Polymer Structure and Metal Ion Selectivity in Silica Polyamine

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Ind. Eng. Chem. Res. 2008, 47, 6765–6774

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Polymer Structure and Metal Ion Selectivity in Silica Polyamine Composites Modified with Sodium Chloroacetate and Nitriloacetic Acid (NTA) Anhydride Mark A. Hughes, Jessica Wood, and Edward Rosenberg* Department of Chemistry, UniVersity of Montana, Missoula, Montana 59812

Previously, silica polyamine composite (SPC) materials (BP-1 and WP-1) containing amine chelating groups were prepared using two polyamines, polyallylamine (PAA), and polyethyleneimine (PEI). In this paper the amine ligands of BP-1 and WP-1 were modified with chloroacetate, yielding the new SPC materials BP-2 and WP-2. We have found that the acetate groups were bound to the amine groups to a greater extent on the SPC prepared using PAA (BP-1) relative to the SPC prepared with PEI (WP-1). BP-2 was selective for Cu2+ over other divalent metal ions from polymetallic solutions in the pH range of 1 to 3. In contrast, WP-2 was selective for Cu2+ over other divalent metal ions at pH 1 only and coloaded significant amounts of Ni2+ at pH 2 and pH 3. Thus, polyamine structure impacts the metal selectivity of the resultant SPC materials, BP-2 and WP-2. Two novel SPCs were prepared from nitriloacetic acid (NTA) anhydride using BP-1 and WP-1, yielding BP-NT and WP-NT, respectively. The resultant materials possess a unique chelating ligand, in which an iminodiacetic acid (IDA) group is covalently bonded to the SPC amine groups via an amide bond. The two materials (BP-NT, WP-NT) have similar metal selectivity profiles indicating that polyamine structure is not influential. Increased ligand denticity and the amide linker prevent the polymer from playing a large role in selectivity. The resulting materials have the ability to remove divalent and trivalent metal ions from low pH aqueous solutions. These materials can be regenerated by treatment with acid solution and showed no evidence of amide bond hydrolysis under acidic conditions. 1. Introduction The selective removal of cations from aqueous solution is a topic of significant industrial and environmental importance.1,2 Continued research has demonstrated that solid phase ion exchange (IX) materials are useful for such applications.3–6 The modification of silica gel surfaces with polyamines has received considerable attention recently.7–9 The patented silica polyamine composites (SPCs) chelating materials discussed herein differ from the previous reports in that extensive effort has been put into making their synthesis and modification efficient enough for commercial production and real world applications.10 These SPCs are comprised of a water soluble polyamine covalently attached to amorphous silica gel. Polyallylamine (PAA) and polyethyleneimine (PEI) have been used for the preparation of SPCs.11 These PAA and PEI composite materials have been arbitrarily dubbed BP-1 and WP-1, respectively. The immobilization of the polyamine is facilitated by the monolayer polymerization of an optimized mixture of two trifunctional silanes (methyl-trichloro-silane and chloropropyl-trichloro-silane) on hydrated silica gel (Scheme 1). We have previously reported a thorough investigation of the nature of the attachment of the polyamine to the functionalized silica gel.12 SPC chelating IX materials possess several advantages over conventional crosslinked polystyrene chelating IX materials.10–12 SPCs show no evidence of shrink/swell, have a high metal ion adsorption capacity per gram of SPC, tolerate elevated temperature, possess long operational lifetimes, and display superior mass transfer kinetics.10b The polymer amine groups of SPCs present sites for further modification with metal selective chelating groups. Pendant functional groups can provide metal ion selectivity if the amine modifying ligand is chosen to resemble a chelating group that has been previously shown to have an exceptionally * To whom all correspondence should be addressed. Tel.: 1-406243-2592. Fax: 1-406-243-4227. E-mail: edward.rosenberg@ mso.umt.edu.

high stability constant for a given metal or group of metals.13 SPCs have been successfully modified to yield materials possessing picolylamine, 7-amino-methyl-8-hydroxyquinoline, amino-methyl-phosphonate, amino-acetate, and ethylenediamine tetraacetic acid functional groups (Scheme 2).14 In general, solid phase sorbents containing immobilized amino acid functional groups, such as iminodiacetic acid (IDA), have been particularly useful for the extraction of divalent metal ions from aqueous media.15 Immobilized amino acid functional groups form stable complexes with many divalent and trivalent metal ions at low pH ( Zn2+ > Co2+. For comparison, a similar pH profile was obtained for a commercially available IDA functionalized cross-linked polystyrene resin, Amberlite IRC 748 (Figure 2c). The trend for Amberlite

Figure 1. Initial 400 min of Cu2+ copper batch kinetic profiles for BP-2 and WP-2.

