TITLE

Chemical and electrochemical considerations on the removal process of hexavalent chromium from aqueous media

AUTHOR(S)
Barrera-Díaz, C.; Palomar-Pardavé, M.; Romero-Romo, M.; Martínez, S.
PUB. DATE
January 2003
SOURCE
Journal of Applied Electrochemistry;Jan2003, Vol. 33 Issue 1, p61
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
Two methods were used to remove Cr(VI) from industrial wastewater. Although both are based in the same general reaction: 3Fe(II)(aq) + Cr(VI)(aq) ⇄ 3Fe(III)(aq) + Cr(III)(aq) the way in which the required amount of FeQT) is added to the wastewater is different for each method. In the chemical method, Fe(II)(aq) is supplied by dissolving FeSO4 · 7(H2O)(s) into the wastewater, while in the electrochemical process Fe(II)(aq) ions are formed directly in solution by anodic dissolution of an steel electrode. After this reduction process, the resulting Cr(VI)(aq) and Fe(III)(aq) ions are precipitated as insoluble hydroxide species, in both cases, changing the pH (i.e., adding Ca(OH)2(s)). Based on the chemical and thermodynamic characteristics of the systems Cr(VI)-Cr(III)-H2O-e- and Fe(III)-Fe(II)-H20-e- both processes were optimized. However we show that the electrochemical option, apart from providing a better form of control, generates significantly less sludge as compared with the chemical process. Furthermore, it is also shown that sludge ageing promotes the formation of soluble polynuclear species of Cr(III). Therefore, it is recommended to separate the chromium and iron-bearing phases once they are formed. We propose the optimum hydraulic conditions for the continuous reduction of Cr(VI) present in the aqueous media treated in a plug-flow reactor.
ACCESSION #
15102802

 

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