Journal of Environmental Radioactivity 134 (2014) 120e127
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Potentiality of uranium biosorption from nitric acid solutions using shrimp shells S.H. Ahmed, E.M. El Sheikh*, A.M.A. Morsy Nuclear Materials Authority, P.O. Box 530, El Maadi, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 July 2013 Received in revised form 17 February 2014 Accepted 11 March 2014 Available online
Biosorption has gained important credibility during recent years because of its good performance and low cost. This work is concerned with studying the potentiality of the chitin component of the shrimp shells for uranium biosorption from nitric acid liquid solutions. The structural characteristics of the working chitin have been determined via Fourier Transform Infrared Spectroscopy (FTIR). The surface morphology was examined using Scanning Electron Microscopy (SEM). The adsorption capacity of biomass was investigated experimentally. The influence of contact time, pH, metal ion concentration, solution volume to mass ratio and temperature were evaluated and the results were fitted using adsorption isotherm models. The kinetic of uranium biosorption was also investigated as well as biosorption thermodynamic. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Uranium biosorption Shrimp shell Adsorption isotherm Adsorption kinetics
1. Introduction The chemical and radiological toxicity of natural uranium is actually well documented (Brugge et al., 2005). The environmental protection agency (EPA) has classified uranium as a confirmed human carcinogen and suggested that zero tolerance is the only safe acceptable limit (USEPA, 1996). In addition, the EPA finalized a realistic regulation level of 30 mg l1 is the maximum uranium contaminant level. According to the stringent environmental regulations that exist against the release of uranium contaminants into the environment, it is therefore greatly desirable to develop efficient, economical and viable methods for the treatment of uranium wastes. Various kinds of adsorbents have been widely produced and applied for the removal of radionuclides and heavy metals (Kuribayashi et al., 1987). Although many adsorbents have excellent performance, the cost is relatively high in comparison with the greatly available natural waste products (Kuribayashi et al., 1988). Biosorption is a physicochemical process that occurs naturally in certain biomass which allows it to passively concentrate and bind contaminants onto its cellular structure (Volesky and Bohumil, 1990). In practice scientists and engineers are hoping that biomass can provide an economical alternative for removing toxic
* Corresponding author. Tel.: þ20 1064481197. E-mail address: [email protected] (E.M. El Sheikh). http://dx.doi.org/10.1016/j.jenvrad.2014.03.007 0265-931X/Ó 2014 Elsevier Ltd. All rights reserved.
heavy metals and radionuclides from industrial wastewater and aid in environmental remediation (Kratochvil and Volesky, 1998). Abundant natural polymers or agriculture waste products can be economically used as potential biosorbents for different metals (Demirbas, 2008; Faroog et al., 2010; Ray et al., 2010; Sud et al., 2008). Thus, extensive research has evaluated variety of biosorbents such as fungi (Kapoor and Viraraghavan, 1998), yeast (Ashkenazy et al., 1997), bacteria (Diels et al., 1995), algae (Zhang et al., 1999), chitin (Hoshi et al., 1997) and chitosan (Kang et al., 1999). Chitin, an environmental friendly material, is considered as biodegradable and biocompatible. It is a natural long chain polysaccharide polymer of N-acetyl-D-glucosamine, a derivative of glucose. It is the second most abundant resource (next to cellulose) in nature. Chitin is the main component of the exoskeletons of anthropods such as crustaceans (e.g.; crabs, lobsters and shrimps). Besides its resistance to the action of acids, it is worth noting that chitin is recognized as an excellent metal ligand, forming stable complexes with many metal ions (Chui et al., 1996). The formation of coordination complex between the metal and the chitin nitrogen and Aktay, 2000). Gyliene et al. or oxygen has been reported (Sag (2002) have pointed that some of metal ions, such as Fe3þ and Pb2þ, are sorbed much better on chitin. The use of chitin as powder is very difficult for its separation after adsorption as well as application in chromatograph column (Yan and Viraraghavan, 2001). It is also well known that chitin is insoluble in many solvents however; it is very brittle leading to a limitation in its reactivity and process ability for utilization.
S.H. Ahmed et al. / Journal of Environmental Radioactivity 134 (2014) 120e127
The aim of this research was to study the ability of chitin for grafting uranium from nitric acid solutions. Therefore, the chitin component of the working shrimp shell was separated using a proper extraction procedure and its structural characteristics were determined. The relevant optimum conditions for uranium adsorption were then studied under varying experimental conditions using batch operation mode. Adsorption isotherm modeling, sorption kinetics and thermodynamics were investigated to determine the probable physical characteristics of the applied process. 2. Material and method 2.1. Material 2.1.1. Material preparation Fresh shrimp shells provided for the experiments were supplied from local market Cairo, Egypt. The shells were first separated from the head and legs then washed for several times with deionized water before drying at 40 C. The dried shells were cut to almost uniform flakes. The shrimp shell flakes characterized by the presence of chitin, the material which is responsible for uranium grafting in our study, so it was recommended to quantify its percent before use. 2.2. Chitin extraction Chitin extraction parameters were occurred by mild acidic and alkaline treatments (Manni et al., 2010). Initial step of extraction was carried out by acidic treatment using 1 N HCl solution at room temperature for 2 h followed by filtration, neutralization and washing with deionized water. Next step, deproteination, was performed using alkaline treatment with 2 N sodium hydroxide solution at 60e65 C then followed by neutralization by washing. Final step, demineralization, has done by 1 N HCl solution at room temperature for 3e5 h. Chitin extraction yield was 24e28%.
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The given out CO2 bubbles from the reaction of calcium carbonate in the shell with the nitrate medium may delay the process of uranium adsorption. Therefore when all calcium carbonate in the shells react with HCl, most of the pore spaces are already opened which accommodate the adsorbed uranium (Eq. (2)) CaCO3 þ 2 HCl / CaCl2 (aq) þ CO2 þ H2O
(2)
2.5. Adsorption studies Several batch biosorption experiments were carried out using 100 ml conical flasks by stirring 50 ml uranium solutions with different concentrations after adding 1 g dry weight of the working biosorbent for 1 h and then all the conical flasks were sealed with a silicon cap to minimize evaporation. The amount of uranium metal ion adsorbed was calculated from the following equation:
Qe ¼ ðC0 Ce Þ V=M
(3)
where Qe is the amount of uranium metal ions adsorbed onto the unit mass of the sorbent (mg g1), C0 and Ce are the initial and equilibrium metal concentrations (mg l1) in the solution, respectively, while V is the solution volume (L) and M is the dry weight of biosorbent (g). Uranium concentration in the different aqueous stream solutions was measured via its arsenazo (III) complex using SP-8001 UVeVIS Spectrophotometer at wavelength 655 nm (Marczenko, 1976). The arsenazo (III) reagent (Avocado) solution was prepared by dissolving 0.25 g together with 0.5 g sodium acetate in 100 ml deionized water. The uranium solutions were prepared by diluting the standard uranium stock solution assaying 1000 mg l1 in nitric acid solution (TEDIA, USA) to the desired concentrations using deionized water. On the other hand, a digital pH meter (Jenway, UK) was used for pH adjustment. 3. Results and discussion
2.3. Material characterization 3.1. Environment friendly preparation Chitin in the shrimp shell was characterized by the following technique: a) Fourier Transform Infrared Spectrometer (FTIR): (FTIR) model Thermo Scientific Nicolet IS10, Germany was used for the determination of the structural characteristics of the working chitin. b) Scanning Electron Microscope (SEM): SEM model Philips XL 30 ESEM is considered as the most reliable and convenient tool for the study of physical structure of biosorbents (Warshawsky et al., 1981) as well as mineralogical investigations. The analytical conditions involved 25e30 kV accelerating voltage, 1e2 mm beam diameter and 60e120 s counting times. Minimum detectable weight concentration is ranging from 0.1 to 1 wt% while the realized precision is well below 1%.
