Adsorption characteristics of lead on cotton-stalk-derived activated carbon fibre by steam activation

Abstract

Lead adsorption from aqueous solutions was studied with the aim of detoxifying industrial effluents before their safe disposal onto land or into river waters. Cotton stalk, a waste and renewable agricultural by-product, was synthesized as an effective adsorbent by steam activation for lead removal. The effect of various parameters such as solution pH, contact time, initial lead concentration, adsorbent dose and temperature was studied to optimize the conditions for maximum adsorption. The obtained equilibrium data were mathematically modeled using Langmuir, Freundlich and Langmuir-Freundlich equations to describe the equilibrium isotherms at different temperatures, and the kinetics data were fitted with the pseudo-first-order, pseudo-second-order and Elovich models. The optimum solution pH for the removal of lead ions was found to be 5.8. The maximum adsorption capacity was found to be 53.5 mg of lead per gram of activated carbon, and the adsorption isotherms followed well the Langmuir-Freundlich adsorption models. The kinetic rates were best fitted to the pseudo-second-order model. Thermodynamic study showed the adsorption was a spontaneous and exothermic process. The above results showed that the activated carbon fibre prepared in this study does offer favorable characteristics in lead adsorption from weak acidic wastewater.