Investigation of the continuous flow sorption of heavy metals in a biomass-packed column: revisiting the Thomas design model for correlation of binary component systems

Remediation of aquatic environments polluted by toxic heavy metals has become a focus of interest for many chemical and environmental engineers throughout the world. In the present study, rice straw was employed as a low-cost agricultural waste material for the removal of Cd(II) and Pb(II) ions from single and binary solutions. Isothermal biosorption experiments were conducted at 303.15 K using a column at various flow rates and bed heights. The breakthrough curves for single metal systems were fitted with the Thomas, Yoon-Nelson, bed-depth-service-time (BDST) and dose-response models. A new semi-empirical model based on the classical Thomas equation has been developed for simulation of the breakthrough curves for binary metal systems. This modified Thomas model, combined with sorption-inhibiting coefficients determining competitive sorption behavior, was found to represent the breakthrough data very adequately. The exhausted biosorbent bed was readily regenerated using an acid elution method involving a 0.05 mol l(-1) HCl solution, and was reused for five consecutive sorption-regeneration cycles without significant loss of adsorption capacity. The used biosorbent also showed economic promise in the packed bed treatment of actual electroplating wastewater containing Cd(II) and Pb(II) ions.