  Diffusion and reaction of initially separated ions A- and B+ in the presence
of counter ions A'+ and B'- is studied. The dynamics is described in terms of
reaction-diffusion equations obeying local electroneutrality, and the
time-evolution of ion-concentrations is determined. We find that, in the
absence of reactions, unequal mobility of ions generate nontrivial features in
the macroscopically observable concentration profiles. Switching on the
reaction (A-) + (B+) -> C leads to the formation of a localized, diffusive
reaction front and one finds that the properties of the front (e.g. effective
diffusion constant) are affected by the background ions. The consequences of
this effect on the formation of Liesegang patterns is discussed.

Statistical Mechanics;Chemical Physics