Journal of Environmental Radioactivity 134 (2014) 99e108
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Uranyl ions adsorption by novel metal hydroxides loaded Amberlite IR120 A.A. Elabd a, *, W.I. Zidan a, M.M. Abo-Aly b, E. Bakier b, M.S. Attia b a b
Nuclear and Radiological Regulatory Authority, Cairo, Egypt Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 November 2013 Received in revised form 7 February 2014 Accepted 17 February 2014 Available online 1 April 2014
In this work, Ni(OH)2-loaded Amberlite IR120 (NieMA) and Co(OH)2-loaded Amberlite IR120 (CoeMA) removal from aqueous solutions. The resins were prepared, characterized and applied for UO2þ 2 adsorption characteristics were investigated in a batch system with respect to effect of contact time, pH, equilibrium isotherms and removal kinetics data. The results indicated that the UO2þ 2 could be efficiently removed from aqueous solutions at pH ¼ 3.5 using NieMA and CoeMA resins. The maximum adsorption capacities for the UO2þ 2 of NieMA and CoeMA were found to be 439 mg/g and 451 mg/g respectively. The equilibrium data fit well with the Langmuir adsorption isotherm. Kinetics study showed that the adsorption process was fast and reached equilibrium within 60 min and the kinetics data fit well with pseudo-second order and intra-particle diffusion models for both resins. The adsorption mechanism has been proposed and discussed. It was found that both NieMA and CoeMA resins could be used effectively for UO2þ 2 removal from aqueous solutions. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Loaded-resin Metal hydroxides Uranium Adsorption Amberlite IR120
1. Introduction Many studies on materials for the adsorption and separation of uranium species from aqueous systems have been done (Geckeler and Volchek, 1996; Guibal et al., 1994; Bayer et al., 1985). Uranium adsorption on various natural sorbents and Amberlite resins are important from economical and environmental point of view (Qadeer et al., 1995). Quantitative studies and adsorption kinetics of uranium (VI) were reported on use of Amberlite IR120 in aqueous solutions (Khopkar and De, 1960; Stamberg et al., 1980). Amberlite IR120 was used to concentrate uranium (VI) in samples of natural water for spectrophotometric determination (Bermejo-Barrera et al., 1990). Also, Amberlite IR120 was loaded by rhodamine B for the removal of some soluble metals (Nabi et al., 2011) and loaded by magnetite nano iron oxide for uranium removal (Elabd et al., 2013). There are many examples of the use of specially prepared resins to remove ions from aqueous solutions. Hristovski et al. (2008) prepared impregnated non-crystalline iron hydroxide nanoparticles onto strong base ion-exchange (IX) resins (Amberlite PWA2, A-530E, SIR-110, CalRes 2103, A-520E and SIR-100) to * Corresponding author. Tel.: þ2 0122 5781529; fax: þ2 2274 02 38. E-mail addresses: [email protected] (A.A. Elabd), [email protected], [email protected] (W.I. Zidan), [email protected] (M.M. Abo-Aly), [email protected] (E. Bakier), [email protected] (M.S. Attia). http://dx.doi.org/10.1016/j.jenvrad.2014.02.008 0265-931X/Ó 2014 Elsevier Ltd. All rights reserved.
achieve simultaneous removal of arsenate and perchlorate. Shao et al. (2008) studied the feasibility of using La(III)-, Ce(III)-, Y(III)-, Fe(III)- and Al(III)-loaded 200CT resin as adsorbents for the removal of As (III and V) from waste water. Dong et al. (2010) and Zhi-liang et al. (2007) used MnO2-loaded D301 ion exchange resin as adsorbent for simultaneous removal of lead and cadmium from aqueous solution. Pan et al. (2010) prepared impregnating hydrated iron oxide nanoparticles within a cation exchange resin D-001 for removal of soluble metals from contaminated water. Suzuki et al. (2000) prepared zirconium oxide e loaded Amberlite XAD-7 resin for arsenic removal. Huang and Chen (2009) developed a cationic magnetic nano-adsorbent using iron oxide nanoparticles for the adsorption of Cu(II) and Cr(VI) ions. A number of innovative adsorbents have been prepared and reported in recent years (Zhang et al., 2003; Balaji et al., 2005; Choi et al., 2006). Among them, oxides and hydroxides are often applied because of their high surface areas and their affinity to several soluble metals (Mallikarjuna and Venkataraman, 2003; Tripathy and Kanungo, 2005). However, these oxides and hydroxides are usually in the colloidal forms and are difficult to prepare in spherical beads of suitable size for practical applications. In recent years, this situation has led to a growing interest in the syntheses and the application of novel adsorbents by loading an oxide on another solid (Rau et al., 2000; Thirunavukkarasu et al., 2001; Munoz et al., 2002).
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Mustafa et al. (2003) and Jyo et al. (1993) reported that, hydroxides of cobalt can be employed as an adsorbent. Also, it was reported that hydrated UO2þ 2 adsorbed preferentially on top of a surface nickel atom through a NieO-bond, with a strong adsorption energy of 8.89 eV (Roques et al., 2009). This means that the loading amount of functional groups increases significantly. For this reason, it is expected that the new sorbent materials will show high adsorption capacity for UO2þ 2 . In this study, the surface of Amberlite IR-120 was loaded by two metal hydroxides, Co(OH)2 and Ni(OH)2 as adsorbents. The prepared resins (NieMA and CoeMA) were characterized and applied for UO2þ 2 removal from aqueous solutions. 2. Materials and methods 2.1. Materials Amberlite IR120 (Hþ form) was purchased from (Alfa Aesar Company). Uranyl nitrate hexahydrate, UO2(NO3)2$6H2O was manufactured by (Mallinckrodt Company). Nickel nitrate hexahydrate, Ni(NO3)2$6H2O and cobalt nitrate hexahydrate, Co(NO3)2$6H2O were purchased from (Rankem Company). 25% NH4OH solution was purchased from (Merck Company). HNO3 and KOH were purchased from (Fisher Chemicals Company). All chemicals were used without further purification. A standard uranium solution of 2000 mg/L was prepared by dissolving the appropriate amount of UO2(NO3)2$6H2O in deionized water. Deionized water used for all experiments was obtained from a Milli-Q (Millipore Corporation) water purification system. The experimental work was carried out in safeguards analytical laboratory (ETZ, KMP-I) at the Egyptian Nuclear and Radiological Regulatory Authority (ENRRA). 2.2. Instruments Fourier Transforms Infrared Spectrometer (FTIR), Jasco FT/IR6100 type A, from USA was used. The FTIR spectra (4000e 400 cm1) measured at room temperature, was used to investigate any observed changes of the prepared resins with Amberlite IR120, and these included new peaks, intensity variations of peaks originally present and wavelength shifts. A Scanning Electron Microscope (SEM) with Energy-Dispersive X-ray Spectrometer (EDX), JEOL 6510 LA SEM, from JEOL, Jaban was used to obtain an image of the resin before and after loading of metal hydroxides. EDX detector which was attached to the SEM system was used to investigate the distribution of Co, Ni and U lines of the prepared resins before and after adsorption of UO2þ 2 . Inductively Coupled Plasma Optical Emission Spectrometry (iCAP 6500 ICP-OES) from Thermo Fisher Scientific, UK, with ITEVA operating software for full control of all instrument functions and data handling, was used for the measurement of U concentration. This instrument is equipped with a high performance solid state Charge Injection Device (CID) camera. 2.3. Preparation of metal hydroxides loaded resin 2.3.1. Preparation of Ni(OH)2-loaded resin The method of preparation is similar to that of Motlagh et al. (2011) with minor modifications. An aliquot of 2.5 g dry Amberlite IR120 resin was added to 50 mL of Ni(NO3)2 solution (0.5 M). The initial pH of the solution was adjusted to 12.5 by dropwise addition of NH4OH solution (100 mL, 2 M) with continuous stirring for 3 h, with the temperature maintained at 60 C. During the addition of NH4OH, it was observed that the resin color changed from the original pale brown to green. The color change of the resin was due to its loading by Ni(OH)2, as expected. Any change in pH
