Chlorinated paraffins (CPs) are high-production-volume industrial chemicals, yet their occurrence and distribution in deep-ocean basins remain poorly understood. Here, this study investigated 771 homologues of CPs with various carbon chain lengths (i.e., C6-C40), including very short-chain (vSCCPs, C6-C9; semi-quantified), short-chain (SCCPs, C10-C13), medium-chain (MCCPs, C14-C17), long-chain (LCCPs, C18-C20), and very long-chain CPs (vLCCPs, C21-C40; semi-quantified) in surface sediment samples collected from 17 sites in the Indian Ocean basins using high-resolution mass spectrometry. CPs were detected in 65% of the samples, with total concentrations of 15-100 ng/g dry weight (dw) (mean: 40 ± 27 ng/g dw). MCCPs (51%) and SCCPs (43%) predominated the homologue profiles, while vSCCPs, LCCPs, and vLCCPs were also frequently semi-quantitatively detected, indicating the widespread dispersion of lesser-monitored CP classes into deep-sea sediments. A clear spatial fractionation was observed: Western sediments (Arabian Sea) were enriched in heavier CP groups (MCCPs, 64%; C14-C15 homologues), whereas eastern sediments showed higher proportions of lighter CP groups (SCCPs, 53%; C10-C11 homologues). The positive correlation between concentrations of CPs and total organic carbon suggests that organic matter and particle-associated transport play an important role in CP accumulation, whereas the lack of a depth trend indicates that overlying water depth alone is not a primary predictor of sedimentary CP burdens. This study provides first-hand baseline data on C6-C40 CPs in deep-sea sediments, revealing the previously unrecognized presence of vSCCPs and vLCCPs in remote basins, and highlighting the need to include homologue-specific transport and deep-sea sequestration in future CP monitoring and risk assessment frameworks.

Benthic plumes generated by deep-sea polymetallic nodule mining pose significant threats to the marine ecological environment and represent one of the primary challenges hindering the commercialization of deep-sea mining. This study investigates the sedimentation behavior of deep-sea sediment plumes in the West Philippine Basin to assess the potential environmental impacts of mining activities. The results reveal that the presence of marine inorganic salts markedly enhances the sedimentation efficiency of suspended sediment particles, and the settling rate in seawater was approximately two to three times higher than that in pure water, highlighting the strong promotion effect of inorganic ions—especially divalent cations such as Ca2+ and Mg2+—on particle aggregation and sedimentation efficiency. A characteristic thickness parameter introduced through numerical simulations quantitatively describes interparticle electrostatic interactions and provides a predictive tool for plume-settling behavior under different salinity and concentration conditions. By linking plume sedimentation kinetics with marine physicochemical processes, this study enhances understanding of how electrochemical properties of particles influence plume motion and dispersion in deep-sea environments.

Local scour can significantly degrade the horizontal performance of offshore wind bucket foundations, yet its post-scour response remains insufficiently understood. This study conducted model tests on bucket foundation to investigate its horizontal bearing behavior, failure characteristics, and H-M failure envelope under scour. Based on Froude similarity, the effects of scour depth, loading direction, and combined horizontal-moment loading were examined. The normalized horizontal ultimate capacity decreased from 1.722 without scour to 1.559, 1.396, and 1.163 at scour depths of 0.1D, 0.2D, and 0.3D, respectively. The reduction was approximately linear within 0-0.2D, and reached 32.46% at 0.3D. After scour, downstream-side loading produced a larger ultimate capacity than upstream-side loading, owing to the distinct scour pit on the upstream side and slight deposition downstream. Scour also reduced the initial stiffness, intensified displacement development, promoted an earlier transition to pure rotation, and shifted the stable rotation point downward. Under combined loading, the H-M failure envelope remained approximately elliptical, but became markedly narrower after scour. A dimensionless envelope expression was fitted for both conditions. The results provide an experimental basis for evaluating the post-scour horizontal performance of bucket foundations and for improving their engineering design.

