Adsorption of Ni(II) ions using modified walnut shell: Factorial design analysis

The removal of Ni(II) ions from aqueous solutions by chemically modified walnut shell was studied .A 24 full factorial design analysis was performed to screen the variables affecting Ni(II) removal efficiency. The effects of individual variables (solution pH, adsorbent dose, initial concentration of Ni(II) ions, and temperature) and their interactions on metal removal efficiency were examined in a batch system. Using the experimental results, a linear mathematical model representing the influence of variables and their interactions was obtained. Analysis of variance (ANOVA), F-test and Student’s t-test showed that Ni(II) ions adsorption is strongly pH dependent and metal removal markedly increased with this factor. Adsorbent dose, initial metal concentration, temperature and interaction of solution pH and initial metal concentration also had positive effects on Ni(II) adsorption. Maximum removal efficiency of Ni(II) by modified walnut shell was 95.6% and corresponded to the values of: pH = 9, adsorbent dose = 20 g/L, initial metal concentration = 90 mg/L, and temperature = 45°C.