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Ion exchange equilibria of heavy metals in aqueous solution on new chelating resins of sporopollenin
Reactive polymers ELSEVIER
Reactive Polymers 24 (1995) 195-202
Ion exchange equilibria of heavy metals in aqueous solution on new chelating resins of sporopollenin M. Ersoz
a,*, E. Pehlivan a, H.J. D u n c a n b, S. Yildiz a, M. Pehlivan c
a Department of Chemistry, Faculty of Arts and Sciences, University of Selcuk, 42079, Konya, Turkey. b Department of Chemistry, University of Glasgow, Glasgow G12 8QQ~ Scotland, U.K. c Department of Chemistry, Faculty of Education, Universityof Selcuk, Konya, Turkey Received 7 March 1994; accepted in revised form 13 October 1994
Abstract
Studies have been conducted on the sorption of several heavy metal ions Cu(II), Ni(II), Zn(II), Cd(II) and AI(III) from aqueous solutions on the new chelating exchangers of sporopollenin (Lycopodium clavatum) as a function of pH at several temperatures between 20 and 50°C. The novel metal-ligand exchange resins possessing oxime and carboxylic acid side arm functionality were prepared through the reaction of diaminosporopollenin with dichloroantiglyoxime and bromoacetic acid. The sorption of all metals increased considerably in the range of pH 6-10 and was observed in sequence as: Cu > Ni > Zn > Cd > AI for carboxylated-diaminoethyl-sporopollenin (DAEC) and Ni > Cu > Zn > Cd > AI for bis-diaminoethyl-glyoxime-sporopollenin (bDAEG). The level of pH of the aqueous medium had a large influence on the sorption capacity, and the uptake of metals, except AI(III), was found to be 90% or more. The metal-form resins afforded complete recovery of the sorbed species by acid stripping. Both resins also showed high stability towards concentrated acids and bases and retained their high capacity for heavy metals.
Keywords: Chelating resin; Sorption; Heavy metal; Sporopollenin
1. Introduction The chelating resins are ion-exchange resins containing functional groups which are able to complex with metal ions. Their sorption mechanism is supposed to be through chelation instead of simple ion exchange, and as a consequence, they should be much more selective than ionexchange resins. They are widely used for separation, removal and preconcentration of metal ions, particularly from complicated matrices, where high amounts of interfering ions are present. * Corresponding author.
The sorption of heavy metal ions onto ion exchangers has been studied in recent years. In particular, the effect of pH [1-4], ionic strength [5,6] and the nature of the adsorbent [7,8] have all been extensively investigated. The sorption of metal ions at trace level concentration in aqueous solution is very important. Only very low concentrations of heavy metals are permitted to be discharged in waste waters in order to prevent public streams and water resources from becoming contaminated. Heavy metals are often present in various industrial waste waters, together with complex-forming organic compounds. Under these conditions, various metal-
0923-1137/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved.
SSDI 0 9 2 3 - 1 1 3 7 ( 9 4 ) 0 0 0 8 4 - 0
196
M. Ersoz et aL /Reactive Polymers 24 (1995) 195-202
ligand complexes are formed and consequently, the removal and the recovery of heavy metal cations from aqueous solutions and their separation from complexing compounds is very complicated because of the high stability constants of these complexes. Chelating resins have been used for the removal and recovery of heavy metals and also for the concentration and analysis of heavy trace metals. However, the majority of these chelating resins have not shown a satisfactory degree of selectivity towards the specific metal ion to be separated, thus requiring the use of very large amounts of resin per unit volume of process solution, at a fixed pH. A full description of the effects of temperature on sorption must take pH variation into account. Sporopollenin is a natural polymer [9-11] obtained from Lycopodiurn clavatum which is highly resistant to chemical attack, has a high capacity, is stable, has a constant chemical structure and occurs naturally as a component of spore walls, and exhibits very good stability even after prolonged exposure to mineral acids and alkalies. Sporopollenin is produced by oxidative polymerization of carotenoids and carotenoid esters, which lead to the proposed monomer structures of the macromolecular sporopollenin. At present sporopollenin is generally considered to be a biopolymer and the detailed chemical structure of sporopollenin is as yet unknown. Its empirical formula has been found to be C90H144027 [12]. The aim of the present paper is to investigate the sorption capacity of metal-ligand complexes derived from Lycopodium clavaturn with respect to aqueous solutions of some metal ions, specifically Cu(II), Ni(II), Zn(II), Cd(II) and AI(III), and to obtain fundamental information for the application of sporopollenin. This will permit the evaluation of modified new metal-ligand exchangers for their utilization as sorbents in the recovery, pollution control and elimination of these ions from waste water.
2. Experimental
2.1. Materials The resin used was Lycopodium clavatum with 20 /zm particle size mesh from BDH Chemicals. Reagent grades of CuSOa.5H20, A12(SOa)3"8H20 , and CdSO4-8H20 were used as the sulfate series, NiCI2.7H20 as the chloride and also reagent grade Zn(NO3)2-6H20 as the nitrate of these metals. Solutions were prepared by dissolving appropriate weights of the chloride, sulfate or nitrate of the metals in deionized water. Nitric acid (65%), hydrochloric acid (37%) and sodium hydroxide standard solutions were used.
