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Synthesis and application of poly(Acrylamide-Itaconic Acid)/Zirconium tungstate compositematerial for cesium removal from differentsolutions

K. F. Allan, E. M. El Afifi & M. Holial

To cite this article: K. F. Allan, E. M. El Afifi & M. Holial (2015): Synthesis and application ofpoly(Acrylamide-Itaconic Acid)/Zirconium tungstate composite material for cesium removal fromdifferent solutions, Particulate Science and Technology, DOI: 10.1080/02726351.2015.1131793

To link to this article: http://dx.doi.org/10.1080/02726351.2015.1131793

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PARTICULATE SCIENCE AND TECHNOLOGY http://dx.doi.org/10.1080/02726351.2015.1131793

Synthesis and application of poly(Acrylamide-Itaconic Acid)/Zirconium tungstate composite material for cesium removal from different solutions K. F. Allan, E. M. El Afifi, and M. Holial

Hot Laboratories and Waste Management Centre (HLWMC), Atomic Energy Authority of Egypt, Cairo, Egypt

ABSTRACT This study is conducted to find the conditions required to synthesize composite material for cesium (134Csþ) removal from the generated liquid waste associated with nuclear, medical, industrial, and/or research activities. The study shows that the optimum conditions required for synthesizing “poly [acrylamide (AM)- itaconic acid (IA)]/N,N0-methylenediacrylamide (DAM)/zirconium tungstate (ZrW)” or “poly(AM-IA)/DAM/ ZrW” are 0.01 g DAM dose as a cross-linker, a co-monomer concentration of 20%, a co-monomer composition (AM-IA) (12:88), and 0.03 g (melted at 450 °C–500 °C) ZrW with gamma irradiation dose of 30 kGy. The composite material was characterized by Fourier infrared (FTIR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscope (SEM), and Brunauer-Emmett-Teller (BET) surface area measurements. The adsorption performance of the composite was investigated. The maximum removal efficiency of 134Csþ ions was found to be 93%� in moderate alkaline solutions at pH 8 � 0.2 after 90 min. Kinetic studies indicated that the adsorption process is controlled by the pseudo-second-order kinetic model as a chemisorption process. Fitting of the adsorption data has pointed out that the adsorption process follows the Freundlich isotherm model as heterogeneous process. The maximum adsorption capacity (qmax) is 5.298 mmol Csþ g� 1 adsorbent. Applicability of the synthesized composite material was also examined to remove 134Csþ ions in different aqueous solutions.

KEYWORDS 134Csþ; adsorption; isotherm; kinetic; liquid waste; polyamide composite; treatment

Introduction

Radionuclides of 134Cs and 137Cs with the half-lives of 2.6 and 30 years, respectively, belong to the main long-lived fission products of 235U. These radionuclides undergo radioactive decays with the emission of beta particles and relatively strong gamma radiation. Cesium salts, the most common form of the element easily dissolved in water, causes a serious hazard if an accident appears with a nuclear reactor, such as that occurred at Three Mile Island in Pennsylvania (USA 1979), Chernobyl (Ukraine 1986), and the last big accident in 2011 at Fukushima (Japan 2011) (Barbara et al. 2014; Delchet et al. 2012). 137Cs decays by beta mode either to 37Ba or 137mBa with γ-ray emission of 662 keV. One gram of 137Cs has an activity of 3.215 TBq. A considerable amount of 137Cs has been released into the environment over the years: ∼1018 Bq were dispersed in nuclear test fallout from 1950 to 1963, ∼1017 Bq in the Chernobyl accident (Giani and Helmers 1997), and an estimated 1016 Bq in the Fukushima accident (Yasunaria et al. 2011; Chino et al. 2011; Morino, Ohara, and Nishizawa 2011).

In recent years, considerable interest has arisen with regard to the fate and transport of radionuclides such as 137Cs in aqua-tic environments. 137Cs is an important indicator of radioactive pollution in aquatic environments. The transport and fate of anthropogenic 137Cs are related to the chemical properties of ionic Csþ, which generally dictates a high degree of mobility and bioavailability of this radionuclide. Therefore, removal of the pollutants from industrial wastewaters has recently become

one of the most important processes because of it becoming more profound with increasing industrial activities. Cesium in radioactive waste produced from industry, medicine, research and nuclear establishments is one of these pollutants that its separation from aqueous solution is mostly needed. In addition to some toxic organic compounds that are sus-pected to be carcinogens, these compounds can cause fatal damages (Fessenden, Fessenden, and Landgrebe 1986).

