Biosorption of Pb2+ from aqueous solution onto unmodified African oil bean (Pentaclethra macrophylla) pod: Isotherm, kinetic and thermodynamic studies

Lead (Pb 2+ ) is particularly hazardous due to its high toxicity even at low concentrations. However, various conventional methods employed for sequestration of Pb(II) from wastewater has shown several degrees of limitations ranging from cost to environmental impacts. Thus, the performance analysis of Unmodified African Oil Bean (Pentaclethra macrophylla) Pod (UAOBP) as an economical and efficient adsorbing material for Pb 2+ removal from its aqueous solution was investigated. To achieve this, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM EDX), Braunauer-Emmett Teller (BET) and Thermogravimetric analyzer (TGA) were used for the characterization of the adsorbent before and after adsorption while the adsorption parameters were evaluated using batch adsorption studies. The result showed that the adsorption process follows multi- pathway consisting of surface-associated transport on the active sites, functional group interaction via deprotonation, electrostatic attraction, ion exchange, surface complexation and pore filling. This adsorption mechanism is supported by the characterization result which suggested that the presence of functional groups and a porous surface structure enable Pb 2+ binding on adsorbent surface. From the experimental data, kinetic analysis showed that the pseudo-second-order model best described the adsorption behaviour (R 2 = 0.999), with close agreement between experimental and calculated adsorption capacities. The results suggest that UAOBP could be effective in the sequestration of Pb(II) from contaminated wastewater and serves as a credible alternative for conventional methods.