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Studies on uptake behaviour of copper(II) and lead(II) by amine chelating resins with different textural properties
Separation and Purification Technology 33 (2003) 295 /301 www.elsevier.com/locate/seppur
Studies on uptake behaviour of copper(II) and lead(II) by amine chelating resins with different textural properties Asem A. Atia, Ahmed M. Donia *, Saeda A. Abou-El-Enein, Ahmed M. Yousif Chemistry Department, Faculty of Science, Menoufia University, Shebin El-Kom, Egypt Received 25 June 2002; received in revised form 17 January 2003; accepted 5 February 2003
Abstract Glycidyl methacrylate resins with different ratios of divinylbenzene as cross-linking agent have been prepared. The textural properties such as density, porosity, pore area and pore diameter of the resins obtained were elucidated. The resins were anchored by chelating amino groups through the treatment with ethylenediamine (en). The amino group concentration on the resins was determined. The uptake behaviour of Cu(II) and Pb(II) from their aqueous solutions by the resins was studied. Both uptake capacity and selectivity of the resins towards the studied metal ions were discussed in terms of amino group concentration as well as the textural properties. The study indicated that metal-resin interaction proceeds via surface and diffusion mechanisms. The pH 5.8 found to be the most suitable for the uptake of the investigated metal ions. Copper was selectively separated from lead (using resin RI-en). The studied resins showed good durability and regeneration using HNO3. # 2003 Elsevier B.V. All rights reserved. Keywords: Glycidyl methacrylate; Porous; Chelating; Amino; Resins
1. Introduction Heavy metals in the wastewater are a major threat to human being and environment due to their toxicity [1]. Many research efforts are devoted to extract metal ions from their solutions. Different techniques have been employed such as solvent extraction, precipitation, co-precipitation, sorption and ion exchange [2]. Chelate-forming
* Corresponding author. Fax: /20-2-835-6313. E-mail address: [email protected] (A.M. Donia).
resins have been widely applied as ion exchangers for various metal ions in different environmental and industrial areas [3,4]. These resins show greater selectivity compared to the conventional types of ion exchangers [5]. Besides, they show good physical and chemical properties such as porosity, high surface area, durability and purity. Many chelating resins with different functionalities have been emphasized for interaction with metal ions. Among these moieties, sulfonic acid [6], hydroxamic acid [7], thiol groups [8,9], amidoxime [10], Schiff base [11 /14] and amine [15 / 23]. The complexing properties of polymer glycidyl
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methacrylate (GMA) loaded with chemically bonded ethylenediamine (en) were reported [24 / 27]. In the present work, resins of GMA/divinylbenzene (DVB) loaded with en will be prepared and characterized. The uptake behaviour of the resins obtained towards copper and lead will be studied and correlated to the surface and textural properties of the resins.
2.3. Preparation of en loaded resins The resins obtained were loaded by en as follows: 1 g of resin obtained in the previous step and 4 g en were dissolved in 12 ml DMF. The reaction mixture was heated at 75/80 8C for 72 h in oil bath. A pale yellow product was formed, filtered, washed with cold methanol and then dried. Thereafter the chelating resins obtained are known as RI-en, RII-en and RIII-en. 2.4. Physical measurements of the chelating resins
2. Experimental
2.1. Chemicals GMA, DVB, benzoyl peroxide (B2O2) and en were Aldrich products. All other chemicals were Prolabo products. Copper acetate and lead acetate were used as sources for Cu2 and Pb2, respectively. All chemicals were used as received except B2O2 which was purified by crystallization from methanol to give pure needles which collected and used for experiments.
2.2. Preparation of (GMA/DVB) resins Resins were prepared through the polymerization of GMA in the presence of DVB as a crosslinking agent. Resins with different textural properties were prepared by changing the volume ratio of the cross-linking agent (DVB) relative to that of the monomer (GMA). The ratios of DVB used in this study were 5, 15, and 50 vol.% for resins RI, RII and RIII, respectively. The requisite volumes of DVB and GMA were mixed well with 0.1 g B2O2 (initiator) until complete dissolution of the B2O2. One millilitre isopropyl alcohol and 12.6 ml cyclohexane were mixed then added to the former solution. The contents are then poured into a flask containing 73 ml of 1% polyvinyl alcohol and refluxed on a water bath at 75 /80 8C with continuous stirring for 6 h. A heavy white precipitate was formed, filtered, washed with methanol and dried in air.
