Adsorption of lead ion from aqueous solution by modified walnut shell: kinetics and thermodynamics

Abstract

The novel modified walnut shell (WNS-MAH) with higher adsorption capacity for lead ion was prepared by reacting walnut shell (WNS) with maleic anhydride. Both WNS and WNS-MAH were analyzed by SEM and FTIR. The adsorption capacity of WNS-MAH for lead ion was evaluated at different adsorbent doses, pHs, time and temperatures. The adsorption kinetics and adsorption isotherms were investigated from (298 to 318) K. The adsorption kinetics of lead ion onto WNS-MAH were fitted using pseudo-first-order, pseudo-second-order and Elovich models. It was found that pseudo-second-order model gives the best correlation results. The diffusion mechanism was determined according to the intraparticle diffusion equation and Boyd equation. Results suggested the adsorption process was governed by film diffusion. The equilibrium adsorption data were fitted with the Freundlich model and the Langmuir model. The maximum adsorption capacity of WNS-MAH for lead ion removal was 221.24 mg/g at 318 K. The equilibrium adsorption data were analyzed using the D-R model, and the feature concentration ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>C</mml:mi></mml:mrow><mml:mi>e</mml:mi><mml:mrow><mml:mi>'</mml:mi></mml:mrow></mml:msubsup></mml:math> ) was determined to distinguish chemisorption and physisorption. The thermodynamic parameters (ΔG, ΔH and ΔS) were calculated. Additionally, the regeneration property was studied and the adsorption process was confirmed by energy disperse spectroscopy.