and liquid membrane techniques are examples of these approaches [6].
Liquid radioactive waste can be categorized as easily detectable high-energy gammaray emitters; numerous investigations into enhancing their treatment [7,8], immobilization [9,10], and isolation [11] from the environment have been reported.
Particularly, radionuclides like 137 Cs and 60 Co, components of low-level radioactive waste (LLRW), pose significant risks to human well-being due to their capacity for efficient transfer, high solubility, extended half-lives, and propensity to accumulate in living organisms [12]. 137Cs and 60 Co are used in irradiation and for investigating the sensitivity of dosimeters [13,14] Cesium has a high water solubility and easily spreads in the surrounding environment [15], while cobalt is a corrosive, toxic element and seriously affects the environment [16].The contamination of soil and water by the common fission product radionuclides, namely, 137 Cs and 60 Co, leads in prolonged radiation and subsequent probable contamination of the food chain, posing an environmental concern to human health [17].Given these attributes, it is crucial to eliminate 137 Cs and 60 Co from waste streams prior to releasing them into the environment.Over the years, a range of distinct techniques have been developed for treatment purposes, such as chemical precipitation, solvent extraction, reverse osmosis, ion exchange, and adsorption [18], with adsorption being widely adopted to remove heavy metals from contaminated water.
A growing fascination within the scientific realm centers on the development of innovative nanoscale composite materials that incorporate various metal oxides.This focus is particularly geared towards tackling pressing environmental issues, including the elimination of harmful dyes and metal ions from water matrices.These nanoscale composites, comprising multiple metal oxides, not only retain the advantages of their individual constituents but also exhibit synergistic effects that enhance the overall physicochemical properties of the composite [19,20].The production of nanoscale multi-metal oxides has been successfully accomplished using a variety of ceramic processing methods, encompassing precipitation, sol-gel, and hydrothermal pathways [21,22].Among these, the sol-gel approach stands out due to its simplicity, cost-effectiveness, well-established, flexible synthetic route, and environmentally benign nature [23].
One such composite is the MnO-Fe 2 O 3 nanocomposite.The MnO-Fe 2 O 3 composite can easily be prepared and has been proven to be a low-cost material [1]; however, in this study, synthetic MnO-Fe 2 O 3 nanocomposites were produced using the sol-gel autocombustion technique.The physicochemical attributes of these nanocomposites were thoroughly assessed.The primary objectives encompassed an exploration of the influence of initial metal ion concentrations, initial solution pH, and temperature on the capacity of synthetic MnO-Fe 2 O 3 nanocomposites to remove 137 Cs and 60 Co from their aqueous solutions.The underlying adsorption mechanisms were also subjected to kinetic and thermodynamical investigations.The insights garnered from this study concerning the adsorption of 137 Cs and 60 Co onto MnO-Fe 2 O 3 nanocomposites under varying conditions offer valuable input for addressing the challenges posed by low-level radioactive waste (LLRW).Thus, the objective of the presented work was to assess the removal effectiveness of MnO-Fe 2 O 3 nanocomposite for 137 Cs and 60 Co under various conditions.

Preparation of MnO-Fe 2 O 3 Nanocomposite
The process of sol-gel involves forming a colloidal suspension termed as a sol, which subsequently transforms into a solid three-dimensional structure within a continuous liquid medium, leading to the formation of a gel.These colloids are typically composed of a metal or metalloid element enclosed by different reactive compounds.To initiate the process, MnSO 4 •5H 2 O and FeSO 4 •6H 2 O were dissolved in distilled water, employing predetermined stoichiometric ratios, and then agitated for 15 min on a heated plate furnished with a magnetic stirrer.Subsequently, a chosen precipitating agent was carefully introduced in a drop-wise manner.The resulting precipitates were separated through filtration and left to desiccate for a duration of one night at 110 • C. The resultant precipitate was amalgamated with an aqueous solution of citric acid, and this mixture was then dissolved by gradually adding concentrated nitric acid.In this context, citric acid functioned as the fuel while nitric acid acted as the oxidizer during the combustion process.The ultimate step involved adjusting the pH value to 7, a level that facilitates improved complexation of the metal ions [24].This pH adjustment was realized by incorporating a 25 vol% aqueous ammonia solution.Following this, the sols were subjected to heat until a gel-like structure emerged, which was subsequently pulverized to obtain a uniform powder.The final product underwent calcination at temperatures of 500, 800, and 1100 • C for a period of 4 h each.

