Mass transfer kinetics of adsorption on suspended solid particles

Abstract

A theoretical kinetic model for adsorption from an agitated liquid phase to solid spherical particles suspended therein has been formulated, solved numerically and compared with the results of experiment. Important aspects of the model include the fact that it accounts for the influence of forced convection as well as the influence of adsorbate concentration changes in the bulk liquid on the mass transfer. The integration of the general equations has been carried out for systems in which equilibrium is described by Langmuir, Freundlich and linear adsorption isotherms. Results of the analysis are presented in the form of graphical relations between dimensionless quantities, which permit the description of concentration changes in the vessel vs time for systems under a wide range of conditions of practical interest. Results obtained theoretically have been applied to adsorption of dextrose and urea on ordinary and on oxidized active carbon from dilute aqueous solutions. Very good agreement between theory and experiment has been observed. Adsorption equilibrium of these systems and the influence of temperature on adsorption kinetics has been investigated as well. The adsorption of dextrose and urea are of practical importance because these substances occur as polutants in wastewater; adsorption of urea on active carbon is also of importance since this process can be applied to the removal of urea from dialysate in artificial kidney machines, thereby improving the speed and efficiency of treatment.