零价铁还原地下水硝酸盐动力学研究

Kinetic Study of Reduction of Nitrate from Groundwater by Zero-valent Iron

地下水作为中国重要的饮用和灌溉水源,可能受到硝酸盐污染,为净化地下水硝酸盐污染,该研究通过批实验研究,考察零价铁投加量、pH、硝酸盐初始浓度和温度等条件对零价铁去除模拟地下水硝酸盐的影响。零价铁还原硝酸盐是酸驱动反应,较低的pH有利于反应的进行,pH=2、NO_3^--N初始浓度100 mg/L、反应3 h硝酸盐被零价铁完全去除。反应初期NO_3^-得电子被还原为中间产物NO_2^-,NO_2^-得电子后进一步被还原为N_2和NH_4^+,88.1%的硝酸盐氮转化为N_2,最终产物氨氮占总氮的11.9%。零价铁在还原反应中供电子后转化为Fe^(2+)、Fe^(3+)和Fe_3O_4,可能还生成铁的羟基氧化物,在铁的表面形成氧化膜。运用准一级动力学模型拟合不同温度的实验数据,零价铁在293、303、313 K还原硝酸盐的表观反应速率分别为0.020 8、0.036 7、0.049 4 min。根据阿伦尼乌斯公式计算出反应活化能E_a=33.08 k J/mol,说明相较于分子扩散固体表面的化学反应是速率控制步骤。零价铁可作为渗透性反应墙的填料修复地下水硝酸盐污染。

As an important drinking and irrigation water source in China,groundwater is extremely polluted by nitrate.To purify the groundwater contaminated by nitrate,this study investigated effects of dosage of zero-valent iron (ZVI),pH,initial concentration of nitrate and temperature on the removal of nitrate from simulated groundwater by batch experiments.The process of reduction of nitrate by ZVI is an acid driven reaction.The lower pH is favorable for the reaction.Nitrate with the initial concentration of 100mg/L was completely removed by ZVI at pH 2and 3hours.Nitrate was reduced to an intermediate product of nitrite at preliminary stage.Nitrite was further reduced to N2 and NH4^+,88.1percent of nitrate was converted to N2,11.9 percent of nitrate was converted to the final product of NH4^+.After donating electron,iron was converted to ferrous,ferric and magnetite,iron oxyhydroxide may be produced.Oxide film was formed on the surface of iron.The observed rate constants were calculated according to the experimental data of different temperatures fitted by the pseudo-first-order model.The results at 293K,303K,313K were 0.0208,0.0367 and 0.0494min,respectively.The activation energy Ea=33.08kJ/mol according to Arrhenius formula indicates that the chemical reaction of the solid surface is the rate controlling step rather than diffusion.ZVI can be used as filling materials of permeable reactive barrier (PRB)to purify the groundwater contaminated by nitrate.