Zhe-Yuan Jiang, Run Zhang, Zhong-Yuan Li, Xian-Lei Fu, Yu-Ling Yang, Ning-Jun Jiang, Yan-Jun Du
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When exposed to the simulated Pb-contaminated groundwater, the amended backfill exhibited lower hydraulic conductivity value than 10<sup>–9</sup> m/s, while that of unamended backfill increased approximately two orders of magnitude. A series of microscopic tests were conducted to understand why SHMP amendment could improve the chemical compatibility of the backfill. The X-ray diffraction analyses showed an intercalation of SHMP into montmorillonite platelets in the amended backfill permeated with 500 mM Pb(NO<sub>3</sub>)<sub>2</sub> solution. The environmental scanning electron microscopy coupled with energy-dispersive spectrometry analyses indicated that the hydrated amended bentonite along with needle-shaped Pb<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> and PbHPO<sub>4</sub> were found in amended backfill after permeating with 500 mM Pb(NO<sub>3</sub>)<sub>2</sub> solution in accordance with the X-ray diffraction analysis. The micropore and macropore proportions of amended backfill increased after permeating with 500 mM Pb(NO<sub>3</sub>)<sub>2</sub> solution. The mechanisms of superior hydraulic performance of the amended backfill exposed to lead contamination were attributed to the chemical reaction between lead and SHMP-amended backfill, steric stabilization imposed by the SHMP, and intercalation of SHMP into montmorillonite platelets.</p></div>","PeriodicalId":49308,"journal":{"name":"Acta Geotechnica","volume":"20 3","pages":"1235 - 1250"},"PeriodicalIF":5.6000,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Hydraulic conductivity and microscopic properties of sodium hexametaphosphate-amended sand-sodium-activated calcium bentonite backfill in vertical cutoff walls exposed to lead-contaminated groundwater\",\"authors\":\"Zhe-Yuan Jiang, Run Zhang, Zhong-Yuan Li, Xian-Lei Fu, Yu-Ling Yang, Ning-Jun Jiang, Yan-Jun Du\",\"doi\":\"10.1007/s11440-024-02444-3\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>This study aims to investigate the hydraulic conductivity of sodium hexametaphosphate (SHMP)-amended sand-sodium-activated calcium bentonite backfill in vertical cutoff walls to contain flow of lead nitrate solutions (Pb(NO<sub>3</sub>)<sub>2</sub>), used as simulated lead (Pb)-contaminated groundwater. Workability of SHMP-amended slurry, grain-size distributions and Atterberg limits of SHMP-amended sodium-activated calcium bentonite (conventional bentonite, CB) were evaluated. The results indicated that the SHMP content in slurry was optimized as 2% of the dry weight of bentonite via workability. The SHMP amendment yielded reduced particle diameter and increased clay-sized fraction of the bentonite. When exposed to the simulated Pb-contaminated groundwater, the amended backfill exhibited lower hydraulic conductivity value than 10<sup>–9</sup> m/s, while that of unamended backfill increased approximately two orders of magnitude. A series of microscopic tests were conducted to understand why SHMP amendment could improve the chemical compatibility of the backfill. The X-ray diffraction analyses showed an intercalation of SHMP into montmorillonite platelets in the amended backfill permeated with 500 mM Pb(NO<sub>3</sub>)<sub>2</sub> solution. The environmental scanning electron microscopy coupled with energy-dispersive spectrometry analyses indicated that the hydrated amended bentonite along with needle-shaped Pb<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> and PbHPO<sub>4</sub> were found in amended backfill after permeating with 500 mM Pb(NO<sub>3</sub>)<sub>2</sub> solution in accordance with the X-ray diffraction analysis. The micropore and macropore proportions of amended backfill increased after permeating with 500 mM Pb(NO<sub>3</sub>)<sub>2</sub> solution. 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引用次数: 0