2.4. Decalcification of shrimp shells before uranium adsorption The shrimp shells consist of several layers where calcium carbonate is concentrated mainly in the outer tough layer. The principle behind decalcification of shrimp shell is that calcium carbonate in the shells will react with dilute nitric acid medium to form soluble calcium nitrate, water and carbon dioxide (Eq. (1)). CaCO3 þ 2HNO3 / Ca (NO3)2 þ H2O þ CO2
(1)
The particles’ size, shape and surface morphology as well as specific surface area of bio-adsorbent fully depend on the preparation method. In addition, easy to prepare, easy to use, hazard free and environment friendly treatments are the requirement for sustainable preparation of bio-adsorbents. In these circumstances, this research adopted a simple preparation method rather than the expensive and high-tech pyrolysis and non-environment friendly acid/base treated methods. In this research the shrimp shells were treated with 0.5 N HCl solution in order to remove calcium carbonate present in the shells before the adsorption experiments then dried and ground to uniform flakes. 3.2. Characteristics of biosorbent 3.2.1. Fourier transform infrared spectrometer characterization FTIR spectra are a useful tool to identify molecular to functional groups (Dong and Ozaki, 1997). The yield of chitin from the separated shell is 1.245 g obtained from 5 g shrimp shell sample. The IR spectrum of the chitin (Fig. 1) isolated from the shrimp shell contains six major peaks; 3433 cm1, 2929 cm1, 1647 cm1, 1548 cm1, 1213 cm1 and 1024 cm1. The band observed at 3433 cm1 in shell spectra indicates the presence of NeH (primary amine) and OeH (alcoholic) stretching groups, this result agrees with (Gow et al., 1987) which found that the IR spectrum of a chitin exhibited major peaks at 3446 cm1 for eOH stretching and eNH
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stretching vibrations, while band observed at 2929 cm1 refers to CeH stretch band for alkanes. The wavenumber 1647 cm1 was found to be attributed to NeH bend (primary amine), which is also agree with Gow et al. (1987), and C¼O while peak value 1548 cm1 attributed to CH2 bending in alkanes. Finally the two intense absorption bands appeared at 1213 cm1 and 1024 cm1 in spectra refer to CeOeC in ether and CeN stretch vibration, respectively. Among these active groups the amine and hydroxyl groups play the major role for metal complexation (Memon et al., 2008). The IR characteristics performance of the whole peaks of chitin is tabulated in Table 1. 3.2.2. Scanning electron microscope characterization It has been reported that Scanning Electron Microscope (SEM) is the most reliable and convenient tool for the study of physical
structure of biosorbents. Thus, the surface of shrimp shell flakes were observed using SEM in order to illustrate the change in the surface feature of the flakes after adsorption. Scanning Electron Microscope photographs of the surface of the shrimp shell flakes before and after adsorption are given in Fig. 2 (a,b). The micrograph apparently shows the original flakes possess many vacant pores showing the cross-sections have much more wrinkle and regular structure before grafting. On the other hand, the rough surface turned to be relatively brilliant after grafting with uranium showing an interconnected flow-through polymeric network with irregular pores at higher magnification.
3.3. Uranium adsorption mechanism A three-step process has been used to describe the biosorption of chitin (Zhang et al., 2002; Yan and Viraraghavan, 2001). The first process involves the formation of a complex between the dissolved uranium ionic species and the chitin chain, where the complex forms between the uranium ions and the amineenitrogen of the chitin; the second process involves the adsorption of uranium metal ions by the chitin network close to that complexed by the chitin nitrogen; the third process is the hydrolysis of the complex formed by the first process and the precipitation of the hydrolysis product. In addition, the network structure and hydrophilic skeleton of the chitin flakes could promote adsorption (Al-Rub, 2006). The reaction of the chitin with U is illustrated in the following equation:
3.4. Experimental parameters of uranium biosorption 3.4.1. Effect of contact time To understand the effect of contact time on uranium adsorption onto shrimp shell flakes, experiments were conducted with 50 ml uranium solutions having 175 mg l1 concentration with initial pH 3.6 at room temperature of 25 1 C using 1 g of adsorbent. The samples were analyzed after each experiment to estimate the concentration of dissolved uranium as a function of equilibration time. Fig. 3 shows that the process is characterized by a rapid adsorption in the first 30 min of equilibration time, followed by a
Fig. 1. IR spectra for chitin extracted from shrimp shell flakes.
S.H. Ahmed et al. / Journal of Environmental Radioactivity 134 (2014) 120e127
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Table 1 IR characteristic performance of chitin Peak no.
Spectra value (cm1)
Functional group
1
3433
2 3
2929 2362
Primary amines, alcohols Alkanes Alkanes
4
1647
5
Peak no.
Spectra value (cm1)
Functional group
8
1316
9 10
1213 1159
Alcohols, esters Ether Aliphatic amines Aliphatic amines
11
1114
1548
Primary amines, aldehydes, saturated aliphatic Alkanes
12
1071
6
1444
Alkanes
13
1024
7
1379
Alkanes
14
590
Aliphatic amines Aliphatic amines Alkyl halides
Fig. 3. Effect of contact time upon uranium adsorption efficiency onto shrimp shell flakes.
distribution of uranium species versus pH (Fig. 5), it is clear that at pH 3.6 the complex [(UO2) (OH)]þ is mostly abundant. slow process, leading to maximum adsorption in around 1 h. Uranyl ion is a bulky cation and the diffusion of the bulk ion into the chitin flakes is a slow process leading to the overall slow kinetics of the adsorption process therefore 60 min shaking time was found to be appropriate and used in all subsequent experiments. 3.4.2. Effect of initial pH For studying the effect of initial pH on uranium adsorption efficiency, uranium solutions were prepared with different pH values ranging from 1.21 to 7.3 with keeping the other factors constant at 50 ml uranium solution with 175 mg l1 concentration, 1 g adsorbent, 60 min contact time and 25 1 C room temperature. The qe dependence on pH of the uranium solution for single adsorption is shown in Fig. 4. Adsorption increased with an increase in pH of the solution in the range 1.2e3.6. As pH was over 3.6, the qe values decreased. A pH of 3.6 was found to be an optimum for uranium adsorption on shrimp flakes. This could be explained that at slight acidic solution, amine groups in the flakes easily form protonation that induced an electrostatic repulsion of metal ions (Wan Ngah et al., 2002). The equilibrium values were slightly higher than initial pH at pH ¼ 3.6. This is a result of competition between uranium ions and H3Oþ for binding sites. So only some of glucosamine nitrogen atoms become available to uranium metal ions for coordination. Low pH of solutions increases H3Oþ concentration and intensifies the competition between H3Oþ and uranium ions for complexation sites (Tsezos and Volesky, 1982). However, at pH > 5.0, the qe values of uranium decreased with an increase of pH, owing to the interaction between OH and uranium ions in the solution. This revealed that adsorption of uranium on chitin flakes was complexation, namely nonstochiometric, rather than ion-exchange adsorption mode. From the results obtained by Sylva and Davidson (1979) for the
3.4.3. Effect of initial uranium concentration The effect of initial uranium concentration on the adsorption of uranium onto shrimp shell flakes were investigated under the following conditions: 50 ml solutions having initial uranium concentration varying from 50 mg l1 to 875 mg l1 with pH of 3.6 and a fixed mass of 1 g of adsorbant for 60 min. All the experiments were done at room temperature of 25 1 C. Fig. 6 shows the percentage of adsorbed uranium versus the initial uranium concentrations. As expected, the adsorption efficiency increased with the initial metal concentration. With more uranium content in a solution, larger fraction of the active sites is involved in the adsorption process then the increase in adsorption efficiency becomes less significant at [Co] > 175.8 mg l1 where 85% from uranium was grafted on 1 g shrimp shell flakes. As comparative study between chitin extracted from shrimp shells and other biosorbents (Table 2), it is clear that the chitin flakes have a good adsorption efficiency in regarding to other biosorbents from economical point of view, as well as environmental safety procedure. 3.4.4. Effect of solution volume to mass ratio The effect of uranium solution volume to chitin flakes mass (v/ m) on uranium adsorption efficiency was plotted in Fig. 7. Experiments were done at contact time of 60 min using different volumes of uranium solution ranging from 25 to 300 ml at pH 3.6 with uranium concentration of about 175 mg l1 and 1 g of chitin shell flakes at room temperature of 25 1 C. The obtained results reveal that the percent of adsorption increased steadily with the uranium solution volume then tend to decrease with further increase in the solution volume. This is probably because the active sites on the adsorbent become saturated at this concentration and subsequent
Fig. 2. SEM for shrimp shell flakes before (a) and after (b) uranium biosorption.
