Deep-sea Polymetallic Nodule Research Articles

CFD-DEM simulation and experimental investigations on continuous hydraulic sampling of deep-sea polymetallic nodules

The physical sampling to grasp the distribution of deep-sea polymetallic nodules is essential for efficient mining. A hydraulic sampling scheme is proposed that balances low environmental disturbance, high sampling precision, broad coverage, and statistical data viability to address the limitations of existing methods. This paper utilizes a coupled approach of Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) to explore innovative solutions for precise and continuous hydraulic sampling of deep-sea polymetallic nodules. Focusing on the optimization of the double-row nozzle sampling mechanism design, simulations are conducted to analyze the dynamic characteristics of solid-liquid two-phase flow during the hydraulic sampling process under various nozzle configurations and operational water pressures of the pump. Laboratory experiments with the hydraulic sampling mechanism validate the accuracy of the simulation and the effectiveness of the optimization suggestions. The configuration is finalized with a front nozzle diameter of 10 × φ9 mm, a rear nozzle diameter of 10 × φ7 mm, and an initial working water pressure for the pump of 80 kPa. Subsequently, integrated driving-sampling experiments are conducted using a self-propelled tracked vehicle, validating the feasibility of the proposed configuration.

Characterizing nodule motion in abyssal environments induced by double-row jets: A machine learning approach

Double-row hydraulic collectors are extensively utilized for deep-sea polymetallic nodule harvesting. Understanding the movement behavior of particles within the flow field is crucial for evaluating the efficiency collection system and guiding the design of deep-sea hydraulic collectors. This study first investigates the settling characteristics of particles in various deep-sea environments to assess the effects of high-pressure and low-temperature conditions on particle motion. Subsequently, the motion and force characteristics of particles under different double-row jet parameters were measured and analyzed in the laboratory using high-speed imaging. The results indicate that ambient pressure has a negligible effect on particle motion when the ambient temperature is considered. Particle is mainly lifted in an irregular spiral path by the turbulence of the upper fountain. The lifting height or force of a particle in the vertical direction is positively correlated with the frequency of horizontal fluctuations and inversely related to the average amplitude of these fluctuations. Finally, a neural network was constructed to predict the particle motion characteristics, demonstrating strong generalization and providing a reference for further use of artificial intelligence in extracting physical information of particles from the jet field. This study offers potential benefits for optimizing the design of the double-row jet collectors.

Preliminary Assessment of Environmentally Friendly Mining Options Based on Various Mineral Resources—A Case Study of the Clarion-Clipperton Fracture Zone in Pacific

Deep-sea polymetallic nodules are associated with rich rare substances, such as rare-earth elements (REEs), Mo, Ti, Te, Li, which are currently in demand and are used in various applications. Deep-sea sediments near nodules are another important source of REEs, which will increase the resource potential of polymetallic nodules. Given the similarity of the mining technologies for deep-sea REEs and polymetallic nodules, this study proposed environmentally friendly mining options and developed a technoeconomic evaluation model by combining deep-sea polymetallic nodules and REEs. Using the Clarion-Clipperton Fracture Zone as an example, this study revealed that the development of polymetallic nodules together with REEs of nearby sediments in the form of by-products will improve the economic and environmental benefits. In addition, the effects of discount rate, cost, and price on the economic benefits of nodule mining were discussed, and a technical development direction was proposed based on scientific and technological needs.

A Study on the Optimization of Water Jet Decontamination Performance Parameters Based on the Response Surface Method

