Closed-circuit preparation and recovery method of alkaline electrolysis water electrode

Abstract

The invention discloses a closed-loop preparation and recovery method of an alkaline electrolysis water electrode, and belongs to the technical field of electrochemistry. The method comprises the following steps: thermally spraying nickel-aluminum alloy powder on a nickel net substrate to prepare an electrode precursor, and activating with a sodium hydroxide solution to form the porous Raney nickel structure electrode. The method is characterized in that an internal circulation system is constructed, the aluminum-containing waste alkali liquid activated by an electrode and over-spraying alloy powder subjected to thermal spraying are combined for treatment, and aluminum is selectively leached; carbon dioxide is introduced into the aluminum-rich alkali liquor for carbonization decomposition, and a high-purity aluminum hydroxide product is separated out; carrying out causticization reaction on the carbonized sodium carbonate-containing mother liquor by using calcium oxide to regenerate a sodium hydroxide solution and a calcium carbonate byproduct; and finely adjusting the regenerated alkali liquor, returning to electrode production, and treating the nickel-rich solid to obtain regenerated nickel powder. According to the method, electrode production and material circulation are deeply coupled, near-zero emission closed loop of sodium, nickel, aluminum and calcium elements is achieved, and the aluminum resource product value and recycling economy are improved through the process of first carbonization and then causticization.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, and particularly relates to a closed-loop preparation and recovery method for an alkaline water electrolysis electrode. Background Technology

[0002] Alkaline water electrolysis for hydrogen production, as one of the most promising green hydrogen production pathways, has been widely regarded as the mainstream technology for realizing the large-scale commercial application of hydrogen energy. In this technology system, porous Raney nickel electrodes, prepared using nickel-aluminum alloy as the precursor material through thermal spraying and subsequent alkaline activation treatment (i.e., dealloying), have become a key focus of research and industrial application due to their optimal balance between hydrogen production efficiency, material cost, and structural stability.

[0003] However, despite the numerous advantages of this preparation route, two inherent pain points remain in the process that have long been unresolved: First, the alkaline activation stage of the electrode generates a large amount of hazardous waste liquid with complex composition, extremely high alkalinity, and significant aluminum content, mainly composed of sodium aluminate (NaAlO2) and sodium hydroxide (NaOH). This type of waste liquid is highly corrosive and poses a significant environmental hazard, classifying it as strictly controlled hazardous waste. Its safe disposal and compliant treatment require advanced technologies and are extremely costly, imposing a significant environmental and economic burden on actual production.

[0004] Secondly, in the early-stage thermal spraying process, due to the characteristics of the spraying process, approximately 15% to 40% of the total raw material input is generated as waste alloy powder from overspraying. This waste powder not only directly wastes precious metal resources, but also, due to its complex composition, surface oxidation, and impurity contamination, it is difficult to efficiently recycle and reuse using traditional methods, further increasing the overall material cost and environmental impact of the process.

[0005] Currently, industry and academia focus primarily on developing novel electrode materials with superior performance (such as Ni(OH)2-CeOx heterostructure layers prepared by electrodeposition) or improving electrode structures (such as partitioned electrodes based on non-uniform electrodeposition). However, insufficient attention is paid to the waste disposal issues arising during the production process. Existing patents, such as CN118207420B, disclose methods for treating nickel-aluminum slag, but these methods target existing solid waste and involve complex processes that are not integrated with the upstream electrode production process.

[0006] In the field of aluminum resource recycling, the carbonization reaction of sodium aluminate solution to precipitate aluminum hydroxide (i.e., the carbonization method) is a mature and widely used unit operation technology in the alumina industrial production process. Meanwhile, in alkali regeneration, the method of restoring the alkalinity of sodium carbonate solution by causticizing it with calcium oxide (i.e., lime) is a traditional process in industries such as papermaking. However, although these two technologies have a long history of application in their respective industrial scenarios, the innovative system coupling of four key links—electrode preparation, co-processing of waste alkali solution and waste metal powder, preferential extraction of aluminum components based on the carbonization method, and efficient regeneration of alkali solution through causticization—to construct a complete closed-loop circular production system capable of internal material self-consumption and resource self-regeneration, has not yet been reported in existing technologies. This deep integration and system optimization, forming an integrated process solution for efficient resource recycling, is the core technical problem that this invention aims to solve. Summary of the Invention

[0007] This invention overcomes the shortcomings of the prior art by providing a closed-loop preparation and recovery method for alkaline water electrolysis electrodes, thereby solving the problems existing in the prior art.

