Nakajima Akira, Baba Yoshinari
Department of Chemistry, Faculty of Medicine, Miyazaki Medical College, University of Miyazaki, Kiyotake, Miyazaki 889-1692, Japan.
Water Res. 2004 Jul;38(12):2859-64. doi: 10.1016/j.watres.2004.04.005.
Mechanism of chromium adsorption by the persimmon tannin (PT) gel was examined. The PT gel can adsorb Cr highly effectively from aqueous solutions containing Cr(VI), while it adsorbed far smaller amounts of Cr from the solution containing Cr(III). The maximum Cr adsorption from the Cr(VI) solution occurred at pH 3. The Cr adsorption from the Cr(VI) solution by the PT gel was rapid, was faster than VO2+ and Fe3+ adsorptions, and was obeyed the Langmuir adsorption isotherm (Qe= 5.27 mmol g(-1) and K= 16.2 mM). The gel adsorbed Cr from the Cr(VI) solution (pH 1 and 3) showed no ESR signal of Cr(III), while the ESR signal of Cr(III) was observed in the residual solution at pH 1. Hexavalent chromium was, therefore, adsorbed on the PT gel through the esterification of chromate with catechol group. In other words, Cr(VI) should combine with catechol as a hard acid, CrO2(2+) cation. Through the treatment of a Cr(VI) solution with the PT gel, chromium should be recovered as a Cr(IV)-tannin complex at pH 3 or a Cr(III) solution at pH 1 or lower pH region.
研究了柿单宁（PT）凝胶对铬的吸附机制。PT凝胶能从含Cr（VI）的水溶液中高效吸附Cr，而从含Cr（III）的溶液中吸附的Cr量则少得多。从Cr（VI）溶液中吸附Cr的最大值出现在pH 3时。PT凝胶对Cr（VI）溶液中Cr的吸附很快，比VO2 +和Fe3 +的吸附更快，且符合朗缪尔吸附等温线（Qe = 5.27 mmol g(-1)，K = 16.2 mM）。从Cr（VI）溶液（pH 1和3）中吸附Cr的凝胶未显示出Cr（III）的电子自旋共振（ESR）信号，而在pH 1的残留溶液中观察到了Cr（III）的ESR信号。因此，六价铬通过铬酸盐与邻苯二酚基团的酯化作用吸附在PT凝胶上。换句话说，Cr（VI）应作为硬酸CrO2(2+)阳离子与邻苯二酚结合。通过用PT凝胶处理Cr（VI）溶液，铬应以pH 3时的Cr（IV）-单宁络合物或pH 1或更低pH区域的Cr（III）溶液形式回收。
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