摘要
本研究旨在研究六偏磷酸钠（SHMP）改性砂-钠活化钙膨润土充填体在垂直防渗墙中控制硝酸铅溶液（Pb(NO3)2）流动的导水性，以模拟铅污染地下水。评价了shmp改性浆料的可工作性、shmp改性钠活化钙膨润土（常规膨润土，CB）的粒度分布和阿特伯格极限。结果表明，通过和易性，浆料中SHMP的含量为膨润土干重的2%。SHMP改性后的膨润土颗粒直径减小，粘土级分数增加。在模拟铅污染地下水中，修正后的充填体的导水系数低于10 ~ 9 m/s，而未修正的充填体的导水系数提高了约2个数量级。为了了解SHMP改性剂改善充填体化学相容性的原因，进行了一系列微观试验。x射线衍射分析表明，在500 mM Pb(NO3)2溶液渗透的改性充填体中，SHMP嵌入蒙脱土片中。环境扫描电镜和能谱分析结果表明，经500 mM Pb(NO3)2溶液渗透后，回填体中出现了水合改性膨润土以及针状Pb3(PO4)2和phbhpo4。500 mM的Pb(NO3)2溶液渗透后，改性充填体的微孔和大孔比例增加。铅污染下，改性充填体具有优异的水力性能，其机理主要是铅与改性充填体发生化学反应、SHMP的空间稳定作用以及SHMP嵌入蒙脱土薄片。
Hydraulic conductivity and microscopic properties of sodium hexametaphosphate-amended sand-sodium-activated calcium bentonite backfill in vertical cutoff walls exposed to lead-contaminated groundwater
This study aims to investigate the hydraulic conductivity of sodium hexametaphosphate (SHMP)-amended sand-sodium-activated calcium bentonite backfill in vertical cutoff walls to contain flow of lead nitrate solutions (Pb(NO3)2), used as simulated lead (Pb)-contaminated groundwater. Workability of SHMP-amended slurry, grain-size distributions and Atterberg limits of SHMP-amended sodium-activated calcium bentonite (conventional bentonite, CB) were evaluated. The results indicated that the SHMP content in slurry was optimized as 2% of the dry weight of bentonite via workability. The SHMP amendment yielded reduced particle diameter and increased clay-sized fraction of the bentonite. When exposed to the simulated Pb-contaminated groundwater, the amended backfill exhibited lower hydraulic conductivity value than 10–9 m/s, while that of unamended backfill increased approximately two orders of magnitude. A series of microscopic tests were conducted to understand why SHMP amendment could improve the chemical compatibility of the backfill. The X-ray diffraction analyses showed an intercalation of SHMP into montmorillonite platelets in the amended backfill permeated with 500 mM Pb(NO3)2 solution. The environmental scanning electron microscopy coupled with energy-dispersive spectrometry analyses indicated that the hydrated amended bentonite along with needle-shaped Pb3(PO4)2 and PbHPO4 were found in amended backfill after permeating with 500 mM Pb(NO3)2 solution in accordance with the X-ray diffraction analysis. The micropore and macropore proportions of amended backfill increased after permeating with 500 mM Pb(NO3)2 solution. The mechanisms of superior hydraulic performance of the amended backfill exposed to lead contamination were attributed to the chemical reaction between lead and SHMP-amended backfill, steric stabilization imposed by the SHMP, and intercalation of SHMP into montmorillonite platelets.
期刊介绍：
Acta Geotechnica is an international journal devoted to the publication and dissemination of basic and applied research in geoengineering – an interdisciplinary field dealing with geomaterials such as soils and rocks. Coverage emphasizes the interplay between geomechanical models and their engineering applications. The journal presents original research papers on fundamental concepts in geomechanics and their novel applications in geoengineering based on experimental, analytical and/or numerical approaches. The main purpose of the journal is to foster understanding of the fundamental mechanisms behind the phenomena and processes in geomaterials, from kilometer-scale problems as they occur in geoscience, and down to the nano-scale, with their potential impact on geoengineering. The journal strives to report and archive progress in the field in a timely manner, presenting research papers, review articles, short notes and letters to the editors.
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