[0008] To achieve the above objectives, the technical solution adopted by this invention is: a closed-loop preparation and recovery method for an alkaline water electrolysis electrode, comprising the following steps:

[0009] S1. Electrode preparation and activation: Nickel-aluminum alloy powder is coated onto a pretreated nickel mesh substrate using a thermal spraying process. The coating is then activated with sodium hydroxide alkaline solution to obtain a porous electrode and a waste alkaline solution containing sodium aluminate.

[0010] S2. Waste co-processing: Collect the nickel-aluminum alloy powder used in the thermal spraying process, mix it with the waste alkaline solution generated in step S1, and heat it to react, so that the aluminum in the nickel-aluminum alloy powder is converted into sodium aluminate and enters the solution to form a slurry, thereby achieving the enrichment of nickel and the leaching of aluminum.

[0011] S3. Solid-liquid separation: The slurry produced in step S2 is subjected to solid-liquid separation to obtain nickel-rich solid slag and liquid rich in sodium aluminate;

[0012] S4. Carbonization to extract aluminum: Carbon dioxide is introduced into the liquid rich in sodium aluminate obtained in step S3 to carry out carbonization decomposition reaction. The pH value at the end of the reaction is controlled to precipitate aluminum in the form of aluminum hydroxide. Then, solid-liquid separation is performed to obtain aluminum hydroxide product and carbonization mother liquor.

[0013] S5. Causticization and regeneration: Add calcium oxide to the carbonized mother liquor obtained in step S4 to carry out a causticization reaction. After the reaction, the solid and liquid are separated to obtain calcium carbonate precipitate and regenerated sodium hydroxide solution.

[0014] S6. Alkali reuse: Use sodium hydroxide to adjust the regenerated sodium hydroxide solution obtained in step S5 to the concentration required by the process, and obtain the sodium hydroxide alkali solution in step S1;

[0015] S7. Nickel Resource Recovery: The nickel-rich solid slag obtained in step S3 is acid-washed, water-washed, and dried to obtain recycled nickel powder.

[0016] In a preferred embodiment of the present invention, in step S4, the pH value at the end point of the carbonization decomposition reaction by introducing carbon dioxide is controlled between 10.5 and 11.5.

[0017] In a preferred embodiment of the present invention, the aluminum hydroxide product obtained in step S4 is washed and dried or further calcined at 1000-1200°C for 1-3 hours to obtain a high-purity α-alumina product.

[0018] In a preferred embodiment of the present invention, in step S5, the amount of calcium oxide added is 105%-110% of the amount of sodium carbonate in the mother liquor after carbonization required for complete reaction.

[0019] In a preferred embodiment of the present invention, in step S7, a 5%-15% dilute sulfuric acid or dilute hydrochloric acid solution is used in the pickling operation.

[0020] In a preferred embodiment of the present invention, the method further includes step S31, which processes the nickel-rich solid slag obtained in step S3 by using acid to perform a secondary leaching of the nickel-rich solid slag, transferring the residual aluminum into a solution, which can be returned to step S2 or step S4 for aluminum recovery.

[0021] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0022] 1. Achieves closed-loop recycling of all materials, resulting in outstanding environmental benefits: This invention eliminates the problem of hazardous waste alkali and heavy metal waste powder emissions. The main medium (NaOH) and metal elements (Ni, Al) are recycled or productized within the system, meeting the highest standards of green manufacturing and circular economy.

[0023] 2. High value and significant benefits of resource recycling products: "Pre-carbonization" enables aluminum to be recycled in the form of high-purity aluminum hydroxide or aluminum oxide, increasing the revenue from resource recycling. At the same time, it produces calcium carbonate and recycled nickel powder, broadening the profit channels. Internal regeneration of alkali solution reduces the procurement cost of major chemical raw materials.

