Micro-bubble sparging encapsulation method and system for deep sea ore lifting

Abstract

The application belongs to the technical field of deep-sea mineral resources development, and discloses a micro-bubble foaming wrapping method and system for deep-sea ore lifting. The method actively injects air into molten paraffin under high pressure, and uses a high-speed shearing device to shear the air into stable micro-bubbles to form a paraffin micro-bubble slurry with controllable gas volume fraction. Then, the slurry is uniformly coated on the surface of deep-sea ore to construct a low-density composite structure of "ore-micro-bubble-paraffin". By controlling the foaming ratio, micro-bubble particle size distribution, slurry viscosity and coating thickness, the overall density of the obtained composite is reduced to below the density of seawater, so that the net positive buoyancy is obtained, and the natural floating or low-energy auxiliary lifting of the ore in the lifting pipe is realized. The system part comprises a high-pressure molten wax module, a gas injection and shearing foaming module, a mixing and coating module and a pressure compensation and foaming control unit, so as to realize the stable preparation of the micro-bubble slurry and the reliable coating in the deep-sea environment.

Description

Technical Field

[0001] This invention relates to the development of deep-sea mineral resources, and in particular to a microbubble foaming and encapsulation method and system for deep-sea ore hoisting. Background Technology

[0002] Deep-sea polymetallic nodules are mineral resources rich in strategic metals such as nickel, cobalt, copper, and manganese, mainly distributed in seabed sediments at depths of 4,000–6,000 meters. With the rapid development of new energy and energy storage industries, the demand for these metals continues to grow. However, terrestrial mineral resources face challenges such as declining grades, rising mining costs, and environmental constraints, making it difficult to meet long-term demand. Therefore, deep-sea nodules have become an important supplement to future key metal resources.

[0003] Existing methods for lifting deep-sea nodules mainly include hydraulic lifting, pneumatic lifting, and mechanical lifting. Hydraulic lifting uses high-pressure water to transport ore to the surface; this technology is mature, but suffers from high energy consumption, severe equipment wear, and clogging of long-distance risers. Pneumatic lifting relies on gas or bubbles to reduce the weight of the ore and achieve buoyancy; it is feasible in shallow water or experimental conditions, but bubbles are easily compressed or even disappear under high hydrostatic pressure, failing to provide stable buoyancy, and obtaining a gas source is difficult. Mechanical lifting uses chains, ropes, or screw conveyors to lift the ore, enabling closed-loop transport; however, it is limited by mechanical strength, length, and reliability under high pressure, resulting in high long-term operational risks and maintenance costs.

[0004] Chinese invention patent application CN119878172A discloses a deep-sea polymetallic nodule boiling lifting system and lifting method, including a collection platform on the sea surface and a relay station suspended in the sea. The relay station and the collection platform are connected by a pipeline. The pipeline includes several lifting risers. Adjacent lifting risers are connected by boiling heating devices. Each boiling heating device has the same structure. The polymetallic nodule particles mined by the seabed mining vehicle are transported to the relay station via a collection hose. The power supply device then supplies power to the copper wires of each boiling heating device, energizing the copper coils and creating a high-frequency changing internal magnetic field. The metal heating tubes inside the copper coils form a short circuit based on electromagnetic induction, causing the tube walls to heat up and exchange heat with the liquid inside the tubes. This causes the liquid to boil and surge upwards, simultaneously generating upward-moving boiling bubbles. These boiling bubbles then interact with the liquid, further propelling its upward flow. The upward-moving liquid carries the polymetallic nodule particles in the relay station upwards at a certain concentration until they reach the collection platform on the sea surface.

[0005] Regarding the power generation mechanism and energy consumption, CN119878172A attempts to use electromagnetic induction to heat the deep-sea seawater inside the riser tube to make it "boil" and provide gas-phase power. However, according to thermodynamic principles, the hydrostatic pressure in the deep sea (e.g., 4000-5000 meters) is as high as 40-50 MPa. Under this high pressure, the boiling point of water rises sharply (even approaching or exceeding the critical point). To heat the continuously flowing deep-sea seawater with an initial temperature of only about 2°C to the phase transition point, it is necessary to overcome the huge sensible heat rise and latent heat of vaporization, which is obviously difficult and has extremely low thermal efficiency.

[0006] Regarding improving the stability of the flow pattern, the steam bubbles generated by CN119878172A are prone to disappear automatically during the ascent due to the supercooling of the surrounding medium after rising away from the heating area, resulting in insufficient upward momentum.

[0007] Regarding equipment maintenance and pipeline protection, the CN119878172A scheme requires the dense arrangement of multiple boiling heating devices on risers thousands of meters deep. Although the core power supply and frequency converter circuits are located at the sea surface, the copper coils, insulation layers, and high-voltage cable joints distributed underwater constitute a large number of underwater distributed electrical nodes. The high pressure at deep sea (approximately 50 MPa) and complex dynamic loads easily cause insulation damage and seawater infiltration at these nodes, leading to short-circuit faults and making maintenance extremely difficult. Simultaneously, the direct contact between the ore inside the pipeline and the pipe wall causes severe wear.