Studies on the removal of Csþ ion from aqueous solution have been focused largely on adsorption and ion-exchange methods (EI-Kamash 2008; Dahiya, Tripathi, and Hedge 2008; Chen and Wang 2008; Sangvanich et al. 2010; Younjin, Chorong, and Sang-June 2015; Abdel-Galil, Khalil, and El-Aryan 2015; Choong and Ju-Hyun 2015; Amin, Ali, and Mohammad 2015; Hun, Jung-Seok, and Wooyong 2015; Yang, Okada, and Nagatsu 2016). Natural and synthetic zeolites, clay minerals, and synthetic organic or inorganic ion exchangers have been used on a large scale for separation of radioactive Cs from low- and intermediate-level radioactive waste effluents or contaminated water (Panswed and Wongchaisuwan 1986; Smiciklas, Dimovic, and Plecas 2007; EI-Kamash 2008; Sangvanich et al. 2010). However, the majority of these materials appear to be not economically attractive because of their high operational cost and poor performance. Also, many technologies have been developed for pollutant removal from aquatic environments, including flocculation and coagulation (Panswed and Wongchaisuwan 1986), membrane separation (Ciardelli, Cors, and Marucci 2000), oxidation or ozonation

CONTACT E. M. El Afifi em_afifi1968@yahoo.com Hot Laboratories and Waste Management Centre (HLWMC), Atomic Energy Authority of Egypt, Cairo, Egypt. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/upst. © 2015 Taylor & Francis

(Swaminathan 2003; Muthukumar and Selvakumar 2004), elec-tro-coagulation (Alinsafi et al. 2005), and adsorption (Mall et al. 2005). Adsorption has been found to be an effective, cheap, and potential technique for removing Cs.

Composite adsorbents/ion exchangers have been widely used for treatment of liquid wastes. The composite ion exchan-gers have improved qualities compared to pure organic or inorganic exchangers, such as better selectivity for the capture of some ions, increased mechanical and chemical resistance, more regularity form of the grains, smaller solubility in water, and better kinetics of exchange relative to the pure organic or inorganic exchangers. The composite ion exchangers are generally obtained by implantation of an inorganic part in the wide range of organic materials during the polymerization pro-cess (Kilincarslan and Akyil 2007). Linear low-density polyethylene-based and metal oxide (PbO and WO3)-filled composites were prepared and characterized for ionizing electromagnetic radiation (IEMR) shielding applications (Belgin and Aycik 2015). A graphene-based magnetic com-posite (Fe3O4/GO) was prepared, characterized, and utilized as an efficient adsorbent for immobilization of U(VI) from aqueous solutions in nuclear waste management (Donglin et al. 2015; Shujun et al. 2015). New composite of cellulose, chitin, and chitosan modified with Ti or Ni nanoparticles was developed and tested for removal of 137Cs,85Sr, 60Co, and 152þ154Eu from radioactive wastewater (Jana et al. 2015). Graphene oxide (GO) and two magnetic graphene oxide (MGO) composites with a different amount of magnetite were synthesized and used for sorption of Am3þ and Pu4þ isotopes as well as Co2þ, N2þ, Cu2þ, and Pb2þ (Galina et al. 2015). The tita-nate/GO composites were successfully synthesized by thermal treatment and applied as a new adsorbent for removal or pre-concentration of radiocobalt (60Co) and other kinds of radionu-clides from aqueous solutions in environmental pollution cleanup (Xiangxue, Songsheng, and Mancheng 2015). A novel composite material of SiO2–Al2O3 based on poly(acrylic acid– maleic acid) was synthesized, characterized, and used for removal of 134Cs in different concentrations of acid or salt solu-tions. The poly(AA–MA)/SiO2/Al2O3 composite is a promising adsorbent for Cs removal from acidic liquid radioactive waste (Attallah, Allan, and Mahmoud 2015).

The novelty statement of the present work is in optimizing the conditions required to synthesize organic/inorganic composite, namely “poly(AM-IA)/DAM/ZrW.” Herein, the composite material was characterized and applied as an efficient adsorbent for removal of 134Csþ radionuclide from different aqueous solutions. The sorption performance of 134Csþ ions onto the composite surface was also investigated by different kinetic and isotherm models.

Materials and methods

Reagents

All chemical reagents were of analytical grade (AR grade). Distilled water was used for preparing the working solutions. The reagents of acrylamide (AM, 98%), itaconic acid (IA, 99%), and N,N`-methylenediacrylamide (DAM) were provided by Merck (Germany). Zirconium hydrous oxide

(99%) was obtained from Riedel (Germany). Sodium tungstate (98%) was obtained from LOBA Chemie Company.

Preparation of the composite material

Preparation of zirconium tungstate (ZrW) The inorganic ZrW was prepared by mixing equimolar (0.1 M) and equal volumes (250 mL) of zirconyl chloride (ZrOCl2.8H2O) and sodium tungstate (Na2WO4.2H2O) solutions with constant stirring at ambient temperature (Wu, Badrinarayanan, and Kessler 2012). The pH of the reaction mixture was adjusted (pH 8) and stirred for 60 min. The precipitate was filtered and washed with distilled water to constant pH 4.5 and dried at 50 °C for 24 h. The produced granulated white material was grounded and sieved. The fraction below 0.25 mm was taken for further work.

Preparation of co-monomer solution

The AM and IA were dissolved in ethanol mixture (1:1 v/v), and the crosslinker DAM was dissolved in deoxygenated water at the required concentrations to form (AM-IA)–DAM mixture.