was readjusted from time to time by addition of 0.1 M HNO3/KOH. The resulted loaded sorbent was thoroughly washed with deionized water to remove excess nitrate ions and dried at 80 C for 3 h in an oven and kept for further investigation. The obtained NieMA resin was further characterized by both IR and EDX. 2.3.2. Preparation of Co(OH)2-loaded resin The method of preparation is similar to that of Konga et al. (2009) with minor modifications. An aliquot of 2 g dry Amberlite IR120 resin was added to 25 mL of Co(NO3)2 solution (1 M). The initial pH of the solution was adjusted to 9 by dropwise addition of NH4OH solution with continuous stirring for 3 h, with the temperature maintained at 60 C. During the addition of NH4OH, it was observed that the resin color changed from the original pale brown to red. The color change of the resin was due to its loading by Co(OH)2, as expected. Any change in pH was readjusted from time to time by addition of 0.1 M HNO3/KOH. The resulted loaded sorbent was thoroughly washed with deionized water to remove excess nitrate ions and dried at 80 C for 24 h in an oven and kept for further investigation. The obtained CoeMA resin was further characterized by both IR and EDX. 2.4. Batch experiment Batch experiments were conducted for evaluating the extent of UO2þ 2 adsorption on NieMA and CoeMA. Batch adsorption experiments were carried out in flasks with fixed magnetic stirring. The resin (50 mg) was added to 50 mL solution containing various uranium concentrations for various contact times at room temperature. The pH was adjusted by adding of 0.1 M HNO3/KOH to the solutions at each experiment. The pH of the solutions was measured on a pH meter 780 of Metrohm Herison, Switzerland. The resin was filtered using Whatman filter paper no: 44. The uranium remained in solution was analyzed using ICP-OES instrument. The influence of specific process parameters such as initial uranium concentration, pH of the solution and contact time was determined by calculating uranium adsorption keeping other parameters constant. The adsorption capacity of UO2þ at time t (mg/g) was 2 calculated using the following equation (Bhattacharyya et al., 2006):
qt ¼
ðCo Ct ÞV m
(1)
where Co and Ct are the initial and at time (t) concentrations of UO2þ 2 (mg/L), respectively. V is the volume of the solution (L) and m is the mass of sorbent (g). 3. Results and discussion 3.1. Sorbent characterization The FTIR spectra of Amberlite IR120 and NieMA are shown in Fig. 1.These spectra show a broad band located at 3424 cm1 which may be associated to the OeH stretching vibration of interlayer water molecules and the H-bonded OH groups. At low wavenumbers, the band at about 578 cm1 is associated to the NieO stretching vibration (Li et al., 2012). This strongly support the presence of the Ni(OH)2 and may indicate the formation of a bond between Amberlite IR120 and the NieO group. The FTIR spectra of Amberlite IR120 and CoeMA are shown in Fig. 2. These spectra show a broad peak in the wave number range of 3440e3570 cm1 which can be assigned to the OeH stretching vibration of interlayer water molecules and the H-bonded OH group. Below 800 cm1, the bands are associated with CoeO
A.A. Elabd et al. / Journal of Environmental Radioactivity 134 (2014) 99e108 110
50 4000
3500
3000
2500
2000
1500
835
674 578
1173 1036
1637
70
1403
2925
80
3424
%T
90
60
surface while Fig. 3b and c are shown a change of the surface morphologies of the resin after its loading by both metal hydroxides, NieMA and CoeMA respectively. EDX characterization confirmed the presence of elements (Ni, Co and U) in the loaded resins. The samples used for EDX characterization were:
Ni-MA
100
1000
101
500
110
- NieMA: Ni(OH)2-loaded Amberlite IR120 resin before adsorption; - CoeMA: Co(OH)2-loaded Amberlite IR120 resin before adsorption; - NieMAeU: Ni(OH)2-loaded Amberlite IR120 resin after UO2þ 2 adsorption in optimum conditions; - CoeMAeU: Co(OH)2-loaded Amberlite IR120 resin after UO2þ 2 adsorption in optimum conditions.
Amberlite IR120
3000
2500
2000
835
678
1038
1410
1500
1000
500
-1
Wavenumber [cm ]
Fig. 1. Comparison between IR spectra of Amberlite IR120 and NieMA.
stretching and CoeOH bonding vibrations. The appeared two absorbance bands at 672 and 577 cm1 for CoeMA spectra can be assigned to in plane bonding of (CoeOeH) and the v (CoeO) stretching vibrations (Morsya et al., 2009). This strongly support the presence of the Co(OH)2 and may indicate the formation of a bond between Amberlite IR120 and the CoeO group. The SEM images of Amberlite IR120, NieMA and CoeMA are shown in Fig. 3(a, b, c) respectively. Fig. 3(a) is shown a smooth
This method is semiquantitative and it measures the ions fraction located close to the matrix surface. The EDX spectra of NieMA before and after adsorption of UO2þ are shown in Fig. 4(a, b) 2 respectively. The EDX spectra of CoeMA before and after adsorption of UO2þ are shown in Fig. 5(a, b) respectively. The EDX spectra 2 revealed the presence of the elements C, O, S and Ni for NieMA and Co for CoeMA before adsorption of UO2þ 2 , showing that, the Ni(OH)2 and Co(OH)2 particles were distributed onto the surface of Amberlite IR120. After the UO2þ adsorption, the EDX spectra 2
100 Co-MA
835 3440
84 80
1034
88
1649
2924
%T
92
672 577
96
100 Amberlite IR120
95
75 70 65
835
1634
2925
80
3411
%T
85
678
90
1038
3500
1185
50 4000
1185
60
1634
70
2925
80
3411
%T
90
1457
100
60 4000
3500
3000
2500
2000
1500
1000
Wavenumber [cm-1]
Fig. 2. Comparison between IR spectra of Amberlite IR120 and CoeMA.
Fig. 3. (a, b, c) SEM images for (a) Amberlite IR120, (b) NieMA and (c) CoeMA.
500
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showed a new distinct peak associated with the presence of the U line, showing that, the UO2þ 2 was adsorbed onto the surface of both NieMA and CoeMA. 3.2. Effect of pH The effect of pH on UO2þ 2 adsorption efficiency for NieMA and CoeMA is shown in Fig. 6. This experimental work is carried out at pH range of 2e3.5. This due to the fact that, UO2þ 2 forms a precipitate as hydroxides above the pH values 3.5 (Niboua et al.,
2011). It was clear that, the adsorption increased with increasing pH ¼ 3.5 for NieMA and CoeMA. Ulusoy and Simek (2013) reþ ported that there was a competition between UO2þ 2 and H for the same exchange sites or donating atoms and this caused a decrease in the adsorption at low pH, because most of the electron donor atoms were in the protonated form at low pH. Also, Hþ is preferentially adsorbed by the resin in comparison to UO2þ 2 (Jha et al., 2009). The pH dependence of UO2þ adsorption on NieMA and 2 CoeMA is similar to that previously reported for adsorption on manganese oxide coated zeolite, and activated carbon (Han et al.,
Fig. 4. (a, b) EDX spectra for (a) NieMA and (b) after UO2þ 2 adsorption.
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103
Fig. 5. (a, b) EDX spectra for (a) CoeMA and (b) after UO2þ 2 adsorption.
2007; Mellah et al., 2006). It could be concluded that, the adsorption efficiency of the two prepared resins for UO2þ was 2 optimal at pH 3.5. Consequently, the working media was adjusted at pH 3.5 for further UO2þ 2 adsorption experiments conducted in this study. 3.3. Effect of contact time The adsorption experiments were carried out for contact times ranging from 1 to 100 min with 50 mL of solution having
2000 mg/L uranium and 50 mg of adsorbent at room temperature. Samples of 50 mL were analysed at various time intervals to estimate the concentration of dissolved uranium as a function of equilibration time (Fig. 7). It is clear that the adsorption efficiency increased with contact time and reached an apparent adsorption equilibrium within 60 min. Two phases of uranium adsorption kinetics were observed: an initial rapid phase where adsorption was fast and contributed significantly to equilibrium uptake, and a slower second phase whose contribution to the total metal adsorption was relatively small. Consequently, the
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14
78 77
12 10
75 74
Ni-MA Co-MA 0.008 0.012 438 446
R
0.999
2
72 71
6 4
70 69
2
Ni-MA
68
Co-MA 1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
Ni-MA y =0.28103+0.00228*X Co-MA y =0.17996+0.00224*X
0
3.6
pH
0
adsorption equilibrium time considered for further experiments was 60 min. After obtaining the optimum adsorption conditions of the Nie MA and CoeMA, the uranium adsorption capacities were determined for NieMA, CoeMA and Amberlite IR120. For this, 50 mg of the adsorbent was contacted with 100 mL of 2000 mg/L of UO2þ 2 solution at pH 3.5, with continuous stirring at room temperature for 24 h. The amount of adsorbed uranium was estimated from the difference of the uranium concentrations in the aqueous solution, before and after adsorption. Consequently, uranium adsorption capacities of NieMA, CoeMA and Amberlite IR120 were calculated as 439 mg/g, 451 mg/g and 312 mg/g adsorbent, respectively. 3.4. Effect of initial uranium concentration and adsorption isotherm models At low concentration, UO2þ 2 was adsorbed at specific sites on adsorbent and reaching saturation as a result of its concentration increase. The different concentrations of UO2þ 2 solutions ranging from 1000 to 10,000 mg/L (20 mL) were performed with constant
1000
2000
3000
4000
5000
6000
Ce (mg/L)
Fig. 6. The adsorption efficiency of UO2þ versus pH by NieMA and CoeMA 2 (Co ¼ 1000 mg/L, V ¼ 50 mL and m ¼ 50 mg).