[0024] 3. Strong process synergy and optimized process: Overspray powder is treated with waste alkaline solution to achieve synergistic treatment of two types of waste, simplify the disposal process, and carbonization and causticization are carried out in steps to make the reaction more thorough and the product purer, avoid impurity interference, and improve the overall process stability and reliability.

[0025] 4. Good technical compatibility and easy implementation: This invention can be integrated with existing thermal spraying electrode production lines without major modifications to the core electrode preparation process, resulting in low resistance to industrialization and promotion. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments;

[0027] Figure 1 A flowchart of a preferred embodiment of the present invention; Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0029] Example 1

[0030] like Figure 1 As shown, this embodiment provides a closed-loop preparation and recovery method for an alkaline water electrolysis electrode, specifically including the following steps:

[0031] S1. Electrode Preparation and Activation: First, using atmospheric plasma spraying equipment, NiAl alloy powder (Ni:Al mass ratio 70:30) with a particle size of 45-75μm was uniformly sprayed onto the surface of a sandblasted activated nickel mesh substrate. By precisely controlling the spraying parameters, a uniform and dense metal coating with a thickness of approximately 150μm was finally formed on the substrate. Subsequently, the resulting coated electrode was immersed in a 30wt% NaOH solution and activated at 85℃ for 5 hours. During this process, the aluminum component was selectively dissolved, thereby forming a well-developed porous structure on and inside the electrode surface, significantly increasing its specific surface area and catalytic activity. After the above treatment, an activated electrode with high porosity was finally obtained, while approximately 1m³ of sodium aluminate-containing waste alkaline solution was generated. 3 The concentration of NaAlO2 is approximately 55 g / L, requiring further processing or resource utilization.

[0032] S2. Waste Co-processing: During this batch of spraying operations, approximately 45 kg of oversprayed alloy powder was collected. To effectively achieve resource recycling and waste reduction, all of this alloy powder was added to the waste alkaline solution reaction system prepared in step S1. Under a constant temperature of 90℃, the reaction was carried out continuously for 6 hours using mechanical stirring to ensure sufficient contact and mass transfer between the solid and liquid phases. After the reaction, analysis showed that over 92% of the aluminum element in the oversprayed powder was effectively leached and transferred to the liquid phase, achieving efficient recovery and separation of the aluminum component.

[0033] S3. Solid-Liquid Separation: A high-efficiency plate and frame filter press is used to perform solid-liquid two-phase separation on the mixed slurry after the reaction. After thorough filtration, a nickel-rich solid filter cake with a moisture content of approximately 35% is obtained, with a total mass of approximately 38 kg. Simultaneously, a clear and transparent sodium aluminate solution is separated, which can be further recycled or subjected to subsequent treatment. The entire separation process achieves efficient separation and recovery of valuable metals.

[0034] S4. Carbonization for Aluminum Extraction: A sodium aluminate solution is pumped into a carbonization reactor and heated to 75°C under stirring, maintaining this temperature. Industrial-grade carbon dioxide gas, with a concentration strictly exceeding 99%, is then continuously introduced into the reactor, with real-time online monitoring using a high-precision pH meter. By precisely controlling the rate and total amount of carbon dioxide introduced, the pH at the reaction endpoint is stabilized at 11.0. Once the target pH is reached, gas flow is immediately stopped, allowing the reaction system to age in a static state for 1 hour to promote precipitate formation and aggregation. After aging, solid-liquid separation is performed to obtain a white aluminum hydroxide filter cake. This filter cake is washed multiple times with deionized water to remove residual soluble impurities and then thoroughly dried in a 110°C oven, ultimately yielding approximately 15 kg of high-purity aluminum hydroxide product with a chemical purity exceeding 99%. The resulting filtrate, primarily composed of sodium carbonate solution, can be further recycled.

[0035] S5. Causticization Regeneration Process: First, the sodium carbonate solution is heated to 90℃, and industrial-grade calcium oxide powder is slowly added under continuous stirring. The amount added is 108% of the theoretically calculated amount to ensure a complete reaction. After the addition is complete, the system is kept at a constant temperature of 90℃ for 2 hours to promote complete causticization. After the reaction, solid-liquid separation is performed by vacuum filtration to obtain calcium carbonate filter cake (dry basis weight approximately 28 kg) and regenerated sodium hydroxide solution. Testing shows that the concentration of the regenerated alkali solution is approximately 25 wt%, which can be directly reused in the production process.

