Effects of pH and particle size on kinetics of nitrobenzene reduction by zero-valent iron

Nitrobenzene has been considered as a significant groundwater contaminant due to its wide usage in explosives, insecticides, herbicides, pharmaceuticals and dyes. Nitrobenzene is of environmental concern because of its toxicity. In the presence of zero-valent iron （ZVI）, reduction of the nitro group is the dominant transformation process for nitrobenzene. A series of experiments were carried out to investigate the kinetics of nitrobenzene reduction by ZVI and the effects of pH and ZVI particle size on nitrobenzene removal in groundwater. The results indicated that nitrobenzene could be reduced to aniline by ZVI; the reduction of nitrobenzene by ZVI followed a pseudo first-order kinetics; the observed nitrobenzene reduction rate constant （k obs ） was 0.0006 min^-1 and the half-life of nitrobenzene （t 1/2 ） was 115.5 min; the mass balance achieved 87.5% for nitrobenzene reduction by the 1 mm ZVI particle and the final removal efficiency was 80.98%. In addition, the pH and ZVI particle size were found to exhibit significant influences on the nitrobenzene reduction. The observed nitrobenzene reduction rate constant linearly decreased with increase pH and the data fitted on polynomial regression equation for the observed nitrobenzene reduction rate constant and ZVI particle size. Therefore, use of ZVI based permeable reactive barrier technology to remedy nitrobenzene contaminated groundwater was feasible.

Nanoscale zero-valent iron supported on biochar for the highly efficient removal of nitrobenzene

The application of nanoscale zero-valent iron (nZVI) in the remediation of contaminated groundwater or wastewater is limited due to its lack of stability, easy aggregation and iron leaching. To address this issue, nZVI was distributed on oak sawdust-derived biochar (BC) to obtain the nZVI/BC composite for the highly efficient reduction of nitrobenzene (NB). nZVI, BC and nZVI/BC were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). For nZVI/BC, nZVI particles were uniformly dispersed on BC. nZVI/BC exhibited higher removal efficiency for NB than the simple summation of bare nZVI and BC. The removal mechanism was investigated through the analyses of UV-Visible spectra, mass balance and XPS. NB was quickly adsorbed on the surface of nZVI/BC, and then gradually reduced to aniline (AN), accompanied by the oxidation of nZVI to magnetite. The effects of several reaction parameters, e.g., NB concentration, reaction pH and nZVI/BC aging time, on the removal of NB were also studied. In addition to high reactivity, the loading of nZVI on biochar significantly alleviated Fe leaching and enhanced the durability of nZVI.

pH值对零价铁还原降解模拟地下水中硝基苯的影响

通过批次实验,研究了不同pH值对零价铁还原模拟地下水中硝基苯的影响.结果表明:零价铁通过还原反应可有效降解地下水中的硝基苯,在控制pH值为3—12的硝基苯还原降解试验中,反应的最佳pH值为3;随着反应的进行pH值呈现逐渐升高的趋势;在各种pH值条件下,硝基苯的还原速率符合假一级动力学模型,表观速率常数kobs随pH值的降低而增加;硝基苯的还原速率和苯胺的生成速率都随pH值升高而减小;另外,零价铁还原硝基苯的最终还原产物为苯胺.

Kinetics and corrosion products of aqueous nitrate reduction by iron powder without reaction conditions control

Although considerable research has been conducted on nitrate reduction by zero-valent iron powder （Fe^0）, these studies were mostly operated under anaerobic conditions with invariable pH that was unsuitable for practical application. Without reaction conditions （dissolved oxygen or reaction pH） control, this work aimed at subjecting the kinetics of denitrification by microscale Fe^0 （160-200 mesh） to analysis the factors affecting the denitrification of nitrate and the composition of iron reductive products coating upon the iron surface. Results of the kinetics study have indicated that a higher initial concentration of nitrate would yield a greater reaction rate constant. The reduction rate of nitrate increased with increasing Fe^0 dosage. The reaction can be described as a pseudo-first order reaction with respect to nitrate concentration or Fe^0 dosage. Experimental results also suggested that nitrate reduction by microscale Fe^0 without reaction condition control primarily was an acid-driven surface-mediated process, and the reaction order was 0.65 with respect to hydrogen ion concentration. The analyses of X-ray diffractometry and X-ray photoelectron spectroscopy indicated that a black coating, consisted of Fe2O3, Fe3O4 and FeO（OH）, was formed on the surface of iron grains as an iron corrosion product when the system initial pH was lower than 5. The proportion of FeO（OH） increased as reaction time went on, whereas the proportion of Fe3O4 decreased.

催化还原法处理硝基苯废水的技术经济分析

采用Fe-Cu催化还原法处理硝基苯废水，优化了Cu和Fe的投加比例，并对反应过程中溶液pH值的变化，铁离子质量浓度的变化，铁的耗量和铜的溶出量进行分析．结果表明：Cu和Fe的质量比在0．2左右较为适宜；初始pH值为3．0～10．0的硝基苯废水，经该工艺处理后其pH值基本稳定在8．1左右；铁的溶解消耗量随着溶液初始pH值的降低而增大，但在30mg·L^-1之内；铁的总消耗量随着溶液初始pH值的升高而增大，但在50mg·L^-1以内；铜基本不发生溶出．与用铁碳内电解法处理工艺相比，采用本工艺处理硝基苯废水具有运行管理方便、铁的消耗量少、费用低和效果好等优点．

Nitrobenzene contamination of groundwater in a petrochemical industry site

Organic contamination of groundwater is a major concern in China.However,remediation technology for groundwater contamination to address the potential harm and danger brought by the abovementioned serious issue is still in the research stage.This study aims to improve the current research findings.In the research project,drilling,soil,and groundwater sampling and analysis were conducted in a contamination site of a petrochemical plant,migration of contaminants to the river was predicted using a numerical model,the sequence permeable reactive barrier(PRB)for treating nitrobenzene(NB)and benzene was proposed,and simulation was carried out.Research findings demonstrated that three leaking locations had been identified in the plant,the major pollutants were NB and benzene,and the groundwater contamination area was around 640000 m2.Computation results of the numerical model indicated that,in the worst case,the groundwater plume would reach the river after migration for nearly 9 years,which would endanger the safety of surface water supply.Furthermore,the twoPRB system with the filling of zero-valent iron(ZVI)and granular activated carbon attached with biofilm exerted strong remediation effects.Experimental results indicated that ZVI could transform NB to aniline effectively with a rate of approximately 93%.Meanwhile,aniline,benzene,and other organic pollutants could easily be biodegraded.