Chemical activation of olive tree pruning to remove lead(II) in batch system: Factorial design for process optimization

Biosorption of Pb(II) by olive tree pruning (OTP) treated with three chemical agents (HNO3, H2SO4 and NaOH) using a batch system was studied. The effect of pH over a range from 3.0 to 5.0, the initial lead concentration over a range from 50 to 250 g m−3 and the treatment concentration over a range from 100 to 2000 mol m−3 on the metal removal was investigated. All treatments improved the percentage of lead removal by native OTP. Improvements obtained with treatments of treated OTP respect to untreated OTP at pH 5, an initial lead concentration of 250 g m−3 and treatment at 1000 mol m−3 were 64.72, 55.05 and 64.82% to HNO3, H2SO4 and NaOH respectively. The metal uptake also increased by increasing the pH and the initial lead concentration. A 33 factorial experimental design was employed to study the effect of three factors (pH, initial lead concentration and treatment concentration) for olive tree pruning treated with three treatment (HNO3, H2SO4 and NaOH) and at three levels (low, intermediate and high). A second-order polynomial regression model was used to fit experimental data obtained, and results showed a good agreement with experimental data for the three cases studied. Results obtained for the three treatments were compared and the best response was obtained with OTP treated with NaOH. Optimization process predicted the optimum conditions for the maximum biosorption capacity of Pb(II) for each treatment: 25.54, 23.87 and 26.63 g kg−1 for treatments with HNO3, H2SO4 and NaOH respectively. The equilibrium data for biosorption of lead onto olive tree pruning were represented by the Langmuir and Freundlich isotherms, giving the best fit the Langmuir model.