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Figure 3. BP-2 Cu(II)/Ni(II) dynamic separation: 1.5 g/L each metal ion and 0.1 mL/min flow rate. (a) Feed solution at pH 1. (b) Feed solution at pH 3.

Figure 2. (a) First row transition metal ion pH profiles for BP-2. (b) First row transition metal ion pH profiles for W-2. (c) First row transition metal ion pH profiles for Amberlite IRC 748. Table 2. Separation Factors for Batch Separations of Cu2+ from Ni2+ from Solutions Containing 1 g/L Cu2+ and 1 g/L Ni2+ separation factor SPC

pH 1

pH 2

pH 3

BP-2 BP-NT

3.53 35.1

26.79 12.98

44.62 13.74

WP-2 WP-NT

6.21 34.2

9.38 17.42

10.54 12.80

IRC-748, which contains isolated IDA functional groups only, is Cu2+, Fe3+ . Ni2+, Zn2+, Co2+. The major observation from this data is that BP-2 does not sequester Ni2+, Zn2+, and Co2+ in the pH range studied. It is also notable that the pH profiles of BP-2 and IRC-748 are similar with the exception of the data at pH 2. This is in agreement with the presence of IDA groups in BP-2 as indicated by elemental analysis. Table 2 provides the batch separation factors (the equilibrium ratio of the copper to nickel adsorbed by the SPC at a given pH from a solution

containing equal amounts of each metal) for the batch adsorption of Cu2+ and Ni2+ from a solution that contains 1 g/L of both metal ions for WP-2 and BP-2. A greater selectivity factor indicates increased preference for Cu2+ relative to Ni2+. At pH 1 the order of preference for Cu2+ over Ni2+ is WP-2 > BP-2. At pH 2, the order is BP-2 . WP-2, and at pH 3 BP-2 . WP2. The pH of the solution impacts the batch separation factor for Cu2+ and Ni2+ to a larger degree for BP-2 relative to WP2. This dramatic change in selectivity with pH is surprising considering the similar functionality of these two composites. To further investigate the differences between BP-2 and WP2, column studies for the separation of Cu2+ and Ni2+ using BP-2 and WP-2 were conducted as a function of pH. In general column studies provide a better description of how a material will perform in an actual application, relative to batch experiments. Packed columns of BP-2 and WP-2 were supplied an influent solution containing both Cu2+ and Ni2+ at pH values of 1, 2, and 3. For comparison, the breakthrough profiles for BP-2 for pH 1 and pH 3 are shown in parts a and b of Figure 3, respectively). The breakthrough profiles for WP-2, for pH 1 and pH 3, are shown in parts a and b of Figure 4, respectively. The initial concentration of each metal ion was 1.5 g/L Cu2+ and 1.5 g/L Ni2+. Cu2+ and Ni2+ were completely recovered (eluted) from the column using a 2 M sulfuric acid strip solution. In terms of Cu2+ purity in the recovered acid solution, WP-2 performed best at pH 1 where Cu2+ purity in the acid strip was >99%. For WP-2 at pH 2, the Cu2+ purity in the recovered solution decreased to 87%. At pH 3, the Cu2+ purity in the recovered solution was 86% for WP-2. In contrast, BP-2 did not adsorb Ni2+ at any pH in the range studied. BP-2 showed a slight affinity for Cu2+ at pH 1, which increases dramatically with pH. For BP-2, the Cu2+ purity in the recovered solution after elution was >99% for each pH studied, but the loading of copper was very low at pH 1 as evidenced by the early breakthrough (Figure 3). In summary, WP-2 shows the best selectivity for Cu2+at pH 1, while BP-2 performs best for Cu2+

Ind. Eng. Chem. Res., Vol. 47, No. 17, 2008 6771

Figure 4. WP-2 Cu(II)/Ni(II) dynamic separation: 1.5 g/L each metal ion and 0.1 mL/min flow rate. (a) Feed solution at pH 1. (b) Feed solution at pH 3.