2.2. Preparation of bis-diaminoethyl-glyoximesporopollenin and carboxylated-diaminoethylsporopollenin Methods from our earlier papers, to obtain bis-diaminoethyl-glyoximated sporopollenin (bDAEG-sporopollenin) as represented in Scheme 1 [13] and carboxylated diamino-sporopollenin (DAEC-sporopollenin) as Scheme 2 [14] were used The DAEC-sporopollenin and bDAEG-sporopollenin resins were treated with heavy metal ions which are fixed to the resin matrix. The metal-ligand complexes of sporopollenin derivatives for divalent cations are shown in Schemes 1 and 2, where ('if) indicates sporopollenin (Lycopodium clavatum).
2.3. Sorption experiments All the experiments were carried out batchwise; the sorption equilibrium was attained by shaking 0.2 g of the resin and 10 cm 3 (1 x 10 -3 and 4 x 10 -3 M) of aqueous solution containing metal ions which were shaken in an incubator at controlled temperature for 24 h using a mechanical shaker maintained at 25 4- 1°C. The shaker was set at 180 rpm. The initial pH was adjusted by adding a small amount of nitric acid or sodium hydroxide to maintain constant pH. For
197
M. Ersoz et al. / Reactive Polymers 24 (1995) 195-202
CI
+ NH2(CH2)NH 2
,OH "C~N @--NH(CH2)2NH2 + I /C :~N. H OH
H
I
+ HCI
2 R--N--C ~ N --OH
i
H
C~
N---OH
MC12
i O
R-R
jH
O
~N ~ N
/ N
H
"~,, ~," %C- I N
t N--C%[
u 2+ /2 ¢ \
R
I S C--N
-R
O H~O Scheme 1. Metal(II) loaded-bis-diaminoethylglyoximesporopollenin(Me2+-loadedbDAEG-sporopollenin).
r~l - -
NH(C H2)2NH2
BrCH2COOH
~--
N(CH2)2N-- CH2COOH
I
I
CH 2
CH2
I
I
COOH COOH I MCI 2
x C-// O-~ .
J O "j~
(S) C. \
~ / M2+ i ~
o~ c -
CH l ~% I O--C
// / N~CH N j.
2 ! C H2
CH2 /
Scheme2. Metal(II) loadedcarboxylated-diaminoethyl-sporopollenin(Me2+-loadedDAEC-sporopollenin).
198
M. Ersoz et aL / Reactive Polymers 24 (1995) 195-202
temperature experiments 20, 30, 40 and 50°C were selected and carried out on maximum sorption at pH 8, and each treatment was replicated three times, before initiating the experiment. Initial and equilibrated metal concentrations in the aqueous solution were determined by AAS using a Perkin-Elmer 1100 B atomic absorption spectrophotometer. The amount of sorbed metal ion was calculated from the change in the metal concentration in the aqueous solution before and after equilibrium and the weight of the dry resin used. The resin was washed after equilibrium with 2.0 M HCI and the concentration of metal cations in the resin phase was also determined. In all cases, mass balance was confirmed. The pH values at equilibrium were measured using an Orion model 720 pH meter. Each resin was used after pretreatment by washing with hydrochloric acid and rinsing with distilled water to ensure that impurities did not remain in the resin.
A
0.6
•
Z{I
0.4 -6 E E o- 0.2
0.0
i
,
0
0.6
[
I
1
I
2 3 C (retool)
I
i
4
5
B
0.4
e
~
° / ~ 0.2
3. Results and discussion
Fig. 1 shows typical sorption isotherms of Zn(II), Cd(II) and AI(III) ions on the DAEC-sporopollenin (Fig. 1A) and bDAEGsporopollenin (Fig. 1B) chelating resins. The concentration of metals in the resin phase was calculated as: q = (Co - C) V~ W
0.0
~
,
~
0
1
2 3 C (mrnol)
,
~
4
5
Fig. 1. Sorption isotherms of Zn(ll), Cd(lI) and Al(lII) ions the DAEC-sporopollenin (A) and bDAEG-sporopoUenin (B). on
(1)
where Co and C denote the initial and equilibrium concentrations of the metals in the aqueous phase, V is the volume of the aqueous phase and W is the dry weight of the resin. Sorption isotherms were obtained by plotting metal adsorbed (mmol) per g of resin against concentration of metal remaining in solution at equilibrium. The initial solute concentration ranged from 1 to 4 mmol/l. Fig. 1 shows that both chelating resins sorbed Zn more than Cd and AI. Although the uptake of heavy metals was very similar on both resins. As shown in Fig. 1A and B, the sorption isotherms of uptake metals could
be expressed either as Langmuir or Freundlich isotherms. Metal sorption constants and correlation coefficients for the Zn, Cd and AI on the both chelating resins were calculated from Freundlich as well as Langmuir plots and are given in Table 1. The sorption data on both resins were fitted to both Freundlich and Langmuir isotherm equations. The sorption data in respect of all metals provide an excellent fit to the Freundlich isotherm, giving correlation coefficients in the range of 0.992-0.997 for the Freundlich isotherm and 0.837-0.984 for the Langmuir isotherm for both resins. To test the fit of data, the Freundlich isotherm equation is written as:
M. Ersoz et aL / Reactive Polymers 24 (1995) 195-202
199
Table 1 Parameters of Langmuir and Freundlich isotherms for sorption on DAEC-sporopollenin and bDAEG-sporollenin Metal
Langmuir isotherm Eq. 3 As (mmol/g dry resin)
Freundlich isotherm Eq. 2 Correlation coefficient
Kb
Correlation
k
(1 mmo1-1)
coefficient
(mmol/g dry resin)
0.117 0.133 0.186
0.897 0.980 0.984
0.181 0.176 0.163
1.112 1.138 1.198
0.993 0.997 0.994
0.112 0.164 0.179
0.837 0.976 0.983
0.178 0.167 0.159
1.092 1.178 1.192
0.992 0.995 0.995
DAEC-sporopollenin Zn Cd AI
1.801 1.500 1.119
bDAEG-sporopollenin Zn Cd AI
1.855 1.261 1.127
q = kC 1In
(2)
2.0
• Cu A Ni
where k and n are empirical parameters. The Langmuir isotherm is written as: C/q = 1/KbA, + C/As
(3)
where the parameters Kb and A, are the sorption binding constant (1/mmol) and saturation capacity (mmol metal/g dry wt. of resin), respectively. The Langmuir and Freundlich isotherm parameters were determined by least-squares fit of the sorption data in Fig 1. Equilibrium distribution of metals was measured in the sorption on DAEC and bDAEGsporopollenin resins from aqueous solutions. Figs. 2 and 3 show the relationship between the equilibrium pH and distribution coefficient D. The distribution ratios of all metals increase with increasing pH after passing through a maximum (pH ~8), then level off. The characteristic curves are analogous to each other, exhibiting a strong pH dependence as Figs. 2 and 3 illustrate, although the sorption characteristics have shifted to a higher pH region. Metal-ligand complexes of sporopollenin were prepared from sporopollenin (Lycopodium clavatum), ethylenediamine, bromoacetic acid and chloroglyoxime. Ethylenediamine complexes possess a very stable structure and have a very minor dissociation tendency, and they act as suitable functional groups for a ligand exchange matrix [15]. Oxime functional group resins are,
1.0
2
0.0
-1.0
i
i
J
i
i
2
4
6
8
10
pH
2.0
• Zn •
Cd
o AI
1.0
2
0.0
-1.0
i
i
i
i
i
2
4
6
8
10
pH
Fig. 2. The distribution coefficients of metals on the DAECsporopollenin as a function of pH at a concentration of 10-3 M.
200
M. Ersoz et al./ Reactive Potymers 24 (1995) 195-202
2.0
• Cu
1.0
10 -3 M. At low pH values the sorption of metal ions was low. At low pH values the electrostatic repulsion between the complex and the metal ions prevents their sorption. The amount of the sorbed metal at pH 8-10 increases in the order Cu > Ni > Zn > Cd > A1 for DAEC and Ni > Cu > Zn > Cd > A1 for bDAEG. This order is determined by many factors, the most significant of which are: ionic potential q/r (q is the ionic charger, r is the ionic radius), chemical properties, ionic radius and hydrolysis. The results and analysis presented here indicate that the metal-ligand complexes of sporopollenin show an ability to sorb metal ions from aqueous solution with increasing pH. It is noteworthy that the sorption of metallic ions increased considerably in the range of pH 6-10. This high sorption ability of the resin may be due to the formation of metal chelate in the carboxyl groups with the coordinations of the nitrogen atoms in the glyoxime and ethylene diamine. It was mentioned above that the metal-ligand complex resins contain carboxyl and phenolic groups. Metal ion sorption is unfavorable at the lower pH value of 3 since this is below the dissociation constant pK value of the functional groups of carboxyl and phenolic. At near-neutral and alkaline pH values, i.e. close to and above the pK of carboxyl and phenolic groups, the sorption of the metal is appreciable. However, the sorption with these resins takes place at a much higher pH for all metal ions, which may be attributed to the large difference between the acid dissociation constant of the alcoholic hydroxyl group of carotenoid ester unit of sporopollenin and that of the carboxyl group. Glyoxime and carboxylic acid well preferably be a multidentate ligand with a metal ion. From the above-mentioned cases the following conclusion can be drawn: the uptake efficiency of metal will depend preferentially on the type of forces (coordination of metal to the donor atom or electrostatic attraction) that prevail between ligand and metal in the complex compound. These resins show high stability towards concentrated m
o _.1
0.0
-1.0
i
i
i
i
w
2
4
6
8
10
~ 6
, 8
, 10
pH 2.0
.J:~
•
Zn
•
Cd
o
AI
1.0
0.0
-1.0
, 0
, 2
, 4 pH
Fig. 3. T h e distribution coefficients of metals on the b D A E G sporopollenin as a function of p H at a concentration of 10 -3 M.