The textural properties of the prepared resins were measured using High Pressure Mercury Pore Size Analyzer, Micromeritics 9320, USA. 2.5. Estimation of the amino groups loaded on the resins The concentration of amino group was estimated using the volumetric method [28]. Twenty millilitres HCl (0.05 N) was added to 0.1 g resin and conditioned for 15 h on a shaker. The residual concentration of HCl was measured through the titration against 0.05 N NaOH. The number of moles of HCl interacted by the amino groups and consequently the amino group concentration was calculated. 2.6. Uptake measurements using batch method Stock solution (1 /10 2 M) of the metal salt under study was prepared in distilled water. Stock solution of EDTA (5 /10 3 M) was prepared and standardized against a solution of MgSO4 ×/7H2O using Ereochrome Black-T (EBT) as indicator. Buffers of acetic acid/acetate (pH 3.8 /5.8), sodium phosphate (pH 6/8), and ammonium hydroxide/ ammonium chloride (pH 9/10) were used for the experiments carried out at acidic or basic conditions [29]. Uptake experiments carried out at controlled pH were done by conditioning 0.1 g resin with 100 ml metal ion solution at initial concentration of 5 /10 3 M for 3 h using a Vibromatic-384 shaker at 3000 rpm and 229/2 8C. The pH of the medium was adjusted by using the suitable buffer. Five
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Table 1 Textural properties of resins with different cross-linking ratios Resin
Density (g/ml)
Porosity (%)
Total pore area (m2/g)
Average pore diameter (mm)
RI RII RIII
0.47 0.28 0.23
39.66 41.41 69.46
47.54 39.15 191.57
0.07 0.15 0.06
millilitre of the solution (free of the suspended solid) were taken at the end of the experiment where the residual concentration of metal ion was determined via the titration against 5 /10 3 M EDTA using the suitable indicator. Mureoxide indicator was used for Cu2 while EBT was used for Pb2. In the case of lead, traces of solid tartaric acid were added to avoid precipitation of lead ions as lead hydroxide in basic medium. Complexation of lead ions with tartaric acid gives soluble lead /tartarate complex [29]. Experiments of adsorption isotherms were performed by adding 0.1 g resin to 100 ml metal ion solution at the desired initial concentration and pH 5.8. The contents of the flask were conditioned at 3000 rpm and 229/2 8C for 3 h. Later, the residual concentration was determined where the metal uptake was estimated as described above. Kinetic studies were done by shaking 0.1 g of resin with 100 ml (5 /10 3 M) of the metal ion at pH 5.8 and 229/2 8C. Five millilitre of the supernatant were taken at different intervals of time where the concentration of metal ion in the supernatant was determined. 2.7. Elution and durability experiments Elution experiments were performed by sharking 0.1 g resin with 100 ml (5 /10 3 M) of metal ion solution at pH 5.8 for 3 h. The total uptake was estimated then the solution was decanted then washed thoroughly with distilled water. The resin obtained (loaded by metal ions) was treated by 100 ml HNO3 at concentrations of 0.1, 0.2 or 0.5 N. After shaking for 3 h, the concentration of the released metal ion was detected. Afterwards, the resin was washed repeatedly with distilled water till the filtrate becomes free of the acid and the previous steps were repeated for 10 cycles.
3. Results and discussions The amine chelating resins (RI-en, RII-en and RIII-en) were obtained from GMA/DVB resins (RI, RII and RIII, respectively) through the treatment by en. The loading process takes place via the opening of epoxy ring by en. This behaviour was confirmed from IR measurements of the resins. The epoxy band at 1265/cm in the spectra of RI, RII and RIII disappeared in those of RI-en, RII-en and RIII-en. On the other hand, the spectra of the amino-resins are characterized by n NH at 3442/3250 per cm. 3.1. Physical measurements Table 1 presents the data of textural properties for the resins obtained. The density was found to follow the order, RI /RII /RIII. This indicates that as the cross-linking degree increases, the resin formed becomes less dense and expected to be more porous. This is confirmed from the data of porosity which increases in the order RI B/RII B/ RIII. On the other hand, the values of the total pore area and the average pore diameter change irregularly with the change in the ratio of crosslinking agent. So, while resin RII gave large average pore diameter and low total pore area, resin RIII showed low pore diameter and high pore area. Moreover, resin RI showed higher pore area and lower pore diameter compared to RII. Such variations in resins characteristics would reflect different uptake behaviour as discussed later on. 3.2. Amino group content Table 2 gives the amino group content loaded on the resins obtained. Clearly, the amino group
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Table 2 Concentration of amino group on resins with different crosslinking ratios Resin
Concentration of amino group (mmol/g)
RI-en RII-en RIII-en
5.4 4.8 2.9
content on the resins decreases as the cross-linking agent increases in the matrix. This decrease in the concentration of the amino group is closely related to the decrease in the ratio of GMA monomer (which later transforms into the amino resin) and the skeletal structure of each resin. 3.3. Metal ions uptake studies
Fig. 2. Effect of pH on the uptake of Pb2 by resins RI-en, RII-en and RIII-en.
