Sawdust of lam tree (Cordia africana) as a low-cost, sustainable and easily available adsorbent for the removal of toxic metals like Pb(II) and Ni(II) from aqueous solution

Abstract

Sawdust of lam tree (Cordia africana) has been investigated as an adsorbent for the removal of lead and nickel ions from aqueous solution. Since lam tree is widely grown in almost all the eastern, western, central and southern tropical African countries (United States Department of Agriculture, GRIN, Maryland), it can be a common most easily available, sustainable, low cost adsorbent for the treatment of wastewaters in this part of the world where growing industrialization is affecting water quality like elsewhere in the world. Therefore, it is worthwhile to investigate the potential of sawdust of lam tree as an adsorbent for the removal of lead and nickel ions from aqueous solution as a first step. The effect of contact time, pH, metal ion concentration and temperature on adsorption of these metal ions has been investigated to identify the optimum conditions for maximum adsorption. The equilibrium time was found to be 50 min for Pb++ and 70 min for Ni++ adsorption. Adsorption starts at a low pH and increases steadily as the pH increases. The equilibrium adsorption data at temperatures of 25, 40 and 60°C were analyzed by the Langmuir and Freundlich isotherm models. Although equilibrium adsorption data conforms to both the models, the best fit was obtained with the Langmuir isotherm. Thermodynamic parameters like equilibrium constant, enthalpy change, free energy change, and entropy change were calculated and discussed. The maximum adsorption capacity of sawdust for Pb++ and Ni++ were calculated from the Langmuir isotherms. The metal uptake was found to increase with increase in temperature. The positive values of ΔHo and negative values of ΔGo together indicate that the adsorption of Pb++ and Ni++ on sawdust of lam tree is endothermic and spontaneous in nature. The study demonstrated that the sawdust of lam tree can be effectively used as an adsorbent for the removal of metal ions from aqueous solutions.