in fact, solvent impregnated resins and differ from the conventional chelating ion-exchange resins, which contain chelating ligands covalently bonded to a polymeric matrix [16]. Glyoxime complexes especially dichloro-antiglyoxime possess strong metal-binding properties and selectivities towards transition metals which are capable of undergoing incorporation in a resin matrix [15]. The resin readily sorbs various kinds of metal ions in a 10-3 mol/1 aqueous solution with a pH range of 2-10, and distribution coefficients (showing the variation in sorption with pH) are presented in Figs. 2 and 3 for heavy metal ions. In each case the initial cation concentration was
M. Ersoz et al./ Reactive Polymers 24 (1995) 195-202
acids and bases during regeneration and, in turn, retain their high capacity for heavy metals, and are cheaper and easier to prepare than many commercial resins. They possess higher selectivity, which makes them more versatile ion exchangers for industrial purposes. These resins are particularly suited to this application because optimum metal binding occurs in the pH range 6-8. Heavy metal cations are taken up by coordination with the donor nitrogen atoms of the functional group of the glyoxime and nitrogen and oxygen donor atoms of the functional groups of the carboxylated resin, thus creating very strong coordination compounds in the resin phase. Electrostatic attractive forces between metal and carboxyl or hydroxyl groups prevail in a complex formation. In the case of glyoxime and bromoacetic acid, the coordination bonds between metal and N-donor atoms play a very important part in the overall complex stability. More commonly used is the iminodiacetate chelating resin, Chelex-100, but diffusion in and out of this resin is slow and chromatographic performance is poor. Furthermore, the ligand binding capacity is limited by the coordination of the metal ion to the resin functional group. The precise determination of the coordination behavior of the functional group towards metal ions and the geometry around the metal ion is essential for the further development of metal-ion selective ion-exchange resins. A further experiment was attempted to compare the sorption equilibria of Zn(II), Cd(II) and AI(III) as a function of temperature. Bearing in mind the importance of temperature in the study of sorption of trace metals, the present work was initiated with the aim of having a thermodynamic approach for trace metal sorption of sporopollenin derivatives. It was decided to conduct an experiment under controlled conditions to study how the different temperatures affect the sorption of heavy metals in both resins and the possible mechanisms controlling their sorption in metal-ligand complexes. The effectsof temperature on the sorption
201
2.0
1.5
~Z
1.2
o
0.5
0.4
0.0
285
295
305 Temperature
t
i
315
325
315
325
("K)
S
2.0
1.6
~Z
1.2
o
0.~
0.4
0.0
, 285
295
305 Temperature ('K)
Fig. 4. Sorptionof zinc (e), cadmium(A) and aluminum( • ) on to DAEC-sporopollenin (A) and bDAEG-sporopollenin (B) as a function of temperature at a concentration of 10 -3 M.
of metal ions by metal-ligand complexes of sporopollenin derivatives are represented in Fig. 4, by plotting the distribution coefficient of the amount of metals sorbed in both resins versus different temperatures. Both resins gave a positive response to the increase in temperature with respect to metal sorption. The extent of sorption at a given pH was found to increase with temperature; the magnitude of the increase depending on the cation. The sorption of metal ions increased with increasing temperature. This is based on thermodynamics and sorption reactions for many
202
M. Ersoz et al. / Reactive Polymers 24 (1995) 195-202
divalent cations are endothermic [8,17]. The equilibrium constants for such reactions increase with temperature, i.e., the reaction products (the sorbed species) are favored at higher temperatures. In all systems, the distribution coefficient shifted to higher pH as the temperature increased. Another reason assumed that the surface charge and skeleton of metal-ligand complexes of sporopollenin at a given pH decreases, and hydrolysis of the cations proceeds to a greater extent, as temperature increases. Thus, an increase in temperature will reduce the electrostatic repulsion between the surface and the sorbing species, allowing sorption to occur more readily. In most cases an increase in temperature increased the sorption of cations - a n effect compatible with the effects of temperature on both the rate of reaction and the position of a sorption equilibrium involving cations. In conclusion, it can be seen from Figs. 2 and 3 that these chelating resins are useful over a wide pH range (6-10), and are stable and have strong chelating ability with various kinds of metal ions, and are also reversible over a long period of time. These resins appear promising as preconcentration agents for trace elements, to establish and maintain known ionic activities of metals at constant pH, and for the recovery of metal ions from the secondary effluent of petrochemical plants and industrial waste water.
Acknowledgements The authors wish to thank the Universities of Selcuk and Glasgow for the use of their research facilities.
References [1] R.O. James and TW. Healey, J. Colloid Interface Sci., 40 (1972) 42. [2] R.R. Gadde and H.A. Laitinen, Anal Chem., 46 (1974) 2022. [3] B. Bar-Yosef, Soil Sci. Soc. Am. J., 43 (1979) 1095. [4] D.G. Kinniburgh and M.L. Jackson, Soil Sci. Soc. Am. J., 46 (1982) 56. [5] G.H. Luttrell, Jr., C. More and C.T. Kenner, Anal, Chem., 43 (1971) 1370. [6] J.L. Sides and C.T. Kenner, Anal. Chem., 38 (1966) 707. [7] M.M. Benjamin and J.O. Leckie, J. Colloid Interface Sci., 79 (1981) 209. [8] P.H. Tewari, A.B. Campbell and W. Lee, Can. J. Chem., 50 (1972) 1642. [9] G. Shaw. In: J.B. Harborne (Ed.) Phyto Chemical Phylogeny, Academic Press, London, 1970, Chapter 3. [10] J. Brook and G. Shaw, Nature, 220 (1968) 678. [11] G. Mackenzie and G. Shaw, Int. J. Pep. Prot. Res., 15 (1980) 298. [12] G. Shaw. In: J. Brooks, ER. Grant, M. Muir, E Van Gijzel and G. Shaw (Eds.) Sporopollenin, The Chemistry of Sporopollenin. Academic Press, London, 1971, p. 305. [13] M. Ersoz, E. Pehlivan and S. Yildiz, Ann. Lett., 22 (1989) 1829. [14] E. Pehlivan and S. Yildiz, Anal. Lett., 21 (1988) 297. [15] M. Ersoz, S. Yildiz and E. Pehlivan, J. Chrom. Sci., 31 (1993) 61. [16] S.K. Sahni and J. Reedijk, Coon. Chem. Rev., 59 (1984) 1. [17] N.J. Barrow, J. Soil Sci., 37 (1986) 277.