Figs. 1 and 2 show the uptake of Cu2 and Pb2 as a function of pH, and indicate maximum uptake capacities at pH 5.8 for both copper and lead. This higher uptake may be attributed to the presence of free lone pair of electrons on the nitrogen atom suitable for coordination with the metal ion to give the corresponding resin /metal complex. The uptake shows lower values in both acidic and basic mediums. In acidic medium, the amino groups become protonated and therefore
the coordination with the metal ion is hindered giving lower uptake values. The observed lower uptake in basic medium may be explained by the partial precipitation of metal hydroxides and/or formation of metal complexes (amine for Cu2 and tartarate for Pb2). Such complexes may decrease the ability of the metal ion to attack the resin resulting in a decrease in the total uptake.
Fig. 1. Effect of pH on the uptake of Cu2 by resins RI-en, RII-en and RIII-en.
Fig. 3. Uptake of Cu2 by resins RI-en, RII-en and RIII-en as a function of conditioning time at pH 5.8.
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Table 3 Maximum uptake of Cu2 and Pb2 at same level of amino group concentration for resins with different cross-linking ratios Resin
RI-en RII-en RIII-en a
Fig. 4. Uptake of Pb2 by resins RI-en, RII-en and RIII-en as a function of conditioning time at pH 5.8.
Figs. 3 and 4 show the change of the uptake of Cu2 and Pb2 as a function of time by resins RIen, RII-en and RIII-en at pH 5.8 and 229/2 8C. The uptake equilibrium of Cu2 was attained after 160, 80, and 40 min for resins RI-en, RII-en and RIII-en, respectively. For Pb2, the equilibrium was attained after 100, 40, and 24 min for resins RI-en, RII-en and RIII-en, respectively. It is seen that the equilibrium of Pb2 is shifted to lower time values compared to Cu2 for the same resin. This may indicate to the lower affinity of Pb2 towards resin compared to Cu2. The total uptake of both Cu2 and Pb2 by different resins follows the order RI-en /RII-en /RIII-en. This order could be explained based on the concentration of the amino group on the resin as well as their textural properties. The total uptake of copper with RI-en is higher than that of RII-en by approximately 1.5 times and than RIII-en by approximately 2.6 times. Such differences in the uptake are not consistent with the differences in the concentration of the amino group on the resins (Table 2). The concentration of amino group on resin RI-en is higher than that on RII-en and RIIIen by approximately 1.1 and 1.9 times, respectively. So, we expect other factors affecting the uptake in addition to the concentration of the amino groups. Such conclusion was verified by
Resin weight (g)a
0.1000 0.1125 0.1860
Maximum uptake (mmol/g) Cu2
Pb2
1.244 0.831 1.109
0.323 0.285 0.306
Using resin weights containing 5.4 mmol of amino groups.
studying the uptake of both copper and lead on resins having same level of amino group concentration. The data of maximum uptake of copper and lead along with the resin weights is reported in Table 3. The weights taken from different resins were specified so as to achieve the same level of amino group concentration (5.4 mmol). It can be seen in Table 3 that the maximum uptake of both RII-en and RIII-en is slightly lower than that of RI-en although the level of amino group concentration is the same. Such differences confirm the effective role of textural properties of resins on the uptake values. The uptake values of resin RII-en are lower than that of RI-en in case of copper or lead by approximately 1.5 and 1.0 times, respectively. This may be attributed to the differences in the values of the total pore area of resin RII compared to RI (Table 1). Although the total pore area of resin RIII is significantly higher than RI, the uptake values by resin RIII-en are lower than RI-en for copper and lead by approximately 1.1 and 0.5 times, respectively. This may be attributed to the difference in the values of the average pore diameter of the two resins (Table 1). Similar findings were reported by other authors [10,16,19,28,30]. Fig. 5 shows the adsorption isotherms of copper and lead at pH 5.8 and 229/2 8C. Inspection of Fig. 5 reveals that the uptake of copper is higher than that of lead at all concentration ranges. The uptake increases markedly until reaching maximum values at 1.24 and 0.32 mmol/g for copper and lead, respectively. The higher uptake of copper may be attributed to that copper (transition element) is able to form a stable metal /ligand
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Fig. 5. Adsorption isotherms of Cu2 and Pb2 using resin RI-en at equilibrium time and 229/2 8C.
