Equilibrium and Thermodynamic Studies using Eco-Friendly Cola lepidota Seed Resins as Novel Adsorbents in the Removal of Pb (II) and Cd (II) Ions from Aqueous System

This study reveals the removal of Pb (II) and Cd (II) ions from aqueous system using unmodified Cola lepidota extract (UCE) and modified Cola lepidota extract resin (ECER). The modification was achieved by using ethanedioic acid and the adsorption process was carried out with respect to initial concentrations, temperature and pH. Phytochemical analysis of the seeds was done by Gas Chromatography Mass Spectrometry (GC-MS). The zero point charge was evaluated and Pb (II) and Cd (II) ions equilibrium concentration was determined using Atomic Absorption Spectrophotometer (AAS). The GC-MS spectra suggested the seed contained 22 compounds. The zero point charge of UCE and ECER was found to be 4.0 and 7.0, respectively. Percentage removal of Pb (II) and Cd (II) ions onto ECER and UCE gave 89.35%, 83.45%, 75.32% and 80.11%, respectively. Optimal temperatures were 313 K and 303 K for Pb (II) and Cd (II) ions onto UCE, 303 K and 353 K for Pb (II) and Cd (II) ions onto ECER with 97.60%, 91.04%, 97.44% and 90.22% metal ions removal. Optimal pH was 4.0 for Pb (II) ion onto UCE and ECER, 8.0 for Cd (II) ion onto UCE and 6.0 to 8.0 for Cd (II) ion onto ECER with 98.40%, 98.40%, 95.11% and 98.37% removal. Langmuir, Freundlich, Temkin, Dubinin-Radushkevich and Redlich-Peterson isotherm model equations were tested and the result showed that Freundlich adsorption isotherm model equation fitted well with the removal of the metal ions onto UCE and ECER. Adsorption of Pb (II) ion onto UCE and ECER and Cd (II) ion onto UCE was exothermic with negative entropy while Cd (II) ion onto ECER was endothermic with positive entropy. The change in Gibbs free energy, 11G0, was negative for all the metal ions. The unmodified Cola lepidota extract (UCE) and the ethanedoic acid Cola lepidota extract resin (ECER) can be recommended empirically as surfaces for heterogeneous reactions.