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Fig. 6. Effect of initial uranium concentration on uranium adsorption efficiency onto shrimp shell flakes. Fig. 4. Effect of pH upon uranium adsorption efficiency onto shrimp shell flakes.
increase in solution volume does not affect the adsorption capacity. So, the effective uranium solution volume to mass ratio was found to be 50 ml g1 shrimp shell flakes at which 85% adsorption efficiency was achieved. 3.4.5. Effect of temperature Effect of temperature on removal of uranium was performed at four different temperatures: 25, 35, 50 and 70 C. The results shown in Fig. 8 indicate that the uranium adsorption efficiency decreases with the increase in the temperature where the highest adsorption efficiency occurs at room temperature after that the adsorption efficiency decreases to reach the lowest values at 70 C which was 47.1%. Therefore, we can conclude that the room temperature (z25 C) is the most suitable temperature in the experimental uranium adsorption study. Summing up, it can be mentioned from the above data that stirring a volume of 50 ml uranium solution of 175 mg l1 concentration at pH of 3.6 with 1 g shrimp shell flakes for 60 min at the room temperature of 25 1 C can considered as optimum conditions for sorption of 7.48 mg uranium on shrimp shell flakes. 3.5. Physical characteristics of biosorption process Adsorption isotherm describes how pollutant interacts with adsorbent materials in relation to equilibrium data. 3.5.1. Equilibrium modeling Equilibrium data, commonly known as adsorption isotherms, are basic requirements for the design of adsorption systems. This set of experiments was performed at different initial concentration of uranium, 50e875 mg l1. Classical adsorption models (Langmuir
and Freundlich) were used to describe the equilibrium between adsorbed metal ions on the shrimp shell flakes (qeq) and that in solution (Ceq) at a constant temperature. The Langmuir equation is valid for monolayer sorption on to a surface with a finite number of identical sites and the linearized form is:
Ce =qe ¼ 1=bQ o þ Ce =Q o
(4)
where qe is the amount of solute sorbed per unit weight of adsorbent (mg g1), Ce is the equilibrium concentration of the solute in the bulk solution (mg l1), Qo is the monolayer adsorption capacity (mg g1) and b is the constant related to the free energy of adsorption (b ¼ aeDG/RT). The graphic representation of (Ce/qe) versus Ce gives a straight line for uranium sorbet onto shrimp shell flakes, Fig. 8, confirming that this expression is a reasonable representation of chemisorptions isotherm. The numerical value of constants Qo and b evaluated from the slope and intercept of the plot is given in Table 3. The value of saturation capacity Qo corresponds to the monolayer coverage and defines the total capacity of the adsorbent for uranium. The linearized Langmuir adsorption isotherms of uranium ions obtained at the temperature of 25 C are given in Fig. 9. The Langmuir adsorption constants evaluated from the isotherms with the correlation coefficients are also presented in Table 3. As investigated from the table, very high regression correlation coefficients (>0.92) were found for Langmuir models. According to these results the Langmuir model is suitable for describing the sorption equilibrium of uranium by shrimp shell flakes in the studied concentration range. The value of saturation capacity Qo determined from the Langmuir isotherm defines that the total theoretical capacity of uranium sorption is 25.31 mg g1 shrimp shell flakes at 25 C which is near to the experimental value of 19.62 mg g1. One of the essential characteristics of the Langmuir model could be expressed by dimensionless constant called equilibrium parameters RL (Mohan and Chander, 2006): Table 2 Uranium adsorption capacity by different biosorbent.
Fig. 5. Distribution of uranium species versus pH for 103 M uranium concentration (after Sylva and Davidson, 1979).
Biosorbent
Adsorbed uranium mg/g
Ref.
Cross-linked chitosan (CCTS) Aspergillus fumigatus beads
52.63 mg/g
Wang et al. (2009)
98.4 mg U per g dry biosorbent with the initial U concentration of 200 mg l1 Range between 2 and 38 mg/g
Wang et al. (2010)
Different organic resins prepared from the cotton stalks Brown algae
1.3 mmol/g
Current study
25.77
El-Sheikh (2006)
Moghaddam et al. (2013)
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Table 3 Sorption isotherm coefficients of Langmuir and Freundlich models applied to uranium sorbed onto shrimp shell flakes. Parameters Langmuir isotherm Q0 (mg g1) b (L mg1) RL Freundlich isotherm Kf (mg g 1) 1/n
Fig. 7. Effect of solution volume to mass ratio upon uranium adsorption efficiency onto shrimp shell flakes.
RL ¼ 1=1 þ bCo
(5)
where C0 is the highest initial metal ion concentration (mg/l). The value of RL indicates the type of isotherm to be irreversible (RL ¼ 0), favorable (0 < RL < 1), linear (RL ¼ 1), or unfavorable (RL > 1). RL value (Table 3) was found to be less than 1 and greater than 0 indicating the favorable sorption isotherms of uranium ions. The empirical Freundlich equation based on sorption on a heterogeneous surface is given below as logarithmic form
Value
R2
25.77 0.0065 0.1497
0.994
2.648 0.322
0.999
batch system, all the material surface binding sites are made readily available for metal uptake so the effect of external film diffusion on sorption rate can be assumed not significant and ignored in any engineering analysis (Aksu, 2001). The kinetic models included the pseudo first-order and pseudo second-order equations can be used in this case assuming that measured concentrations are equal to powder surface concentrations. The firstorder rate expression of Lagergren (1898) based on solid capacity (integrated form) is generally expressed as follows:
logðqe qt Þ ¼ log qe ðK1 =2:303Þt
(7)
3.5.2. Kinetic modeling In order to investigate the kinetic equilibrium of sorption and potential rate controlling step such as mass transport and chemical reaction processes, kinetic models have been used to test experimental data. When the biomass is employed in a well-agitated
where qe and qt (mg g1) are the amount of metal ion sorbed onto the adsorbent at equilibrium and at time t, respectively and k1 is the pseudo first order rate constant (min1). The slope and intercept of the plot of log (qe qt) versus t, as shown in Fig. 11, were used to determine the first order rate constant (k1) and the theoretical equilibrium sorption capacities (qe), respectively. The calculated values of k1 and qe with the value of the linear correlation coefficients (R2) of the plot are presented in Table 4. Straight line obtained from the pseudo first-order kinetic plot suggests the applicability of the pseudo first-order kinetic model to fit the experimental data over the initial stage of the sorption process (5e 180 min). But it is also required that theoretically calculated equilibrium sorption capacity, qe, should be in accordance with the experimental sorption capacity value. As can be seen from Table 4, although the linear correlation coefficient of the plot is so good, the qe (calculated) value, 4.709 mg g1 is not in agreement with qe (experimental), 7.484 mg g1 for the studied sorption process. So, it could suggest that the sorption of uranium on shrimp shell flakes is not a first-order reaction. The pseudo second-order equation is also based on the sorption capacity of the solid phase (Ho and McKay, 1999). Contrary to the other model it predicts the behavior over the whole range of adsorption and is in agreement with an adsorption mechanism being the rate controlling step. If the rate of sorption is a secondorder mechanism, the pseudo second-order chemisorption kinetic rate equation is expressed as:
Fig. 8. Effect of the temperature upon uranium adsorption onto shrimp shell flakes.
Fig. 9. Langmuir adsorption isotherm of uranium onto shrimp shell flakes.
. log qe ¼ log Kf þ 1 n log Ce
(6)
where Kf is the constant indicative of the relative adsorption capacity of the adsorbent (mg g1) and 1/n is the constant indication of the intensity of the adsorption process. The illustration of log qe versus log Ce is shown in Fig. 10 which suggests that the sorption of uranium obeys Freundlich isotherm over the entire range of sorption concentration studied. The numerical values of the constants 1/n and Kf are computed from the slope and intercepts by means of a linear least square fitting method and are given in Table 3 where regression correlation coefficients were found for Freundlich models is 0.828 which means that Langmuir model fit more than Freundlich model in describing sorption equilibrium of uranium by shrimp shell flakes. The Freundlich isotherm is also more widely used but provides no information on the monolayer adsorption capacity, in contrast to the Langmuir model (Dönmez et al., 1999; Matheickal et al., 1999).
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S.H. Ahmed et al. / Journal of Environmental Radioactivity 134 (2014) 120e127 Table 4 Kinetic model parameters applied to uranium sorbed onto shrimp shell flakes. Parameters First order parameters qe (mg g1) k1 (min1) Second-order parameters qe (mg g1) k2 (g mg1 min1)
Kd ¼ Fig. 10. Freundlich adsorption isotherm of sorption uranium onto shrimp shell flakes.