[0008] Chinese invention patent application CN120159427A discloses a closed-loop lifting system and mining method for deep-sea mining. The system includes a surface support unit comprising a mining vessel, and a mineral-water separation mechanism, a storage tank, and a booster pump located on the mining vessel; a mineral transfer unit located underwater, comprising a storage tank and a confluence chamber located below the storage tank; a return water pipe connecting the outlet of the booster pump to the second inlet of the confluence chamber; and a ore conveying pipe connecting the outlet of the confluence chamber to the inlet of the mineral-water separation mechanism. The booster pump draws liquid from the storage tank and transports it to the confluence chamber via the return water pipe. The liquid mixes with the ore from the storage tank to form a slurry, which then enters the ore conveying pipe and is sent to the mineral-water separation mechanism. The ore-water separation mechanism separates the ore from the slurry to form liquid, which is then discharged to the storage tank. Foam is uniformly mixed into the slurry, and the slurry is lifted using a foam lifting method in the conveying pipe to provide the conveying power. As the lifting fluid in the lifting circuit flows, the slurry containing foam is lifted.

[0009] CN120159427A employs a foam-lift slurry method. Its core power relies on the booster pump of the water surface support unit to provide high-pressure hydraulic energy to overcome the enormous hydrostatic pressure and fluid friction resistance at a depth of several thousand meters. The mixing of foam only plays an auxiliary role in weight reduction, and the system still falls into the category of high-energy-consuming active slurry transport.

[0010] The reliability of CN120159427A is strictly limited by the foam state. In high-pressure, high-speed and turbulent slurry transport fluids, foam units are prone to rupture, coalescence or instability due to high shear forces, resulting in drastic fluctuations in the density and velocity of the boosted fluid, unstable flow patterns, and a high risk of pipeline blockage.

[0011] As a slurry conveying system, CN120159427A states that ore particles in high-speed fluids can cause continuous and severe wear and corrosion to the inner wall of the riser pipe, booster pump, valves, and other equipment, significantly increasing equipment maintenance costs and scrapping frequency.

[0012] In summary, existing hoisting technologies suffer from high energy consumption, poor equipment reliability, significant environmental disturbance, and high economic costs. Achieving safe, low-energy, environmentally friendly, and reliable hoisting of ore in the extreme high-pressure environment of the deep sea remains a technological bottleneck. Therefore, a new hoisting scheme is urgently needed to achieve natural buoyancy or low-energy assisted hoisting of deep-sea ore within the riser, thereby improving system efficiency and reducing energy consumption and environmental impact. Summary of the Invention

[0013] The purpose of this invention is to overcome the shortcomings of the prior art and provide a microbubble foaming and encapsulation method and system for deep-sea ore hoisting. By coating the surface of deep-sea ore with microbubble paraffin wax to form a low-density composite, the ore can obtain net positive buoyancy in the hoisting pipe, achieving low-energy assisted or natural floating, improving system reliability and reducing the impact on the marine environment.

[0014] To achieve the above objectives, the present invention adopts the following technical solution: A microbubble foaming and encapsulation method for deep-sea ore hoisting. (1) Ore pretreatment The collected polymetallic nodules are conveyed into the drying unit via a conveyor device. A closed-loop hot air system maintains the temperature at 50±2℃, and the drying time is controlled within 2–5 minutes, reducing the surface moisture content of the nodules to below 5%. During the drying process, low-temperature seawater or hot air is used for heat exchange, ensuring energy efficiency while drying and smoothing the ore surface, providing good surface conditions for subsequent uniform paraffin adhesion and microbubble coating. The dried ore is then conveyed into the coating unit by a heat-resistant conveyor belt, ensuring a continuous and stable processing flow.

[0015] (2) Heating of melted wax Industrial or food-grade paraffin wax is placed in a molten wax storage tank and heated by electric heating or circulating hot oil to maintain the paraffin wax temperature at a molten state of 60–65°C. This temperature range ensures good fluidity and excellent wettability of the paraffin wax while reducing the risk of volatilization and decomposition. During the heating process, a stirrer is installed inside the storage tank to ensure uniform paraffin wax temperature and prevent localized overheating or cooling that could reduce fluidity. The molten paraffin wax is then transported to the microbubble preparation module through insulated pipes to ensure a continuous process.

[0016] (3) Microbubble preparation Gas is generated using a deep-sea in-situ gas generation module and injected into molten paraffin wax (air or an inert gas, such as nitrogen or a mixture thereof). The injection pressure deviates from the surrounding hydrostatic pressure by no more than ±0.3 MPa to ensure bubble stability under the high-pressure environment of the deep sea. The gas is dispersed into microbubbles with a diameter of 10–300 μm by a high-speed mechanical shearing device and evenly distributed in the paraffin wax slurry to ensure that the composite has net positive buoyancy in seawater. The foamed paraffin wax slurry is kept at a constant temperature before coating to prevent bubble rupture or aggregation.

