Congo Red-Attached Poly(EGDMA-HEMA) Micro beads for Removal of Heavy Metal Ions

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Abstract
In this study we investigated a new sorbent system, Congo Red-attached poly (EGDMA-HEMA) micro beads, for removal of heavy metal ions from aqueous solutions. Poly(EGDMA-HEMA) micro beads were prepared by suspension copolymerization of ethylene glycol di methacrylate (EGDMA) and hydroxyethyl methacrylate (HEMA) by using poly(vinyl alcohol), benzoyl peroxide, and toluene as the stabilizer, the initiator, and the diluent, respectively. Congo Red molecules were then covalently attached to these micro beads. Micro beads (150–200 ö in diameter) with a swelling ratio of 55% and carrying 14.5 ömol Congo Red/g polymer were used in the adsorption/desorption studies. Adsorption rate and capacity of the micro beads for selected metal ions, i.e., Cd(II), Cu(II), Zn(II) and Pb(II), were investigated in aqueous media containing different amounts of these ions (1–500 ppm) and at different pH values (1.5–7.5). Very high adsorption rates were observed at the beginning, and adsorption equilibria were then gradually achieved in about 5–90 minutes. The maximum adsorptions of metal ions onto the Congo Red attached micro beads were 18.3 mg/g for Cd(II), 2.9 mg/g for Cu(II), 53.8 mg/ g for Zn(II), and 165 mg/g for Pb(II). However, when the metal ions competed (in the case of adsorption from their mixture), the amounts of adsorption for Cd(II), Zn(II), and Pb(II) were quite close. Desorption of metal ions was studied by using 2 M NaCl (pH 7.0) for Cd(II) ions and 0.1 M HNO3 (pH 1.0) for Cu(II), Zn(II), and Pb(II) ions. High desorption ratios (more than 85%) were achieved in all cases. Adsorption/desorption cycles showed the feasibility of repeated use of this novel sorbent system.