Method for recovering metals from deep-sea polymetallic nodule by high-temperature hydrogen plasma reduction

Abstract

The application discloses a method for recovering metals from deep-sea polymetallic nodule by high-temperature hydrogen plasma reduction, and comprises the following steps: dehydrating and drying the deep-sea polymetallic nodule collected from the seabed, and then adjusting the binary alkalinity of the deep-sea polymetallic nodule to 0.15-0.20, wherein the binary alkalinity is expressed as the mass ratio of CaO to SiO2; smelting the deep-sea polymetallic nodule by using a hydrogen plasma arc furnace; pouring out the melt after the smelting is completed; separating the smelting slag and the smelting alloy; and collecting the nickel-copper-cobalt-iron smelting alloy and the manganese-rich slag. Finally, the high-value alloy and the manganese-rich slag are obtained in one step through the separation of the slag and the metal alloy.

Description

Technical Field

[0001] This invention belongs to the field of deep-sea mineral smelting, processing and utilization technology, and in particular relates to a method for recovering metals from polymetallic oxide ores by reducing them with hydrogen plasma. Background Technology

[0002] The deep sea is rich in mineral resources, especially deep-sea polymetallic nodules and cobalt-rich crusts. Statistics predict that deep-sea polymetallic nodules have reserves of 3 trillion tons, of which 75 billion tons have commercial development potential. Cobalt-rich crusts have reserves of 35.1 billion tons, with manganese, cobalt, nickel, and copper content several times or even tens of times that of terrestrial deposits. Furthermore, the number of oceanic polymetallic nodules is increasing at a rate of 10-15 million tons per year. Deep-sea polymetallic oxides contain enormous mineral resources and have the potential to replace terrestrial resources such as manganese, cobalt, and nickel.

[0003] Both polymetallic nodules and cobalt-rich crusts in the ocean are microcrystalline and closely associated with various components, making it difficult to separate valuable metals using conventional beneficiation methods. Therefore, direct smelting is typically employed to extract valuable metals. Currently, metallurgical extraction methods for polymetallic nodules and cobalt-rich crusts in the ocean can be mainly divided into two types: pyrometallurgical-hydrometallurgical and hydrometallurgical-hydrometallurgical. Pyrometallurgical-hydrometallurgical methods involve pretreatment by roasting or smelting followed by leaching to extract valuable elements. Hydrometallurgical-hydrometallurgical methods primarily involve pressurized / atmospheric pressure leaching in acidic or ammoniacal media under the action of a reducing agent, as well as bioleaching. Typical processes include smelting-leaching, cuprous ion ammonia leaching, hydrochloric acid leaching, and high-temperature, high-pressure sulfuric acid leaching. Pyrometallurgical smelting can yield high-grade CoNiCu alloys, significantly reducing the amount of subsequent hydrometallurgical processing. However, traditional smelting processes typically use carbon as a reducing agent, inevitably generating large amounts of carbon dioxide, resulting in high carbon emissions. Furthermore, the smelting process is usually energy-intensive and time-consuming.

[0004] Chinese patent application CN102358919A discloses a method for extracting valuable metals from seabed metal ores, using hydrogen as a reducing agent. While this avoids carbon emissions, the leaching process of the reduced material after low-temperature hydrogen reduction consumes a large amount of acid, making manganese recovery uneconomical. Although the all-wet process avoids carbon emissions, it requires the addition of leaching reagents equal to 25%–150% of the ore content, resulting in high reagent costs, complex separation processes, and long process flows. Therefore, there is an urgent need to develop a low-carbon, green, short-process, and highly efficient method for extracting valuable metals from deep-sea polymetallic oxide ores. Summary of the Invention

[0005] To overcome the problems in the prior art, the present invention provides a method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction, thereby achieving efficient and clean extraction of valuable metals such as nickel, copper, cobalt and iron from deep-sea polymetallic oxide ores.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] This invention provides a method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction, comprising the following steps:

[0008] S1. Dehydrate and dry the deep-sea polymetallic oxide ore collected from the seabed;

[0009] S2. Adjust the binary basicity of the deep-sea polymetallic oxide ore obtained in S1 to 0.15-0.20, and then smelt it using a hydrogen plasma arc furnace. The binary basicity is expressed as the mass ratio of CaO to SiO2.

[0010] S3. After smelting, pour out the melt, separate the smelting slag and smelting alloy, and collect the nickel-copper-cobalt-iron smelting alloy and manganese-rich slag.

