Biosorption of Cr(III) and Pb(II) from synthetic wastewater under dynamic conditions – diffusion characteristics

Investigation of diffusion characteristics of adsorption systems under dynamic conditions has not received much attention despite its necessity of extending findings of static systems toward real-time applications. A biosorption system consisting of peel (710 < d < 1000 μm) of the fruit of Artocarpus nobilis biosorbent and Cr(III) or Pb(II) adsorbate shows that the rate constant evaluated according to the Thomas model (k_Th), saturation concentration (N_o) of the Adams-Bohart model and the rate constant of the Yoon Nelson model (k_YN) show a direct relationship with the flow rate and an inverse relationship with equilibrium uptake per unit mass of adsorbent (q_o). The opposite trend is observed with increase in bed height. The Weber and Morris intra-particle diffusion model shows that the boundary layer thickness (C) of the biosorbent depends on both the flow rate and the bed height. On the other hand, the intercept of the linear relationship between the extent of adsorption qt vs. t^1/2 (contact time) decreases with increase in bed height for both Cr(III) and Pb(II). The special feature of the negative intercepts observed in this dynamic biosorption system is indicative of retardation of intra-particle diffusion of Cr(III) and Pb(II) toward the biosorbent. The next logical step of this research would be the extension of this research in prototype systems.