NiFe-LDH regenerated based on catalytic decomplexing of alpha-nickel hydroxide and preparation method and application of NiFe-LDH

Abstract

The invention belongs to the technical field of nickel resource regeneration treatment, and particularly relates to NiFe-LDH regenerated based on alpha-nickel hydroxide catalytic decomplexing and a preparation method and application thereof. An alpha-Ni (OH) 2 catalyst is added into the waste liquid containing EDTA-Ni, sodium hypochlorite is added for oxidation, an EDTA structure is broken through oxidation of sodium hypochlorite, Ni is released from a complexing state, and new nickel hydroxide is formed in catalytic circulation. And then NiFe-LDH is constructed in a co-precipitation mode of acid dissolution and alkali precipitation, and high-value utilization of nickel and iron elements in the waste liquid is achieved. A lithium polysulfide catalysis experiment and a lithium-sulfur battery 2C rate cycle test prove that the prepared NiFe-LDH obviously promotes conversion of lithium polysulfide, and the positive electrode reaction kinetics and the battery cycle stability are improved. According to the method, efficient recovery and valuable utilization of nickel resources in the waste liquid are achieved, waste nickel is converted into the high-performance lithium-sulfur battery positive electrode catalyst, and economic and environmental benefits are both achieved.

Description

Technical Field

[0001] This invention belongs to the technical field of nickel resource recycling, specifically relating to a method for regenerating NiFe-LDH based on α-nickel hydroxide catalytic decomposition and its preparation and application. Background Technology

[0002] EDTA-Ni complexes are commonly found in decommissioned chemical water treatment systems in industrial applications, with stability constants as high as 10. 20 Conventional precipitation methods struggle to recover Ni, leading to resource waste and increased heavy metal emissions. Current EDTA complex treatment methods primarily include: direct complex disruption with strong oxidants (such as ozone and persulfate), high-temperature incineration or advanced oxidation methods, ion exchange, or membrane separation. However, these methods suffer from high energy consumption, high cost, poor reducibility, or secondary pollution. On the other hand, NiFe-LDH, due to its excellent polysulfide adsorption and catalytic conversion capabilities, has become an important novel catalyst in lithium-sulfur battery research. However, the preparation of NiFe-LDH typically relies on chemically pure nickel and iron salts, resulting in high costs and a lack of integration with solid waste resource utilization. Existing technologies lack a green pathway for "complex disruption-recovery-conversion" of Ni resources in EDTA-Ni wastewater into high-performance battery materials. Summary of the Invention

[0003] To address the aforementioned problems, the present invention aims to provide a method and application for the preparation of NiFe-LDH based on α-nickel hydroxide catalytic decomposition and regeneration.

[0004] The technical content of this invention is as follows: This invention provides a method for preparing NiFe-LDH based on α-nickel hydroxide catalytic decomplexing regeneration, comprising the following steps: 1) Oxidative decomposition of EDTA-Ni complex α-Nickel hydroxide was added as a catalyst to waste liquid containing EDTA-Ni complex, followed by the addition of sodium hypochlorite. An oxidation reaction was carried out under alkaline conditions, causing the EDTA skeleton to undergo ring-opening and breakage, releasing Ni. 2+ And new nickel hydroxide precipitate is generated in situ during the catalytic cycle; The amount of α-nickel hydroxide used accounts for 1-20% of the molar amount of Ni in the EDTA-Ni complex; The concentration of sodium hypochlorite is 0.05~1 mol / L; The oxidation reaction is carried out at a temperature of 20-60 °C and a pH of 8-12. 2) Separation of nickel and iron by acid dissolution The precipitate obtained in step 1) was dissolved in hydrochloric acid, and Fe was introduced. 3+ Ni-containing 2+ with Fe 3+ Chloride solution; The concentration of the hydrochloric acid is 0.1-2 mol / L, and the dissolution time is 5-60 min; Ni in chloride solution 2+ with Fe 3+ The molar ratio is (2~4):1; 3) Co-precipitation preparation of NiFe-LDH precursor Add an alkaline mixture of NaOH and Na2CO3 solution dropwise to the solution obtained in step 2) to maintain the pH of the system at 7.5-10, forming a NiFe-LDH hydrotalcite precursor precipitate; The concentration of the NaOH solution is 0.5-3 mol / L; The concentration of the Na₂CO₃ solution is 0.05-0.5 mol / L; 4) Aging and Collection The precipitate was aged at 60-120 °C for 2-24 h, and then washed and dried to obtain NiFe-LDH solid powder. The aging temperature is preferably 80~100℃, and the time is 6~12h.