[0011] This invention utilizes the ultra-high temperature and highly active hydrogen atoms in a hydrogen plasma arc furnace to achieve selective reduction of deep-sea polymetallic oxide ores in the molten state. By precisely controlling the binary basicity of the deep-sea polymetallic oxide ores within a slightly acidic range of 0.15–0.20, nickel, cobalt, copper, and iron oxides are efficiently reduced to metals and aggregated into alloy phases in the molten state. Simultaneously, the slightly acidic slag containing silica and alumina obtained after molten reduction fixes manganese into stable manganese silicate (MnSiO3), inhibiting its reduction and solidifying it to enrich it in the slag. Finally, through the separation of the slag and the metal alloy, high-value alloys and manganese-rich slag are obtained in one step.

[0012] In this invention, the binary basicity of deep-sea polymetallic oxide ores is controlled within the range of 0.15 to 0.20, primarily to achieve selective reduction, allowing manganese to enter the slag and nickel, cobalt, and copper to enter the alloy. Below this basicity, the slag may become viscous, preventing the generated molten metal droplets from settling effectively, resulting in poor slag-metal separation. Above this basicity, the alkaline slag corrodes the acidic furnace lining, manganese enters the alloy, reducing the nickel and cobalt grades, and may still cause poor slag shape and poor slag-metal separation.

[0013] As an optional implementation, in the method provided by the present invention, in step S2, a slag-forming agent is added to adjust the binary basicity of the deep-sea polymetallic oxide ore to 0.15-0.20.

[0014] As an optional implementation, in the method provided by the present invention, the slag-forming agent is selected from one or more combinations of silicon dioxide, calcium oxide, calcium fluoride, aluminum oxide, etc.

[0015] In this invention, the binary basicity is the total calcium / silicon ratio in oxide form. Calcium fluoride can increase the total calcium content, and correspondingly increase the calcium content in terms of calcium oxide. Another function of calcium fluoride is to adjust the slag viscosity, and fluoride salts can increase the slag fluidity. Alumina can be used to adjust the quaternary basicity R4=(CaO+MgO) / (SiO2+Al2O3), and is also a commonly used additive for slag conditioning, which can increase the acidity of the slag.

[0016] As an optional implementation, in the method provided by the present invention, in step S2, the hydrogen content in the hydrogen plasma arc furnace is 10-100 vol%. Preferably, the hydrogen content is 20 vol.

[0017] In this invention, a plasma environment is provided by filling the electric arc melting furnace with hydrogen gas or hydrogen gas containing an inert gas. The core of plasma hydrogen reduction is the ionization of hydrogen gas to produce active hydrogen atoms (H) and hydrogen ions. Industrially, an inert gas, such as argon, is generally used. This serves three purposes: first, to stabilize the electric arc; second, to reduce costs; and third, to control the reduction potential.

[0018] As an optional implementation, in the method provided by the present invention, in step S2, the hydrogen plasma arc furnace is obtained by igniting an arc of 100 to 500 A between the electrode and the input material, with a discharge time of 0.5 to 15 min.

[0019] As an optional implementation, in the method provided by the present invention, the temperature of the high-temperature arc zone in the hydrogen plasma arc furnace is greater than 1500°C.

[0020] In this invention, the current range of 100-500A can generate a high-temperature environment sufficient to instantly melt deep-sea ore (temperature exceeding 1500℃), providing the necessary thermodynamic conditions for the reduction reaction of metal oxides. If the current is too low, complete melting of the material cannot be achieved, or the melting rate is extremely slow, resulting in poor slag-metal separation; if the current is too high, excessive energy input leads to a surge in energy consumption, equipment wear and tear, and increased production costs.

[0021] Furthermore, 100A is preferred, and the discharge time for each discharge is preferably 3 minutes.

[0022] As an optional implementation, in the method provided by the present invention, the deep-sea polymetallic oxide ore is selected from one or a combination of two of deep-sea polymetallic nodules or deep-sea cobalt-rich crusts.

[0023] As an optional implementation, in the method provided by the present invention, in step S3, after the melt is poured out, it is allowed to slowly cool and separate into layers.

[0024] As an optional implementation, in the method provided by the present invention, in step S2, the fumes generated during the smelting process are collected to obtain manganese-containing fumes.

[0025] As an optional implementation, in the method provided by the present invention, in step S1, dehydration refers to dehydrating the deck after collection from the seabed and transporting it to land for air drying or sun drying; drying refers to drying at 100°C.