complex compared to lead (non-transition element). Such uptake affinity of copper and lead may be inferred by plotting their adsorption data according to Langmuir adsorption isotherm [1]: q
Qmax Ce K Ce
where q is the uptake at equilibrium concentration (mmol/g), Ce is the equilibrium concentration (mM), Qmax is the maximum uptake (mmol/g), and K is a constant indicates to the affinity and equal to the reciprocal of the binding constant (mM). Plotting 1/q against 1/Ce gives straight line with intercept and slope values equal to 1/Qmax and K /Qmax, respectively. The values of K and Qmax were obtained and reported in Table 4. The values of Qmax for copper and lead found to be 1.26 and 0.35 mmol/g, respectively. The values of K are 0.358 and 0.630 mM for copper and lead,
respectively. The lower value of K of copper compared to that of lead indicates to the higher binding of copper with resin than of lead. The kinetics of metal uptake process and its relation to the textural characteristics of the studied resins were also studied. The rate plots for uptake of copper and lead on resin RI-en are shown in Fig. 6. Clearly the rate follows the first order kinetics for both copper and lead where a straight line was obtained at the first period of uptake reaction up to :/20 min. Afterwards, the lines were deviated from straightened at advanced stages of interaction. This indicates that the uptake was controlled by two phenomena: (i) surface phenomenon where the interaction rate mainly controlled by the concentration of metal ion in the bulk of solution giving first order kinetics (first period), (ii) diffusion phenomenon where the rate of interaction is mainly controlled by the textural properties of the resin and the diffusion of the metal ions through the pores to interact with the internal surface (advanced period). The uptake studies may also give valuable information about the management of the removal of the studied metal ions from aqueous solutions. For instance, the removal of copper or lead ions using resin RI-en approaches 90% of the maximum capacity within 50 min (Figs. 3 and 4). The
Table 4 Langmuir parameters for the adsorption of Cu2 and Pb2 on resin RI-en Metal ion 2
Cu Pb2
Qmax (mmol/g)
K (mM)
1.26 0.35
0.358 0.630
Fig. 6. Plots of relative concentration of Cu2 and Pb2 on resin RI-en against time.
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values of the maximum uptake by resin RI-en are 1.24 and 0.32 mmol/g, for Cu2 and Pb2, respectively. This indicates to that copper could be selectively separated from lead in their mixture. The durability of the studied resins was tested using different concentrations of HNO3. Complete elution of copper and lead was achieved with 0.5 HNO3. The regenerated resins showed 979/1% efficiency compared to the fresh resins for 10 cycles.
4. Conclusions Various amino chelating resins with different textural properties have been obtained. The resins were applied to the recovery of heavy metals such as copper and lead. Both the uptake capacity and selectivity of the resins towards the investigated metal ions was found related to many factors such as amino group concentration, textural characteristics of the resin, type of metal ion, and uptake conditions. High concentration of active sites along with porous structure and wide average pore size support the high uptake. The studied resins were found to have high durability towards mineral acids. The regenerated resins showed uptake behaviour similar to that of the fresh resins up to 10 cycles.
References [1] P. Malakul, K. Srinivasan, Y.H. Wang, Industrial and Engineering Chemistry Research 37 (11) (1998) 4296. [2] S.B. Filiz, B. Niyazi, Reactive and Functional Polymers 49 (2) (2001) 151. [3] M. Ahuja, A. Rai, P. Mathur, Talanta 43 (11) (1996) 1955. [4] T.M. Suzuki, T. Yokoyama, Polyhedron 2 (2) (1983) 127. [5] H. Eccles, H. Greenwood, Solvent Extraction and Ion Exchange 10 (4) (1992) 713. [6] R. Chiarizia, E. Horwitz, S. Alexandratos, Solvent Extraction and Ion Exchange 12 (1) (1994) 211.