The substrate that adheres between the teeth of the traveling track plate during the operation of a deep-sea polymetallic nodule mining vehicle affects the driving performance, so this study aimed to investigate the effect of the water jet on the cleaning and decontamination performance of the track under different conditions. An optimization design method based on response surface methodology (RSM) is proposed. Based on the Box–Behnken design, the optimization variables of jet pressure, jet target distance, and impact angle, and the target response of jet strike pressure on tracks, were selected, and the numerical simulation method was combined with the response surface method to establish the regression model of the response of each optimization variable to the jet strike pressure on tracks and to determine the optimal parameter combinations. The study findings indicate that the primary factor influencing the pressure of the jet striking the crawler is the jet pressure. The hierarchical order of influence on the pressure of the jet striking the crawler, under the interaction of the three factors, is as follows: jet pressure and impact angle, jet pressure and target distance of the jet, and target distance of the jet and impact angle. The maximum pressure of the jet striking the crawler occurs when the jet pressure is 0.983 MPa, the target distance is 0.14 m, and the impact angle is 89.5°. Overall, the proposed design serves as a systematic framework for parameter optimization in the cleaning and decontamination process, and the research method and results provide theoretical references for the optimal design of mining truck desorption efficiency, which is critical for increasing mining efficiency and lowering energy consumption.

An Interpretable Multi-Model Machine Learning Approach for Spatial Mapping of Deep-Sea Polymetallic Nodule Occurrences

AbstractHigh-resolution mapping of deep-sea polymetallic nodules is needed (a) to understand the reasons behind their patchy distribution, (b) to associate nodule coverage with benthic fauna occurrences, and (c) to enable an accurate resource estimation and mining path planning. This study used an autonomous underwater vehicle to map 37 km2 of a geomorphologically complex site in the Eastern Clarion–Clipperton Fracture Zone. A multibeam echosounder system (MBES) at 400 kHz and a side scan sonar at 230 kHz were used to investigate the nodule backscatter response. More than 30,000 seafloor images were analyzed to obtain the nodule coverage and train five machine learning (ML) algorithms: generalized linear models, generalized additive models, support vector machines, random forests (RFs) and neural networks (NNs). All models ML yielded similar maps of nodule coverage with differences occurring in the range of predicted values, particularly at parts with irregular topography. RFs had the best fit and NNs had the worst spatial transferability. Attention was given to the interpretability of model outputs using variable importance ranking across all models, partial dependence plots and domain knowledge. The nodule coverage is higher on relatively flat seafloor ( < 3°) with eastward-facing slopes. The most important predictor was the MBES backscatter, particularly from incident angles between 25 and 55°. Bathymetry, slope, and slope orientation were important geomorphological predictors. For the first time, at a water depth of 4500 m, orthophoto-mosaics and image-derived digital elevation models with 2-mm and 5-mm spatial resolutions supported the geomorphological analysis, interpretation of polymetallic nodules occurrences, and backscatter response.

Metal Release from Manganese Nodules in Anoxic Seawater and Implications for Deep-Sea Mining Dewatering Operations.

The potential mining of deep-sea polymetallic nodules has been gaining increasing attention due to their enrichment in metals essential for a low-carbon future. To date, there have been few scientific studies concerning the geochemical consequences of dewatered mining waste discharge into the pelagic water column, which can inform best practices in future mining operations. Here, we report the results of laboratory incubation experiments that simulate mining discharge into anoxic waters such as those that overlie potential mining sites in the North Pacific Ocean. We find that manganese nodules are reductively dissolved, with an apparent activation energy of 42.8 kJ mol-1, leading to the release of associated metals in the order manganese > nickel > copper > cobalt > cadmium > lead. The composition of trace metals released during the incubation allows us to estimate a likely trace metal budget from the simulated dewatering waste plume. These estimates suggest that released cobalt and copper are the most enriched trace metals within the plume, up to ∼15 times more elevated than the background seawater. High copper concentrations can be toxic to marine organisms. Future work on metal toxicity to mesopelagic communities could help us better understand the ecological effects of these fluxes of trace metals.

Design and multi-body dynamic analysis of inline and offset track configuration in deep-sea mining vehicles for enhanced traction in soft seabed