Figure 5. Concentration dependent sorption isotherms for Cu2+ onto BP-1 and WP-1 at pH 2: (a) Cu2+ and (b) Ni2+. Table 3. Langmuir and Freundlich Parameters for BP-2 and WP-2

2+

at pH 2 and 3. A greater pH dependence for Cu for BP-2, relative to WP-2, and negligible affinity for Ni2+, is indicative of a lower formation constant for both metals. WP-2 is somewhat less dependent on pH and has an appreciable affinity for Ni2+. As a result of its branched polyamine structure, the potential coordination groups (amine groups and amino-acetate groups) of WP-2 are more densely packed than those of BP-2 (Scheme 5). A higher functional group density for WP-2 should result in metal ion coordination of higher denticity than for BP2. BP-2 is constructed from a linear polyamine containing a large fraction of isolated IDA groups separated by five carbon atoms. Cooperation between ligand functional groups is limited to a single IDA ligand with a maximum denticity of 3. The higher denticity of the WP-2 sorption sites results in a greater formation constant (the chelate effect), especially for those ions that prefer to form higher coordinate complexes such as Fe3+ and Ni2+. The lower denticity of the BP-2 coordination sites favors metal ions that prefer low coordination complexes such as Cu2+. This explains the increased affinity for Fe3+ and Ni2+ for WP-2 and the preference for Cu2+ of BP-2. Figure 5a,b illustrates the adsorption isotherms for BP-2 and WP-2 with Cu2+ and Ni2+, respectively, at pH 2. It is immediately clear that for all concentrations WP-2 removes a greater fraction of Cu2+ than BP-2. Furthermore, it is apparent that BP-2 removes only negligible amounts of Ni2+ whereas WP-2 removes substantial amounts of Ni2+. Metal ion sorption by chelating materials has commonly been modeled using the theoretical Langmuir adsorption model and the empirical Freundlich model.11,21 The Langmuir model provides an estimate of the theoretical quantity of surface sites available for sorption, Qmax (mmol/g), and the driving force for the sorption process (Kads) for the coordination of a metal ion onto the chelating surface. The full derivation of the Langmuir

Langmuir

Freundlich

metal Qm Kads ion (mmol/g) (mmol/L)-1

A

R2

(mmol1-1/n g-1 L1/n)

1/n

R2

BP-2 Cu2+ Ni2+

0.48

0.48

0.99 0.48

Cu2+ Ni2+

0.54 0.41

2.92 2.03

0.99 0.99

3.08

0.33 0.91 0.55

8.81 5.99

0.22 0.91 0.23 0.93

WP-2

equation can be found elsewhere.20 The rearranged Langmuir relationship is shown in eq 3. Ce/Qe)1/QmaxKads + Ce/Qmax

(3)

Ce represents the concentration of metal ions in solution at equilibrium (mmol/L), and Qe is the concentration of metal ions adsorbed onto the composite (mmol/g). Qm can be calculated from the slope of the straight line for a plot of Ce/Qe versus Ce. The constant Kads can be derived from the y intercept of the same straight line (1/QmaxKads). The Freundlich sorption model is an empirically derived model that describes the relationship between concentration of metal ions in solution at equilibrium (Ce) and the concentration of metal ions adsorbed onto the composite (Qe) at low metal ion concentrations. The equation is exponential in nature as shown in eq 4. Qe ) ACe1/n

(4)

The constant A is defined as the adsorption coefficient and represents the quantity of metal adsorbed (mg/g) at unit equilibrium concentration. The value 1/n is a measure of the surface heterogeneity. Values of 1/n above 1 indicate cooperative adsorption whereas a value below 1 indicates normal Langmuir (monolayer and noncooperative) adsorption. A plot of log Qe

