Proficiency of some synthetic alginate derivatives for sequestration of Iodine-131 from radioactive liquid waste

ABSTRACT The current effort in environmental remediation is aimed at removing iodine-131 radionuclide from radioactive liquid waste produced by an Egyptian nuclear power plant using some synthesised alginate derivatives. Two different copolymers, namely sodium alginate poly (acrylic acid) (P1) and sodium alginate poly (acrylic acid-methacrylic acid) (P2), are prepared using gamma radiation. The ability of these polymers to remove 131I radionuclide as sorbents has been investigated. The synthesised polymers exhibit excellent adsorption performance for 131I ions, and the adsorption equilibrium requires only 30 min, which reveals that the sorption process is kinetically faster than most of the other materials reported previously. The removal percents for 131I radionuclide at a pH of 3.0 at room temperature on P1 and P2 are 77.7% and 84.2%, respectively. The sorption capacities of the two polymers demonstrate that P2 > P1, with capacities of 67.9 and 58.5 mg/g, respectively. Four linear kinetic models are investigated: pseudo-first order, pseudo-second order, Elovich, and Weber–Morris models. Regarding their calculated parameters, these models indicate that the adsorption process of I-ions on both P1 and P2 is controlled by chemisorption. Four equilibrium isotherm models (Redlich-Peterson, Langmuir, Freundlich, and Harkin-Jura) are investigated, revealing that the adsorption process is a monolayer and multilayer process on a heterogeneous surface. GRAPHICAL ABSTRACT


Introduction
Since radioactive liquid isotopes have some radiological effects on living things, they can be created by nuclear power plants, research reactors, and other institutions that use radioisotopes.Therefore, the main focus is on reducing or eliminating particular dangerous radio nuclides from radioactive liquid waste.These radioactive wastes include iodine radioisotopes like 125 I (half-life: 59.41 days), 129 I (half-life: 1.57 × 10 7 years), and 131 I (half-life: 8.02 days), which are among the most feared radio nuclides since they are halogen gases and easily move to the environment if released [1][2][3].
Iodine is a halogen, making it simple to release volatile radioactive isotopes into the environment in the event of a nuclear disaster.In the four well-known nuclear accidents that have happened around the world [5,6], some radioactive iodine has been found in the surrounding area.Dispersion, deposits, uptake by plant leaves, root absorption, and ingestion by animals and people all contribute to its translocation to the food chain.Iodine deposited on grass that is consumed by lactating animals makes its way into milk a few hours after intake, with the maximum amount emerging after three days [4].
Due to their capacity to absorb and hold water, sorbent materials like polymers have attracted a lot of research.Alginate salt is a natural polymer that has been used to mix with synthetic polymers like acrylic acid and its derivatives [7][8][9].
Brown algae are the source of the natural polysaccharide known as alginate.It is easily modifiable using a variety of physical and chemical methods, such as grafting copolymerisation with other useful substances like acrylic acid or its derived molecules.Alginate's functional groups serve as a defining feature (OH and COO).Additionally, it is distinguished by its lengthy existence, reasonably low cost, non-toxicity, and biodegradability [8].
G P Rajalekshmy et.al. : The objective of this study was to create a stable alginate-based scaffold for the delivery of insulin for wound treatment.As one of the most popular biopolymers for wound healing, alginate its use is however restricted by its weak mechanical strength and degradability, particularly as a drug delivery matrix.Alginate xerogel's strength and stability were increased through grafting, and the results point to the possible use of insulin-loaded AGM2S xerogels as a wound-healing material [9].
Clara et.al.: Novel sodium alginate-based hydrogels were prepared by grafting the binary mixture of methacrylic acid and sodium-2-acrylamido-2-methyl-1propane sulphonate on to sodium alginate (SA) with N, N'-methylenebisacrylamide (MBA) and ammonium persulphate (APS) as crosslinker and initiator respectively.The resultant SA-g-poly(AMPSNa-co-MAA) hydrogels which used as a candidate system for controlled drug delivery [10].
Gamma ray polymerisation is used in the current study to create high-capacity polymers such as poly (sodium alginate-acrylic acid) and poly (sodium alginate-acrylic acid-methacrylic acid).The ability of the produced polymers to remove 131 I (a substitute for I) radionuclides from aqueous solutions is assessed since the removal of radioactive waste from their environment is hampered by anion sorption, which is caused by their negative charges.Important variables affecting adsorption and their mechanisms are thoroughly investigated in order to achieve the best results.

