Natural zeolite for nickel ions removal from aqueous solutions: optimization and modeling using response surface methodology based on central composite design

Abstract

Natural zeolite was tested as a low-cost adsorbent for Ni(II) removal from aqueous solutions. In order to reduce the total number of experiments necessary for achieving the best conditions of the batch sorption procedure, response surface methodology based on central composite design was carried out for the natural zeolite. Four independent variables, viz. initial nickel ion concentration (10–200 mg/L), adsorbent dose (0.1–0.7 g/L), contact time (5–120 min), and initial pH of solution (2–8) were transformed to coded values and the quadratic model was built to predict the responses. Very high regression coefficients between the variables and the response indicate excellent evaluation of experimental data using a second-order polynomial regression model. Three-dimensional plots demonstrate relationships between the nickel ion uptake with the paired factors (as the fourth factor was kept at its optimal level), which illustrate the behavior of the sorption system in a batch process. The model showed that nickel uptake in aqueous solution was affected by all four factors studied. An optimum nickel uptake was achieved at an initial nickel ion concentration of 10–15 mg/L, clinoptilolite dosage of 0.37–0.43 g/L, a contact time of 56–68 min, and a pH of 4.8–6. On the basis of experimental results and model parameters, it can be inferred that the adsorbent, which exhibits a relatively high adsorption capacity, can be utilized for the removal of nickel from aqueous solution.