The deep sea polymetallic nodule mining vehicle maneuverability depends on the vehicle track parameters and track configuration. The traction force offered by the deep sea soil is very limited for the mining vehicle during dynamic operating conditions on the seabed and it is very critical to maneuver against the external resistances. The present study strives to arrive at optimum track parameters for enhancing the traction of the vehicle for the pre-determined seabed conditions. The efficacy of the four tracks in Inline and Offset track configurations on the soft soil has been compared. To improve the traction force estimation, the existing mathematical model was modified with the inclusion of dynamic variation of shear stress-shear displacement characteristics and variation in shear residual displacement concerning the track parameters. The modified mathematical model was solved in a well-established mathematical tool and found that there are 30 percent improvements in the traction force generation for the offset configuration over inline track configuration. The optimum track length to width ratio (L/b) was also estimated for the given contact area to configure the vehicle track for improvement of the traction. Further, a Multi-Body Dynamic (MBD) analysis has been carried out in commercially available soil-machine interaction tool for the inline and offset track configurations with actual measured seabed soil parameters. The MBD analysis proved that the sinkage and vehicle gradient is significantly increased in the inline track configuration due to disturbance created by the front tracks. The simulation results confirm that the offset track configuration is suitable for the deep sea soil conditions for handling the higher payload of a deep sea mining vehicle.

Research Status of Deep-Sea Polymetallic Nodule Collection Technology

The bottom of the ocean is rich in mineral resources, and deep-sea mining has been a research hotspot in recent years. As a key part of deep-sea mining operation, polymetallic nodule collection technology has been researched in many countries around the world. The distribution of deep-sea polymetallic nodule mining areas and the characteristics of nodules are summarized, which provides a reference for the study of collection technology and the optimization of pick-up device structure. In order to further establish a deep-sea mining collection technology system, the current development status of polymetallic nodule mechanical, mechanical–hydraulic composite and hydraulic collection technologies are summarized, and the analysis shows that hydraulic collection technology has a more promising commercialization prospect. For the hydraulic collection technology, the research progress of suck-up-based collection technology, Coandă-effect-based collection technology, double-row hydraulic collection sluicing technology and other collection technologies are summarized from three aspects: collecting principle, device structure parameter optimization, and sea trial situation, and the key technical problems of hydraulic ore collection are put forward. Through the comparative analysis of the pick-up efficiency, energy consumption, environmental disturbance and other performances of different devices, it is found that the Coandă-effect-based hydraulic collection technology has better comprehensive performance. A structural design evaluation indicator for the collection head of hydraulic collection technology is proposed, and the prospect of further research on hydraulic collection technology is put forward.

Experimental investigation of the inhibition of deep-sea mining sediment plumes by polyaluminum chloride

Deep-sea sediment disturbance may occur when collecting polymetallic nodules, resulting in the creation of plumes that could have a negative impact on the ecological environment. This study aims to investigate the potential solution of using polyaluminum chloride (PAC) in the water jet. The effects of PAC are examined through a self-designed simulation system for deep-sea polymetallic nodule collection and sediment samples from a potential deep-sea mining area. The experimental results showed that the optimal PAC dose was found to be 0.75 g/L. Compared with the test conditions without the addition of PAC, the presence of PAC leads to a reduction in volume, lower characteristic turbidity, smaller diffusion velocity, and shorter settling time of the plume. This indicates that PAC inhibits the entire development process of the plume. The addition of PAC leads to the flocculation of mm-sized particles, resulting in the formation of cm-sized flocs. The flocculation of particles decreases the rate of erosion on the seabed by around 30%. This reduction in erosion helps to decrease the formation of plumes. Additionally, when the size of suspended particles increases, it reduces the scale at which they diffuse. Furthermore, the settling velocity of flocs (around 10−2 m/s) is much higher that of compared to sediment particles (around 10−5 m/s), which effectively reduces the amount of time the plume remains in suspension.

Recovery of critical battery metals from cobalt-rich deep-sea polymetallic nodules: Selective carbothermal reduction based on kinetics