The mobility performance of deep-sea mining vehicles (DSMVs) is a critical factor governing both the operational efficiency and commercial viability of deep-sea mining systems. When traversing soft seafloor sediments, DSMVs experience coupled interactions between the ore hose and soft substrates, resulting in significant alterations to vehicle attitude. These attitude changes can not only impair the efficiency of the collection system but may also lead to loss of traction and eventual mobility failure. Experimental simulations investigated the effects of varying towing forces on vehicle attitude. Two analytical models were established: a pitch angle variation model quantifying attitude dynamics under combined cable-substrate interactions; and a destabilization pitch angle model identifying locomotion failure thresholds. Experimental results demonstrate strong agreement with model predictions. The developed models provide reliable quantitative tools for analyzing and predicting the critical pitch behavior of seabed mining vehicles operating under coupled pipeline towing and seabed sinkage. Through the tests, the optimal range of hose drag force to body gravity ratio that does not affect the driving performance of the DSMV was obtained(<15 degrees), enabling practical engineering calculations of required buoyancy material. This study provides computational methods and solutions for pitch angle control in pipeline-seabed tracked vehicles-soft sediment systems, with applications to analogous deep-sea operations.

With the advancement of deep-sea mining technology, long-distance continuous operation and extraction represent the key technical challenges for the commercialization of deep-sea mineral resources. This paper quantifies the degree of reduction in mining performance under different mine vehicle orientations and conducts research on flow field optimization. The results indicate that when the inclination angle is <= 3 degrees, the Coand & abreve; jet maintains a stable wall-attached flow, with the collection efficiency remaining above 70%. As the inclination angle increases to 8 degrees-14 degrees, the pressure-induced flow structure generated by wall adhesion progressively deteriorates. The low-pressure region significantly narrows, and collection efficiency drops below 40%. This demonstrates its high sensitivity to attitude changes. Therefore, this study proposes a flow field optimization method aimed at enlarging the effective fluid action zone. The results show that after optimizing the flow field structure, the momentum coupling within the channel is significantly enhanced, and the wall-attached flow region is expanded. Under the 3 degrees condition, the collection efficiency increases from 20% to 98%. Based on this, a dimensionless ratio parameter k was introduced to characterize the relationship between the vehicle posture, traveling parameters, and jet operating conditions. The results show that k effectively distinguishes the collection characteristics under different working conditions: when k < 50, the collection efficiency is significantly low, whereas when k >= 150, the efficiency approaches saturation. Therefore, in practical engineering design, k >= 150 should be ensured to achieve efficient mining. This study provides both theoretical and technical support for achieving efficient collection performance of deep-sea mining equipment under complex seabed conditions.

Deep-sea hydrate-based carbon sequestration represents a promising strategy to mitigate global climate change and restore balance in the carbon cycle. This study conducts high-pressure simulation experiments to investigate the kinetics and morphology of hydrate formation induced by submerged liquid CO2 jets, thereby providing support for the development of deep-sea hydrate sequestration technologies. The experiments demonstrate that liquid CO2 spontaneously sinks and forms stable solid hydrates rapidly under deep-sea conditions exceeding 30 MPa. Under submerged jet conditions, hydrates exhibit spherical, hair-like, and filamentous morphologies, with their growth mechanisms governed by a reaction-diffusion-controlled mass transfer process. Hair-like and filamentous hydrates constitute more than 90% of the total moles of hydrates formed. The formation of hair-like and filamentous hydrates is strongly influenced by the porous structure of the hydrate film and by capillary effects. Furthermore, high ambient pressure accelerates hydrate formation during the early stages of CO2 injection, thereby enhancing the overall conversion ratio eta. This enhancement is primarily attributed to the increased formation of hair-like and filamentous hydrates under elevated pressure. Increasing the initial CO2-to-water molar ratio within a fixed volume boosts total hydrate yield but reduces the formation rate, providing valuable insights for optimizing injection strategies and pipeline configurations in deep-sea carbon sequestration systems.

To reveal the mechanism of surface pit-induced adiabatic shear failure in titanium alloy penetrators during concrete penetration, this paper establishes a theoretical framework by integrating cavity expansion theory and adiabatic shear theory. Based on the modified Johnson-Cook (MJC) constitutive model, numerical simulations of defect zone failure evolution at different initial velocities are performed via thermo-mechanical coupling, adaptive mesh refinement and FEM-SPH coupling method, and the local critical shear strain is derived. Results show that a thermo-mechanical concentration zone forms on the target-facing side of the defect, where shear stress, temperature rise and adiabatic shear failure region are highly consistent. Numerical predictions agree well with theoretical failure distributions, verifying the convergence and robustness of the model. The deviations of adiabatic shear initiation temperature and critical shear strain from published experimental data are less than 5% and 10%, respectively. This work quantifies the local mechanism of defect-induced adiabatic shear failure, providing theoretical and numerical support for defect control and structural optimization of titanium alloy components under extreme dynamic loads.