t=qt ¼ 1=k2 q2e þ ð1=qe Þt
(8)
where k2 is the rate constant of pseudo second-order equation (g mg1 min1). The kinetic plot of t/qt versus t for uranium grafting on shrimp shell flakes is represented in Fig. 12. The relation is linear and the correlation coefficient (R2) suggests a strong correlation between the parameters and also explains that the sorption process of uranium follows pseudo second-order kinetics. The product k2q2e is the initial sorption rate represented as h ¼ k2q2e . From Table 4, it can be shown that the correlation coefficient R2 has an extremely high value (>0.99), and its calculated equilibrium sorption capacity (qe), 8.196 mg/g, is consistent with the experimental data, 7.484 mg/g. These results explain that the pseudo second-order sorption mechanism is predominant and that the overall rate constant of the sorption process appears to be controlled by the chemical sorption process. 3.5.3. Adsorption thermodynamics The adsorption studies were carried out at different temperatures 25, 35, 50 and 70 C. The thermodynamic parameters can be determined from following equations (Boparai et al., 2011; AlAnbar and Matouq, 2008):
DGo ¼ RT Ln Kd DGo ¼ DH o T DSo
(9)
R2
4.709 0.043
0.960
8.196 0.008
0.992
Co Ct V M Ct
log Kd ¼
DHt 1 þC 2:303R t
(12)
where Kd is the distribution coefficient of the metal ion, R is the gas constant, C is constant and t is the temperature in K. DG , DH and DS are changes in Gibbs free energy (kJ mol1), enthalpy (kJ mol1) and entropy (J mol1 K1), respectively. The change of enthalpy (DH ) was determined from the slope and intercept of the linear plot of log Kd versus 1/t (Fig. 13). The value of DS was found to be 123.75 J mol1 K1. The calculated parameter of Gibbs free energy change (DG ) of U (IV) biosorption onto chitin flakes at different temperatures is presented in Table 5. The values of DG were found to increase as temperature increased indicating more driving force and hence resulting in higher biosorption capacity. The value of DH ¼ 33.8 kJ mol1, which indicates that room temperature of 25 1 C is quite enough to promote the biosorption reaction and assure the reaction is exothermic and that complexion is more significant than dehydration. The magnitude and sign of enthalpy change (DH) associated with the extraction process will consist of (1) enthalpy change for dehydration (DHd) which will cause DH to be endothermic because energy is required to break the ionewater and watere water bonding of the hydrated metal ions, and (2) enthalpy change for complexity (DHc) which will make DH more endothermic due to the formation of metal complex. The positive value obtained with the extraction of U (IV) indicates that the dehydration is more significant than complexation and the opposite is true for U (VI) biosorption.
(10)
where Kd can be defined as:
Kd ¼
Value
mg: of uranium adsorbed to 1 g: of adsorbent mg: of uranium remaining in 1 cm3 of aqueous solution (11)
Fig. 11. Pseudo first-order sorption kinetics of uranium onto shrimp shell flakes.
4. Conclusion Physicochemical process of biosorption is known to be promising technique due to the ease of operation and comparable low
Fig. 12. Pseudo second-order sorption kinetics of uranium onto shrimp shell flakes.
S.H. Ahmed et al. / Journal of Environmental Radioactivity 134 (2014) 120e127
Fig. 13. Thermodynamics of uranium sorption onto shrimp shell flakes.
Table 5 Gibbs free energy change (DG ) of U (IV) biosorption onto chitin flakes at different temperatures. T (K) DG
298 70.80
308 71.91
323 73.17
343 76.20
cost of biosorbant application. This study showed the potentially for shrimp shell flakes to adsorb uranium ions from nitric acid solutions and a value of 7.484 mg uranium has been grafted on 1 g shrimp shell flakes under the studied conditions of 60 min contact time, 3.66 pH, 50 ml solution volume and 25 1 C room temperature. Uranium sorption fitted with Langmuir isotherm model and the theoretical sorption capacity of shrimp shell flakes was found to be 25.31 mg g1. The rate of sorption follows pseudo second-order. The nature of biosorption process is spontaneous and exothermic. Finally, as shrimp shells flakes are stable and selective for uranium, they could be used for field applications References Aksu, Z., 2001. Equilibrium and kinetic modelling of cadmium(II) biosorption by C. vulgaris in a batch system: effect of temperature. Separ. Purif. Technol. 21, 285e294. Al-Anbar, Z.A., Matouq, M.A.D., 2008. Batch adsorption of cadmium ions from aqueous solutions by means of olive cake. J. Hazard. Mater. 151, 194e201. Al-Rub, F.A., 2006. Biosorption of zinc on palm tree leaves: equilibrium, kinetics, and thermodynamics studies. Separ. Sci. Technol. 41 (15), 3499e3515. Ashkenazy, R., Gottlieb, L., Yannai, S., 1997. Characterization of acetone-washed yeast biomass functional groups involved in lead biosorption. Biotechnol. Bioeng. 55 (1), 1e10. Boparai, H.K., Joseph, M., O’Carroll, D.M., 2011. Kinetics and thermodynamics of cadmium ion removal by adsorption onto nano zerovalent iron particles. J. Hazard. Mater. 186, 458e465. Brugge, D., deLomos, J.L., Oldmixon, B., 2005. Exposure pathways and health effects associated with chemical and radiological toxicity of natural uranium. Rev. Environ. Health 20, 177e193. Chui, V.W.D., Mok, K.W., Ng, C.Y., Luong, B.P., Ma, K.K., 1996. Removal and recovery of copper (II) chromium (III), and nickel (II) from solutions using crude shrimp chitin packed in small columns. Environ. Int. 22 (4), 463e468. Demirbas, A., 2008. Heavy metal adsorption onto agro-based waste materials: a review. J. Hazard. Mater. 157 (2-3), 220e229. Diels, L., RoyS, Van, Somers, K., Willems, I., Doyen, W., Mergeay, M., Spuingael, D., Leysen, R., 1995. The use of bacteria immobilized in tubular membrane reactors for heavymetal recovery and degradation of chlorinated aromatics. J. Membr. Sci. 100 (3), 249e258. Dong, J., Ozaki, Y., 1997. FTIR and FT-Raman studies of partially miscible poly(methy1 methacrylate)/poly(4-vinylphenol) blends in solid states. Macromolecules 30 (2), 286e292. Dönmez, G.C., Aksu, Z.O., Ztürk, A., Kutsal, T., 1999. A comparative study on heavy metal bio-sorption characteristics of some algae. Process Biochem. 34, 885e 892. El-Sheikh, E.M., 2006. Geochemical Studies and Uranium Minerals Concentration Using Organic Surfactants From Radioactive Syenite Rocks, El-Grra El-Hamra, Tushki area, South Western Desert. Ph.D. thesis. Faculty of Science, Ain Shams University, Egypt, p. 125.
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Faroog, U., Kozinski, J.A., Khan, M.A., Athar, M., 2010. Biosorption of heavy metal ions using wheat based materials e a review. Bioresour. Technol. 10 (14), 5043e 5053. Gow, N.A.R., Gooday, G.W., Russell, G.D., Wilson, M.J., 1987. Infrared and X-ray diffraction data on chitins of variable structure. Carbohydr. Res. 165 (1), 105e 110. Alkauskas, M., 2002. Removal of free and complexed Gyliene, O., Rekertas, R., heavy-metal ions by sorbents produced from fly (Musca domestica) larva shells. Water Res. 36 (16), 4128e4136. Ho, YSa, McKay, G., 1999. Pseudo-second order model for sorption processes. Process Biochem. 34, 451e465. Hoshi, S., Kanuma, K., Sugamara, K., Uto, M., Akotsuka, K., 1997. The spectrophotometric determination of trace molybdenum(VI) after collection and elution as molybdate ion on protomated chitin. Talanta 44 (8), 1473e1478. Kang, D.W., Choi, H.R., Kweon, D.K., 1999. Stability constants of amidoximated chitosan-g-poly (acrylonitrile) copolymer for heavymetal ions. J. Appl. Polym. Sci. 73 (4), 469e476. Kapoor, A., Viraraghavan, T., 1998. Removal of heavymetals from aqueous solutions using immobilized fungal biomass in continuous mode. Water Res. 32 (6), 1968e1977. Kratochvil, D., Volesky, B., 1998. Advances in the bio-sorption of heavy metals. Trend. Biotechnol. 16 (7), 291e300. Kuribayashi, H., Kosbiba, Y., Suzuki, K., Shibuya, M., 1987. Radionuclide separation process (RASEP). Proc. Waste Manage. 3, 89e96. Kuribayashi, H., Watanabe, M., Sbibuya, M., Suzuki, K., 1988. Selective separation process of radionuclide in liquid waste. In: PMT. DOE Model Oak Ridge, USA, vol. 1, pp. 169e174. Lagergren, S., 1898. Zur Theorie der sogenannten adsorption geloster stöffe. K. Sevenska Vetenskapsakad. Handl. 24, 1e39. Manni, Laila, Ghorbel-Bellaaj, Olfa, Jellouli, Kemel, Younes, Islem, Nasri, Moncef, 2010. Extraction and characterization of chitin, chitosan, and protein hydrolysates prepared from shrimp waste by treatment with crude protease from Bacillus cereus SV1. Appl. Biochem. Biotechnol. 162 (2), 345e357. Marczenko, Z., 1976. Spectrophotometric Determination of Elements. Ellis Horwood Ltd., Halsted Press, New York, p. 580. Matheickal, J.T., Yu, Q., Woodburn, G.M., 1999. Biosorption of cadmium(II) from aqueous solutions by pre-treated biomass of marine alga Durvillaea potatorum. Water Res. 33, 335e342. Memon, J.R., Memon, S.Q., Bhanger, M.I., Memon, G.Z., El-Turki, A., Allen, G.C., 2008. Characterization of banana peel by scanning electron microscopy and FT-IR spectroscopy and its use for cadmium removal. Colloid. Surf. B Biointerf. 