Study On Removal Of Para-Chloronitrobenzene In Water By FeOOH/H₂O₂ System

The synthetic organic compounds presented in water have serious affect on the safe utilization of water resources, and conventional water treatment process on the removal of refractory organic pollutants shows a little effect. Fenton reagent can decompose most organic pollutants by producing strong oxidative and non-selective hydroxyl radicals, but Fenton reaction which uses Fe²⁺ as catalyst requires for strong acidic water, and has two disadvantages: one is the loss of catalyst and oxidant, the other is the retreatment of sludge, so the development of the solid catalyst is the new direction of Fenton technology. Iron hydroxide (FeOOH), the major component of soil and water sediments, has attracted more and more attention in the fields of adsorption and catalysis duo to its unique surface structure, high surface area and fine particle size. The research on the basic law of decomposition of hydrogen peroxide by FeOOH is the foundation to find cost-effective heterogeneous Fenton catalyst and strengthen the organic pollutants treatment in water.Laboratory synthesized FeOOH was used as catalyst in the paper and characterized for its microstructure and surface properties. The effects of FeOOH adsorption and catalysis of hydrogen peroxide to remove p-chloronitrobenzene (pCNB) and the mechanism of catalytic oxidation were analysed.Three kinds of FeOOH catalysts were prepared by different precursors under controllable reaction conditions. All as-prepared catalysts areα-FeOOH possess of well crystalline, nano-sized monomers and certain gas adsorption capacity. Among three kinds of catalysts, the catalystâ… , which is synthesized with iron sulphate by activation process at room temperature, possesses the surface properties that suitable for water treatment. The catalystâ… present strong catalytic activity for decompose of hydrogen peroxide to oxidize pCNB in water, with the removal rate of 80% at reacting time of 30min.FeOOH has certain ability for the adsorption of pCNB in the water, and its adsorption effect is connected with dosage of FeOOH and initial pH value of solution. Because of the high catalytic activity, the pCNB removal rate by FeOOH/H₂O₂ is 30% more than the sum of that by adsorption using FeOOH and oxidation using H₂O₂ after reaction of 30min. The dissolution of metal ions during the reaction gets weaker with increasing catalyst used times, and in the neutral condition, it is much less than the limit in national standard. Reuse has little effect on the catalytic activity.Efficiency and affecting factors on removing pCNB by FeOOH/H₂O₂ were investigated. Results show that, the removal of pCNB increases with increasing FeOOH and H₂O₂ dosage to some extent, while the optimal dosage of FeOOH and H₂O₂ are 333mg/L and 6.6mg/L, respectively. Initial pH value of solution impact surface properties of catalysts that acidic and near neutral environment can ensure the effective catalytic activity. HCO₃^- alkalinity and humic acid have obvious inhibition on catalytic oxidation of pCNB, and the inhibition increases with increasing HCO₃^- and humic acid concentration.FeOOH can significantly promote the decomposition of H₂O₂, whose catalytic activity is more than that of Fe²⁺ catalyst. While in FeOOH/H₂O₂ system, tert-butanol can significantly inhibit the removal of pCNB, which proves that FeOOH/H₂O₂ mainly depends on the adsorption and decomposition of H₂O₂ on the surface of FeOOH to produce hydroxyl radical which can oxidize pCNB in the water effectively. The mineralization rate of pCNB by catalytic oxidation is about 60%, and chlorine and nitro group on benzene ring are converted into Cl- and NO₃^- to a certain extent after being attacked.