Deep-sea polymetallic nodules are characterized by their high grade and enormous reserves, and their commercial development is of great significance in addressing the shortage of terrestrial resources. Locomotion technology of mining vehicles is a core component of mining systems, and it directly determines the efficiency and productivity of collection operations. The feasibility verification stage remains in most existing research and technologies, and a large-scale, intelligent, and highly reliable locomotion technology system has not yet been established. Based on the basic dynamic characteristics of mining vehicles, this review systematically consolidates the research on structural optimization of vehicles, motion control, and dynamic coupling with trajectory control systems, and provides an integrated perspective connecting these domains with recent advances in path planning and intelligent navigation for deep-sea polymetallic nodule collection. It further examines path planning and navigation control in extreme environments by analyzing the inherent mechanisms of traction failure, along with existing prediction models and classical algorithms. The study identified theoretical gaps in the multibody dynamics analysis of deep-sea mining vehicles, outlined emerging trends in trajectory control, and clarified the challenges related to reliability and intelligence under extreme operating conditions. This integrative approach highlights the systemic interactions overlooked in previous studies, and proposes a novel framework for the development of intelligent mining vehicle in the future. In addition, some key future research directions aimed at laying a solid foundation for the commercial development of deep-sea polymetallic nodules were identified.

Deep-sea mining is increasingly viewed as a potential source of critical metals needed for the global energy transition, including those used in batteries, electric mobility, renewable power systems, and grid infrastructure. The deep-sea mining faces a critical environmental challenge: sediment plumes generated by collector vehicles disturbing the seabed. These plumes, composed of fine-grained deep-sea clays, can persist for extended periods and disperse across vast oceanic areas, posing a threat to benthic ecosystems. Current plume management predominantly adopts a reactive approach, focusing on monitoring and containment rather than addressing the root cause. This paper argues that effective plume control necessitates an understanding and active management of the geotechnical properties of deep-sea sediments. We find that the unique characteristics of deep-sea sediments, including high water content, fine particle size, flocculated microstructure, high surface activity, and the interactions between particles and hydrodynamics, are not only the origin of the plume issue but also the key to its resolution. Targeting three fundamental pathways, namely reducing particle entrainment, limiting transport range, and shortening suspension duration, we propose a comprehensive mitigation framework grounded in geotechnical principles. We conclude that a transition from passive monitoring to proactive particle-level intervention is essential for reducing plume-related environmental risks and for enabling the environmentally and commercially sustainable extraction of energy-critical metals from the deep sea.

Abundant mineral resources exist in the deep sea.However,in current deep-sea mining practices in China and abroad,tailwater is generally discharged directly into the middle layer of the ocean,leading to large-scale midwater plumes;and the carbon emissions of mother ships are extremely high.These have become core environmental bottlenecks restricting commercial deep-sea mining.To address these challenges,the study proposes a novel model for commercial deep-sea mining that leverages the green and low-carbon utilization of tailwater and exhaust gas.This model innovatively integrates source control with resource recovery,establishing a systematic pathway of"midwater plume control-resource transformation-synergistic enhancement."Based on the physicochemical properties of tailing mineral sludge,a safe treatment system encompassing"efficient flocculation-pressure filtration and dewatering-leaching desalination-heavy metal stabilization"is developed to prevent the formation of midwater plumes at the source,achieving solid-liquid separation,desalination,and harmless treatment of the sludge.Shipboard carbon capture and deep-sea sequestration technologies are integrated,capitalizing on the high-pressure and low-temperature conditions of the deep sea to realize mineralized sequestration of carbon dioxide in the form of hydrates.Carbon trading mechanisms are further incorporated to improve economic feasibility.The results indicate that,after safe treatment,the moisture content,salinity,and heavy metal concentrations in the tailing mineral sludge are significantly reduced,enabling its use in agricultural soils of islands and reefs,eco-friendly construction materials for island-reef systems,and daily chemical products,thereby creating considerable economic values.In parallel,the deep integration of exhaust gas carbon sequestration with mining operations minimizes redundant equipment and energy allocation,enhancing the overall operational efficiency of the system.Moreover,it offers a scalable technical solution for the low-carbon transition of marine engineering systems.The study also outlines future technological directions for the green and low-carbon utilization of tailwater and exhaust gas in commercial deep-sea mining.These include a safe treatment system for tailing mineral sludge aimed for large-scale commercial mining,coordinated development of deep-sea mining and agricultural cultivation on islands and reefs,green building material preparation technologies adapted to island and reef environments,integrated technologies for exhaust gas treatment and carbon sequestration,as well as technologies for producing high-quality daily chemical products from tailing mineral sludge.By establishing a circular system that integrates deep-sea mining,resource transformation,and industrial synergy,this study provides a systematic solution to overcome the environmental constraints in the commercial development of deep-sea resources,contributing an efficient technological paradigm to the global blue economy.