Metal recovery from deep-sea polymetallic nodules (DPN) is a promising option to ensure the future supply of critical battery metals due to terrestrial resource constraints. In this study, the leaching efficiency of Mn and critical metals (Co, Ni, and Cu) that hosted in the crystal lattice of Mn(IV) mineral is significantly enhanced by selective carbothermal reduction. The reduction kinetics of Mn(Ⅳ) is consistent with the CO gas diffusion-controlled mechanism, and the kinetic equation can be expressed as 1−23R−1−R23=0.024e−10.06RT∙t. Under the optimal conditions of 600 °C, 60 min, and 3 wt% carbon addition, 61.54 % of Mn(IV) minerals are reduced to Mn(Ⅱ) and the rest was converted to Mn(Ⅲ), while the leachable metal oxides (CoO, NiO, and CuO) are hardly reduced, therefore, the leaching efficiency of Co and Mn increased from 8.18 % and 5.12–98.03 % and 96.23 %, respectively. In order to limit the leaching of the impurities Fe and Al, high-pressure acid leaching was carried out after selective carbothermal reduction, and the leaching parameters were optimized to 160 °C, H2SO4/DPN 0.77 wt%, and leaching for 4 h with a liquid/solid ratio of 5:1 mL/g. As a result, only 2.35 % Fe and 3.34 % Al were leached, and the leaching efficiencies of Co, Ni, Mn and Cu were 98.47 %, 95.72 %, 97.24 % and 94.99 %, respectively.

REE distribution in sequential leached phases from deep-sea polymetallic nodules and sediments

REE distribution in sequential leached phases from deep-sea polymetallic nodules and sediments

Revealing Heavy Metal-Resistant Mechanisms and Bioremediation Potential in a Novel Croceicoccus Species Using Microbial-Induced Carbonate Precipitation

Polymetallic nodules and polymetallic sulfides are currently the major mineral resources found on the seabed. The motivation behind deep-sea mining arises from the pursuit of valuable metals, driven by both economic and geopolitical considerations. However, before mining can be authorized, it is crucial to understand the microbial adaptation and biomineralization process related to heavy metals in deep-sea environments. To search for potential candidate materials for bioremediation in deep-sea environment, two strains with high resistance to manganese and the ability to form rhodochrosite precipitates were isolated from the deep-sea polymetallic nodule areas and hydrothermal polymetallic sulfide areas. Genomic analysis revealed that the strains employed various effective survival strategies, such as motility, chemotaxis, biofilm formation, metal redox, and transporters, to adapt to heavy metal environments. The bacterial strains Ery5 and Ery15 promote the formation of carbonate crystals by creating an excessively alkaline environment and releasing extracellular polymeric substances (EPSs). Furthermore, strains Ery5 and Ery15 were identified using polyphasic taxonomy methods and proposed as a new species belonging to the genus Croceicoccus. This study presents potential candidates for bioremediation in deep-sea environments.

Optimization of Gas–Solid Co-Reduction Conditions for Deep-Sea Polymetallic Nodules

Optimization of Gas–Solid Co-Reduction Conditions for Deep-Sea Polymetallic Nodules

Impact of the Mining Process on the Near-Seabed Environment of a Polymetallic Nodule Area: A Field Simulation Experiment in a Western Pacific Area.

With the consumption of terrestrial metal resources, deep-sea polymetallic nodule minerals have been widely exploited around the world. Therefore, the environmental impact of deep-sea polymetallic nodule mining cannot be ignored. In this study, for the first time, a field disturbance and observation device, integrated with multiple sensors, is used to simulate the disturbance process of mining on seabed sediments in the polymetallic nodule area of the western Pacific Ocean at a depth of 5700 m. The impact of the process of stroking and lifting on the bottom sediment in the polymetallic nodule area is 30 times higher than that caused by the waves or the current. The time for turbidity to return to normal after the increase is about 30 min, and the influence distance of a disturbance to the bottom bed on turbidity is about 126 m. The time it takes for density to return to normal is about four hours, and the influence is about 1000 m. At the same time, the resuspension of the bottom sediment leads to an increase in density anomaly and salinity. Moreover, suspended sediments rich in metal ions may react with dissolved oxygen in water, resulting in a decrease in the dissolved oxygen content and an increase in ORP. During the observation period, the phenomenon of a deep-sea reciprocating current is found, which may cause the suspended sediment generated by the continuous operation of the mining vehicle to produce suspended sediment clouds in the water near the bottom of the mining area. This could lead to the continuous increase in nutrients in the water near the bottom of the mining area and the continuous reduction in dissolved oxygen, which will have a significant impact on the local ecological environment. Therefore, the way mining vehicles dig and wash in water bodies could have a marked impact on the marine environment. We suggest adopting the technology of suction and ore separation on mining ships, as well as bringing the separated sediment back to the land for comprehensive utilization.

