RIDVAN SAY, SIBEL EMIR. Department of Chemistry, Anadolu University, Eskisehir, Turkey. BORA GARIPCAN. Department of Chemistry, Hacettepe University, ...
Novel Methacryloylamidophenylalanine Functionalized Porous Chelating Beads for Adsorption of Heavy Metal Ions RIDVAN SAY, SIBEL EMIR Department of Chemistry, Anadolu University, Eskis¸ehir, Turkey
BORA GARIPCAN Department of Chemistry, Hacettepe University, Ankara, Turkey
¨ SULEYMAN PATIR Department of Science Education, Hacettepe University, Ankara, Turkey
ADIL DENIZLI Department of Chemistry, Hacettepe University, Ankara, Turkey Received: August 6, 2002 Accepted: December 31, 2002
ABSTRACT: The purpose of this study was to investigate in detail the adsorption performance of poly(2-hydroxyethylmethacrylate– methacryloylamidophenylalanine) [p(HEMA–MAPA)] beads. The metal-complexing comonomer MAPA was synthesized by reacting methacryloyl chloride with phenylalanine. Spherical beads with an average size of 150–200 m were obtained by radical suspension polymerization of HEMA and MAPA, conducted in an aqueous dispersion medium. The beads had a specific surface
Correspondence to: Adil Denizli; e-mail: denizli@hacettepe. edu.tr. Contract grant sponsor: Anadolu University, Research Foundation. Contract grant number: AUAF: 001033.
Advances in Polymer Technology, Vol. 22, No. 4, 355–364 (2003) C 2003 Wiley Periodicals, Inc.
ADSORPTION OF HEAVY METAL IONS area of 19.1 m2 /g, and were characterized by means of swelling studies, FTIR, and elemental analysis. Beads with a swelling ratio of 68% and containing 3.2 mmol MAPA/g were used for the removal of heavy metal ions. Adsorption experiments were conducted with the MAPA-functionalized beads involving the heavy metal ions cadmium, arsenic, chromium, mercury, and lead. Metal adsorption was found to be dependent on the characteristics of the solution (i.e., medium pH and metal concentration) and the type of metals to be adsorbed. We have obtained adsorption capacities equal to 669.4 mg/g for Hg(II), 584.4 mg/g for Pb(II), 268.4 mg/g for Cd(II), 204.1 mg/g for As(III), and 115.2 mg/g for Cr(III). The adsorption capacities on molar basis were in the order of Hg(II) > Pb(II) > Cd(II) > As(III) > Cr(III). Adsorption of heavy metal ions from synthetic wastewater was also studied. The adsorption capacities were 24.5 mg/g for Cd(II), 16.9 mg/g for Cr(III), 144.4 mg/g for Hg(II), 90.9 mg/g for Pb(II), and 8.0 mg/g for As(III) at 0.5 mmol/l initial metal concentration. Naturally, depending on the desired goals, the beads containing metal could be regenerated for appropriate disposal. Our results suggest that p(HEMA–MAPA) beads are good C 2003 metal adsorbers and have a great potential for environmental protection. Wiley Periodicals, Inc. Adv Polym Techn 22: 355–364, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10062
KEY WORDS: Arsenic(III), Cadmium(II), Chelating beads, Chromium(III), Lead(II), Mercury(II), Methacryloylamidophenylalanine
Introduction
I
ndustrial wastewater is one of the major sources of environmental pollution. Among the environmental pollutants, heavy metals have gained relatively more significance in view of their persisting presence and toxicity.1 They can cause mental retardation, cancer, and nervous system damage.2 Heavy metals are nonbiodegradable and, therefore, must be removed from water.3 Heavy metals in wastewater come from battery manufacturing, painting, printing, coal combustion, sewage wastewaters, automobile emissions, mining activities, tanneries, alloy industries and the utilization of fossil fuels, which are just a few examples.4 Various methods of heavy metal removal from wastewaters have been reported in the literature; amongst these methods are precipitation, membrane filtration, neutralization, ion exchange, and adsorption. Among these techniques, adsorption is generally preferred for the removal of heavy metal ions because of its high efficiency, easy handling, and availability of different adsorbents.5 The search for cost-effective adsorbents has also become the focus of attetion of many studies.6 Removal of heavy metal by using chelating polymers would be of great importance in environmental applications.7–18 Several criteria are important
