Removal of lead(II) ions from aqueous solutions using activated carbon from Militia ferruginea plant leaves

Abstract

The adsorption of lead(II) on to activated carbon developed from an indigenous Ethiopian medicinal plant leaves namely Birbira (Militia ferruginea) was investigated to assess the possible use of this adsorbent. The influences of contact time, adsorbent dose, Pb(II) concentration, pH and temperature on adsorption were investigated. The maximum adsorption took place at 3 h. at a dose of 4.0 g of adsorbent, and 97.3 % of Pb²⁺ adsorption at pH of 4.0. The amount of lead ion adsorbed per gram of the adsorbent increased with decreasing concentration of Pb²⁺. The percentage of adsorption had increased with the increasing temperature. The positive value of ∆H indicated that the adsorption of lead ions on the adsorbent was an endothermic process. The values of free energy (∆G) were negative as expected for a spontaneous process. The decrease in ∆G value with increasing temperature revealed that adsorption of the ion on the adsorbent became favorable at a higher temperature. The calculated value of ∆H was 25.05 kJ mol^–1, ∆S was 135.48 JK^-1 mol^-1 and ∆G was also calculated for each temperature. The two theoretical adsorption isotherms, namely, Langmuir and Freundlich were used to describe the experimental results. The Freundlich adsorption isotherm best fits and adsorption capacity was calculated to be 3.3 mg of Pb(II) per g of adsorbent. The adsorption followed the first order kinetics and was found to be pH dependent being maximum at pH 4.0. The pH effect and desorption studies showed that ion exchange mechanism might be involved in the adsorption process. Reuse of the desorbed bio-adsorbent is possible. The effect of foreign ions on the removal of Pb(II) has been investigated. The removal of Pb(II) from industrial wastewater sample was also tested and showed that more than 97 % removal was possible. The results showed that activated carbon prepared from Birbira (Militia ferruginea) leaves could be used for the removal of Pb(II) from wastewater.

KEY WORDS: Industrial wastewater, Lead removal, Adsorbent, Militia ferruginea

Bull. Chem. Soc. Ethiop. 2008, 22(3), 349-360.