A novel algal-based sorbent for heavy metal removal

Two sorbents have been synthesized for the efficient removal of heavy metals (e.g., Pb(II), Cu(II), Cd(II), Zn(II) and Ni(II)) from aqueous solutions. Originally, the Alginate/PEI (A-PEI) sorbent containing calcium alginate (as an encapsulating matrix) and polyethylenimine derivatives was manufactured by using internal ionotropic gelation and tested in batch and continuous system. The introduction of Fucus vesiculosus alga improved this material by partially replacing the industrial alginate contained in the biosorbent; it provided a practical one-pot process for faster fabrication, and allowed the manufacturing of a novel environmentally-friendly material (Alginate/Fucus vesiculosus/PEI; AF-PEI). The sorbents have been compared in batch system and characterized using ESEM-EDX and FTIR analyses. The uptake kinetics data were modeled using pseudo-second order rate equation and the sorption isotherms were fitted using the Langmuir, Freundlich and Sips equations. Experimental data were better described with the Sips model and the sorption capacities followed the order: Pb (II) approximate to Cu(II) > Cd(II) approximate to Ni(II) > Zn(II) for A-PEI and Cu(II) > Pb(II) > Zn(II) approximate to Ni(II) > Cd(II) for AF-PEI. Among the synthesized beads, AF-PEI material had the highest sorption capacities for heavy metal removal (1.44 mmol g(-1) for Cu(II); 1.09 mmol g(-1) for Pb(II); 1.03 mmol g(-1) for Ni(II); 1.07 mmol g(-1) for Zn(II); 0.87 mmol g(-1) for Cd(II) at pH 4). The recycling of the sorbents was tested with 0.1 M HCl/0.05 M CaCl2 solution; the materials had a higher selectivity for Pb(II) and Cu(II), maintaining the removal efficiency over 70% and 40% for these species in five successive sorption-desorption cycles.