Adsorption Studies Of Cu (Ii) And Pb (Ii) Metal Ions From Aqueous Solution Using Maize Cob As Biosorbent

ABSTRACT

The use of raw maize cob (rmc) and activated maize cob (amc) as a low-cost natural adsorbent for the removal of Pb2+ and Cu2+ ions from simulated waste water was studied. Batch experiments were conducted to determine the effects of varying contact time, initial metal ion concentration, adsorbent dosage, pH and temperature of adsorption on adsorption equilibrium quantity (qe ) and percentage removal (% R). % R increased with increasing adsorbent dosage for the two metal ions. It also increased with increase in temperature from 20 °C to 70 °C for Cu2+ but decreased with temperature increase for Pb2+ in the same temperature range. The maximum adsorption of Pb2+ was found to be 92.68 % at contact time of 105 minutes and pH of 6 for rmc and 95.23 % at contact time of 45 minutes and pH of 12 for amc. The adsorption of Cu2+ was found to be maximum 89.15 % at pH of 12 and contact time of 75 minutes for rmc and 99.62 % at pH of 10 and contact time of 30 minutes for amc. Thermodynamic parameters such as ∆H and ∆S were determined. On rmc, ∆H and ∆S for Pb2+ were -31.70 kJ/mole and -81.31 J/mol/K respectively while those of Cu2+ were 30.39 kJ/mole and 114.82 J/mol/K. On amc, ∆H and ∆S for Pb2+ were -32.26 kJ/mol and -79.50 J/mol/K respectively while those of Cu2+ were 22.88 kJ/mol and 92.12 J/mol/K respectively. The kinetics of the adsorption mechanism of Cu2+ and Pb2+ on the adsorbents was evaluated using Pseudo-first order (Lagergren) rate, Pseudo-second order (Ho-model) rate, Elovich equation, power function and intra-particle diffusion. The results showed that Pseudo-second order model provides a more appropriate description of the metal ions adsorption onto the adsorbents (rmc and amc). Adsorption isotherms were determined and correlated using Langmuir, Freundlich, Harkins and Jura, Temkin, Halsey and Dubinnim-Radushkevich models. It was found that Freundlich, Temkin, Langmuir and Halsey models best fitted the isotherm data. FTIR and SEM analyses were carried out on rmc and amc to determine their structural information. These morphological investigations showed that rmc has rough structures without any crack while amc has active pores at the surface which enhance its adsorption capacity. It is therefore concluded that both rmc and amc can be used as an effective adsorbents for removal of heavy metals (Pb 2+ and Cu2+) from waste water.