Removal properties of dissolved boron by glucomannan gel

Boron ions have long been known to form complexes with the cis-diol group of a polysaccharide. Konjac glucomannan (KGM) which is one of polysaccharides was used to remove dissolved boron in this study. KGM forms a complex with boron, but does not remove boron from contaminated waters as well as other polysaccharides because of its high water solubility. Therefore, the removal efficiencies of dissolved boron were examined using both an insoluble KGM gel and KGM semi-gel. The former did not remove dissolved boron, but the latter did. The difference in the ability of boron removal was due to the presence of diol group inside. KGM loses free diol group during the process of gelation. On the other hand, the semi-gel gelated only surface layer in water has diol group inside. The boron removal capacity of the semi-gel was highest at pHs ⩾ 11, when the boron species is present as B(OH)4-. The capacity was slightly increased by the addition of Al, Ca and Mg under high pH conditions. This was due to co-precipitation of boron with Ca dissolved from the semi-gel. The boron adsorbed to the semi-gel easily was desorbed under low pH conditions and the hysteresis was not found.

► The boron removal efficiency was compared between the gel and semi-gel of glucomannan.
► The semi-gel removed the boron at pH ⩾ 11, which boron species is present as B(OH)4-.
► The semi-gel retained the free diol group had a high boron removal capacity.
► The gel lost diol group in the gelation process was not able to remove the boron.
► The presence of metals did not effect to boron removal capacity.