Performance Of Nitrobenzene Removal Using Iron Sulfide

Iron sulfide widely exists in soil and sediment. Organic matter in soil and sediment is the carbon source of sulfatereducing bacteria. Sulfatereducing bacteria can reduce sulfate to sulfide, which subsequently dissolves sedimentary metal oxide/hydroxide minerals to form metal sulfides. Ferrous sulfide(FeS) has good performance in the reduction of heavy metals and chlorinated organic compounds. The influencing factors of nitrobenzene reduction in synthetized wastewater by chemically pure FeS, and the enhancement of nitrobenzene reduction caused by the addition of Fe2+were investigated in batch experiments, in order to search a new way to treat wastewater including nitrobenzene.The influence posed by factors such as reaction time, dose of FeS, initial nitrobenzene concentration, initial pH, temperature, rotation rate, and reused times of FeS on nitrobenzene removal was discussed in batch experiments. In the system, the partical size of FeS was50-60mesh, the wastewater was prepared artificially, the reaction temperature was constant, the reaction was carried on in40mL brown vials, and the mixture was realized by using a vertical rotary reactor. The result was as follows. After180min, the nitrobenzene removal ratio was90%with initial nitrobenzene concentration0.97mmol/L and dose of FeS1.2g. In the process, nitrobenzene was reduced to nitrosobenzene and aniline. Nitrosobenzene was intermediate product, and aniline was the ended product. The concentration of nitrosobenzene was always lower than0.1mmol/L during the whole reaction process, while the concentration of aniline was ascended linearly. The factors posing distinctive influence on reaction were dose of FeS, initial pH, temperature and reused times of FeS. With initial nitrobenzene concentration0.97mmol/L and reaction time120min, when dose of FeS increased from0.3to1.5g, the concentration of nitrobenzene in the solution decreased linearly and the concentration of aniline in the solution increased linearly. As the dosage of FeS was in range of0.3to1.5g increasing dose of FeS could quicken the reaction. H+is one of the reactants, so pH of the solution can pose important influence on nitrobenzene reduction by FeS. With initial nitrobenzene concentration0.96mmol/L, after120min, when initial pH varied from3to5, the nitrobenzene removal ratios were always100%. When initial pH varied from6to9, the nitrobenzene removal ratio slowly decreased from72%to61%as initial pH increased. When initial pH was10, the removal ratio was only32%. With initial nitrobenzene concentration0.97mmol/L, after120min, when temperature increased from5to10℃, the nitrobenzene removal ratio slightly varied from70%to71%. When temperature increased from10to25℃, the nitrobenzene removal ratio increased linearly as temperature increased, and temperature increasing1℃would make the nitrobenzene removal ratio increase1.6%. When temperature varied from30to40℃, the nitrobenzene removal ratio kept at100%. According to Arrhenius formula, reaction activation energy could be calculated, and its value was24.2kJ/(K-mol). In the process of nitrobenzene reduction by FeS, due to the oxidation by nitrobenzene, the existence of dissolved oxygen and the increase of pH, the surface of FeS partical could produce the oxide or hydroxide passivation layer which could hinder the reaction, so the reused times of FeS could pose influence on nitrobenzene reduction. The nitrobenzene removal ratio decreased as the reused times of FeS increased. With initial nitrobenzene concentration0.97mmol/L and dose of FeS2.4g, after60min, when the used times of FeS varied from the first to fourth, the nitrobenzene removal ratio decreased linearly from57%to7%, and when the used times of FeS was the fifth, the nitrobenzene removal ratio was only4%. In order to investigate the influence posed by coexisting organics, the simulated chemical wastewater with nitrobenzene concentration0.96mmol/L, was prepared using chemical industrial wastewater as the basic liquor. FeS had perfect performance towards simulated chemical wastewater with low pH. With initial nitrobenzene concentration0.96mmol/L, after60min, nitrobenzene in the system was completely converted to aniline.The influence posed by the addition of Fe2+on nitrobenzene removal was discussed in batch experiments. In the system, the partical size of FeS was40-50mesh, the wastewater was prepared artificially, the reaction temperature was constant, the reaction was carried on in40mL brown vials, and the mixture was realized by using a vertical rotary reactor. The result was as follows. The addition of Fe2+could distinctively promote the nitrobenzene reduction by FeS. With initial nitrobenzene concentration0.96mmol/L, after60min, when the initial Fe+concentration was0mmol/L, the nitrobenzene removal ratio was29%. As the initial Fe2+concentration increased, the nitrobenzene removal ratio increased greatly. Compared to the system of no addition of Fe2+, the system with initial Fe2+concentration0.1mmol/L and the system with initial Fe2+concentration0.3mmol/L, the nitrobenzene removal ratio increased by39%and69%, respectively.