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in the design of chelating polymers with substantial stability for the selective removal of metal ions. These include specific and fast complexation of the metal ions as well as the reusability of the chelating polymeric ligands.12 A large number of polymers incorporating a variety of chelating ligands, such as textile dyes, poly(ethylene imine), iminodiacetate, amidoxime, phosphoric acid, dithiocarbamate, and thiazolidine, have been prepared and their adsorption and analytical properties have been investigated.14–18 Amino acids incorporated polymers and their different applications have been reported in a series of recent publications.19–23 The idea of using different amino acids as metalchelating ligands stems from the fact that these ligands are very reactive with different chemical substances including metal ions. The higher structural flexibility and stability of these ligands as well as significantly lower material and manufacturing costs are also very important.24 Furthermore, amino acid based metal-complexing ligands may be easily modified by existing chemical methods to facilitate elution under mild conditions. For these reasons, recently we have focused our attention on the development of chelating beads for the assembly of a new class of heavy metal adsorbents. This paper describes the synthesis of a new metal-complexing comonomer, methacryloylamidophenylalanine (MAPA), and the preparation and
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ADSORPTION OF HEAVY METAL IONS characterization of poly(2-hydroxyethylmethacrylate–methacryloylamidophenylalanine [p(HEMA– MAPA)] beads for heavy metal removal. The results of the adsorption and elution studies with Cd(II), As(III), Pb(II), Hg(II), and Cr(III) ions are reported here.
Experimental MATERIALS Phenylalanine methyl ester and methacryloyl chloride were supplied by Sigma (St. Louis, MO, USA) and used as received. 2-Hydroxyethyl methacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA) were obtained from Fluka A.G. (Buchs, Switzerland), distilled under reduced pressure in the presence of hydroquinone inhibitor, and stored at 4◦ C until use. Azobisisobutyronitrile (AIBN) was obtained from Fluka (Switzerland). Poly(vinyl alcohol) (PVAL; 98% hydrolyzed) was obtained from Aldrich Chemical Co. (USA) and had a molecular weight of 100.000 by viscosity. All other chemicals used were reagent grade from Merck A.G. (Darmstadt, Germany) unless otherwise noted. All water used in the adsorption experiments was purified using a Barnstead (Dubuque, IA, USA) ROpure LPR reverse osmosis unit with a high-flow cellulose acetate membrane (Barnstead D2731) followed by a Barnstead D3804 NANOpureR organic/colloid removal and ion-exchange packed-bed system. The resulting purified water (deionized water) had a specific conductivity of 18 S/cm.
SYNTHESIS OF 2METHACRYLOYLAMIDOPHENYLALANINE The following experimental procedure was applied for the synthesis of 2-methacryloylamidophenylalanine (MAPA): Phenylalanine (5.0 g) and NaNO2 (0.2 g) were dissolved in 30 ml of K2 CO3 aqueous solution (5%, v/v). This solution was cooled down to 0◦ C. Methacryloyl chloride (4.0 ml) was slowly poured into this solution under nitrogen atmosphere and this solution was then stirred magnetically at room temperature for 2 h. At the end of this chemical reaction period, the pH of the solution was adjusted to 7.0 and subsequently the solution was extracted with ethyl acetate. The aqueous phase was evaporated in a rotary evaporator. The
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residue (i.e., MAPA) was crystallized in ethyl alcohol and ethyl acetate.
PREPARATION OF p(HEMA–MAPA) BEADS HEMA and MAPA were polymerized in suspension by using benzoyl peroxide and poly(vinyl alcohol) as the initiator and the stabilizer, respectively. Toluene and ethylene glycol dimethacrylate (EGDMA) were included in the recipe as the pore former and cross-linker, respectively. A typical preparation procedure is as follows: The suspension medium was prepared by dissolving PVAL (200 mg) in water (50 ml). For the preparation of dispersion phase, HEMA (4.0 ml), EGDMA (8.0 ml), and toluene (12.0 ml) were mixed together and then MAPA (1.0 g) and benzoyl peroxide (100 mg) were dissolved in the resulting homogeneous organic phase. The organic phase was dispersed in the aqueous medium by stirring the mixture magnetically (300 rpm) in a sealed-cylindrical Pyrex polymerization reactor. The contents were heated to the polymerization temperature (i.e., 65◦ C) within 4 h and then the polymerization was conducted for 2 h with a 600 rpm stirring rate at 90◦ C. The resulting polymer beads were extensively washed with ethyl alcohol and water to remove any unreacted monomer or diluent and then stored in distilled water at 4◦ C.