Fig. 8. Langmuir isotherm for UO2þ 2 adsorption by NieMA and CoeMA.
contact time (60 min), pH (3.5) and amount (50 mg) of loaded resins with continues stirring at room temperature. The uptake of UO2þ 2 increases as the initial concentration increased up to 6000 mg/L, thereafter reached a plateau. In order to define the mechanism of UO2þ 2 adsorption onto NieMA and CoeMA, the experimental data were applied to Langmuir and Freundlich linear isotherm models. 3.4.1. Langmuir isotherm model The conceptual model underlying Langmuir isotherm assumes monolayer adsorption on a uniform surface with a finite number of adsorption sites. Once a site is filled, no further adsorption can take place at that site (Langmuir, 1916). As such, the surface will eventually reach a saturation point where the maximum adsorption of the surface will be achieved. The linear form of the Langmuir isotherm model (Langmuir, 1916) is:
Ce 1 Ce ¼ þ KL qm qm qe
2.68 80
Kf (mg/g) 1/n (L/g) 2 2.64 R
70
(2)
Ni-MA 224 0.078 0.992
Co-MA 257 0.065 0.984
60
Log q e
Adsorption efficiency (%)
0.999
8
73
Ce/qe(g/L)
Adsorption efficiency (%)
76
KL (L /mg) qm (mg /g)
50
40
2.60
2.56 30
Ni-MA Co-MA
20 0
20
40
60
80
100
Contact time (min) Fig. 7. The contact time versus the adsorption efficiency of UO2þ 2 for NieMA and Coe MA (Co ¼ 2000 mg/L, V ¼ 50 mL and m ¼ 50 mg).
Ni-MA y= 2.346+0.0787*X Co-MA y= 2.409+0.0652*X
2.52 2.0
2.5
3.0
3.5
Log C e Fig. 9. Freundlich isotherm for UO2þ 2 adsorption by NieMA and CoeMA.
4.0
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3.0 2.8 2.6 2.4
K1 (L/min) qe (mg/g)
Ni-MA Co-MA 0.092 0.072 378 388
R
0.985 0.995
2
RL ¼
Log(q e-q t)
1 1 þ kL C0
(3)
There are four probabilities for the RL value: for favorable sorption, 0 < RL < 1; for unfavorable sorption, RL > 1; for linear sorption, RL ¼ 1; for irreversible sorption, RL ¼ 0 (Webber and Chakkravorti, 1974). The resulted values of RL were in the range of 0e1 which support that, the exchange of UO2þ 2 is favorable for both NieMA and CoeMA.
2.2 2.0 1.8 1.6
3.4.2. Freundlich isotherm model The Freundlich isotherm is assumed to be applicable to both monolayer (chemisorption) and multilayer adsorption (physisorption) and is based on the assumption that the adsorbate is adsorbed onto the heterogeneous surface of a sorbent. The linear form of Freundlich equation is expressed (Yang, 1998) as follows:
1.4 1.2 1.0
Co-MA y=2.591-0.03126*X Ni-MA y=2.577-0.04*X
0.8 0
5
10
15
20
25
30
35
40
45
50
55
60
time (min) Fig. 10. Pseudo-First order kinetic plots for UO2þ 2 adsorption of by NieMA and CoeMA.
where Ce is concentration of adsorbed at equilibrium (mg/L), KL is the Langmuir constant related to the energy of adsorption (L/mg) and qm is the monolayer adsorption capacity (mg/g). Linear plots of the Langmuir isotherm of UO2þ 2 are shown in Fig. 8. The regression coefficients values were R2 ¼ 0.999 for NieMA and CoeMA. The qm and KL values for NieMA were 438 mg/g and 0.008 L/mg, respectively. The qm and KL values for CoeMA were 446 mg/g and 0.012 L/mg, respectively. By comparing qm values, it suggests that CoeMA has a higher maximum adsorption capacity than NieMA. The reason of that may be due to that the atomic size of cobalt is higher than that of nickel. Consequently, the charge per unit area in case of nickel will be higher than that of cobalt and leads to the more repulsion between the nickel ion and uranyl ion. This may explain the higher adsorption capacity in case of cobalt compared with nickel. The features of the Langmuir isotherm can be expressed in terms of dimensionless constant sorption factor RL defined by Webber and Chakkravorti (1974) as follows:
0.11 0.10 0.09
log qe ¼ log KF þ 1=n log Ce
R
2
0.987
(4)
where KF is Freundlich isotherm constant related to adsorption capacity (mg/g) and 1/n is the heterogeneity factor constant related to surface heterogeneity. Linear plots of the Freundlich isotherm of UO2þ 2 are shown in Fig. 9. The regression coefficients were R2 ¼ 0.992 and 0.984 for Nie MA and CoeMA, respectively. The KF and 1/n values for NieMA were 224 mg/g and 0.078 L/g, respectively. The KF and 1/n values for CoeMA were 257 mg/g and 0.065 L/g, respectively.
3.5. Kinetic studies The kinetics of UO2þ adsorption on the NieMA and CoeMA 2 were analyzed using pseudo-first order, pseudo-second order, and intra-particle diffusion models. The pseudo-first order and pseudosecond order models are macroscopic kinetic models commonly used for describing the adsorption processes. These models suggest that adsorption can be considered as either first or second order chemical reaction where the adsorption process is the rate determining step. An intra-particle diffusion model is used to describe the adsorption process where the intra-particle diffusion resistance is the rate determining step (Sureshkumar et al., 2010).
400
Ni-MA Co-MA K2 (g/mg min) 3.35E-4 2.81E-4 qe (mg/g) 438 463
350
0.998
0.08
300
0.07
250
qt (mg/g)
0.06
t/qt
105
0.05 0.04
200 150 100
0.03 0.02
50
Co-MA y=0.0166+0.00216*X Ni-MA y=0.0155+0.00228*X
0.01 0.00
Ni-MA C0-MA
0 1
0
5
10
15
20
25
30
35
40
time (min) Fig. 11. Pseudo-second order kinetic plots for UO2þ 2 adsorption by NieMA and CoeMA.
2
3
4 1/2
t
5
6
7
0.5
(min )
Fig. 12. Intra-particle diffusion plots for UO2þ adsorption by NieMA and CoeMA 2 (Co ¼ 1000 mg/L, V ¼ 50 mL and m ¼ 50 mg).
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Fig. 13. A schematic representation for the proposed adsorption mechanism (M ¼ Ni or Co).
3.5.1. The pseudo-first order model The Lagergren pseudo-first order equation can be expressed as follows (Ho, 2004):
dq ¼ K1 ðqe qt Þ dt
(5)
where qt is the amount of metal adsorbed at time t, qe is the amount of metal adsorbed at equilibrium and K1 is the adsorption rate constant. Integrating Eq. (5) for the boundary conditions t ¼ 0 to t ¼ t and q ¼ 0 to q ¼ qt and rearranging it for linearized data plotting, the following equation is obtained (Ho, 2004):
logðqe qt Þ ¼ log qe
K1 t 2:303
(6)
This model can be applied if log (qe e qt) versus t gives a straight line, in which case qe and K1 can be calculated from intercept and slope of the plot. Linear plots of Log (qe e qt) versus t of UO2þ 2 adsorption on the Nie MA and CoeMA are shown in Fig. 10, with regression coefficients of 0.985 and 0.995, respectively. This suggests the applicability of the pseudo-first order kinetics model to fit the experimental data. The calculated values of the adsorption capacities, qe,cal (378 mg/g) and (388 mg/g) were lower than the values of experimental adsorption capacities, qe,exp (416 mg/g) and (429 mg/g) for NieMA and CoeMA respectively. 3.5.2. The pseudo-second order model The pseudo-second order model is based on sorbent capacity, which suggests that chemisorption is the rate-controlling step and can be expressed as a differential equation (Ho and McKay, 1999):
dq ¼ K2 ðqe qt Þ2 dt
(7)
where k2 is the adsorption rate constant. Integrating Eq. (7) for the boundary conditions t ¼ 0 to t ¼ t and q ¼ 0 to q ¼ qt and rearranging it for linearized data plotting gives (Ho and McKay, 1999):
t 1 1 ¼ þ t qt K2 qe 2 qe
respectively. Therefore, it could be concluded that adsorption of UO2þ 2 onto NieMA and CoeMA follows the pseudo-second order better than the pseudo-first order model. The pseudo-second order kinetic model assumes that chemical adsorption is the rate-limiting step. 3.5.3. The intra-particle diffusion model The intra-particle model assumes that adsorption of metal ions from the aqueous onto the solid phase is a multi-step process involving transport of metal ions from aqueous phase to the surface of the solid particles (bulk diffusion) and then, diffusion of metal ions via the boundary layer to the surface of the solid particles (film diffusion) followed by transport of metal ions from the solid particles surface to its interior pores (pore diffusion or intra-particle diffusion), the later is likely to be a slow process and, therefore, it may be the rate determining step (Crini et al., 2007). The possibility of intra-particle diffusion resistance affecting the sorption was explored by Weber and Morris (1963) using the intra-particle diffusion model as follows: 1=2
t qt ¼ Kid þI
(9)
Kid (mg g1 min1/2) is the intra-particle diffusion rate constant. Fig. 12 shows that, the plot of qt versus t1/2 may present multi linearity, which indicates that two or more steps occur in the sorption processes. According to this model, the plot of uptake, (qt), versus the square root of time (t1/2) should be linear if intra-particle diffusion is involved in the adsorption process and if these lines pass through the origin then intra-particle diffusion is the rate-controlling step. When the plots do not pass through the origin, this is an indication of some degree of boundary layer control and the intra-particle diffusion is not the only rate-limiting step, but also other kinetic models may control the sorption rate, all of which may be operating simultaneously (Mezenner and Bensmaili, 2009). In addition, it can also be observed that the straight lines do not pass through the origin, which indicates that both intra-particle diffusion and film diffusion are the rate limiting steps for UO2þ 2 adsorption by both NieMA and CoeMA.