66 (2), 260e265. Moghaddam, Mohammad Ramezani, Fatemi, Shohreh, Keshtkar, Alireza, 2013. Adsorption of lead (Pb2þ) and uranium cations by brown algae: experimental and thermodynamic modeling. Chem. Eng. J. 231 (2013), 294e303. Mohan, D., Chander, S., 2006. Single, binary, and multi component sorption of iron and manganese on lignite. J. Colloid Interf. Sci. 299, 57e76. Ray, K.R., Kardan, A., Arrora, J.K., Srivatava, M.M., Srivastava, S., 2010. Neural network modeling for Ni(II) removal from aqueous system using agricultural waste. J. Water Resour. Prot. 2, 331e338. , Y., Aktay, Y., 2000. Mass transfer and equilibrium studies for the sorption of Sag chromium ions onto chitin. Process Biochem. 36 (1-2), 157e173. Sud, D., Majayan, G., Kaur, M.P., 2008. Agricultural waste material as potential adsorbent for sequestering heavy metal ions from aqueous solutions e a review. Bioresour. Technol. 99 (14), 6017e6027. Sylva, R.N., Davidson, M.R., 1979. The hydrolysis of metal ions. Part. 2. Dioxouranium(VI). J. Chem. Soc. Dalton Trans., 465e471. Tsezos, M., Volesky, B., 1982. The mechanism of uranium biosorption by Rhizopus arrhizus. Biotechnol. Bioeng. 24, 385e401. USEPA, 1996. EPA Integrated Risk Information System (IRIS), Electronic Database. USEPA, Washington DC. Volesky, B., Bohumil, T., 1990. Biosorption of Heavy Metals. CRC Press, Inc, Florida. Wan Ngah, W.S., Endud, C.S., Mayanar, R., 2002. Removal of copper (II) ions from aqueous solution onto chitosan and cross-linked chitosan flakes. React. Funct. Polym. 50 (2), 181e191. Wang, Jing-Song, Hu, Xin-Jiang, Liu, Yun-Guo, Xie, Shui-Bo, Bao, Zheng-Lei, 2010. Biosorption of uranium (VI) by immobilized Aspergillus fumigatus beads. J. Environ. Radioact. 101 (2010), 504e508. Wang, Guanghui, Liu, Jinsheng, Wang, Xuegang, Xie, Zhiying, Deng, Nansheng, 2009. Adsorption of uranium (VI) from aqueous solution onto cross-linked chitosan. J. Hazard. Mater. 168, 1053e1058. Warshawsky, A., Marinsky, J.A., Marcus, Y. (Eds.), 1981. Ion Exchange and Solvent Extraction, vol. 8. Marcel-Dekker Inc., New York, p. 229. Yan, G.Y., Viraraghavan, T., 2001. Heavy metal removal in a biosorption column by immobilized M. rouxii biomass. Bioresour. Technol. 78 (3), 243e249. Zhang, L., Zhou, J., Zhou, D., 1999. Adsorption of cadmium and strontium on cellulose/alginic acid ion-exchange membrane. J. Membr. Sci. 162 (1-2), 103e109. Zhang, L., Ruan, D., Gao, S., 2002. Dissolution and regeneration of cellulose in NaOH/thiourea aqueous solution. J. Polym. Sci. Part B Polym. Phys. 40 (14), 1521e1529.
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Potentiality of uranium biosorption from nitric acid solutions using shrimp shells S.H. Ahmed, E.M. El Sheikh*, A.M.A. Morsy Nuclear Materials Authority, P.O. Box 530, El Maadi, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 July 2013 Received in revised form 17 February 2014 Accepted 11 March 2014 Available online
Biosorption has gained important credibility during recent years because of its good performance and low cost. This work is concerned with studying the potentiality of the chitin component of the shrimp shells for uranium biosorption from nitric acid liquid solutions. The structural characteristics of the working chitin have been determined via Fourier Transform Infrared Spectroscopy (FTIR). The surface morphology was examined using Scanning Electron Microscopy (SEM). The adsorption capacity of biomass was investigated experimentally. The influence of contact time, pH, metal ion concentration, solution volume to mass ratio and temperature were evaluated and the results were fitted using adsorption isotherm models. The kinetic of uranium biosorption was also investigated as well as biosorption thermodynamic. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Uranium biosorption Shrimp shell Adsorption isotherm Adsorption kinetics
1. Introduction The chemical and radiological toxicity of natural uranium is actually well documented (Brugge et al., 2005). The environmental protection agency (EPA) has classified uranium as a confirmed human carcinogen and suggested that zero tolerance is the only safe acceptable limit (USEPA, 1996). In addition, the EPA finalized a realistic regulation level of 30 mg l1 is the maximum uranium contaminant level. According to the stringent environmental regulations that exist against the release of uranium contaminants into the environment, it is therefore greatly desirable to develop efficient, economical and viable methods for the treatment of uranium wastes. Various kinds of adsorbents have been widely produced and applied for the removal of radionuclides and heavy metals (Kuribayashi et al., 1987). Although many adsorbents have excellent performance, the cost is relatively high in comparison with the greatly available natural waste products (Kuribayashi et al., 1988). Biosorption is a physicochemical process that occurs naturally in certain biomass which allows it to passively concentrate and bind contaminants onto its cellular structure (Volesky and Bohumil, 1990). In practice scientists and engineers are hoping that biomass can provide an economical alternative for removing toxic
* Corresponding author. Tel.: þ20 1064481197. E-mail address: [email protected] (E.M. El Sheikh). http://dx.doi.org/10.1016/j.jenvrad.2014.03.007 0265-931X/Ó 2014 Elsevier Ltd. All rights reserved.
heavy metals and radionuclides from industrial wastewater and aid in environmental remediation (Kratochvil and Volesky, 1998). Abundant natural polymers or agriculture waste products can be economically used as potential biosorbents for different metals (Demirbas, 2008; Faroog et al., 2010; Ray et al., 2010; Sud et al., 2008). Thus, extensive research has evaluated variety of biosorbents such as fungi (Kapoor and Viraraghavan, 1998), yeast (Ashkenazy et al., 1997), bacteria (Diels et al., 1995), algae (Zhang et al., 1999), chitin (Hoshi et al., 1997) and chitosan (Kang et al., 1999). Chitin, an environmental friendly material, is considered as biodegradable and biocompatible. It is a natural long chain polysaccharide polymer of N-acetyl-D-glucosamine, a derivative of glucose. It is the second most abundant resource (next to cellulose) in nature. Chitin is the main component of the exoskeletons of anthropods such as crustaceans (e.g.; crabs, lobsters and shrimps). Besides its resistance to the action of acids, it is worth noting that chitin is recognized as an excellent metal ligand, forming stable complexes with many metal ions (Chui et al., 1996). The formation of coordination complex between the metal and the chitin nitrogen and Aktay, 2000). Gyliene et al. or oxygen has been reported (Sag (2002) have pointed that some of metal ions, such as Fe3þ and Pb2þ, are sorbed much better on chitin. The use of chitin as powder is very difficult for its separation after adsorption as well as application in chromatograph column (Yan and Viraraghavan, 2001). It is also well known that chitin is insoluble in many solvents however; it is very brittle leading to a limitation in its reactivity and process ability for utilization.
S.H. Ahmed et al. / Journal of Environmental Radioactivity 134 (2014) 120e127
The aim of this research was to study the ability of chitin for grafting uranium from nitric acid solutions. Therefore, the chitin component of the working shrimp shell was separated using a proper extraction procedure and its structural characteristics were determined. The relevant optimum conditions for uranium adsorption were then studied under varying experimental conditions using batch operation mode. Adsorption isotherm modeling, sorption kinetics and thermodynamics were investigated to determine the probable physical characteristics of the applied process. 2. Material and method 2.1. Material 2.1.1. Material preparation Fresh shrimp shells provided for the experiments were supplied from local market Cairo, Egypt. The shells were first separated from the head and legs then washed for several times with deionized water before drying at 40 C. The dried shells were cut to almost uniform flakes. The shrimp shell flakes characterized by the presence of chitin, the material which is responsible for uranium grafting in our study, so it was recommended to quantify its percent before use. 2.2. Chitin extraction Chitin extraction parameters were occurred by mild acidic and alkaline treatments (Manni et al., 2010). Initial step of extraction was carried out by acidic treatment using 1 N HCl solution at room temperature for 2 h followed by filtration, neutralization and washing with deionized water. Next step, deproteination, was performed using alkaline treatment with 2 N sodium hydroxide solution at 60e65 C then followed by neutralization by washing. Final step, demineralization, has done by 1 N HCl solution at room temperature for 3e5 h. Chitin extraction yield was 24e28%.