Preparation of Radioactive Waste Solutions
For the creation of radioactive waste solutions, two radioisotopes, namely 137 Cs and 60 Co, were procured from the Institute of Atomic Energy, POLATOM, Poland.A radioactivity of 127 MBq/mL and a purity exceeding 99.5% were achieved for CsCl, which represented the 137 Cs source.Similarly, CoCl 2 , containing 60 Co, had a radioactivity of 115 MBq/mL with a purity exceeding 99%.These activities were then appropriately diluted to suitable levels for experimental purposes.
Diverse aqueous solutions, characterized by varying initial radioactivity and ascending pH values, were meticulously prepared.Subsequently, these solutions underwent the remediation process using the designated equipment.Diluted solutions of HNO 3 or NaOH were employed to establish media with predefined pH values.

Techniques for Characterization of Adsorbent
X-ray diffraction (XRD) patterns were generated using a powder X-ray diffractometer (BRUKER D8 Advance, Billerica, MA, USA) equipped with a Cu target and a wavelength of 1.54 Å, operating at 40 kV and 40 mA, from Germany.Surface morphology and compositional analysis of the films were observed utilizing a scanning electron microscope (JEOL JSM6360, Peabody, MA, USA) at an operational voltage of 20 kV.Fourier transform infrared (FT-IR) spectra were acquired via an FT-IR spectrophotometer (Nicolet is 10 spectrometer, Rhinelander, WI, USA), covering the range of 4000-400 cm −1 with a resolution of 2 cm −1 , employing KBr pellets at room temperature.The progression of the adsorption process was tracked by measuring the remaining activity content within the solutions, employing a multichannel analyzer connected to a NaI detector (PCAP, Wilmington, DE, USA).

Conducting Adsorption Experiments
To assess the highest adsorption capacity of MnO-Fe 2 O 3 nanocomposites for 137 Cs and 60 Co, the experimental outcomes were processed employing the following Equation (1): Uptake% = initial activity of waste solution − remaining activity in waste solution initial activity of waste solution × 100 Thermodynamic parameters pertinent to the adsorption mechanisms of 137 Cs and 60 Co onto MnO-Fe 2 O 3 nanocomposites were computed.
The influence of solution pH value was explored across a pH range spanning from 2 to 12, maintaining a temperature of 25 • C. For each test, 50 mL of a solution containing both 137 Cs and 60 Co was introduced into a 50 mL conical centrifuge tube made of polyethylene (SPL Labware, Pocheon-si, Republic of Korea).Subsequently, these solutions were mixed with 0.2 g of MnO-Fe 2 O 3 nanocomposites.The initial pH of the solutions was tailored by adding either 0.1 N HNO 3 or 0.1 N NaOH solution.The resulting suspensions were subjected to agitation in a rotary shaker, set at 200 rpm, for a duration of 24 h.Subsequently, these mixtures underwent filtration using a 0.2 mm pore size syringe filter, after which they were analyzed for their final pH values and the concentration of metal ions.The pH measurement was carried out using a pH meter (Thermo Orion, model 720A+, Waltham, MA, USA).

Surface Morphology and Composition Analysis via SEM-EDX
The morphology of MnO-Fe 2 O 3 nanocomposites synthesized at different temperatures can describe the degree of interaction between the sorbent and the metal ion species.The morphological structure and surface properties of MnO-Fe 2 O 3 nanocomposites were examined using scanning electron microscopy (SEM).The results are depicted in Figure 1, which show a rough surface, and the presence of a uniformly porous structure nanocomposite on a large scale [25].The surface area and porous structure of the produced nanocomposite will play an important role in the adsorption process.To establish the composition of the composite oxide, energy-dispersive X-ray (EDX) analysis was performed.In the EDX spectrum illustrated in Figure 2, the spectral lines identified in this EDX analysis align consistently with the outcomes documented in other sources [26].A quantitative assessment derived from the EDX data determined the elemental percentages within the matrix, including their energy distribution.This analysis method enabled the direct determination of the composition of the examined samples such as iron based on the EDX data.

