The adsorption behavior of chromium(III, VI) onto activated carbon (AC, Merck Co. Ltd.) and oxine-impregnated activated carbon (AC(HOx)) was investigated by use of a column method. The adsorption of chromium(III, VI) onto activated carbon, and of chromium(VI) onto AC(HOx) showed remarkable pH-dependency. The optimum pH for the adsorption of chromium(VI) from 1.00 × 10
-3 mol dm
-3 chromium(VI) solution were about 2.5 for activated carbon and about 3.0 for AC(HOx). The amount of chromium(VI) adsorbed onto adsorbents at the optimum pH was 13.5 mg for 5.0 g of activated carbon and 22.0 mg for 5.0 g of activated carbon impregnated with 0.5 g of oxine. Chromium (VI) adsorbed onto activated carbon at pH 4.9 was completely desorbed with 0.10 mol dm
-3 NaOH solution in the form of chromium(III) (33%) and chromium(VI) (67%). While less than 6% of the total chromium(VI) adsorbed onto AC(HOx) at pH 4.9 was desorbed with 0.10 mol dm
-3 NaOH solution. It seems probable that the chromium(VI) which was adsorbed onto activated carbon in the forms of Cr(OH)(H
2O)
52+ appeared from the reduction of some portion of chromium(VI) with activated carbon, HCrO
4- and Cr
2O
7-2. On the other hand, chromium(VI) may be adsorbed onto AC(HOx) mainly in the form of Cr(III)-oxine complex.
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