121
The given out CO2 bubbles from the reaction of calcium carbonate in the shell with the nitrate medium may delay the process of uranium adsorption. Therefore when all calcium carbonate in the shells react with HCl, most of the pore spaces are already opened which accommodate the adsorbed uranium (Eq. (2)) CaCO3 þ 2 HCl / CaCl2 (aq) þ CO2 þ H2O
(2)
2.5. Adsorption studies Several batch biosorption experiments were carried out using 100 ml conical flasks by stirring 50 ml uranium solutions with different concentrations after adding 1 g dry weight of the working biosorbent for 1 h and then all the conical flasks were sealed with a silicon cap to minimize evaporation. The amount of uranium metal ion adsorbed was calculated from the following equation:
Qe ¼ ðC0 Ce Þ V=M
(3)
where Qe is the amount of uranium metal ions adsorbed onto the unit mass of the sorbent (mg g1), C0 and Ce are the initial and equilibrium metal concentrations (mg l1) in the solution, respectively, while V is the solution volume (L) and M is the dry weight of biosorbent (g). Uranium concentration in the different aqueous stream solutions was measured via its arsenazo (III) complex using SP-8001 UVeVIS Spectrophotometer at wavelength 655 nm (Marczenko, 1976). The arsenazo (III) reagent (Avocado) solution was prepared by dissolving 0.25 g together with 0.5 g sodium acetate in 100 ml deionized water. The uranium solutions were prepared by diluting the standard uranium stock solution assaying 1000 mg l1 in nitric acid solution (TEDIA, USA) to the desired concentrations using deionized water. On the other hand, a digital pH meter (Jenway, UK) was used for pH adjustment. 3. Results and discussion
2.3. Material characterization 3.1. Environment friendly preparation Chitin in the shrimp shell was characterized by the following technique: a) Fourier Transform Infrared Spectrometer (FTIR): (FTIR) model Thermo Scientific Nicolet IS10, Germany was used for the determination of the structural characteristics of the working chitin. b) Scanning Electron Microscope (SEM): SEM model Philips XL 30 ESEM is considered as the most reliable and convenient tool for the study of physical structure of biosorbents (Warshawsky et al., 1981) as well as mineralogical investigations. The analytical conditions involved 25e30 kV accelerating voltage, 1e2 mm beam diameter and 60e120 s counting times. Minimum detectable weight concentration is ranging from 0.1 to 1 wt% while the realized precision is well below 1%.
2.4. Decalcification of shrimp shells before uranium adsorption The shrimp shells consist of several layers where calcium carbonate is concentrated mainly in the outer tough layer. The principle behind decalcification of shrimp shell is that calcium carbonate in the shells will react with dilute nitric acid medium to form soluble calcium nitrate, water and carbon dioxide (Eq. (1)). CaCO3 þ 2HNO3 / Ca (NO3)2 þ H2O þ CO2
(1)
The particles’ size, shape and surface morphology as well as specific surface area of bio-adsorbent fully depend on the preparation method. In addition, easy to prepare, easy to use, hazard free and environment friendly treatments are the requirement for sustainable preparation of bio-adsorbents. In these circumstances, this research adopted a simple preparation method rather than the expensive and high-tech pyrolysis and non-environment friendly acid/base treated methods. In this research the shrimp shells were treated with 0.5 N HCl solution in order to remove calcium carbonate present in the shells before the adsorption experiments then dried and ground to uniform flakes. 3.2. Characteristics of biosorbent 3.2.1. Fourier transform infrared spectrometer characterization FTIR spectra are a useful tool to identify molecular to functional groups (Dong and Ozaki, 1997). The yield of chitin from the separated shell is 1.245 g obtained from 5 g shrimp shell sample. The IR spectrum of the chitin (Fig. 1) isolated from the shrimp shell contains six major peaks; 3433 cm1, 2929 cm1, 1647 cm1, 1548 cm1, 1213 cm1 and 1024 cm1. The band observed at 3433 cm1 in shell spectra indicates the presence of NeH (primary amine) and OeH (alcoholic) stretching groups, this result agrees with (Gow et al., 1987) which found that the IR spectrum of a chitin exhibited major peaks at 3446 cm1 for eOH stretching and eNH
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stretching vibrations, while band observed at 2929 cm1 refers to CeH stretch band for alkanes. The wavenumber 1647 cm1 was found to be attributed to NeH bend (primary amine), which is also agree with Gow et al. (1987), and C¼O while peak value 1548 cm1 attributed to CH2 bending in alkanes. Finally the two intense absorption bands appeared at 1213 cm1 and 1024 cm1 in spectra refer to CeOeC in ether and CeN stretch vibration, respectively. Among these active groups the amine and hydroxyl groups play the major role for metal complexation (Memon et al., 2008). The IR characteristics performance of the whole peaks of chitin is tabulated in Table 1. 3.2.2. Scanning electron microscope characterization It has been reported that Scanning Electron Microscope (SEM) is the most reliable and convenient tool for the study of physical
structure of biosorbents. Thus, the surface of shrimp shell flakes were observed using SEM in order to illustrate the change in the surface feature of the flakes after adsorption. Scanning Electron Microscope photographs of the surface of the shrimp shell flakes before and after adsorption are given in Fig. 2 (a,b). The micrograph apparently shows the original flakes possess many vacant pores showing the cross-sections have much more wrinkle and regular structure before grafting. On the other hand, the rough surface turned to be relatively brilliant after grafting with uranium showing an interconnected flow-through polymeric network with irregular pores at higher magnification.
3.3. Uranium adsorption mechanism A three-step process has been used to describe the biosorption of chitin (Zhang et al., 2002; Yan and Viraraghavan, 2001). The first process involves the formation of a complex between the dissolved uranium ionic species and the chitin chain, where the complex forms between the uranium ions and the amineenitrogen of the chitin; the second process involves the adsorption of uranium metal ions by the chitin network close to that complexed by the chitin nitrogen; the third process is the hydrolysis of the complex formed by the first process and the precipitation of the hydrolysis product. In addition, the network structure and hydrophilic skeleton of the chitin flakes could promote adsorption (Al-Rub, 2006). The reaction of the chitin with U is illustrated in the following equation:
3.4. Experimental parameters of uranium biosorption 3.4.1. Effect of contact time To understand the effect of contact time on uranium adsorption onto shrimp shell flakes, experiments were conducted with 50 ml uranium solutions having 175 mg l1 concentration with initial pH 3.6 at room temperature of 25 1 C using 1 g of adsorbent. The samples were analyzed after each experiment to estimate the concentration of dissolved uranium as a function of equilibration time. Fig. 3 shows that the process is characterized by a rapid adsorption in the first 30 min of equilibration time, followed by a
Fig. 1. IR spectra for chitin extracted from shrimp shell flakes.
S.H. Ahmed et al. / Journal of Environmental Radioactivity 134 (2014) 120e127
123
Table 1 IR characteristic performance of chitin Peak no.
Spectra value (cm1)
Functional group
1
3433
2 3
2929 2362
Primary amines, alcohols Alkanes Alkanes
4
1647
5
Peak no.
Spectra value (cm1)
Functional group
8
1316
9 10
1213 1159
Alcohols, esters Ether Aliphatic amines Aliphatic amines
11
1114
1548
Primary amines, aldehydes, saturated aliphatic Alkanes
12
1071
6
1444
Alkanes
13
1024
7
1379
Alkanes
14
590
Aliphatic amines Aliphatic amines Alkyl halides
Fig. 3. Effect of contact time upon uranium adsorption efficiency onto shrimp shell flakes.