Materials
Acids (Acrylic acid (AcA), mthacrylic acid (MAcA), methylene bisacrylamide (MBA)) are purchased from sigma-Aldrich.Sodium alginate (Na.Alg) is purchased as alginic acid sodium salt from Fluka.The majority of the chemicals and reagents employed are of analytical quality; dissolving, preparation, and dilution all include bi-distilled water.

Preparation of sodium alginate poly(acrylic acid) P1
In order to create sodium alginate (Na Alg)-acrylic acid (AcA) polymer (PAM-AAc), Na Alg is free radical polymerised with AcA as the monomer, N,N ′ -methylene bisacrylamide (MBA) as the crosslinking agent, and gamma radiation as the radiation source.The ideal synthetic conditions are AcA 20 weight percent, (Na Alg) 1 weight percent, and MBA 0.5 weight percent.All ingredients are combined in glass tubes and given a 25 kGy dose of 60 Co gamma radiation.

Preparation of sodium alginate poly(acrylic acid-methacrylic acid) P 2
It is possible to create sodium alginate (Na Alg)-acrylic acid (AcA)-methacrylic acid (MAcA) polymer (PAM-AcA-MAcA) by free radical polymerising Na Alg and MAcA with AcA as monomers, N,N ′ -methylene bisacrylamide (MBA) as a crosslinking agent, and gamma radiation as the radiation source.The obtained results showed that employing 20% AcA, 10% MAcA, and 0.4 weight percent NaAlg at an irradiation dose of 15 KGy with the addition of 0.03% MBA as a crosslinker are the ideal circumstances for producing a good grafted copolymer.All ingredients are combined in glass tubes and given a 25 kGy dose of 60Co gamma radiation [12,13].

Characterisation
In order to identify function groups, the Fourier transformed infrared spectrum (FT-IR) is used to describe both produced polymers (P 1 and P 2 ).The samples are mixed with KBr and then compressed into pellets using the Nicolet 560 FTIR model of equipment.Additionally, the surface morphology of the produced polymers is studied using a JEOL-JSM 6510 LA scanning electron microscope (SEM) (Japan).Finally, to prevent thermal oxidation of the sample, thermal analysis of both polymers (P 1 and P 2 ) is carried out using a Shimadzu DT-60 thermal analyzer from Japan at a heating rate of 10 o C/min.

Batch adsorption studies
The removal of iodine radio-nuclides from liquid radioactive waste solution is explored using batch testing to examine the sorption behaviour of the two generated polymers.Aqueous solution pH (1.0-10.0),starting iodine ion concentration (10-500 mg/L), sorbent weight (0.012-0.2 g), contact time (5-120 min) of mixing the adsorbate with the sorbent material, and counter anions are among the parameters that are the subject of experiments (bicarbonate and sulphate).Unless otherwise stated, each batch experiment comprises mixing 0.05 g of a suitable sieve size polymer with 10 ml of a solution containing 100 mg/L of I ions solution spiked with 131 I at 25°C.After centrifuging the suspension, the final iodine ion concentration is determined radiometrically.To carry out the experiment, one of the aforementioned parameters is modified while the others are not.
The removal percentage (R%), distribution coefficient (K d ) mL/g, amount of metal ions adsorbed at any given time (q t ), and maximal I-adsorption capacity (q e ) mg/g are each calculated using the corresponding equations below: Iodine's initial and ultimate radio-activity is represented by (A 0 ) and (A e ), respectively.The initial concentration of iodine is represented by (C o ), which is mg/L, V is the solution volume (L) and m is the sorbent mass (g).

Radioisotopes
131 I radioisotope (t 1/2 = 8.02 days) is purchased from the Radioisotope Production Facility, Atomic Energy Authority, Egypt.It is detected radio-metrically by γ counter using a NaI (TI) scintillation crystal (Nucleus-Model 500) & scalar rate amplifier model 2010.

Effect of co-existing ions
Different concentrations of two anions (bicarbonate and sulphate) ranging in concentration from 0.5-5 mM are chosen to evaluate the uptake of iodine as a function of individual anions added to DI water in order to determine the impact of individual co-existing ions on the adsorption of iodine onto the two polymers under investigation.100 mg/L of iodine is added to a 5 ml volume of each solution before being combined with 0.05 g of P1 and P2, separately.

