Understanding of soil physics phenomena of Imogolite-humic substances complex from a standpoint of colloid and interface science

2021 Fiscal Year Final Research Report

• Project/Area Number: 17K15343
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Rural environmental engineering/Planning
• Research Institution: University of Tsukuba
• Principal Investigator: Yamashita Yuji 筑波大学, 生命環境系, 助教 (30543227)
• Project Period (FY): 2017-04-01 – 2022-03-31
• Keywords: 土壌物理 / イモゴライト / 腐植物質 / 粘土腐植複合体 / コロイド / 凝集分散 / 濡れ性

Outline of Final Research Achievements

Since volcanic ash soils accumulate a large amount of humus produced by degradation of vegetation, it is necessary to clarify the properties of clay-humus complexes as well as the properties of the minerals alone in order to link the properties of clay minerals to the understanding of soil engineering properties. In this study, the interaction between imogolite, a major clay mineral that characterizes volcanic ash soils, and humic substances was clarified based on an adsorption isotherm model. Contact angle measurements of adsorption complex thin films prepared under various pH conditions revealed that the wettability of the complex depends on the charge state of the humic substances at the time of adsorption. Aggregation and dispersion experiments revealed that humus adsorption has both an aggregation-promoting and an aggregation-inhibiting effect on imogolite.

Free Research Field

農業工学

Academic Significance and Societal Importance of the Research Achievements

従来の土壌有機物研究では，粘土-腐植複合体が土壌のマクロな特性にどう影響するかに関してスポットが当てられてこなかった。一方の土壌物理学分野では，火山灰土の性質に対する有機物の影響はあまり考慮されてこなかった。本研究は，従来の土壌有機物研究と土壌物理学との境界領域の未解決問題に焦点をあて，化学と物理の両面から粘土-腐植複合体の性質を明らかにした。このときさらに，物理化学を出発点とするコロイド界面化学に論拠を求めて実験系と解析手法を構築して研究を展開した。その結果，イモゴライト-腐植複合体の土壌物理学的特性が明らかになり，更に，理論に基づいて再構築された粘土-腐植複合体の解析方法が確立された。