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[7] M.R. Lutfor, S. Sidik, W.M.Z. Yunus, M.Z.A. Rahman, A. Mansor, M.J. Haron, Journal of Applied Polymer Science 79 (7) (2000) 1256. [8] A. Lezzi, S. Cobianco, A. Roggero, Journal of Polymer Science. Part A. Polymer Chemistry 32 (10) (1994) 1877. [9] A.B. Utkelov, E.E. Ergozhin, K.R. Ashkeeva, Reactive Polymers 14 (3) (1991) 187. [10] H. Egawa, T. Nonaka, M. Nakayama, Journal of Macromolecular Science Chemistry A25 (10 /11) (1988) 1407. [11] A. Syamal, M. Singh, Reactive Polymers 21 (3) (1993) 149. [12] S. Samal, R. Das, D.l. Sahoo, S. Acharya, R. Panda, R. Rout, Journal of Applied Polymer Science 62 (9) (1996) 1437. [13] L.D. Prabhakar, A. Marysaral, Polymer International 42 (2) (1997) 149. [14] A. Syamal, M. Singh, D. Kumar, Reactive and Functional Polymers 39 (1) (1999) 27. [15] K. Dev, G. Rao, Talanta 43 (3) (1996) 451. [16] M. Chanda, G. Rempel, Industrial and Engineering Chemistry Research 36 (6) (1997) 2190. [17] K. Inoue, K. Yoshizuka, Y. Baba, Solvent Extraction and Ion Exchange 8 (2) (1990) 309. [18] N. Bicak, G. Koza, T. Atay, Journal of Applied Polymer Science 61 (5) (1996) 799. [19] Y. Kawamura, M. Mitsuhashi, H. Tanibe, H. Yoshida, Industrial and Engineering Chemistry Research 32 (2) (1993) 386. [20] P.K. Tewari, A.K. Singh, Talanta 56 (2002) 735. [21] W.C. Chein, C.C. Yung, C.C. Yuan, Journal of Applied Polymer Science 84 (7) (2002) 1353. [22] C. Zhang, X. Li, J. Pang, Journal of Applied Polymer Science 82 (2001) 1587. [23] S.A. Ramadani, Y. Lekchiri, M. Morcellet, G. Crini, J. Morcellet, L. Janus, European Polymer Journal 36 (2000) 1885. [24] E. Kalalova, Z. Radova, K. Ulbert, J. Kalal, F. Svec, European Polymer Journal 13 (1977) 299. [25] E. Kalalova, Z. Radova, F. Svec, J. Kalal, European Polymer Journal 13 (1977) 293. [26] E. Kalalova, Z. Radova, J. Kalal, F. Svec, European Polymer Journal 13 (1977) 287. [27] J. Kalal, F. Svec, E. Kalalova, Z. Radova, Die Angewandte Makromoleculare Chemie 49 (1976) 93. [28] G.A. Latha, K.B. George, G.K. Kannan, N.K. Ninan, Journal of Applied Polymer Science 43 (6) (1991) 1159. [29] T.S. West, Complexometry with EDTA and Related Reagents, BDH Chemicals Ltd, 1969. [30] Y. Kawamura, H. Yoshida, S. Asai, I. Kurahashi, H. Tanibe, Separation Science and Technology 32 (12) (1997) 1959.
Studies on uptake behaviour of copper(II) and lead(II) by amine chelating resins with different textural properties Asem A. Atia, Ahmed M. Donia *, Saeda A. Abou-El-Enein, Ahmed M. Yousif Chemistry Department, Faculty of Science, Menoufia University, Shebin El-Kom, Egypt Received 25 June 2002; received in revised form 17 January 2003; accepted 5 February 2003
Abstract Glycidyl methacrylate resins with different ratios of divinylbenzene as cross-linking agent have been prepared. The textural properties such as density, porosity, pore area and pore diameter of the resins obtained were elucidated. The resins were anchored by chelating amino groups through the treatment with ethylenediamine (en). The amino group concentration on the resins was determined. The uptake behaviour of Cu(II) and Pb(II) from their aqueous solutions by the resins was studied. Both uptake capacity and selectivity of the resins towards the studied metal ions were discussed in terms of amino group concentration as well as the textural properties. The study indicated that metal-resin interaction proceeds via surface and diffusion mechanisms. The pH 5.8 found to be the most suitable for the uptake of the investigated metal ions. Copper was selectively separated from lead (using resin RI-en). The studied resins showed good durability and regeneration using HNO3. # 2003 Elsevier B.V. All rights reserved. Keywords: Glycidyl methacrylate; Porous; Chelating; Amino; Resins
1. Introduction Heavy metals in the wastewater are a major threat to human being and environment due to their toxicity [1]. Many research efforts are devoted to extract metal ions from their solutions. Different techniques have been employed such as solvent extraction, precipitation, co-precipitation, sorption and ion exchange [2]. Chelate-forming
* Corresponding author. Fax: /20-2-835-6313. E-mail address: [email protected] (A.M. Donia).
resins have been widely applied as ion exchangers for various metal ions in different environmental and industrial areas [3,4]. These resins show greater selectivity compared to the conventional types of ion exchangers [5]. Besides, they show good physical and chemical properties such as porosity, high surface area, durability and purity. Many chelating resins with different functionalities have been emphasized for interaction with metal ions. Among these moieties, sulfonic acid [6], hydroxamic acid [7], thiol groups [8,9], amidoxime [10], Schiff base [11 /14] and amine [15 / 23]. The complexing properties of polymer glycidyl
1383-5866/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1383-5866(03)00089-3
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methacrylate (GMA) loaded with chemically bonded ethylenediamine (en) were reported [24 / 27]. In the present work, resins of GMA/divinylbenzene (DVB) loaded with en will be prepared and characterized. The uptake behaviour of the resins obtained towards copper and lead will be studied and correlated to the surface and textural properties of the resins.