(8)
The pseudo-second order plot of UO2þ 2 adsorption on the NieMA and CoeMA are shown in Fig. 11 and is also linear with regression coefficients of 0.987 and 0.998 respectively, however the calculated values of the adsorption capacities, qe,cal (438 mg/g) and (463 mg/g) are closer to the values of the experimental adsorption capacities, qe,exp (416 mg/g) and (429 mg/g) for NieMA and CoeMA
3.6. Desorption and regeneration In order to minimize operation cost and make the process more feasible, the reusability of both NieMA and CoeMA is an important aspect to evaluate its applicability. Desorption of UO2þ 2 from both NieMA and CoeMA were carried out in a batch mode by using 0.1 mol/L HNO3 solution and the desorption efficiency was found to
A.A. Elabd et al. / Journal of Environmental Radioactivity 134 (2014) 99e108
be 96.3% and 96.7%, respectively within the experimental conditions considered in this work. 3.7. Adsorption mechanism discussion Adsorbents may form different types of bonds with the metal surface (Koretsky, 2000). In general, if the adsorption between the adsorbate and the surface sites is caused by relatively strong chemical bonds such as ionic and covalent bonds, the adsorption is identified as “specific” adsorption. The adsorption complex formed during this process was named as “inner-sphere” type complexes. When the adsorption between the adsorbate and the surface sites results from the weaker Coulomb attraction or Van der Waals bond, the adsorption is identified as “nonspecific” adsorption. The adsorption complex formed during this process was named as “outer-sphere” type complexes (Koretsky, 2000). Fig. 13 shows the schematic representation of the proposed adsorption mechanism. The adsorption mechanism is carried out in two steps, first by chemical precipitation of metal hydroxides into Amberlite IR120 in view of the characterization results as shown in Figs. 1e3, 4a and 5a which support the presence of metal hydroxides into Amberlite IR120 surface. Second, UO2þ 2 adsorbent into Nie MA and CoeMA in view of the characterization results as shown in Figs. 4b and 5b which support the presence of UO2þ 2 into NieMA and CoeMA respectively. Some researchers have been reported that UO2þ and other 2 soluble metals were strongly adsorbed as an inner sphere complexes by means of surface complexation with NieO bond (Roques et al., 2009; Pretorius and Linder, 2001; Xu et al., 2006). It could be concluded that the UO2þ 2 is specifically adsorbed on the Ni(OH)2 or Co(OH)2 loaded Amberlite IR120 resin through an inneresphere complex via surface complexation rather than the electrostatic interaction. The experimental results suggest that the higher adsorption capacity of both NieMA and CoeMA may be due to the presence of double effect of an inner sphere complex via surface complexation with Ni(OH)2 and Co(OH)2 with high capacity of adsorption due to their high surface area and ionic exchange by Amberlite IR120 (Predescu and Nicolae, 2012). 4. Conclusions In this work, it was found that both NieMA and CoeMA resins could be used effectively for UO2þ 2 removal from aqueous solutions. The adsorption reaction mechanism for both resins could be explained by the presence of a double effect of an inneresphere complex via surface complexation with Ni(OH)2 and Co(OH)2 as well as ionic exchange by Amberlite IR120. CoeMA was found to be of higher adsorption capacity compared to NieMA. The adsorption of UO2þ by both NieMA and CoeMA followed the Langmuir 2 adsorption isotherm. The adsorption kinetics for both NieMA and CoeMA could be described by a pseudo-second order and intraparticle diffusion models. References Balaji, T., Yokoyama, T., Matsunaga, H., 2005. Adsorption and removal of As(V) and As(III) using Zr-loaded lysine diacetic acid chelating resin. J. Chemosphere 59, 1169e1174. Bayer, E., Eberhardt, H., Grathwohl, P.A., Geckeler, K., 1985. Soluble of polychelatogenes for separation of actinide ions by membrane filtration. Isr. J. Chem. 26, 40e47. Bermejo-Barrera, A.B., Yebra-Biurrun, M.C., Fraga-Trillo, L.M., 1990. Spectrophotometric determination of uranium in natural waters. Anal. Chim. Acta 239, 321e323.
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Bhattacharyya, A., Mohapatra, P.K., Pathak, P.N., Manchanda, V.K., 2006. Cationexchange separation of uranium from thorium in nitric acid medium. J. Radioanal. Nucl. Chem. 268, 323e328. Choi, J.H., Kim, S.D., Noh, S.H., 2006. Adsorption behaviors of nano-sized ETS-10 and Al-substituted-ETAS-10 in removing heavy metal ions, Pb2þand Cd2þ. J. Micropor. Mesopor. Mater. 87, 163e169. Crini, G., Peindy, H.N., Gimbert, F., Robert, C., 2007. Removal of C.I. basic green 4 (malachite green) from aqueous solutions by adsorption using cyclodextrinbased adsorbent: kinetic and equilibrium studies. Sep. Purif. Technol. 53, 97e110. Dong, L., Zhu, Z., Ma, H., Qiu, Y., Zhao, J., 2010. Simultaneous adsorption of lead and cadmium on MnO2-loaded resin. J. Environ. Sci. 22, 225e229. Elabd, A.A., Abo-aly, M.M., Zidan, W.I., Bakier, E., Attia, M.S., 2013. Modified amberlite IR120 by Magnetic nano iron-oxide for uranium removal. Anal. Chem. Lett. 3, 46e64. Geckeler, K.E., Volchek, K., 1996. Removal of hazardous substances from water using ultrafiltration in conjunction with soluble polymers. Environ. Sci. Technol. 30, 725e734. Guibal, E., Saucedo, I., Roussy, J., Le Cloirec, P., 1994. Uptake of uranyl ions by new sorbing polymers: discussion of adsorption isotherms and pH effect. React. Polym. 23, 147e156. Han, R., Zou, W., Wang, Y., Zhu, L., 2007. Removal of uranium(VI) from aqueous solutions by manganese oxide coated zeolite: discussion of adsorption isotherms and pH effect. J. Environ. Radioact. 93, 127e143. Ho, Y.S., 2004. Citation review of Lagergren kinetic rate equation on adsorption reactions. Scientometrics 59, 171e177. Ho, Y.S., McKay, G., 1999. Pseoudo-second-order model for sorption processes. Process Biochem. 34, 451e465. Hristovski, K., Westerhoff, P., Moller, T., Sylvester, P., Condit, W., Mashe, H., 2008. Simultaneous removal of perchlorate and arsenate by ion-exchange media modified with nanostructured iron (hydr)oxide. J. Hazard. Mater. 152, 397e406. Huang, S.H., Chen, D.H., 2009. Rapid removal of heavy metal cations and anions from aqueous solutions by an amino-functionalized magnetic nano-adsorbent. J. Hazard. Mater. 163, 174e179. Jha, M.K., Nguyen, N.V., Lee, J.C., Jeong, J., Yoo, J.M., 2009. Adsorption of copper from the sulphate solution of low copper contents using the cationic resin Amberlite IR 120. J. Hazard. Mater. 164, 948e953. Jyo, A., Weber, R., Egawa, H., 1993. An anion adsorbent of the anti-Hofmeister type based on cobalt(III)-loaded chelating resins containing 1,4,8,11Tetraazacyclotetradecane-5,7-dione. Anal. Sci. 9, 599e603. Khopkar, S.M., De, A.K., 1960. Cation-exchange behaviour of uranium (vi) on amberlite ir-120: separation from mixtures. Anal. Chim. Acta 22, 153e158. Konga, L.B., Langa, J.W., Liua, M., Luob, Y.C., Kangb, L., 2009. Facile approach to prepare loose-packed cobalt hydroxide nano flakes materials for electrochemical capacitors. J. Power Sources 194, 1194e1201. Koretsky, C., 2000. The significance of surface complexation reactions in hydrologic systems: a geochemist’s perspective. J. Hydrol. 230, 127e171. Langmuir, I., 1916. The constitution and fundamental properties of solids and liquids. Part I. Solids. J. Am. Chem. Soc. 38, 2221e2295. Li, Y., Yao, J., Zhu, Y., Zou, Z., Wang, H., 2012. Synthesis and electrochemical performance of mixed phase a/b nickel hydroxide. J. Power Sources 203, 177e183. Mallikarjuna, N.N., Venkataraman, A., 2003. Adsorption of Pb2þions on nanosized gFe2O3 formation of surface ternary complexes on ligand complexation. Talanta 60, 139e147. Mellah, A., Chegrouche, S., Barkat, M., 2006. The removal of uranium(VI) from aqueous solutions onto activated carbon: kinetic and thermodynamic investigations. J. Colloid Interface Sci. 296, 434e441. Mezenner, N.Y., Bensmaili, A., 2009. Kinetics and thermodynamic study of phosphate adsorption on iron hydroxide-eggshell waste. J. Chem. Eng. 147, 87e96. Morsya, S.M.I., Shaban, S.A., Ibrahim, A.M., Selim, M.M., 2009. Characterization of cobalt oxide nanocatalysts prepared by microemulsion with different surfactants, reduction by hydrazine and mechano chemical method. J. Alloys Compd. 486, 83e87. Motlagh, M.M.K., Youzbashi, A.A., Sabaghzadeh, L., 2011. Synthesis and characterization of nickel hydroxide/oxide nanoparticles by the complexationprecipitation method. Inter. J. Phys. Sci. 6, 1471e1476. Munoz, J.A., Gonzalo, A., Valiente, M., 2002. Arsenic adsorption by Fe(III)-loaded open-celled cellulose sponge. Thermodynamic and selectivity aspects. Environ. Sci. Technol. 36, 3405e3411. Mustafa, S., Nawab, G., Naeem, A., Rehana, N., Safdar, M., 2003. Sorption of phosphate on cobalt hydroxide. J. Chem. Soc. Pak. 25, 25e28. Nabi, S.A., Shahadat, M., Shalla, A.H., Khan, A.M.T., 2011. Removal of heavy metals from synthetic mixture as well as pharmaceutical sample via cation exchange resin modified with rhodamine B: its thermodynamic and kinetic studies. Clean. e Soil Air Water 39, 1120e1128. Niboua, D., Khemaissiab, S., Amokranea, S., Barkatb, M., Chegroucheb, S., Mellah, A., 2011. Removal of UO2þ 2 onto synthetic NaA zeolite. Characterization, equilibrium and kinetic studies. J. Chem. Eng. 172, 296e305. Pan, B., Qiu, H., Pan, B., Nie, G., Xiao, L., Lv, L., Zhang, W., Zhang, Q., Zheng, S., 2010. Highly efficient removal of heavy metals by polymer-supported nanosized hydrated Fe(III) oxides: behavior and XPS study. Water Res. 44, 815e824. Predescu, A., Nicolae, A., 2012. Adsorption of Zn, Cu and Cd from waste waters by means of maghemite nanoparticles. U.P.B. Sci. Bull. 74, 255e264. Pretorius, P.J., Linder, P.W., 2001. The adsorption characteristics of d-Manganese dioxide: a collection of diffuse double layer constants for the adsorption of Hþ, Cu2þ, Ni2þ, Zn2þ, Cd2þ and Pb2þ. Appl. Geochem. 16, 1067e1082.