[0005] The present invention also provides a NiFe-LDH material obtained by the above method, wherein the NiFe-LDH has a typical layered hydrotalcite structure, with a layer thickness of 5~30 nm, a layer diameter of 50~300 nm, and contains a small number of surface carboxyl / hydroxyl defect sites induced by EDTA oxidation residues.

[0006] This invention also provides the application of the above-mentioned NiFe-LDH material in the preparation of battery electrode materials; The battery electrode material includes lithium battery cathode material; The NiFe-LDH material is used as an electrode catalyst to adsorb / catalyze the conversion of polysulfide anions, thereby improving the conversion kinetics, capacity retention, and rate performance of lithium polysulfide cathodes in lithium-sulfur batteries.

[0007] The beneficial effects of this invention are as follows: The present invention relates to a method for preparing NiFe-LDH based on α-nickel hydroxide catalytic decomposition and regeneration. In this method, EDTA-Ni-containing waste liquid is added to an α-Ni(OH)₂ catalyst followed by sodium hypochlorite (NaClO) for oxidation. Under alkaline conditions, the EDTA complex is broken down, releasing Ni. 2+ Simultaneously, a new Ni(OH)₂ precipitate is formed in the system; the obtained precipitate is dissolved in hydrochloric acid to obtain Ni-containing... 2+ / Fe 3+A mixed salt solution was prepared; then, NiFe-LDH precursor was synthesized via NaOH / Na2CO3 co-precipitation, and finally aged, washed, and dried to obtain NiFe-LDH powder. The EDTA structure was oxidized and broken using sodium hypochlorite to release Ni from the complexed state, forming nascent nickel hydroxide in the catalytic cycle. Subsequently, NiFe-LDH was constructed via acid dissolution and alkali precipitation co-precipitation, achieving high-value utilization of nickel and iron elements in the waste liquid and converting the nickel obtained from complexation into NiFe-LDH as a resource. The morphology and crystal phase changes of Ni(OH)2 before and after the reaction, as well as the structure and morphology of the final NiFe-LDH, were analyzed by SEM and XRD comparison. Nickel ion concentration monitoring showed that Ni resources in the waste liquid were effectively recovered. Catalytic experiments on lithium polysulfides and 2C rate cycling tests of lithium-sulfur batteries demonstrated that the prepared NiFe-LDH significantly promoted the conversion of lithium polysulfides, improved the cathode reaction kinetics, and enhanced battery cycle stability. This invention enables the efficient recovery and value utilization of nickel resources in waste liquid, transforming waste nickel into a high-performance lithium-sulfur battery cathode catalyst, thus achieving both economic and environmental benefits. Attached Figure Description

[0008] Figure 1 Comparison of SEM morphology of α-Ni(OH)2 and regenerated Ni(OH)2 (before / after sedimentation); Figure 2 The XRD patterns of α-Ni(OH)2 (original catalyst) and regenerated Ni(OH)2 after reaction are compared. Figure 3 SEM image of NiFe-LDH; Figure 4 The XRD pattern (characteristic peaks of layered hydrotalcite structure) of NiFe-LDH prepared by the method of this invention is shown. Figure 5 In the example, Ni was recovered from the waste liquid before and after the process. 2+ Concentration changes (such as ICP-OES assay results) are used to calculate the recovery rate; Figure 6 The diagram shows the catalytic performance of NiFe-LDH on lithium polysulfides. Figure 7 The curves show the cycle performance (discharge capacity vs. number of cycles) of the NiFe-LDH based composite cathode in a lithium-sulfur battery (2C condition). Detailed Implementation

[0009] The present invention will be further described in detail below through specific implementation examples and accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope of the appended claims.

