The Fluid Mechanics of Deep-Sea Mining

Abstract

Fluid mechanics lies at the heart of many of the physical processes associated with the nascent deep-sea mining industry. The evolution and fate of sediment plumes that would be produced by seabed mining activities, which are central to the assessment of the environmental impact, are entirely determined by transport processes. These processes, which include advection, turbulent mixing, buoyancy, differential particle settling, and flocculation, operate at a multitude of spatiotemporal scales. A combination of historical and recent efforts that combine theory, numerical modeling, laboratory experiments, and field trials has yielded significant progress, including assessing the role of environmental and operational parameters in setting the extent of sediment plumes, but more fundamental and applied fluid mechanics research is needed before models can accurately predict commercial-scale scenarios. Furthermore, fluid mechanics underpins the design and operation of proposed mining technologies, for which there are currently no established best practices. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 55 is January 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Oceanic bottom mixed layer in the Clarion-Clipperton Zone: potential influence on deep-seabed mining plume dispersal

“…Commercial mining activities of polymetallic nodules (baseball sized concretions on the seabed comprising critical minerals such as nickel and cobalt), regulated by the International Seabed Authority, are expected to commence in the CCZ in the coming decade, yet many asepcts of the potential environmental impact are still poorly understood [14]. In the deep water column, a key environmental consideration is the release of sediment plumes generated by nodule collector vehicles traversing on the seabed [19]. The released plume particles would form (i) gravity currents [20] and (ii) associated ambient plumes with suspended small particles (typically with diameter < 63 m) that behave largely as passive tracers [21].…”

Deep seabed mining: Frontiers in engineering geology and environment

“…In deep seabed mining activities, the collection of minerals, the beneficiation on the ship, and the discharge of underwater tailings have serious impacts on the marine environment, especially plumes (Fig. 23) (Muñoz-Royo et al 2022;Peacock and Ouillon 2022). The mining of 3 × 10 6 t of polymetallic nodules per year is estimated to result in a total volume of 5 × 10 9 m 3 of resuspended sediment (Sharma There can be two stages of plume generation: the seafloor sediment plume discharged during extraction and the midwater plume discharged during beneficiation and the treatment of underwater tailings (Sharma et al 2017;Muñoz-Royo et al 2021).…”

“…The mining of 3 × 10 6 t of polymetallic nodules per year is estimated to result in a total volume of 5 × 10 9 m 3 of resuspended sediment (Sharma There can be two stages of plume generation: the seafloor sediment plume discharged during extraction and the midwater plume discharged during beneficiation and the treatment of underwater tailings (Sharma et al 2017;Muñoz-Royo et al 2021). During the extraction stage, the travel of mining vehicles and the dragging of the ground-touching part of the pipelines disturb the seabed sediments and form the seafloor sediment plume (Peacock and Ouillon 2022). The composition of the midwater plume is diverse and includes tailings, sediments brought to the production support vessel, and effluent from mineral cleaning.…”

“…The composition of the midwater plume is diverse and includes tailings, sediments brought to the production support vessel, and effluent from mineral cleaning. The evolution and fate of the sediment plume are determined by the transport process, which operates on multiple spatiotemporal scales (Peacock and Ouillon 2022). The propagation range of the plume depends on the duration, velocity, volume, concentration, particle size distribution, and emission depth along with the state of the ocean in the discharge zone (Gillard et al 2019;Fan et al 2021).…”

“…The propagation range of the plume depends on the duration, velocity, volume, concentration, particle size distribution, and emission depth along with the state of the ocean in the discharge zone (Gillard et al 2019;Fan et al 2021). The scale of the sediment plume is underpinned by transport phenomena and fundamental fluid mechanics and depends on the design of the mining system and rheology of sediment-laden flows (Guo et al 2020b(Guo et al , 2021b, the flocculation and settling behavior of the sediments, and the process of ambient flow (Spearman et al 2020;Peacock and Ouillon 2022). For a 12 × 12 km 2 nodular mining site, the diffusion distance of particles larger than 0.1 mm is estimated to reach 50 km in one year (Ding et al 2021).…”