Article pubs.acs.org/IECR
Selective Separation of Aluminum from Biological and Environmental Samples Using Glyoxal-bis(2-hydroxyanil) Functionalized Amberlite XAD-16 Resin: Kinetics and Equilibrium Studies Aminul Islam,* Hilal Ahmad, Noushi Zaidi, and Sudesh Yadav† Analytical Research Laboratory, Department of Chemistry, Aligarh Muslim University, Aligarh, India 202 002 S Supporting Information *
ABSTRACT: A new glyoxal-bis(2-hydroxyanil) anchored Amberlite XAD-16 chelating resin was synthesized and characterized by elemental analyses and scanning electron microscopy along with energy dispersive X-ray spectroscopy (SEM/EDAX), infrared spectral, and thermal studies. The resin was found to selectively bind aluminum in aqueous medium over a large number of competitive cations, at pH 9. Experimental conditions, for effective sorption of Al(III) were optimized systematically and were found to have fast kinetics (t1/2 10 min), high preconcentration flow rate (5.0 mL min−1), very high sorption capacity (24.28 mg g−1), regenerability up to 66 sample loading/elution cycles, and low preconcentration limit (3.3 ppb) from test solutions of different interferent to analyte ratio. The chemisorption and identical, independent binding site behavior were evaluated by Dubinin−Radushkevich isotherm and Scatchard plot analysis. Equilibrium data fit well to Langmuir adsorption isotherms (r2 = 0.998) indicating a typical monolayer sorption. We confirmed the analytical reliability of the method by the analysis of standard reference materials (SRMs), recovery experiments, and precision expressed as coefficient of variation (98% recovery of the sorbed metals from the resin could be achieved at a flow rate of 2 mL min−1. In consequence, a flow rate of 5 and 2 mL min−1 was maintained for sorption and elution studies, respectively. 3.2.5. Type of Eluting Agent. In order to elute Al(III) from the solid phase, different mineral acids have been tested by varying their volumes and concentrations. The percent recovery for Al(III) by using 5 mL each of 2 M HCl, 2 M HNO3, and 2 M H2SO4 were found to be 98.2 ± 1, 72 ± 3, and 68 ± 2, respectively. In all further studies, 5.0 mL of 2 M HCl was used as eluent. 3.2.6. Effect of Sample Loading Volume. To explore the maximum volume in the SPE beyond which the quantitative recovery of the metal ion is not feasible, the sample loading volume containing 5 μg of Al(III) was constantly increased. Following the column procedure, the recoveries of analyte at different volumes were obtained. The result shows that the analyte can be preconcentrated up to a concentration of 3.3 μg L−1 corresponding to a high preconcentration factor of 300 obtained on using 5.0 mL of eluate. 3.3. Sorption Isotherm. A sorption isotherm is fundamental in understanding the sorption mode of an adsorbate on sorbent surface once the equilibrium is attained. The experimentally obtained adsorption isotherm data were applied to both Langmuir and Freundlich isotherms. The data treatment for the linearized form of both isotherm equations is as follows.32
Freundlich model equation (Figure 5) ln Q e = ln k + (1/n) ln Ce
gave correlation coefficient values >0.9 but resulted in a better fit to the Langmuir model, as was evidenced from the higher value of r2 (Table 1).
Figure 4. Langmuir sorption isotherm of Al(III) on XAD−GBH.
Figure 5. Freundlich sorption isotherm of Al(III) on XAD−GBH.
The experimentally obtained sorption capacity for Al(III) was found to be 24.28 mg g−1 of resin, this agrees well with the capacity determined by Langmuir model. It further confirms the Langmuir fit to the present data. From the Langmuir model, the separation factor RL can be obtained from the Langmuir sorption constant (Kb) RL = 1/(1 + KbCo)
(3)
where Co is the initial Al(III) concentration. Table 2 lists the calculated RL values at various initial Al(III) concentrations. For all the tested Al(III) concentrations, RL values (0 < RL < 1) elucidate the favorability of XAD−GBH as a good Al(III) sorbent. The Dubinin−Radushkevich (DR) isotherm was studied to interpret the sorption on a single type of uniform pores. Its linear expression is27 ln Q e = ln Q m − K ,2
(4)
The mean free energy E used to estimate the sorption type can be calculated from constant K: E = ( −2K )−0.5
Langmuir model equation (Figure 4) Ce/Q e = 1/Q mKb + Ce/Q m
(2)
(5)
This K is obtained from the linear plot of ln Qe against , 2 (Figure 6). Since the numerical value of E in the range of 1−8 and 8−16 kJ mol−1 forecasts the physical sorption and chemical
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dx.doi.org/10.1021/ie303300u | Ind. Eng. Chem. Res. 2013, 52, 5213−5220
Industrial & Engineering Chemistry Research
Article
Table 1. Isotherm Models for Al(III) Sorption by XAD−GBH sorption capacity from column experiment
Langmuir isotherm
Freundlich isotherm
DR isotherm
Q (mg g−1)
Q (mg g−1)
kb (mL mg)
r2
Q (mg g−1)
r2
Q (mg g−1)
K (mol2 kJ2)
E (kJ mol)
r2
24.28
25.64
0.055
0.998
11.65
0.994
22.12
0.007
8.45
0.992
Table 2. RL Values for Al(III) Sorption Obtained from the Langmuir Equation RL a
Coa = 97.12
Coa = 118.71
Coa = 140.29
Coa = 161.88
0.16
0.13
0.11
0.10
−1
Initial Al(III) concentration (mg L ).
