Weak Base Anion

A weak base anion resin does not have the ability to remove weak acid anions (silica and carbon dioxide). It does, however, have a high capacity (kg/ft3) for the anions associated with the strong acids (SO₄^-, Cl^-, NO₃^-, etc.). The weak base anion resin would be the resin of choice where a decarbonator was in place at the cation effluent and where silica levels in the treated water were not a major consideration.

A demineralizer train that does not incorporate a decarbonator after the cation unit would be a good candidate for an anion bed consisting of a combination of weak and strong base resins. The weak base resin would be loaded on top of the strong base resin during the initial resin installation. During normal operation, the resin bed would be regenerated prior to backwashing. This is necessary to prevent the mixing of the two resins during backwash. In their exhausted state, the density of the resins is very nearly the same. In the regenerated state, their densities are different enough for the resins to separate during backwashing. Consequently, the weak base resin is always on top. This is the preferred position, because it insures that the resin with the greatest capacity for the strong acid anions receives the effluent from the strong acid cation first. Another advantage of this arrangement is that, like the strong base anion resins, the weak base resins also absorb organics; however, the organics absorbed by a weak base resin are removed during standard regeneration. This helps protect the strong base resin from irreversible organic fouling.