Computer simulation of diffusion of metal ions in resins – phenomenological analysis of diffusion process

Abstract

In this study, a series of photographs of a Cu(NH 3) 4 2+ loaded resin contacted with EDTA solutions at different concentrations was taken by an instrument set which consisted of a microscope with a Panasonic colour digital camera and a PC matching with Moviestar software. The evaluation of the photographs provides evidence for the development of ion exchange kinetic process occurring in the investigated system and the state of swelling can be followed exactly. A three-dimensional dynamic photograph model of the ion exchange was fitted to the diffusion process of the Cu(NH 3) 4 2+ load resin ∼NH 4 + using Matlab 5.1 software. The dynamic photograph model of the ion exchange process supports the `moving-boundary' process hypothesis in ion exchange kinetics. In the process of the exchange, the bulk of the resin showed no significant increase and the exchanging boundary of Cu(NH 3) 4 2+ loaded resin with NH 4 + exchange gradually shrank as the exchange proceeded. The results show that the Cu(NH 3) 4 2+ loaded resin with NH 4 + exchange process may consist of the following four consecutive steps: (1) detention period; (2) film diffusion; (3) combination of film diffusion and inner diffusion and (4) inner diffusion. The exchange rate of Cu(NH 3) 4 2+ loaded resin with NH 4 + increase with increasing EDTA concentration. In addition, it was demonstrated that the boundary profiles recorded by single particle microphotograph technology can be used for evaluating the diffusion coefficients of metal ions in ion exchange process.