Mechanism And Process Studies For Iron-Mediated Reduction Of Nitrobenzene In Slurry

As the important chemical raw material, nitrobenzene has been widely used inchemical production, resulting in more than 10,000t nitrobenzenes each year discharged orleaked to the environment, and finally encroachs into the soil and sediment media. In thispaper, the combined technology with slurry reactor and zerovalent reducing technologywas studied for the remediation of the contaminated sediments with nitrobenzene.The procedures used to quantity analysis of nitrobenzene in water or sediment mediawere described in detail. Firstly, nitrobenzene was extracted by hexane with interfacesolvent extraction technique of liquid-liquid or liquid-solid phases, after centrifugalseparation at 3000 r.minl for 15 min, the extraction was collected and measured by gaschromatography equipped with ECD detertor, while the recovery was fluctuating between70%～80%.The availability of slurry reactor in the remediation of contaminated sediments wasverified by the charateristics of desorption kinetics of nitrobenzene. The results showedthat desorption was evidently influenced by the nitrobenzene concentration, temperatureand desorption potential, and the distribution of nitrobenzene between water phase andsolid particles quitely fitted the none-equilibrium model. In addition, the statistical datarevealed that desorption culminated in the value of 60% then levelled off in 1～2 h,indicating that adsorption of nitrobenzene by sediment appeared to be easily destroyed.For the studies of iron-mediated remediation of nitrobenzene contaminated sediment,the key factors influencing the reduction of nitrobenzene were taken in accouont, and theresults showed that nitrobenzene was facilely reduced under the acid and Eh＜0 conditions,while the optimal condition was at pH value of 3～4. In the iron-mediated slurry, theresidual NB in sediment decreased negative exponentially with the concentration of ironsurface area, and the nitrobenzene removal rate was influened by mineral and humic acid(HA), which ranked following as grey desert soil mineral＞red soil mineral＞fluvo-aquicsoil mineral＞black soil mineral, and fluvo-aquic soil HA＞red soil HA＞grey desert soil HA＞black soil HA.Based on the mechanism studies of zerovalent reducing nitrobenzene in sedimentslurry, the results showed that the degradation of nitrobenzene was mainly depended on theoxidation -reduction reaction performed on the iron surface, while stimulated at thepresence of minerals, it also revealed that the contribution of Fe²⁺ to the reduction was verylimited. In the iron mediated reduction of nitrobenzene, it followed the pseudo-first orderkinetics, which incessantly reflected by Eh and EC values, and the topographs with SEMtechnique exhibited the tremendous changes of iron surface. The pathway of zerovalentiron reducing nitrobenzene was summarized by GC/MS analysis, proceeding throughnitroso and hydroxylamino intermediates to aniline.