Effect of adsorbent amount
In order to investigate how the decontamination factor (DF) varies with polymer weight, experiments are carried out at room temperature while holding all other variables constant.Different weights of polymers, ranging from 0.0125 to 0.2 g, are shaken with 5 ml of a 100 mg/L concentration of iodine ions.The following equation [14] is used to compute the decontamination factor.

Results and discussion
3.1 Characterisation

FTIR of prepared polymer
The produced copolymer (P 1 ) FTIR spectrum (shown in Figure 1) exhibits bands at 3000 cm −1 , which may be indicative of O-stretching H's vibration.The stretching of SP3 C-H may be the cause of the absorption band at 2400 cm1.The stretching of a carboxylic acid's C = O may be responsible for the absorption band at 1640 cm1.The bending SP 3 C-H absorption band at 1250 and 1150 cm1 may exist [15].The produced copolymer's (P 2 ) FTIR spectrum, as seen in Figure 1, exhibits bands at 2980 and 2854 cm −1 that are typical for the stretching vibrations of O-H, C-H, and CH 2 , respectively.The stretching of SP3 C-H may be the cause of the absorption band at 2330 cm1.Absorption band at 1670 cm1 may be related to carboxylic acid's C = O stretching.Splitting SP3 C-H and -CH 3 methyl groups may be responsible for the absorption bands at 1250 and 1150 cm −1 .A band at 680 might be a CH stretching band.

Scanning electron microscope
SEM is important to clarify the topography (Texture/ surface) of a sample, morphology (size, shape) and approve the compatibility of the monomers.From Figure 2 the surface showed a smooth surface and relatively a homogeneous appearance.This indicates an increase incompatibility between the constituents used.
3.1.3Thermal Analysis (TGA and DTA) Figure 3 shows the thermal decomposition of the prepared grafted polymers P 1 and P 2 .For P 1 , The degradation passes in three stages.The first stage from 69.33 to 140°C shows that at 140°C exhibits a weight loss of 3.49% with an endothermic peak at 69.3°C, which may be due to the removal of absorbed water molecules.The second stage from (140 to 207.5)°C with endothermic peaks at 207.5°C there is a weight loss of 3.79%, which may be due to the release of COOH, water, and NH 3 .The third stage from 207.5 to 286.89°C, shows endothermic peaks at 286.89°C exhibits a weight loss of 2.15%, which may be due to the removal of volatile hydrocarbons and complete degradation to the oxide form [13].The results showed that the polymer possesses thermal stability until near 400°C.For P 2 , the degradation passes in three stages.The first stage from 50 to 170°C which shows that at 170°C exhibits a weight loss of 5.819% with an endothermic peak, which may be due to the removal of absorbed water molecules.The second stage from (170 to 330)°C with endothermic peaks at 216.57°C exhibits a weight loss of 41.465%, which may be due to the release of COOH,  water, and NH3 (LI, Chen, et al.2020).The third stage from 330 to 600°C, shows endothermic peaks at 524.69°C exhibits a weight loss of 36.186%, which may be due to the removal of volatile hydrocarbons and complete degradation to the oxide form.The results showed that the polymer possesses thermal stability until near 400°C.

Surface area
A novel synthesised polymer's physical properties, such as porosity, surface area, and pore size distribution, are thought to be crucial for sorption performance.Table 1 provides the BET surface area, pore volume, and distribution of pore sizes for P1 (sodium alginate-acrylic acid) and P2 (sodium alginate-acrylic acid-methacrylic acid).P1 and P2 were characterised by the BET method (N2 adsorption/desorption isotherms and pore size distributions analysis) in order to determine specific surface area and porous volumes.P1 and P2 have pore volumes of 5.9*10-3 and 1.61*10-3 cc/g and BETspecific surface areas of 4.1 and 8.41 m2/g, respectively.
The specific surface area, pore volume, and pore size distribution of the prepared adsorbents were determined using nitrogen adsorption/desorption isotherm at 77 K by Brunauer-Emmett-Teller (BET) equation on the Quantachrome Nova instrument, Model 184 Nova1000e series, USA.The analysis was done at Hot Laboratories Center, Egyptian Atomic Energy Authority.

