Batch Studies for Sorption of Ga(III), Cu(II), Ni(II) and Zn(II) Ions onto Synthetic Polymeric Resins

Poly(acrylamide-acrylic acid-dimethyl amino ethylmethacrylate), p(AM-AA-DMAEM) and Poly(acrylamide-acrylic acid)-ethylene diamine tetracetic acid disodium, p(AM-AA)-EDTANa2 were prepared by gamma radiation-induced template polymerization technique. The prepared polymeric materials were used for the sorption of Ga(III), Cu(II), Ni(II) and Zn(II) in aqueous solution. The effect of pH, weight of resins, metal ion concentrations and contact time on the sorption of these metal ions were studied.


Introduction
Polymeric substrates are being continuously developed and used for the purpose of complexation with metal ions either for ion-exchange or selective adsorption purpose.These polymeric ligands are tailored synthesized to remove certain metal ions or groups from aqueous media [1]- [3].A number of chelating polymers, containing different active groups such as carboxylic, amide, amino amidoxime and hydroxamic groups, were prepared by different polymerization techniques [4]- [19].The functional groups are interacted with the metal ions through complexation or formation of covalent bonds by ion-exchange mechanism [17]- [21].These resins contain as a rule one or more donor atoms which can form a coordination bond with the metal ion.The selective ionexchange phenomenon in a system mainly depends on the combination of three factors, the metal ion chemistry in aqueous solution and the resin, the structure of the functional groups in the resin phase and the macromolecular structure as present under the separation condition [21].The efficiency of the resins increases by decreasing the degree of crosslinking.The resins can be regenerated and reused for continuous process [22].The removal process of the metal ions from the solution depends on the type of the metal ion, pH of the solution, metal ion concentration and the properties of the ion exchanger such as crosslinking degree, swelling and the type of the ligand [23].
Poly(N-acryloyldiethyliminodiacetate acrylic acid) was used for the removal of 152 Eu at pH 4 [30].Poly(hydroxymic acid) was used for separation of Fe(III) from solution containing Cu(II) and Ni(II) at pH < 4 [31] and poly(methyl acrylohydroxamic acid) was also used the separation of metal ions such as Cu(II), Ni(II), Co(II), Pb(II) and Fe(III) at pH 3.5 -5 [32].Polymeric composite such as poly(acrylamide-acrylic acid)-EDTANa 2 , poly(acrylamide-acrylic acid)-montmorillonite, poly(acrylamide-acrylic acid)-KNiHCF, poly(acrylamide-acrylic acid)-KZnHCF, poly(acrylamide-acrylic acid-DMAEM)-KNiHCF were used for the removal of metallic ions such as Cu(II) and Cr(II) as test ions from waste water and were also used for treatment of radioactive liquid waste containing radioactive isotopes such as 60 Co and 152 Eu [33].Generally, acrylamide polymeric materials were used for the removal of various metallic ions, heavy metal, and radioactive isotopes from their aqueous solution [4]- [19] [33].In the present work, acrylamide polymeric resins are used for the sorption of Ga(III), Cu(II), Ni(II) and Zn(II).

Materials
N, N-methylene diacrylamide andacrylamide, were obtained from BDH, acrylic acid monomer and dimethylaminoethyl methacrylate were obtained from Merk (Germany), and EDTANa 2 was obtained from Oxoford laboratory reagent.

Preparation of Polymeric Materials
Polyacrylamide, p(AM), was prepared by gamma radiation-initiated polymerization of 10% acrylamide monomer solution using gamma radiation at a dose 10 kGy [17].
, was prepared by gamma radiation induced template polymerization of acrylic acid on p(AM) in the presence of EDTANa 2 and N, N-methylene diacrylamide (DAM) as across-linker.