Reactive Polymers 24 (1995) 195-202
Ion exchange equilibria of heavy metals in aqueous solution on new chelating resins of sporopollenin M. Ersoz
a,*, E. Pehlivan a, H.J. D u n c a n b, S. Yildiz a, M. Pehlivan c
a Department of Chemistry, Faculty of Arts and Sciences, University of Selcuk, 42079, Konya, Turkey. b Department of Chemistry, University of Glasgow, Glasgow G12 8QQ~ Scotland, U.K. c Department of Chemistry, Faculty of Education, Universityof Selcuk, Konya, Turkey Received 7 March 1994; accepted in revised form 13 October 1994
Abstract
Studies have been conducted on the sorption of several heavy metal ions Cu(II), Ni(II), Zn(II), Cd(II) and AI(III) from aqueous solutions on the new chelating exchangers of sporopollenin (Lycopodium clavatum) as a function of pH at several temperatures between 20 and 50°C. The novel metal-ligand exchange resins possessing oxime and carboxylic acid side arm functionality were prepared through the reaction of diaminosporopollenin with dichloroantiglyoxime and bromoacetic acid. The sorption of all metals increased considerably in the range of pH 6-10 and was observed in sequence as: Cu > Ni > Zn > Cd > AI for carboxylated-diaminoethyl-sporopollenin (DAEC) and Ni > Cu > Zn > Cd > AI for bis-diaminoethyl-glyoxime-sporopollenin (bDAEG). The level of pH of the aqueous medium had a large influence on the sorption capacity, and the uptake of metals, except AI(III), was found to be 90% or more. The metal-form resins afforded complete recovery of the sorbed species by acid stripping. Both resins also showed high stability towards concentrated acids and bases and retained their high capacity for heavy metals.
Keywords: Chelating resin; Sorption; Heavy metal; Sporopollenin
1. Introduction The chelating resins are ion-exchange resins containing functional groups which are able to complex with metal ions. Their sorption mechanism is supposed to be through chelation instead of simple ion exchange, and as a consequence, they should be much more selective than ionexchange resins. They are widely used for separation, removal and preconcentration of metal ions, particularly from complicated matrices, where high amounts of interfering ions are present. * Corresponding author.
The sorption of heavy metal ions onto ion exchangers has been studied in recent years. In particular, the effect of pH [1-4], ionic strength [5,6] and the nature of the adsorbent [7,8] have all been extensively investigated. The sorption of metal ions at trace level concentration in aqueous solution is very important. Only very low concentrations of heavy metals are permitted to be discharged in waste waters in order to prevent public streams and water resources from becoming contaminated. Heavy metals are often present in various industrial waste waters, together with complex-forming organic compounds. Under these conditions, various metal-
0923-1137/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved.
SSDI 0 9 2 3 - 1 1 3 7 ( 9 4 ) 0 0 0 8 4 - 0
196
M. Ersoz et aL /Reactive Polymers 24 (1995) 195-202
ligand complexes are formed and consequently, the removal and the recovery of heavy metal cations from aqueous solutions and their separation from complexing compounds is very complicated because of the high stability constants of these complexes. Chelating resins have been used for the removal and recovery of heavy metals and also for the concentration and analysis of heavy trace metals. However, the majority of these chelating resins have not shown a satisfactory degree of selectivity towards the specific metal ion to be separated, thus requiring the use of very large amounts of resin per unit volume of process solution, at a fixed pH. A full description of the effects of temperature on sorption must take pH variation into account. Sporopollenin is a natural polymer [9-11] obtained from Lycopodiurn clavatum which is highly resistant to chemical attack, has a high capacity, is stable, has a constant chemical structure and occurs naturally as a component of spore walls, and exhibits very good stability even after prolonged exposure to mineral acids and alkalies. Sporopollenin is produced by oxidative polymerization of carotenoids and carotenoid esters, which lead to the proposed monomer structures of the macromolecular sporopollenin. At present sporopollenin is generally considered to be a biopolymer and the detailed chemical structure of sporopollenin is as yet unknown. Its empirical formula has been found to be C90H144027 [12]. The aim of the present paper is to investigate the sorption capacity of metal-ligand complexes derived from Lycopodium clavaturn with respect to aqueous solutions of some metal ions, specifically Cu(II), Ni(II), Zn(II), Cd(II) and AI(III), and to obtain fundamental information for the application of sporopollenin. This will permit the evaluation of modified new metal-ligand exchangers for their utilization as sorbents in the recovery, pollution control and elimination of these ions from waste water.
2. Experimental
2.1. Materials The resin used was Lycopodium clavatum with 20 /zm particle size mesh from BDH Chemicals. Reagent grades of CuSOa.5H20, A12(SOa)3"8H20 , and CdSO4-8H20 were used as the sulfate series, NiCI2.7H20 as the chloride and also reagent grade Zn(NO3)2-6H20 as the nitrate of these metals. Solutions were prepared by dissolving appropriate weights of the chloride, sulfate or nitrate of the metals in deionized water. Nitric acid (65%), hydrochloric acid (37%) and sodium hydroxide standard solutions were used.
