Process for producing insoluble tannin and method for adsorbing hexavalent chromium by using the tannin

摘要

The process of the present invention comprises the steps of (a) a step of dissolving a condensed tannin powder in an aqueous alkaline solution, (b) a step of admixing an aqueous aldehyde solution with the aqueous solution obtained in the step (a), (c) a step of adding the aqueous solution obtained by the above step (b) to a hydrophobic solvent containing a polyether type nonionic surfactant under heating and stirring to disperse the aqueous solution in the form of droplets in said hydrophobic solvent and (d) evaporating water components from the above-mentioned droplets to form a spherical and gelled insoluble tannins. Water content of the gel can be widely controlled as 5 to 90% as compared with the conventional adsorbent and the network structure and molecular space are changed depending on the size of the metal ion to be adsorbed so that a gelled insoluble tannin which can increase an adsorption capacity of metals can be obtained. Also, when it is used as an adsorbent, it is not necessary to be pulverized and a gelled insoluble tannin having a desired particle size and water content can be obtained.