Preparation of composite material

The proposed organic–inorganic polymer composite material was prepared by the direct mixing of the inorganic component with the polymer matrix. Mixing can be achieved by either solution or melt blending, provided both components may be dispersed in a common solvent or melt at high temperature. Melt blending is more common because of its efficiency and environmental containment (Zhang, Rong, and Friedrich 2003). After the solution was irradiated in 6oCo γ-ray source, a white viscous product was obtained in acidic medium (pH 3) which was then washed with acetone to remove the free monomers. Finally, the product of the synthesized composite material was dried at 80 °C for 24 h.

Radioactive isotope

For the radiochemical investigations, radioactive isotope of 134Cs was produced through the irradiation of cesium carbon-ate at the Egyptian second Research Reactor (ETRR-2). Accu-rate amounts of cesium carbonate (Cs2CO3) samples (10 mg) were wrapped in thin aluminum foils that were previously cleaned with acetone and finally placed in thick aluminum irradiation capsules. They were transferred to an aluminum irradiation box of 670 mm length and then irradiated in the ETRR-2 core adjacent to thermal neutron flux of 1013 n. cm� 2.s� 1 for about 24 h.

Batch uptake studies

The initial pH of the solutions was adjusted by adding either HCl or NaOH solution. The adsorption behavior of the prepared composite material as a function of pH and different media has been performed using batch method. For this purpose, 10 mL of the aqueous solutions of radioactive 134Csþ was shaken with 0.05 g of the composite material poly (AM-IA)/DAM/ZrW at 25 °C � 1 °C. Thereafter, 2 mL from

2 K. F. ALLAN ET AL.

Csþ solution was withdrawn for the radiometric measurement. The uptake (A, %) on the solid could be calculated by Equation (1) (El Afifi, Attallah, and Borai 2016):

A ¼Ci � Cf

Ci

� �

� 100 ð1Þ

where Ci and Cf are the initial and final net counts of 134Csþ, respectively.

Sorption isotherm experiments were conducted batch wise. In this concern, the equilibrium was attained by shaking 0.05 g of the poly(AM-IA)/DAM/ZrW composite in 10 mL of aqueous solutions containing 0.004–400 mmol · L� 1 of Csþ

and tracer of the radioactive isotope (134Csþ) at constant pH, temperature (°C), and contact time (min). The initial and equilibrium concentrations of metal ion in the aqueous phase were determined, and the amount of metal ion per gram (q, mmol · g� 1) of the composite material was obtained using Equation (2) (El Afifi, Attallah and Borai 2016):

q ¼Ai � Af

Ai

� �

CoVm

ð2Þ

where Ai and Af are the initial and the final activity of 134Cs and Co is the initial concentration of Cs-carrier (mmol · L� 1). V and m are the volume of the sample solution (Liter) and the weight (g) of composite material, respectively.

Instruments

The thermal analysis (TGA and DTA) of the synthesized poly (AM-IA)/DAM/ZrW composite was performed by synchro-nized thermal analysis (model-50 Shimadzu, Japan). The phase evolution at various stages of synthesis was analyzed using a Shimadzu X-ray diffractometer (model XD 490, Japan) with Cu-Ka radiation and Bragg–Brentano focusing geometry was employed. The FTIR spectra of the composite were also carried out using Nicolet is10 spectrometer from Meslo (USA). The surface parameters of composite sample were measured by

sorptometer instrument model NOVA 1000e Quantachrome (USA). The radiometric measurements were achieved by NaI (Tl) scintillation counter (model-500 Nucleus). The surface morphology of the free composite material and after loading by Csþ was performed by scanning electron microscope (JSM-6510A, Japan).

Results and discussion

Optimizing parameters of the prepared composite

Table 1 summarizes the different parameters affecting the prep-aration of the prepared composite. The γ-radiation induced copolymerization of AM with IA in the presence of DAM as a crosslinker and zirconium tungstate (ZrW) as an inorganic material was studied by a free radical mechanism to determine the optimum conditions to produce an efficient poly(AM-IA)/ DAM/ZrW as an exchanger. The effects of (i) DAM, (ii) comonomer concentration, (iii) comonomer composition, (iv) amount of melt inorganic zirconium tungstate (ZrW), and (v) radiation dose on the adsorption capacity toward Cu2þ were studied. From the experimental data (Table 1), it can be seen that the optimum conditions for preparing the composite material after studying the above parameters are 0.01 g DAM as a crosslinker, a comonomer concentration 20%, a comono-mer composition (AM-IA) (12:88), and 0.03 g ZrW with radiation dose 30 kGy. The polymerization is achieved by free radicals (occasionally ions) created in the material at the end of the process. When AM and IA are irradiated with ionizing radiation by γ-rays in aqueous solutions, free radicals are generated. Random reactions of these radicals with the monomers lead to the formation of copolymers of AM/IA.

