The equations for the fixed-bed ion exchange process have been rigorously solved to give breakthrough curves using analog, digital and hybrid computers.

The models developed for the ion exchange column process are general enough to include:- • Linear and non-linear equilibrium • Constant or variable separation factor • Mass transfer resistance in either the solution or the resin phase, or both • Axial dispersion • General initial conditions for column presaturation • Arbitrary boundary conditions for partial or complete break- through curves.

Results indicate that simple rate relations are adequate to express column behaviour for most requirements. In particular, the Thomas model as developed by Hiester and Vermeulen is easy to use and sufficiently accurate for normal applications.

A comparison of computed results with experimental data has shown that the ion exchange column process can be accurately simulated. However, this required the use of a variable separation factor for some systems.