[0017] The density of the paraffin slurry is precisely controlled by adjusting the bubble volume fraction (10%–30%) and the stirring speed (1000–2000 rpm). This precise control is achieved by constructing a closed-loop density feedback control system for gas-liquid two-phase flow. Specifically, this involves connecting a high-precision online Coriolis mass flow meter (such as the Emerson Micro Motion ELITE series) in series on the outlet pipe of the high-speed mechanical shearing device to monitor the actual density value of the gas-containing paraffin slurry in real time; transmitting this real-time density signal to the central PLC controller for comparison with the preset target density value; and adjusting the opening of the gas mass flow controller (MFC) on the front-end gas injection pipe and the variable frequency motor speed of the shearing device based on the deviation signal using a PID algorithm. When the actual density is higher than the target value, the system automatically increases the gas injection flow rate or increases the shearing speed to increase the bubble volume fraction, and vice versa, ensuring the consistency of the buoyancy unit. (4) Ore coating The dried ore is quantitatively fed into the coating channel, allowing the microbubble paraffin slurry to adhere evenly to the ore surface. Through tumbling, vibration, or roller operation, the ore is ensured to fully contact the paraffin slurry within the channel, forming a uniform coating layer with a thickness controlled at 2–5 mm. This is precisely controlled by adjusting the ore's residence time and the slurry's viscosity. After coating, the ore enters the cooling section, where heat exchange with the surrounding low-temperature seawater causes the paraffin to rapidly solidify, locking in the internal microbubble structure and forming a stable low-density composite of "ore-microbubble-paraffin".

[0018] Utilizing the temperature-sensitive viscosity of paraffin wax, a precision temperature control unit in the molten wax storage tank and conveying pipeline locks the temperature of the paraffin slurry within its optimal rheological range. For example, to increase the thickness of a single wax coating, the control system fine-tunes by lowering the slurry temperature to increase its dynamic viscosity. The rollers or conveying mechanisms within the coating channel are driven by servo motors, and the system adjusts the motor speed according to a preset thickness model. Lowering the speed extends the effective residence time of the ore in the slurry, thereby increasing the coating thickness; conversely, increasing the speed utilizes the centrifugal shearing effect to thin the coating layer. Furthermore, an online laser profile sensor is installed at the coating channel outlet to scan the characteristic dimensions of the coated ore in real time and feeds the data back to the controller to dynamically correct the motor speed, achieving precise closed-loop control of a 2–5 mm thickness.

[0019] (5) Riser lifting The resulting low-density composite material is injected into the riser. Since the composite material's density is 0.7–0.95 g / cm³, lower than seawater's density of 1.03 g / cm³, it will float naturally. During the lifting process, a low-power water flow booster or screw conveyor can be used to overcome fluid resistance and prevent pipe blockage. The riser's diameter and length are optimized based on the composite material's dimensions and the lifting depth, reducing material costs while ensuring lifting stability and continuity.

[0020] (6) Paraffin recovery and recycling Once the composite reaches the water surface, the paraffin wax is softened by a heating device and then separated from the ore using a centrifuge or differential vibrating screen. The separated paraffin wax is then filtered, precipitated, and purified to remove impurities and moisture, before being returned to the molten wax storage tank through an insulated pipeline, achieving a closed-loop recycling process. This process saves material costs, reduces the impact on the marine environment, and achieves efficient resource recycling.

[0021] (7) Optional solutions and parameter optimization To adapt to different operating conditions, the microbubble volume fraction, coating thickness (2–10 mm), microbubble diameter (10–500 μm), drying temperature (45–55 °C), and drying time (2–8 minutes) can be adjusted.

[0022] Microbubble foaming encapsulation systems for deep-sea ore hoisting include: Ore pretreatment module: used to complete the pretreatment of minerals in situ; its lower end is connected to the deep-sea mining vehicle through the mineral transport pipeline, and its upper end is connected to the coating channel module. Wax melting heating module: used to heat paraffin wax and maintain a constant temperature, and connected to the microbubble preparation module; Microbubble preparation module: used to inject air or inert gas into molten paraffin to form microbubbles, and connected to the ore coating channel module; Ore coating channel module: used for contact and uniform coating of ore with microbubble paraffin slurry, and connected to the mineral lifting and flotation channel; Density control unit: connected to the ore coating channel module; achieves the required density of the composite by adjusting the bubble volume fraction and coating layer thickness; The density control unit employs passive feedforward control technology based on linear coupling of mechanical volumetric flow rate. Considering the interference from weighing sensors in the high pressure and fluid environment of the deep sea, this invention does not introduce additional electronic weighing or visual inspection modules. Instead, it directly utilizes the volumetric quantitative feeding device (such as a high-pressure rotary feeder or screw conveyor) that is essential at the inlet of the ore coating channel as the metering core. The specific control method and algorithm are as follows: The core control logic is based on a "speed-flow linear following" model. The system utilizes the mechanical characteristic of the fixed discharge volume per rotation of the volumetric feeder to transform "ore mass flow rate metering" into real-time monitoring of the "feeder motor speed." The embedded calculation formula in the control system is: , , In the formula: Q wax Output command: The mass flow rate that the paraffin slurry injection pump needs to execute; n Input signal: Real-time rotational speed (RPM) of the volumetric feeder; l This is a safety redundancy factor (taken as 0.05–0.1, used to ensure buoyancy surplus). K coupling This is the system coupling constant, which is determined by the following intrinsic parameters: V 0 The theoretical discharge volume of the feeder in one revolution (equipment factory parameters); F This is the ore filling coefficient (an empirical value based on ore particle size statistics). r bul for k Underwater bulk density of ore; r ore The average density of the ore particles; r target The target density of the complex; r slurry This represents the actual density of the paraffin slurry.