pH and point zero charge
The pH of the aqueous medium is one of the primary factors influencing I-ion sorption by influencing the degree of dissociation of functional groups on adsorbent surfaces, its overall surface charge, and the chemistry or speciation of Iodine ions in a solution.The effect of pH on the removal percentage of 131 I by P1 and P2 is studied at pH values ranging from 1.0 to 10.0, as illustrated in Figure 4.The results showed that the removal percentage of iodine ions increased with increasing pH values, peaking at pH 3 with the investigated two polymers, when protonation of carboxylic and amid groups began, leading to an increase in the adsorption amount of I [16,17].After pH-3 removal, % decreases as pH increases, which may be attributed to the repulsion force between the negative charge of the sorbent surface and the anionic radionuclide I-.
On comparing the affinity of the two polymers towards 131 I, it is found that it takes the order P 2 > P 1 .The removal percentages for P 1 and P 2 are found to be 77.5% and 83.0%, respectively, at a pH value of 3.0, which is selected as the optimum pH.This preferential sorption activity could be explained by the fact that iodine is a highly polarised molecule that behaves as an electrophilic ion in the presence of a suitable Lewis base such as an alkene or an alkyl.In addition, amide (CONH2), carboxyl (-COOH), and hydroxyl (-OH) groups have been considered as the main functional groups to play key roles during the adsorption process [18].The effect of pH on the distribution coefficient, Kd, is a parameter utilised to present the ratio of ions adsorbed into the solid phase to ions in the liquid phase.Therefore, it can be used as a valuable parameter to investigate ion mobility.The high values of K d demonstrated that the ions are adsorbed by the polymer, while the low values of K d indicated that a large fraction of the ions remains in the solution.
Figure 4 also displays that the distribution coefficient (K d ) at the optimum pH value of 131 I reaches 345 ml/g for P 1 and 517 ml/g for P 2 .These results also illustrate that the sorption property of P 2 towards the anionic species is greater than that of P 1 .
Both synthesised polymers have a point zero charge at pH 8 (Figure 5), after which the final pH values for both polymers decrease.This may be due to the liberation of OH-, which is formed by the hydrolysis of the polymer's function group.Otherwise, at pH greater than 7.0, the release of protons caused by the polymer adsorption of sodium ions in solution results in a decrease in the final pH [16].

Effect of shaking time
Figure 6 shows the effect of shaking time on the removal and amount of sorbet of 131 I radionuclide by the two investigated polymers, P 1 and P 2 .The removal percentage clearly increased rapidly, reaching equilibrium  after only 30 min with the two investigated polymers.This means that the I-ion reacts chemically with the two polymers, and the rate of the reaction process is kinetically fast.This fast rate of adsorption at the beginning stage may be due to the availability of all reaction groups and sites and the presence of a relatively high iodine ion concentration [19].While adsorption is taking place, a large number of reacted groups are occupied, and the iodine ion I-concentration decreases, causing the adsorption rate to decrease.The removal percent of iodine ions is computed for the two polymers P 1 and P 2 and found to be 77.76% and 84.23%, respectively.The amount of I -sorbed by the investigated two polymers is also calculated, and the data show that the amount sorbed gradually increased until reaching equilibrium at 7.7 and 8.4 mg/g for P 1 and P 2 , respectively.

