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Carbohydr Polym. 2014 Dec 19;114:1-11. doi: 10.1016/j.carbpol.2014.07.065. Epub 2014 Aug 8.

Reduction of hypervalent chromium in acidic media by alginic acid.

Author information

1
Área Química General, Departamento de Químico-Física, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Santa Fe, Argentina; Instituto de Química de Rosario-CONICET, Suipacha 570, S2002LRK Rosario, Santa Fe, Argentina.
2
Área Química General, Departamento de Químico-Física, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Santa Fe, Argentina; Instituto de Química de Rosario-CONICET, Suipacha 570, S2002LRK Rosario, Santa Fe, Argentina. Electronic address: sbellu@iquir-conicet.gov.ar.

Abstract

Selective oxidation of carboxylate groups present in alginic acid by Cr(VI) affords CO2, oxidized alginic acid, and Cr(III) as final products. The redox reaction afforded first-order kinetics in [alginic acid], [Cr(VI)], and [H(+)], at fixed ionic strength and temperature. Kinetic studies showed that the redox reaction proceeds through a mechanism which combines Cr(VI)→Cr(IV)→Cr(II) and Cr(VI)→Cr(IV)→Cr(III) pathways. The mechanism was supported by the observation of free radicals, CrO2(2+) and Cr(V) as reaction intermediates. The reduction of Cr(IV) and Cr(V) by alginic acid was independently studied and it was found to occur more than 10(3) times faster than alginic acid/Cr(VI) reaction, in acid media. At pH 1-3, oxo-chromate(V)-alginic acid species remain in solution during several hours at 15°C. The results showed that this abundant structural polysaccharide present on brown seaweeds is able to reduce Cr(VI/V/IV) or stabilize high-valent chromium depending on pH value.

KEYWORDS:

Alginic acid; Chromium; Kinetics; Oxidation

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