[0023] Before operation, the ore physical properties and equipment parameters are substituted into the formula to calculate a fixed coupling constant. K coupling During operation, the controller reads the feeder speed at millisecond-level frequency via Hall effect sensors. n The required paraffin flow rate can be directly calculated linearly. Q wax The controller drives the variable frequency motor of the paraffin injection pump, ensuring that its flow output strictly follows the speed changes of the feeder.

[0024] Mineral lifting and buoyancy channel: The composite is guided into the riser for natural buoyancy or low-energy assisted lifting, and is connected to the mother ship and auxiliary modules at sea; Paraffin wax recovery module: Separates, purifies, and recycles paraffin wax, reducing material consumption.

[0025] The high-speed mechanical shearing device in this invention can be selected from the IKA DRS 2000 series or the Silverson UHS (Ultra Hygienic Shear) series. These products are equipped with a high-pressure resistant double-end mechanical seal and a pressure balancing system to ensure the shaft's sealing performance under deep-sea hydrostatic pressure. These high-speed mechanical shearing devices are existing equipment and are commercially available; therefore, further details are omitted.

[0026] Compared to Chinese patent application CN119878172A, this invention uses "microbubble-paraffin encapsulation" technology, which only requires heating the encapsulation medium (paraffin) to a molten state of 60-65℃ to achieve foaming and encapsulation. There is no need to heat the seawater used as the transport medium in the pipeline. After the paraffin solidifies, it relies on the Archimedes' principle of buoyancy to achieve natural floating or low-energy assisted floating of the ore. This completely avoids the huge energy consumption trap of heating seawater to boiling under high pressure, and realizes truly low-energy mining.

[0027] Compared to Chinese patent application CN119878172A, this invention rapidly solidifies paraffin wax on the ore surface through heat exchange, "locking" microbubbles inside the solid paraffin wax layer to form a stable low-density composite (density 0.7-0.95 g / cm³). Regardless of external pressure fluctuations, as long as the ambient temperature is below the melting point of paraffin wax, the buoyancy units (microbubbles) will not rupture, escape, or condense and disappear, ensuring a constant and predictable net positive buoyancy throughout the lifting process. The system reliability is significantly superior to that of boiling-type lifting.

[0028] Compared to Chinese patent application CN119878172A, the riser pipe structure of this invention is relatively simple, and the paraffin coating layer on the surface of the ore naturally has excellent self-lubricating properties, effectively isolating the hard ore from direct friction with the pipe wall, greatly extending the service life of the riser pipe, and achieving environmentally friendly green operation through the closed-loop recycling of paraffin.

[0029] This invention differs fundamentally from CN120159427A in its dynamic principle. This invention reduces the equivalent density of the ore composite to below that of seawater by coating the ore surface with paraffin containing microbubbles, thus giving the ore net positive buoyancy. This innovation represents a fundamental shift in power source from high-energy-consuming hydraulic thrust to low-energy-consuming static buoyancy, requiring only low-power auxiliary devices to achieve natural buoyancy, offering advantages in energy efficiency.

[0030] Compared to Chinese patent application CN120159427A, the microbubbles of this invention are physically locked to the ore surface by a rapidly solidifying paraffin layer, forming a stable low-density composite with constant buoyancy and density, unaffected by the external hydrodynamic environment. This passive floating mode ensures stable flow and controllable density during the lifting process, completely eliminating the risks caused by foam instability, and exhibiting extremely high system reliability and predictability.

[0031] Compared to Chinese patent application CN120159427A, the paraffin coating layer of this invention acts as an excellent lubricant and buffer during the lifting process, effectively isolating the hard ore from direct contact and friction with the inner wall of the riser pipe, significantly reducing the wear rate of the pipeline and extending the service life of the entire system. Furthermore, this invention also incorporates a paraffin recovery and closed-loop circulation module, achieving efficient separation, purification, and reuse of paraffin materials, demonstrating higher material resource utilization and environmental friendliness while improving efficiency.