distribution of uranium species versus pH (Fig. 5), it is clear that at pH 3.6 the complex [(UO2) (OH)]þ is mostly abundant. slow process, leading to maximum adsorption in around 1 h. Uranyl ion is a bulky cation and the diffusion of the bulk ion into the chitin flakes is a slow process leading to the overall slow kinetics of the adsorption process therefore 60 min shaking time was found to be appropriate and used in all subsequent experiments. 3.4.2. Effect of initial pH For studying the effect of initial pH on uranium adsorption efficiency, uranium solutions were prepared with different pH values ranging from 1.21 to 7.3 with keeping the other factors constant at 50 ml uranium solution with 175 mg l1 concentration, 1 g adsorbent, 60 min contact time and 25 1 C room temperature. The qe dependence on pH of the uranium solution for single adsorption is shown in Fig. 4. Adsorption increased with an increase in pH of the solution in the range 1.2e3.6. As pH was over 3.6, the qe values decreased. A pH of 3.6 was found to be an optimum for uranium adsorption on shrimp flakes. This could be explained that at slight acidic solution, amine groups in the flakes easily form protonation that induced an electrostatic repulsion of metal ions (Wan Ngah et al., 2002). The equilibrium values were slightly higher than initial pH at pH ¼ 3.6. This is a result of competition between uranium ions and H3Oþ for binding sites. So only some of glucosamine nitrogen atoms become available to uranium metal ions for coordination. Low pH of solutions increases H3Oþ concentration and intensifies the competition between H3Oþ and uranium ions for complexation sites (Tsezos and Volesky, 1982). However, at pH > 5.0, the qe values of uranium decreased with an increase of pH, owing to the interaction between OH and uranium ions in the solution. This revealed that adsorption of uranium on chitin flakes was complexation, namely nonstochiometric, rather than ion-exchange adsorption mode. From the results obtained by Sylva and Davidson (1979) for the
3.4.3. Effect of initial uranium concentration The effect of initial uranium concentration on the adsorption of uranium onto shrimp shell flakes were investigated under the following conditions: 50 ml solutions having initial uranium concentration varying from 50 mg l1 to 875 mg l1 with pH of 3.6 and a fixed mass of 1 g of adsorbant for 60 min. All the experiments were done at room temperature of 25 1 C. Fig. 6 shows the percentage of adsorbed uranium versus the initial uranium concentrations. As expected, the adsorption efficiency increased with the initial metal concentration. With more uranium content in a solution, larger fraction of the active sites is involved in the adsorption process then the increase in adsorption efficiency becomes less significant at [Co] > 175.8 mg l1 where 85% from uranium was grafted on 1 g shrimp shell flakes. As comparative study between chitin extracted from shrimp shells and other biosorbents (Table 2), it is clear that the chitin flakes have a good adsorption efficiency in regarding to other biosorbents from economical point of view, as well as environmental safety procedure. 3.4.4. Effect of solution volume to mass ratio The effect of uranium solution volume to chitin flakes mass (v/ m) on uranium adsorption efficiency was plotted in Fig. 7. Experiments were done at contact time of 60 min using different volumes of uranium solution ranging from 25 to 300 ml at pH 3.6 with uranium concentration of about 175 mg l1 and 1 g of chitin shell flakes at room temperature of 25 1 C. The obtained results reveal that the percent of adsorption increased steadily with the uranium solution volume then tend to decrease with further increase in the solution volume. This is probably because the active sites on the adsorbent become saturated at this concentration and subsequent
Fig. 2. SEM for shrimp shell flakes before (a) and after (b) uranium biosorption.
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S.H. Ahmed et al. / Journal of Environmental Radioactivity 134 (2014) 120e127
Fig. 6. Effect of initial uranium concentration on uranium adsorption efficiency onto shrimp shell flakes. Fig. 4. Effect of pH upon uranium adsorption efficiency onto shrimp shell flakes.
increase in solution volume does not affect the adsorption capacity. So, the effective uranium solution volume to mass ratio was found to be 50 ml g1 shrimp shell flakes at which 85% adsorption efficiency was achieved. 3.4.5. Effect of temperature Effect of temperature on removal of uranium was performed at four different temperatures: 25, 35, 50 and 70 C. The results shown in Fig. 8 indicate that the uranium adsorption efficiency decreases with the increase in the temperature where the highest adsorption efficiency occurs at room temperature after that the adsorption efficiency decreases to reach the lowest values at 70 C which was 47.1%. Therefore, we can conclude that the room temperature (z25 C) is the most suitable temperature in the experimental uranium adsorption study. Summing up, it can be mentioned from the above data that stirring a volume of 50 ml uranium solution of 175 mg l1 concentration at pH of 3.6 with 1 g shrimp shell flakes for 60 min at the room temperature of 25 1 C can considered as optimum conditions for sorption of 7.48 mg uranium on shrimp shell flakes. 3.5. Physical characteristics of biosorption process Adsorption isotherm describes how pollutant interacts with adsorbent materials in relation to equilibrium data. 3.5.1. Equilibrium modeling Equilibrium data, commonly known as adsorption isotherms, are basic requirements for the design of adsorption systems. This set of experiments was performed at different initial concentration of uranium, 50e875 mg l1. Classical adsorption models (Langmuir
and Freundlich) were used to describe the equilibrium between adsorbed metal ions on the shrimp shell flakes (qeq) and that in solution (Ceq) at a constant temperature. The Langmuir equation is valid for monolayer sorption on to a surface with a finite number of identical sites and the linearized form is:
Ce =qe ¼ 1=bQ o þ Ce =Q o
(4)
where qe is the amount of solute sorbed per unit weight of adsorbent (mg g1), Ce is the equilibrium concentration of the solute in the bulk solution (mg l1), Qo is the monolayer adsorption capacity (mg g1) and b is the constant related to the free energy of adsorption (b ¼ aeDG/RT). The graphic representation of (Ce/qe) versus Ce gives a straight line for uranium sorbet onto shrimp shell flakes, Fig. 8, confirming that this expression is a reasonable representation of chemisorptions isotherm. The numerical value of constants Qo and b evaluated from the slope and intercept of the plot is given in Table 3. The value of saturation capacity Qo corresponds to the monolayer coverage and defines the total capacity of the adsorbent for uranium. The linearized Langmuir adsorption isotherms of uranium ions obtained at the temperature of 25 C are given in Fig. 9. The Langmuir adsorption constants evaluated from the isotherms with the correlation coefficients are also presented in Table 3. As investigated from the table, very high regression correlation coefficients (>0.92) were found for Langmuir models. According to these results the Langmuir model is suitable for describing the sorption equilibrium of uranium by shrimp shell flakes in the studied concentration range. The value of saturation capacity Qo determined from the Langmuir isotherm defines that the total theoretical capacity of uranium sorption is 25.31 mg g1 shrimp shell flakes at 25 C which is near to the experimental value of 19.62 mg g1. One of the essential characteristics of the Langmuir model could be expressed by dimensionless constant called equilibrium parameters RL (Mohan and Chander, 2006): Table 2 Uranium adsorption capacity by different biosorbent.
Fig. 5. Distribution of uranium species versus pH for 103 M uranium concentration (after Sylva and Davidson, 1979).
Biosorbent
Adsorbed uranium mg/g
Ref.
Cross-linked chitosan (CCTS) Aspergillus fumigatus beads
52.63 mg/g
Wang et al. (2009)
98.4 mg U per g dry biosorbent with the initial U concentration of 200 mg l1 Range between 2 and 38 mg/g
Wang et al. (2010)
Different organic resins prepared from the cotton stalks Brown algae
1.3 mmol/g
Current study
25.77
El-Sheikh (2006)
Moghaddam et al. (2013)
S.H. Ahmed et al. / Journal of Environmental Radioactivity 134 (2014) 120e127
125
Table 3 Sorption isotherm coefficients of Langmuir and Freundlich models applied to uranium sorbed onto shrimp shell flakes. Parameters Langmuir isotherm Q0 (mg g1) b (L mg1) RL Freundlich isotherm Kf (mg g 1) 1/n
Fig. 7. Effect of solution volume to mass ratio upon uranium adsorption efficiency onto shrimp shell flakes.
RL ¼ 1=1 þ bCo
(5)
where C0 is the highest initial metal ion concentration (mg/l). The value of RL indicates the type of isotherm to be irreversible (RL ¼ 0), favorable (0 < RL < 1), linear (RL ¼ 1), or unfavorable (RL > 1). RL value (Table 3) was found to be less than 1 and greater than 0 indicating the favorable sorption isotherms of uranium ions. The empirical Freundlich equation based on sorption on a heterogeneous surface is given below as logarithmic form
Value
R2
25.77 0.0065 0.1497
0.994
2.648 0.322
0.999
batch system, all the material surface binding sites are made readily available for metal uptake so the effect of external film diffusion on sorption rate can be assumed not significant and ignored in any engineering analysis (Aksu, 2001). The kinetic models included the pseudo first-order and pseudo second-order equations can be used in this case assuming that measured concentrations are equal to powder surface concentrations. The firstorder rate expression of Lagergren (1898) based on solid capacity (integrated form) is generally expressed as follows:
logðqe qt Þ ¼ log qe ðK1 =2:303Þt
(7)
3.5.2. Kinetic modeling In order to investigate the kinetic equilibrium of sorption and potential rate controlling step such as mass transport and chemical reaction processes, kinetic models have been used to test experimental data. When the biomass is employed in a well-agitated
where qe and qt (mg g1) are the amount of metal ion sorbed onto the adsorbent at equilibrium and at time t, respectively and k1 is the pseudo first order rate constant (min1). The slope and intercept of the plot of log (qe qt) versus t, as shown in Fig. 11, were used to determine the first order rate constant (k1) and the theoretical equilibrium sorption capacities (qe), respectively. The calculated values of k1 and qe with the value of the linear correlation coefficients (R2) of the plot are presented in Table 4. Straight line obtained from the pseudo first-order kinetic plot suggests the applicability of the pseudo first-order kinetic model to fit the experimental data over the initial stage of the sorption process (5e 180 min). But it is also required that theoretically calculated equilibrium sorption capacity, qe, should be in accordance with the experimental sorption capacity value. As can be seen from Table 4, although the linear correlation coefficient of the plot is so good, the qe (calculated) value, 4.709 mg g1 is not in agreement with qe (experimental), 7.484 mg g1 for the studied sorption process. So, it could suggest that the sorption of uranium on shrimp shell flakes is not a first-order reaction. The pseudo second-order equation is also based on the sorption capacity of the solid phase (Ho and McKay, 1999). Contrary to the other model it predicts the behavior over the whole range of adsorption and is in agreement with an adsorption mechanism being the rate controlling step. If the rate of sorption is a secondorder mechanism, the pseudo second-order chemisorption kinetic rate equation is expressed as:
Fig. 8. Effect of the temperature upon uranium adsorption onto shrimp shell flakes.
