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 trappingand 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), thermogravimetricanalysis (TGA) and surface area measurement. Pb(II) adsorption by the composites was investigated ina 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 at293 K was more appropriate for the Langmuir isotherm model, with maximum adsorption capacitystanding at 18.9 mg Pb g1. 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 theevaluation of the thermodynamic parameters of the adsorption process, namely DG0 (5 kJ mol1),DH0 (7.20 kJ mol1) and DS0 (18.0 J mol1 K1); it was revealed as a spontaneous and endothermic process.0.5 mol L1 HCl was recommended for composite regeneration and Pb(II) recovery. Fixed bed experimentwas attempted for treatment of Pb(II)-bearing battery industrial wastewater with an efficient levelof reversible performance through an extended period of time. Overall, the proposed silica/CA–XG compositewould be a very promising adsorbent for lead removal and recovery from aqueous solutions, withremarkable advantages in terms of biocompatibility, recyclability, ease of operation and low cost.