CHARACTERIZATION OF p(HEMA–MAPA) BEADS Surface Area Measurements The surface area of the p(HEMA–MAPA) beads was measured with a surface area apparatus (BET method). The average size and size distribution of the p(HEMA–MAPA) beads were determined by screen analysis performed by using Tyler standard sieves.
Swelling Test Water uptake ratio of the pHEMA and p(HEMA– MAPA) beads was determined using distilled water. The experiment was conducted as follows: Initially, dry beads were carefully weighed before being placed in a 50-ml vial containing distilled water; the vial was then put into an isothermal water bath at a fixed temperature (25 ± 0.5◦ C) for 2 h. The beads were taken out from the water, wiped using a filter paper, and weighed. The weight ratio of dry to wet samples was recorded.
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ADSORPTION OF HEAVY METAL IONS
Elemental Analysis To evaluate the degree of MAPA incorporation the synthesized p(HEMA–MAPA) adsorbents were subjected to elemental analysis using a Leco Elemental Analyzer (Model CHNS-932).
FTIR Studies The characteristic functional groups of the p(HEMA–MAPA) beads were analyzed by using a Fourier transform infrared spectrophotometer (FTIR, 8000 Series, Shimadzu, Japan). The samples were prepared by mixing with approximately 100 mg of dry, powdered KBr (0.1 g, IR Grade, Merck, Germany), and pressed into a pellet form. The FTIR spectrum was then recorded.
Surface Morphology The surface morphology of the beads was examined using scanning electron microscopy (SEM). The samples were initially dried in air at 25◦ C for 7 days before being analyzed. A fragment of the dried beads was mounted on a SEM sample mount and was sputter coated with gold for 2 min. The sample was then mounted in a scanning electron microscope (model: Raster Electronen Microscopy, Leitz-AMR1000, Germany). The surface of the sample was then scanned at the desired magnification to study the morphology of the beads.
HEAVY METAL ADSORPTION FROM AQUEOUS SOLUTIONS Adsorption of heavy metal ions from aqueous solutions was investigated in batch experiments. The effect of the initial heavy metal ion concentration and pH of the medium on the equilibrium adsorption time and adsorption capacity was studied. Aliquots (100 ml) of aqueous solutions containing different amounts of heavy metal ions (in the range of 5–750 mg/l) were treated with the chelating beads. Nitrate salts were used for metal ion source. Adsorption flasks were stirred magnetically at 600 rpm. The suspensions were brought to the desired pH by adding sodium hydroxide or nitric acid. The pH was maintained in a range of ±0.1 units until equilibrium was attained. Investigations were made for pH values in the range of 3.0–7.0. In all experiments, the polymer amount was kept constant at 100 mg for 100 ml solution. Blank trials without polymer beads addition were performed for each tested metal concentra-
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tion. The concentration of the sample was analyzed by graphite furnace atomic absorption spectrophotometer (AAS 5EA, Carl Zeiss Technology) at appropriate intervals. The concentration of the Hg(II) ions in the supernatant liquid was measured by using a graphite furnace atomic absorption spectrophotometer connecting a cold vapor unit. A Photron mercury hallow cathode lamp was used. The instrument response was periodically checked with known metal solution standards. The experiments were performed in replicates of three and the samples were also analyzed in replicates of three. The 95% confidence limits were calculated for each set of samples in order to determine the margin of error. Adsorption experiments were carried out at 20◦ C. The amount of metal ions adsorbed, q (mg/g polymer) was obtained as follows: q = [(C0 − C) · V]/m where C0 and C are the initial and equilibrium concentrations (mg/l), respectively; V is the volume of the aqueous phase (l); and m is the mass of the beads used (g).
