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Oct 28, 2010 - Iminodiacetic acid functionality has been introduced on styrene–divinyl benzene co-polymeric beads and characterized by FT-IR in order to ...
Journal of Hazardous Materials 185 (2011) 1508–1512

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Iminodiacetic acid functionalized cation exchange resin for adsorptive removal of Cr(VI), Cd(II), Ni(II) and Pb(II) from their aqueous solutions R.K. Misra, S.K. Jain ∗ , P.K. Khatri Desert Environmental Science and Technology Division, Defence Laboratory, Jodhpur 342011, India

a r t i c l e

i n f o

Article history: Received 29 April 2010 Received in revised form 17 September 2010 Accepted 20 October 2010 Available online 28 October 2010 Keywords: Iminodiacetic acid Cation exchange resin Heavy metal ion removal Chromium removal Kinetic studies

a b s t r a c t Iminodiacetic acid functionality has been introduced on styrene–divinyl benzene co-polymeric beads and characterized by FT-IR in order to develop weak acid based cation exchange resin. This resin was evaluated for the removal of different heavy metal ions namely Cd(II), Cr(VI), Ni(II) and Pb(II) from their aqueous solutions. The results showed greater affinity of resin towards Cr(VI) for which 99.7% removal achieved in optimal conditions following the order Ni(II) > Pb(II) > Cd(II) with 65%, 59% and 28% removal. Experiments were also directed towards kinetic studies of adsorption and found to follow first order reversible kinetic model with the overall rate constants 0.3250, 0.2393, 0.4290 and 0.2968 for Cr(VI), Ni(II), Pb(II) and Cd(II) removal respectively. Detailed studies of Cr(VI) removal has been carried out to see the effect of pH, resin dose and metal ion concentration on adsorption and concluded that complexation enhanced the chromium removal efficacy of resin drastically, which is strongly pH dependent. The findings were also supported by the comparison of FT-IR spectra of neat resin with the chromium-adsorbed resin. © 2010 Elsevier B.V. All rights reserved.

1. Introduction The presence of heavy metals such as chromium, cadmium, copper, nickel, lead, mercury, etc. in aqueous environment may result in a major concern due to their toxicity and carcinogenicity, which may cause damage to various systems of the human body. Among these heavy metals cadmium is of considerable environmental and health significance because of its increasing mobilization and human toxicity. The major sources for the introduction of cadmium in water are smelting and refining of nonferrous metals, manufacturing processes related to chemicals and metals and domestic wastewater [1]. The atmospheric deposition which contributes about 15% cadmium contamination, from natural sources such as volcanoes, windborne soil particles and biogenic particles cannot be ignored [2]. Chromium another common pollutant with its toxicity and mutagenic effect is introduced into natural waters from a variety of industrial processes such as electroplating, metal finishing industries (hexavalent chromium) and tanneries (trivalent chromium). Chromium occurs most frequently as Cr(VI) and Cr(III) in aqueous solutions. Both valences of chromium are potentially harmful but Cr(VI) possesses a greater risk due to its carcinogenic properties [3]. Lead introduced in waterstreame by

∗ Corresponding author. Tel.: +91 291 2567510; fax: +91 291 2511191. E-mail addresses: [email protected] (R.K. Misra), skj [email protected] (S.K. Jain). 0304-3894/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2010.10.077