Analysis of X-ray Diffraction (XRD)
X-ray diffraction was used to determine the formed structure of the produce composites at three selected temperatures.Figure 3 illustrates a representative X tern of the synthesized MnO-Fe2O3 nanocomposites under optimized conditions sively affirming the identity of the synthesized sample as MnO-Fe2O3 nanocom Furthermore, the XRD patterns obtained for the synthesized samples demonstra tions resulting from calcination at distinct temperatures (500, 800, and 1100 °C).Ob the XRD pattern at 500 °C, the conspicuous elevated background within the di spectra of both samples signifies the presence of an amorphous phase within the r materials.
As for the XRD pattern at 800 °C, the distinctive diffraction pattern unveils lin acteristic of Fe2O3.Upon reaching 1100 °C, the XRD pattern distinctly reveals lin

Analysis of X-ray Diffraction (XRD)
X-ray diffraction was used to determine the formed structure of the produced nanocomposites at three selected temperatures.Figure 3

FTIR Analysis
FTIR spectroscopy was employed in the range of 4000-400 cm −1 to investigate the su face of the nano-adsorbents, enabling insights into the chemical bonds present on the su face materials, as shown in Figure 4.The broad band at 3340 cm −1 was attributed to the H stretching vibrations of hydroxyl groups or adsorbed water molecules, while the ba at 1625 cm −1 confirmed the presence of adsorbed water molecules at low temperatu only [28].
At all temperatures, the noticeable bands centered at 473 and 541 cm −1 are attribut to the mixed oxides associated with the stretching vibrations of M-O (Mn-O/Fe-O bon in the MO4 tetrahedron and MO6 octahedron, respectively) [29].[27].This assertion was substantiated by Fourier transform infrared (FTIR) analysis, as described in the following Section 3.1.3.

FTIR Analysis
FTIR spectroscopy was employed in the range of 4000-400 cm −1 to investigate the surface of the nano-adsorbents, enabling insights into the chemical bonds present on the surface materials, as shown in Figure 4.The broad band at 3340 cm −1 was attributed to the O-H stretching vibrations of hydroxyl groups or adsorbed water molecules, while the band at 1625 cm −1 confirmed the presence of adsorbed water molecules at low temperatures only [28].
At all temperatures, the noticeable bands centered at 473 and 541 cm −1 are attributed to the mixed oxides associated with the stretching vibrations of M-O (Mn-O/Fe-O bonds in the MO 4 tetrahedron and MO 6 octahedron, respectively) [29].

Impact of Calcination Temperature on Radioisotope Adsorption by Nanocomposites
The adsorption capacity of synthesized MnO-Fe 2 O 3 nanocomposites prepared under different calcination temperatures has been performed as a preliminary test to evaluate the optimal calcination temperature that produces the most efficient adsorbent.As shown in Figure 5, the MnO-Fe 2 O 3 nanocomposite prepared under higher calcination temperature had a higher adsorption capacity of 137 Cs than the others prepared through at a lower temperature.The higher the calcination temperature, the higher the crystallinity and the lower the proportion of amorphous phase in the nanocomposite structure with a welldefined morphology [30].This behavior agreed with the high calcination temperature of the TiO 2 -ZnO nanocomposite that influenced the dye adsorption and also the dye decolorization by photocatalysis [31].In this context, the MnO-Fe 2 O 3 nanocomposite prepared at a higher calcination temperature (1100 • C) was chosen to evaluate its efficiency for the removal of cesium and cobalt from contaminated aqueous solutions, as illustrated in the following experiments.