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Qadeer, R., Hanif, J., Khan, M., Saleem, M., 1995. Uptake of uranium ions by molecular sieve. Radiochim. Acta 68, 197e201. Rau, I., Gonzalo, A., Valiente, M., 2000. Arsenic(V) removal from aqueous solutions by Fe(III) loaded chelating resin. J. Radioanal. Nucl. Chem. 246, 597e600. Roques, J., Veilly, E., Simoni, E., 2009. Periodic density functional theory investigation of the uranyl ion sorption on three mineral surfaces: a comparative study. Int. J. Mol. Sci. 10, 2633e2661. Shao, W., Li, X., Cao, Q., Luo, F., Li, J., Du, Y., 2008. Adsorption of arsenate and arsenite anions from aqueous medium by using metal(III)-loaded amberlite resins. J. Hydrometall. 91, 138e143. Stamberg, K., Cabicar, J., Havlíek, L., 1980. Ion-exchange kinetics in systems with non-linear equilibrium isotherms: sorption of uranium(VI) on strong acid cation exchangers. J. Chromatogr. A 201, 113e120. Sureshkumar, M.K., Das, D., Mallia, M.B., Gupta, P.C., 2010. Adsorption of uranium from aqueous solution using chitosan-tripolyphosphate (CTPP) beads. J. Hazard. Mater. 184, 65e72. Suzuki, T.M., Bomani, J.O., Matsunaga, H., Yokoyama, T., 2000. Preparation of porous resin loaded with crystalline hydrous zirconium oxide and its application to the removal of arsenic. React. Funct. Polym. 43, 165e172. Thirunavukkarasu, O.S., Viraraghavan, T., Subramanian, K.S., 2001. Removal of arsenic in drinking water by iron oxide-coated sand and ferrihydrite, batch studies. Water Qual. Res. J. Can. 36, 55e70.
Tripathy, S.S., Kanungo, S.B., 2005. Adsorption of Co2þ, Ni2þ, Cu2þand Zn2þ from 0.5 M NaCl and major ion sea water on a mixture of d-MnO2 and amorphous FeOOH. J. Colloid Interf. Sci. 284, 30e38. Ulusoy, H.I., Simek, S., 2013. Removal of uranyl ions in aquatic mediums by using a new material: gallocyanine grafted hydrogel (pHZ). J. Hazard. Mater. 255, 397e 405. Webber, T.W., Chakkravorti, R.K., 1974. Pore and solid diffusion models for fixed-bed adsorbers. J. AlChE 20, 228e238. Weber, W.J., Morris, J.C., 1963. Kinetics of adsorption on carbon from solution. J. Sanit. Eng. Div. Am. Soc. Civ. Eng. 89, 31e59. Xu, Y., Boonfueng, T., Axea, L., 2006. Surface complexation of Pb(II) on amorphous iron oxide and manganese oxide: spectroscopic and time studies. J. Colloid Interf. Sci. 299, 28e40. Yang, C.H., 1998. Statistical mechanical study on the Freundlich isotherm equation. J. Colloid Interface Sci. 208, 379e387. Zhang, Y., Yang, M., Huang, X., 2003. Arsenic removal with a Ce(VI)-doped iron oxide adsorbent. J. Chemosphere 51, 945e952. Zhi-liang, Z., Hong-mei, M., Rong-hua, Z., Yuan-xin, G., Jian-fu, Z., 2007. Removal of cadmium using MnO2 loaded D301 resin. J. Environ. Sci. 19, 652e656.
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Uranyl ions adsorption by novel metal hydroxides loaded Amberlite IR120 A.A. Elabd a, *, W.I. Zidan a, M.M. Abo-Aly b, E. Bakier b, M.S. Attia b a b
Nuclear and Radiological Regulatory Authority, Cairo, Egypt Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 November 2013 Received in revised form 7 February 2014 Accepted 17 February 2014 Available online 1 April 2014
In this work, Ni(OH)2-loaded Amberlite IR120 (NieMA) and Co(OH)2-loaded Amberlite IR120 (CoeMA) removal from aqueous solutions. The resins were prepared, characterized and applied for UO2þ 2 adsorption characteristics were investigated in a batch system with respect to effect of contact time, pH, equilibrium isotherms and removal kinetics data. The results indicated that the UO2þ 2 could be efficiently removed from aqueous solutions at pH ¼ 3.5 using NieMA and CoeMA resins. The maximum adsorption capacities for the UO2þ 2 of NieMA and CoeMA were found to be 439 mg/g and 451 mg/g respectively. The equilibrium data fit well with the Langmuir adsorption isotherm. Kinetics study showed that the adsorption process was fast and reached equilibrium within 60 min and the kinetics data fit well with pseudo-second order and intra-particle diffusion models for both resins. The adsorption mechanism has been proposed and discussed. It was found that both NieMA and CoeMA resins could be used effectively for UO2þ 2 removal from aqueous solutions. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Loaded-resin Metal hydroxides Uranium Adsorption Amberlite IR120
1. Introduction Many studies on materials for the adsorption and separation of uranium species from aqueous systems have been done (Geckeler and Volchek, 1996; Guibal et al., 1994; Bayer et al., 1985). Uranium adsorption on various natural sorbents and Amberlite resins are important from economical and environmental point of view (Qadeer et al., 1995). Quantitative studies and adsorption kinetics of uranium (VI) were reported on use of Amberlite IR120 in aqueous solutions (Khopkar and De, 1960; Stamberg et al., 1980). Amberlite IR120 was used to concentrate uranium (VI) in samples of natural water for spectrophotometric determination (Bermejo-Barrera et al., 1990). Also, Amberlite IR120 was loaded by rhodamine B for the removal of some soluble metals (Nabi et al., 2011) and loaded by magnetite nano iron oxide for uranium removal (Elabd et al., 2013). There are many examples of the use of specially prepared resins to remove ions from aqueous solutions. Hristovski et al. (2008) prepared impregnated non-crystalline iron hydroxide nanoparticles onto strong base ion-exchange (IX) resins (Amberlite PWA2, A-530E, SIR-110, CalRes 2103, A-520E and SIR-100) to * Corresponding author. Tel.: þ2 0122 5781529; fax: þ2 2274 02 38. E-mail addresses: [email protected] (A.A. Elabd), [email protected], [email protected] (W.I. Zidan), [email protected] (M.M. Abo-Aly), [email protected] (E. Bakier), [email protected] (M.S. Attia). http://dx.doi.org/10.1016/j.jenvrad.2014.02.008 0265-931X/Ó 2014 Elsevier Ltd. All rights reserved.
achieve simultaneous removal of arsenate and perchlorate. Shao et al. (2008) studied the feasibility of using La(III)-, Ce(III)-, Y(III)-, Fe(III)- and Al(III)-loaded 200CT resin as adsorbents for the removal of As (III and V) from waste water. Dong et al. (2010) and Zhi-liang et al. (2007) used MnO2-loaded D301 ion exchange resin as adsorbent for simultaneous removal of lead and cadmium from aqueous solution. Pan et al. (2010) prepared impregnating hydrated iron oxide nanoparticles within a cation exchange resin D-001 for removal of soluble metals from contaminated water. Suzuki et al. (2000) prepared zirconium oxide e loaded Amberlite XAD-7 resin for arsenic removal. Huang and Chen (2009) developed a cationic magnetic nano-adsorbent using iron oxide nanoparticles for the adsorption of Cu(II) and Cr(VI) ions. A number of innovative adsorbents have been prepared and reported in recent years (Zhang et al., 2003; Balaji et al., 2005; Choi et al., 2006). Among them, oxides and hydroxides are often applied because of their high surface areas and their affinity to several soluble metals (Mallikarjuna and Venkataraman, 2003; Tripathy and Kanungo, 2005). However, these oxides and hydroxides are usually in the colloidal forms and are difficult to prepare in spherical beads of suitable size for practical applications. In recent years, this situation has led to a growing interest in the syntheses and the application of novel adsorbents by loading an oxide on another solid (Rau et al., 2000; Thirunavukkarasu et al., 2001; Munoz et al., 2002).