HEAVY METAL ADSORPTION FROM SYNTHETIC WASTEWATER Adsorption of heavy metal ions from synthetic wastewater was carried out in a batch system. A solution (20 ml) containing 0.5 mmol/l from each metal ion [i.e., Cd(II), As(III), Pb(II), Cr(III), and Hg(II)] was incubated with the p(HEMA–MAPA) beads at pH 7.0 at room temperature, in flasks, and stirred magnetically at 600 rpm. Synthetic wastewater also contains Ni(II), Zn(II), Fe(II), Co(II), Sn(II), and Ag(I). Concentration of each metal ion in synthetic wastewater is 0.1 mmol/l. To adjust the salinity, 700 mg/l NaCl was added into the synthetic wastewater. After adsorption, the concentration of the metal ions in the remaining solution was determined by AAS as described above.
ELUTION/REUSABILITY STUDIES The elution efficiecy from the p(HEMA–MAPA) beads was measured for all the metals using solutions of the same concentrations as the adsorption experiments. The initial and final concentrations were measured for the adsorption solutions to estimate the amount of metal ion removed. The elution efficiency was calculated by comparing this value
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ADSORPTION OF HEAVY METAL IONS with the amount of metal ion eluted and measured. Elution of the metals from the polymer beads was carried out in 25 ml of 0.1 M HNO3 solution for 30 min. The chelating beads adsorbed metal ions were placed in the elution medium and stirred with a magnetic stirrer at 600 rpm at room temperature. The metal ion concentrations were determined using a graphite furnace atomic absorption spectrometer (GFAAS) according to the guidelines of the manufacturers. To determine the reusability of the chelating beads, consecutive adsorption–elution cycles were repeated five times by using the same chelating beads.
Results and Discussion PROPERTIES OF POLYMER BEADS Suspension polymerization procedure provided cross-linked p(HEMA–MAPA) beads in the spherical form in the size range of 150–200 m. The surface morphology and internal structure of p(HEMA– MAPA) beads are revealed by the micrographs in Fig. 1. As clearly seen here, the beads have a spherical form and a very rough surface because of the pores
that are formed during polymerization. The roughness of the surface should be considered as a factor providing an increase in the surface area. In addition, these pores reduce the mass transfer resistance and facilitate the diffusion of metal ions because of the high internal surface area. This also provides higher metal adsorption capacity. The surface area of the p(HEMA–MAPA) beads was found to be 19.1 m2 /g. The p(HEMA–MAPA) beads are cross-linked hydrogels. They do not dissolve in aqueous media, but will swell by amounts depending on the degree of cross-linking and on the hydrophilicity of the matrix. The equilibrium swelling ratio of the chelating beads used in this study is 68%. Compared with pHEMA systems, the water uptake ratio of the p(HEMA–MAPA) beads is higher. Several possible factors may contribute to this result. First, incorporating MAPA actually introduces more hydrophilic functional groups into the polymer chain, which can attract more water molecules into polymer matrices. Second, copolymerizing MAPA with HEMA could effectively decrease the molecular weight. Therefore, the water molecules penetrate into the entangled polymer chains more easily, resulting in an increase of polymer water uptake in aqueous solutions. It should also be noted that these beads are quite rigid, and
FIGURE 1. SEM micrographs of p(HEMA–MAPA) beads.
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ADSORPTION OF HEAVY METAL IONS strong enough due to highly cross-linked structure, and therefore they are suitable for column applications. As mentioned before, MAPA was selected as the metal-chelating comonomer. In the first step, MAPA was synthesized from phenylalanine and methacryloyl chloride. Then MAPA was incorporated into the bulk structure of the pHEMA beads. The structure of the chelating beads is shown in Fig. 2. To show the incorporation of MAPA within the polymeric structure, FTIR spectra of the pHEMA and p(HEMA–MAPA) were taken (Fig. 3). As shown in Fig. 3, FTIR spectra of both MAPA and p(HEMA– MAPA) have the characteristic stretching vibration band of hydrogen bonded alcohol, O H, around 3440 cm−1 . The FTIR spectrum of p(HEMA–MAPA) has characteristic amide I and amide II absorption bands at 1625 and 1575 cm−1 , respectively. On the other hand, hydrogen bonded alcohol O H stretching band intensity of plain pHEMA is higher than that of p(HEMA–MAPA) beads because of the incorporation of MAPA comonomer in the polymer structure. To evaluate the degree of MAPA incorporation, an elemental analysis of the synthesized p(HEMA– MAPA) was performed. The incorporation of the MAPA was found to be 3.2 mmol MAPA/g from the nitrogen stoichiometry.
