A comparative study of Helianthemum and Citrullus Colocynthis Biomass as Low-Cost Biosorbents for Ce(III) and Gd(III) Removal from Aqueous Solutions

Abstract

This study aimed to investigate the potential of Helianthemum and Citrullus colocynthis biomass as biosorbents for removing Ce(III) and Gd(III) ions. Various experimental parameters, including initial metal ion concentration, adsorbent dosage, and contact time, were examined to assess their impact on removal efficiency. The biosorption process was analyzed using isotherm and kinetics models. Samples underwent pretreatment to eliminate impurities and were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The Langmuir isotherm model exhibited a good fit for Gd(III) adsorption onto Helianthemum biomass, while it was unsuitable for Ce(III) adsorption. The isotherm models were employed to determine the optimal adsorption capacities of the biosorbents. Helianthemum biomass exhibited maximum adsorption capacities of 250 mg/g for Gd(III) and 103.09 mg/g for Ce(III), whereas Citrullus colocynthis biomass demonstrated capacities of 100 mg/g for Gd(III) and 66.62 mg/g for Ce(III). While the Freundlich isotherm model showed moderate agreement for both Gd(III) and Ce(III) adsorption onto Citrullus colocynthis biomass, it was inadequate for Helianthemum biomass. The adsorption of Gd(III) onto Helianthemum biomass was attributed to a chemisorption mechanism, indicating irreversible interactions between the metal ion and the adsorbent. In contrast, the adsorption of Ce(III) involved a physisorption process, allowing for the possibility of reversible desorption. The experimental data exhibited a better fit to the pseudo-first-order model for both Gd(III) and Ce(III) adsorption onto Helianthemum and Citrullus colocynthis biomass. The equilibrium adsorption capacities (qe) predicted by the model for Helianthemum biomass containing Gd(III) and Ce(III) were relatively similar to the experimental values. The regeneration and reuse of Helianthemum and Citrullus colocynthis biomass demonstrate high economic feasibility and environmental sustainability, with adsorption efficiencies of 85% and 77%, respectively, retained after three regeneration cycles using a mild 0.1 M HCl solution.

Graphical Abstract