Impact of Calcination Temperature on Radioisotope Adsorption by Nanocomposites
The adsorption capacity of synthesized MnO-Fe2O3 nanocomposites prepared under different calcination temperatures has been performed as a preliminary test to evaluate the optimal calcination temperature that produces the most efficient adsorbent.As shown in Figure 5, the MnO-Fe2O3 nanocomposite prepared under higher calcination temperature had a higher adsorption capacity of 137 Cs than the others prepared through at a lower temperature.The higher the calcination temperature, the higher the crystallinity and the lower the proportion of amorphous phase in the nanocomposite structure with a welldefined morphology [30].This behavior agreed with the high calcination temperature of the TiO2-ZnO nanocomposite that influenced the dye adsorption and also the dye decolorization by photocatalysis [31].In this context, the MnO-Fe2O3 nanocomposite prepared at a higher calcination temperature (1100 °C) was chosen to evaluate its efficiency for the removal of cesium and cobalt from contaminated aqueous solutions, as illustrated in the following experiments.Based on the spectroscopic analyses including SEM, XRD, and FTIR and the prelim inary experiment performed with 137 Cs, it could be confirmed that the nanocomposite pro duced at 1100 °C is more suitable for adsorption technique according to its morphologica

Impact of Contact Time on 137 Cs and 60 Co Removal
Based on the spectroscopic analyses including SEM, XRD, and FTIR and the preliminary experiment performed with 137 Cs, it could be confirmed that the nanocomposite produced at 1100 • C is more suitable for adsorption technique according to its morphological structure and porous surface.To establish the optimal equilibrium time for achieving maximum sorption efficiency and to comprehend the kinetics of the sorption of 137    The outcomes revealed a remarkably swift sorption process for both 137 Cs and 60 Co by the MnO-Fe 2 O 3 nanocomposite.Equilibrium was effectively attained within approximately 100 min for both cations.This finding underscores the rapid nature of the sorption process.Consequently, a contact time of 100 min was deemed adequate for efficient sorption and thus was adopted for all subsequent experiments.

Effect of Dose Amount on Removal of 137 Cs and 60 Co
In order to optimize the adsorption of Cs and Co ions, the quantity of nanomaterial adsorbent was systematically adjusted within the range of 0.012 to 0.25 g, as depicted in Figure 7. Evidently, the results highlighted that a dose of 0.2 g of adsorbent (nanocomposite) proved to be sufficient for achieving maximum removal of both ions.At this juncture, the adsorption of Cs or Co ions reached its optimal capacity, with only a marginal further increment observed as the adsorbent dose increased.This slight increase can be attributed to the heightened availability of adsorption sites on the adsorbent due to a larger free surface area.
Maintaining a constant concentration of metal ions, the adsorption capacity exhibited an upward trend in correlation with the augmented availability of adsorption sites stemming from the increased surface area of the adsorbent.Conversely, as the concentration of ions bound to the adsorbent sites increased, the adsorption capacity gradually declined due to the reduction in available sites.This phenomenon is attributed to the eventual saturation of adsorption sites.Furthermore, at higher concentrations of adsorbed ions, the ratio of the initial number of ion molecules to the accessible adsorption sites increased, resulting in a reduction in adsorption capacity [32].

Effect of Temperature on Removal of 137 Cs and 60 Co
The significant influence of temperature fluctuations on the sorption process is widely recognized.In light of this, a series of experiments at temperatures of 25, 35, 45, and 55 • C were systematically undertaken to comprehensively examine the impact of temperature on the sorption process (Figure 8).Precisely, the sorption characteristics of 4 g/L of 137 Cs and 60 Co ions were investigated.