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Mustafa et al. (2003) and Jyo et al. (1993) reported that, hydroxides of cobalt can be employed as an adsorbent. Also, it was reported that hydrated UO2þ 2 adsorbed preferentially on top of a surface nickel atom through a NieO-bond, with a strong adsorption energy of 8.89 eV (Roques et al., 2009). This means that the loading amount of functional groups increases significantly. For this reason, it is expected that the new sorbent materials will show high adsorption capacity for UO2þ 2 . In this study, the surface of Amberlite IR-120 was loaded by two metal hydroxides, Co(OH)2 and Ni(OH)2 as adsorbents. The prepared resins (NieMA and CoeMA) were characterized and applied for UO2þ 2 removal from aqueous solutions. 2. Materials and methods 2.1. Materials Amberlite IR120 (Hþ form) was purchased from (Alfa Aesar Company). Uranyl nitrate hexahydrate, UO2(NO3)2$6H2O was manufactured by (Mallinckrodt Company). Nickel nitrate hexahydrate, Ni(NO3)2$6H2O and cobalt nitrate hexahydrate, Co(NO3)2$6H2O were purchased from (Rankem Company). 25% NH4OH solution was purchased from (Merck Company). HNO3 and KOH were purchased from (Fisher Chemicals Company). All chemicals were used without further purification. A standard uranium solution of 2000 mg/L was prepared by dissolving the appropriate amount of UO2(NO3)2$6H2O in deionized water. Deionized water used for all experiments was obtained from a Milli-Q (Millipore Corporation) water purification system. The experimental work was carried out in safeguards analytical laboratory (ETZ, KMP-I) at the Egyptian Nuclear and Radiological Regulatory Authority (ENRRA). 2.2. Instruments Fourier Transforms Infrared Spectrometer (FTIR), Jasco FT/IR6100 type A, from USA was used. The FTIR spectra (4000e 400 cm1) measured at room temperature, was used to investigate any observed changes of the prepared resins with Amberlite IR120, and these included new peaks, intensity variations of peaks originally present and wavelength shifts. A Scanning Electron Microscope (SEM) with Energy-Dispersive X-ray Spectrometer (EDX), JEOL 6510 LA SEM, from JEOL, Jaban was used to obtain an image of the resin before and after loading of metal hydroxides. EDX detector which was attached to the SEM system was used to investigate the distribution of Co, Ni and U lines of the prepared resins before and after adsorption of UO2þ 2 . Inductively Coupled Plasma Optical Emission Spectrometry (iCAP 6500 ICP-OES) from Thermo Fisher Scientific, UK, with ITEVA operating software for full control of all instrument functions and data handling, was used for the measurement of U concentration. This instrument is equipped with a high performance solid state Charge Injection Device (CID) camera. 2.3. Preparation of metal hydroxides loaded resin 2.3.1. Preparation of Ni(OH)2-loaded resin The method of preparation is similar to that of Motlagh et al. (2011) with minor modifications. An aliquot of 2.5 g dry Amberlite IR120 resin was added to 50 mL of Ni(NO3)2 solution (0.5 M). The initial pH of the solution was adjusted to 12.5 by dropwise addition of NH4OH solution (100 mL, 2 M) with continuous stirring for 3 h, with the temperature maintained at 60 C. During the addition of NH4OH, it was observed that the resin color changed from the original pale brown to green. The color change of the resin was due to its loading by Ni(OH)2, as expected. Any change in pH
was readjusted from time to time by addition of 0.1 M HNO3/KOH. The resulted loaded sorbent was thoroughly washed with deionized water to remove excess nitrate ions and dried at 80 C for 3 h in an oven and kept for further investigation. The obtained NieMA resin was further characterized by both IR and EDX. 2.3.2. Preparation of Co(OH)2-loaded resin The method of preparation is similar to that of Konga et al. (2009) with minor modifications. An aliquot of 2 g dry Amberlite IR120 resin was added to 25 mL of Co(NO3)2 solution (1 M). The initial pH of the solution was adjusted to 9 by dropwise addition of NH4OH solution with continuous stirring for 3 h, with the temperature maintained at 60 C. During the addition of NH4OH, it was observed that the resin color changed from the original pale brown to red. The color change of the resin was due to its loading by Co(OH)2, as expected. Any change in pH was readjusted from time to time by addition of 0.1 M HNO3/KOH. The resulted loaded sorbent was thoroughly washed with deionized water to remove excess nitrate ions and dried at 80 C for 24 h in an oven and kept for further investigation. The obtained CoeMA resin was further characterized by both IR and EDX. 2.4. Batch experiment Batch experiments were conducted for evaluating the extent of UO2þ 2 adsorption on NieMA and CoeMA. Batch adsorption experiments were carried out in flasks with fixed magnetic stirring. The resin (50 mg) was added to 50 mL solution containing various uranium concentrations for various contact times at room temperature. The pH was adjusted by adding of 0.1 M HNO3/KOH to the solutions at each experiment. The pH of the solutions was measured on a pH meter 780 of Metrohm Herison, Switzerland. The resin was filtered using Whatman filter paper no: 44. The uranium remained in solution was analyzed using ICP-OES instrument. The influence of specific process parameters such as initial uranium concentration, pH of the solution and contact time was determined by calculating uranium adsorption keeping other parameters constant. The adsorption capacity of UO2þ at time t (mg/g) was 2 calculated using the following equation (Bhattacharyya et al., 2006):
qt ¼
ðCo Ct ÞV m
(1)
where Co and Ct are the initial and at time (t) concentrations of UO2þ 2 (mg/L), respectively. V is the volume of the solution (L) and m is the mass of sorbent (g). 3. Results and discussion 3.1. Sorbent characterization The FTIR spectra of Amberlite IR120 and NieMA are shown in Fig. 1.These spectra show a broad band located at 3424 cm1 which may be associated to the OeH stretching vibration of interlayer water molecules and the H-bonded OH groups. At low wavenumbers, the band at about 578 cm1 is associated to the NieO stretching vibration (Li et al., 2012). This strongly support the presence of the Ni(OH)2 and may indicate the formation of a bond between Amberlite IR120 and the NieO group. The FTIR spectra of Amberlite IR120 and CoeMA are shown in Fig. 2. These spectra show a broad peak in the wave number range of 3440e3570 cm1 which can be assigned to the OeH stretching vibration of interlayer water molecules and the H-bonded OH group. Below 800 cm1, the bands are associated with CoeO
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surface while Fig. 3b and c are shown a change of the surface morphologies of the resin after its loading by both metal hydroxides, NieMA and CoeMA respectively. EDX characterization confirmed the presence of elements (Ni, Co and U) in the loaded resins. The samples used for EDX characterization were:
Ni-MA
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101
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110
- NieMA: Ni(OH)2-loaded Amberlite IR120 resin before adsorption; - CoeMA: Co(OH)2-loaded Amberlite IR120 resin before adsorption; - NieMAeU: Ni(OH)2-loaded Amberlite IR120 resin after UO2þ 2 adsorption in optimum conditions; - CoeMAeU: Co(OH)2-loaded Amberlite IR120 resin after UO2þ 2 adsorption in optimum conditions.
Amberlite IR120
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Fig. 1. Comparison between IR spectra of Amberlite IR120 and NieMA.
stretching and CoeOH bonding vibrations. The appeared two absorbance bands at 672 and 577 cm1 for CoeMA spectra can be assigned to in plane bonding of (CoeOeH) and the v (CoeO) stretching vibrations (Morsya et al., 2009). This strongly support the presence of the Co(OH)2 and may indicate the formation of a bond between Amberlite IR120 and the CoeO group. The SEM images of Amberlite IR120, NieMA and CoeMA are shown in Fig. 3(a, b, c) respectively. Fig. 3(a) is shown a smooth
This method is semiquantitative and it measures the ions fraction located close to the matrix surface. The EDX spectra of NieMA before and after adsorption of UO2þ are shown in Fig. 4(a, b) 2 respectively. The EDX spectra of CoeMA before and after adsorption of UO2þ are shown in Fig. 5(a, b) respectively. The EDX spectra 2 revealed the presence of the elements C, O, S and Ni for NieMA and Co for CoeMA before adsorption of UO2þ 2 , showing that, the Ni(OH)2 and Co(OH)2 particles were distributed onto the surface of Amberlite IR120. After the UO2þ adsorption, the EDX spectra 2
100 Co-MA
835 3440
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Fig. 2. Comparison between IR spectra of Amberlite IR120 and CoeMA.
