| To study the removal of nitrochlorobenzenes (NCBs) in contaminated soil after the relocation of Nanjing Chemical Company, we used the two different methods which are direct oxidation of chemical oxidants and oxidation of chemical oxidants after the reduction of zero-valent iron. And then we studied the effect of the removal of nitrochlorobenzenes, such as soil moisture, pH, temperature, oxidant dose, etc. In addition, the degradation process was also studied by gas chromatography, liquid chromatography, GC-MS, LC-MS and other equipment. Research of this paper was to provide a theoretical reference for remediating the contaminated soil of nitrochlorobenzenes.The paper was divided into three parts:Part I:Comparing the removal of nitrochlorobenzenes, we used two different methods which were the direct oxidation by chemical oxidants and the oxidation by chemical oxidants after reduction of zero-valent iron. The results showed that when the oxidant dosage was 2.0 mmol-g"1, the direct oxidation of the order of the removal of chloronitrobenzenes was potassium permanganate> Fenton reagent> persulfate> 30% hydrogen peroxide. However, the order of the removal of chloronitrobenzenes by ZVI-chemical oxidants was potassium permanganate> Fenton reagent> 30% hydrogen peroxide> persulfate. During the oxidation, the temperature in the Fenton's reagent and 30% hydrogen peroxide increased from 25? to over 35? significantly. While, the temperature in the reaction of persulfate and potassium permanganate increased slightly. The removal of ortho-chloronitrobenzene and para-chloronitrobenzene were higher than meta-chloronitrobenzene.Part II:The effects of initial pH value, the amount of zero-valent iron, temperature and soil moisture and other factors persulfate-zero valent iron system for chloronitrobenzene degradation. The results showed that the o-NCB removal rate increases significantly from 15.1% to 97.3% with an increase of iron dosage from 0.1 mmol-g-1 to 1.0 mmol-g"1. The o-NCB removal rate increases with the decrease of initial solution pH and a removal efficiency of 90.3% is obtained at an initial pH value of 6.8 in this combined system. It is found that temperature and soil moisture could also increase the o-NCB removal rate. The o-NCB degradation rate increases from 83.9% to 96.2%,41.5% to 82.4% with an increase of temperature (15? to 35?) and soil moisture (0.25 to 1.50 mL-g-1), respectively. Compared to the persulfate oxidation system and ZVI system, the persulfate-iron system shows high o-NCB removal capacity. The o-NCB removal rates of 41.5% and 62.4% are obtained in both in the persulfate oxidation system and the ZVI system, while the removal rate of o-NCB is 90.3% in the persulfate-iron system.Part III:Scanning electron microscopy (SEM) was adopted to observe the changes of surface morphology of zero-valent iron before and after reaction. The generated radical species at different pH values at ambient temperature were identified by Electron paramagnetic resonance (EPR) technique, and the results showed that sulfate radicals (SO4-·) were predominant under acidic condition and hydroxyl radicals (·OH) were predominant under basic condition. The results showed that removal of p-NCB by persulfate or ZVI alone was slow at ambient temperature. However, the removal rate was markedly increased when ZVI and persulfate coexist due to the generation of·OH and SO4-·, which were more efficient oxidizing agents for organic contaminants. Increased ZVI dosages resulted in enhanced p-NCB degradation due to increased activation of persulfate by ZVI. The removal of p-NCB was facilitated in acid condition. MS analysis in combination with literature review of p-NCB degradation, intermediates identified in this work include 4-chlorobenzeneamine, N-(4-chlorophenyl)-p-phenylene di-imine, 1-(4-Chlorophenyl)-3-phenlurea,1,4-benzoquinone and 5-chloro-2-((3-chlorophenyl) diazenyl) phenol, respectively. |
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