combustion of leaded fuels, pyrometallurgical nonferrous metal processes and coal combustion is known for its toxicity and carcinogenicity. Nickel, another pollutant is the major part of municipal wastewater followed by waste of smelting and refining of nonferrous metals causes respiratory cancer in nickel refinery workers [4]. Conventional methods for removing dissolved heavy metals, includes precipitation, phytoextraction, ultra filtration, reverse osmosis and electro dialysis, etc. [5,6]. Nevertheless many of these approaches are marginally cost effective or difficult to implement in developing countries. Therefore the need exists for a treatment strategy that is simple, robust and that addresses local resources and constraints. Sorption operations, including adsorption and ion exchange are potential alternatives for wastewater treatment. In an adsorption process, atom or ions (adsorbate) in a fluid phase diffuse to the surface of a solid (adsorbent), where they bond with the solid surface or are held there by weak intermolecular forces [7]. A number of investigators have studied the removal of inorganic metal ions namely cadmium, cobalt, zinc, silver, copper, mercury, chromium and lead from aqueous solution using different adsorbents [8–15]. However, the improved ion exchange capacity of ion exchange resins may have advantages over such non-specific adsorbents. In this regard, ion exchange resins hold great potential for the removal of heavy metals from water and industrial wastewater [16–20]. Here we are reporting an effective weak acid based cation exchange resin coupled with complexation property, namely Styrene–DVB co-polymeric matrix functionalized with iminodiacetic

R.K. Misra et al. / Journal of Hazardous Materials 185 (2011) 1508–1512

acid for the comparative removal of cadmium, chromium, lead and nickel from their aqueous solutions. The main objective of this study was to investigate the equilibrium time and to test the efficacy of resin towards different metal ions by varying contact time and pH conditions. Desorption studies have been also carried out in different solutions to test the reusability of resin.

The starting material chloromethylated styrene–DVB copolymeric resin beads (1–2 mm diameter, specially procured from Thermax Ltd., India) were soaked in DMF and then refluxed with 30% (w/v) solution of iminodiacetic acid (ACS grade, Sigma–Aldrich) for 20 h and washed with distilled water till the neutral pH reached and then dried at 140–160 ◦ C for 2 h. Introduction of iminodiacetic acid functionality on the surface of resin beads has been confirmed by FT-IR spectroscopy (Model- Jasco-610). All the chemicals used were of ACS grade and obtained from Sigma–Aldrich, India. Pretreatment of indigenously functionalized resin was done by soaking it in distilled water to increase its surface area for 48 h followed by regeneration with 0.1 N HCl [3]. Finally it was washed with distilled water. Thermo gravimetric analysis (TGA 500 of TA Q500 series) of swollen resin beads were carried out to evaluate its water intake capacity and to find out its thermal stability. Stock solutions of chromium and lead of 1000 mg/l concentration were prepared by dissolving, 2.848 g of K2 Cr2 O7 , 1.598 g of Pb(NO)3 , respectively in 1000 ml of ultrapure water (Elix, Millipore), whereas cadmium solution was prepared by dissolving 1 g of cadmium metal in minimum volume of (1 + 1) HCl and then making it up to 1000 ml with ultrapure water. Stock solution of nickel was prepared by dissolving 1.273 g of NiO in minimum volume of 10% (v/v) HCl and then diluted up to 1000 ml with ultrapure water.

The solutions were further diluted to obtain 20 ppm standard solutions of different metal ions with pH value 3.5. The pH of chromium solution was further adjusted to 7.4 and 10.2 by the addition of 0.1 N solution of NaOH during dilution process. Batch experiments were carried out in different stoppered glass bottles at room temperature (25 ± 1 ◦ C) using known amount, i.e. 200 mg of pretreated resin in 20 ml standard solution of 20 ppm concentration of different metal ions in ordinary mixing conditions using rotary shaker (Revotech) at the stirring speed of 120 rpm. The samples were taken after regular time interval and filtered through whatman’s filter paper. Concentrations of metal ions in filtrates were determined using Atomic Absorption Spectrophotometer (Analytikjena model Nova 400). These data were used for comparative removal studies and kinetic establishment. Control experiments in absence of resin have been carried out in order to correct any adsorption of metal on container surface. These experiments indicated that no adsorption by the container walls was detectable. Desorption studies of metal containing resin beads have also been carried out to test the reusability of resin in 0.1 N HCl, 0.1 N NaOH and distilled water. FT-IR spectra of neat and chromium-loaded resin were recorded for the better understanding of interactions between metal and resin and evaluate structural changes during the process of Cr(VI) adsorption. Very high efficacy of resin towards chromium tends to detailed studies of pH dependent behavior and adsorption kinetics. These studies were carried out with different initial concentra-

A % T (a.u.)

