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

Abstract

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 293K was more appropriate for the Langmuir isotherm model, with maximum adsorption capacity standing at 18.9mgPbg−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 313K enabled the evaluation of the thermodynamic parameters of the adsorption process, namely ΔG0 (−5kJmol−1), ΔH0 (7.20kJmol−1) and ΔS0 (18.0Jmol−1K−1); it was revealed as a spontaneous and endothermic process. 0.5molL−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.