2.2. Preparation of bis-diaminoethyl-glyoximesporopollenin and carboxylated-diaminoethylsporopollenin Methods from our earlier papers, to obtain bis-diaminoethyl-glyoximated sporopollenin (bDAEG-sporopollenin) as represented in Scheme 1 [13] and carboxylated diamino-sporopollenin (DAEC-sporopollenin) as Scheme 2 [14] were used The DAEC-sporopollenin and bDAEG-sporopollenin resins were treated with heavy metal ions which are fixed to the resin matrix. The metal-ligand complexes of sporopollenin derivatives for divalent cations are shown in Schemes 1 and 2, where ('if) indicates sporopollenin (Lycopodium clavatum).
2.3. Sorption experiments All the experiments were carried out batchwise; the sorption equilibrium was attained by shaking 0.2 g of the resin and 10 cm 3 (1 x 10 -3 and 4 x 10 -3 M) of aqueous solution containing metal ions which were shaken in an incubator at controlled temperature for 24 h using a mechanical shaker maintained at 25 4- 1°C. The shaker was set at 180 rpm. The initial pH was adjusted by adding a small amount of nitric acid or sodium hydroxide to maintain constant pH. For
197
M. Ersoz et al. / Reactive Polymers 24 (1995) 195-202
CI
+ NH2(CH2)NH 2
,OH "C~N @--NH(CH2)2NH2 + I /C :~N. H OH
H
I
+ HCI
2 R--N--C ~ N --OH
i
H
C~
N---OH
MC12
i O
R-R
jH
O
~N ~ N
/ N
H
"~,, ~," %C- I N
t N--C%[
u 2+ /2 ¢ \
R
I S C--N
-R
O H~O Scheme 1. Metal(II) loaded-bis-diaminoethylglyoximesporopollenin(Me2+-loadedbDAEG-sporopollenin).
r~l - -
NH(C H2)2NH2
BrCH2COOH
~--
N(CH2)2N-- CH2COOH
I
I
CH 2
CH2
I
I
COOH COOH I MCI 2
x C-// O-~ .
J O "j~
(S) C. \
~ / M2+ i ~
o~ c -
CH l ~% I O--C
// / N~CH N j.
2 ! C H2
CH2 /
Scheme2. Metal(II) loadedcarboxylated-diaminoethyl-sporopollenin(Me2+-loadedDAEC-sporopollenin).
198
M. Ersoz et aL / Reactive Polymers 24 (1995) 195-202
temperature experiments 20, 30, 40 and 50°C were selected and carried out on maximum sorption at pH 8, and each treatment was replicated three times, before initiating the experiment. Initial and equilibrated metal concentrations in the aqueous solution were determined by AAS using a Perkin-Elmer 1100 B atomic absorption spectrophotometer. The amount of sorbed metal ion was calculated from the change in the metal concentration in the aqueous solution before and after equilibrium and the weight of the dry resin used. The resin was washed after equilibrium with 2.0 M HCI and the concentration of metal cations in the resin phase was also determined. In all cases, mass balance was confirmed. The pH values at equilibrium were measured using an Orion model 720 pH meter. Each resin was used after pretreatment by washing with hydrochloric acid and rinsing with distilled water to ensure that impurities did not remain in the resin.
A
0.6
•
Z{I
0.4 -6 E E o- 0.2
0.0
i
,
0
0.6
[
I
1
I
2 3 C (retool)
I
i
4
5
B
0.4
e
~
° / ~ 0.2
3. Results and discussion
Fig. 1 shows typical sorption isotherms of Zn(II), Cd(II) and AI(III) ions on the DAEC-sporopollenin (Fig. 1A) and bDAEGsporopollenin (Fig. 1B) chelating resins. The concentration of metals in the resin phase was calculated as: q = (Co - C) V~ W
0.0
~
,
~
0
1
2 3 C (mrnol)
,
~
4
5
Fig. 1. Sorption isotherms of Zn(ll), Cd(lI) and Al(lII) ions the DAEC-sporopollenin (A) and bDAEG-sporopoUenin (B). on
(1)
where Co and C denote the initial and equilibrium concentrations of the metals in the aqueous phase, V is the volume of the aqueous phase and W is the dry weight of the resin. Sorption isotherms were obtained by plotting metal adsorbed (mmol) per g of resin against concentration of metal remaining in solution at equilibrium. The initial solute concentration ranged from 1 to 4 mmol/l. Fig. 1 shows that both chelating resins sorbed Zn more than Cd and AI. Although the uptake of heavy metals was very similar on both resins. As shown in Fig. 1A and B, the sorption isotherms of uptake metals could
be expressed either as Langmuir or Freundlich isotherms. Metal sorption constants and correlation coefficients for the Zn, Cd and AI on the both chelating resins were calculated from Freundlich as well as Langmuir plots and are given in Table 1. The sorption data on both resins were fitted to both Freundlich and Langmuir isotherm equations. The sorption data in respect of all metals provide an excellent fit to the Freundlich isotherm, giving correlation coefficients in the range of 0.992-0.997 for the Freundlich isotherm and 0.837-0.984 for the Langmuir isotherm for both resins. To test the fit of data, the Freundlich isotherm equation is written as:
