Adsorption Studies of Pb<sup>2+</sup>, Cu<sup>2+</sup> and Cr<sup>3+</sup> from Aqueous Solution Using <i>Azadirachta Indica </i>(Neem) Seed Husk and <i>Adansonia Digitata </i>(Baobab) Seeds

Abstract

The adsorption of Pb<sup>2+</sup>, Cu<sup>2+</sup> and Cr<sup>3+</sup> from aqueous solution using Neem seed husk (NSH) and baobab seed (BS) were studied through the use of batch adsorption system. The adsorbents were prepared by drying at 120°C for 24hours and were characterized using FT-IR, XRD, and SEM analysis. The FTIR spectroscopy revealed the presence of O-H, N-H, C-H, C=C, C=O, and C-O stretching; XRD revealed the particle sizes as 44.51nm for NSH and 42.61nm while the morphology of the NSH and BS were revealed by SEM to be porous for NSH and BS. Various parameters such as, initial metal ion concentration, adsorbent dosage, contact time, Temperature and pH of metal ion solution were investigated in a batch-adsorption System. The adsorption uptake was found to increase with increase in adsorbent dose, contact time and temperature but decreases with the initial concentration. The uptake of the metal ions increases and reaches optimum at pH of 4-6. The maximum adsorption capacity was found to be Pb-NSH (15.267mg/g) and Cu-NSH (19.46mg/g). Adsorption of Cu<sup>2+</sup>onto NSH fitted Langmuir isotherm model with (R<sup>2</sup> > 0.93) while Adsorption of Pb-NSH Fitted Freundlich isotherm Model with (R<sup>2</sup>> 0.99). Kinetic data fitted pseudo-second-order model (R<sup>2</sup> > 0.98) which was more suitable in explaining the adsorption rate. Thermodynamic data showed that Gibb’s free energy (ΔG°) values for all metal ions were negative indicating feasibility and favorability of adsorption. Positive enthalpy change (ΔH°) and Entropy change (ΔS°) values indicate endothermic processes and increase in randomness.