A near-zero waste process for the full-component utilization of deep-sea polymetallic nodules based on reductive leaching with SO2 followed by separation and recovery

Recovery of critical metals from marine minerals is a promising option to ensure the sustainable supply of critical metals, but existing recovery processes suffer from technical bottlenecks in terms of low resource utilization and large waste discharge. This paper presents a complete hydrometallurgical route for the full-component utilization of deep-sea polymetallic nodules (DPN). Leaching experiments were first carried out in the presence of SO2 because cheap SO2 can destroy the original mineral structure based on a reductive mechanism. The leaching efficiencies of Ni, Co, Mn, Cu, La, Ce, and Fe were reached 99.2%, 99.3%, 98.7%, 95.9%, 95.3%, 95.4%, and 91.4%, respectively, under the optimal conditions of 30 °C, L/S ratio of 6:1 mL/g, H2SO4 dosage of 37.5 wt%. The downstream process aimed at the sequential recycling of metal ions from the pregnant leach solution (PLS) consists of Fe recovery by the hematite process, selective solvent extraction of Cu and rare earth elements (REEs), co-extraction of Ni/Co/Mn, and Mn electrowinning. As a result, high-grade hematite (60 wt% of Fe), industrial-grade CuSO4, mixed rare earth oxides, battery-grade (Ni, Co, Mn)SO4 solution, and electrolytic manganese were obtained. During the whole process, the recovery efficiency of Ni, Co, Mn, Cu, La, Ce, and Fe reached 97.1%, 97.1%, 96.9%, 91.5%, 91.1%, 91.1%, and 91.3%, respectively. Since the hydrometallurgical process achieves the resource utilization of all the DPN constituents, it has the advantages of near-zero waste and low energy consumption.

Logistical Assessment of Deep-Sea Polymetallic Nodules Transport from an Offshore to an Onshore Location Using a Multiobjective Optimization Approach

The increasing growth in the global population has led to a substantial demand for low-carbon energy infrastructure, metals, and minerals. This has put more pressure on land-based deposits, which have been unsustainably exploited over the years. As a result, attention has shifted towards exploring minerals in sea-based environments. Currently, industry and researchers have identified potentially commercially viable locations for the exploration of these nodules. However, significant knowledge gaps remain in the sustainable, efficient, and effective recovery and transportation of the nodules to onshore locations. To address these gaps, the study develops a logistics and cost model embedded in a multiobjective optimization (MOO) approach. This model considers several parameters, such as the production targets, port distance and location, storage capacity, vessel characteristics, transportation options, and cost inputs. By incorporating these parameters, the study analyzes different combinations of vessel classes and onshore locations and provides insights into optimizing offshore–onshore logistics and transportation options. The findings reveal that small and medium-sized vessels require lower storage capacity because they can complete more trips. Furthermore, the analysis reveals the cost of deploying additional vessels outweighs the benefits of reduced storage space for long-distance transport; therefore, smaller and medium-sized vessels are more suitable for locations closer to the offshore production site. Additionally, proximity to the onshore location is important, as it reduces transport costs and simplifies logistics operations. Subsequently, there is a need to have a reasonable buffer rate as this reduces the impact of potential disruptions during transport. From a managerial viewpoint, the study highlights the need to carefully consider vessel types based on transport requirements and journey characteristics. The analysis further identifies the benefits of having an onshore location close to the offshore production site. This will lead to optimized transport and logistics operations. Based on this, the study contributes to the body of knowledge in offshore logistics by developing a multiobjective optimization model for offshore–onshore transport logistics and cost analysis. This model provides a practical tool for informed decision-making and provides insight into vessel size and location considerations. Finally, the study establishes how simultaneous consideration of multiple factors in transport operations can lead to optimized and informed decision-making.

