Experimental study on compacted steel slag-bentonite mixtures as hydraulic barrier material of cover

doi:10.3785/j.issn.1008-973X.2022.12.017

Journal of ZheJiang University (Engineering Science)

2022, Vol. 56

Issue (12): 2478-2486 DOI: 10.3785/j.issn.1008-973X.2022.12.017

Experimental study on compacted steel slag-bentonite mixtures as hydraulic barrier material of cover

Jia-qi NI1,2(

),Liang-tong ZHAN1,2,*(

),Song FENG1,2,3,Ling-gang KONG1,2,Tian FENG1,2

1. Geotechnical Engineering Department, Zhejiang University, Hangzhou 310058, China
2. Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education, Zhejiang University, Hangzhou 310058, China
3. College of Civil Engineering, Fuzhou University, Fuzhou 350108, China

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Abstract

Bentonite was used to modify steel slag to improve impermeability of steel slag in cover liner of solid waste landfills. The saturated hydraulic conductivity of the compacted steel slag-bentonite mixtures k_s was investigated through the flexible-wall permeation tests. Then, the pore size distributions, interlayer spacing of montmorillonite and mineral morphology were investigated through mercury intrusion porosimetry tests, X-ray diffraction tests and scanning electron microscopy tests, in order to analyse the impact mechanism of the k_s at the microscopic scale. Thereafter, a formula and a preparation method were proposed, which meets the permeability requirement of the hydraulic barrier (k_s≤10^?9 m/s). Results showed that the k_s of the specimen, treated by pre-hydration of bentonite, was reduced to 1/2 of that of the untreated one. After improving the gradation of steel slag, the content of macropores between the steel slag particles was decreased, reducing the k_s of the specimens to 1/5 of that of the specimen with poorly graded steel slag. The k_s and pore size distribution of the specimens mixed steel slag with Wyoming were similar to those of sodium-activated calcium bentonite. The high salt content leachate of steel slag results in the increase of the interlayer spacing and the decrease of the bound water of montmorillonite. Subsequently, the osmotic swelling of bentonite is suppressed. Water-washing treatment of steel slag can alleviate the suppression effect and the formation of montmorillonite clusters, and reduce the k_s of specimens to 1/10 of that of the untreated one.

Key words： steel slag bentonite saturated hydraulic conductivity hydraulic barrier microscopic characteristic

Received: 11 November 2021 Published: 03 January 2023

CLC:

TU 443

Fund: 国家重点研发计划(2019YFC1806003）；国家自然科学基金杰出青年基金项目(51625805)

Corresponding Authors: Liang-tong ZHAN E-mail: n310414394@foxmail.com;zhanlt@zju.edu.cn

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Cite this article:

Jia-qi NI,Liang-tong ZHAN,Song FENG,Ling-gang KONG,Tian FENG. Experimental study on compacted steel slag-bentonite mixtures as hydraulic barrier material of cover. Journal of ZheJiang University (Engineering Science), 2022, 56(12): 2478-2486.

URL:

https://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2022.12.017 OR https://www.zjujournals.com/eng/Y2022/V56/I12/2478

压实钢渣-膨润土覆盖防渗材料试验研究

为了实现钢渣在工业固废堆场覆盖层中的应用，采用膨润土改良钢渣的防渗性. 通过柔性壁渗透试验，测量压实钢渣-膨润土混合材料的饱和渗透系数k_s. 结合压汞法、X射线衍射和扫描电镜技术，分别观察试样的孔隙分布、蒙脱石矿物层间距和矿物形态，从微观尺度分析k_s的影响机理. 提出满足防渗层渗透性要求(k_s≤10^?9 m/s)的配方与制备方法. 结果表明，膨润土预水化处理使试样的k_s降低至未处理试样的1/2. 改良钢渣级配后，钢渣颗粒间的大孔隙比例降低，使试样的k_s降低至不良级配试样的1/5. 钢渣掺和怀俄明膨润土试样的k_s和孔隙分布与掺和钠化钙基膨润土试样的相似. 钢渣的高盐浸出液使蒙脱石层间距增大、结合水减少，对膨润土的渗透溶胀起抑制作用；钢渣水洗处理可以缓解该抑制作用，减少蒙脱石团簇的产生，使试样的k_s降低至未处理试样的1/10.

关键词： 钢渣, 膨润土, 饱和渗透系数, 防渗层, 微观特征

Tab.1 Physical and chemical properties of steel slag and bentonite

Fig.1 Particle-size distributions of steel slag and bentonite

Fig.2 Compaction characteristics of steel slag-bentonite mixtures (steel slag of particle distribution Ⅰ)

Tab.2 Scheme of hydraulic conductivity tests using flexible-wall permeater

Fig.3 Effects of specimen preparation method on saturated hydraulic conductivity of compacted steel slag-bentonite specimens at different sodium-activated calcium bentonite contents

Fig.4 Effects of steel slag gradation on saturated hydraulic conductivity of compacted steel slag-bentonite specimens

Fig.5 Effects of steel slag gradation on pore size distribution of compacted steel slag-bentonite specimens

Fig.6 Effects of bentonite type on hydraulic conductivity of compacted steel slag-bentonite specimens under different bentonite contents

Fig.7 X-ray diffraction curves of bentonite specimens

Fig.8 Effects of type of bentonite on pore size distribution of compacted steel slag-bentonite specimens

Fig.9 Effect of water-washing treatment of steel slag on saturated hydraulic conductivity of compacted steel slag-bentonite specimens

Fig.10 X-ray diffraction curves of sodium-activated calcium bentonite specimens

Fig.11 Scanning electron microscope images of compacted steel slag-bentonite specimens


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