Zero-valent iron (ZVI) was tested for the removal of 150 mu g L-1 As(V) and 350 mu g L-1 Se(VI) in high salinity (ionic strength 0.35-4.10 M) flowback water of hydraulic fracturing. Over 90% As(V) and Se(VI) was removed by 2.5 g L-1 ZVI in Day-14 flowback water up to 96-h reaction, with the remaining concentration below the maximum contaminant level for As(V) and criterion continuous concentration for Se(VI) recommended by US EPA. The kinetics of As(V) and Se(VI) removal followed a pseudo-second order rate expression with the observed rates of 4.51 x 10(-2)-4.91 x 10(-1) and 3.48 x 10(-2)-6.58 x 10(-1) h(-1) (with 0.5-10 g L-1 ZVI), respectively. The results showed that Se(VI) removal significantly decreased with increasing ionic strength, while As(V) removal showed little variation. Common competing anions (nitrate, bicarbonate, silicate, and phosphate), present in shallow groundwater and stormwater, caused marginal Se(VI) desorption (2.42 +/- 0.13%) and undetectable As(V) desorption from ZVI. The competition between As(V) and Se(VI) for ZVI removal depended on the initial molar ratio and surface sites, which occurred when the Se(VI) concentration was higher than the As(V) concentration in this study. The characterization of As(V)- and Se(VI)-loaded ZVI by X-ray diffraction and Raman analysis revealed that ZVI gradually converted to magnetite/maghemite corrosion products with lepidocrocite in flowback water over 30 days. Similar corrosion compositions were confirmed in, aerobic and anaerobic conditions regardless of the molar ratio of As(V) to Se(VI). The high reactivity and stability of ZVI showed its suitability for in-situ prevention of As(V) and Se(VI) migration due to accidental leakage, spillage, or overflow of flowback water.
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机译：测试了零价铁（ZVI）在水力压裂的高盐度（离子强度0.35-4.10 M）回流水中去除150μgL-1 As（V）和350μgL-1 Se（VI）的方法。在第14天的返排水中，通过96 g反应中的2.5 g L-1 ZVI去除了90％以上的As（V）和Se（VI），其余浓度低于As（V）和标准的最大污染物水平美国环保署建议的硒（VI）的连续浓度。去除As（V）和Se（VI）的动力学遵循伪二级速率表达，观察到的速率为4.51 x 10（-2）-4.91 x 10（-1）和3.48 x 10（-2）- 6.58 x 10（-1）h（-1）（分别使用0.5-10 g L-1 ZVI）。结果表明，随着离子强度的增加，Se（VI）的去除显着降低，而As（V）的去除几乎没有变化。存在于浅层地下水和雨水中的常见竞争阴离子（硝酸根，碳酸氢根，硅酸根和磷酸根）导致少量的Se（VI）脱附（2.42 +/- 0.13％）和不可检测的As（V）从ZVI脱附。去除ZVI的As（V）和Se（VI）之间的竞争取决于初始摩尔比和表面位点，这是在本研究中当Se（VI）浓度高于As（V）浓度时发生的。通过X射线衍射和拉曼分析表征了负载有As（V）和Se（VI）的ZVI，结果表明，在倒流水中，ZVI在30天内逐渐转化为含铁水云母的磁铁矿/磁赤铁矿腐蚀产物。在有氧和厌氧条件下，无论As（V）与Se（VI）的摩尔比如何，都确认了相似的腐蚀成分。 ZVI的高反应活性和稳定性表明，它适合就地预防由于偶然的漏水，溢出或溢流而引起的As（V）和Se（VI）迁移。
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