A Radiochemical Study of the Kinetics and Mechanism of Caesium Ion Adsorption on Potassium Copper Nickel Hexacyanoferrate(II)

Abstract

The adsorption of caesium ions on potassium copper nickel hexacyanoferrate(II) (KCNF) was carried out under optimum conditions to ascertain whether such adsorption occurred via an ion-exchange process. The results show that the adsorption takes place by means of a pure caesium-potassium ion-exchange reaction. Batch kinetic studies of the replacement of potassium ions on KCNF by caesium ions were carried out in aqueous solution at a pH value of 4.0 over the temperature range 293–333 K at a caesium ion concentration of 7.5 × 10 −3 mol/l. From the various thermodynamic quantities calculated, it was deduced that the ion-exchange process was endothermic. Kinetic studies of caesium adsorption on KCNF were carried out as a function of the particle size of KCNF and of the temperature. The data obtained at a caesium ion concentration of 7.5 × 10 −7 mol/l fitted the film diffusion model. Different physical parameters such as the effective diffusion coefficient and the activation energy were calculated. From an Arrhenius plot at a caesium ion concentration of 7.5 × 10 −7 mol/l, the activation energy was evaluated as 19.3 kJ/mol, thereby confirming the film diffusion nature of the process. However, the data obtained at the higher caesium ion concentration of 7.5 × 10 −3 mol/l could not be interpreted via the particle diffusion model but rather by a fast chemical reaction model. At this concentration, the reaction followed shell progressive reaction kinetics as confirmed by the linear Arrhenius plot obtained. This plot gave an activation energy of 68.5 kJ/mol for the process, thereby confirming the applicability of shell progressive reaction kinetics under these circumstances.