Oxidation Of Nitrobenzene In Groundwater By Fenton-like Technology Based On Iron In Aquifer Materials

Simulated experiments were conducted to investigate the oxidation of nitrobenzene （NB） ingroundwater by a Fenton-like technology under the condition of neutral pH and8¹0℃in order tosolve the problems which traditional Fenton oxidation technology had in organic contamination ingroundwater such as low pH condition needed, mass consumption of Fe²⁺and frequentlyoccurrence of iron secondary pollution. The new technology combined iron extraction of aquifermaterials which were found in a contaminated site in China with hydrogen peroxide catalyticoxidation. The mechanisms of catalytic oxidation reaction, a comparison of theextraction efficiency by different extraction agent and the production rule of hydroxyl radical wereall studied in this research. Influence on different velocity of groundwater flow and groundwaterchemical composition were studied respectively. The results could provide theoretical basis onin-situ chemical remediation technology of nitrobenzene contaminated site.Experimental results indicated that the production rule of hydroxyl radical has three stages. Inthe first stage hydroxyl radical generated rapidly in0³0min, then decreased slowly between30min and120min, at last the generation tending to steady from120h to240h. Extracting methodcould enhance iron extraction efficiency but had hysteresis property because the highestextraction efficiency occured after36h. An extraction agent called DCB has the highest efficiency,for Fe³⁺was62.92%and Fe²⁺was30.17%. The attenuation of NB is similar with index equation,the highest removal efficiency could reach80.2%and attenuation coefficient was0.0831while themole ratio of NB: H₂O₂is1:200. The attenuation of NB fitting pseudo-first order reaction kinetics.The oxiding ability of H₂O₂catalyzed by iron oxides is: magnetite＞goethite＞ferric hydroxide＞hematite. The final removal efficiencies were91%,92%,75%,82%for nitrobenzene in theNa-SO₄,Na-Cl,Ca-HCO₃and Ca-SO₄types of groundwater, and the time required to reachequilibrium concentrations were approximately90,30,120,30minutes, respectively.Groundwater flow velocity could strongly impact the occurrence of extraction agents and aquifermaterials so that the effective degradation of NB were repressed due to the lack of extractionreaction time or scavenging effect of hydroxyl radical by H₂O₂. Oxidation reaction zone wassetting up When groundwater velocity reached10cm/d. As the same time oxidation rate becomefaster than pollutant recovery rate in oxidation reaction zone. The more groundwater velocity grows, the less help for the transformation and enrichment of Fe³⁺and Fe²⁺in the direction ofgroundwater flow. Different H₂O₂injection mode could effect nitrobenzene removal efficiency tosome extent. A continuous and sustained stable oxidation reaction zone could be setup due tointermittent injection so that nitrobenzene maintained in low concentration for a long time. In theinjection point downstream intermittent injection makes low amplitude concentration decreased ofnitrobenzene. To the injection point upstream, removal efficiency of nitrobenzene was not obviousand the function radius is small.