2. Experimental

1509

B

4000

3500

3000

2500

2000

1500

1000

500

-1

Wavenumber (cm ) Fig. 1. (A) FT-IR spectra of chloromethylated resin, (B) FT-IR spectra of iminodiacetic acid functionalized resin.

tions of chromium solution maintaining resin dosage at constant level. 3. Results and discussion 3.1. Functionalization of resin Iminodiacetic acid works as tridentate chelating species in complexation reactions. The same functionality has been introduced on chloromethylated styrene–DVB co-polymeric resin to form weak acid based cation exchange resin, by using following reaction scheme.

3.2. FT-IR spectra of resin FT-IR spectra of chloromethylated and functionalized resin are showed in Fig. 1. Spectra B shows the presence of stretching band at 1650 cm−1 corresponding to  (C O), the appearance of  (C O) at lower wave number may be explained on the basis of the presence of dimeric form of acid group as a result of intra-molecular hydrogen bonding between carboxylic acid groups, broad band at 3540 cm−1 attributes for  (O–H) and presence of a sharp band at 3650 cm−1  (N–H) may be due to the traces of unreacted iminodiacetic acid present on resin after purification. Figure also shows the disappearance of  (C–Cl) band which was present at 674 cm−1 in reactant spectra A, confirms the introduction of iminodiacetic acid group on resin surface. FT-IR spectra A and B of Fig. 2 show the comparison of functionalized resin and chromium loaded resin, recorded to describe the higher efficacy of resin towards chromium is due to the complexation between metal ion and iminodiacetic acid chelating species present on resin. On comparison of spectra A and B, appearance of new C O stretching peak at 1709 cm−1 may be observed, due to the fact that on complex formation, cleavage of hydrogen bonding takes place resulting in the stretching band at higher wavenumber. The bond at 2907 cm−1 is attributes to C–H stretching. Reduction of O–H band at 3550 cm−1 is also in good agreement of complex formation.

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80

Percent Removal (%)

70

% T (a.u.)

A

60 50 40 30 20

B

Cr Removal Ni Removal Pb Removal Cd Removal

10

4000

3500

3000

2500

2000

1500

1000

0

500

0.0

0.5

1.0

1.5

Wavenumber (cm-1)

2.0

2.5

3.0

3.5

4.0

Time (Hrs.) Fig. 4. Percent removal of different metal ions versus time.

Fig. 2. (A) FT-IR spectra of iminodiacetic acid functionalized resin, (B) FT-IR spectra of chromium adsorbed functionalized resin.

3.5. Effect of pH 3.3. TGA of resin Thermo gravimetric analysis graph of swollen resin shows its degradation pattern with temperature increase (Fig. 3). The water intake capacity of resin is found up to 97% of its dry weight, can be observed in the graph, which is the indirect measure of increased surface area of resin beads. It provides larger space for interaction to coming species, i.e. metal ions and reduces steric hindrance between bulky chelating species. Thermal stability of resin is found very high and degradation starts only after 336 ◦ C and promises its usability at higher temperature also.

3.4. Effect of time Agitation time plays an important role in adsorption of metal ion on solid surface. Percent removal is found to be proportional to contact time up to equilibrium achieved, after which it is independent of time due to the fact that at equilibrium the rate of adsorption and desorption will be same. Fig. 4 represents percent removal of different metals versus time and showing the increasing value of removal with time. It is cleared from figure that maximum removal is achieved for chromium whereas minimum removal for cadmium in same time duration, i.e. 3.5 h.

