Kinetics and Modeling of the Fe(III)/H₂O₂ System in the Presence of Sulfate in Acidic Aqueous Solutions

Abstract

This work examined the effect of sulfate ions on the rate of decomposition of H2O2 by Fe(III) in homogeneous aqueous solutions. Experiments were carried out at 25 degrees C, pH < or = 3 and the concentrations of sulfate ranged from 0 to 200 mM ([Fe(III)]0 = 0.2 or 1 mM, [H2O2]0 = 10 or 50 mM). The spectrophometric study shows that addition of sulfate decreased the formation of iron(III)-peroxo complexes and that H2O2 does not form complexes with iron(III)-sulfato complexes. The rates of decomposition of H2O2 markedly decreased in the presence of sulfate. The measured rates were accurately predicted by a kinetic model based on reactions previously validated in NaClO4/HClO4 solutions and on additional reactions involving sulfate ions and sulfate radicals. At a fixed pH, the pseudo-first-order rate constants were found to decrease linearly with the molar fraction of Fe(II) complexed with sulfate. The model was also able to predict the rate of oxidation of a probe compound (atrazine) by Fe(III)/H2O2. Computer simulations indicate that the decrease of the rate of oxidation of organic solutes by Fe(III)/H2O2 can be mainly attributed to the complexation of Fe(III) by sulfate ions, while sulfate radicals play a minor role on the overall reaction rates.

A complete phenol oxidation pathway obtained during electro-Fenton treatment and validated by a kinetic model study

“…classical Fenton process [9][10][11][12][13][14][15][16], Fenton-like treatment [17][18][19] and photo-Fenton process [20][21][22]. However, only two papers refer to electro-Fenton process [23,24].…”

“…The hydroperoxo iron complexes that could be formed [17] would not reduce the availability of iron since they can regenerate Fe 2+ from Eqs. 4a to 4c [5],…”

Fundamental Mechanistic Studies of the Photo-Fenton Reaction for the Degradation of Organic Pollutants

“…Sulfate ion is often present in photo-Fenton reactions as a result of the addition of iron in the form of readily available sulfate salts (De Laat & Le, 2005). Sulfate ion complexes strongly with Fe(III) over a wide pH range ( Figure 7) and the quantum yield of production of Fe 2+ plus a sulfate anion radical from photolysis of Fe(SO 4 ) + is only about 0.05 (Benkelberg & Warneck, 1995).…”

Iron(III)-induced activation of chloride from artificial sea-salt aerosol

“…A more detailed summary and description of Fe III -induced Cl 2 formation can be found in Lim et al [24] or Wittmer et al [15] In addition to the photosensitive iron-induced halogen release mechanism, further trace gas species, such as O 3 , NO x and sulfur dioxide (SO 2 ), possibly influence Cl 2 release, mainly when dissolved in the aqueous phase where they can change the pH, [25] coordinate with Fe 2þ or Fe 3þ , [26] scavenge Cl [22] or additionally activate halides by the known heterogeneous mechanisms. [13] Concerning O 3 , Sadanaga et al [27] observed an enhancement of the O 3 uptake rate and Cl 2 release in the presence of water-soluble Fe 3þ and O 3 in the dark.…”