Characterization of the Composite Material

Figure 1 illustrates the FTIR spectra of the free poly(AM-IA)/ DAM/ZrW composite (a) and after adsorption of Csþ ions (b). It is observed that the broad absorption peak at 3446 cm� 1 is

Table 1. Optimization of the conditions for synthesizing the poly(AM-IA)/DAM/ZrW composite material. Experimental condition DAM dose [Co-monomer], %� Co-monomer compositions ZrW, g Dose, kGy Capacity, qe (mmol.g� 1)

i. DAM concentration 0.01 10%�� 90:10 0.03 20 1.17 0.03 0.95 0.05 0.84 0.07 0.77

ii. Co-monomer composition (AM:IA) 0.01 10%�� 2:98 0.03 20 0.316 8:92 0.911

12:88 1.18 16:84 0.71 20:80 0.8

iii. [Co-monomer], %�� 0.01 5%�� 12:88 0.03 20 1.18 10%�� 1.84 15%�� 2.15 20%�� 2.73

iv. Added ZrW, g 0.01 20%�� 12:88 0.03 20 1.78 0.10 1.86 0.15 1.94 0.20 2.73

v. c - dose, kGy 0.01 20%�� 12:88 0.03 10 1.17 20 2.55 30 3.22 40 3.05 50 2.99

The optimized value for each parameter is bolded.

PARTICULATE SCIENCE AND TECHNOLOGY 3

attributed to the stretching vibration of the bonded OH groups of the water molecules having intermolecular H-bonds and a peak at 1650 cm� 1 which can also be attributed to water molecules.

As a result of H-O-H, the hydrogen ions can easily move on the surface of ZrW. So it acts as cation exchanger (Galsden 1975). The bands observed at 1454 cm� 1 correspond to symmetric stretching vibrations of carboxyl groups, while the bands at 1315 cm� 1 correspond to –COO� bending group (Allan, Siyam, and Sanad 2001). The difference in both spectra can be due to the possible chelating between the active sites, e.g., carboxylate in the composite surface and Csþ ions. This was confirmed by the significant difference in the band which appeared at 1650 cm� 1. The interaction between the active sites of the synthesized composite with the metal ion, e.g., Csþ, was also ensured by the appearance of a band at ∼700 cm� 1 which may be due to the metal oxygen bonds (M ← O) bonds (Socrates 1980; Boukhalfa 2010).

The XRD spectrum of the prepared composite material showed a large broadening of the diffraction maxima. These broadenings can be attributed to the disordering character of

the synthesized composite. Consequently, the composite can be considered as an amorphous adsorbent in nature.

The TGA and DTA of the composite poly(AM-IA)-DAM/ ZrW was done with a heating rate of 10 °C.min� 1 as given in Figure 2. It is observed that the behavior of TGA occurred via main four-stage processes (Lanthong, Nuisin, and Kiatkamjornwong 2006). The first stage was within 75 °C– 171 °C. This may be attributed to the removal of humidity attached to surface and/or matrix from the polymeric resin with weight loss ∼7%. The second stage occurred between 171 °C and 300 °C due to the decarboxylation of IA and removal of CO2 gas. The weight loss of this stage was ∼17%. The third stage was at 300 °C–540 °C due to the degra-dation of the AM portion with removal of NH3 gas and weight loss percentage of ∼40.5%. The last stage was from 540 °C to 800 °C due to chain scission and removal of the volatile hydrocarbons with weight loss ∼27.4%. Beyond 800 °C, there is complete decomposition to the inorganic part.

The DTA displayed many endothermic peaks. The first one is at 97.3 °C, due to the removal of the external water molecules. Two endothermic peaks at 198.2 °C and 242.9 °C are attributed

Figure 1. The FTIR spectra of (a) free composite and (b) composite loaded by Csþ.

4 K. F. ALLAN ET AL.

to decarboxylation of IA and removal of CO2 gas. Two endothermic peaks at 409 °C and 507 °C can be due to the release of ammonia gas. On the other hand, there is an exother-mic peak at the 715 °C corresponding to the chain scission and finally the formation of the metal oxides and/or carbide.

The emission scanning electron microscopy (SEM) was used to observe the surface morphology of the prepared composite poly(AM-IA)/DMA/ZrW material before and after loading with Csþ ions. Figure 3 (a and b) illustrates the SEM micro-graphs of the prepared composite and after adsorption of Csþ. From these photomicrographs, it can be seen that the porous structure of the synthesized material has a porous basic structure, Figure 3a. Thereby, the material of this composite can be used as an adsorbent. It could be observed that there is a distinct change in the surface morphology after adsorption. Figure 3b illustrates the SEM micrographs of composite by the loading with Csþ ions. Therefore, the clear difference between both images (a and b) supports that the synthesized composite material has a reactive site and affinity toward the metal ions (e.g., Csþ).

Furthermore, the surface analysis of the prepared composite has shown that the surface area and the interior pore volume are 15.4 m2 g� 1 and 1.92 × 10� 2 cc · g� 1, respectively. Thereby, the prepared poly(AM-IA)/DAM/ZrW composite can be used as a suitable adsorbent material for removal and/or immobili-zation of 134Csþ in the next sub-sections.

Sorption performance of 134Csþ

The poly(AM-IA)/DAM/ZrW composite contains carboxylate (–CO.O-) and amide groups (–CO.NH-) which are of anionic type superabsorbent polymers. It is well known that this type normally ionizes at a high pH but unionizes at a low pH. The first and second dissociation constants of the IA in the composite are pKa1 ¼ 3.85 and pKa2 ¼ 5.44, respectively, as described by Sen et al. (1999).