2.3. Preparation of en loaded resins The resins obtained were loaded by en as follows: 1 g of resin obtained in the previous step and 4 g en were dissolved in 12 ml DMF. The reaction mixture was heated at 75/80 8C for 72 h in oil bath. A pale yellow product was formed, filtered, washed with cold methanol and then dried. Thereafter the chelating resins obtained are known as RI-en, RII-en and RIII-en. 2.4. Physical measurements of the chelating resins
2. Experimental
2.1. Chemicals GMA, DVB, benzoyl peroxide (B2O2) and en were Aldrich products. All other chemicals were Prolabo products. Copper acetate and lead acetate were used as sources for Cu2 and Pb2, respectively. All chemicals were used as received except B2O2 which was purified by crystallization from methanol to give pure needles which collected and used for experiments.
2.2. Preparation of (GMA/DVB) resins Resins were prepared through the polymerization of GMA in the presence of DVB as a crosslinking agent. Resins with different textural properties were prepared by changing the volume ratio of the cross-linking agent (DVB) relative to that of the monomer (GMA). The ratios of DVB used in this study were 5, 15, and 50 vol.% for resins RI, RII and RIII, respectively. The requisite volumes of DVB and GMA were mixed well with 0.1 g B2O2 (initiator) until complete dissolution of the B2O2. One millilitre isopropyl alcohol and 12.6 ml cyclohexane were mixed then added to the former solution. The contents are then poured into a flask containing 73 ml of 1% polyvinyl alcohol and refluxed on a water bath at 75 /80 8C with continuous stirring for 6 h. A heavy white precipitate was formed, filtered, washed with methanol and dried in air.
The textural properties of the prepared resins were measured using High Pressure Mercury Pore Size Analyzer, Micromeritics 9320, USA. 2.5. Estimation of the amino groups loaded on the resins The concentration of amino group was estimated using the volumetric method [28]. Twenty millilitres HCl (0.05 N) was added to 0.1 g resin and conditioned for 15 h on a shaker. The residual concentration of HCl was measured through the titration against 0.05 N NaOH. The number of moles of HCl interacted by the amino groups and consequently the amino group concentration was calculated. 2.6. Uptake measurements using batch method Stock solution (1 /10 2 M) of the metal salt under study was prepared in distilled water. Stock solution of EDTA (5 /10 3 M) was prepared and standardized against a solution of MgSO4 ×/7H2O using Ereochrome Black-T (EBT) as indicator. Buffers of acetic acid/acetate (pH 3.8 /5.8), sodium phosphate (pH 6/8), and ammonium hydroxide/ ammonium chloride (pH 9/10) were used for the experiments carried out at acidic or basic conditions [29]. Uptake experiments carried out at controlled pH were done by conditioning 0.1 g resin with 100 ml metal ion solution at initial concentration of 5 /10 3 M for 3 h using a Vibromatic-384 shaker at 3000 rpm and 229/2 8C. The pH of the medium was adjusted by using the suitable buffer. Five
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Table 1 Textural properties of resins with different cross-linking ratios Resin
Density (g/ml)
Porosity (%)
Total pore area (m2/g)
Average pore diameter (mm)
RI RII RIII
0.47 0.28 0.23
39.66 41.41 69.46
47.54 39.15 191.57
0.07 0.15 0.06
millilitre of the solution (free of the suspended solid) were taken at the end of the experiment where the residual concentration of metal ion was determined via the titration against 5 /10 3 M EDTA using the suitable indicator. Mureoxide indicator was used for Cu2 while EBT was used for Pb2. In the case of lead, traces of solid tartaric acid were added to avoid precipitation of lead ions as lead hydroxide in basic medium. Complexation of lead ions with tartaric acid gives soluble lead /tartarate complex [29]. Experiments of adsorption isotherms were performed by adding 0.1 g resin to 100 ml metal ion solution at the desired initial concentration and pH 5.8. The contents of the flask were conditioned at 3000 rpm and 229/2 8C for 3 h. Later, the residual concentration was determined where the metal uptake was estimated as described above. Kinetic studies were done by shaking 0.1 g of resin with 100 ml (5 /10 3 M) of the metal ion at pH 5.8 and 229/2 8C. Five millilitre of the supernatant were taken at different intervals of time where the concentration of metal ion in the supernatant was determined. 2.7. Elution and durability experiments Elution experiments were performed by sharking 0.1 g resin with 100 ml (5 /10 3 M) of metal ion solution at pH 5.8 for 3 h. The total uptake was estimated then the solution was decanted then washed thoroughly with distilled water. The resin obtained (loaded by metal ions) was treated by 100 ml HNO3 at concentrations of 0.1, 0.2 or 0.5 N. After shaking for 3 h, the concentration of the released metal ion was detected. Afterwards, the resin was washed repeatedly with distilled water till the filtrate becomes free of the acid and the previous steps were repeated for 10 cycles.
