The adsorption mechanism of Cr(VI) to the tannin molecules was clarified. The adsorption
mechanism consists of four reaction steps; the esterification of chromate with tannin molecules, the
reduction of Cr(VI) to trivalent chromium Cr(III),
the formation of carboxyl group by the oxidation of
tannin molecules and the ion exchange of the reduced Cr(III) with the carboxyl and hydroxyl groups.