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S. de Jong
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Flocculation of Deep-Sea Clay from the Cook Islands Region
Laboratory Investigation of Sediment Flocculation and Settling Behavior
Master thesis
(2025)
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S. de Jong, R.L.J. Helmons, C. Chassagne, B. Nieuwboer, M. Biesheuvel, Alex Kirichek
The growing demand for critical metals such as cobalt, nickel, and copper, essential for renewable energy and green technologies, has intensified interest in deep-sea mining of polymetallic nodules. However, such activities generate sediment plumes that may severely impact mining operation and deep-sea ecosystems. The behavior of these plumes is strongly influenced by flocculation, the process through which fine sediment particles aggregate into larger flocs, altering their settling velocity and transport. While flocculation behavior and settling velocities are well documented for the Clarion–Clipperton Zone (CCZ), no data currently exist for the Cook Islands (CI) region. Differences in sediment characteristics may lead to distinct flocculation and settling behavior, highlighting the importance of region-specific data for reliable plume modeling.
This study characterizes the flocculation and settling behavior of deep-sea clay from the CI region to evaluate the applicability of existing CCZ-based plume models. Laboratory experiments were conducted under controlled conditions using jar tests, laser diffraction, rheometry, and imaging techniques to quantify floc size and settling velocity under varying shear and concentration ranges.
The CI clay exhibited non-Newtonian and thixotropic behavior, with a yield stress above the gelling concentration. Floc growth followed a sigmoidal pattern, well described by a logistic growth model. Higher shear rates and clay concentrations were found to limit the floc size. Importantly, flocs of similar size displayed comparable settling velocities, regardless of their formation history. When compared with CCZ sediments, CI material showed similar gelling behavior but notably slower settling velocities. In addition, floc sizes observed for flocculation under the same conditions also differ. Consequently, plume dispersion in the CI region is likely to be more extensive, and models calibrated for CCZ sediments are not directly transferable. This study provides the first experimental dataset on CI sediment flocculation and settling behavior, offering critical insights for developing region-specific plume models and designing environmentally responsible deep-sea mining operations. ...
This study characterizes the flocculation and settling behavior of deep-sea clay from the CI region to evaluate the applicability of existing CCZ-based plume models. Laboratory experiments were conducted under controlled conditions using jar tests, laser diffraction, rheometry, and imaging techniques to quantify floc size and settling velocity under varying shear and concentration ranges.
The CI clay exhibited non-Newtonian and thixotropic behavior, with a yield stress above the gelling concentration. Floc growth followed a sigmoidal pattern, well described by a logistic growth model. Higher shear rates and clay concentrations were found to limit the floc size. Importantly, flocs of similar size displayed comparable settling velocities, regardless of their formation history. When compared with CCZ sediments, CI material showed similar gelling behavior but notably slower settling velocities. In addition, floc sizes observed for flocculation under the same conditions also differ. Consequently, plume dispersion in the CI region is likely to be more extensive, and models calibrated for CCZ sediments are not directly transferable. This study provides the first experimental dataset on CI sediment flocculation and settling behavior, offering critical insights for developing region-specific plume models and designing environmentally responsible deep-sea mining operations. ...
The growing demand for critical metals such as cobalt, nickel, and copper, essential for renewable energy and green technologies, has intensified interest in deep-sea mining of polymetallic nodules. However, such activities generate sediment plumes that may severely impact mining operation and deep-sea ecosystems. The behavior of these plumes is strongly influenced by flocculation, the process through which fine sediment particles aggregate into larger flocs, altering their settling velocity and transport. While flocculation behavior and settling velocities are well documented for the Clarion–Clipperton Zone (CCZ), no data currently exist for the Cook Islands (CI) region. Differences in sediment characteristics may lead to distinct flocculation and settling behavior, highlighting the importance of region-specific data for reliable plume modeling.
This study characterizes the flocculation and settling behavior of deep-sea clay from the CI region to evaluate the applicability of existing CCZ-based plume models. Laboratory experiments were conducted under controlled conditions using jar tests, laser diffraction, rheometry, and imaging techniques to quantify floc size and settling velocity under varying shear and concentration ranges.
The CI clay exhibited non-Newtonian and thixotropic behavior, with a yield stress above the gelling concentration. Floc growth followed a sigmoidal pattern, well described by a logistic growth model. Higher shear rates and clay concentrations were found to limit the floc size. Importantly, flocs of similar size displayed comparable settling velocities, regardless of their formation history. When compared with CCZ sediments, CI material showed similar gelling behavior but notably slower settling velocities. In addition, floc sizes observed for flocculation under the same conditions also differ. Consequently, plume dispersion in the CI region is likely to be more extensive, and models calibrated for CCZ sediments are not directly transferable. This study provides the first experimental dataset on CI sediment flocculation and settling behavior, offering critical insights for developing region-specific plume models and designing environmentally responsible deep-sea mining operations.
This study characterizes the flocculation and settling behavior of deep-sea clay from the CI region to evaluate the applicability of existing CCZ-based plume models. Laboratory experiments were conducted under controlled conditions using jar tests, laser diffraction, rheometry, and imaging techniques to quantify floc size and settling velocity under varying shear and concentration ranges.
The CI clay exhibited non-Newtonian and thixotropic behavior, with a yield stress above the gelling concentration. Floc growth followed a sigmoidal pattern, well described by a logistic growth model. Higher shear rates and clay concentrations were found to limit the floc size. Importantly, flocs of similar size displayed comparable settling velocities, regardless of their formation history. When compared with CCZ sediments, CI material showed similar gelling behavior but notably slower settling velocities. In addition, floc sizes observed for flocculation under the same conditions also differ. Consequently, plume dispersion in the CI region is likely to be more extensive, and models calibrated for CCZ sediments are not directly transferable. This study provides the first experimental dataset on CI sediment flocculation and settling behavior, offering critical insights for developing region-specific plume models and designing environmentally responsible deep-sea mining operations.