Ion Exchange Column Performance Model for Separation of Zr(IV) and Hf(IV) in Elution Process

A mathematical model of sorption of Zirconium and Hafnium cations mixture and elution of these ions from a cation exchange resin bed is developed. Sulfuric acid is selected as the eluent for selective separation of Zr and Hf in a packed bed of Dowex cation exchange resin. The column model is a dispersed plug flow model,and assumed to consist of randomly packed synthetic and spherical resin beads with constant diameter. The beads are assumed to be porous containing not only active sites on their solid structure but also solution-filled pores. The model incorporates mass transfer resistances including inter and intra-particle effects within the solid and fluid phases. Intra-particle diffusion is treated by employing pore diffusion model. The adsorption phenomena of the cations on the active sites is expressed by the equilibrium relationship characterized by a form of the extended Langmuir equation. The batch experiments are carried out in order to determine Langmuir parameters at equilibrium, and pore diffusivity at transitional conditions. These parameters are used in the dynamic model of adsorption and desorption of the mentioned cations. Unlike a number of earlier models the present mathematical model does not have assumptions such as the linearity of the sorption isotherms, uniform concentration profile in the resin particles and ideal plug liquid flow along the bed. It is found that the present model predicts the breakthrough and chromatographic curves with a fair degree of accuracy. It is concluded that the eluent  acid concentration and  flow rate of the liquid along the bed are the most two important variables which influence the efficiency of separation.