function of kinetic models
Four kinetic models (pseudo-first-order, pseudo-secondorder, Elovich, and Weber-Morris) are used to fit the data of the adsorption tests in order to explain the adsorption mechanism of I-131 onto P 1 and P 2 .
The first model is Lagergren model (pseudo-firstorder model (PFO)) in which the linear form can be given by the following equation [20]: ln (q e − q t ) = ln q e − K 1 t Where q e and q t are the amounts adsorbed at equilibrium and at time t respectively (mg/g), K 1 is the rate constant of the kinetic model (min −1 ) which can be used to describe how fast the adsorption equilibrium is achieved; t is the time (min).Parameters K 1 and q e are calculated from the slop and intercept, respectively by blotting ln(qe-qt) vs. t.The second model is the Ho and Mckay (pseudosecond-order model (PSO)) which was used in the majority of published articles, the adsorption experimental data and adsorption rate constants were predicted and calculated using this model.The linear form of this model can be given by the following equation [21,22]: In this equation, q e and q t are defined as before in Pseudo-first-equation; K 2 is the model constant rate (min −1 ) and t is the time (min).By plotting t vs. t/q t , the parameters q e and K 2 are calculated from slop and intercept, respectively.The third model is the Elovich model which presupposes that the heterogeneous nature of the solid surface-active sites results in a range of activation energies.Its fundamental principle is a second order heterogeneous reaction, and its linear form can be given by the following equation [23]: Where q t represents the quantity of Iodine removed at time t (mg/kg), a represents the initial rate of desorption (mg/kg.h),b represents a kinetic coefficient associated with the covered surface and desorption activation energy (kg/mg), and t represents time (min).By plotting ln(t) vs. q t , b and a are calculated from slop and intercept respectively.
The Weber-Morris model, the fourth model, is frequently used in the adsorption process to describe the mass transfer mechanism from the outside surface to the pores of the adsorbent.It is based on Fick's second law of mass transfer.The following equation describes the linear form of this model, which was utilised to determine the intra-particle diffusion coefficient, is stated [24].
Where K t (mg/g.min 1/2 ) and C (mg/g) are the Weber and Morris diffusion coefficient and boundary layer thickness, respectively which can be calculated by linear plots between qt vs. t 1/2 .Figure 7 shows the linear fitting plots of the four kinetic models, which indicate that all models exhibit good fit, but the Weber and Morris models' fitting lines do not pass through the origin point for both the polymers (P1 and P2).Table 2 displays the calculated kinetic parameters that were derived for each model.With regard to this table, it is evident that PSO has higher regression coefficients, or R 2 , values (0.996 for P 1 and 0.997 for P 2 ) than that of PFO (0.958 for P 1 and 0.946 for P 2 ).Moreover, in PSO, the calculated qe (calc) values are quite close to the experimental qe (exp) values; in PFO, with the two polymers, they show a significant divergence.As a result, the pseudo-secondorder model, which suggests chemo-sorption as the mechanism, is better suited to describe the adsorption reaction of I-131 onto P 1 and P 2 .Elovich model also has high R 2 values for P 1 and P 2 , 0.981and 0.996, respectively, confirming the chemo-sorption mechanism.However, α and β constant values in P 2 are greater those in P 1 (β = 0.851 and 0.817 for P 2 and P 1 respectively), (α = 0.448 and 0.422 for P 2 and P 1 respectively) indicating that P 2 has more active sorption sites than P 1 .
Weber and Morris parameters suggest that the adsorption of iodine onto P1 and P2 is only controlled by intra-particle diffusion if the plot is linear and passes through the origin.Indeed, the data did not pass through the origin, indicating that intra-particle diffusion was not the rate-limiting mechanism [25].

Equilibrium isotherm models
Using the Redlich-Peterson, Langmuir, Freundlich, and Harkins-Jura isotherm models, the equilibrium adsorption data collected in this study is assessed.
The first model is the hybrid Redlich-Peterson model, which combines the Freundlich and Langmuir models and may be used in both heterogeneous and homogeneous environments.The following equation can be used to illustrate this model's linear form [26]: The Redlich-Peterson isotherm constants g and a can be determined from the slop and intercept of a plot of ln C e /q e vs ln C e , respectively, where C e (mg/L) and q e (mg/g) represent concentration and quantity adsorbed at equilibrium, respectively.The fitted lines, which are displayed in Figure 8(a), show how well this model fits the experimental data, especially at high Ce.
The estimated parameters are shown in Table 3, and they show that the surface has a significant degree of heterogeneity because the values of (g) for the two polymers are both less than 1 (g = 0.46 and 0.49 for P1 and P2, respectively).Given that P 1 and P 2 have R 2 values of 0.97 and 0.98, respectively, and that the surface of the produced composite may be homogeneous or heterogeneous, this model is able to predict the sorption process.
The Langmuir (1) model, which is generally used to fit the adsorption data, is the second model.By utilising the  following formula, one may estimate the adsorption equilibrium for the two polymers using the Langmuir linear formula [27]: The equilibrium concentration (C e ) is expressed in mg/L, the amount adsorbed per unit mass (q e ) is expressed in mg/g, the Langmuir constant is expressed in b, the monolayer saturation adsorption (Qmax) is expressed in mg/g, and the equilibrium adsorption energy constant (K L ) is expressed in L/mg.The adsorption nature is indicated by the separation factor, R L (g.L./mg 2 ) value which can be calculated from the following equation: If (R L = 1) the adsorption is linear, if (R L = 0), the adsorption is irreversible, if (R L >1), the adsorption is unfavourable, if (0< R L <1), the adsorption is favourable.
The experimental data suit this model well, as indicated by the linear plots of C e / q e vs. C e in Figure 8(b).The slop and intercept of the linear plot, which are shown in Table 3, can be used to compute the values of qmax and K L .This makes it clear that even though this model's q max is not in agreement with the experimental value and its R 2 for both polymers is low (R 2 = 0.94 and 0.95 for P 1 and P 2 , respectively), it has an R L value greater than 0 and less than 1 (R L = 0.53 and 0.42 for P 1 and P 2 , respectively), indicating favourable adsorption.
The third model is Freundlich isotherm model which defines the heterogeneity of the surface as well as the exponential distribution of the active sites and the active sites energies, its linear form can be given by the following equation [28].Where, q e = Sorption amount at equilibrium (mg/g), K F = Freundlich isotherm constant, and n = Heterogeneity factor.n and K F can be calculated from the slop and intercept of the linear plot between log(q e ) and log(C e ) respectively as given in Figure 8(C).The calculated parameters are shown in Table 3, where it is obvious that the high correlation coefficients for both atoms (R 2 = 0.98 and 0.99 for P 1 and P 2 , respectively) support the multi-layer adsorption process in addition to the close agreement between the calculated and experimental adsorption capacity values for both polymers.On the other hand, the high heterogeneity (n) values support the existence of a heterogeneous surface.
The Harkins-Jura model, the fourth model, is investigated to support the multilayer adsorption of iodine atoms onto the prepared two polymers, and its linear form is as follows [29][30][31]: Where A (quantitative adsorption) and B are Harkins constants that can be calculated from the slop and intercept of the linear plots of q e 2 vs log C e respectively as given in Figure 8(D).The calculated parameters are illustrated in Table 2 from which it is clear that the high values of correlation coefficient for Iodine ions atoms (R 2 = 0.98 for P 1 and P 2 ) confirms the existence of heterogeneous pore distribution and multilayer sorption.
From the previous data we concluded that, Freundlich isotherm model can describe this reaction more than Langmuir model and the adsorption of 131 I onto P 1 and P 2 is monolayer and multilayer sorption on a heterogeneous surface.
The Comparison data for the sorption capacity of 131 I using the synthesis polymers and various sorbents are illustrated in Table 4.