[0026] As an optional implementation, in the method provided by the present invention, in step S3, the mass fraction of iron in the smelting alloy is >69wt%, the mass fraction of cobalt is >2.8wt%, the mass fraction of nickel is >12wt%, the mass fraction of copper is >9.7wt%, the mass fraction of manganese is <7wt%, and the mass fraction of manganese in the manganese-rich slag is >27wt%.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) In order to collect manganese separately from deep-sea polymetallic oxide ores, this invention first adjusts the binary basicity of the deep-sea polymetallic oxide ores to 0.15-0.20, and then uses a hydrogen plasma arc furnace for smelting. The hydrogen plasma energy is highly concentrated and can generate ultra-high temperature instantaneously. The heating rate is fast and the temperature is high, which greatly accelerates the reduction reaction rate of the ore, improves the energy utilization efficiency and reaction efficiency, and enables nickel, cobalt, copper and iron oxides to be efficiently reduced to metals and aggregated into alloy phases to obtain nickel-copper-cobalt-iron smelting alloys. At the same time, manganese is enriched in the slag in the form of manganese oxide. Finally, through the separation of slag and metal alloy, high-value alloys and manganese-rich slag are obtained in one step. The manganese-rich slag can be used to smelt ferrosilicon or manganese-iron alloys.

[0029] (2) This invention uses hydrogen as both energy and reducing agent, and the reaction tail gas is only water vapor, fundamentally eliminating carbon dioxide emissions from traditional carbothermal reduction processes and achieving zero carbon emissions in the smelting process. Reduction and smelting are completed in one step, eliminating multiple steps such as roasting and carbon reduction in traditional methods. The entire process does not involve carbon combustion or acid leaching reagents, avoiding the generation of pollutants such as sulfur dioxide, nitrogen oxides, and acidic wastewater, significantly reducing secondary pollution to the environment. Short-range recovery is achieved.

[0030] (3) In this invention, hydrogen plasma arc furnace is used for smelting. Compared with some traditional hydrogen utilization methods, plasma hydrogen is used as a reaction medium, which effectively avoids safety risks such as hydrogen embrittlement and improves the reliability of the process. Moreover, hydrogen plasma has extremely strong reducing properties and can efficiently reduce metal oxides. The resulting alloy has high purity, which is beneficial for subsequent processing and purification. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a technical roadmap for the present invention. Detailed Implementation

[0033] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0034] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0036] Example 1

[0037] A method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction, the process flow is as follows: Figure 1 As shown, it includes the following steps:

[0038] (1) The deep-sea polymetallic nodules collected from the seabed were dehydrated on the deck, transported to land for further drying, and dried at 100℃ for 12 hours until constant weight. The composition of the dried deep-sea polymetallic nodules is listed in Table 1. The results showed that the natural binary alkalinity (mass ratio of CaO to SiO2) of the deep-sea polymetallic nodules was 0.14, and the binary alkalinity was adjusted to 0.15 by adding CaO.

[0039] (2) Take 50g of dried deep-sea polymetallic nodules and place them in a hydrogen plasma arc furnace. First, introduce 0.04MPa of high-purity argon gas and 100A of current to melt the polymetallic nodules. Then, the hydrogen plasma arc furnace provides a plasma environment through an arc melting furnace filled with a mixture of argon and hydrogen gas. The hydrogen gas accounts for 20 vol%. The hydrogen plasma environment is obtained by igniting a 100A arc between the electrode and the input material. The temperature of the high-temperature arc zone is greater than 1500℃. Each discharge lasts for 3 minutes. Repeat this process three times until all the manganese nodules are melted.

[0040] (3) After smelting, the metal was naturally cooled. After slag-metal separation, 29.2g of smelting slag and 4.7g of smelting alloy were obtained. The composition of the smelting alloy and smelting slag is listed in Tables 2 and 3, respectively. The recovery rates of copper, cobalt, and nickel in the alloy were 97.53%, 97.80%, and 97.73%, respectively, and the recovery rate of manganese in the slag was 77.07%. The recovery rate of manganese in the alloy was 1.86%, and another 21.07% of manganese volatilized into the flue dust, which can be collected and recovered.

[0041] Table 1. Composition of deep-sea polymetallic nodules, wt%

[0042]

[0043] Table 2. Main components of the smelted alloy, wt%

[0044]

[0045] Table 3. Main components of smelting slag, wt%

[0046]

[0047] Example 2

[0048] A method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction, the process flow is as follows: Figure 1 As shown, it includes the following steps:

[0049] (1) Take 50g of dried deep-sea polymetallic nodules (composition as shown in Table 1) and place them in a hydrogen plasma arc furnace. First, introduce 0.04MPa of high-purity argon gas and 100A of current to melt the polymetallic nodules. Then, introduce a mixture of 50% vol argon gas and 50% vol hydrogen gas at a total pressure of 0.08MPa. The hydrogen plasma environment is obtained by igniting a 500A arc between the electrode and the input material, so that the temperature of the high-temperature arc zone is greater than 1500℃. Perform hydrogen plasma reduction melting, each treatment lasting 3 minutes, and repeat three times until all the manganese nodules are melted.

