Pedosphere 17(3): 318--323, 2007
ISSN 1002-0160/CN 32-1315/P
©2007 Soil Science Society of China
Published by Elsevier B.V. and Science Press
| Catalysis of manganese(Ⅱ) on chromium(Ⅵ) reduction by citrate |
LI Chen1, LAN Ye-Qing1 and DENG Bao-Lin2 |
1 College of Science, Nanjing Agricultural University, Nanjing 210095 (China). E-mail: lanyq102@njau.edu.cn
2 Department of Civil and Environmental Engineering, University of Missouri-Columbia, Columbia MO 65211(USA) |
| ABSTRACT |
| The catalysis of manganese(Ⅱ) (Mn2+) on chromium(Ⅵ) (Cr6+) reduction by citrate was studied through batch experiments with the concentration of citrate greatly in excess of Cr6+ at 25℃ and in pH ranges of 4.0 to 5.0. Results showed that at pH 4.5 within 22 h direct reduction of Cr6+ by citrate was not observed, but for the same time when Mn2+ (50 to 200μmol L-1) was added, nearly all Cr6+ was reduced, with the higher initial Mn2+ concentration having faster Cr6+ reduction. In the initial stage of the reaction, the Cr6+ reduction could be described with a pseudo-first-order kinetics equation. In the later stage of the reaction, plots of lnc(Cr6+) versus t, where c(Cr6+) is the Cr6+ concentration in the reaction and t is the reaction time, deviated from the initial linear trend. The deviations suggested that the pseudo-first-order kinetics did not apply to the whole experimental period and that some reaction intermediates could have greatly accelerated Cr6+ reduction by citrate. The catalysis of the intermediates increased with the reaction time and gradually reached stability. Then, the plot of lnc(Cr6+) versus t in the presence of Mn2+ was linear again, with the rate constant increasing by 102 times compared with the absence of Mn2+. Complexation between Mn2+ and citrate was likely a prerequisite for the catalysis of Mn2+ on the reaction. Additional experiments showed that introducing ethylenediaminetetraacetic acid (EDTA) into the reaction system strongly suppressed the catalysis of Mn2+. |
| Key Words: catalysis, chromium(Ⅵ), citrate, manganese(Ⅱ), reduction |
| Citation: Li, C., Lan, Y. Q. and Deng, B. L. 2007. Catalysis of manganese(Ⅱ) on chromium(Ⅵ) reduction by citrate. Pedosphere. 17(3): 318-323. |
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