Copper(II) ion removal from aqueous solutions using biosorption technology: thermodynamic and SEM–EDX studies

The present study uses biosorption technology to remove copper(II) ions from aqueous solutions. Mature leaves of neem (Azadirachta indica) were developed into powder form of size 32–45 μm and used as the biosorbent, while copper(II) ion solutions were prepared to be used as adsorbates. Parameters varied include copper(II) ion concentration and adsorption temperature. The neem leaf powder (NLP) dosage which was kept constant at 1.0 g L⁻¹ and pH was between 5 and 6. Adsorption occurred at a high rate initially and reached equilibrium after 50 min. Adsorption seemed to be more favourable at higher temperatures. Optimal temperature was found to be 333 K, with a high adsorption capacity of 146.30 mg g⁻¹. Thermodynamic studies showed that the system is spontaneous and endothermic in nature, based on the parameters of Gibbs free energy (∆G°), biosorption enthalpy (∆H°) and biosorption entropy (∆S°) obtained, which gave values of −2.74, 26.70 and 0.07 kJ mol⁻¹ K⁻¹, respectively. The adsorption mechanism was found to be predominantly chemisorption. SEM and EDX results show that copper(II) ions were adsorbed on the micropores of NLP. Results indicate that NLP is a suitable biosorbent for removing copper(II) ions from solutions.