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Résumé :
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Hydrogen peroxide is activated by homogeneous Fe-TAML catalysts in aqueous solutions containing very high levels of sodium hydroxide, sodium aluminate, and other inorganic salts. Under these conditions, the Fe-TAML catalyst system facilitates oxidation of humic and humic-derived compounds under ambient conditions and efficiently uses catalyst and oxidant. Darkly colored process liquor from aluminum refining (Bayer liquor) is decolorized by 40−70% (in the wavelength range 450−650 nm) in just 5 min. Humic substances and phenolic species were targeted by the oxidation process. In addition to color reduction, Fe-TAML/H2O2 in 5 M NaOH can also extensively degrade the five- or six-carbon polyols, mannitol, sorbitol, dulcitol, xylitol, and adonitol. This is the first time Fe-TAML catalysts have been shown to activate degradation of carbohydrate alcohols. We show that mannitol, a nuisance contaminant in alumina production, can be oxidized at millimolar levels in process liquor containing a wide variety of other organic components at high background concentrations.
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