Low-cost hemp biomaterials for nickel ions removal from aqueous solutions

This study investigates an alternative use of hemp-based materials either in hemp fiber (HF) or shive (HS) form as biosorbents for the removal of Ni(II) from aqueous solutions. The hemp materials were used either in raw form or after chemical modification with sodium hydroxide and citric acid in order to remove any impurities and add extra carboxyl groups (which improve the adsorption), respectively. A series of adsorption experiments was carried out to determine the effect of (i) solution pH on Ni(II) adsorption, (ii) contact time (kinetics fitted to linear pseudo-first, -second order equations and Elovich model), and (iii) initial ion concentration (fitting to Langmuir, Freundlich and Langmuir-Freundlich equations). Furthermore, a complete characterization study (FTIR, XRD, SEM/EDAX, crystallinity, and cellulose content) demonstrated the surface morphology of the prepared hemp-materials along with some possible adsorption interactions between them and ions. The regeneration of materials was confirmed running desorption experiments (effect of solution pH on desorption) finding also the optimum desorption contact time (kinetics fitted to non-linear pseudo-first and -second order equations). Ten sequential reuse cycles (at the optimum conditions found after adsorption and desorption experiments) revealed the reuse potential of the low-cost hemp-based materials.