[0050] (2) After smelting, the metal was naturally cooled. After slag-metal separation, 26.6g of smelting slag and 4.1g of smelting alloy were obtained. The composition of the smelting alloy and smelting slag is listed in Tables 4 and 5, respectively. The recovery rates of copper, cobalt, and nickel into the alloy were 97.20%, 99.43%, and 97.86%, respectively, and the recovery rate of manganese into the slag was 64.13%. The recovery rate of manganese into the alloy was 2.20%, and another 33.67% of manganese volatilized into the flue dust, which can be collected and recovered.

[0051] Table 4. Main components of the smelted alloy, wt%

[0052]

[0053] Table 5. Main components of smelting slag, wt%

[0054]

[0055] Example 3

[0056] A method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction, the process flow is as follows: Figure 1 As shown, it includes the following steps:

[0057] (1) The composition of deep-sea cobalt-rich crust after drying is listed in Table 6. The results show that the natural binary basicity of deep-sea cobalt-rich crust is 0.44, which is higher than the smelting basicity requirement. Silica powder was added to adjust the basicity (mass ratio of CaO to SiO2) to 0.20. That is, 50g of deep-sea cobalt-rich crust was taken, 2.97g of silica powder (containing 95% SiO2) was added, and after mixing, material A was obtained.

[0058] (2) Place material A in a hydrogen plasma arc furnace, first introduce 0.04 MPa high-purity argon gas and 300 A current to melt the cobalt-rich shell. Then introduce 50 vo 1% argon gas and 50 vo 1% hydrogen gas, with a total mixed gas pressure of 0.08 MPa. The hydrogen plasma environment is obtained by igniting a 100 A arc between the electrode and the input material, so that the temperature of the high-temperature arc zone is greater than 1500 °C, and hydrogen plasma reduction melting is performed. Each treatment lasts 3 minutes, and is repeated three times until the cobalt-rich shell is completely melted.

[0059] (3) After smelting, the metal was naturally cooled. After slag-metal separation, 26.4g of smelting slag and 8.5g of smelting alloy were obtained. The composition of the smelting alloy and smelting slag is listed in Tables 7 and 8, respectively. The recovery rates of copper, cobalt, and nickel in the alloy were 98.60%, 93.05%, and 96.33%, respectively, and the recovery rate of manganese in the slag was 73.74%. The recovery rate of manganese in the alloy was 2.23%, and another 24.03% of manganese volatilized into the flue dust, which can be collected and recovered.

[0060] Table 6. Composition of cobalt-rich crusts in deep seas, wt%

[0061]

[0062] Table 7. Main components of the smelted alloy, wt%

[0063]

[0064] Table 8. Main components of smelting slag, wt%

[0065]

[0066] Comparative Example 1

[0067] The difference from Example 1 is that the deep-sea polymetallic nodules were smelted using hydrogen reduction instead of hydrogen plasma reduction. The reaction conditions were as follows: 50g of dried deep-sea polymetallic nodules were placed in a tube furnace and hydrogen was introduced. Argon was introduced through an alumina tube to purge air, followed by hydrogen to purge argon. The hydrogen flow rate was 200mL / min. When the temperature reached 1350-1500℃, it was held at that temperature for different times. The results are listed in Tables 9 and 10.

[0068] Table 9. Main components of alloys melted at different times, wt%

[0069]

[0070] Table 10. Main components of smelting slag at different times, wt%

[0071]

[0072] The results showed that, under direct hydrogen reduction, the recovery rates of copper, cobalt, and nickel in the alloy were only 36.64%, 21.39%, and 34.47%, respectively, within the same time period (10 min). Manganese was almost not reduced to metal, and it mainly accumulated in the slag as manganese silicate. With increasing time, the recovery rate of valuable metals increased. When the reaction time was 120 min, the recovery rates of copper, cobalt, and nickel in the alloy were 86.14%, 90.48%, and 92.39%, respectively, while the manganese alloying rate was less than 1%. Compared with hydrogen plasma reduction, direct hydrogen reduction smelting resulted in a slower reduction rate and lower recovery rate of valuable metals.