M. Ersoz et aL / Reactive Polymers 24 (1995) 195-202
199
Table 1 Parameters of Langmuir and Freundlich isotherms for sorption on DAEC-sporopollenin and bDAEG-sporollenin Metal
Langmuir isotherm Eq. 3 As (mmol/g dry resin)
Freundlich isotherm Eq. 2 Correlation coefficient
Kb
Correlation
k
(1 mmo1-1)
coefficient
(mmol/g dry resin)
0.117 0.133 0.186
0.897 0.980 0.984
0.181 0.176 0.163
1.112 1.138 1.198
0.993 0.997 0.994
0.112 0.164 0.179
0.837 0.976 0.983
0.178 0.167 0.159
1.092 1.178 1.192
0.992 0.995 0.995
DAEC-sporopollenin Zn Cd AI
1.801 1.500 1.119
bDAEG-sporopollenin Zn Cd AI
1.855 1.261 1.127
q = kC 1In
(2)
2.0
• Cu A Ni
where k and n are empirical parameters. The Langmuir isotherm is written as: C/q = 1/KbA, + C/As
(3)
where the parameters Kb and A, are the sorption binding constant (1/mmol) and saturation capacity (mmol metal/g dry wt. of resin), respectively. The Langmuir and Freundlich isotherm parameters were determined by least-squares fit of the sorption data in Fig 1. Equilibrium distribution of metals was measured in the sorption on DAEC and bDAEGsporopollenin resins from aqueous solutions. Figs. 2 and 3 show the relationship between the equilibrium pH and distribution coefficient D. The distribution ratios of all metals increase with increasing pH after passing through a maximum (pH ~8), then level off. The characteristic curves are analogous to each other, exhibiting a strong pH dependence as Figs. 2 and 3 illustrate, although the sorption characteristics have shifted to a higher pH region. Metal-ligand complexes of sporopollenin were prepared from sporopollenin (Lycopodium clavatum), ethylenediamine, bromoacetic acid and chloroglyoxime. Ethylenediamine complexes possess a very stable structure and have a very minor dissociation tendency, and they act as suitable functional groups for a ligand exchange matrix [15]. Oxime functional group resins are,
1.0
2
0.0
-1.0
i
i
J
i
i
2
4
6
8
10
pH
2.0
• Zn •
Cd
o AI
1.0
2
0.0
-1.0
i
i
i
i
i
2
4
6
8
10
pH
Fig. 2. The distribution coefficients of metals on the DAECsporopollenin as a function of pH at a concentration of 10-3 M.
200
M. Ersoz et al./ Reactive Potymers 24 (1995) 195-202
2.0
• Cu
1.0
10 -3 M. At low pH values the sorption of metal ions was low. At low pH values the electrostatic repulsion between the complex and the metal ions prevents their sorption. The amount of the sorbed metal at pH 8-10 increases in the order Cu > Ni > Zn > Cd > A1 for DAEC and Ni > Cu > Zn > Cd > A1 for bDAEG. This order is determined by many factors, the most significant of which are: ionic potential q/r (q is the ionic charger, r is the ionic radius), chemical properties, ionic radius and hydrolysis. The results and analysis presented here indicate that the metal-ligand complexes of sporopollenin show an ability to sorb metal ions from aqueous solution with increasing pH. It is noteworthy that the sorption of metallic ions increased considerably in the range of pH 6-10. This high sorption ability of the resin may be due to the formation of metal chelate in the carboxyl groups with the coordinations of the nitrogen atoms in the glyoxime and ethylene diamine. It was mentioned above that the metal-ligand complex resins contain carboxyl and phenolic groups. Metal ion sorption is unfavorable at the lower pH value of 3 since this is below the dissociation constant pK value of the functional groups of carboxyl and phenolic. At near-neutral and alkaline pH values, i.e. close to and above the pK of carboxyl and phenolic groups, the sorption of the metal is appreciable. However, the sorption with these resins takes place at a much higher pH for all metal ions, which may be attributed to the large difference between the acid dissociation constant of the alcoholic hydroxyl group of carotenoid ester unit of sporopollenin and that of the carboxyl group. Glyoxime and carboxylic acid well preferably be a multidentate ligand with a metal ion. From the above-mentioned cases the following conclusion can be drawn: the uptake efficiency of metal will depend preferentially on the type of forces (coordination of metal to the donor atom or electrostatic attraction) that prevail between ligand and metal in the complex compound. These resins show high stability towards concentrated m
o _.1
0.0
-1.0
i
i
i
i
w
2
4
6
8
10
~ 6
, 8
, 10
pH 2.0
.J:~
•
Zn
•
Cd
o
AI
1.0
0.0
-1.0
, 0
, 2
, 4 pH
Fig. 3. T h e distribution coefficients of metals on the b D A E G sporopollenin as a function of p H at a concentration of 10 -3 M.
