Thermodynamics and intra-particle diffusion studies of Lead (II) ions in aqueous solution using modified and unmodified Cucumeropsis manii (Melon) pod husk

Abstract

This study describes the kinetics, mode of transport and thermodynamics of lead (II) Pb 2+ ions from aqueous solution onto modified and unmodified melon pod husk using batch adsorption method. Application of pseudo first-order, pseudo second order and intra particle diffusion models showed that the pseudo second-order gave the best fit to the experimental data with R2 values of 0.9986 and 0.9997 for unmodified (UCM) and citric acid modified (CA-CM) adsorbents respectively. The intra particle diffusion rate constants (Kid) obtained were high (66.22 and 98.20) for both unmodified and modified adsorbents, indicating an excellent adsorption mechanism. The fractional attainment, αe increased as the contact time increased. McKay and Poots equation employed showed that the adsorption process was film diffusion controlled. Thermodynamic parameters; ∆Go, ∆Ho and ∆So were evaluated. The values of ∆Ho and ∆So obtained were all positive suggesting physisorption. The ∆Go values were all negative indicating that the sorption was endothermic, spontaneous and feasible. The sticking probability, S* evaluated for the sorption of Pb (II) ions suggest that physisorption is the predominant mechanism. The results show that melon pod husk could be a good adsorbent for adsorption of Pb (II) ions and other heavy metals from aqueous solution and industrial waste water.