Silica modified calcium alginate-xanthan gum hybrid bead composites for the removal and recovery of Pb(II) from aqueous solution

An organic-inorganic bio-hybrid bead composite was fabricated through a sol-gel reaction by trapping and condensing amorphous silica into the network structures of calcium ion cross-linked alginate (CA)-xanthan gum (XG) gel beads. The reinforced silica/CA-XG composite was characterized by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and surface area measurement. Pb(II) adsorption by the composites was investigated in a batch mode by changing the relevant parameters which included solid/liquid ratio, contact time, pH, temperature, effect of co-existing metal ions and particle size. The analysis of the equilibrium data at 293 K was more appropriate for the Langmuir isotherm model, with maximum adsorption capacity standing at 18.9 mg Pb g(-1). It evidenced that Pb(II) adsorption was based on chemical binding process, along with intra-particle diffusion contribution. Experiments carried out at 293 and 313 K enabled the evaluation of the thermodynamic parameters of the adsorption process, namely Delta G(0) (-5 kJ mol(-1)), Delta H-0 (7.20 kJ mol(-1)) and Delta S-0 (18.0J mol(-1) K-1); it was revealed as a spontaneous and endothermic process. 0.5 mol L-1 HCl was recommended for composite regeneration and Pb(II) recovery. Fixed bed experiment was attempted for treatment of Pb(II)-bearing battery industrial wastewater with an efficient level of reversible performance through an extended period of time. Overall, the proposed silica/CA-XG composite would be a very promising adsorbent for lead removal and recovery from aqueous solutions, with remarkable advantages in terms of biocompatibility, recyclability, ease of operation and low cost. (C) 2013 Elsevier B.V. All rights reserved.