Interaction of H₂O₂ with iron oxide for oxidation of organic compounds in water
Authors:   , Lin Shu-Sung , Gurol Mirat D. 
Published: July 2024

A novel heterogeneous catalytic oxidation process involving the use of hydrogen peroxide with granular goethite particles (H₂O₂/FeOOH) has been investigated for removal of synthetic organic pollutants from aqueous solution. The experiments were performed by using a bench-scale batch reactor to examine the effect of water quality and operational variables on the rates of H₂O₂ decomposition and oxidation of a target organic compound n-butylchloride (BuCl). BuCl, a known ·OH probe, was effectively oxidized by the proposed system. The oxidation rate of BuCl was directly proportional to the rate of H₂O₂ decomposition. Hence, it was demonstrated that BuCl was oxidized by ·OH produced as a result of interaction of H₂O₂ with goethite. The decomposition rate of H₂O₂ was found to follow first order kinetics with respect to the concentrations of goethite and H₂O₂. The rate increased with increasing pH and temperature, but decreased with increasing phosphate concentration. However, the rate was not affected by the size of goethite particles, the dissolved oxygen and iron, and the levels of carbonate alkalinity observed in most natural waters. The oxidation rate of BuCl was not significantly affected by the pH. Furthermore, the results showed that the effect of phosphate and bicarbonate was due to the specific complexation of the species with the oxide surface. The apparent reaction rates for this process were observed to be controlled by the intrinsic reaction rates on the oxide surfaces rather than the mass-transfer rates of solution reagents to the surface. Two reaction mechanisms for the H₂O₂ decomposition and the BuCl oxidation were proposed based on the reaction chemistry of ferric ion and ·OH, and the surface complexation chemistry for iron oxide. The first mechanism involves the reactions that occur only on the surface. The second mechanism involves the reactions that occur on the surface and in the solution. The kinetic models for the H₂O₂ decomposition, which were derived according to both proposed mechanisms, were found to be exactly the same, and also similar to the Langmuir-Hinshelwood rate model, which was later extended to describe the oxidation kinetics of BuCl. The kinetic models were calibrated and successfully verified based on the laboratory observations made under various experimental conditions. The models confirmed that goethite particles can catalyze the decomposition of H₂O₂ through Fenton-like reactions leading to the generation of ·OH and the oxidation of organic compounds. This research provides a thorough understanding of the reaction chemistry governing the H₂O₂/FeOOH process, and it contributes to literature valuable information on an important pathway for oxidation of organic compounds in natural and atmospheric waters. The results of this study imply that the H₂O₂/FeOOH process can be a very cost-effective alternative to the existing oxidation technologies. Additional research should be conducted using a variety of organic compounds for full assessment of the strengths and limitations of this new process.