Modelling of electrochemical ion exchange

Electrochemical Ion Exchange (EIX) is a process developed at the Harwell laboratory of AEA Technology, initially designed as a potential treatment for liquid wastes containing soluble radioactive species. Other applications for solutions containing dissociated substances are also possible. This thesis focuses on cation EIX, where the solution passes through a cell-a packed bed of ion exchange resin subject to an electric field produced by a pair of electrodes and a flux of protons, which displace the feed solution cations. These cations can be concentrated and eluted from the cathode. Much of the material would be completely analogous in anion EIX. After a general introduction to EIX, I derive a figure of merit which describes the efficiency of the cell. This will ultimately be the main subject for theoretical prediction and optimization. I briefly outline the methods for the theoretical treatment of the EIX process which I validated on experimental data. I developed a code to study porosity and transport properties of packed beds of resin by hard-spheres molecular dynamics for several types of bead size distributions. This makes the link between individual beads on the mesoscopic scale and the macroscopic properties of the resin bed, such as the hydraulic conductivity. Following this, I develop an integrated model of the whole cell based on macroscopic transport equations. These are solved numerically in order to study the steady state of the EIX process while the various process parameters are varied. Finally, I make specific recommendations for the future development of the EIX process based on the modelling experience