Under acidic conditions (pH � 6), the carboxylate groups are protonated and the copolymer network shrinks signifi-cantly. If the composite material is exposed to an alkaline medium at pH ∼ 8 for a longer time, it can hydrolyze AM moiety to acrylic acid moiety, which is also an anionic type superabsorbent. Thus, it can be concluded that the adsorption uptake of Csþ ions is high in alkaline media till pH 8 followed by a gradual decrease. Therefore, the adsorption reaction of Cs ions onto composite can proceed according to Equation (3):

where R ¼ composite pattern (poly(AM-IA)/DAM/ZrW, –COOH ¼ carboxylic groups on composite surface, nHþ¼number of protons released. Figure 4 demonstrates the influence of the hydrogen ion concentration (i.e., pH) on the adsorption performance of radiotracer 134Csþ ions from aqueous solution within pH 1.5–12 by using the synthesized

Figure 2. The thermal analysis (TGA and DTA) of the synthesized composite material.

Figure 3. The SEM micrograph of (a) free composite and (b) composite loaded by Csþ.

PARTICULATE SCIENCE AND TECHNOLOGY 5

composite material. The maximum retention efficiency (%) of radiotracer 134Cs onto surface of the composite reached ∼93%�

in moderately alkaline medium at pH 8 � 0.2.

Adsorption kinetics

The kinetics of adsorption process of Csþ ions onto the synthe-sized composite poly(AM-IA)/DAM/ZrW was carried out at constant temperature 25 °C � 1 °C, V/m ratio 0.2 l.g� 1, pH 8, and metal ion concentration of 0.04 mM. The adsorption of Csþ on the adsorbent material has been investigated as a function of contact time (5–120 min) and the data obtained are illustrated in Figure 5.

It was found that adsorption of Csþ increased gradually during the first 1 h of the adsorption process, saturated slowly, and reached a maximum adsorption capacity at the time of equilibrium after 90 min. The highest retention efficiency (R, %) and uptake (qt) of 134Csþ onto the synthesized com-posite material were ∼93%�and 0.0074 mmol · g� 1, respectively. Therefore, 90 min was chosen as enough contact time between Cs ions and the adsorbent to obtain the maximum adsorption capacity in the further investigations.

On the other hand, the adsorption data were studied accord-ing to three kinetic models to verify the order of adsorption performance. The pseudo-first-order kinetics model was tested according to Equation (4) (Doniaa et al. 2009; Feihong et al. 2015; Ümit et al. 2015, El Afifi, Attallah, and Borai 2016):

log qe � qtð Þ ¼ logqe �k1

2:303t ð4Þ

where qe and qt (mmol · g� 1) refer to the amount of Csþ ions adsorbed at equilibrium and at time (t), respectively; k1 is the rate constant of pseudo-first-order (min� 1). Values of k1 and qe were calculated from the slope and intercept values of the straight line of log (qe–qt) versus (t); the results are shown in Figure 6 and reported in Table 2.

The adsorption data were also treated according to the pseudo-second-order kinetics using Equation (5) (Yu et al. 2013):

tqt¼

1k2q2

eþ

1qe

t ð5Þ

where k2 is the overall rate constant of the pseudo-second- order adsorption. The plot of t/qt versus (t) gives a straight line with slope and intercept equal to 1/qe and 1/k2qe

2, respectively. The calculated values of qe and k2 were obtained from Figure 7 and are reported in Table 2.

An intraparticle mass transfer diffusion model proposed by Weber and Morris can be written as given in Equation (6) (Machida, Aikawa, and Tatsumoto 2005):

qt ¼ kidt1=2 þ C ð6Þ

where C(mmol · g� 1) is the intercept and Kid(mmol · g� 1 · min� 1/2) is the intraparticle diffusion rate constant which can be calculated from the slope of the linear plots of qt versus t1/2. The calculated values of c and kid were obtained from Figure 8 and are reported in Table 2.

One of the major discrepancies was observed when qe values obtained from straight line of plotting were compared with the experimental sorption capacity (qe) value (Table 2).

Figure 4. Influence of pH on adsorption performance of 134Csþ ions onto synthesized poly(AM-IA)/DAM/ZrW composite.

Figure 5. Influence of contact time on adsorption of 134Csþ ions onto synthesized poly(AM-IA)/DAM/ZrW composite.

Figure 6. The pseudo-first-order plots for adsorption of 134Csþ ions onto the synthesized poly(AM-IA)/DAM/ZrW composite.

6 K. F. ALLAN ET AL.

The experimental qe value (0.0074 mmol · g� 1) differs from the corresponding calculated value (0.0060 mmol · g� 1). Thus, the good linearity of the plot does not guarantee that the interac-tion of Csþ with the synthesized sorbent will follow first-order kinetics. On the other hand, the calculated qe based on the data fitted by the pseudo-second-order kinetic model is closer (0.0070 mmol · g� 1) to experimental value as given in Table 2. Therefore, the sorption reaction can be approximated more favorably by the pseudo-second-order kinetic model. These results suggest that a pseudo-second-order sorption is the predominant mechanism, and the overall rate constant of Csþ ions appears to be controlled by the chemisorption process. The rate of adsorption process is less controlled by the intraparticle mass transfer diffusion mechanism due to the moderate bulky size of Csþ ions. This implies that the adsorption of Csþ is dependent on the concentration of both metal ions and active sites of the composite characters.

