Biosorption of Pb (II) ion from aqueous solution using unmodified and modified Cola acuminata fruit husk

Effective use of agricultural wastes has become one of the promising fields of wastewater treatment technology due to their cost effectiveness as well as their eco-friendly nature. Unmodified Cola acuminata (UCA), phosphoric acid modified Cola acuminata (PMCA) and thermally modified Cola acuminata (TMCA) fruit husk were used in this study as a low cost adsorbents for the removal of Pb (II) ion from aqueous solution. Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDX), and a Brunauer-Emmett-Teller (BET) surface area analyzer were used to characterize the adsorbents. The impact of pH, metal ion concentration, adsorbent dose, contact time, and temperature on bisorption was evaluated using the batch adsorption approach. The data obtained were then applied to suitable isotherm and kinetic models. The percentage adsorption of Pb (II) decreased with increase in metal ion concentration while for pH, adsorbent dose, contact time and temperature there was an increase in percentage adsorption as their parameters increases while the optimum was at pH of 6. The percentage adsorption of Pb (II) increased from 15.86 to 73.14, 28.32 to 84.00, and 26.15 to 79.12%, for UCA, PMCA, and TMCA respectively. The trend of metal adsorption on the adsorbents was in the order PMCA > TMCA > UCA. The adsorption data were fitted to the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) with the Langmuir isotherm providing the best fit. The FTIR showed that the O-H, C≡C and C = O groups were the major sites for the adsorbent material. The energy dispersive X-ray spectrum displayed the principal elements, such as nitrogen, silicon, carbon, oxygen, calcium, potassium, and magnesium, in different percentages, while the scanning electron microscope (SEM) image demonstrated its high porosity and numerous pore cavities that served as adsorption sites. Only pseudo-second order and physisorptions were found to offer the best fit to the experimental data of Pb (II) ions, according to the kinetics and thermodynamic analyses. TMCA showed the highest desorption 86.92% after fourth cycles of desorption experiment. These results show that the three adsorbents have the potential to be used as low-cost and efficient adsorbents for the removal of lethal heavy metals from aqueous solutions.