Sorption mechanism
The sorption mechanism is a major factor in understanding the retention process between the investigated metal ion and the sorbent.as well as to know the features of the material, which help to design a new sorbent for any application [32].
Based on the previous results, the sorption mechanism of the two investigated polymers towards 131 I is proposed in Figure 9.For the two polymers, the main functional groups present in P 1 and P 2 are the COOH, NH 2 , and OH groups.The persuasive explanation for the above results is that the protonation of polymer function groups such as (-COOH and -NH 2 ) starts at pH = 2 and reaches maximum at pH = 3.These groups Figure 9. Predicted sorption mechanism for the sorption of iodine ions using P 1 and P 2 .possess positive charge at this pH range and can react electrostatically with I [33][34][35].
At pH 4, a part of the COOH group starts changing to its deprotonated form, COO -, leading to a decrease in the removal percent of 131 I. Thus, at pH = 3, the two investigated polymers have a good sorption capacity [36].

Effect of adsorbent weight:
To investigate the variation in decontamination factor (DF) based on adsorbent amount, various amounts of adsorbents ranging from 0.0125 to 0.2 g are investigated, and data calculated are listed in Table 5.From this table, it is clear that increasing sorbent weight increases removal percent and DF of 131 I for the two investigated polymers as the active groups increase.When the DF of the investigated polymers is compared to the literature, it is discovered that the two-polymers have a higher DF than many other sorbents [37][38][39].

Effect of co-existing ions
Figure 10 depicts the effect of bicarbonate and sulphate anions concentration on iodine-131 sorption using P 2 .From this figure, it is clear that increasing bicarbonate concentrations from 0.5 M to 5 M decreases iodine sorption substantially, which reaches 19.9% for P 2 .This decrease could be explained by the fact that the presence of bicarbonate raises the pH of a solution as it dissociates and liberates the OH-group [40,41], as shown in the following equations: Otherwise, increasing sulphate concentrations show a slight decrease in the iodide uptake from the aqueous solution.This may be attributed to the adsorption of sulphate onto specific adsorption sites of the polymer surface, separate from the adsorption sites for iodide [30].

