Transactions of Nonferrous Metals Society of China The Chinese Journal of Nonferrous Metals

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中国有色金属学报(英文版)

Transactions of Nonferrous Metals Society of China

Vol. 24    No. 3    March 2014

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Electrochemical reduction process of Co(II) in citrate solution
Yan LIU1, Zhe-jun LI1, Yi-cheng WANG2, Wei WANG1

1. School of Chemical Engineering, Tianjin University, Tianjin 300072, China;
2. Faculty of Metallurgy and Energy Engineering, Kunming University of Science and Technology,
Kunming 650093, China

Abstract:Effects of citrate concentration and pH on the electrochemical reduction process of Co(II) were investigated by cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS). The results show that Co(II) is reduced into two species which are free Co2+ and [Co(C6H6O7)] in the solution composed of 0.05 mol/L CoSO4·5H2O, 0.20 mol/L Na2SO4 and 0-0.40 mol/L C6H5O7Na3·2H2O in the pH range of 3-9. The reduction behavior depends on the pH of the solution. Co(II) is mainly reduced into the form of free Co2+ at pH 3 and into the form of [Co(C6H6O7)] at the pH range of 4-6 in citrate solution. The [Co(C6H6O7)] is first reduced to an intermediate state and then to Co0. Adsorption of the intermediate state exists on the surface of the electrode. Co(II) is difficult to be reduced in the solution with the pH above 7, because the existing Co(II)-citrate complex species [Co(C6H5O7)]- and [Co(C6H4O7)]2- are more difficult to be reduced than the hydrogen ion.

 

Key words: Co(II) ion; electrochemical reduction process; citrate; complex species

ISSN 1004-0609
CN 43-1238/TG
CODEN: ZYJXFK

ISSN 1003-6326
CN 43-1239/TG
CODEN: TNMCEW

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