Kinetics of nitrobenzene oxidation and iron crystallization in fluidized-bed Fenton process

Abstract

This research investigated the nitrobenzene oxidation and iron removal by fluidized-bed Fenton process using metal oxide as the carriers. It was found that the removal efficiency of nitrobenzene was not affected in the presence of metal oxide. However, metal oxide could retard the degradation rate of nitrobenzene with Fenton process due to ferrous adsorption/complexation onto its surface leaving insufficient free Fe 2+ to catalyze the decomposition of H 2O 2. Nonetheless, as the free Fe 2+ was sufficient, nitrobenzene was oxidized at the same rate as that by the conventional Fenton process. Fenton's reagent and nitrobenzene concentrations have an impact on nitrobenzene oxidation rate. The empirical kinetic equation for nitrobenzene oxidation by the fluidized-bed Fenton process under the conditions of 0.667–5 mM of Fe 2+, 10–50 mM of H 2O 2, 5–12.5 mM of nitrobenzene, 76.9 g/l of metal oxide, and pH 2.8 ± 0.2, can be described as: − d [ NB ] d t = 0.259 [ F e 2 + ] 1.02 [ H 2 O 2 ] 0.34 [ NB ] − 0.094 Considering on iron removal performance, it was found that the fluidized-bed Fenton process could remove 30–65% of iron via iron crystallization onto the carriers’ surface which could lead to a significant reduction in ferric hydroxide sludge production. H 2O 2 played an important role in iron crystallization and once it was exhausted, the re-dissolution of iron occurred. In addition, it was found that the metal oxide could be repeatedly used up to 5 cycles without any significant deterioration in its surface activity. Hence, it implies that the metal oxide can be used successfully in the fluidized-bed Fenton process operated under a continuous mode.