Attempts were also directed to study the effect of pH on removal capacity of resin. Solutions of 0.1 N concentrations of HCl and NaOH were added during the dilution process of stock solutions of metal ions for the adjustment of acidic and basic pH, respectively. Only the pH of chromium could be adjusted as per requirements, i.e. 3.5, 7.4 and 10.2, precipitation of hydroxides occurred for the other metals on addition of NaOH. These metals were studied at the acidic pH 3.5 only. Fig. 5 shows the chromium adsorption at different pH conditions and indicates that acidic pH favors the adsorption of chromium. For the ion exchange resins, the adsorption at pH above 6 shows a decreasing trend because of the formation of hydroxyl complexes of chromium [21]. The significant metal ion removal is achieved at basic pH 10.2, may be due to the fact that basic pH favors trivalent stage of chromium [22] and hydroxides formation took place also contributes in complete removal of metal ion from its aqueous solution. 3.6. Effect of metal ion behavior Removal of different metal ions is the result of interaction of metal ions with chelating ion. These interactions strongly depend upon the nature of both the metal ion and ligand. Iminodiacetic 100 90

14

37.61°C 98.99%

80

80

Weight (%)

10 60

155.18°C 50.08%

8

336.05°C 44.37%

6

40

4 20 2 0

0

200

400

600

Temperature (°C) Fig. 3. TGA of swollen functionalized resin.

0 800

D eriv. Weight (%/min)

12

Percent Removal

100

70 60 50 40 30 At pH 3.5 At pH 7.4 At pH 10.2

20 10 0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Time (Hrs.) Fig. 5. Percent removal of chromium at different pH versus time.

4.0

R.K. Misra et al. / Journal of Hazardous Materials 185 (2011) 1508–1512

-0.4 -0.8 -1.2

ln(1-Ut)

acid generally works as tridentate ligand and as bidentate ligand in certain cases. Since the chelating ligand is common in all the cases the nature of metal ion is one which plays an important role in removal. Cr(VI) is having high positive charge with smaller size, better suited for the complexation and forms very stable octahedral complex with iminodiacetic acid group. This is why the highest removal has been achieved for chromium. The other two transition metal ions Ni(II) and Cd(II), both are bivalent means exhibiting similar charge form square planar complexes with the iminodiacetic acid. The mechanism of Pb(II) removal is entirely different and ion exchange process rather than complexation is responsible for its removal. The H+ ions present on carboxylic acid group get replaced by lead in this process.

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-1.6 -2.0 -2.4 -2.8 Cr Removal Ni Removal Pb Removal Cd Removal

-3.2 -3.6 0.5

3.7. Adsorption kinetics

1.0

1.5

2.0

2.5

3.0

Time (Hrs.)

k1 A↔B k2

(1)

Fig. 6. Kinetic fits for different metal ion removal.

-0.2

-0.6

dt

-1.0 -1.2

−d(a − x) = = k(a − x) dt

-1.6 -1.8 0.5

dx = k1 (a − x) − k2 x dt

(2)

(3)

Putting the value Xe as the concentration of metal adsorbs at equilibrium and Kc as the equilibrium constant, the equation became at equilibrium: k1 (a − Xe ) − k2 Xe = 0, because dx/dt = 0, under these conditions

(4)

or Xe k1 = a − Xe k2

1.0

(5)

1.5

2.0

2.5

3.0

Time (Hrs.) Fig. 7. Kinetic fits for chromium removal at different pH.

Here k is the overall rate constant and algebraic sum of forward rate constant k1 and backward rate constant k2 . Now the rate can be expressed as:

Kc =

-0.8

-1.4

In above equation k1 is the rate constant for forward reaction and k2 is the rate constant for backward reaction. Taking ‘a’ as the initial concentration of metal ion and x is the amount adsorbed at time t, the reaction rate will be:

 dx 

At pH 3.5 At pH 7.4 At pH 10.2

-0.4

ln(1-Ut)

The kinetics of sorption describing the solute uptake rate, which in turn, governs the residence time of the sorption reaction, is one of the important characteristics that define the sorption efficiency. Present study includes the experiments directed towards kinetic studies of different metal ions removal at acidic pH as well as removal of chromium at different pH conditions. It is a wellestablished fact that the adsorption of ions in an aqueous system follows reversible first order kinetics, when a single species is considered on a heterogeneous surface [23]. The sorption of metal ion from liquid phase to solid phase may be represented by:

