Single and dual fixed-bed columns for the removal of cd(Ii) and ni(ii) from water using volcanic rocks: Application of box–behnken design

Abstract

In this study, a continuous fixed-bed column adsorption system was employed for the removal of Cd(II) and Ni(II) from water using volcanic rocks, virgin pumice (VPum), and virgin scoria (VSco), as adsorbents. The effects of operating parameters such as particle size of adsorbents, initial heavy metal concentrations, flow rates, and media bed type (single and dual) on the adsorption performance of the column were examined at constant bed depth. The adsorption process parameters such as breakthrough time, retardation factors, total removal capacity of the adsorbents for Cd(II), and Ni(II) ions, adsorption exhaustion rate, and breakthrough volume were obtained. When the influent solution was fed to the column at a slow flow rate (Q = 2.5 mL min–1), the breakthrough volume increased significantly compared to the influent solution at a faster flow rate (Q = 5 mL min–1). The influent contained 2 mg L–1 Cd(II) and Ni(II), and better than 99% removal was achieved under optimum conditions. Box–Behnken design, a common approach of response surface methodology, was applied to optimize the variables affecting the adsorption of the heavy metals. The quadratic regression models with estimated coefficients were developed and it was observed that model pre-dictions matched with experimental values with an R2 value of 0.91 and 0.98 for Cd(II) and Ni(II) removal respectively. Relatively higher sorption capacities were observed in dual bed (VSco + VPum) column operation compared to a single bed (VSco) operation. Finally, the results obtained have shown that both volcanic rocks have a high potential for use as a filter bed material in water and wastewater treatment technologies.