Rheology of deep-sea mining plumes: Dependence on properties of sediments in Western Pacific Ocean

Deep-sea mineral resources, including polymetallic nodules, cobalt-rich crusts, polymetallic sulfides, and rare earth elements, are increasingly recognized as vital strategic reserves due to their scarcity and significant economic potential for advancing sustainable, environmentally-conscious development. However, the sediment plumes generated by deep-sea mining operations pose substantial environmental risks, particularly to fragile benthic ecosystems. This study systematically investigates the rheological properties of sediment plumes and examines the influences of four key parameters: sediment concentration, particle size distribution, mineral composition, and pH. Sediment samples from the Western Pacific Ocean surficial sediment, kaolin, seawater, and freshwater to simulate different plume types are investigated through experimentation. The rheological analysis of the samples has revealed that sediment plumes exhibit shear-thinning behavior, characteristic of non-Newtonian fluids, with their dynamic viscosity significantly affected by sediment concentration and mineral composition. Kaolin plumes exhibit higher viscosity and more pronounced shear-thinning behavior than Western Pacific Ocean sediment plumes. Furthermore, mineral composition and pH affect the formation of flocculation structures, which in turn alter the overall rheological behavior of the plumes. Based on these findings, a power-law rheological model is proposed to quantify the flow behavior of sediment plumes, effectively capturing density-dependent variations during transport. This model supports more accurate environmental impact assessments of deep-sea mining and informs future numerical and experimental studies.