ADSORPTION ISOTHERMS In Fig. 4 are shown the Cd(II), As(III), Cr(III), Pb(II), and Hg(II) adsorption isotherms of the metalchelating beads. The amount of metal ions adsorbed per unit mass of the beads increased first with the
FIGURE 2. Molecular structure of p(HEMA–MAPA) beads.
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initial concentration of metal ions and then reached a plateau value, which represents saturation of the active adsorption sites (available and accessible for metal ions) on the beads. The adsorption of Cr(III) reached a saturation level at lower bulk concentrations, i.e., at about 100 mg/l, whereas the adsorption of other ions reached saturation at higher concentration, i.e., at about 500 mg/l. In view of the precipitation possibility of the metal ions we did not increase the initial concentration above 750 mg/l. The binding capacities of the chelating beads are 268.4 mg/g (2.4 mmol/g) for Cd(II), 115.2 mg/g (2.2 mmol/g) for Cr(III), 204.1 mg/g (2.7 mmol/g) for As(III), 584.4 mg/g (2.8 mmol/g) for Pb(II), and 669.4 mg/g (3.4 mmol/g) for Hg(II). This indicates that the affinity of the p(HEMA–MAPA) beads toward the adsorption of Hg(II) was stronger than that toward Pb(II), Cd(II), As(III), and Cr(III). The affinity order of these five types of metal ion adsorption for the single component metal is Hg(II) > Pb(II) > Cd(II) > As(III) > Cr(III). This trend is presented on the mass basis metal adsorption per gram beads and these units are important in quantifying respective metal capacities in real terms. However, a more appropriate approach for this work is to compare metal adsorption on a molar basis; this gives a measure of the total number of metal ions adsorbed, as opposed to total mass, and gives an indication of the total number of attachment sites available on the adsorbent matrix, to each metal. Additionally, the molar basis calculation is the only accurate way of investigating competition in multicomponent metal mixtures. Molar basis units are expressed as mmol per gram of dry-adsorbent. It is evident from the results that the order of capacity of the metal-chelating beads, on molar basis, for the single component metals is Hg(II) > Pb(II) > As(III) > Cd(II) > Cr(III). It should also be noted that the nonspecific adsorption of heavy metal ions onto the pHEMA beads (carrying no MAPA) was also determined under the same experimental conditions. The heavy metal ions adsorption on the pHEMA beads are very low, i.e., about 0.75 mg/g for As(III), 12.3 mg/g for Pb(II), 0.93 mg/g for Cd(II), 3.1 mg/g for Cr(III), and 2.2 mg/g for Hg(II). Note that pHEMA beads are both swellable and porous, and therefore can absorb heavy metal ions also within the pores of the swollen beads. In addition, the hydroxyl and carbonyl groups of HEMA may interact with heavy metal ions (similarly to the solvatation with water), which may also cause this nonspecific adsorption.
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ADSORPTION OF HEAVY METAL IONS
FIGURE 3. FTIR spectrum of pHEMA and p(HEMA–MAPA) beads.
EFFECT OF pH ON METAL BINDING Metal ion adsorption on chelating adsorbents is pH-dependent. Ionization of the metal-complexing ligand and the stability of the metal–ligand complexes change with pH.25–27 Furthermore, the precipitation of the metal ions are affected by the concentration and form of soluble metal species. The solubility of metal ions is governed by the concentration of hydroxide or carbonate ions. Precipitation of metal
FIGURE 4. Adsorption isotherms of heavy metal ions onto p(HEMA–MAPA) beads. MAPA loading: 3.2 mmol/g; pH: 6.0; T: 20◦ C.