[0032] This invention addresses existing problems in deep-sea ore hoisting technology by coating the surface of deep-sea ore with microbubbles of paraffin wax, forming a low-density composite that enables the ore to achieve net positive buoyancy in the riser. The microbubble paraffin wax coating significantly reduces the equivalent density of the ore, enabling low-energy assisted or natural ascent, improving system reliability, and reducing the impact on the marine environment. This invention achieves low-energy, reliable, and environmentally friendly ore hoisting in the high hydrostatic pressure environment of the deep sea; it also improves hoisting efficiency, reduces equipment wear and maintenance costs, minimizes the impact on the marine ecosystem, and provides a feasible technical approach for the commercial mining of deep-sea polymetallic nodules. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the system of the present invention; Figure 2This is a schematic diagram of the overall structure of the present invention; Among them, 1-deep-sea mining vehicle, 2-mineral transport pipeline, 3-ore pretreatment module, 4-wax melting heating module, 5-microbubble preparation module, 6-coating channel module, 7-density control unit, 8-mineral lifting and floating channel, and 9-marine mother ship and auxiliary modules. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] The structures, proportions, and sizes illustrated in the accompanying drawings are merely for illustrative purposes and to aid those skilled in the art in understanding and reading the invention. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, provided they do not affect the effectiveness or purpose of the invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention's implementation.

[0036] Example 1: A microbubble foaming and encapsulation method for deep-sea ore lifting, the standard operating procedure is as follows: (1) Ore pretreatment Polymetallic nodules collected from the seabed are transported via a deep-sea mining vehicle 1 and a mineral transport pipeline 2 to the drying unit of the mineral pretreatment module 4. The drying unit employs a closed-loop hot air system, with the temperature controlled at 50±2℃ and a drying time of 3 minutes, reducing the surface moisture content of the ore to below 5%. During the drying process, heat exchange is conducted using low-temperature seawater or hot air to ensure a dry and smooth ore surface, providing favorable conditions for paraffin adhesion and uniform distribution of microbubbles. The dried ore is then conveyed to the coating unit via a heat-resistant conveyor belt, ensuring continuous processing.

[0037] (2) Heating of melted wax Industrial-grade paraffin wax is placed in the molten wax storage tank of the molten wax heating module 4, and heated by electric heating or circulating hot oil to maintain the paraffin wax temperature at a molten state of 62°C. This temperature range ensures good fluidity and excellent wettability of the paraffin wax, while reducing the risk of volatilization and decomposition. During the heating process, a stirrer is installed in the storage tank to ensure uniform temperature and avoid local overheating or cooling that could lead to a decrease in fluidity. The molten paraffin wax is transported to the microbubble preparation module 5 through insulated pipes to ensure a continuous supply.

[0038] (3) Microbubble preparation and injection Gas, such as air, nitrogen, or a mixture thereof, is injected into molten paraffin wax. The injection pressure deviates from the surrounding hydrostatic pressure by no more than ±0.3 MPa to ensure bubble stability under the high pressure environment of the deep sea. A high-speed shearing device (rotor speed 1000–2000 rpm, rotor linear speed 10–35 m / s) disperses the gas into microbubbles with a diameter of approximately 50 μm. The viscosity of the molten paraffin wax is 0.02–0.2 Pa·s, ensuring that the coefficient of variation of the microbubble size distribution is no greater than 0.35 and that the microbubble is uniformly distributed in the paraffin slurry. By adjusting the bubble volume fraction (10%–30%) and stirring speed, the slurry density is controlled to achieve net positive buoyancy of the composite in seawater. The foamed paraffin slurry is kept at a constant temperature before coating to prevent bubble collapse or aggregation.

[0039] The deep-sea in-situ gas generation module is a seawater electrolysis device that produces hydrogen, oxygen, or a mixture thereof from seawater electrolysis.

[0040] The density of the paraffin slurry is precisely controlled by adjusting the bubble volume fraction (10%–30%) and the stirring speed (1000–2000 rpm). This precise control is achieved by constructing a closed-loop density feedback control system for gas-liquid two-phase flow. Specifically, this involves connecting a high-precision online Coriolis mass flow meter (such as the Emerson Micro Motion ELITE series) in series on the outlet pipe of the high-speed mechanical shearing device to monitor the actual density value of the gas-containing paraffin slurry in real time; transmitting this real-time density signal to the central PLC controller for comparison with the preset target density value; and adjusting the opening of the gas mass flow controller (MFC) on the front-end gas injection pipe and the variable frequency motor speed of the shearing device based on the deviation signal using a PID algorithm. When the actual density is higher than the target value, the system automatically increases the gas injection flow rate or increases the shearing speed to increase the bubble volume fraction, and vice versa, ensuring the consistency of the buoyancy unit.

