Batch biosorption of lead(II) from aqueous solutions by olive tree pruning waste: Equilibrium, kinetics and thermodynamic study

A new biosorbent for removing lead(II) ions from aqueous solutions has been investigated. This new adsorbent is olive tree pruning waste, an agricultural by-product in the Mediterranean region. Removal of lead(II) was studied at pH 5 in a batch system. The pseudo-first-order, pseudo-second-order and Weber and Morris kinetic models were applied to test the kinetic experimental data. The pseudo-second-order kinetic model provided the best correlation of the experimental data, indicating that sorption may be the rate limiting step for lead(II) biosorption by olive tree pruning waste. Equilibrium experimental results were fitted to Langmuir, Freundlich and Sips model isotherms to obtain the characteristic parameters of each model. The Langmuir and Sips isotherms best represented the measured biosorption data. According to an evaluation using the Sips equation, the maximum lead(II) biosorption capacities of olive tree pruning wastes were 26.24, 33.39 and 32.15 mg/g at 25, 40 and 60 °C. Using thermodynamic equilibrium coefficients obtained at different temperatures, various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, were calculated. The thermodynamics of the investigated lead ion–olive tree pruning system indicate a spontaneous and exothermic process.