Mass transfer modeling for fixed bed sorption of metal ions on bone char.

摘要

This research focused on the sorption of copper (II), cadmium (II) and zinc (II) ions onto bone char in fixed bed systems. The Langmuir, Freundlich, Sips and Redlich-Peterson isotherm equations have been used to correlate batch equilibrium experimental data and the Sips isotherm equation was found to give the most accurate correlation of the equilibrium relationship between these metal ions and bone char.; Column design requires dynamic data, and experiments with different feed concentrations, process flowrates and adsorbent particle sizes have been carried out for the three metal ions sorption systems. The Bed Depth Service Time design model and the Empty Bed Residence Time analysis were used to analyze the performance of the column and the effect of the different operating variables has been tested on these simplified fixed bed design models. New capacity loading terms have been incorporated into the BDST model which would estimate a more accurate bed capacity and improve the accuracy of the BDST prediction. New correlations for the operating lines of the EBRT plot have been proposed and verified for the three metal ion sorption systems.; Three mass transfer models, namely a modified film-pore diffusion model and film-surface diffusion models based on constant diffusivity or concentration-dependent diffusivity, were developed to describe the mass transfer process within a porous sorbent in a fixed bed system. These diffusion models were applied to different fixed bed metal ion-bone char column sorption systems for the first time to predict the column performances under different operating conditions. The results from these models demonstrated that the film-surface diffusion model was more successful in correlating the breakthrough profiles, suggesting that it provided a more appropriate description of the mass transfer processes in metal ion sorption onto bone char.; Model predictions for the multicomponent metal ion sorption systems on bone char were made with reasonable accuracy by applying the Ideal Adsorbed Solution theory in combination with a concentration-dependent surface diffusion model. Improved model prediction could be achieved by incorporating activity coefficients into the IAS theory and considering the interaction between the transport processes of the solutes within the particle.