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versus log Ce allows the calculation of the parameters A and 1/n from the y intercept and slope of the linear regression, respectively. Table 3 lists the Langmuir and Freundlich parameters derived from these plots. As a result of the negligible affinity of BP-2 for Ni2+, the Langmuir and Freundlich models were not applicable. This is reflected in an R2 value of 0.44 and 0.55 for the plots modeling the sorption of Ni2+ by BP-2. In contrast the R2 values arrived at for Ni2+ adsorption onto WP-2 indicate that both the Langmuir and Freundlich models are applicable to Ni2+ adsorption. Also, both models are adequate for the sorption of Cu2+ by BP-2 and WP-2. The excellent correlation with the Langmuir model indicates monolayer and noncooperative sorption. Moreover, the model provides a measure of the driving force of the sorption process (Kads) for a given metal as well as an approximation to the theoretical number of sorption sites on the surface (Qmax). Qmax is larger for Cu2+ with both BP-2 (0.48 mmol/g) and WP-2 (0.54 mmol/g) than for Ni2+ with WP-2 (0.41 mmol/g). In the case of WP-2, Kads is significantly higher for Cu2+ and Ni2+ (Table 3). The Freundlich parameter 1/n is less than 1 in all cases, which confirms noncooperative sorption. The parameters derived from the Langmuir and Freundlich models also indicate significantly stronger sorption for WP-2 relative to BP-2. A larger equilibrium constant indicates a more stable complex. A more stable complex results from the formation of a chelate of larger denticity, as described above for WP-2. This is the well-known entropically driven “chelate effect.” A more stable complex can also result when a smaller conformational change (less reorganization) is required for complex formation. Thus, WP-2 must be somewhat templated for the sorption of Ni2+, relative to BP-2, with regard to the number of coordinating ligands and the inherent conformation of the PEI ligand system. These factors contribute to a more positive entropy change for complex formation and constitute a kind of polymer imprinting for WP-2 with regard to accommodating metals with a preference for higher coordination numbers. This is apparently true even at low pH values where the amine ligands are protonated. 3.3. WP-NT and BP-NT. To the best of our knowledge there have been no reports in the literature of the use of NTA anhydride as a reagent for the preparation of a chelating IX material for the selective removal of heavy metal ions from aqueous solution. Elemental analysis of products obtained from the reaction of BP-1 and WP-1 indicate that, as for the reaction with sodium chloroacetate, the loading of NTA anhydride was much higher for BP-1 (Table 1). Indeed for this bulkier ligand the difference in ligand loading between WP-1 and BP-1 is much larger, while the fraction of modified amines is much smaller than for the chloroacetate modifier. Batch studies were performed to characterize BP-NT and WPNT. Figures 6 and 7 display batch pH profiles for BP-NT and WP-NT for several trivalent and divalent metal ions, respectively. In general the quantity of metal ion adsorbed per gram of modified SPC is greater for BP-NT than for WP-NT undoubtedly due to the higher loading. It is clear from the pH profiles that for divalent ions the order of preference for both BP-NT and WP-NT is Cu2+ > Ni2+ > Zn2+, Co2+. Further it is evident that the specific selectivity for trivalent metal ions tested is Ga3+ > Fe3+ > Eu3+ > Al3+ for both materials. These selectivity trends are similar to those previously reported for the EDTA modified BP-ED and WP-ED.11 However, the sorption capacity for Ni2+ is significantly lower than that for BP-ED and WP-ED.11 This is true for Zn2+ and Co2+ also. Although the order of preference for the divalent metal ions is

Figure 6. (a) Divalent transition metal ion pH profiles for BP-NT. (b) Trivalent transition metal ion pH profiles for BP-NT.

Figure 7. (a) Divalent transition metal ion pH profiles for WP-NT. (b) Trivalent transition metal ion pH profiles for WP-NT.

similar to that in BP-ED and WP-ED, the differential selectivity between the metals is much larger in the case of BP-NT and WP-NT. This is probably due to the lower denticity of the NTA ligand relative to the EDTA ligand which allows for better discrimination between metals of similar charge but with slightly different ionic radii. Breakthrough profiles for slurry packed columns (typically 6.7-7.0 mL) of BP-NT and WP-NT are shown in Figure 8. Each SPC was challenged with an aqueous solution containing

Ind. Eng. Chem. Res., Vol. 47, No. 17, 2008 6773 Table 5. Acid and Base Stability Study of Amide Linked Composites Cu2+ adsorbed (mg/g)

Figure 8. Cu(II)/Ni(II) dynamic separation: 1.5 g/L each metal ion and 0.1 mL/min flow rate. Feed solution pH ) 1.5. (a) BP-NT profiles. (b) WP-NT profiles. Table 4. Langmuir and Freundlich Parameters for BP-NT and WP-NT Langmuir metal Qm Kads ion (mmol/g) (mmol/L)-1

