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Membrane behavior of clay under mixed solution conditions.
Zhihong Zhang1, Haowen Yang1, Zhaoyang Song1
1Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing 100124, China.
The Science of the Total Environment
|February 25, 2024
Summary
Compacted clay
Area of Science:
- Geotechnical Engineering
- Environmental Science
- Soil Science
Background:
- Compacted clay serves as a crucial buffer material in landfills, managing leachate ion migration.
- Current membrane tests often use single solute solutions, not reflecting complex leachate conditions.
- Assessing compacted clay's barrier properties under mixed ion solutions is vital for landfill safety.
Purpose of the Study:
- To evaluate the membrane efficiency of bentonite-amended soil under various mixed ion solutions.
- To investigate the micromechanisms influencing membrane behavior using nuclear magnetic resonance (NMR) tests.
- To understand how different cation mixing ratios affect compacted clay's barrier performance.
Main Methods:
- Conducted 13 membrane tests using KCl-NaCl, KCl-CaCl2, and KCl-AlCl3 mixed solutions (20 mM total concentration).
- Utilized nuclear magnetic resonance (NMR) tests on soil specimens post-membrane testing.
- Analyzed the impact of varying cation mixing ratios on membrane efficiency and soil microstructure.
Main Results:
- Membrane efficiency increased with higher Na+ ratios but decreased with higher Ca2+ or Al3+ ratios.
- Pure AlCl3 solution resulted in the lowest membrane efficiency among all tested conditions.
- NMR tests confirmed that increased ion valence correlates with reduced diffuse double layer thickness and increased macropore proportion.
Conclusions:
- The cation composition of leachate significantly impacts the membrane efficiency of compacted clay.
- Monovalent cations (Na+) enhance barrier properties, while divalent (Ca2+) and trivalent (Al3+) cations reduce them.
- Microstructural changes, including diffuse double layer thickness and macropore content, explain the observed membrane behavior.
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