Figure 7. Scatchard plot for sorption of Al(III) on XAD−GBH.
Table 3. Effect of Interfering Ions on the Recovery of Al(III) (Resin Amount 300 mg, Sample Volume 100 mL, Amount of Al(III) Loaded 5 μg, N = 3) on XAD−GBH in Aqueous Samples Using SPE−FAAS Figure 6. Dubinin−Radushkevich isotherm of Al(III) on XAD−GBH.
interfering ions
sorption, respectively. The E value obtained in our work is in full agreement with the chemisorption of Al(III) by XAD− GBH. The Scatchard plot analysis is also used to investigate the sorption process and nature of binding sites in solid phase. The Scatchard equation is represented as27 Q e/Ce = Q mKb − Q eKb
added as
Cl−
NaCl
Br−
NaBr
I−
NaI
F−
NaF
PO42−
Na2HPO4
SO42−
Na2SO4
CO32−
Na2CO3
C2O42−
Na2C2O4
CH3COO−
CH3COONa
C6H5O73−
Na3C6H5O7
C4H4O62−
Na2C4H4O6
Na+
NaCl
K+
KCl
Ca2+
CaCl2
Mg2+
MgCl2
(6)
The type of the interactions of analyte with adsorbent is related to the shape of the Scatchard plot. The presence of a deviation from linearity on a plot based on Scatchard analysis usually points out the presence of more than one type of binding site, while the linearity of the Scatchard plot indicates that the binding sites are identical and independent. The Qe/Ce versus Qe plot of Al(III) is linear with a negative slope (Figure 7). The applied adsorption isotherms, Scatchard plot analysis, and software run inferred that the chemical interaction between Al(III) and the identical binding sites of XAD−GBH follows a typical uniform and monolayer sorption, as well as our conclusions from other studies that Al(III) ions are adsorbed through complexation with the tetradentate ligand. 3.4. Study on Nonspectroscopic Interference. The preconcentration procedures can be substantially affected by various potential concomitants through precipitate formation, redox reactions, or competing complexation reactions; either of interferent anions with the analyte metal ion or of the metal ions in matrix with the sorbent. The effect of some nonspectroscopic interference was investigated (Table 3). No interference was observed for the most common matrix anions owing to the group-specific character of the XAD−GBH. The Al(III) preconcentration was not significantly affected even in the presence of alkali and alkaline earth metals and common 5217
amount added (× 103 μg)
Al(III) recovery (%)
RSD
750 1500 25 50 25 50 25 50 5 10 50 100 50 100 25 50 50 100 5 12.5 5 12.5 500 1000 100 200 50 100 50 100
100.0 99.7 100.0 98.6 100.1 100.2 100.8 97.5 98.3 97.6 96.4 95.8 96.9 98.5 100.0 99.8 99.4 99.8 98.8 99.1 99.6 97.8 100.4 100.3 100.4 100.1 100.4 97.3 100.3 100.0
0.9 1.6 0.4 0.7 0.7 1.1 1.9 1.8 2.7 1.1 1.4 0.4 1.0 2.8 0.7 0.9 1.4 0.7 1.4 1.5 0.9 0.7 1.2 1.5 0.8 0.9 1.7 0.9 1.4 0.9
dx.doi.org/10.1021/ie303300u | Ind. Eng. Chem. Res. 2013, 52, 5213−5220
Industrial & Engineering Chemistry Research
Article
Table 4. Validation of Proposed Separation/Preconcentration Method by Analysis of SRMs for Al Concentration composition (μg g−1)
NIES 10(c)c
Al: 1.5, Ca: 95 ± 2, Mn: 40.1 ± 2.0, Zn: 23.1 ± 0.8, Fe: 11.4 ± 0.8, Cu: 4.1 ± 0.3, Ni: 0.30 ± 0.03, Cd: 1.82 ± 0.06 Al: 775, Mn: 700, Zn: 33, Cu: 7, Ni: 6.5, Ba: 5.7, Sr: 3.7, Na: 15.5
NIES 7d a
certified value (μg g−1)
SRM
1.5 775
founda (μg g−1) ± standard deviation
calculated student’s t-valueb
1.48 ± 0.02 773.8 ± 0.7
3.89 3.01
N = 3. bAt 95% confidence level. cAl as minor component. dAl as major component.
matrix anions, attributed to the fast kinetics of the present system. This suggested that the structure of the chelate is not suitable for recognition of these anions. The selectivity of the resin toward Al(III) was further ascertained by the competitive experiment. The XAD−GBH resin was treated with Al(III) in the presence of Co2+, Mn2+, Ni2+, Cr3+, Pb2+, Cu2+, and Zn2+ at the concentrations 25 times that of the Al3+. No interference was observed for the determination of Al(III) under competitive and noncompetitive conditions. This unique selectivity of XAD−GBH toward Al(III) can be interpreted in terms of the smaller ionic radius and higher charge density of the Al(III). The smaller radius of the Al(III) permits suitable coordination geometry for the chelating resin and the larger charge density allows strong coordination ability between XAD−GBH and Al(III). 3.5. Method Validation. The bias of the outlined separation/preconcentration method was estimated by the analysis of trace amount of Al(III) present as major and minor component in studied SRMs. The mean concentration values for Al(III) obtained by the proposed method (Table 4) were statistically insignificant from the certified values indicating absence of systematic method errors. The method also had good precision for the analysis of trace Al(III) in sample solutions, as the coefficient of variation for 5 replicate measurements of 5 μg of Al in 100 mL was
