2020 Fiscal Year Research-status Report
Hydraulic and chemical performance of a sandy soil mixed with calcium-magnesium composite as the attenuation layer for geogenic heavy metals
| Project/Area Number |
20K22433
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| Research Institution | Kyoto University |
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Principal Investigator |
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| Project Period (FY) |
2020-09-11 – 2022-03-31
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| Keywords | Attenuation layer / Hydraulic performance / Sorption / Natural contamination |
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| Outline of Annual Research Achievements |
Hydraulic conductivity tests using flexible-wall permeameters with a constant head system and batch sorption tests were carried out to evaluate the hydraulic and attenuation performances of soil mixed with calcium-magnesium composite in the fiscal year 2020. I focused on the influence of different particle sizes of the agent and acidic pH. The conducted tests have succeeded in clarifying two issues. First, the hydraulic conductivity of the soil-agent mixture is ~1.0 × 10-7 m/s at the beginning of permeation, regardless of agent size. However, the hydraulic conductivity of the mixture reduces with continuous permeation, and this phenomenon is drastic if the solution is pH 6. Second, the soil’s attenuation performance is improved after the agent addition, even if agent content was 5%. The sorption behaviour was clarified to be linear for relatively low arsenic concentrations (<0.5 mg/L). Using partition coefficient from Henry isotherm as an index, the soil's attenuation performance was determined to have improved by ~50% because of using the agent with 2.0-9.5 mm in diameter. The attenuation performance of the mixture increases when the agent size reduces. These findings demonstrate that the soil-agent mixture is reliable as the attenuation layer material, even if granular calcium-magnesium composite is the stabilising agent.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Hydraulic and attenuation performances of the soil-agent mixtures have been evaluated through hydraulic conductivity tests and batch sorption tests during the first year. However, the planned evaluation of the attenuation performance of the mixture using a sprinkler-type column has not yet started. While this test is important for the performance evaluation under unsaturated conditions, I have clarified the influence of agent size and acidic pH, which was the main goal for the fiscal year 2020 and a critical issue for the next step. Therefore, I believe I am advancing relatively smoothly with this project.
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| Strategy for Future Research Activity |
In the fiscal year 2021, the plan is to clarify the attenuation performance of the mixture using a sprinkler-type column and the attenuation mechanisms and to simulate the transport of arsenic through the attenuation layer. The simulations will use the hydraulic conductivity values and partition coefficients from the experimental results. Findings from the fiscal year 2020 will be presented at a national symposium organised by Japanese Geotechnical Society (14th Symposium on Environmental Geotechnics) as well as in a Journal paper to introduce the findings to a larger network of researchers.
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| Causes of Carryover |
Due to the COVID-19 pandemic, some of the research activities were postponed to the next fiscal year. Therefore, I plan to purchase chemicals and some equipment to continue with the work. Further, I purchased licenses for data analyses in the fiscal year 2020. However, the licenses are valid for one year. Therefore I plan to renew the licences to continue the analyses. Funds will also be used for attending conferences and journal publications.
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