Hydraulic conductivity and microscopic properties of sodium hexametaphosphate-amended sand-sodium-activated calcium bentonite backfill in vertical cutoff walls exposed to lead-contaminated groundwater

IF 5.6 1区工程技术 Q1 ENGINEERING, GEOLOGICAL

Acta Geotechnica Pub Date : 2024-10-29 DOI:10.1007/s11440-024-02444-3

Zhe-Yuan Jiang, Run Zhang, Zhong-Yuan Li, Xian-Lei Fu, Yu-Ling Yang, Ning-Jun Jiang, Yan-Jun Du

{"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>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.</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":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Acta Geotechnica","FirstCategoryId":"5","ListUrlMain":"https://link.springer.com/article/10.1007/s11440-024-02444-3","RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ENGINEERING, GEOLOGICAL","Score":null,"Total":0}

引用次数: 0

Abstract

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.

Abstract Image

查看原文本刊更多论文

求助全文

约1分钟内获得全文求助全文

来源期刊

Acta Geotechnica ENGINEERING, GEOLOGICAL-

CiteScore

9.90

自引率

17.50%

发文量

297

审稿时长

4 months

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.