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首页> 外文期刊>Environmental Science & Technology: ES&T >Nitrate Reduction by Zerovalent Iron:Effects of Formate,Oxalate,Citrate,Chloride,Sulfate,Borate,and Phosphate
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Nitrate Reduction by Zerovalent Iron:Effects of Formate,Oxalate,Citrate,Chloride,Sulfate,Borate,and Phosphate

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摘要

Recent studies have shown that zerovalent iron (Fe°) may potentially be used as a chemical medium in permeable reactive barriers (PRBs) for groundwater nitrate remediation; however,the effects of commonly found organic and inorganic ligands in soil and sediments on nitrate reduction by Fe° have not been well understood.A 25.0 ml nitrate solution of 20.0 mg of N L~(~1) (1.43 mM nitrate) was reacted with 1.00 g of Peerless Fe° at 200 rpm on a rotational shaker at 23 °C for up to 120 h in the presence of each of the organic acids (3.0 mM formic,1.5 mM oxalic,and 1.0 mM citric acids) and inorganic acids (3.0 mM HCI,1.5 mM H_2S0_4,3.0 mM H_3B0_3,and 1.5 mM H_3P0_4).These acids provided an initial dissociable H~+ concentration of 3.0 mM available for nitrate reduction reactions under conditions of final pH < 9.3.Nitrate reduction rates (pseudo-first-order) increased in the order: H_3PO_4 < citric acid < H_3BO_3 < oxalic acid < H_2S0_4 < formic acid < HCI,ranging from 0.00278 to 0.0913 h~(-1),corresponding to surface area normalized rates ranging from 0.126 to 4.15 h~(~1) m~(~2) ml.Correlation analysis showed a negative linear relationship between the nitrate reduction rates for the ligands and the conditional stability constants for the soluble complexes of the ligands with Fe~2+ (R~2- = 0.701) or Fe~3+ (R~2 = 0.918) ions.This sequence of reactivity corresponds also to surface adsorption and complexation of the three organic ligands to iron oxides,which increase in the order formate < oxalate < citrate.The results are also consistent with the sequence of strength of surface complexation of the inorganic ligands to iron oxides,which increases in the order: chloride < sulfate < borate < phosphate.The blockage of reactive sites on the surface of Fe° and its corrosion products by specific adsorption of the inner-sphere complex forming ligands (oxalate,citrate,sulfate,borate,and phosphate) may be responsible for the decreased nitrate reduction by Fe° relative to the chloride system.nitrate concentrations greater than 10 mg of N L in need of corrective action.It has been shown that zerovalent iron (Fe°) can serve as an electron donor to reduce nitrate (2-17).Two possible mechanisms are direct reduction of nitrate by Fe° and its indirect reduction by hydrogen generated by iron corrosion (7,8,10).Nitrate reduction by Fe° is a spontaneous process under acidic conditions:

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  • 来源
    《Environmental Science & Technology: ES&T》 |2004年第9期|2715-2720|共6页
  • 作者

    Chunming Su; Robert W.Puls;

  • 作者单位

    Ground Water and Ecosystems Restoration Division,National Risk Management Research Laboratory,Office of Research and Development,U.S.Environmental Protection Agency,919 Kerr Research Drive,Ada,Oklahoma 74820;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
  • 原文格式 PDF
  • 正文语种 英语
  • 中图分类 环境化学;
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