[0036] S6. Alkali Solution Reuse: After the regenerated alkali solution used in the electrode activation process is tested and confirmed to have decreased concentration, an appropriate amount of solid sodium hydroxide is added and thoroughly stirred to completely dissolve it, precisely adjusting the effective concentration of the alkali solution to 30 wt%. After adjustment, a corrosion-resistant pump is used to transport it to the electrode activation tank for subsequent recycling. This step not only achieves efficient resource utilization but also reduces waste liquid discharge, demonstrating the environmental friendliness and economic efficiency of the process.

[0037] S7. Nickel Recovery Processing: The nickel-rich filter cake obtained in step S3 is soaked and washed twice at room temperature using a 10% (w / w) dilute sulfuric acid solution to thoroughly remove impurities. Subsequently, the filter cake is thoroughly rinsed multiple times with deionized water until the pH of the washing solution reaches neutral, ensuring no acidic residue remains. Finally, the washed material is placed in an 80°C constant temperature drying oven to remove excess moisture, ultimately obtaining approximately 32 kg of recycled nickel powder.

[0038] In step S4 of this embodiment, when carbon dioxide is introduced for carbonization decomposition, the pH value at the reaction endpoint needs to be precisely controlled, strictly within the range of 10.5 to 11.5, to ensure the reaction proceeds fully and achieves the expected decomposition effect. In the following step S5, the amount of calcium oxide added needs to be precisely calculated based on the sodium carbonate content in the mother liquor after carbonization. The actual amount added is 105% to 110% of the stoichiometric amount required for complete reaction of sodium carbonate, to ensure thorough reaction with a slight excess, thereby improving reaction efficiency. In step S7, during the acid washing operation, a 5% to 15% dilute sulfuric acid solution or dilute hydrochloric acid solution is selected to effectively remove impurities without affecting product performance. Simultaneously, a portion of the aluminum hydroxide product obtained in step S4 is placed in a muffle furnace for high-temperature treatment, with the temperature increased at a strictly controlled rate of 5°C / minute to 1150°C, and calcined at this temperature for 2 hours, ultimately yielding high-purity α-alumina powder with a yield of approximately 9 kg.

[0039] Example 2

[0040] After step S3 in Example 1, the nickel-rich filter cake is subjected to X-ray diffraction (XRD) analysis. If NiAl is detected... 26 O 40 For spinel phases that are sparingly soluble in alkali, the following steps are adopted:

[0041] The nickel-rich filter cake was transferred to an acid-resistant reactor, and an appropriate amount of 1.5 mol / L sulfuric acid solution was slowly added, maintaining a liquid-to-solid ratio of 5:1 to ensure thorough wetting and mixing. The mixture was then continuously stirred and leached at a constant temperature of 80°C for 4 hours. This process effectively promotes the complete dissolution of the aluminum component in the insoluble phase. After leaching, solid-liquid separation was performed. The resulting aluminum sulfate solution could be incorporated into the material stream of step S2 or S4 in Example 1, depending on actual process requirements, for subsequent efficient aluminum recovery. The solid residue after acid leaching, after thorough washing and drying, yielded a nickel concentrate with significantly improved purity, providing a higher-quality intermediate product for subsequent metal extraction or refining processes.

[0042] In summary, the closed-loop preparation and recovery method for an alkaline water electrolysis electrode of this invention has demonstrated excellent performance and significant advantages in practical applications. From an environmental perspective, this method completely solves the problem of hazardous waste alkaline solution and heavy metal waste powder discharge, enabling the main media and metal elements to be recycled or productized within the system, greatly reducing environmental pollution, highly aligning with the requirements of green manufacturing and the circular economy, and making a positive contribution to sustainable development.

[0043] In terms of resource recycling, its economic benefits are considerable. The "pre-carbonization" process allows aluminum to be recycled in the form of high-purity aluminum hydroxide or aluminum oxide, significantly enhancing the economic value of resource recycling. Simultaneously, the production of products such as calcium carbonate and recycled nickel powder further broadens profit channels. Furthermore, the internal regeneration of alkali solution reduces the procurement costs of key chemical raw materials, achieving highly efficient resource utilization.