[0010] Unless otherwise specified, all raw materials and reagents used in this invention are from the conventional market.

[0011] Example 1 A method for recycling waste nickel and preparing NiFe-LDH-based composite cathodes To 1 L EDTA-Ni waste liquid (Ni 2+ With an initial concentration of approximately 300 mg / L and a molar ratio of EDTA to Ni of approximately 1:1, 1 g of α-Ni(OH)₂ was added, and the pH was adjusted to approximately 11. The mixture was stirred for 10 min to ensure thorough and uniform dispersion of α-Ni(OH)₂. Subsequently, 100 mL of 0.7 mol / L NaClO solution was slowly added dropwise over 8 min, maintaining the reaction temperature at 45℃ and pH at 11, and stirring continuously for 80 min to promote the cleavage of the EDTA-Ni complex and the release of Ni. 2+ The reaction is released and induced to precipitate Ni(OH)₂. After standing for 10 min, a clear precipitate is visible. The precipitate is separated by centrifugation, and the supernatant is discarded. The precipitate is washed three times with deionized water to remove residual salts / organic impurities. The washed wet precipitate is then vacuum dried at 60℃ for 6 h to obtain dry Ni(OH)₂ powder. The dry powder is added to 1 mol / L HCl to obtain a greenish-yellow NiCl₂ / FeCl₃ mixed solution, which allows the acid-soluble Ni to be obtained. 2+ with Fe 3+ A mixed alkali of 2 mol / L NaOH and 0.2 mol / L Na₂CO₃ was slowly added dropwise to a chloride solution at a molar ratio of 3:1 (total metal concentration 0.4 mol / L), while maintaining pH=9, to form a precipitate. After addition, the solution was stirred for 8 min, then transferred to a sealed container and aged at 90℃ for 10 h. Following this, the solution was washed five times with deionized water and dried at 75℃ for 8 h to obtain flake-like NiFe-LDH powder.

[0012] Example 2 A method for recycling waste nickel and preparing NiFe-LDH-based composite cathodes To 1 L EDTA-Ni waste liquid (Ni 2+ With an initial concentration of approximately 400 mg / L and a molar ratio of EDTA to Ni of approximately 1:1, 1 g of α-Ni(OH)₂ was added, and the pH was adjusted to approximately 12. The mixture was stirred for 10 min to ensure thorough and uniform dispersion of α-Ni(OH)₂. Subsequently, 100 mL of 1 mol / L NaClO solution was slowly added dropwise over a period of 10 min, maintaining the reaction temperature at 60 ℃ and pH at 12. Stirring was continued for 90 min to promote the cleavage of the EDTA-Ni complex and the release of Ni. 2+The reaction is released and induced to precipitate Ni(OH)₂. After standing for 10 min, a clear precipitate is visible. The precipitate is separated by centrifugation or vacuum filtration, and the supernatant is discarded. The precipitate is washed three times with deionized water to remove residual salts / organic impurities. The washed wet precipitate is then vacuum dried at 60℃ for 6 h to obtain dry Ni(OH)₂ powder. The dry powder is added to 1 mol / L HCl to obtain a greenish-yellow NiCl₂ / FeCl₃ mixed solution, which allows the acid-soluble Ni to be obtained. 2+ with Fe 3+ A mixture of 3 mol / L NaOH and 0.5 mol / L Na₂CO₃ alkali was slowly added dropwise to a chloride solution at a molar ratio of 4:1 (total metal concentration 0.5 mol / L), while maintaining pH=10, resulting in precipitate formation. After addition, the solution was stirred for 10 min, then transferred to a sealed container and aged at 90℃ for 12 h. Following this, the solution was washed five times with deionized water and dried at 80℃ for 6 h to obtain flake-like NiFe-LDH powder.

