Halloysite/alginate nanocomposite beads: Kinetics, equilibrium and mechanism for lead adsorption

This study highlights the potential of Hal/alginate nanocomposite beads for the removal of Pb2+ in aqueous solutions. This is based on comprehensive physicochemical-mechanical characterizations involving adsorption equilibrium, adsorption kinetics, diffusion studies, FTIR, EDX, FESEM, zeta potential, and compression tests. Results show Langmuirian adsorption isotherms and reasonably rapid second order adsorption kinetics. The Hal/alginate nanocomposite beads have high adsorption capacity for Pb2+ (i.e. 325mg/g) compared to that of free Hal nanotubes (i.e. 84mg/g). The overall process was diffusion limited, well described by the shrinking core model. The Hal/alginate beads removed Pb2+ through ion exchange with Ca2+ followed by coordination with carboxylate groups of alginate, in addition to physisorption on Hal nanotubes. Vital for industrial applications, the Young's modulus of the nanocomposite beads was strengthened by Hal nanotubes loading as well as Pb2+ uptake. As such, this adsorbent incorporates distinctive merits of both Hal nanotubes and alginate, which include the high affinity towards Pb2+, strong mechanical properties, and easy separation from the treated solution.