Adsorption isotherm

The study of the concentration dependency was done by chan-ging the initial concentration of Csþ ions in the range 0.004– 400 mmol · L� 1 at 25 °C, pH 8, and contact time 90 min. The results plotted in terms of the amount adsorbed (q, mmol · g� 1)

versus the equilibrium concentration of Csþ ions in the aqueous phase (Ce, mmol · L� 1) onto the prepared composite poly(AM-IA)/DAM/ZrW are demonstrated in Figure 9.

It was found that the amount adsorbed increased as the equilibrium concentration of the ions increased, with a nearly constant value being achieved at higher equilibrium concentra-tions. This is a common phenomenon in adsorption processes which is brought about by the gradual saturation of adsorption sites on the adsorbent surface so that a further addition of ions to the aqueous phase surrounding the adsorbent particles would not be expected to increase the amount adsorbed signifi-cantly (Machida, Aikawa, and Tatsumoto 2005; Doniaa et al. 2009; Yu et al. 2013, Feihong et al. 2015; Ümit et al. 2015; El Afifi, Attallah, and Borai 2016). In this study, the maximum capacity (qe) of Csþ onto the composite surface reached 5 mmol · g� 1 that corresponds to equilibrium concentration (Ce) of 175 mmol · L� 1. The further increase in equilibrium concentration is associated with gradual decrease in the adsorption capacity of Csþ.

Table 2. The kinetic parameters of 134Csþ adsorbed onto poly(AM-IA)/DAM/ ZrW composite.

Parameter Value

Experimental maximum uptake, qe (mmol · g� 1) 0.0074 Pseudo-first-order

qe (mmol · g� 1)c 0.0060 k1 (min� 1) 0.023 R2 0.97

Pseudo-second-order qe, calculated (mmol · g� 1)c 0.0070 k2 (g.mmol� 1.min� 1) 11.915 R2 0.94

Intraparticle mass transfer diffusion kid (mmol · g� 1.min� 1/2) 0.0029 c (g.mmol� 1.min� 1) 0.00016 R2 0.88

ccalculated.

Figure 7. The pseudo-second-order plots for adsorption of 134Csþ ions onto synthesized poly(AM-IA)/DAM/ZrW composite.

Figure 8. The Weber–Morris plots for adsorption of 134Csþ ions onto synthesized poly(AM-IA)/DAM/ZrW composite.

Figure 9. The relation between uptakes (qe) of 134Csþ ions onto synthesized poly(AM-IA)/DAM/ZrW composite and equilibrium concentration (Ce).

PARTICULATE SCIENCE AND TECHNOLOGY 7

The results of adsorption equilibrium isotherm were evaluated and described by using three isotherms: Langmuir, Freundlich, and Temkin adsorption isotherm equations (Ümit et al. 2015; El Afifi, Attallah, and Borai 2016). The most widely used isotherm equations for modeling equilibrium data is the Langmuir model. It is represented by Equation (7) which assumes that the adsorbent surface is homogeneous and the adsorption sites are energetically identical, indicating that the adsorbed molecules do not react with each other. The linear form of Langmuir equation is given by the equation (Feihong et al. 2015; El Afifi et al. 2016):

Ce

qe¼

Ce

qmaxþ

1KLqmax

ð7Þ

where Ce represents the equilibrium concentration of ions in solution (mmol · L� 1), qe refers to the amount adsorbed onto the adsorbent material (mmol · g� 1), qmax is the maximum adsorption capacity (mmol · g� 1), and KL is the binding con-stant which is related to the energy of adsorption (L · molg� 1). Plotting Ce/qe against Ce gives a straight line with slope and intercept equal to 1/qmax and 1/KLqmax, respectively (Figure 10). The values of KL and qmax are reported in Table 3.

The values of KL and qmax are 0.042 L.mmol� 1 and 5.298 mmol · g� 1, respectively. The degree of suitability of the synthesized composite material toward metal ions was esti-mated from the values of the separation factor constant (RL) which gives an indication of the possibility of the adsorption process to proceed, with RL > 1 being unsuitable; RL ¼ 1 linear; 0 <RL < 1 suitable; and RL ¼ 0 irreversible (Attallah, Allan, and Mahmoud 2015; El Afifi, Attallah, and Borai 2016). The value of RL could be calculated from Equation (8):

RL ¼1

1þ KLCoð8Þ

where Co (mmol · L� 1) is the initial concentration of Csþ ions. The RL value ranges from 0.0375 to 0.9998 between 300 and 0.004 mmol · L� 1 and approaches zero with an increase in the Co value. This value (0 <RL < 1) indicates the suitability of

the synthesized poly(AM-IA)/DAM/ZrW composite to be used as adsorbent material for Csþ removal from radioactive aqueous solution.