[0041] The high-speed mechanical shearing device in this invention can be selected from the IKA DRS 2000 series or the Silverson UHS (Ultra Hygienic Shear) series. These products are equipped with a high-pressure resistant double-end mechanical seal and a pressure balancing system to ensure the shaft's sealing performance under deep-sea hydrostatic pressure. These high-speed mechanical shearing devices are existing equipment and are commercially available; therefore, further details are omitted.

[0042] (4) Ore coating The dried ore is quantitatively fed into coating channel module 6, which is equipped with rollers and tumbling devices to ensure full contact and tumbling of the ore in the microbubble paraffin slurry. The coating layer thickness is controlled at 3 mm, and uniform adhesion can be achieved by adjusting the ore's residence time in the channel and the slurry viscosity. After coating, the ore enters the cooling section, where it exchanges heat with low-temperature seawater, causing the paraffin to solidify rapidly, locking in the internal microbubble structure, and forming an "ore-microbubble-paraffin" composite with a density of approximately 0.85 g / cm³. The volume of the microbubbles expands as the external pressure decreases, increasing the buoyancy of the composite by 10%–80%.

[0043] Utilizing the temperature-sensitive viscosity of paraffin wax, a precision temperature control unit in the wax storage tank and conveying pipeline locks the temperature of the paraffin slurry within its optimal rheological range. For example, to increase the thickness of a single wax coating, the control system fine-tunes by lowering the slurry temperature to increase its dynamic viscosity. The rollers or conveying mechanisms within the coating channel are driven by servo motors, and the system adjusts the motor speed according to a preset thickness model. Lowering the speed extends the effective residence time of the ore in the slurry, thereby increasing the coating thickness; conversely, increasing the speed utilizes the centrifugal shearing effect to thin the coating layer. Furthermore, an online laser profile sensor is installed at the coating channel outlet to scan the characteristic dimensions of the coated ore in real time and feeds the data back to the controller to dynamically correct the motor speed, achieving precise closed-loop control of a 2–5 mm thickness.

[0044] (5) Riser lifting The resulting low-density composite material is injected into the riser of the mineral lifting and buoyancy channel 8. The composite material has a density lower than seawater (approximately 1.03 g / cm³), allowing it to naturally float to the mother ship and auxiliary module 9. To prevent pipe blockage, a low-power water flow booster (power < 5 kW) or a screw conveyor can be used. The riser diameter is 0.3–0.5 m, and the length is designed according to the operating water depth (approximately 4300 m) to ensure stable flow velocity and buoyancy while reducing material costs.

[0045] (6) Paraffin wax recycling and reuse After the composite reaches the water surface, it enters a heating and softening device, where the paraffin wax is heated to a temperature above 60°C and softened. Subsequently, it is separated from the ore using a centrifugal separator or differential vibrating screen. The separated paraffin wax is filtered and purified by sedimentation to remove impurities and moisture, and then returned to the molten wax storage tank through insulated pipes, achieving a closed-loop recycling system. The separated ore is sent to the cargo hold for storage, ready to be transported ashore for smelting.

[0046] Example 2: Parameter optimization scheme: The drying temperature can be adjusted within the range of 45–55℃, and the drying time is 2–8 minutes to adapt to ores with different moisture contents; The thickness of the paraffin coating can be adjusted from 2 to 10 mm, and the diameter of the microbubbles can be adjusted within the range of 10 to 500 μm; The volume fraction of microbubbles can be adjusted from 10% to 30%, and the coating thickness is 5% to 25% of the equivalent diameter of the ore, achieving a composite density of 0.7 to 0.95 g / cm³. The gas can be selected from air, nitrogen or helium, alone or in combination, with an injection pressure deviation within ±0.3 MPa to ensure the stability of microbubbles; the temperature control module maintains the paraffin temperature 5–20 ℃ above its melting point, and the pressure compensation chamber counteracts the effect of seawater hydrostatic pressure on the solidification of molten paraffin.

[0047] The riser diameter, auxiliary lifting power, and cooling rate can be optimized according to the size of the composite and the floating depth. Example 3:

[0048] The microbubble foaming and encapsulation system for deep-sea ore hoisting includes the following modules: Ore pretreatment module 3: used to complete the pretreatment of minerals in situ; its lower end is connected to the deep-sea mining vehicle through the mineral transport pipeline, and its upper end is connected to the coating channel module 6; Wax melting heating module 4: used to heat paraffin wax and maintain a constant temperature, ensuring that the paraffin wax melts at a constant temperature and has good fluidity; connected to microbubble preparation module 5; Microbubble preparation module 5 (including in-situ gas generation, isobaric gas injection and high-speed shear foaming): used to inject air or inert gas into molten paraffin to form microbubbles; form a uniform microbubble slurry and control the density; connected to ore coating channel module 6; Coating channel module 6: used for contact and uniform coating of ore and microbubble paraffin slurry; to achieve uniform coating of ore and microbubble slurry; connected to mineral lifting and flotation channel 7; the coating channel module includes spiral flow channel or venturi channel to increase the contact area between ore and microbubble paraffin slurry.