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ions becomes significant at approximately pH 7.0 for all metal ions.28–30 The theoretical and experimental precipitation curves indicate that precipitation begins above this pH, and may also depend on the concentration of metal ions in the adsorption medium. Therefore, in our study, in order to establish the effect of pH on the adsorption of metal ions onto the chelating beads, we repeated the batch equilibrium studies at different pHs within the range 3.0–7.0. In this group of experiments, the initial concentration of metal ions was 50 mg/l for all metal ions. Figure 5 shows the pH effect. The adsorption capacities of the chelating beads are 45 mg/g for As(III) (0.6 mmol/g), 211.3 mg/g for Pb(II) (1.0 mmol/g), 83 mg/g for Cr(III) (1.6 mmol/g), 75.6 mg/g for Cd(II) (0.67 mmol/g), and 193.6 mg/g for Hg(II) (0.96 mmol/g). It is interesting to note that the newly synthesized metal-chelating beads had the strongest affinity for Cr(III) ions at low metal ion concentrations. The affinity order of metal ions at initial concentration of 50 mg/l is Cr(III) > Pb(II) > Hg(II) > Cd(II) > As(III). Newly synthesized p(HEMA–MAPA) chelating beads exhibited a low affinity for heavy metal ions in acidic conditions (pH < 4.0), a somewhat higher affinity between pH 5.0 and 7.0. The difference in adsorption behavior of heavy metal ions can be explained by the different affinity of heavy metal ions for the donor atoms (i.e., oxygen and nitrogen) in the metal-complexing amino acid-ligand/comonomer MAPA. A difference in coordination behavior is
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ADSORPTION OF HEAVY METAL IONS single solutions. The adsorption capacities are 8.0 mg/g for As(III), 16.9 mg/g for Cr(III), 24.5 mg/g for Cd(II), 90.9 mg/g for Pb(II), and 144.4 mg/g for Hg(II). The chelating beads exhibit the following metal ion affinity sequence on molar basis: Hg(II) > Pb(II) > Cr(III) > Cd(II) > As(III). In this case, the chelating beads adsorb also other metal ions, i.e., Ni(II), Zn(II), Fe(II), Co(II), Sn(II), and Ag(I). The presence of other metal ions in the synthetic wastewater decreases the adsorption capacities of chelating beads for Cd(II), As(III), Cr(III), Pb(II), and Hg(II) ions.
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FIGURE 5. Effect of pH on adsorption of metal ions. MAPA loading: 3.2 mmol/g; initial concentration of metal ions: 50 mg/l; T: 20◦ C.
probably also a case for the MAPA ligand to provide a relatively high adsorption of metal ions at high pHs, under noncompetitive adsorption conditions.
ADSORPTION FROM SYNTHETIC WASTEWATER The adsorption capacity of the p(HEMA–MAPA) beads from synthetic wastewater for Cd(II), As(III), Cr(III), Pb(II), and Hg(II) is reported in Table I. It is worth noting that the adsorption capacity of the p(HEMA–MAPA) beads from synthetic wastewater for all metal ions is were much lower than for the
The repeated use (i.e., regenerability) of the polymer beads is likely to be a key factor in improving process economics. Elution of the adsorbed metal ions from the p(HEMA–MAPA) beads was also studied in a batch experimental setup. The p(HEMA– MAPA) beads loading the maximum amounts of the respective metal ions were placed within the elution medium containing 0.1 M HNO3 and the amount of metal ions desorbed in 1 h was measured. The elution efficiency was then calculated. Elution efficiencies were very high (up to 99.3%) with the elution agent and conditions used for all metal ions. To obtain the reusability of the p(HEMA–MAPA) beads, adsorption–elution cycle was repeated five times by using the same adsorbent. As shown in Table II, adsorption capacity of the adsorbent for all metal ions did not significantly change during the repeated adsorption–elution cycles.
Conclusion TABLE I Competitive Metal Ion p(HEMA–MAPA) Beadsa
Adsorption
Capacity
of
Adsorption Capacity Metal Ions
mg/g
mmol/g
Cd(II) Cr(III) Hg(II) Pb(II) As(III)
24.5 16.9 144.4 90.9 8.0
0.22 0.33 0.72 0.44 0.11
a
Concentration of each metal ion: 0.5 mmol/l; pH: 7.0, T: 20◦ C. Each data is average of five parallel studies.