[0044] The synergistic effect of the process is also a major highlight of this method. By using waste alkaline solution to treat the oversprayed powder, the synergistic treatment of the two types of waste is achieved, simplifying the disposal process. The carbonization and causticization processes are carried out in separate steps, resulting in a more thorough reaction, a purer product, and avoiding interference from impurities, thus improving the overall stability and reliability of the process.

[0045] Furthermore, this method exhibits excellent technical compatibility, enabling it to interface with existing thermal spraying electrode production lines without requiring significant modifications to the core electrode preparation process. This reduces obstacles to its industrialization and promotion, demonstrating broad application prospects. As society increasingly emphasizes environmental protection and resource recycling, the closed-loop preparation and recycling method for alkaline water electrolysis electrodes of this invention is expected to find widespread application in related fields, driving the industry towards a greener and more efficient direction.

[0046] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A closed-loop preparation and recovery method for an alkaline water electrolysis electrode, characterized in that, Includes the following steps: S1. Electrode preparation and activation: Nickel-aluminum alloy powder is coated on a pretreated nickel mesh substrate using a thermal spraying process, and then the coating is activated with sodium hydroxide alkaline solution to obtain a porous electrode and a waste alkaline solution containing sodium aluminate. S2. Waste co-processing: Collect the nickel-aluminum alloy powder used in the thermal spraying process, mix it with the waste alkaline solution generated in step S1, and heat it to react, so that the aluminum in the nickel-aluminum alloy powder is converted into sodium aluminate and enters the solution to form a slurry, thereby achieving the enrichment of nickel and the leaching of aluminum. S3. Solid-liquid separation: The slurry produced in step S2 is subjected to solid-liquid separation to obtain nickel-rich solid slag and liquid rich in sodium aluminate; S4. Carbonization to extract aluminum: Carbon dioxide is introduced into the liquid rich in sodium aluminate obtained in step S3 to carry out carbonization decomposition reaction. The pH value at the end of the reaction is controlled to precipitate aluminum in the form of aluminum hydroxide. Then, solid-liquid separation is performed to obtain aluminum hydroxide product and carbonization mother liquor. S5. Causticization and regeneration: Add calcium oxide to the carbonized mother liquor obtained in step S4 to carry out a causticization reaction. After the reaction, the solid and liquid are separated to obtain calcium carbonate precipitate and regenerated sodium hydroxide solution. S6. Alkali reuse: Use sodium hydroxide to adjust the regenerated sodium hydroxide solution obtained in step S5 to the concentration required by the process, and obtain the sodium hydroxide alkali solution in step S1; S7. Nickel Resource Recovery: The nickel-rich solid slag obtained in step S3 is acid-washed, water-washed, and dried to obtain recycled nickel powder.

2. The closed-loop preparation and recovery method of an alkaline water electrolysis electrode according to claim 1, characterized in that, In step S4, the final pH value of the carbonization decomposition reaction, which involves introducing carbon dioxide, is controlled between 10.5 and 11.

5.

3. A closed-loop preparation and recovery method for an alkaline water electrolysis electrode according to claim 1 or 2, characterized in that, The aluminum hydroxide product obtained in step S4 is washed and dried or further calcined at 1000-1200℃ for 1-3 hours to obtain a high-purity α-alumina product.

4. The closed-circuit preparation and recovery method of an alkaline water electrolysis electrode according to claim 1, characterized in that, In step S5, the amount of calcium oxide added is 105%-110% of the amount of sodium carbonate in the mother liquor after carbonization required for complete reaction.

5. The closed-loop preparation and recovery method of an alkaline water electrolysis electrode according to claim 1, characterized in that, In step S7, a 5%-15% dilute sulfuric acid or dilute hydrochloric acid solution is used in the pickling operation.

6. The closed-loop preparation and recovery method of an alkaline water electrolysis electrode according to claim 1, characterized in that, It also includes step S31, which processes the nickel-rich solid slag obtained in step S3: the nickel-rich solid slag is leached a second time with acid to transfer the residual aluminum into a solution, which can be returned to step S2 or step S4 for aluminum recovery.

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