[0049] Density control unit 7: precisely controls the density of the composite by adjusting the bubble ratio and coating thickness; connected to ore coating channel module 6; The density control unit 7 employs a passive feedforward control technology based on linear coupling of mechanical volumetric flow rate. Considering the interference from weighing sensors in the high pressure and fluid environment of the deep sea, this invention does not introduce additional electronic weighing or visual inspection modules. Instead, it directly utilizes the volumetric quantitative feeding device (such as a high-pressure rotary feeder or screw conveyor) that is essential at the inlet of the ore coating channel as the metering core. The specific control method and algorithm are as follows: The core control logic is based on a "speed-flow linear following" model. The system utilizes the mechanical characteristic of the fixed discharge volume per rotation of the volumetric feeder to transform "ore mass flow rate metering" into real-time monitoring of the "feeder motor speed." The embedded calculation formula in the control system is: , , In the formula: Q wax Output command: The mass flow rate that the paraffin slurry injection pump needs to execute; n Input signal: Real-time rotational speed (RPM) of the volumetric feeder; l This is a safety redundancy factor (taken as 0.05–0.1, used to ensure buoyancy surplus). K coupling This is the system coupling constant, which is determined by the following intrinsic parameters: V 0 The theoretical discharge volume of the feeder in one revolution (equipment factory parameters); F This is the ore filling coefficient (an empirical value based on ore particle size statistics). r bul for k Underwater bulk density of ore; r ore The average density of the ore particles; r target The target density of the complex; r slurry This represents the actual density of the paraffin slurry.

[0050] Before operation, the ore physical properties and equipment parameters are substituted into the formula to calculate a fixed coupling constant. K coupling During operation, the controller reads the feeder speed at millisecond-level frequency via Hall effect sensors. n The required paraffin flow rate can be directly calculated linearly. Q wax The controller drives the variable frequency motor of the paraffin injection pump, ensuring that its flow output strictly follows the speed changes of the feeder.

[0051] Pressure and temperature control module: monitors and regulates the pressure and temperature parameters of the system to ensure stable floating of the composite. Auxiliary module: Mineral lifting and buoyancy channel 8, which guides the composite into the riser for natural buoyancy or low-energy assisted lifting, and is connected to the sea mother ship and auxiliary module 9.

[0052] The paraffin wax recovery module separates, purifies, and recycles paraffin wax, achieving low-energy flotation and recycling.

[0053] This invention addresses existing problems in deep-sea ore hoisting technology by coating the surface of deep-sea ore with microbubbles of paraffin wax, forming a low-density composite that enables the ore to achieve net positive buoyancy in the riser. The microbubble paraffin wax coating significantly reduces the equivalent density of the ore, enabling low-energy assisted or natural ascent, improving system reliability, and reducing the impact on the marine environment. This invention achieves low-energy, reliable, and environmentally friendly ore hoisting in the high hydrostatic pressure environment of the deep sea; it also improves hoisting efficiency, reduces equipment wear and maintenance costs, minimizes the impact on the marine ecosystem, and provides a feasible technical approach for the commercial mining of deep-sea polymetallic nodules.

[0054] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A microbubble foaming and encapsulation method for deep-sea ore hoisting, characterized in that, Includes the following steps: (1) Ore pretreatment: The collected polymetallic nodules are sent to the drying unit through a conveying device for drying. The dried ore is then sent to the coating unit by a heat-resistant conveyor belt to ensure a continuous and stable processing flow. (2) Heating the wax: Under the hydrostatic pressure environment of the deep sea, solid paraffin is heated to a molten state to obtain molten paraffin; the molten paraffin is transported to the microbubble preparation module through an insulated pipe to ensure a continuous process; (3) Microbubble preparation: Gas is generated by deep-sea in-situ gas generation module and injected into molten paraffin under conditions of equal or near equal pressure with external hydrostatic pressure. The gas is then dispersed into microbubbles with a diameter of 10–300 μm by a high-speed mechanical shearing device to obtain microbubble paraffin slurry. (4) Ore coating: The microbubble paraffin slurry is uniformly coated on the surface of the ore to form a stable "ore-microbubble-paraffin" low-density composite, ensuring that the low-density composite has net positive buoyancy in seawater. (5) Risers are lifted by injecting the low-density composite material into the riser and achieving natural buoyancy or low-energy assisted lifting to the mother ship and auxiliary modules at sea.

2. The microbubble foaming and encapsulation method for deep-sea ore hoisting as described in claim 1, characterized in that, In step (1), the drying process uses a closed-loop hot air system to maintain a temperature of 48-52°C and a drying time of 2-5 minutes to reduce the surface moisture content of the nodules to below 5%.

3. The microbubble foaming and encapsulation method for deep-sea ore hoisting as described in claim 1, characterized in that, In step (2), industrial or food-grade paraffin wax is placed in a melting wax storage tank and heated by electric heating or circulating hot oil to maintain the temperature of the paraffin wax at 60–65°C in a molten state. During the heating process, a stirrer is installed in the storage tank to ensure that the temperature of the paraffin wax is uniform and to avoid local overheating or cooling that would cause a decrease in fluidity.

