Hydraulic and chemical performance of a sandy soil mixed with calcium-magnesium composite as the attenuation layer for geogenic heavy metals

2021 Fiscal Year Annual Research Report

• Project/Area Number: 20K22433
• Research Institution: Kyoto University
• Principal Investigator: Gathuka Lincoln.Waweru 京都大学, 地球環境学堂, 特定研究員 (70885582)
• Project Period (FY): 2020-09-11 – 2022-03-31
• Keywords: Attenuation layer / Geogenic contamination / Stabilising agent / Hydraulic conductivity / Sorption / Arsenic / Soil management

Outline of Annual Research Achievements

This work was carried out to evaluate the attenuation performance and hydraulic conductivity of a soil mixed with calcium-magnesium composite with different particle sizes, ranging from powder particles (<0.075 mm in size) to granular particles with diameters of 2.0 to 9.5 mm. According to the hydraulic conductivity tests, the original soil and the amended soil were not significantly different in hydraulic conductivity. This suggests that powder or granular particles of stabilising agent will not significantly impact the hydraulic properties of the attenuation layer. As continuous permeation progressed, the hydraulic conductivity of the soil-agent mixture decreased but remained over 1 × 10-8 m/s. The presence of acidic leachates could delay the attenuation layer's decline in hydraulic conductivity. Batch sorption tests demonstrated that amended soil more effectively attenuates contaminants than the original soil. In one experiment, a stabilising agent of granular particles (between 2.0 and 9.5 mm) for the amendment increased the soil’s partition coefficient Kd from 14.5 to 22.2 cm3/g, which is more than a 50% improvement in the attenuation. Using a stabilising agent with a smaller particle size for the amendment has a greater impact. Kd increases linearly as the particle size of the stabilising agent decreases down to 0.075 mm. Using the Kd from laboratory tests, simulations with a one-dimensional advection-dispersion equation demonstrate the durability of the attenuation layer. Both the powder and the granular particles show promise as attenuation layer materials.

Research Products

• [Journal Article] Evaluating the arsenic attenuation of soil amended with calcium-magnesium composites of different particle sizes (2022)
  • Author(s): Gathuka, L.W., Kasai, H., Kato, T., Takai, A., Inui, T., and Katsumi, T.
  • Journal Title: Soils and Foundations Volume: 62 Pages: 101130
  • DOI: 10.1016/j.sandf.2022.101130
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Column test for arsenic attenuation by sandy soil amended with calcium-magnesium composite of different particle sizes (2022)
  • Author(s): Gathuka, L.W., Kato, T., Takai, A., and Katsumi, T.
  • Journal Title: Proceedings of the 20th International Conference on Soil Mechanics and Geotechnical Engineering Volume: N/A Pages: N/A
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Effect of acidity on attenuation performance of sandy soil amended with granular calcium-magnesium composite. (2021)
  • Author(s): Gathuka, L.W., Kato, T., Takai, A., Flores, G., Inui, T., and Katsumi, T.
  • Journal Title: Soils and Foundations Volume: 61 Pages: 1099-1111
  • DOI: 10.1016/j.sandf.2021.05.007
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Compaction characteristics and attenuation performances of soil amended with Ca-Mg stabilising agent of different particle sizes (2021)
  • Author(s): Kasai, H., Gathuka, L.W., Kato, T., Takai, A., and Katsumi, T.
  • Journal Title: Proceedings of the 14th Japanese Geotechnical Society Symposium on Environmental Geotechnics Volume: N/A Pages: 61-64
  • Peer Reviewed