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首页> 外文期刊>Environmental Science & Technology >Longevity of granular iron in groundwater treatment processes: Corrosion product development
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Longevity of granular iron in groundwater treatment processes: Corrosion product development

机译：地下水处理过程中粒状铁的寿命：腐蚀产物的开发

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Permeable reactive barriers employing iron as a reactive surface have received extensive attention. A remaining issue, however, relates to their longevity. As an integral part of a long-term column study conducted to examine the influence of inorganic cosolutes on iron reactivity toward chlorinated solvents and nitroaromatic compounds, Master Builder iron grains were characterized via scanning and transmission electron microscopy, electron energy loss spectroscopy (EELS), micro-Raman spectroscopy, and X-ray diffraction. Prior to exposure to carbonate solutions, the iron grains were covered by a surface scale that consisted of fayalite (Fe2SiO4), wustite (FeO), magnetite (Fe3O4), maghemite (gamma-Fe2O3), and graphite. After 1100 days of exposure to solutions containing carbonate, other inorganic solutes, and organic contaminants, the wustite, fayalite, and graphite of the original scale partially dissolved, and magnetite and iron carbonate hydroxide (Fe-3(OH)(2,2)CO3) precipitated on top of the scale. Raman results indicate the presence of green rust(e.g., [Fe42+Fe23+(OH)(12)]-[CO(3)(.)2H(2)O]) toward the column outlet after 308 days of operation, although this mineral phase disappears at longer operation times. Grains extracted from a column exposed to a high concentration (20 mM) of sodium bicarbonate were more extensively weathered than those from columns exposed to 2 mM sodium bicarbonate. An iron carbonate hydroxide layer up to 100 mu m thick was observed. Even though EELS analysis of iron carbonate hydroxide indicates that this is a redox-active phase, the thickness of this layer is presumed responsible for the previously observed decline in the reactivity of this column relative to low-bicarbonate columns. A silica-containing feed resulted in reduced reactivity toward TCE. Grains from this column had a strong enrichment of silicon in the precipitates, although no distinct silica-containing mineral phases were identified. The substitution of 2 mM calcium carbonate for 2 mM sodium bicarbonate in the feed did not produce a measurable reactivity loss, as the discrete calcium carbonate precipitates that formed in this system did not severely restrict access to the reactive surface.
机译：以铁为反应性表面的渗透性反应性屏障受到了广泛的关注。然而，还有一个问题与它们的寿命有关。作为长期柱研究的组成部分，该研究旨在检验无机溶质对铁对氯化溶剂和硝基芳族化合物的反应性的影响，通过扫描和透射电子显微镜，电子能量损失谱（EELS）对Master Builder铁颗粒进行表征，显微拉曼光谱和X射线衍射。在暴露于碳酸盐溶液之前，铁晶粒被表面鳞片覆盖，该鳞片由方铁石（Fe2SiO4），钙铁矿（FeO），磁铁矿（Fe3O4），磁赤铁矿（γ-Fe2O3）和石墨组成。暴露于含有碳酸盐，其他无机溶质和有机污染物的溶液中1100天后，原始尺度的钙铁矿，铁橄榄石和石墨部分溶解，磁铁矿和氢氧化铁碳酸盐（Fe-3（OH）（2,2） CO3）沉淀在水垢的顶部。拉曼分析结果表明，运行308天后，朝着色谱柱出口的方向出现了生铁锈（例如[Fe42 + Fe23 +（OH）（12）]-[CO（3）（。）2H（2）O]）。矿物质相在更长的运行时间后消失。与暴露于2 mM碳酸氢钠的色谱柱相比，从暴露于高浓度（20 mM）碳酸氢钠的色谱柱中提取的谷物风化程度更高。观察到高达100微米厚的碳酸铁氢氧化物层。即使对碳酸铁氢氧化物的EELS分析表明这是氧化还原活性相，该层的厚度也被认为是造成该柱相对于低碳酸氢根柱反应性下降的原因。含二氧化硅的进料导致对TCE的反应性降低。尽管未鉴定出明显的含二氧化硅的矿物相，但该柱中的颗粒在沉淀物中的硅含量很高。进料中用2 mM碳酸氢钠代替2 mM碳酸钙不会产生可测量的反应性损失，因为在该系统中形成的离散碳酸钙沉淀不会严重限制进入反应性表面。

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