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This work evaluates the potential of using eggshells as biosorbents for the removal of copper (II) ions from aqueous solutions. Two types of eggshells were investigated; untreated raw eggshells (ES) and eggshells that were mechanically ball-milled into the nano-size (NES). TEM imaging confirmed the nano-size of NES which lies in the range of 12–14.8 nm, while BET analysis showed that both types of eggshells are mesoporous and that the surface area of NES is 1.6 times higher than its ES counterpart. FTIR spectra, XRD patterns, and SEM-EDX measurements indicated that there are no structural differences between ES and NES. Optimum adsorption took place at pH 5 and initial Cu (II) concentration of 20 mg/L for both ES and NES where removal efficiencies of 91.36% and 97.21% were achieved, respectively. Although both biosorbents exhibited comparable adsorption capacities, yet the rate of adsorption of Cu (II) onto NES was 17 times higher than its counterpart onto ES probably due to the larger surface area of NES. It could be hypothesized that the mechanism of interaction took place via electrostatic outer-sphere complexation between the positively-charged Cu ions and the negatively-charged ES or NES as zeta potential measurements indicated. Additionally, ES and NES were regenerated for four cycles. From this study, it can thus be deduced that both ES and NES could be potentially utilized as eco-friendly adsorbents for the removal of copper ions from contaminated water. However, NES provides an additional advantage over ES since it offers much rapid removal of Cu (II) while possessing the same adsorption capacity of ES.

Removal of copper (II) ions by eco-friendly raw eggshells and nano-sized eggshells: a comparative study