3. Results and discussions The amine chelating resins (RI-en, RII-en and RIII-en) were obtained from GMA/DVB resins (RI, RII and RIII, respectively) through the treatment by en. The loading process takes place via the opening of epoxy ring by en. This behaviour was confirmed from IR measurements of the resins. The epoxy band at 1265/cm in the spectra of RI, RII and RIII disappeared in those of RI-en, RII-en and RIII-en. On the other hand, the spectra of the amino-resins are characterized by n NH at 3442/3250 per cm. 3.1. Physical measurements Table 1 presents the data of textural properties for the resins obtained. The density was found to follow the order, RI /RII /RIII. This indicates that as the cross-linking degree increases, the resin formed becomes less dense and expected to be more porous. This is confirmed from the data of porosity which increases in the order RI B/RII B/ RIII. On the other hand, the values of the total pore area and the average pore diameter change irregularly with the change in the ratio of crosslinking agent. So, while resin RII gave large average pore diameter and low total pore area, resin RIII showed low pore diameter and high pore area. Moreover, resin RI showed higher pore area and lower pore diameter compared to RII. Such variations in resins characteristics would reflect different uptake behaviour as discussed later on. 3.2. Amino group content Table 2 gives the amino group content loaded on the resins obtained. Clearly, the amino group
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298
Table 2 Concentration of amino group on resins with different crosslinking ratios Resin
Concentration of amino group (mmol/g)
RI-en RII-en RIII-en
5.4 4.8 2.9
content on the resins decreases as the cross-linking agent increases in the matrix. This decrease in the concentration of the amino group is closely related to the decrease in the ratio of GMA monomer (which later transforms into the amino resin) and the skeletal structure of each resin. 3.3. Metal ions uptake studies
Fig. 2. Effect of pH on the uptake of Pb2 by resins RI-en, RII-en and RIII-en.
Figs. 1 and 2 show the uptake of Cu2 and Pb2 as a function of pH, and indicate maximum uptake capacities at pH 5.8 for both copper and lead. This higher uptake may be attributed to the presence of free lone pair of electrons on the nitrogen atom suitable for coordination with the metal ion to give the corresponding resin /metal complex. The uptake shows lower values in both acidic and basic mediums. In acidic medium, the amino groups become protonated and therefore
the coordination with the metal ion is hindered giving lower uptake values. The observed lower uptake in basic medium may be explained by the partial precipitation of metal hydroxides and/or formation of metal complexes (amine for Cu2 and tartarate for Pb2). Such complexes may decrease the ability of the metal ion to attack the resin resulting in a decrease in the total uptake.
Fig. 1. Effect of pH on the uptake of Cu2 by resins RI-en, RII-en and RIII-en.
Fig. 3. Uptake of Cu2 by resins RI-en, RII-en and RIII-en as a function of conditioning time at pH 5.8.
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Table 3 Maximum uptake of Cu2 and Pb2 at same level of amino group concentration for resins with different cross-linking ratios Resin
RI-en RII-en RIII-en a
Fig. 4. Uptake of Pb2 by resins RI-en, RII-en and RIII-en as a function of conditioning time at pH 5.8.
Figs. 3 and 4 show the change of the uptake of Cu2 and Pb2 as a function of time by resins RIen, RII-en and RIII-en at pH 5.8 and 229/2 8C. The uptake equilibrium of Cu2 was attained after 160, 80, and 40 min for resins RI-en, RII-en and RIII-en, respectively. For Pb2, the equilibrium was attained after 100, 40, and 24 min for resins RI-en, RII-en and RIII-en, respectively. It is seen that the equilibrium of Pb2 is shifted to lower time values compared to Cu2 for the same resin. This may indicate to the lower affinity of Pb2 towards resin compared to Cu2. The total uptake of both Cu2 and Pb2 by different resins follows the order RI-en /RII-en /RIII-en. This order could be explained based on the concentration of the amino group on the resin as well as their textural properties. The total uptake of copper with RI-en is higher than that of RII-en by approximately 1.5 times and than RIII-en by approximately 2.6 times. Such differences in the uptake are not consistent with the differences in the concentration of the amino group on the resins (Table 2). The concentration of amino group on resin RI-en is higher than that on RII-en and RIIIen by approximately 1.1 and 1.9 times, respectively. So, we expect other factors affecting the uptake in addition to the concentration of the amino groups. Such conclusion was verified by
Resin weight (g)a
0.1000 0.1125 0.1860
Maximum uptake (mmol/g) Cu2
Pb2
1.244 0.831 1.109
0.323 0.285 0.306
Using resin weights containing 5.4 mmol of amino groups.
