Browsing by Author "Otake, T"

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item: Conference-Abstract
Key factors of metastable phase formation for strength development in steel slag and dredged soil mixtures
Toda, K; Otake, T; Sato, T; Sato, H; Weerakoon, N; Nishimura, S
The usage of by-products from industrial activities, as construction resources is awaited in Japan to decrease the environmental impacts. Steel slag from iron works and dredged soil extracted beneath the ports are examples for such resources. Recently, it is discovered that mixtures of steel slag with dredged soil are hardened. This discovery may expand their application into building materials for undersea construction which may solve the problem. Nonetheless, different combinations of a type of steel slag and dredged soil from various areas show gaps in strength development. The relationship between mixing condition and strength development is not clarified, making the mixture difficult to be utilized for the above application. Understanding of the hardening mechanism of the steel slag-dredged soil mixture would enable the prediction of the strength with a particular combination of steel slag and dredged soil. To achieve it, clarifying the secondary mineral formation that contributes to hardening is essential. Previous studies suggested that the strength development was related to the pozzolanic reaction, which results in cementation by the formation of calcium silicate hydrates (C-S-H). Key factors in the pozzolanic reaction are the increase in pH of the pore water and the supply of calcium and silica ions to pore water. While calcium supply is determined to be Ca(OH)2 in steel slag which also increases pH by its hydration, silica supply is only suggested to be originated in dredged soils. The objective of this study is set to understand the effects of silica-bearing phases in dredged soil on the strength development of steel slag-dredged soil mixture. In this study, dredged soils from various sampling locations (A, B, C and D) and steel slag from ironworks-1 were mixed for the investigation. The unconfined compressive strength showed mixtures with soil-A exhibits the highest strength, followed by those with B, C and D. Firstly, the silica ion which is most likely to be supplied from dredged soils was investigated. The biogenic silica content and inorganic amorphous silica such as volcanic glass content were quantified. XRD analysis showed no significant difference between the mineralogical compositions of all the dredged soils including clay minerals. Then, the effect of humic acid which may limit the supply of soluble calcium is quantified and its functional groups are analysed to see the effect on strength development of the mixtures. Through geochemical modeling for estimation of C-S-H formed from above silica supply, we suggest that the silica supply from each silica-bearing phase of dredged soils may be the driving force for the pozzolanic reaction for the strength development.
item: Conference Full-text
Key factors of metastable phase formation for strength development in steel slag and dredged soil mixtures
Toda, K; Otake, T; Sato, T; Sato, H; Weerakoon, N; Nishimura, S; ; Abeysinghe, AMKB; Dassanayake, ABN; Elakneswaran, Y.;
The usage of by-products from industrial activities, as construction resources is awaited in Japan to decrease the environmental impacts. Steel slag from ironworks and dredged soil extracted beneath the ports are examples for such resources. Recently, it is discovered that mixtures of steel slag with dredged soil are hardened. This discovery may expand their application into building materials for undersea construction which may solve the problem. Nonetheless, different combinations of a type of steel slag and dredged soil from various areas show gaps in strength development. The relationship between mixing condition and strength development is not clarified, making the mixture difficult to be utilized for the above application. Understanding of the hardening mechanism of the steel slag-dredged soil mixture would enable the prediction of the strength with a particular combination of steel slag and dredged soil. To achieve it, clarifying the secondary mineral formation that contributes to hardening is essential. Previous studies suggested that the strength development was related to the pozzolanic reaction, which results in cementation by the formation of calcium silicate hydrates (C-S-H). Key factors in the pozzolanic reaction are the increase in pH of the pore water and the supply of calcium and silica ions to pore water. While calcium supply is determined to be Ca(OH)2 in steel slag which also increases pH by its hydration, silica supply is only suggested to be originated in dredged soils. The objective of this study is set to understand the effects of silica-bearing phases in dredged soil on the strength development of steel slag-dredged soil mixture. In this study, dredged soils from various sampling locations (A, B, C and D) and steel slag from ironworks-1 were mixed for the investigation. The unconfined compressive strength showed mixtures with soil-A exhibits the highest strength, followed by those with B, C and D. Firstly, the silica ion which is most likely to be supplied from dredged soils was investigated. The biogenic silica content and inorganic amorphous silica such as volcanic glass content were quantified. XRD analysis showed no significant difference between the mineralogical compositions of all the dredged soils including clay minerals. Then, the effect of humic acid which may limit the supply of soluble calcium is quantified and its functional groups are analysed to see the effect on strength development of the mixtures. Through geochemical modeling for estimation of C-S-H formed from above silica supply, we suggest that the silica supply from each silica-bearing phase of dredged soils may be the driving force for the pozzolanic reaction for the strength development.
item: Conference-Abstract
Seasonal dynamics of nickel attenuation in acid mine seepage: implications for remediation strategies at BCL copper-nickel mine tailings, Botswana
(Division of Sustainable Resources Engineering, Hokkaido University, Japan, 2024) Godirilwe, J; Otake, T; Kikuchi, R; Iresha, H; Elakneswaran, Y; Dassanayake, A; Jayawardena, C
Mining activities in Botswana have posed significant environmental challenges, notably acid mine drainage (AMD) resulting from sulfide ore processing at the BCL copper-nickel mine tailings. This generates AMD seepage characterized by low pH and high concentrations of dissolved toxic metals such as Fe, Ni, Cu, Pb, Zn, and Mn. The elevated concentration of heavy metals, particularly nickel, in the surrounding environment, groundwater, and nearby river underscores the challenge of remediating nickel contamination from tailings seepage. Thus, understanding nickel's behavior from acidic mine seepage is crucial for developing sustainable recovery and remediation strategies. The study aims to investigate the mechanisms controlling the natural attenuation processes of nickel from tailings seepage during rainy and dry seasons, informing geochemical passive treatment strategies. Objectives include determining the chemistry and behavior of toxic elements (Ni) from tailings seepage to the nearby river system in different seasons, understanding the release and mobility of toxic metals from the tailings, and elucidating the seasonal dynamics of nickel's natural attenuation from the tailings. Field surveys were conducted during both rainy and dry seasons, collecting tailings sediment, precipitate samples around the tailings, and sediment samples. Water samples were collected from the underground mine, tailings, and nearby river system. Heavy metal concentrations (Fe > Ni > Cu > Mn > Co > Pb > Ag > Cr) in the tailings seepage were notably high in both seasons, with higher values during the dry season. However, heavy metal concentrations exceeded the World Health Organization (WHO) and Botswana (BOBS) effluent standards in both seasons. In the dry season, heavy metal concentrations decreased post-treatment, except for nickel concentrations from the holding dam to the river, surpassing BOBS standards. Conversely, in the wet season, toxic metal concentrations, including nickel, fell below BOBS standards. Detailed analyses of tailing seepage, wastewater, river water, tailings sediments, precipitates, and river sediment furthered understanding of nickel's natural attenuation mechanism.