The Freundlich isotherm model (Feihong et al. 2015; Ümit et al. 2015) is an empirical relationship describing the sorption of solutes from a liquid to a solid surface and assumes that different sites with several sorption energies are involved (the surface of the adsorbent is heterogeneous). The linear form of the Freundlich isotherm model can be represented by Equation (9) (Dada et al. 2012; Attallah, Allan, and Mahmoud 2015):

log qe ¼ log KF þ1n

log Ce ð9Þ

where KF (mmol · g� 1) and n are characteristic constants related to the relative sorption capacity of the sorbent and the intensity of sorption, respectively. Plotting logqe against logCe gives a straight line with slope and intercept equal to 1/n and logKF, respectively. The parameter n (i.e., 1.80) characterizes the heterogeneity of the system. Figure 11 shows the adsorption isotherm of Csþ ions, which conforms to the Freundlich equation.

The Freundlich plot gave a slope less than 1, indicating nonlinear sorption behavior with the concentration of Csþ in the range studied. The observed value of KF of Csþ onto the prepared composite material was found to be 0.24 mmol · g� 1

and confirms a significant affinity of the Cs ions to the studied composite.

The data were also represented by the Temkin absorption isotherm model. This model contains a factor that explicitly takes into account the adsorbent–adsorbate interactions. The linearized form of the Temkin isotherm model is described by Equation (10) (Dada et al. 2012; Feihong et al. 2015; Ümit et al. 2015; El Afifi, Attallah, and Borai 2016):

qe ¼RTbT

ln kT þRTbT

ln Ce ð10Þ

where bT is the Temkin constant related to the heat of sorption (kJ · mol� 1), kT is the equilibrium binding constant corre-sponding to the maximum binding energy (L.g� 1), T is the absolute temperature (K), and R is the gas constant (8.314 J · mol� 1 · K� 1). The values of kT and bT were obtained from the slope and intercept of a straight line plot of qe versus lnCe (Figure 12), respectively, and their values are given in Table 3.

It can be seen that the value of correlation coefficient (R2) of Freundlich (0.99) equation is higher than that found for Langmuir (0.95) or Temkin (0.63) isotherm model. Thereby, the Freundlich isotherm correctly fits the equilibrium data with high correlation near unity and equals to 0.99. This supports that the adsorption of Csþ was preceded by means of different sites, e.g., carboxylate and/or amide moieties with several sorption energies. Therefore, the sorption reaction can be more favorable by Freundlich model, confirming the heterogeneous chemisorption of Csþ onto the composite surface.

To evaluate the adsorption efficiency of the synthesized composite, we compared our results with those found in litera-ture (Attallah, Allan, and Mahmoud 2015; Allan, Holiel, and Sanad 2014; Hamoud et al. 2014; El-Gammal et al. 2009; Zhang,

Figure 10. Langmuir plots for adsorption of 134Csþ ions onto synthesized poly (AM-IA)/DAM/ZrW composite.

8 K. F. ALLAN ET AL.

Xu, and Yan 2010; Miah et al. 2010; El-Naggar et al. 2012; Omar and Attia 2013; Kim, Lee, and Jeon 2014; Khotimchenko et al. 2014). Table 4 shows the maximum adsorption capacity (qmax) for various adsorbent materials for adsorption of Csþ, although a direct comparison of the adsorption capacity between the synthesized poly(AM-IA)/DAM/ZrW composite used in this study and other adsorbents reported in literature was difficult due to the variation with experimental conditions applied in those studies.

Applicability of the prepared composite

This part describes the possible applicability of the synthesized poly(AM-IA)/DMA/ZrW composite in the removal of Csþ

ions and/or its radioactive isotope such as 134Csþ or 137Csþ

from the wastes produced from the industrial, medical, or research centers. Therefore, our investigations were carried out to remove Cs from different media in a wide range of concentrations ranging from 10� 1 to 10� 5 M, considering the optimum conditions obtained (pH 8, V/m ratio 0.2 L.g� 1, con-tact time 90 min, free tracer of 134Csþ). Figure 13 represents the uses of the composite in the removal of Csþ ions which exist in wastes containing acidic solutions of mineral acids such as HCl or HNO3. It was found that the removal efficiency (%) depends on the hydrogen ion concentration. The removal efficiency reached 40%�and 34%�of Csþ ions from HCl and HNO3 solutions at 10� 5 M, while it decreased to 6.5%� and 1.3%�in 10� 1 M.

The use of the composite as adsorbent for removal of Cs ions from organic acid solutions was also studied and demonstrated in Figure 14. It was observed that the removal

efficiency varied with simulated solutions of Csþ ions in the presence of three organic acids including acetic, citric, and ascorbic acids. The removal percentage was higher at low concentrations and decreased with the increase in their concentrations. Thereby, the sequence of the removal efficiency can be ordered at [C] = 10� 5 M as citric (42%)>acetic (33%) > ascorbic (28%), whereas at [C] ¼ 10� 1 M the sequence is citric (24%)>acetic (13%) > ascorbic (4%).