Driven by the carbon peaking and carbon neutrality goals as well as the accelerated development of new quality productive forces, the supply-demand tension of critical metals has become increasingly pronounced. As a strategic successor resource, deep-sea polymetallic nodules are entering a pivotal transition from pilot trials to commercial exploitation. However, seabed collection equipment still faces significant technical bottlenecks in long-duration continuous operation, collection efficiency, adaptability to complex environments, and low-disturbance control, which have become key obstacles restricting the commercial development of deep-sea polymetallic nodules in China. This study focuses on the emerging development needs of key seabed collection technologies for the commercialization of deep-sea mining and, centering on tracked seabed mining vehicles, conducts a systematic review across four core dimensions: mobility theory and methods for mining vehicles, operational path planning, high-efficiency nodule collection technologies, and seabed disturbance mechanisms with low-impact control. Moreover, considering the multiple technical demands of commercial development for production scale, adaptability to complex seabed conditions, long-duration continuous operation, and ecological compliance, the study identifies the key technical obstacles that hinder commercial deployment. Four priority research directions are further proposed: long-duration continuous locomotion technologies for mining vehicles, graded assessment of mining areas with long-duration continuous collection planning, efficient and low-energy continuous harvesting under complex seabed topography, and mechanistic understanding of sediment bonding-disaggregation coupled with low-disturbance mining strategies. This study aims to clarify the core technological targets for deep-sea polymetallic nodule seabed collection and to provide guidance for establishing an independent and controllable technical system tailored to commercial needs, thereby laying the foundation for the large-scale, economically viable, and environmentally responsible development of deep-sea polymetallic nodules in China and offering important practical significance for safeguarding national strategic resource security.

When deep-sea tracked mining vehicles operate on soft and unconsolidated seabed sediments, the inherent flexibility of their tracks causes a highly non-uniform distribution of ground contact pressure, which in turn leads to uneven dynamic sinkage of the seabed. Based on plane-strain elastic theory, this study develops a mechanical model to characterize the additional seabed stresses and dynamic sinkage induced by flexible tracks. The model incorporates the evolution of sediment water content under cyclic loading to establish a predictive framework for dynamic seabed deformation. The proposed static framework is examined through comparisons with DEM and FEM results in terms of non-uniform load distribution, stress response, and sinkage characteristics, showing reasonable agreement. Based on this framework, a theoretical approach is further developed to estimate the dynamic sinkage evolution under cyclic loading. The results indicate that stress concentrations caused by track flexibility generate substantially higher vertical stresses in the shallow seabed, resulting in a sinkage pattern characterized by periodic undulations aligned with the spacing of the support rollers. The peak stress near the vehicle's rear can exceed the nominal ground pressure, leading to excessive rear-end sinkage and front-end uplift. Under the flexible-track assumption, the predicted seabed sinkage beneath the rearmost wheel can be more than 35% greater than that predicted under the rigid flat-track assumption. As the number of support rollers increases and the ground pressure distribution becomes more uniform, the influence of track flexibility diminishes correspondingly. These findings provide theoretical guidance for structural design, mobility assessment, and posture-related operating performance evaluation of deep-sea tracked mining vehicles.

