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

Abstract This study highlights the potential of Hal/alginate nanocomposite beads for the removal of Pb 2 + 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 Pb 2 + (i.e. 325 mg/g) compared to that of free Hal nanotubes (i.e. 84 mg/g). The overall process was diffusion limited, well described by the shrinking core model. The Hal/alginate beads removed Pb 2 + through ion exchange with Ca 2 + 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 Pb 2 + uptake. As such, this adsorbent incorporates distinctive merits of both Hal nanotubes and alginate, which include the high affinity towards Pb 2 + , strong mechanical properties, and easy separation from the treated solution.