Freundlich A

R2

(mmol1-1/n g-1 L1/n)

1/n

R2

BP-NT Cu2+

0.78

1.11

0.99

7.88

0.24 0.99

7.96

0.28 0.99

WP-NT Cu2+

0.64

1.13

0.99

1 g/L of Cu2+ and Ni2+ at pH 1.5. The data illustrate the selective removal of copper from nickel. The Ni2+ is initially adsorbed by the SPC; however, it is then displaced by copper as the experiment proceeds. This is evident from the C/C0 value for the nickel profile, which exceeds unity. The copper can be removed and the material regenerated by the use of 2 M sulfuric acid. The resulting solutions were 99.9% pure with respect to copper. There is no detectable difference between BP-NT and WP-NT under the conditions employed. Langmuir and Freundlich models were developed for both BP-NT and WP-NT at pH 2. The parameters derived from each model were collected and are displayed in Table 4. The R2 values show that the data fit both models. As expected the 1/n Freundlich parameter indicates noncooperative metal binding in a monolayer arrangement. The maximum number of theoretical sorption sites is greater for BP-NT than for WP-NT which again fits both the ligand loading and metal ion sorption pH profile data. Interestingly, the Langmuir equilibrium parameters (Kads) for both BP-NT and WP-NT with copper are very similar, being 1.11 mmol/L-1 and 1.13 mmol/L-1, respectively. The sorption of Cu2+ on BP-NT and WP-NT must have similar formation constants. This contrasts with BP-2 and WP-2. Thus, it can be concluded that, for Cu2+ at pH 2, there is no significant effect of the polyamine on sorption. This result also suggests that Cu2+ sorption is similar for both BP-NT and WP-NT

SPC

no treatment

72 h acid

72 h base

BP-2 BP-NT WP-NT

24 60 53

29 61 53

31 69 55

because the coordination geometry, square planar, is satisfied solely by this tetra-dentate ligand. Metals that prefer octahedral geometry should show very different Langmuir equilibrium constants for BP-NT and WP-NT. 3.4. Stability of SPCs with Amide Bound Ligands. In previous investigations the long-term stability of an SPC material was assessed by subjecting a packed column of the materials to multiple load/strip cycle testing. WP-1 has experienced 3000-10 000 cycles without any evidence of material degradation.10b,22,23 For most of the SPCs synthesized to date, metal selective functional groups are attached to either BP-1 or WP-1 by the formation of a robust C-N bond between the polyamine and the functional group.10,22 However, for BP-NT, WP-NT, BP-ED, and WP-ED the functional group is appended to the polymer by an amide linkage. It is well-known that amides are susceptible to acid and base catalyzed hydrolysis. During a typical process cycle SPCs are fed with metal ion solutions that are typically in an aqueous solution of pH < 3. Thus the stability of these SPCs to continued exposure to moderate to strong inorganic acid must be assessed. Samples of BP-NT, WP-NT, and BP-2 were each treated with a 4 M H2SO4 solution for 72 h. To simulate long-term exposure to alkali conditions each sample was also treated with a 4 M NH4OH solution for 72 h. BP-2 was used as a control as this material does not possess an amide bond. Each sample was then tested for Cu2+ adsorption. The acid and base treated materials were compared with samples that were not treated with either acid or base. The results are shown in Table 5. No reduction in Cu2+ adsorption capacity was detected for BP-NT, WP-NT, and BP-2. A second test was conducted in which BP-ED underwent multiple column load/strip cycle testing. A 5 mL column of BP-ED was subjected to 1001 load/strip cycles. For each load cycle the column was fed 200 mL of a solution containing 1.5 g/L Cu2+ at pH 1. The column was then rinsed with deionized water and stripped with a 4.5 M H2SO4 solution. Figure 9 shows three breakthrough profiles for the initial cycle, for cycle 101, and for cycle 1001. Visual examination of the three curves shows no significant variations in the three breakthrough profiles. As a result the full breakthrough sorption capacity for BP-ED in the three cycles tested were all in the range 29-30 mg of

Figure 9. Longevity assessment for the dynamic extraction of copper for BP-ED at pH 1. Column packed with 5.0 mL of BP-ED. Feed solution contains 1.5 g/L copper. Flow rate was 1 mL/min. Breakthrough profiles shown for cycle 1, 101, and 1001.

