The feasibility of Date-palm (Phoenix dactylifera) Leaf Ash (DLA) (a low-cost agricultural-byproduct) was investigated for adsorption of Pb(II) ions. An adsorption process was carried out to evaluate initial concentration, adsorbent dose, contact time, pH and temperature on the removal of Pb(II). The removal efficiency decreased with an increase of initial Pb(II) concentration and optimum removal efficiency of 99.72% was at 50 mg/l Pb(II) solution, 0.5 g/l DLA dose and pH level of 5. The equilibrium data were analyzed using the Langmuir and Freundlich isotherm models by nonlinear regression analysis at 20, 30 and 40 oC. It was found that the Langmuir isotherm model fitted better than the Freundlich isotherm model. The kinetic adsorption of Pb(II) ions was analyzed by the pseudo-first-order, the pseudosecond- order and the intra-particle diffusion model, demonstrating the overall adsorption was the one most suited to the pseudo-second-order kinetic model. Thermodynamic parameters, Gibbs free energy (ΔGo), enthalpy (ΔHo), and entropy (ΔSo) were also evaluated with application of the van’t Hoff equation that describes the dependence of equilibrium constant on temperature. The thermodynamics of Pb(II) adsorption onto DLA demonstrated that adsorption was spontaneous and endothermic.
