BATCH SORPTION BY LIGAND EXCHANGE: DETERMINATION OF INTRAPARTICLE DIFFUSIVITY

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Abstract
A mathematical model has been developed to describe batch sorption by ligand exchange. A ligand is sorbed onto an exchange sorbent from a finite bath. The sorbent particles are uniformly suspended in the fluid bath volume. The transport mechanisms are diffusion through the solid sorbent and external film diffusion. The equilibrium between the solid and fluid phase is described by a Langmuir isotherm. Two approaches are presented for representing the intraparticle mass transfer—diffusion in a pseudohomogeneous solid accompanied by sorption and diffusion through a saturated region to an unreacted shrinking core. The solid diffusion model, consisting of a partial differential equation, has been solved numerically by orthogonal collocation. The shrinking core model, a single ordinary differential equation, has been solved by conventional numerical integration. Both models successfully correlated data on diffusion of ammonia in copper-complexed carboxylic acid type ion exchange resin. The resultant sorbent diffusion coefficient is useful in designing fixed bed continuous ligand exchange columns.

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