In this study, date palm fibres and orange peel in both individual and hybrid forms were studied for the removal of copper, lead, and arsenic. Equilibrium was achieved after 150 minutes, and the highest and the lowest removal efficiencies were for Cu⁺² and As(V), respectively. A slightly higher removal efficiency of metal ions using orange peel was observed, which could be due to the greater number of functional groups on the chemically pre-treated adsorbent. The highest removal was observed at pH 6, and the adsorption data exhibited a linear increase in metal removal capacity with increasing adsorbent concentrations from 0.1 to 2 g/L. A significantly higher removal efficiency was observed for a 45 µm particle size compared to larger particle sizes. Additionally, a 30-40% decrease in removal efficiencies was observed for all three heavy metal ions when using the date palm fibres or the hybrid adsorbent when the initial metal concentrations were increased from 20 to 80 mg/L. The Freundlich model agreed with the experimental data slightly better than the Langmuir model for both date palm fibres and the hybrid adsorbent. A pseudo second-order kinetic model better described the kinetic behaviour of As(V) adsorption on the investigated adsorbents. Date palm fibres exhibited exothermic adsorption, while both orange peel and the hybrid adsorbent displayed exothermic and endothermic reactions. Increased randomness at the solid-liquid interface was observed for all adsorbents, and the Gibbs free energy change values were negative, confirming the spontaneous nature of adsorption, which proceeded in the forward direction.
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