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To determine why silicic acid elution is often incomplete during regeneration of strong base anion exchange resin columns, an OH− type anion exchange resin (OH− type resin) adsorbing silicic acid was prepared and the desorption (elution) behavior of silicic acid adsorbed to the resin was examined by batch and column experiments. It was first found that silicic acid adsorbed to an OH− type resin polymerizes to form polysilicic acids (Q1, Q2 and Q3 structures) even when a smaller amount of silicic acid than the ion exchange capacity was adsorbed (unsaturated adsorption). Consequently, elution of silicic acid from the OH− type resin column is most likely caused by hydrolytic decomposition of polysilicic acid. Silicic acids with Q0, Q1 and Q2 structures can be easily desorbed from the OH− type resin by immersing them in a 1% NaOH solution for 5 min. On the other hand, silicic acid with the Q3 structure is barely desorbed. In this study, incomplete elution of silicic acid from OH− type resin columns has been found to be caused by polymerization of adsorbed silicic acid and the elution behavior may depend on the polymerization mode.

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