APPLICATION OF KOLA NUT POD AS INDUSTRIAL ADSORBENT FOR THE REMOVAL OF HEAVY METALS IN WASTEWATER

Abstract

The potential of using modified and unmodified kola nut pod to remove selected heavy metals (lead (II), cobalt (II) and cadmium (II) ions from aqueous solution was investigated. The kola nut pod in four different forms: unmodified, citric acid, nitric acid and chitosan-oxalic modified adsorbents were used. Morphological characterization of these adsorbents before the removal of these metal ions was done using Scanning Electron Microscope (SEM) and the elemental composition of the kola nut pod samples were determined qualitatively and quantitatively using Energy Dispersive X-ray spectroscopy (EDX) before adsorption studies. The batch adsorption experiments were conducted to investigate the effect on variable parameters such as pH, contact time, temperature, initial metal concentration and adsorbent dose on the removal of heavy metals in wastewater. The optimum conditions established for each metal-adsorbent was used to investigate the adsorption of the same metals from the real industrial effluent of a paint industry. The scanning electron micrographs obtained showed that there were prominent changes (wider pores) in the morphological appearance on the surface of modified and unmodified kola nut pod powder (after modification with different chemicals). The EDX analysis revealed that the unmodified kola nut pod adsorbent contains C (30.82% ), N (16.29% ),O (8.7% ), K (21.46% ),P (0,31% ), S (1.14% ),Si (1.14% ) Ca ( 5.75%) and Cl(0.64%) , citric acid modified adsorbent contains C (44.75%) ), N (26.28% ), K (5.8% ), O (12.25% ), S (2.94%S), Si (3.23% ) and Ca (3.33%); nitric acid modified adsorbent contains C ( 35.32%), N ( 34.37%), P (0.1% ), K ( 17.41%), O (11.01% ), S (1.05% ), Si ( 0.05%) and Cl (0.68% ) and chitosan modified adsorbent contains C (0.01% ), N (14.46% ), K (7.76% ), O (14.48% ), Si (0.09% )and Ca (62.24%). The results of the energy dispersive x-ray analysis of the four different adsorbents clearly indicate that the adsorbents are carbonaceous since carbon was present in a large amount than other elements in all the samples except in chitosan-oxalic modified adsorbent. The percentage composition is in the order of citric acid modified adsorbent, nitric acid kola nut pod adsorbent, unmodified kola nut pod adsorbent and chitosan –oxalic modified kola nut pod adsorbent i.e. CAKPA>NAKPA>UKPA>COKPA. Kinetics parameters obtained showed that this study did not obey the pseudo-first order. The Pseudo-second order was obeyed throughout the adsorption process for the removal of metals. Isotherm model was employed using linearized form of Langmuir, Freundlich, Temkins, HarkinsJura and Dubnin-Radushkevich model. This revealed that the removal of metals by unmodified and nitric acid modified adsorbent obeyed Dubnin-Radushkevich and Temkins isotherm models. However, the removal of metal ions by citric acid modified and chitosan modified adsorbents fitted well into Freundlich model. The n values and Kf values for the selected heavy metals used were favourable except for the removal of cadmium using chitosan-oxalic modified adsorbent. The thermodynamics studies showed that the adsorption of these metal ions was spontaneous except for the removal of cadmium ion using chitosan-oxalic modified adsorbent. The negative value of ΔH (enthalpy change) obtained in this study showed that the adsorption process was exothermic for all the adsorbents except the chitosan-oxalic modified adsorbent. The results obtained from the removal of selected heavy metals Pb (II), Co (II) and Cd (II) ions from industrial effluent using unmodified and modified adsorbents showed that the metal uptake was slightly lower compared to simulated water. For unmodified kola nut pod adsorbent at optimum pH, contact time, temperature and adsorbent dosage, the results for Pb (II) ion were; (71.15%), (76.54%), (78.00%) and (79.34%), Co (II) (78.30%), 78.30%, 80.64% and 89.95% and Cd (II) ions (76.74%), (87.80%), (78.53%) and 85.45% for industrial effluent. Citric acid modified kola nut pod for Pb (II) ion were; (90.15%), (89.10%), (92.50%) and 89.90%; Co (II) ion ; 82.51%, 81.31%, 85.90% and 87.07% and Cd (II) ions ; 99.68%, 99.80%, 99.71% and 99.70% . Nitric acid modified kola nut pod adsorbent for Pb (II) ion were; 89.58%, 97.04%, 97.11% and 84.19%. Co (II) ion; 77.53%, 75.17%, 65.42% and 86.20% and Cd (II) ion ; 96.99%, 97.06%, 96.94% and 96.94%. However, the result obtained for chitosan-oxalic modified kola nut pod adsorbent was almost the same like that of the aqueous water .These were; Pb (II) ion; 97.80%, 97.09%, 98.31% and 98.34%. Co (II) ion; 99.10%, 98.16%, 98.31% and 99.41% and 99.27%, 99.16%, 99.32% and 95.27% Cd (II) ion respectively. However, from the favorability of this adsorption process, based on the results obtained in this research work, these adsorbents can be used industrially in removing the toxic heavy metals in wastewaters.