Discovery and verification of traction weakening effect between multi track shoe of deep-sea miner and sediment

The commercial exploitation of the deep-sea massive deep-sea polymetallic nodules depends on the excellent tractive performance of the deep-sea tracked miner. The walking safety and trafficability of the deep-sea tracked miner are greatly influenced by the traction of the crawler with multi track shoes. The total tractions generated from the two cases of failure surface under the uniformed pressure are deduced and analyzed based on the principle of virtual power. By substituting specified parameters, the traction weakening effect of multi track shoes is discovered, and then corresponding expression is put forward and verified by comparing the tested and theoretical traction relationships based on the traction test of multi track shoes. The research results show that the height and the distance should be considered into the design in a comprehensive way because of the existence of the weakening effect. The mechanism revealing of the source of the multi track shoe tractions could help to achieve the appropriate size of the track shoe and more traction according to the different track shoe distance.

Status and Prospects of the Development of Deep-Sea Polymetallic Nodule-Collecting Technology

The deep-sea is rich in mineral resources, and deep-sea polymetallic nodules are considered to be the most likely resource for commercial exploitation. Since the discovery of polymetallic nodules by mankind, researchers around the world have made long and arduous explorations in the exploitation of deep-sea polymetallic nodules and have proposed various mining methods, such as the dragging bucket type, the continuous bucket rope type, the automatic shuttle boat type, and the pipeline -lifting type, and have carried out technical verification accordingly. In the collection of seabed polymetallic nodules, the development and testing of towed type, spiral-driven type, crawler self-propelled type, and suspended type technologies have been carried out, basically realizing the mining technology verification of seabed polymetallic nodules and providing technical support for commercial development. However, according to the demand for commercial development, there are still many technical difficulties in polymetallic nodule-collecting technology, and more focus needs to be placed on the efficiency, environmental protection, intelligence, safety, and reliability of the collecting system in the future. This paper compares the existing progress in collection technology and equipment, and provides ideas and references for the research and development of deep-sea polymetallic nodule-mining technology and equipment.

Dynamic Traction of Deep-Sea Polymetallic Nodule Collector

The ocean is extremely rich in mineral resources. To cope with the shortage of land mineral resources, countries are focusing on the development of deep-sea mineral mining technology. Owing to its superior traction performance, the deep-sea polymetallic nodule collector (DPNC) has become the preferred solution for ocean mining. This paper proposes a dynamic traction calculation model to address the shortcomings in the classical static traction calculation model with consideration of the dynamic variation rule of grouser–soil interaction in the DPNC process. Lab tests were conducted to formulate materials similar to deep-sea soil, and the corresponding shear stress–displacement models were established using the discrete element method (DEM) and Magic Formula to describe the “shear stress–displacement” relationship more accurately. Considering Kunlong 500, which is a Chinese DPNC, as an example, the periodicity and dynamics of the dynamic traction force were analyzed and compared with the numerical simulation results. The dynamic traction force was smaller than the static traction force and fluctuated significantly when considering the dynamic grousers–soil interaction. The magnitude and fluctuation of the dynamic traction force were influenced by the ratio of the grouser height to the spacing. In the DPNC design, the ratio of the grouser height to the spacing should be optimized according to the properties of the deep-sea subsoil to improve the traction performance and stability of the DPNC.

Development of Hydraulic Lifting System of Deep-Sea Mineral Resources

Lifting coarse mineral particles from thousands of meters of seabed to the supportive vessSel is a crucial part of exploitation of deep-sea mineral resources, and the vertical transportation part is a key component of the deep-sea mining system. Three typical vertical transportation schemes are discussed and compared from the aspects of working mechanism, structural scheme, transportation capacity, system efficiency and implementation feasibility in the context of commercial exploitation of deep-sea polymetallic nodules. The conclusion is that the hydraulic pipeline lifting system with a centrifugal pump is a comprehensive scheme. Furthermore, the basic composition and function of the hydraulic lifting system are introduced, and the transportation performance indicators and technical requirements under commercial mining conditions are analyzed. As the key equipment of the lifting system, the structural characteristics, design theory, transportation performance analysis methods and research progress of the lifting pump are described. A 1000 m sea trial was carried out. The lifting system, the tests of the centrifugal pump and the sea trial are introduced.