Sequestration of Lead Ion in Aqueous Solution onto Chemically Pretreated Pycnanthus angolensis Seed Husk: Implications for Wastewater Treatment

Abstract

This novel study investigated and proposes the use of Pycnanthus angolensis seed husk for the sequestration of Pb(II) from contaminated solutions, with the aim of contributing to the urgent need for accessibility to quality water, sustainable management of water and the environment in line with the Sustainable Development Goals (SDGs). The activated Pycnanthus angolensis seed husk was developed by modifying the pure sample (P-PA) with ethylene-glycol (E-PA) and Iso-butanol (I-PA). Infrared spectroscopy (FTIR), scanning electron microscopy (SEM), the Brunauer-Emmett-Teller (BET) analyzer, thermogravimetric analyzer (TGA), and X-ray diffractometer (XRD) were used to characterize the adsorbents before and after adsorption. The batch adsorption studies carried out revealed the highest adsorption of Pb(II) at pH 6 and 180 min for all the adsorbents. The functional groups, as well as the shifts in peaks after modification, were confirmed using FTIR analysis. In addition, SEM images show a heterogeneous, rough surface with sufficient cavities of the adsorbent after modification. The physiochemical characteristics indicated that BET pore volume and pore diameter increased for E-PA and I-PA compared to P-PA. The experimental data obtained indicated that Langmuir and pseudo-first-order (PFO) best described the isotherm and kinetic models, respectively. The adsorption mechanism revealed that the adsorption of Pb(II) was controlled mainly by pore filling, while electrostatic interaction, surface complexation, and ionic exchange also occurred minimally. The thermodynamic parameters, ΔH° and ΔG°, suggest an endothermic and spontaneous adsorption process, respectively. The findings in this study indicate that Pycnanthus angolensis seed husks offer cost-effective and sustainable solutions that are readily accessible for wastewater treatment.