Figure 15 shows the removal percentage of Csþ ions from solution salts such as NH4Cl, di-sodium of EDTA and NaCl by the composite. It was found that the removal percentage of Csþ ions increased with the decrease in solution con-centration used. Thereby, the removal percentage of Csþ is 1.3%, 3.6%� and 9%� at 0.1 M NH4Cl, Na2EDTA, and NaCl, respectively. With the decrease in concentration to below 10� 5 M, the removal percentage of Csþ increased to ∼27%, 31%, and 45%� from NH4Cl, Na2EDTA, and NaCl solutions, respectively. To learn more about the sorption behavior of the prepared composite, it was used to remove Csþ ions from an aqueous solution containing organic solvent such as acetone. The results obtained are shown in Figure 16. It is noticed that the removal efficiency of Csþ increases with the concentration of acetone till 60%� (v/v). The maximum removal obtained was above 60%�of Csþ ions. Based on the aforementioned results, the lowest removal efficiency of Csþ

at high concentrations could be due to the competitive ions such as Hþ or NH4

þ or Naþ onto the prepared composite surface. Whereas the high removal efficiency of Csþ from diluted solutions and/or at low concentrations may be attributed to the decrease in the competition of ions and/or the increase in the ionization rate of the active sites in surface of the prepared poly(AM-IA)/DAM/ZrW composite.

Table 3. The parameters for the Langmuir, Freundlich, and Temkin models of 134Csþ sorption by the synthesized poly(AM-IA)/DAM/ZrW composite. Langmuir constants Freundlich constants Temkin constants

qmax, mmol · g� 1 KL, L · mmol� 1 R2 KF, mmol · g� 1 n R2 bT, kJ · mol� 1 KT, L · mmol� 1 R2

5.298 0.042 0.95 0.24 1.80 0.99 8.25 598.2 0.63

Figure 11. Freundlich plots for adsorption of 134Csþ ions onto synthesized poly (AM-IA)/DAM/ZrW composite.

Figure 12. Temkin plots for adsorption of 134Csþ onto synthesized poly(AM-IA)/ DAM/ZrW composite.

PARTICULATE SCIENCE AND TECHNOLOGY 9

Conclusion

In this work, poly(AM-IA)/DAM/ZrW composite material was synthesized and characterized by different measurements (FTIR, XRD, TGA, DTA, SEM, and BET). It summarizes that: (i) the optimum conditions for preparing the composite material are 0.01 g DAM as a crosslinker, a co-monomer con-centration 20%, a co-monomer composition (AM-IA) (12:88), and 0.03 g ZrW with gamma irradiation dose 30 kGy; (ii) the maximum adsorption performance of the composite is 93%�

for radiotracer and ions of 134Csþ in aqueous solution at pH 8 after 90 min; (iii) sorption process of Csþ ions was favored by the pseudo-second-order kinetic model and controlled by the Freundlich equation model, confirming the heterogeneous chemisorption process with adsorption capacity (qmax) of 5.29 mmol · g� 1; and (iv) applicability of the adsorbent was also examined to remove Csþ ions or its radioactive isotopes 134Csþ

and/or 137Csþ from different solutions. It is interesting to

Table 4. Comparing the adsorption capacity (qmax) of poly(AM–IA)/DAM/ZrW for cesium with those reported in literatures using other materials.

Adsorbent material

pH media

qmax, mmol · g� 1 References

Poly(AM-IA)/DAM-ZrW 8.0 � 0.2 5.3 This work P(AA-MA)/Al2O3-SiO2 <0.5 0.12 Attallah, Allan, and

Mahmoud (2015) P(AM-AA-AN)/SiO2-ZrO2 8.0 0.24 Allan, Holiel, and

Sanad (2014) P(AM-IA)/ZrO2 8.0 0.32–1.62 Hamoud et al. (2014) P(AA-AN)/Ti-vanadate 6 1.55 El-Gammal et al. (2009) Raw olive pomace 5.4 360 Omar and Attia (2013) Carbonized olive pomace 3.6 565 Omar and Attia (2013) PATiW composite – 1.632 El-Naggar et al. (2012) Sericite 7 0.05 Kim, Lee, and Jeon (2014) Ion-imprinted polymer 6 0.243 Zhang, Xu, and Yan (2010) Ceiling tiles 4.95 0.004 Miah et al. (2010) Na-alginate 6 0.607 Khotimchenko et al. (2014) Ca-alginate 6 0.479 Khotimchenko et al. (2014)

Figure 13. Adsorption performance of 134Csþ in solutions of some mineral acidic by synthesized poly(AM-IA)/DAM/ZrW composite.

Figure 14. Adsorption performance of 134Csþ in solutions of some organic acids by synthesized poly(AM-IA)/DAM/ZrW composite.

Figure 15. Adsorption performance of 134Csþ in solutions of some salts by synthesized poly(AM-IA)/DAM/ZrW composite.

Figure 16. Adsorption performance of 134Csþ in varied acetone solutions by synthesized poly(AM-IA)/DAM/ZrW composite.

10 K. F. ALLAN ET AL.

conclude that the prepared poly(AM-IA)/DAM/ZrW composite material could be used as a suitable adsorbent to immobilize the Csþ ions or its radioactive isotopes from an alkaline waste solution associated with nuclear medical, industrial, or research centers.

Acknowledgment

The authors would like to express their deep thanks to Dr. Mohamed F. Attallah and Dr. J.A. Daoud (Hot Laboratory and Waste Management Center, EAEA, Cairo, Egypt) for their assistance and during preparation of the manuscript in its final version.

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