Calcareous Soil as a New Adsorbent to Remove Lead from Aqueous Solution: Equilibrium, Kinetic and Thermodynamic Study

In this work the feasibility of employing calcareous soil to remove lead (II) ions from its aqueous solutions was investigated under batch mode. The influence of solution pH, sorbent dose, initial lead (II) concentration, contact time, stirring rate and temperature on the removal process were investigated. The lead adsorption was favored with maximum adsorption at pH 6.0. Sorption equilibrium time was observed in 60 min. The equilibrium adsorption data were analyzed by the Freundlich, Langmuir, Dubinin-Radushkevich (D-R) and Temkin adsorption isotherm models. The kinetics of Pb(II) ion was discussed by pseudo-first-order, pseudo-second-order, intraparticle diffusion and surface mass transfer models. It was shown that the adsorption of lead ions could be described by the pseudo-second order kinetic model. The activation energy of the adsorption process (Ea) was found to be -34.64 kJ mol -1 by using the Arrhenius equation, indicating exothermic nature of lead adsorption onto calcareous soil. Thermodynamic quantities such as Gibbs free energy ( G o ), the enthalpy ( H o ) and the entropy change of sorption ( S o ) have also been evaluated and it has been found that the adsorption process was spontaneous, feasible and exothermic in nature. A six layered feed forward neural network with back propagation training algorithm was developed using thirty one experimental data sets obtained from laboratory batch study. The ANN predicted results were compared with the experimental results of the laboratory test. It was concluded that calcareous soil has potential for application as an effective adsorbent for removal of lead ions from aqueous solution.