Submarine power cables in offshore energy are vulnerable to scour-induced free spans and bend restrictor (BR) detachment, yet their coupled effects on deformation and stress concentration remain poorly quantified. Scaled physical-model tests measured cable strain and curvature while varying free-span height, slack length and BR integrity (none, intact, partially detached). Without BR protection, strain responded non-monotonically to freespan height, with a minimum at 0.25 m (model scale); increasing slack length reduced peak mean strain by up to 70%. Strain concentrations consistently occurred at 0.75-1.25 times the bellmouth-touchdown distance from the touchdown point. An intact BR decreased mean strain in the suspended span by 30-70% and mitigated bending, but did not shift the high-risk zone. Partial BR detachment introduced a local stiffness discontinuity ("hard spot") at the interface between the free span and the first detached segment, increasing peak mean strain by 2.0-3.5 times and the stress concentration factor to 2.4 times that of the unprotected case. These findings explain localized overbending triggered by BR detachment and provide quantitative guidance for free-span management, BR layout and maintenance.

Sediment plumes generated during deep-sea mining are enriched with micron-sized cohesive particles, which can remain suspended for prolonged periods and disperse over large spatial scales. This poses a major challenge to deep-sea environmental protection during mining operations. To address the limited efficiency and weak plume particle removal capacity of conventional mitigation approaches, this study evaluates electrocoagulation as a near-source treatment process. Its process performance, removal mechanism, and applicability were assessed. The results show that electrocoagulation removed plume particles more effectively than natural settling. Experimental analyses identified the effects of current density, electrode spacing, electrolysis time, and prepared initial particle concentration on suspended solids concentration reduction. Mechanistic observations revealed that removal followed three successive stages: flocculation, flotation, and sedimentation. In situ generated coagulants promoted particle destabilization and aggregation, while cathodic hydrogen microbubbles regulated effective floc density and transport behavior. These processes accelerated the transformation of dispersed suspended particles into large settleable aggregates. SEM and optical imaging revealed particle surface reconstruction, strengthened interparticle connections, continuous floc growth, and more stable aggregate structures. Based on these findings, a conceptual near-source electrocoagulation route is proposed for plume particle treatment. This route may enable particle capture, SSC reduction, and process integration in deep-sea mining systems.

This study investigates the impact of liquid-gas phase transition on pore clogging during supercritical carbon dioxide (SC-CO2) geological storage. To address this, we developed a pore-scale CFD-DEM-VOF model incorporating phase transition. It is capable of simulating phase transition processes in multiphase flows and their subsequent effects on particle behavior, as well as the resulting coupled dynamics of particle transport, pore clogging, and unclogging. Throughout these simulations, drag forces, contact forces on particles, and the evolution of the flow field were meticulously tracked and analyzed. Crucially, the research employed both constantvelocity and constant-pressure inlet boundary conditions, using non-phase-transition models as controls for comparison. Analysis of the results revealed that phase transition influences particle behavior through two distinct mechanisms. Firstly, volume expansion accelerates particle transport towards pore outlets. Conversely, and simultaneously, phase transition enhances turbulence and vortex formation within the flow field. This secondary effect loosens particle clusters, slows their movement, and traps particles within swirling flow structures that impede passage. Under constant-velocity boundary conditions, higher phase transition rates generally promote faster particle transport through pores. In contrast, under constant-pressure conditions, phase transition reduces the inlet flow velocity at higher rates. Due to the low viscosity and density of gas, it is less effective at carrying particles through pores under these conditions. As a result, moderate phase transition rates yield the highest particle transport rates in the constant-pressure inlet model.

Deep-sea polymetallic nodule mining can generate benthic sediment plumes when hydraulic jets erode weak seafloor sediments. Liquid CO2 has been proposed as an alternative jetting medium that may couple mineral extraction with hydrate-based carbon sequestration, but its sediment-erosion and particle-release behavior remains unclear. This study conducted high-pressure laboratory experiments at 40 MPa and 4 degrees C to examine erosion of simulated deep-sea soft sediment by a liquid CO2 double-row jet. Erosion morphology, effects of jet velocity, stand-off height, and nozzle row spacing, and the relationship between erosion volume and suspended-particle concentration were analyzed and compared with water-jet results. Liquid CO2 jets produced narrow, deep pits with steep margins and irregular wedge-shaped profiles. Erosion depth increased rapidly at first and then approached quasi-equilibrium; jet velocity enhanced erosion, whereas stand-off height and row spacing caused non-monotonic changes through jet-convergence effects. Compared with water jets, liquid CO2 promoted localized splitting and block detachment rather than broad sediment fluidization. For the same erosion volume, it generated lower suspended-particle concentrations, indicating a different particle-release pathway. These findings clarify liquid CO2 jet-induced sediment disturbance and support plume source assessment for deep-sea nodule mining.