Fig. 3. (a, b, c) SEM images for (a) Amberlite IR120, (b) NieMA and (c) CoeMA.
500
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showed a new distinct peak associated with the presence of the U line, showing that, the UO2þ 2 was adsorbed onto the surface of both NieMA and CoeMA. 3.2. Effect of pH The effect of pH on UO2þ 2 adsorption efficiency for NieMA and CoeMA is shown in Fig. 6. This experimental work is carried out at pH range of 2e3.5. This due to the fact that, UO2þ 2 forms a precipitate as hydroxides above the pH values 3.5 (Niboua et al.,
2011). It was clear that, the adsorption increased with increasing pH ¼ 3.5 for NieMA and CoeMA. Ulusoy and Simek (2013) reþ ported that there was a competition between UO2þ 2 and H for the same exchange sites or donating atoms and this caused a decrease in the adsorption at low pH, because most of the electron donor atoms were in the protonated form at low pH. Also, Hþ is preferentially adsorbed by the resin in comparison to UO2þ 2 (Jha et al., 2009). The pH dependence of UO2þ adsorption on NieMA and 2 CoeMA is similar to that previously reported for adsorption on manganese oxide coated zeolite, and activated carbon (Han et al.,
Fig. 4. (a, b) EDX spectra for (a) NieMA and (b) after UO2þ 2 adsorption.
A.A. Elabd et al. / Journal of Environmental Radioactivity 134 (2014) 99e108
103
Fig. 5. (a, b) EDX spectra for (a) CoeMA and (b) after UO2þ 2 adsorption.
2007; Mellah et al., 2006). It could be concluded that, the adsorption efficiency of the two prepared resins for UO2þ was 2 optimal at pH 3.5. Consequently, the working media was adjusted at pH 3.5 for further UO2þ 2 adsorption experiments conducted in this study. 3.3. Effect of contact time The adsorption experiments were carried out for contact times ranging from 1 to 100 min with 50 mL of solution having
2000 mg/L uranium and 50 mg of adsorbent at room temperature. Samples of 50 mL were analysed at various time intervals to estimate the concentration of dissolved uranium as a function of equilibration time (Fig. 7). It is clear that the adsorption efficiency increased with contact time and reached an apparent adsorption equilibrium within 60 min. Two phases of uranium adsorption kinetics were observed: an initial rapid phase where adsorption was fast and contributed significantly to equilibrium uptake, and a slower second phase whose contribution to the total metal adsorption was relatively small. Consequently, the
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14
78 77
12 10
75 74
Ni-MA Co-MA 0.008 0.012 438 446
R
0.999
2
72 71
6 4
70 69
2
Ni-MA
68
Co-MA 1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
Ni-MA y =0.28103+0.00228*X Co-MA y =0.17996+0.00224*X
0
3.6
pH
0
adsorption equilibrium time considered for further experiments was 60 min. After obtaining the optimum adsorption conditions of the Nie MA and CoeMA, the uranium adsorption capacities were determined for NieMA, CoeMA and Amberlite IR120. For this, 50 mg of the adsorbent was contacted with 100 mL of 2000 mg/L of UO2þ 2 solution at pH 3.5, with continuous stirring at room temperature for 24 h. The amount of adsorbed uranium was estimated from the difference of the uranium concentrations in the aqueous solution, before and after adsorption. Consequently, uranium adsorption capacities of NieMA, CoeMA and Amberlite IR120 were calculated as 439 mg/g, 451 mg/g and 312 mg/g adsorbent, respectively. 3.4. Effect of initial uranium concentration and adsorption isotherm models At low concentration, UO2þ 2 was adsorbed at specific sites on adsorbent and reaching saturation as a result of its concentration increase. The different concentrations of UO2þ 2 solutions ranging from 1000 to 10,000 mg/L (20 mL) were performed with constant
1000
2000
3000
4000
5000
6000
Ce (mg/L)
Fig. 6. The adsorption efficiency of UO2þ versus pH by NieMA and CoeMA 2 (Co ¼ 1000 mg/L, V ¼ 50 mL and m ¼ 50 mg).
Fig. 8. Langmuir isotherm for UO2þ 2 adsorption by NieMA and CoeMA.
contact time (60 min), pH (3.5) and amount (50 mg) of loaded resins with continues stirring at room temperature. The uptake of UO2þ 2 increases as the initial concentration increased up to 6000 mg/L, thereafter reached a plateau. In order to define the mechanism of UO2þ 2 adsorption onto NieMA and CoeMA, the experimental data were applied to Langmuir and Freundlich linear isotherm models. 3.4.1. Langmuir isotherm model The conceptual model underlying Langmuir isotherm assumes monolayer adsorption on a uniform surface with a finite number of adsorption sites. Once a site is filled, no further adsorption can take place at that site (Langmuir, 1916). As such, the surface will eventually reach a saturation point where the maximum adsorption of the surface will be achieved. The linear form of the Langmuir isotherm model (Langmuir, 1916) is:
Ce 1 Ce ¼ þ KL qm qm qe
2.68 80
Kf (mg/g) 1/n (L/g) 2 2.64 R
70
(2)
Ni-MA 224 0.078 0.992
Co-MA 257 0.065 0.984
60
Log q e
Adsorption efficiency (%)
0.999
8
73
Ce/qe(g/L)
Adsorption efficiency (%)
76
KL (L /mg) qm (mg /g)
50
40
2.60
2.56 30
Ni-MA Co-MA
20 0
20
40
60
80
100
Contact time (min) Fig. 7. The contact time versus the adsorption efficiency of UO2þ 2 for NieMA and Coe MA (Co ¼ 2000 mg/L, V ¼ 50 mL and m ¼ 50 mg).
Ni-MA y= 2.346+0.0787*X Co-MA y= 2.409+0.0652*X
2.52 2.0
2.5
3.0
3.5
Log C e Fig. 9. Freundlich isotherm for UO2þ 2 adsorption by NieMA and CoeMA.
4.0
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3.0 2.8 2.6 2.4
K1 (L/min) qe (mg/g)
Ni-MA Co-MA 0.092 0.072 378 388
R
0.985 0.995
2
RL ¼
Log(q e-q t)
1 1 þ kL C0
(3)
There are four probabilities for the RL value: for favorable sorption, 0 < RL < 1; for unfavorable sorption, RL > 1; for linear sorption, RL ¼ 1; for irreversible sorption, RL ¼ 0 (Webber and Chakkravorti, 1974). The resulted values of RL were in the range of 0e1 which support that, the exchange of UO2þ 2 is favorable for both NieMA and CoeMA.
2.2 2.0 1.8 1.6
3.4.2. Freundlich isotherm model The Freundlich isotherm is assumed to be applicable to both monolayer (chemisorption) and multilayer adsorption (physisorption) and is based on the assumption that the adsorbate is adsorbed onto the heterogeneous surface of a sorbent. The linear form of Freundlich equation is expressed (Yang, 1998) as follows:
1.4 1.2 1.0
Co-MA y=2.591-0.03126*X Ni-MA y=2.577-0.04*X
0.8 0
5
10
15
20
25
30
35
40
45
50
55
60
time (min) Fig. 10. Pseudo-First order kinetic plots for UO2þ 2 adsorption of by NieMA and CoeMA.
where Ce is concentration of adsorbed at equilibrium (mg/L), KL is the Langmuir constant related to the energy of adsorption (L/mg) and qm is the monolayer adsorption capacity (mg/g). Linear plots of the Langmuir isotherm of UO2þ 2 are shown in Fig. 8. The regression coefficients values were R2 ¼ 0.999 for NieMA and CoeMA. The qm and KL values for NieMA were 438 mg/g and 0.008 L/mg, respectively. The qm and KL values for CoeMA were 446 mg/g and 0.012 L/mg, respectively. By comparing qm values, it suggests that CoeMA has a higher maximum adsorption capacity than NieMA. The reason of that may be due to that the atomic size of cobalt is higher than that of nickel. Consequently, the charge per unit area in case of nickel will be higher than that of cobalt and leads to the more repulsion between the nickel ion and uranyl ion. This may explain the higher adsorption capacity in case of cobalt compared with nickel. The features of the Langmuir isotherm can be expressed in terms of dimensionless constant sorption factor RL defined by Webber and Chakkravorti (1974) as follows:
0.11 0.10 0.09
log qe ¼ log KF þ 1=n log Ce
R
2
0.987
(4)
where KF is Freundlich isotherm constant related to adsorption capacity (mg/g) and 1/n is the heterogeneity factor constant related to surface heterogeneity. Linear plots of the Freundlich isotherm of UO2þ 2 are shown in Fig. 9. The regression coefficients were R2 ¼ 0.992 and 0.984 for Nie MA and CoeMA, respectively. The KF and 1/n values for NieMA were 224 mg/g and 0.078 L/g, respectively. The KF and 1/n values for CoeMA were 257 mg/g and 0.065 L/g, respectively.
