Oxidation of cyanide in water by singlet oxygen generated by the reaction between hydrogen peroxide and hypochlorite

•The kinetics of oxidation of CN by singlet oxygen have been quantified.•Singlet oxidation of cyanide to cyanate is faster than competing processes.•20min for [CN] reduction from 100 to 0.2mg/L in a batch reaction.•Fast oxidation conditions do not require addition of catalysts. The synergistic combi...

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Bibliographic Details
Published in:Minerals engineering 2013-09, Vol.50-51, p.57-63
Main Authors: Teixeira, Luiz Alberto Cesar, Arellano, Meryelem Tania Churampi, Marquez Sarmiento, Cristian, Yokoyama, Lidia, Araujo, Fabiana Valeria da Fonseca
Format: Article
Language:English
Subjects:
Cyanide effluent treatment
Cyanide oxidation
Cyanides
Hydrogen peroxide
Hypochlorite
Oxidants
Oxidation
Oxidizing agents
Reaction kinetics
Singlet oxygen
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Summary:•The kinetics of oxidation of CN by singlet oxygen have been quantified.•Singlet oxidation of cyanide to cyanate is faster than competing processes.•20min for [CN] reduction from 100 to 0.2mg/L in a batch reaction.•Fast oxidation conditions do not require addition of catalysts. The synergistic combination of hydrogen peroxide and hypochlorite ion in water results in formation of the highly oxidizing intermediate species singlet oxygen (1O2), which was effective in the oxidation of free cyanide (CN−) in water. The present work reports the findings of a study of the kinetics of aqueous cyanide oxidation with singlet oxygen generated by the reaction between hydrogen peroxide and hypochlorite, both added separately to the solution to be treated. Experiments were conducted in batch mode using synthetic solutions of free cyanide. The experimental methodology involved a set of kinetic experiments measuring [CN] versus time, up to 60min, with initial [CN−] equal to 10, 100, 500 or 1000mg/L; oxidant type and dose (H2O2 only; NaClO only; and H2O2+NaClO) for various molar ratios of Oxidant/CN; and pH=9–11. The objective was to evaluate the effect of those factors on the reaction kinetics at room temperature. The results showed the synergy between hydrogen peroxide and hypochlorite on the cyanide oxidation reaction rate. The process was fast and efficient over the studied pH range of 9–11, and up to an initial CN− concentration of 1000mg/L. For an initial [CN−]=100mg/L, pH=9, and molar ratio ([H2O2]+[NaClO])/[CN−]=2:1 it was possible to achieve a final concentration of [CN−]
ISSN:0892-6875
1872-9444
DOI:10.1016/j.mineng.2013.06.007