Effectiveness of raw and activated laterite in removing lead and copper from aqueous solutions: A kinetic and thermodynamic study

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Résumé

The growing interest in local materials as natural adsorbents stems from their abundance, low cost, and
eco-friendliness, offering an effective, economical, and sustainable alternative to commercial options. The present
work investigates the removal performance of lead (Pb2+) and copper (Cu2+) ions from synthetic aqueous solutions
using both raw and activated laterite (KN-Ac) under batch conditions. The experiments were carried out to examine
the effects of contact time, adsorbent dose, temperature, pH, and initial metal-ion concentration. High determination
coefficients obtained from the pseudo-second-order kinetics and Langmuir isotherm models indicate that these
models reliably describe the experimental adsorption behavior of the metal ions. The diffusion model-adjusted
data revealed that adsorption occurred rapidly at the beginning, with fast adsorption on the outer surface followed
by slower adsorption controlled by intraparticle diffusion. The KN-Ac, designated KN-Ac, proved to be highly
effective in removing both heavy metals, achieving removal percentages of 97.81 ± 0.23% (4.07 ± 0.01 mg/g) for
Pb2+ and 94.24 ± 0.18% (1.18 ± 0.02 mg/g) for Cu2+ at an initial concentration of 10 mg/L. The ΔG values obtained
for the metal ions were all negative, indicating that the adsorption process is feasible and spontaneous for Pb(II)
and Cu(II) ions on the adsorbents, following the order of thermodynamic stability: Pb2+(KN-Ac) > Cu2+(KN-Ac) >
Pb2+(raw laterite [KN]) > Cu2+(KN) in the temperature range of 303–333 K. The positive ΔH values for all metal
ions suggest that adsorption onto the adsorbents is endothermic and involves physisorption. The energy values
derived from the Dubinin–Radushkevich equation are all below 8 kJ/mol, indicating that the adsorption of Pb2+ and
Cu2+ is physical in nature. Furthermore, the Fourier transform infrared spectra of adsorbent residues loaded with
heavy metals show no changes compared to the spectra of the unloaded adsorbents, confirming physisorption as
the main adsorption mechanism.

Mots-clés

Heavy metals; Removal; Groundwater; Wastewater; Laterite