Batch Sorption Studies
The ion exchange behavior of the metal ions of Ga(III), Cu(II), Ni(II) and Zn(II) towards the synthesized polymeric materials was studied using the batch technique where, 40 mg of each resin was equilibrated with 20 ml aqueous solution containing the desired metal ion.The uptake percentage of the studied ion on the polymeric materials was determined using ICP-a JobinYvon ICP-OES spectrometry model Ultima2.The uptake percentage was determined using the following equation: where A 0 , A are the concentration of the metal ions before and after addition the resin, respectively.

Effect of pH on the Sorption of Metalions
The sorption of Ga(III), Cu(II), Ni(II) and Zn (II) was studied on polymeric materials of p(AM-AA-DMAEM) and p(AM-AA)-EDTANa 2 at different pH values as shown in Figures 1-4.The data showed that the sorption of Ga(III), Cu(II), Ni(II) and Zn(II) on p(AM-AA-DMAEM) and p(AM-AA)-EDTANa 2 increased with increasing the pH value.This can be attributed to the effect of pH on the functional groups of the polymeric materials.At low pH value, the amide and amino groups are most present in protonated form, leading to imidation of amide groups with the formation of intermolecular cross-linking between polymeric chains, which inhibits their complexation with metal ions.With increasing pH, the degree of protonation decreases which leads to increasing interaction between polymeric materials and metal ions.By increasing pH, the degree of ionization of carboxylate groups (pKa = 2.45) of polymeric materials increases as well, which facilitates the cation exchange.Moreover,  at high pH the amide and amine groups of the resins can interact with metal ions [32] [33].It was found that the optimum pH values for the removal of Ga(III), Cu(II), Ni(II) and Zn(II) were found to be 3.5, 5, 6, 4, respectively.This can be attributed to the presence of metal ions as free ions in the solution [32].At higher pH value > 6, the metal ions form metal hydroxides.

Effect of Weight of Polymeric Materials
Different weights of polymeric materials of p(AM-AA-DMAEM) and p(AM-AA)-EDTANa 2 were used for the removal of Ga(III), Cu(II), Ni(II) and Zn(II) individually from aqueous solution at pH = 4.4, 4.5, 5.5 and 5.6, respectively.The results are shown in Figures 5-8.
The uptake percentage increases with increasing the weight of the polymeric materials and reached its maximum value at 40 mg for all metal ions, which means that this is optimum concentration for the sorption process.

Effect of Metalion Concentration
The effect of sorption of Ga(III), Cu(II), Ni(II) and Zn(II) from aqueous solution on p(AM-AA-DMAEM) and p(AM-AA)-EDTANa 2 was studied.
The results are shown in Figures 9-12, which show that the uptake decreases with increasing metal ion concentration due to the specific capacity of the polymeric materials.

Effect of Contact Time
The variation of the uptake percentage of Ga(III), Cu(II), Ni(II) and Zn(II) ions (at concentration 100 ppm and constant pH value) from aqueous solution with time was measured by p(AM-AA-DMAEM) and p(AM-AA)-EDTANa 2 .The results are shown in Figures 13-16.
In all cases, the uptake increases with increasing the time.The equilibrium time for removal of Ga(III), Cu(II), Ni(II) and Zn(II) onto p(AM-AA-DMAEM) and p(AM-AA)-EDTANa 2 was found to be (90, 75), (45, 30), (60, 45), (60, 45) respectively.The uptake value for Ga(III), Cu(II), Ni(II) and Zn(II) on the p(AM-AA-DMAEM) and p(AM-AA)-EDTANa 2 were in the order: p(AM-AA-DMAEM) < p(AM-AA)-EDTANa 2 .The higher uptake value for p(AM-AA)-EDTANa 2 relative to p(AM-AA-DMAEM) can be attributed the complex formation between the amino-and the carboxylate groups of polymeric chain as shown in the schematic [33].This complexation leads to an increase in the degree of crosslinking between the polymeric chains of the prepared polymeric composite resin, consequently, the efficiency of the resin decreases.

Figure 4 .
Figure 4. Effect of hydrogen ion concentration on the uptake of Zn(II) on p(AM-AA-DMAEM) and p(AM-AA)-EDTANa 2 .