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Cu2+ extracted per mL of SPC. If acid hydrolysis of the pendant EDTA derivative had occurred, the sorption capacity would have dropped. As a result it can be concluded that BP-ED is stable to acid catalyzed amide hydrolysis for a minimum of 1001 load and strip cycles. 4. Conclusions The main conclusion that can be drawn from this work is that polymer structure, by virtue of the number of coordinating groups accessible to a given metal atom, can have a significant influence on metal selectivity in cases where the amine group of the SPC is directly functionalized (i.e., WP-2 and BP-2). Thus the selectivity for copper over nickel using BP-2 in the pH range 2-3 could be very useful especially considering the very sharp separations realized with SPC technology relative to polystyrene analogues.24 This selectivity for copper over nickel can be related to the lower coordination number required by copper (4) which is best matched by the denticity of BP-2 sites (2 or 3). On the other hand, when a chelating ligand is tethered to the grafted polyamine, selectivity is independent of polyamine structure. The tethered chelating ligand reported here, NTA, is bound to the polyamine by an amide linkage. The stability of this linkage, as reported here, is surprising in light of the known lability of amides to acid hydrolysis. This is probably due to the protonation of the surface ligand nitrogen atoms (or surface coordination of the positively charged metal) in the ligand which prevents further protonation of the underlying amide nitrogen atoms required for hydrolysis. The order of selectivity for the trivalent metals in the case of the NTA ligand is probably size related where the relatively large Eu3+ (ionic radius ) 109 pm) and small Al3+ (ionic radius ) 53 pm) have lower affinities than the similarly sized Fe3+ and Ga3+ (ionic radii ) 61 and 63 pm, respectively).25 Acknowledgment We gratefully acknowledge the National Science Foundation (0709738) and the Montana Board of Research and Commercialization Technology for support of this research. Literature Cited (1) Allan, R. Introduction: Mining and Metals in the Environment. J. Geochem. Explor. 1997, 58, 95. (2) Mohammed, A.; Najar, P. A. M. Treatment Methods for the Removal of Heavy Metal Pollutants from Water and Wastewaters. J. Ind. Pollut. Control 1997, 13, 85. (3) Mendes, F. D.; Martins, A. H. Recovery of Nickel and Cobalt from Acid Leach Pulp by Ion Exchange using Chelating Resin. Miner. Eng. 2005, 18, 945. (4) Beauvais, R. A.; Alexandratos, S. D. Polymer-Supported Reagents for the Selective Complexation of Metal Ions: an Overview. React. Funct. Polym. 1998, 36, 113. (5) Grinstead, R. R. Copper-Selective Ion-Exchange Resin with Improved Iron Rejection. J. Met. 1979, 31, 13. (6) Alexandratos, S. D.; Crick, D. W. Polymer-Supported Reagents: Application to Separation Science. Ind. Eng. Chem. Res. 1996, 35, 635– 44. (7) Soliman, E. M. Synthesis and metal collecting properties of mono, di, tri and tetramines based on silica gel matrix. Anal. Lett. 1997, 30, 1739.