studying the uptake of both copper and lead on resins having same level of amino group concentration. The data of maximum uptake of copper and lead along with the resin weights is reported in Table 3. The weights taken from different resins were specified so as to achieve the same level of amino group concentration (5.4 mmol). It can be seen in Table 3 that the maximum uptake of both RII-en and RIII-en is slightly lower than that of RI-en although the level of amino group concentration is the same. Such differences confirm the effective role of textural properties of resins on the uptake values. The uptake values of resin RII-en are lower than that of RI-en in case of copper or lead by approximately 1.5 and 1.0 times, respectively. This may be attributed to the differences in the values of the total pore area of resin RII compared to RI (Table 1). Although the total pore area of resin RIII is significantly higher than RI, the uptake values by resin RIII-en are lower than RI-en for copper and lead by approximately 1.1 and 0.5 times, respectively. This may be attributed to the difference in the values of the average pore diameter of the two resins (Table 1). Similar findings were reported by other authors [10,16,19,28,30]. Fig. 5 shows the adsorption isotherms of copper and lead at pH 5.8 and 229/2 8C. Inspection of Fig. 5 reveals that the uptake of copper is higher than that of lead at all concentration ranges. The uptake increases markedly until reaching maximum values at 1.24 and 0.32 mmol/g for copper and lead, respectively. The higher uptake of copper may be attributed to that copper (transition element) is able to form a stable metal /ligand
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300
Fig. 5. Adsorption isotherms of Cu2 and Pb2 using resin RI-en at equilibrium time and 229/2 8C.
complex compared to lead (non-transition element). Such uptake affinity of copper and lead may be inferred by plotting their adsorption data according to Langmuir adsorption isotherm [1]: q
Qmax Ce K Ce
where q is the uptake at equilibrium concentration (mmol/g), Ce is the equilibrium concentration (mM), Qmax is the maximum uptake (mmol/g), and K is a constant indicates to the affinity and equal to the reciprocal of the binding constant (mM). Plotting 1/q against 1/Ce gives straight line with intercept and slope values equal to 1/Qmax and K /Qmax, respectively. The values of K and Qmax were obtained and reported in Table 4. The values of Qmax for copper and lead found to be 1.26 and 0.35 mmol/g, respectively. The values of K are 0.358 and 0.630 mM for copper and lead,
respectively. The lower value of K of copper compared to that of lead indicates to the higher binding of copper with resin than of lead. The kinetics of metal uptake process and its relation to the textural characteristics of the studied resins were also studied. The rate plots for uptake of copper and lead on resin RI-en are shown in Fig. 6. Clearly the rate follows the first order kinetics for both copper and lead where a straight line was obtained at the first period of uptake reaction up to :/20 min. Afterwards, the lines were deviated from straightened at advanced stages of interaction. This indicates that the uptake was controlled by two phenomena: (i) surface phenomenon where the interaction rate mainly controlled by the concentration of metal ion in the bulk of solution giving first order kinetics (first period), (ii) diffusion phenomenon where the rate of interaction is mainly controlled by the textural properties of the resin and the diffusion of the metal ions through the pores to interact with the internal surface (advanced period). The uptake studies may also give valuable information about the management of the removal of the studied metal ions from aqueous solutions. For instance, the removal of copper or lead ions using resin RI-en approaches 90% of the maximum capacity within 50 min (Figs. 3 and 4). The
Table 4 Langmuir parameters for the adsorption of Cu2 and Pb2 on resin RI-en Metal ion 2
Cu Pb2
Qmax (mmol/g)
K (mM)
1.26 0.35
0.358 0.630
Fig. 6. Plots of relative concentration of Cu2 and Pb2 on resin RI-en against time.
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values of the maximum uptake by resin RI-en are 1.24 and 0.32 mmol/g, for Cu2 and Pb2, respectively. This indicates to that copper could be selectively separated from lead in their mixture. The durability of the studied resins was tested using different concentrations of HNO3. Complete elution of copper and lead was achieved with 0.5 HNO3. The regenerated resins showed 979/1% efficiency compared to the fresh resins for 10 cycles.
4. Conclusions Various amino chelating resins with different textural properties have been obtained. The resins were applied to the recovery of heavy metals such as copper and lead. Both the uptake capacity and selectivity of the resins towards the investigated metal ions was found related to many factors such as amino group concentration, textural characteristics of the resin, type of metal ion, and uptake conditions. High concentration of active sites along with porous structure and wide average pore size support the high uptake. The studied resins were found to have high durability towards mineral acids. The regenerated resins showed uptake behaviour similar to that of the fresh resins up to 10 cycles.
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