Application on a Real Radioactive waste
After being diluted to a manageable radioactivity level, an actual radioactive waste solution is obtained and described.It is discovered that, in addition to other radio nuclides not included in this study, it contains both iodine and europium.Sorption tests are performed on the two polymers that have been synthesised under ideal sorption conditions.With 0.05 g of both P 1 and P 2 , 50 mL of radioactive waste is shack for 120 min at pH 4 and room temperature.The two phases are separated after shaking, and the supernatant is then subjected to radiometric examination [19].The decontamination factor (DF) and elimination percentage of each radionuclide identified in the solution are computed; the findings are shown in Table 6.As can be observed, 152 + 154 Eu achieves a decontamination factor of 33 and a removal percentage of 97%, whereas removal percentage of 95%.The polymers will be treated after the sorption process is finished.The processed polymers should be treated using conventional techniques like burning or compaction because they are organic in nature [42,43].Finally, with maximum DF values of 24 and 33 for I - and Eu + 3 , respectively, the synthesised polymers have a remarkable ability to remove radioactive I, Eu, and other radio nuclides such as Ce and Co that may be present in any radioactive waste solution from LLW.These findings imply that after achieving the volume reduction principle in the management of radioactive waste, such polymers can be taken into consideration for the removal or even diminution of some radio nuclides from radioactive waste.

Adsorption-desorption
Pre-concentration of the adsorbate and reusability of an adsorbent are given significant attention in the application technique for the removal of metals from wastewater.In this work, several desorbing agents' capacity to remove iodine ions absorbed by the two produced adsorbent polymers was assessed.The amount of Iions desorbed in 0.5 h (30 mints) after the adsorbent had been loaded with the maximum amount of I-ions and placed in 0.5 M desorbing agents (HNO 3 and NaOH) was measured.Using sodium hydroxide and bidistilled water, there wasn't any observed desorption.Table 6, The results show that the reversibility of the adsorption process is only highly significant in HNO3 medium, according to the kinetic experiments.
The results presented in Table 6 showed that the acid (1M of nitric acid) had a significant impact on I-ion desorption.Table 7 shows that 70% and 66% of the adsorbed iodine ions from the loaded adsorbents of P1 and P2, respectively, were desorbated and transferred to the suspending solution using 1 M HNO3.The desorption rate increased as acid concentration grew.These results demonstrate to the newly prepared polymers' stability in binding irreversible iodine.The high concentration of H + ions at low pH has been postulated to be the source of the displacement of adsorbed iodine ions.

Conclusion
This study systematically evaluated the affinity of both sodium alginate poly (acrylic acid) (P 1 ) and sodium alginate poly (acrylic acid/methacrylic acid) (P 2 ) for I removal.It is observed that the two polymers have superior ability and speed for the removal of radioactive iodine atoms from liquid ester since they pose more than one functional group such as OH, COOH, NH 2 , and SO 3 H, which guarantee a high capacity for I adsorption.At pH 3, the two polymers removed the most I -from the aqueous solution, reaching 77.7% and 84.2% for P 1 and P 2 , respectively.The two polymers exhibited high sorption capacities for the iodine ion, which were found to be 58.5 and 67.9 mg/g for P 1 and P 2 , respectively.Sulphate and carbonate co-existing ions showed some negative influence on the adsorption of iodine.The adsorption kinetics and equilibrium well fit the pseudo-second-order and Freundlich isotherm models.It is predictable that the adsorbent will have great potential for the environmental cleaning of I with a high retention rate.

Figure 4 .
Figure 4. Effect of pH on the removal % and distribution coefficient (K d ) with their error bars for I -using (A) poly sodium alginateacrylic acid and (B) poly sodium alginate-acrylic acid-methacrylic acid.

Figure 6 .
Figure 6.Effect of contact time and their error bars for the sorption of I -using (A) poly sodium alginate-acrylic acid and (B) poly sodium alginate-methacrylic acid.

Figure 5 .
Figure 5. Solution pH changes before and after the adsorption of Iodine-131.
(a) Conception and design, or analysis and interpretation of the data.(b) Drafting the article or revising it critically for important intellectual content.(c) Approval of the final version.

Table 1 .
BET surface area and pores properties of the two prepared polymers.

Table 2 .
Kinetic parameters for adsorption of 131 I using P 1 and P 2 .
e − q t ) = ln q e − k 1 t q e, exp.(mg/

Table 4 .
Comparison data for the sorption capacity of 131 I using various sorbents.

Table 5 .
Effect of sorbent weight on the removal percent and decontamination factor of 131 I.using P 1 and P 2 .
Figure10.Effect of Bicarbonate and sulphate concentrations on the removal and decontamination factor of Iodine-131 using P 2 .