in fact, solvent impregnated resins and differ from the conventional chelating ion-exchange resins, which contain chelating ligands covalently bonded to a polymeric matrix [16]. Glyoxime complexes especially dichloro-antiglyoxime possess strong metal-binding properties and selectivities towards transition metals which are capable of undergoing incorporation in a resin matrix [15]. The resin readily sorbs various kinds of metal ions in a 10-3 mol/1 aqueous solution with a pH range of 2-10, and distribution coefficients (showing the variation in sorption with pH) are presented in Figs. 2 and 3 for heavy metal ions. In each case the initial cation concentration was
M. Ersoz et al./ Reactive Polymers 24 (1995) 195-202
acids and bases during regeneration and, in turn, retain their high capacity for heavy metals, and are cheaper and easier to prepare than many commercial resins. They possess higher selectivity, which makes them more versatile ion exchangers for industrial purposes. These resins are particularly suited to this application because optimum metal binding occurs in the pH range 6-8. Heavy metal cations are taken up by coordination with the donor nitrogen atoms of the functional group of the glyoxime and nitrogen and oxygen donor atoms of the functional groups of the carboxylated resin, thus creating very strong coordination compounds in the resin phase. Electrostatic attractive forces between metal and carboxyl or hydroxyl groups prevail in a complex formation. In the case of glyoxime and bromoacetic acid, the coordination bonds between metal and N-donor atoms play a very important part in the overall complex stability. More commonly used is the iminodiacetate chelating resin, Chelex-100, but diffusion in and out of this resin is slow and chromatographic performance is poor. Furthermore, the ligand binding capacity is limited by the coordination of the metal ion to the resin functional group. The precise determination of the coordination behavior of the functional group towards metal ions and the geometry around the metal ion is essential for the further development of metal-ion selective ion-exchange resins. A further experiment was attempted to compare the sorption equilibria of Zn(II), Cd(II) and AI(III) as a function of temperature. Bearing in mind the importance of temperature in the study of sorption of trace metals, the present work was initiated with the aim of having a thermodynamic approach for trace metal sorption of sporopollenin derivatives. It was decided to conduct an experiment under controlled conditions to study how the different temperatures affect the sorption of heavy metals in both resins and the possible mechanisms controlling their sorption in metal-ligand complexes. The effectsof temperature on the sorption
201
2.0
1.5
~Z
1.2
o
0.5
0.4
0.0
285
295
305 Temperature
t
i
315
325
315
325
("K)
S
2.0
1.6
~Z
1.2
o
0.~
0.4
0.0
, 285
295
305 Temperature ('K)
Fig. 4. Sorptionof zinc (e), cadmium(A) and aluminum( • ) on to DAEC-sporopollenin (A) and bDAEG-sporopollenin (B) as a function of temperature at a concentration of 10 -3 M.
of metal ions by metal-ligand complexes of sporopollenin derivatives are represented in Fig. 4, by plotting the distribution coefficient of the amount of metals sorbed in both resins versus different temperatures. Both resins gave a positive response to the increase in temperature with respect to metal sorption. The extent of sorption at a given pH was found to increase with temperature; the magnitude of the increase depending on the cation. The sorption of metal ions increased with increasing temperature. This is based on thermodynamics and sorption reactions for many
202
M. Ersoz et al. / Reactive Polymers 24 (1995) 195-202
divalent cations are endothermic [8,17]. The equilibrium constants for such reactions increase with temperature, i.e., the reaction products (the sorbed species) are favored at higher temperatures. In all systems, the distribution coefficient shifted to higher pH as the temperature increased. Another reason assumed that the surface charge and skeleton of metal-ligand complexes of sporopollenin at a given pH decreases, and hydrolysis of the cations proceeds to a greater extent, as temperature increases. Thus, an increase in temperature will reduce the electrostatic repulsion between the surface and the sorbing species, allowing sorption to occur more readily. In most cases an increase in temperature increased the sorption of cations - a n effect compatible with the effects of temperature on both the rate of reaction and the position of a sorption equilibrium involving cations. In conclusion, it can be seen from Figs. 2 and 3 that these chelating resins are useful over a wide pH range (6-10), and are stable and have strong chelating ability with various kinds of metal ions, and are also reversible over a long period of time. These resins appear promising as preconcentration agents for trace elements, to establish and maintain known ionic activities of metals at constant pH, and for the recovery of metal ions from the secondary effluent of petrochemical plants and industrial waste water.
Acknowledgements The authors wish to thank the Universities of Selcuk and Glasgow for the use of their research facilities.
References [1] R.O. James and TW. Healey, J. Colloid Interface Sci., 40 (1972) 42. [2] R.R. Gadde and H.A. Laitinen, Anal Chem., 46 (1974) 2022. [3] B. Bar-Yosef, Soil Sci. Soc. Am. J., 43 (1979) 1095. [4] D.G. Kinniburgh and M.L. Jackson, Soil Sci. Soc. Am. J., 46 (1982) 56. [5] G.H. Luttrell, Jr., C. More and C.T. Kenner, Anal, Chem., 43 (1971) 1370. [6] J.L. Sides and C.T. Kenner, Anal. Chem., 38 (1966) 707. [7] M.M. Benjamin and J.O. Leckie, J. Colloid Interface Sci., 79 (1981) 209. [8] P.H. Tewari, A.B. Campbell and W. Lee, Can. J. Chem., 50 (1972) 1642. [9] G. Shaw. In: J.B. Harborne (Ed.) Phyto Chemical Phylogeny, Academic Press, London, 1970, Chapter 3. [10] J. Brook and G. Shaw, Nature, 220 (1968) 678. [11] G. Mackenzie and G. Shaw, Int. J. Pep. Prot. Res., 15 (1980) 298. [12] G. Shaw. In: J. Brooks, ER. Grant, M. Muir, E Van Gijzel and G. Shaw (Eds.) Sporopollenin, The Chemistry of Sporopollenin. Academic Press, London, 1971, p. 305. [13] M. Ersoz, E. Pehlivan and S. Yildiz, Ann. Lett., 22 (1989) 1829. [14] E. Pehlivan and S. Yildiz, Anal. Lett., 21 (1988) 297. [15] M. Ersoz, S. Yildiz and E. Pehlivan, J. Chrom. Sci., 31 (1993) 61. [16] S.K. Sahni and J. Reedijk, Coon. Chem. Rev., 59 (1984) 1. [17] N.J. Barrow, J. Soil Sci., 37 (1986) 277.