3.5. Kinetic studies The kinetics of UO2þ adsorption on the NieMA and CoeMA 2 were analyzed using pseudo-first order, pseudo-second order, and intra-particle diffusion models. The pseudo-first order and pseudosecond order models are macroscopic kinetic models commonly used for describing the adsorption processes. These models suggest that adsorption can be considered as either first or second order chemical reaction where the adsorption process is the rate determining step. An intra-particle diffusion model is used to describe the adsorption process where the intra-particle diffusion resistance is the rate determining step (Sureshkumar et al., 2010).
400
Ni-MA Co-MA K2 (g/mg min) 3.35E-4 2.81E-4 qe (mg/g) 438 463
350
0.998
0.08
300
0.07
250
qt (mg/g)
0.06
t/qt
105
0.05 0.04
200 150 100
0.03 0.02
50
Co-MA y=0.0166+0.00216*X Ni-MA y=0.0155+0.00228*X
0.01 0.00
Ni-MA C0-MA
0 1
0
5
10
15
20
25
30
35
40
time (min) Fig. 11. Pseudo-second order kinetic plots for UO2þ 2 adsorption by NieMA and CoeMA.
2
3
4 1/2
t
5
6
7
0.5
(min )
Fig. 12. Intra-particle diffusion plots for UO2þ adsorption by NieMA and CoeMA 2 (Co ¼ 1000 mg/L, V ¼ 50 mL and m ¼ 50 mg).
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Fig. 13. A schematic representation for the proposed adsorption mechanism (M ¼ Ni or Co).
3.5.1. The pseudo-first order model The Lagergren pseudo-first order equation can be expressed as follows (Ho, 2004):
dq ¼ K1 ðqe qt Þ dt
(5)
where qt is the amount of metal adsorbed at time t, qe is the amount of metal adsorbed at equilibrium and K1 is the adsorption rate constant. Integrating Eq. (5) for the boundary conditions t ¼ 0 to t ¼ t and q ¼ 0 to q ¼ qt and rearranging it for linearized data plotting, the following equation is obtained (Ho, 2004):
logðqe qt Þ ¼ log qe
K1 t 2:303
(6)
This model can be applied if log (qe e qt) versus t gives a straight line, in which case qe and K1 can be calculated from intercept and slope of the plot. Linear plots of Log (qe e qt) versus t of UO2þ 2 adsorption on the Nie MA and CoeMA are shown in Fig. 10, with regression coefficients of 0.985 and 0.995, respectively. This suggests the applicability of the pseudo-first order kinetics model to fit the experimental data. The calculated values of the adsorption capacities, qe,cal (378 mg/g) and (388 mg/g) were lower than the values of experimental adsorption capacities, qe,exp (416 mg/g) and (429 mg/g) for NieMA and CoeMA respectively. 3.5.2. The pseudo-second order model The pseudo-second order model is based on sorbent capacity, which suggests that chemisorption is the rate-controlling step and can be expressed as a differential equation (Ho and McKay, 1999):
dq ¼ K2 ðqe qt Þ2 dt
(7)
where k2 is the adsorption rate constant. Integrating Eq. (7) for the boundary conditions t ¼ 0 to t ¼ t and q ¼ 0 to q ¼ qt and rearranging it for linearized data plotting gives (Ho and McKay, 1999):
t 1 1 ¼ þ t qt K2 qe 2 qe
respectively. Therefore, it could be concluded that adsorption of UO2þ 2 onto NieMA and CoeMA follows the pseudo-second order better than the pseudo-first order model. The pseudo-second order kinetic model assumes that chemical adsorption is the rate-limiting step. 3.5.3. The intra-particle diffusion model The intra-particle model assumes that adsorption of metal ions from the aqueous onto the solid phase is a multi-step process involving transport of metal ions from aqueous phase to the surface of the solid particles (bulk diffusion) and then, diffusion of metal ions via the boundary layer to the surface of the solid particles (film diffusion) followed by transport of metal ions from the solid particles surface to its interior pores (pore diffusion or intra-particle diffusion), the later is likely to be a slow process and, therefore, it may be the rate determining step (Crini et al., 2007). The possibility of intra-particle diffusion resistance affecting the sorption was explored by Weber and Morris (1963) using the intra-particle diffusion model as follows: 1=2
t qt ¼ Kid þI
(9)
Kid (mg g1 min1/2) is the intra-particle diffusion rate constant. Fig. 12 shows that, the plot of qt versus t1/2 may present multi linearity, which indicates that two or more steps occur in the sorption processes. According to this model, the plot of uptake, (qt), versus the square root of time (t1/2) should be linear if intra-particle diffusion is involved in the adsorption process and if these lines pass through the origin then intra-particle diffusion is the rate-controlling step. When the plots do not pass through the origin, this is an indication of some degree of boundary layer control and the intra-particle diffusion is not the only rate-limiting step, but also other kinetic models may control the sorption rate, all of which may be operating simultaneously (Mezenner and Bensmaili, 2009). In addition, it can also be observed that the straight lines do not pass through the origin, which indicates that both intra-particle diffusion and film diffusion are the rate limiting steps for UO2þ 2 adsorption by both NieMA and CoeMA.
(8)
The pseudo-second order plot of UO2þ 2 adsorption on the NieMA and CoeMA are shown in Fig. 11 and is also linear with regression coefficients of 0.987 and 0.998 respectively, however the calculated values of the adsorption capacities, qe,cal (438 mg/g) and (463 mg/g) are closer to the values of the experimental adsorption capacities, qe,exp (416 mg/g) and (429 mg/g) for NieMA and CoeMA
3.6. Desorption and regeneration In order to minimize operation cost and make the process more feasible, the reusability of both NieMA and CoeMA is an important aspect to evaluate its applicability. Desorption of UO2þ 2 from both NieMA and CoeMA were carried out in a batch mode by using 0.1 mol/L HNO3 solution and the desorption efficiency was found to
A.A. Elabd et al. / Journal of Environmental Radioactivity 134 (2014) 99e108
be 96.3% and 96.7%, respectively within the experimental conditions considered in this work. 3.7. Adsorption mechanism discussion Adsorbents may form different types of bonds with the metal surface (Koretsky, 2000). In general, if the adsorption between the adsorbate and the surface sites is caused by relatively strong chemical bonds such as ionic and covalent bonds, the adsorption is identified as “specific” adsorption. The adsorption complex formed during this process was named as “inner-sphere” type complexes. When the adsorption between the adsorbate and the surface sites results from the weaker Coulomb attraction or Van der Waals bond, the adsorption is identified as “nonspecific” adsorption. The adsorption complex formed during this process was named as “outer-sphere” type complexes (Koretsky, 2000). Fig. 13 shows the schematic representation of the proposed adsorption mechanism. The adsorption mechanism is carried out in two steps, first by chemical precipitation of metal hydroxides into Amberlite IR120 in view of the characterization results as shown in Figs. 1e3, 4a and 5a which support the presence of metal hydroxides into Amberlite IR120 surface. Second, UO2þ 2 adsorbent into Nie MA and CoeMA in view of the characterization results as shown in Figs. 4b and 5b which support the presence of UO2þ 2 into NieMA and CoeMA respectively. Some researchers have been reported that UO2þ and other 2 soluble metals were strongly adsorbed as an inner sphere complexes by means of surface complexation with NieO bond (Roques et al., 2009; Pretorius and Linder, 2001; Xu et al., 2006). It could be concluded that the UO2þ 2 is specifically adsorbed on the Ni(OH)2 or Co(OH)2 loaded Amberlite IR120 resin through an inneresphere complex via surface complexation rather than the electrostatic interaction. The experimental results suggest that the higher adsorption capacity of both NieMA and CoeMA may be due to the presence of double effect of an inner sphere complex via surface complexation with Ni(OH)2 and Co(OH)2 with high capacity of adsorption due to their high surface area and ionic exchange by Amberlite IR120 (Predescu and Nicolae, 2012). 4. Conclusions In this work, it was found that both NieMA and CoeMA resins could be used effectively for UO2þ 2 removal from aqueous solutions. The adsorption reaction mechanism for both resins could be explained by the presence of a double effect of an inneresphere complex via surface complexation with Ni(OH)2 and Co(OH)2 as well as ionic exchange by Amberlite IR120. CoeMA was found to be of higher adsorption capacity compared to NieMA. The adsorption of UO2þ by both NieMA and CoeMA followed the Langmuir 2 adsorption isotherm. The adsorption kinetics for both NieMA and CoeMA could be described by a pseudo-second order and intraparticle diffusion models. References Balaji, T., Yokoyama, T., Matsunaga, H., 2005. Adsorption and removal of As(V) and As(III) using Zr-loaded lysine diacetic acid chelating resin. J. Chemosphere 59, 1169e1174. Bayer, E., Eberhardt, H., Grathwohl, P.A., Geckeler, K., 1985. Soluble of polychelatogenes for separation of actinide ions by membrane filtration. Isr. J. Chem. 26, 40e47. Bermejo-Barrera, A.B., Yebra-Biurrun, M.C., Fraga-Trillo, L.M., 1990. Spectrophotometric determination of uranium in natural waters. Anal. Chim. Acta 239, 321e323.
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