Catalysis of manganese(II) on chromium(VI) reduction by citrate

被引:61
作者
Li Chen
Lan Ye-Qing [1 ]
Deng Bao-Lin
机构
[1] Nanjing Agr Univ, Coll Sci, Nanjing 210095, Peoples R China
[2] Univ Missouri, Dept Civil & Environm Engn, Columbia, MO 65211 USA
关键词
catalysis; chromium(Vl); citrate; manganese(II); reduction;
D O I
10.1016/S1002-0160(07)60038-1
中图分类号
S15 [土壤学];
学科分类号
0903 ; 090301 ;
摘要
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 degrees C 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 200 mu mol 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 Inc(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 Inc(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+.
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页码:318 / 323
页数:6
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