The conventional theory of silica removal by strong base anion resins doesn't fit the observed behavior of silica very well at all. What is needed is a model that does a better job of explaining observed behavior.Suppose that silicic acid is neutralized by hydroxide form anion resin and is not exchanged for another anions. Silicic acid remains ionized, only so long as
there are sufficient hydroxide exchange sites available to keep it ionized. Since ion exchange resins do not have selectivity for un-ionized substances, when the pH drops in the resin phase, silica falls off the resin