Fig. 9. Langmuir adsorption isotherm of uranium onto shrimp shell flakes.
. log qe ¼ log Kf þ 1 n log Ce
(6)
where Kf is the constant indicative of the relative adsorption capacity of the adsorbent (mg g1) and 1/n is the constant indication of the intensity of the adsorption process. The illustration of log qe versus log Ce is shown in Fig. 10 which suggests that the sorption of uranium obeys Freundlich isotherm over the entire range of sorption concentration studied. The numerical values of the constants 1/n and Kf are computed from the slope and intercepts by means of a linear least square fitting method and are given in Table 3 where regression correlation coefficients were found for Freundlich models is 0.828 which means that Langmuir model fit more than Freundlich model in describing sorption equilibrium of uranium by shrimp shell flakes. The Freundlich isotherm is also more widely used but provides no information on the monolayer adsorption capacity, in contrast to the Langmuir model (Dönmez et al., 1999; Matheickal et al., 1999).
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S.H. Ahmed et al. / Journal of Environmental Radioactivity 134 (2014) 120e127 Table 4 Kinetic model parameters applied to uranium sorbed onto shrimp shell flakes. Parameters First order parameters qe (mg g1) k1 (min1) Second-order parameters qe (mg g1) k2 (g mg1 min1)
Kd ¼ Fig. 10. Freundlich adsorption isotherm of sorption uranium onto shrimp shell flakes.
t=qt ¼ 1=k2 q2e þ ð1=qe Þt
(8)
where k2 is the rate constant of pseudo second-order equation (g mg1 min1). The kinetic plot of t/qt versus t for uranium grafting on shrimp shell flakes is represented in Fig. 12. The relation is linear and the correlation coefficient (R2) suggests a strong correlation between the parameters and also explains that the sorption process of uranium follows pseudo second-order kinetics. The product k2q2e is the initial sorption rate represented as h ¼ k2q2e . From Table 4, it can be shown that the correlation coefficient R2 has an extremely high value (>0.99), and its calculated equilibrium sorption capacity (qe), 8.196 mg/g, is consistent with the experimental data, 7.484 mg/g. These results explain that the pseudo second-order sorption mechanism is predominant and that the overall rate constant of the sorption process appears to be controlled by the chemical sorption process. 3.5.3. Adsorption thermodynamics The adsorption studies were carried out at different temperatures 25, 35, 50 and 70 C. The thermodynamic parameters can be determined from following equations (Boparai et al., 2011; AlAnbar and Matouq, 2008):
DGo ¼ RT Ln Kd DGo ¼ DH o T DSo
(9)
R2
4.709 0.043
0.960
8.196 0.008
0.992
Co Ct V M Ct
log Kd ¼
DHt 1 þC 2:303R t
(12)
where Kd is the distribution coefficient of the metal ion, R is the gas constant, C is constant and t is the temperature in K. DG , DH and DS are changes in Gibbs free energy (kJ mol1), enthalpy (kJ mol1) and entropy (J mol1 K1), respectively. The change of enthalpy (DH ) was determined from the slope and intercept of the linear plot of log Kd versus 1/t (Fig. 13). The value of DS was found to be 123.75 J mol1 K1. The calculated parameter of Gibbs free energy change (DG ) of U (IV) biosorption onto chitin flakes at different temperatures is presented in Table 5. The values of DG were found to increase as temperature increased indicating more driving force and hence resulting in higher biosorption capacity. The value of DH ¼ 33.8 kJ mol1, which indicates that room temperature of 25 1 C is quite enough to promote the biosorption reaction and assure the reaction is exothermic and that complexion is more significant than dehydration. The magnitude and sign of enthalpy change (DH) associated with the extraction process will consist of (1) enthalpy change for dehydration (DHd) which will cause DH to be endothermic because energy is required to break the ionewater and watere water bonding of the hydrated metal ions, and (2) enthalpy change for complexity (DHc) which will make DH more endothermic due to the formation of metal complex. The positive value obtained with the extraction of U (IV) indicates that the dehydration is more significant than complexation and the opposite is true for U (VI) biosorption.
(10)
where Kd can be defined as:
Kd ¼
Value
mg: of uranium adsorbed to 1 g: of adsorbent mg: of uranium remaining in 1 cm3 of aqueous solution (11)
Fig. 11. Pseudo first-order sorption kinetics of uranium onto shrimp shell flakes.
4. Conclusion Physicochemical process of biosorption is known to be promising technique due to the ease of operation and comparable low
Fig. 12. Pseudo second-order sorption kinetics of uranium onto shrimp shell flakes.
S.H. Ahmed et al. / Journal of Environmental Radioactivity 134 (2014) 120e127
Fig. 13. Thermodynamics of uranium sorption onto shrimp shell flakes.
Table 5 Gibbs free energy change (DG ) of U (IV) biosorption onto chitin flakes at different temperatures. T (K) DG
298 70.80
308 71.91
323 73.17
343 76.20
cost of biosorbant application. This study showed the potentially for shrimp shell flakes to adsorb uranium ions from nitric acid solutions and a value of 7.484 mg uranium has been grafted on 1 g shrimp shell flakes under the studied conditions of 60 min contact time, 3.66 pH, 50 ml solution volume and 25 1 C room temperature. Uranium sorption fitted with Langmuir isotherm model and the theoretical sorption capacity of shrimp shell flakes was found to be 25.31 mg g1. The rate of sorption follows pseudo second-order. The nature of biosorption process is spontaneous and exothermic. Finally, as shrimp shells flakes are stable and selective for uranium, they could be used for field applications References Aksu, Z., 2001. Equilibrium and kinetic modelling of cadmium(II) biosorption by C. vulgaris in a batch system: effect of temperature. Separ. Purif. Technol. 21, 285e294. Al-Anbar, Z.A., Matouq, M.A.D., 2008. Batch adsorption of cadmium ions from aqueous solutions by means of olive cake. J. Hazard. Mater. 151, 194e201. Al-Rub, F.A., 2006. Biosorption of zinc on palm tree leaves: equilibrium, kinetics, and thermodynamics studies. Separ. Sci. Technol. 41 (15), 3499e3515. Ashkenazy, R., Gottlieb, L., Yannai, S., 1997. Characterization of acetone-washed yeast biomass functional groups involved in lead biosorption. Biotechnol. Bioeng. 55 (1), 1e10. Boparai, H.K., Joseph, M., O’Carroll, D.M., 2011. Kinetics and thermodynamics of cadmium ion removal by adsorption onto nano zerovalent iron particles. J. Hazard. Mater. 186, 458e465. Brugge, D., deLomos, J.L., Oldmixon, B., 2005. Exposure pathways and health effects associated with chemical and radiological toxicity of natural uranium. Rev. Environ. Health 20, 177e193. Chui, V.W.D., Mok, K.W., Ng, C.Y., Luong, B.P., Ma, K.K., 1996. Removal and recovery of copper (II) chromium (III), and nickel (II) from solutions using crude shrimp chitin packed in small columns. Environ. Int. 22 (4), 463e468. Demirbas, A., 2008. Heavy metal adsorption onto agro-based waste materials: a review. J. Hazard. Mater. 157 (2-3), 220e229. Diels, L., RoyS, Van, Somers, K., Willems, I., Doyen, W., Mergeay, M., Spuingael, D., Leysen, R., 1995. The use of bacteria immobilized in tubular membrane reactors for heavymetal recovery and degradation of chlorinated aromatics. J. Membr. Sci. 100 (3), 249e258. Dong, J., Ozaki, Y., 1997. FTIR and FT-Raman studies of partially miscible poly(methy1 methacrylate)/poly(4-vinylphenol) blends in solid states. Macromolecules 30 (2), 286e292. Dönmez, G.C., Aksu, Z.O., Ztürk, A., Kutsal, T., 1999. A comparative study on heavy metal bio-sorption characteristics of some algae. Process Biochem. 34, 885e 892. El-Sheikh, E.M., 2006. Geochemical Studies and Uranium Minerals Concentration Using Organic Surfactants From Radioactive Syenite Rocks, El-Grra El-Hamra, Tushki area, South Western Desert. Ph.D. thesis. Faculty of Science, Ain Shams University, Egypt, p. 125.
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