(8) Yoshitake, H.; Joiso, E.; Tatsumi, T.; Horie, H.; Yoshimora, H. Preparation and Characterization of Polyamine functionalized Mesoporous Silica. Chem. Lett. 2004, 33, 872. (9) J Kramer, J.; Driessen, W. L.; Koch, K. R.; Riedek, J. Highly Selective and Efficient Recovery of Pd, Pt and Rh from Precious MetalContaining Industrial Effluents with Silica based (Poly)amine Ion Exchangers. Sep. Sci. Technol. 2004, 39, 63. (10) (a) Rosenberg, E.; Pang, D. System for Extracting Soluble Heavy Metals from Liquid Solutions, Especially Aqueous Solutions. U.S. Patent, 5,695,882, 1997. (b) Beatty, S. T.; Fischer, R. J.; Hagers, D. L.; Rosenberg, E. A Comparative Study of the Removal of Heavy Metal Ions from Water Using a Silica-Polyamine Composite and a Polystyrene Chelator Resin. Ind. Eng. Chem. Res. 1999, 38, 4402. (c) Beatty, S. T.; Fischer, R. J.; Rosenberg, E.; Pang, D. Comparison of Novel and Patented Silica-Polyamine Composite Materials as Aqueous Heavy Metal Ion Recovery Materials. Sep. Sci. Technol. 1999, 34 (14), 2723. (d) Fan, Z. L.; Li, D. Q.; Rosenberg, E. Synthesis and Adsorption Property of Poly(allylamine)-Silica Composite. Yingyong Huaxue 2003, 20 (9), 867. (11) Hughes, M. A.; Rosenberg, E. Characterization and Applications of Poly-Acetate Modified Silica Polyamine Composites. Sep. Sci. Technol. 2007, 42, 261. (12) Hughes, M. A.; Nielsen, D.; Rosenberg, E.; Gobetto, R.; Viale, A.; Burton, S. D.; Ferel, J. Structural Investigations of Silica Polyamine Composites: Surface Coverage, Metal Ion Coordination, and Ligand Modification. Ind. Eng. Chem. Res. 2006, 45, 6538. (13) Alexandratos, S. D. New Polymer-Supported Ion-Complexing Agents: Design, Preparation and Metal Ion Affinities of Immobilized Ligands. J. Hazardous Mater. 2007, 139, 467. (14) Nielsen, D. Synthesis and Reclamation of Novel Silica Polyamine Composites and their Application to the Reclamation of Hazardous Mining Wastewater and Tailings. Ph.D. Thesis, The University of Montana, MT, USA, 2006. (15) El-Nahhal, I. M.; Zaggout, F. R.; Nassar, M. A.; El-Ashgar, N. M.; Maquet, J.; Babonneau, F.; Chehimi, M. M. Synthesis, Characterization and Applications of Immobilized Iminodiacetic Acid-Modified Silica. J. Sol-Gel Sci. Technol. 2003, 28, 255. (16) Shiraishi, Y.; Nishimura, G.; Hirai, T.; Komasawa, I. Separation of Transition Metals using Inorganic Adsorbents Modified with Chelating Ligands. Ind. Eng. Chem. Res. 2002, 41, 5. (17) Shimizu, Y.; Izumi, S.; Saito, Y.; Yamaoka, H. Ethylenediaminetetraacetic Acid Modification of Crosslinked Chitosan Designed for a Novel Metal-Ion Adsorbent. J. Appl. Polym. Sci. 2004, 92, 2758. (18) Inoue, K.; Yoshizuka, K.; Ohto, K. Adsorptive Separation of some Metal Ions by Complexing Agent Types of Chemically Modified Chitosan. Anal. Chim. Acta 1999, 388, 209. (19) Hindersinn, R. R.; Hopkins, G. C.; Ilardo, C. S. Compositions of Epoxy Resins with 2,6-dioxo-N-(carboxymethyl)morpholine. U.S. Patent 3,621,018, 1971. (20) Adamson, A. W.; Gast, A. P. Physical Chemistry of Surfaces, 6th ed.; Wiley Interscience: New York, 1997; p 97. (21) Wang, W.; Fthenakis, V. Kinetics Study on the Separation of Cadmium from Tellurium in Acidic Solution Media using Ion-Exchange Resins. J. Hazardous Mater. 2005, 125, 80. (22) Rosenberg, E. Silica Polyamine Composites: Advanced Materials for Metal Ion Recovery and Remediation. In Macromolecules Containing Metal and Metal Like Elements; Carraher, C. E., Pittman, C. U., Abd-ElAziz, A. S., Zeldin, M., Sheats, J. E., Eds.; J. Wiley & Sons: New York, 2005; Vol. 4, p 51. (23) Rosenberg, E.; Clancy, J.; McKenzie, J. Unpublished results. (24) Rosenberg, E.; Hart, C.; Hughes, M.; Kailasam, V.; Allen, J.; Wood, J.; Cross, B. Performance Improvement through Structural Design and Comparison with Polystyrene Resins of Silica Polyamine Composites. Proceedings of the 67th International Water Conference, 2007; IWC 07-4. (25) Huheey, J. E.; Keiter E. A. ; Keiter, R. L. Inorganic Chemistry Principles of Structure and ReactiVity, 4th ed.; Harper Collins: New York, 1991, p 114.

ReceiVed for reView March 4, 2008 ReVised manuscript receiVed May 20, 2008 Accepted June 7, 2008 IE800359K