A comparative study of the effects of chloride, sulfate and nitrate ions on the rates of decomposition of H 2O 2 and organic compounds by Fe(II)/H 2O 2 and Fe(III)/H 2O 2

Abstract

The effects of chloride, nitrate, perchlorate and sulfate ions on the rates of the decomposition of hydrogen peroxide and the oxidation of organic compounds by the Fenton’s process have been investigated. Experiments were conducted in a batch reactor, in the dark at pH ⩽ 3.0 and at 25 °C. Data obtained from Fe(II)/H 2O 2 experiments with [Fe(II)] 0/[H 2O 2] 0 ⩾ 2 mol mol −1, showed that the rates of reaction between Fe(II) and H 2O 2 followed the order SO 4 2− > ClO 4 −NO 3 −Cl −. For the Fe(III)/H 2O 2 process, identical rates were obtained in the presence of nitrate and perchlorate, whereas the presence of sulfate or chloride markedly decreased the rates of decomposition of H 2O 2 by Fe(III) and the rates of oxidation of atrazine ([atrazine] 0=0.83 μM), 4-nitrophenol ([4-NP] 0=1 mM) and acetic acid ([acetic acid] 0=2 mM). These inhibitory effects have been attributed to a decrease of the rate of generation of hydroxyl radicals resulting from the formation of Fe(III) complexes and the formation of less reactive (SO 4 − ) or much less reactive (Cl 2 − ) inorganic radicals.