Modeling and optimization of energy-efficient procedures for removing lead(II) and zinc(II) ions from aqueous solutions using the central composite design

Abstract

The objective of study was to model and optimize the adsorption procedures for the removal of lead(II), i.e. zinc(II) ions from the aqueous solutions using bentonite clay as an efficient and low cost adsorbent. A central composite design (CCD) was employed to optimize the conditions of independent variables (adsorption time, pH value and bentonite clay concentration). Both batch adsorption processes were performed at room temperature, adsorption time of 5–75 min, pH of 1–7 and bentonite clay concentration of 1000–9000 mg/dm3. The response (the percentage of adsorbed lead(II), i.e. zinc(II) ions) was fitted by a quadratic polynomial regression model using least square analysis in a five-level-three-factor CCD. The optimal conditions for zinc(II) adsorption were achieved at adsorption time of 60.8 min, pH value of 5.8 and bentonite clay concentration of 7378.4 mg/dm3, and at adsorption time of 56.6 min, pH of 5.73 and bentonite clay concentration of 6606.15 mg/dm3 for lead(II) adsorption. After adsorption, the concentrations of lead(II) and zinc(II) ions were reduced from 50 to 6.9 mg/dm3 and to 17.6 mg/dm3, respectively. Unlike the concentration of zinc(II) ions, the concentration of lead ions was in the allowed range in the aqueous medium after adsorption.