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Heavy metal ions are known to be toxic and especially cadmium, arsenic, mercury, chromium, copper, lead, nickel, selenium, silver, and zinc are released into the environment in quantities that pose a risk to living systems. Adsorption technology allows the use of polymer-based adsorbents for rapid, costeffective, and selective heavy metal removal. In this study novel metal-chelating beads were prepared and were applied to the removal of arsenic, lead, mercury, chromium, and cadmium ions from aqueous solutions, including synthetic wastewater. We have shown that these MAPA-functionalized beads have extremely high capacity for heavy metals. This
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ADSORPTION OF HEAVY METAL IONS TABLE II Heavy Metal Ions Adsorption Capacity of Chelating Beads After Repeated Adsorption–Elution Cycle Hg(II) Cycle Adsorption No. (mg/g) 1 2 3 4 5
669.4 ± 5.6 665.3 ± 5.2 663.5 ± 4.9 660.3 ± 5.4 654.2 ± 4.8
Pb(II)
Cd(II)
As(III)
Cr(III)
Elution (%)
Adsorption (mg/g)
Elution (%)
Adsorption (mg/g)
Elution (%)
Adsorption (mg/g)
Elution (%)
Adsorption (mg/g)
Elution (%)
98.5 ± 1.6 97.2 ± 1.1 97.8 ± 1.5 98.5 ± 1.4 98.3 ± 1.2
584.4 ± 4.5 580.3 ± 4.7 577.6 ± 4.9 575.6 ± 4.8 572.3 ± 4.5
97.5 ± 1.5 98.3 ± 1.0 98.5 ± 1.1 98.7 ± 1.9 98.0 ± 1.1
268.4 ± 4.0 265.6 ± 4.5 261.9 ± 4.7 260.5 ± 4.5 256.7 ± 4.6
98.0 ± 1.0 98.2 ± 1.8 98.5 ± 1.1 99.0 ± 1.4 99.3 ± 1.8
204.1 ± 3.4 201.6 ± 3.6 197.5 ± 3.7 195.5 ± 3.5 192.6 ± 3.4
98.5 ± 1.7 98.2 ± 1.2 98.8 ± 1.8 97.9 ± 1.6 97.5 ± 1.6
115.2 ± 2.6 110.7 ± 2.8 108.5 ± 2.9 105.5 ± 2.2 103.2 ± 2.0
97.6 ± 1.4 99.4 ± 1.2 99.2 ± 1.5 97.4 ± 1.6 98.3 ± 1.4
Initial concentrations of metal ions 50 mg/l; pH: 6.0; T: 20◦ C.
novel approach for the preparation of metal-chelatig matrix has also many advantages over conventional techniques, which require the activation of the matrix for metal-complexing ligand immobilization. In this procedure, MAPA acts as the metal-complexing group, and there is no need to activate the matrix for the metal-complexing ligand immobilization. MAPA is polymerized with HEMA and no leakage of the ligand is necessary. Some important results are as follows: (1) The adsorption capacities of the chelating beads are 268.4 mg/g for Cd(II), 204.1 mg/g for As(III), 115.2 mg/g for Cr(III), 584.4 mg/g for Pb(II), and 669.4 mg/g for Hg(II). (2) The affinity order of metal ions on molar basis is as follows: Hg(II) > Pb(II) > As(III) > Cd(II) > Cr(III). The adsorption capacity increased with increasing pH, reaching plateau values at around pH 5.0. Adsorption of heavy metal ions from synthetic wastewater was also studied. The adsorption capacities are 24.5 mg/g for Cd(II), 16.9 mg/g for Cr(III), 144.4 mg/g for Hg(II), 90.9 mg/g for Pb(II), and 8.0 mg/g for As(III) at 0.5 mmol/l initial metal concentration. Repeated adsorption and elution operations showed the feasibility of these newly synthesized chelating beads for heavy metal adsorption. These results suggest that p(HEMA–MAPA) beads can be good metal adsorbers and have great potential applications in environmental protection.
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