Effect of pH-Value on Removal of 137 Cs and 60 Co
Due to its impact on the surface of the adsorbent and the ionic form of the metal ion in an aqueous solution, the pH value of the solution is a crucial dominating parameter in sorption processes [34].The effect of the initial pH value on the removal efficiency of 137 Cs and 60 Co by the MnO-Fe 2 O 3 nanocomposite from an aqueous solution was followed as shown in Figure 9.The removal efficiency was firstly increased when increasing the initial pH value up to 8 and 9 for 60 Co and 137 Cs , respectively; then, it nearly attained a constant value when the pH value was further increased.The pH value of the solution affects the surface charge of the adsorbent and the chemical speciation of both adsorbates.
The uptake percentages of 137 Cs were increased by raising the pH value from 3 to 9.This is due to the fact that H3O + had a large concentration at lower pH values and com- The effect of different temperatures on the removal percentage and the amounts of both radioisotopes sorbed from their aqueous solutions was conducted at the optimal contact time and constant initial activity contents.The sorbed amounts and the associated removal of 60 Co were greater than those of 137 Cs, with a positive effect of temperature reflecting the endothermic natures of sorption [33].During contact time at different temperatures, about 89% and 59% of the sorbed amounts were reached for 60 Co and 137 Cs, respectively.This may be due to the higher availability of both metal ions around the MnO-Fe 2 O 3 nanocomposite during contact time.

Effect of pH-Value on Removal of 137 Cs and 60 Co
Due to its impact on the surface of the adsorbent and the ionic form of the metal ion in an aqueous solution, the pH value of the solution is a crucial dominating parameter in sorption processes [34].The effect of the initial pH value on the removal efficiency of 137 Cs and 60 Co by the MnO-Fe 2 O 3 nanocomposite from an aqueous solution was followed as shown in Figure 9.The removal efficiency was firstly increased when increasing the initial pH value up to 8 and 9 for 60 Co and 137 Cs, respectively; then, it nearly attained a constant value when the pH value was further increased.The pH value of the solution affects the surface charge of the adsorbent and the chemical speciation of both adsorbates.

Kinetic Studies
Figures 10-15 and Table 1 provide an in-depth illustration of the kinetic studies.These investigations were geared towards determining the underlying mechanisms governing sorption behavior.To probe these mechanisms, the pseudo-first-order (PFO) and pseudo-second-order (PSO) rate equations were employed to analyze the experimental sorption data.The uptake percentages of 137 Cs were increased by raising the pH value from 3 to 9.This is due to the fact that H 3 O + had a large concentration at lower pH values and competed with cesium ions for free active sites [35].With increasing pH value, the concentration of H 3 O + decreased and the deprotonation of the active site on the adsorbent surface increased, thus enabling these sites to attract cesium ions and hence the uptake of cesium increased.At higher pH values, the uptake was slightly decreased when increasing pH value up to 11 [36].
On the other hand, the uptake of 60 Co increased by a lot when the pH value increased from 3 up to 6 and increased slightly when pH increased from 6 to 9, then reached equilibrium, and remained constant when the pH value increased up to 11.At pH values higher than 6.5, the removal was attributed to the precipitation of 60 Co and the presence of Co(OH) 2 as the predominant species [37].

Kinetic Studies
Figures 10-15 and Table 1 provide an in-depth illustration of the kinetic studies.These investigations were geared towards determining the underlying mechanisms governing sorption behavior.To probe these mechanisms, the pseudo-first-order (PFO) and pseudo-second-order (PSO) rate equations were employed to analyze the experimental sorption data.
of the experimental values, a plot of qt against t 0.5 was utilized.If the plot exhibited linearity and passed through the origin, it indicated that internal diffusion was the slowest (rate-determining) step in the adsorption process.Conversely, if the plot was non-linear or linear but did not intersect the origin, it suggested a potential combined influence of film diffusion and internal diffusion on the adsorption process.It is concluded that the kinetics of 137 Cs and 60 Co removal on MnO-Fe2O3 nanocomposites aligned well with the pseudo-second-order model.