The interaction between deep-sea sediments and the polymetallic nodule mining subsystem is inherently governed by the evolution of the sediment's mechanical state under disturbance. To investigate the solid-liquid transition behavior and the associated shear strength degradation mechanism of deep-sea sediments with different water contents under external disturbance, this study conducted a series of systematic disturbance mechanics tests. The results indicate that the undrained shear strength of both in-situ deep-sea sediments and laboratory-prepared simulated soil decreases regularly with increasing water content, and the parameters of their fitting models are highly consistent. This confirms the universal mechanism by which water content weakens interparticle bonding through microscopic effects such as lubrication, thickening of adsorbed water films, and partial dissolution of cementitious materials. Meanwhile, the shear strength of both materials shows a positive correlation with the shear strain rate, and this rate dependency is weakly related to water content. This reveals that external disturbance primarily drives the transition from a solid to a significantly fluidized state by disrupting the inherent cemented flocculated structure of the soil. Based on the above mechanisms, a unified constitutive model was developed that couples the synergistic effects of water content and shear rate on soil structure, capable of accurately describing the post-disturbance degradation of shear strength. The findings provide a theoretical basis for analyzing water-sediment and track-sediment interactions in deep-sea mining from the perspective of soil structure evolution, offering fundamental support for enhancing mining efficiency and operational capability.

Sediment plumes generated during deep-sea mining are enriched with micron-sized cohesive particles, which can remain suspended for prolonged periods and disperse over large spatial scales. This creates a major challenge for efficient plume particle separation in deep-sea mining systems. To address the limited efficiency and weak fine-particle removal capacity of conventional plume mitigation approaches, this study evaluates electrocoagulation as an electrochemical separation process for plume particle removal. Its separation performance, mechanism, and applicability are systematically assessed. The results show that electrocoagulation removes plume particles much more effectively than natural settling. Experimental analyses further identify the effects of current density, electrode spacing, electrolysis time, and particle concentration on plume particle settling. Mechanistic results reveal that plume particle removal follows three successive stages: flocculation, flotation, and sedimentation. In situ generated coagulants promote particle destabilization and aggregation, while fine hydrogen bubbles released from the cathode regulate floc effective density and transport behavior. These processes accelerate the transformation of dispersed suspended particles into large settleable aggregates. Microscopic characterization further confirms that electrocoagulation alters particle surface morphology and interparticle connections, promotes continuous floc growth, and forms more stable aggregate structures. Based on these findings, a conceptual near-source electrocoagulation route is proposed for plume particle separation. This route may enable particle capture, solid–liquid separation, and process integration in deep-sea mining systems.

Environmental disturbances caused by seabed mining have garnered significant international attention. Deep-sea hydraulic mining inevitably disrupts seafloor sediments, transforming them into fine particles that remain suspended, posing long-term threats to marine ecosystems. This study systematically investigates sediment disturbance characteristics under varying jet parameters through model experiments, aiming to assess the environmental impact of jetting operations and optimize jet parameters. The jet parameters investigated include jet velocity, target distance, and nozzle height. Results indicate that seabed disturbance process can be divided into three stages: critical suspension, critical erosion, and plume dispersion. Seabed morphology exhibits distinct V-shaped or U-shaped features, with target-to-nozzle height ratios (B/H) equals to 1 identified as the critical threshold for shape transition. Plume transformation rate increases with jet velocity, ranging from 15% to 55%. After disturbance, the plume suspended concentration decreases with increasing nozzle height, reaching a maximum reduction of up to 70%. These findings provide valuable data for minimizing environmental disturbance in deep-sea jetting operations. Based on experimental results, a new method for calculating the relationship between jet parameters and plume dispersion is proposed, offering a theoretical and technical basis for reducing environmental impact in deep-sea mining.