In the above equation CA(0) is the initial concentration (mg/l) of metal ion, CA(t) the concentration (mg/l) of metal at time t, CA(e) is the concentration (mg/l) of metal at equilibrium. The ln(1 − Ut ) is plotted against time t, for different metal ions, the kinetic plots for chromium removal at different pH (Figs. 6 and 7). The straight line is observed in all above plots verifying the first order reversible kinetic model, overall rate constants k were calculated by using slopes of these lines, the equilibrium constants Kc , forward reaction rate constants k1 and backward reaction rate constants k2 were calculated for different metal ion removal and Chromium removal at different pH, using Eqs. (5) and (7) are tabulated in Tables 1a and 1b.

Solving the equation:

ln

1 − x Xe

= (k1 + k2 )t

(6) Table 1a Rate constants for different metal ion removal.

or ln(1 − Ut ) = −(k1 + k2 )t = −kt

(7)

where Ut = x/Xe and called fractional attainment of equilibrium, it may be calculated by the formula: CA(0) − CA(t) CA(0) − CA(e)

=

x = Ut Xe

(8)

S. no.

Metal undertaken

Overall rate constant k = k1 + k2 (h−1 )

Forward rate constant k1 (h−1 )

Backward rate constant k2 (h−1 )

1 2 3 4

Cr(VI) Ni(II) Pb(II) Cd(II)

0.3250 0.2393 0.4290 0.2968

0.3241 0.1536 0.2532 0.0861

0.0009 0.0837 0.1758 0.2097

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Table 1b Rate constants for chromium removal at different pH.

References

S. no.

pH value

Overall rate constant k = k1 + k2 (h−1 )

Forward rate constant k1 (h−1 )

Backward rate constant k2 (h−1 )

1 2 3

3.5 7.4 10.2

0.3250 0.0692 0.2177

0.3241 0.0547 0.1987

0.0009 0.0145 0.0130

3.8. Regeneration studies Desorption and regeneration studies have also been carried out in different solutions, to test the reusability of resin for various cycles. It has been observed that up to 65%, Cr(VI) can be recovered in 0.1 N solution of NaOH, whereas 13% Cr(VI) was recovered in 0.1 N HCl. No recovery has been observed in distilled water indicating the absence of physical bonding. Similarly up to 70% recovery in NaOH solution and 15.5% in HCl solution of Ni(II), has been achieved. The recovery of Pb(II) was also good in NaOH solution, i.e. 45% but There is no significant recovery observed for Cd(II) in any solution. 4. Conclusion Ion exchange resins have been identified as potentially and efficient materials for use in the treatment of water contaminated with selected heavy metals. The results of present study indicates that iminodiacetic acid functionalized styrene–DVB co-polymeric resin can efficiently remove different metal ions namely Cr(VI), Ni(II), Pb(II) and Cd (II) from their aqueous solutions and it can be reused for different cycles after desorption and regeneration treatment. The ion exchange reaction showed strong pH dependent behavior of resin and following first order reversible reaction kinetics. The overall, forward and backward rate constants were also calculated and showing spontaneous forward reaction in case of Cr(VI), Ni(II), Pb(II) because of higher value of forward rate constants than backward rate constants. Kinetics of Cd removal is a different case having higher value of backward rate constant than forward rate constant supporting lesser removal, i.e. 28% of cadmium. The higher removal of chromium has been explained on the basis of complexation took place between tridentate iminodiacetic acid chelating group and chromium metal. Acknowledgements Authors are thankful to Dr. N. Kumar, Director, Defence Laboratory, Jodhpur for help and support. One of the authors R.K. Misra is thankful to Defence Research & Development Organization (DRDO), India for awarding Senior Research Fellowship.

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