Exploration of Adsorption Isotherms
To ascertain the adsorption capacity of the MnO-Fe2O3 nanocomposite for 137 Cs and 60 Co, adsorption isotherms were conducted at 25 °C and pH 7. The adsorption data related to the interaction of 137 Cs and 60 Co with the MnO-Fe2O3 nanocomposite in aqueous solutions (as illustrated in Figure 16) were analyzed by fitting them to the Langmuir, Freun-  The pseudo-first-order model (PFO), a straightforward framework describing the sorption rate based on sorption capacity, was utilized to explain the kinetics of metal ion sorption onto the adsorbent.The expression for the PFO model is represented by Equation ( 2 Here, k 1 represents the PFO rate constant (min −1 ), and qe and qt (mg g −1 ) denote the amounts of metal ion adsorbed at equilibrium and at time t, respectively.Additionally, the PSO model is expressed as Equation (3): Here, k 2 (g mg −1 min −1 ) is the PSO rate constant of adsorption.The validity of the model was checked by calculating the correction coefficient value of straight lines (R 2 ) as well as consistency between the experimental and calculated values of the PFO model and PSO.
Most adsorption processes entail a multi-step mechanism comprising (i) external film diffusion, (ii) intraparticle diffusion, and (iii) interaction between the adsorbate and active sites [38].In this study, the agitation of the solution eliminated the external film diffusion step.As a result, the rate-controlling aspect resided within the remaining two steps.The evaluation of intraparticle diffusion was conducted to ascertain whether it acted as the rate-determining step or not, employing the Fickian diffusion equation (Equation ( 4)): qt = Ki t 0.5 + Xi (4) where qt is the amount of metal ion adsorbed at time t and Ki is the intraparticle diffusion rate (mg g −1 min −0.5 ), while Xi represents the boundary layer diffusion effect.As the value of Xi decreases, the effect of external diffusion on the reaction rate decreases.The Weber-Morris intra-particle diffusion model was employed to explore the likelihood of both intra-particle and liquid-film diffusion mechanisms [39].To test the linearity of the experimental values, a plot of qt against t 0.5 was utilized.If the plot exhibited linearity and passed through the origin, it indicated that internal diffusion was the slowest (rate-determining) step in the adsorption process.Conversely, if the plot was non-linear or linear but did not intersect the origin, it suggested a potential combined influence of film diffusion and internal diffusion on the adsorption process.It is concluded that the kinetics of 137 Cs and 60 Co removal on MnO-Fe 2 O 3 nanocomposites aligned well with the pseudo-second-order model.

Exploration of Adsorption Isotherms
To ascertain the adsorption capacity of the MnO-Fe 2 O 3 nanocomposite for 137 Cs and 60 Co, adsorption isotherms were conducted at 25 • C and pH 7. The adsorption data related to the interaction of 137 Cs and 60 Co with the MnO-Fe 2 O 3 nanocomposite in aqueous solutions (as illustrated in Figure 16) were analyzed by fitting them to the Langmuir, Freundlich, and Dubinin-Raduskevich (D-R) isotherms.The derived constants have been computed and are displayed in Table 2.The Langmuir equation takes the form of Equation ( 5): 1 q e = 1 k L q max C e + 1 q max (5) Here, C e represents the equilibrium concentration of ion in the solution (mg L −1 ), qe stands for the adsorbed ion quantity at equilibrium concentration (mg g −1 ), q max signifies the maximum adsorption capacity (mg g −1 ), and k L is the Langmuir binding constant associated with the energy of adsorption (L mg −1 ).Plotting 1/q e against 1/C e yields a linear relationship, with a slope and intercept equivalent to 1/k L q max and q max , respectively.The calculated values of k L and q max were determined for ion adsorption at varying temperatures.The q max values derived from the Langmuir plots are largely in agreement with the experimental values.This observation suggests that the adsorption process predominantly follows a monolayer mechanism and adheres to the Langmuir isotherm across all conditions.The degree of suitability of the adsorbent towards ions was estimated from the values of the separation factor (R L ) (Equation ( 6)).
Here, K L represents the Langmuir equilibrium constant, and C o indicates the initial concentration of the metal ion.R L values within the range of 0 to 1 indicate the suitability of the process.The Freundlich equation is expressed as Equation ( 7): ln q e = ln K f + 1 n ln C e (7) lnq e was plotted against lnC e , with the slope and intercept at 1/n and lnK f , respectively, where C e is the equilibrium concentration of the metal ion solution (mg L −1 ), qeis is the amount of adsorbed metal ion at equilibrium (mg g −1 ), K f (mg 1−1/n L 1/n g −1 ) is the Freundlich constant for the adsorption capacity, and n is the adsorption intensity.It is noteworthy that the data exhibited good fits with both the Langmuir and Freundlich isotherms, as evidenced by high correlation coefficients (R 2 ) at 25 • C.

