Optimization of Ni(II) adsorption onto Cloisite Na⁺ clay using response surface methodology

The aim of this study was to investigate the adsorption of Ni(II) from aqueous solutions onto Cloisite Na⁺ clay. The effects of the initial concentration of Ni(II), adsorbent dose, pH, and temperature on adsorption capacity were studied using response surface methodology. A second-order regression model was determined based on the experimental results. Analysis of variance used to evaluate the individual and combined effects of process variables showed that initial Ni(II) concentration and adsorbent dose were more significant than solution pH and temperature. Moreover, the interaction effects of the initial concentration of nickel and the adsorbent dose, as well as the solution pH and adsorbent dose were significant. High coefficient of determination (R² = 0.93) and low probability values signify the validity of the model for predicting the adsorption capacity of Cloisite Na⁺ for Ni(II) ions. The optimal conditions for pH and adsorbent dose were found to be 6.9 and 0.21 g/L, respectively at a constant temperature of 25 °C and initial Ni(II) concentration of 50 mg/L. Under these conditions, the adsorption capacity of clay was found to be 31.43 mg/g. Moreover, the adsorption isotherms results indicated that these data could be best fitted to the Langmuir isotherm model (R² = 0.99). The Langmuir maximum adsorption capacity was estimated to be 32.05 mg/g for an adsorbent dose of 0.2 g/L at pH 7 and 25 °C. In conclusion, the results showed that Cloisite Na⁺ clay can be utilized as an effective adsorbent for the removal of Ni(II) from aqueous solutions.