Porous dye affinity beads for nickel adsorption from aqueous solutions: A kinetic study

Abstract

We investigated a new adsorbent system, Reactive Red 120 attached poly(2-hydroxyethyl methacrylate ethylene dimethacrylate) [poly(HEMA-EDMA)] beads, for the removal of Ni2+ ions from aqueous solutions. Poly(HEMA-EDMA) beads were prepared by the modified suspension copolymerization of 2-hydroxyethyl methacrylate and ethylene dimethacrylate. Reactive Red 120 molecules were covalently attached to the beads. The beads (150-250 mu m), having a swelling ratio of 55% and carrying 25.5 mu mol of Reactive Red 1.20/g of polymer, were used in the removal of Ni2+ ions. The adsorption rate and capacity of the Reactive Red 120 attached poly(HEMA-EDMA) beads for Ni2+ ions was investigated in aqueous media containing different amounts of Ni2+ ions (5-35 mg/L) and having different pH values (2.0-7.0). Very high adsorption rates were observed at the beginning, and adsorption equilibria were then gradually achieved in about 60 min. The maximum adsorption of Ni2+ ions onto the Reactive Red 120 attached poly(HEMA-EDMA) beads was 2.83 mg/g at pH 6.0. The nonspecific adsorption of Ni2+ ions onto poly(HEMA-EDMA) beads was negligible (0.1 mg/g). The desorption of Ni2+ ions was studied with 0.1M HNO3. High desorption ratios (> 90%) were achieved. The intraparticle diffusion rate constants at various temperatures were calculated as k(20 degrees C) = 0.565 mg/g min(0.5), k(30 degrees C) = 0.560 mg/g min(0.5), and k(40 degrees C) = 0.385 mg/g min(0.5). Adsorption-desorption cycles showed the feasibility of repeated use of this novel adsorbent system. The equilibrium data fitted very well both Langmuir and Freundlich adsorption models. The pseudo-first-order kinetic model was used to describe the kinetic data.