Sorption Equilibrium, Kinetics and Thermodynamic Studies of Pb (II), Ni (II) and Co (II) ions adsorption in Aqueous Solution by Sweet dattock (Detarium microcarpum) shell

Abstract

Chemically activated Detarium microcarpum shell was used as an adsorbent to remove Pb (II), Ni (II) and Co (II) ions from aqueous solution by batch adsorption technique. Batch adsorption experiments were performed as a function of pH, contact time, initial metal ion concentrations and temperature. The residual concentra tions were determined using Atomic Absorption Spectrophotometer (AAS). The optimum pH required for maximum adsorption was found to be 5.0 for Co (II) ion, 6.0 for Pb (II) and Ni (II) ion respectively. Equilibrium times of 60 minutes were attained for Ni (II) and Co (II) ions and 90 minutes for Pb (II) ions. The amount of metal ions adsorbed by the substrate increased with increase in initial metal ion concentration. The equilibrium data correlated well with Freundlich and Dubinin-Radushkevich (D-R) adsorption model. The trend of adsorption isotherm was Freundlich > Dubinin –Radushkevich (D-R) > Langmuir adsorption isotherm. Adsorption kinetics data were modeled using the pseudo-first and pseudosecond order models. The results indicated that pseudo-second order model best described adsorption kinetic data. The thermodynamic parameters (standard Gibbs Free energy (∆Go), standard Enthalpy (∆H o) and standard Entropy (∆So)) showed that the adsorption process of the metal ions was feasible, non-spontaneous, endothermic and decreased randomness at the sorbent-sorbate interface. The biosorption study showed that Detarium microcarpum shell could be a viable alternative to commercial activated carbon in the removal of potentially toxic elements from aqueous solution.