Optimization of heavy metal removal from aqueous solutions by maghemite (γ-Fe2O3) nanoparticles using response surface methodology

• Pb, Zn and Cd ions were removed from aqueous solutions by maghemite nanoparticles.
• Effects of some critical parameters and their interactions were evaluated by RSM.
• The selectivity order for competitive removal was Pb(II) > Zn(II) > Cd(II).

The presence of heavy metals in the wastewaters is a serious threat to the environment. In this research, the removal of some heavy metal ions, including Pb(II), Zn(II) and Cd(II) using maghemite (γ-Fe2O3) nanoparticles as adsorbent was studied in an aqueous system. Experiments were carried out at a laboratory scale in 100 mL Erlenmeyer flasks at 150 rpm for 120 min. A response surface methodology (RSM) with a Box–Behnken Design was employed to evaluate the effects of solution pH, temperature, initial heavy metal concentration and adsorbent dosage on the removal efficiency of the heavy metals. Results of analysis of variance (ANOVA) showed that the initial metal concentration and pH were the most significant parameters for Cd(II) ion removal. Adsorbent dosage, pH and their interaction effect had significant influences on the removal efficiency of Pb(II) ions. The interaction effect of pH and initial concentration of metals had the most significant influences on the removal efficiency of Zn(II) ions. The optimum pH, temperature, initial concentration of metals and adsorbent dosage were found to be 7.5, 45 °C, 50 mg/L, and 4.74 g/L, respectively. The observed selectivity order was as follows: Pb(II) (10.55 mg/g) > Zn(II) (4.79 mg/g) > (1.75 mg/g) Cd(II). It was confirmed from SEM-EDAX analyses that heavy metal ions were present on the surface of nanoparticles after adsorption. Results indicated that maghemite nanoparticles can be used as an effective adsorbent for effluent decontamination especially in Pb–Zn bearing wastewaters.