Oxidation of humic substances by environmentally friendly oxidants iron(VI) and hydrogen peroxide
The kinetics of the reactions between humic and fulvic acids (HA and FA) and potassium ferrate were investigated under pseudo order conditions. The rates of HA and FA oxidation with ferrate(VI) were determined at pH 9.0, 25°C. The reactions were found to be first order for each reactant. The oxidation of HA and FA with Fe(VI) occurred by two different pathways allowing for two different pseudo first order rate constants. Rate constant values for an estuarine FA (Mullet Creek) were very similar to those for SRFA (Suwannee River Fulvic Acid) increasing the likelihood that the values are applicable to other natural aqueous systems. The degradation of HA and FA in aqueous solution by means of a photolytic method was also studied. Both FA and HA oxidation by H2O2 followed first-order kinetics for HS (humic substances) and fractional order kinetics for H2O 2, respectively. The optimum H2O2 dose was found to be 86 mM for the oxidation of HS from this study.
The oxidation efficiency of Fe(VI) and oxidation by-products were analyzed by TOC, NMR and GC/MS. The TOC experiments were conducted by measuring organic carbon contents after the oxidation of FA. The results showed that the oxidation of HS by Fe(VI) occurred efficiently and led to 48% mineralization within 30min. The NMR results showed a decrease in aromaticity and carbohydrates after oxidation, and the GC/MS analysis positively identified small carboxylic acid and polycarboxylic acid residues.
The heterogeneous photocatalytic degradation of FA and HA by Fe(VI) with UV/TiO2 was investigated at pH 9.0, 25°C. The oxidation of HS by the Fe(VI) was enhanced by the addition of TiO 2 in the presence of UV light.
0768: Environmental science