[0073] Comparative Example 2

[0074] The difference from Example 1 is that the deep-sea polymetallic nodules were smelted using traditional coke reduction in the same electric arc furnace, without the introduction of hydrogen or argon. 50g of dried deep-sea polymetallic nodules were mixed with 3g of coke and placed in the electric arc furnace for reaction. The current was set to 100A, and the smelting temperature was controlled at approximately 1400℃. Different holding times were recorded, and the results are shown in Tables 11 and 12.

[0075] Table 11 Main components of alloys melted at different times, wt%

[0076]

[0077] Table 12 Main components of smelting slag at different times, wt%

[0078]

[0079] The results showed that, in the same time period (10 min), the recovery rates of copper, cobalt, and nickel in the alloy during carbothermal reduction smelting were only 33.31%, 18.81%, and 28.69%, respectively. As the time increased to 60 min, the recovery rates of copper, cobalt, nickel, and manganese in the alloy increased to 88.51%, 93.83%, 95.31%, and 2.47%, respectively. Compared with hydrogen plasma reduction, carbothermal reduction smelting resulted in a slower reduction rate of valuable metals, lower reduction recovery rates, and the generation of a large amount of CO2 gas, increasing carbon emissions.

[0080] Comparative Example 3

[0081] The difference from Example 3 is that silica powder was added to adjust the alkalinity to 0.10. After smelting, the metal was naturally cooled, resulting in poor slag-metal separation. The slag was viscous and contained many small metal particles. The alloy particles could only be separated by crushing and magnetic separation. After magnetic separation, only 0.79g of alloy and 30.23g of smelting slag were collected. The results are listed in Tables 13 and 14, respectively.

[0082] Table 13 Main components of smelted alloys, wt%

[0083]

[0084] Table 14 Main components of smelting slag, wt%

[0085]

[0086] The results showed that the recovery rates of copper, cobalt, and nickel in the alloy were 42.30%, 27.60%, and 33.00%, respectively, while the recovery rate of manganese was only 0.2%. Most of the manganese was enriched in the slag, with a small amount lost through volatilization. Excessively low alkalinity caused the slag to become viscous, preventing the formation of an effective slag pattern and resulting in poor slag-metal separation and a low metallization rate.

[0087] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction, characterized in that, Includes the following steps: S1. Dehydrate and dry the deep-sea polymetallic oxide ore collected from the seabed; S2. Adjust the binary basicity of the deep-sea polymetallic oxide ore obtained in S1 to 0.15-0.20, and then smelt it using a hydrogen plasma arc furnace. The binary basicity is expressed as the mass ratio of CaO to SiO2. The hydrogen plasma arc furnace is obtained by igniting an arc of 100-500A between the electrode and the input material, with each discharge lasting 0.5-15 minutes. S3. After smelting, pour out the melt, separate the smelting slag and smelting alloy, and collect the nickel-copper-cobalt-iron smelting alloy and manganese-rich slag.

2. The method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction according to claim 1, characterized in that, In step S2, a slag-forming agent is added to adjust the binary basicity of the deep-sea polymetallic oxide ore to 0.15–0.

20.

3. The method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction according to claim 2, characterized in that, The slag-forming agent is selected from one or a combination of several of silicon dioxide, calcium oxide, calcium fluoride, and aluminum oxide.

4. The method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction according to claim 1, characterized in that, In step S2, the hydrogen content in the hydrogen plasma arc furnace is 10-100 vol.

5. The method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction according to claim 1, characterized in that, The temperature of the high-temperature arc zone in the hydrogen plasma arc furnace is greater than 1500℃.

6. The method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction according to claim 1, characterized in that, Deep-sea polymetallic oxide minerals are selected from one or a combination of two of deep-sea polymetallic nodules or deep-sea cobalt-rich crusts.

7. The method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction according to any one of claims 1 to 6, characterized in that, In step S3, the melt is poured out and then allowed to cool and separate into layers. In step S2, the fumes generated during the smelting process are collected to obtain manganese-containing fumes.

8. The method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction according to claim 1, characterized in that, In step S1, dehydration refers to dehydrating the seabed sample on the deck and then transporting it to land for air drying or sun drying; drying refers to drying at 100°C.

9. The method for recovering metals from deep-sea polymetallic oxide ores by high-temperature hydrogen plasma reduction according to claim 1, characterized in that, In step S3, the mass fraction of iron in the smelted alloy is >69wt%, the mass fraction of cobalt is >2.8wt%, the mass fraction of nickel is >12wt%, the mass fraction of copper is >9.7wt%, the mass fraction of manganese is <7wt%, and the mass fraction of manganese in the manganese-rich slag is >27wt%.

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