4. The microbubble foaming and encapsulation method for deep-sea ore hoisting as described in claim 1, characterized in that, In step (3), the gas injection pressure deviates from the surrounding hydrostatic pressure by no more than ±0.3 MPa to ensure the stability of the bubbles under the high pressure environment of the deep sea.

5. The microbubble foaming and encapsulation method for deep-sea ore hoisting as described in claim 1, characterized in that, In step (3), the microbubble paraffin slurry is kept at a constant temperature before coating to prevent bubbles from breaking or aggregating.

6. The microbubble foaming and encapsulation method for deep-sea ore hoisting as described in claim 1, characterized in that, In step (3), the density of the microbubble paraffin slurry is precisely controlled by adjusting the bubble volume fraction and stirring speed. The precise control of the microbubble paraffin slurry density is achieved by constructing a gas-liquid two-phase flow closed-loop density feedback control system, which specifically includes: connecting a high-precision online Coriolis mass flow meter in series on the outlet pipeline of the high-speed mechanical shearing device to monitor the actual density value of the gas-containing paraffin slurry in real time; transmitting the real-time density signal to the central PLC controller for comparison with the preset target density value; adjusting the opening of the gas mass flow controller on the front gas injection pipeline and the speed of the variable frequency motor of the shearing device according to the deviation signal through the PID algorithm; when the actual density is higher than the target value, the system automatically increases the gas injection flow or increases the shearing speed to increase the bubble volume fraction, and vice versa, to ensure the consistency of the buoyancy unit.

7. The microbubble foaming and encapsulation method for deep-sea ore hoisting as described in claim 1, characterized in that, In step (4), the ore is brought into full contact with the paraffin slurry in the channel by tumbling, vibration or roller method, and is evenly distributed in the paraffin slurry to form a uniform coating layer with a thickness controlled at 2-5 mm. The ore residence time and slurry viscosity are precisely controlled by adjusting the ore residence time. After the coating is completed, the ore enters the cooling section and the paraffin is rapidly solidified by heat exchange with the surrounding low-temperature seawater, locking the internal microbubble structure and forming a stable "ore-microbubble-paraffin" low-density composite.

8. The microbubble foaming and encapsulation method for deep-sea ore hoisting as described in claim 1, characterized in that, In step (4), the density of the low-density composite is 0.7–0.95 g / cm³.

9. The microbubble foaming and encapsulation method for deep-sea ore hoisting as described in claim 1, characterized in that, It also includes paraffin recovery and recycling. After the low-density composite reaches the water surface, the paraffin is softened by a heating device and separated from the ore by a centrifugal separator or differential vibrating screen. The separated paraffin is filtered, precipitated, and purified to remove impurities and moisture, and then returned to the molten wax storage tank through an insulated pipeline to achieve closed-loop recycling.

10. A microbubble foaming and encapsulation system for deep-sea ore hoisting, characterized in that it comprises: Ore pretreatment module: used to complete the pretreatment of minerals in situ; its lower end is connected to the deep-sea mining vehicle through the mineral transport pipeline, and its upper end is connected to the coating channel module; Wax melting heating module: used to heat paraffin wax and maintain a constant temperature, and connected to the microbubble preparation module; Microbubble preparation module: used to inject air or inert gas into molten paraffin to form microbubbles, and connected to the ore coating channel module; Ore coating channel module: used for contact and uniform coating of ore with microbubble paraffin slurry, and connected to the mineral lifting and flotation channel; Density control unit: connected to the ore coating channel module; achieves the required density of the composite by adjusting the bubble volume fraction and coating layer thickness; The density control unit employs a passive feedforward control technology based on linear coupling of mechanical volume and flow rate. The specific control method and algorithm are as follows: The core control logic is based on a "speed-flow linear following" model, utilizing the mechanical characteristic of a fixed discharge volume per rotation of the volumetric feeder to transform "ore mass flow rate measurement" into real-time monitoring of the "feeder motor speed." The embedded calculation formula in the control system is: ， ， In the formula: Q wax Output command: The mass flow rate that the paraffin slurry injection pump needs to execute; n Input signal: Real-time rotational speed of the volumetric feeder; λ This is the safety redundancy factor; K coupling Here is the system coupling constant; V 0 This represents the theoretical discharge volume per revolution of the feeder; Ф This is the ore filling coefficient; ρ bulk The underwater bulk density of the ore; ρ ore The average density of the ore particles; ρ target The target density of the complex; ρ slurry This refers to the actual density of the paraffin slurry; Mineral lifting and buoyancy channel: The composite is guided into the riser for natural buoyancy or low-energy assisted lifting, and is connected to the mother ship and auxiliary modules at sea; Paraffin wax recovery module: Separates, purifies, and recycles paraffin wax, reducing material consumption.

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