Figure 5 .
Figure 5.Effect of calcination temperature of nanocomposites on the sorption efficiency of 137 Cs from aqueous solution.
Cs and  60 Co by the MnO-Fe 2 O 3 nanocomposite, an investigation was conducted by varying the contact time.

Figure 6
illustrates the influence of contact time on the sorption of 137 Cs and 60 Co by the MnO-Fe 2 O 3 nanocomposite from an aqueous solution at various initial radioactivity contents ranging from 1 to 2.46 Bq for 60 Co and from 19.5 to 55 Bq for 137 Cs.

Figure 6 .
Figure 6.Effect of contact time on the sorption efficiency of 137 Cs and 60 Co by MnO-Fe 2 O 3 nanocomposite from aqueous solution.

Figure 7 . 21 Figure 8 .
Figure 7. Effect of dose amount on the sorption efficiency of 137 Cs and 60 Co by MnO-Fe 2 O 3 nanocomposite from aqueous solution.ng 2023, 7, x FOR PEER REVIEW 11 of 21

Figure 8 .
Figure 8. Influence of temperature on sorption efficiency of 137 Cs and 60 Co by MnO-Fe 2 O 3 nanocomposite from aqueous solution.

ng 2023, 7 , 21 Figure 9 .
Figure 9.Effect of pH value on the sorption efficiency of 137 Cs and 60 Co by MnO-Fe2O3 nanocomposite from aqueous solution.

Figure 9 .
Figure 9.Effect of pH value on the sorption efficiency of 137 Cs and 60 Co by MnO-Fe 2 O 3 nanocomposite from aqueous solution.

Figure 10 .
Figure 10.Pseudo-first-order sorption kinetics of adsorption of 60 Co on MnO-Fe2O3 nanocomposite from aqueous solution.

Figure 11 .
Figure 11.Pseudo-first-order sorption kinetics of adsorption of 137 Cs on MnO-Fe2O3 nanocomposite from aqueous solution.Figure 11.Pseudo-first-order sorption kinetics of adsorption of 137 Cs on MnO-Fe 2 O 3 nanocomposite from aqueous solution.

Figure 11 .
Figure 11.Pseudo-first-order sorption kinetics of adsorption of 137 Cs on MnO-Fe2O3 nanocomposite from aqueous solution.

Figure 12 .
Figure 12.Pseudo-second-order reaction of adsorption of 60 Co on MnO-Fe2O3 nanocomposite from aqueous solution.

Figure 13 .
Figure 13.Pseudo-second-order reaction of adsorption of 137 Cs on MnO-Fe2O3 nanocomposite from aqueous solution.Figure 13.Pseudo-second-order reaction of adsorption of 137 Cs on MnO-Fe 2 O 3 nanocomposite from aqueous solution.

Figure 13 .
Figure 13.Pseudo-second-order reaction of adsorption of 137 Cs on MnO-Fe2O3 nanocomposite from aqueous solution.

Figure 14 .
Figure 14.Morris-Weber plot for adsorption of 60 Co on MnO-Fe2O3 nanocomposite from aqueous solution.

Figure 15 .
Figure 15.Morris-Weber plot for adsorption of 137 Cs on MnO-Fe 2 O 3 nanocomposite from aqueous solution.

Table 1 .
Parameters of kinetic models for the adsorption of 137 Cs and 60 Co onto MnO-Fe2O3 nanocomposite from aqueous solution.

Table 1 .
Parameters of kinetic models for the adsorption of 137 Cs and 60 Co onto MnO-Fe 2 O 3 nanocomposite from aqueous solution.