[0013] Example 3 A method for recycling waste nickel and preparing NiFe-LDH-based composite cathodes To 1 L EDTA-Ni waste liquid (Ni 2+ With an initial concentration of approximately 200 mg / L and a molar ratio of EDTA to Ni of approximately 1:1, 1 g of α-Ni(OH)₂ was added, and the pH was adjusted to approximately 10. The mixture was stirred for 10 min to ensure uniform catalyst dispersion. Then, 100 mL of 0.3 mol / L NaClO was slowly added dropwise over 7 min, maintaining the reaction temperature at 35 ℃ and pH at 10. Stirring was continued for 60 min to promote the cleavage of the EDTA-Ni complex and the formation of Ni... 2+ The reaction is released and induced to precipitate Ni(OH)₂. After standing for 10 min, a clear precipitate is visible. The precipitate is separated by centrifugation or vacuum filtration, and the supernatant is discarded. The precipitate is washed three times with deionized water to remove residual salts / organic impurities. The washed wet precipitate is then vacuum dried at 60℃ for 6 h to obtain dry Ni(OH)₂ powder. The dry powder is added to 1 mol / L HCl to obtain a greenish-yellow NiCl₂ / FeCl₃ mixed solution, which allows the acid-soluble Ni to be obtained. 2+ with Fe 3+ A mixed alkali of 1.5 mol / L NaOH and 0.1 mol / L Na₂CO₃ was slowly added dropwise to a chloride solution at a molar ratio of 1.5:1 (total metal concentration 0.3 mol / L), while maintaining the pH at 8.5, resulting in precipitation. After addition, the solution was stirred for 7 min, then transferred to a sealed container and aged at 90 °C for 9 h. Following this, the solution was washed four times with deionized water and dried at 70 °C for 9 h to obtain flake-like NiFe-LDH powder.

[0014] Example 4 A method for recycling waste nickel and preparing NiFe-LDH-based composite cathodes To 1 L EDTA-Ni waste liquid (Ni 2+ With an initial concentration of approximately 100 mg / L and a molar ratio of EDTA to Ni of approximately 1:1, 0.5 g of α-Ni(OH)₂ was added, and the pH was adjusted to approximately 8. The mixture was stirred for 10 min to ensure thorough and uniform dispersion of α-Ni(OH)₂. Subsequently, 100 mL of 0.05 mol / L NaClO solution was slowly added dropwise over a period of 5 min, maintaining the reaction temperature at 20 ℃ and pH at 8. The mixture was stirred continuously for 30 min to promote the cleavage of the EDTA-Ni complex and the release of Ni. 2+ The reaction is released and induced to precipitate Ni(OH)₂. After standing for 10 min, a clear precipitate is visible. The precipitate is separated by centrifugation or vacuum filtration, and the supernatant is discarded. The precipitate is washed three times with deionized water to remove residual salts / organic impurities. The washed wet precipitate is then vacuum dried at 60℃ for 6 h to obtain dry Ni(OH)₂ powder. The dry powder is added to 1 mol / L HCl to obtain a greenish-yellow NiCl₂ / FeCl₃ mixed solution, which allows the acid-soluble Ni to be obtained. 2+ with Fe 3+ A mixed alkali of 0.5 mol / L NaOH and 0.05 mol / L Na₂CO₃ was slowly added dropwise to a chloride solution at a molar ratio of 1:1 (total metal concentration 0.5 mol / L), while maintaining the pH at 7.5, resulting in precipitation. After addition, the solution was stirred for 5 min, then transferred to a sealed container and aged at 90 °C for 12 h. The solution was then washed five times with deionized water and dried at 80 °C for 6 h to obtain flake-like NiFe-LDH powder.

[0015] The dry powders Ni(OH)2 and NiFe-LDH powder prepared above were subjected to the following tests: 1. Structural / morphological characterization SEM analysis was performed on the dried Ni(OH)2 powder, as shown below. Figure 1 As shown, a uniform lamellar / particle structure with consistent morphology is visible; and XRD tests were performed, such as... Figure 2 As shown, typical diffraction peaks of α-Ni(OH)2 were obtained, consistent with the standard card.

[0016] 2. Synthesis of NiFe-LDH To verify the universality of the route of this invention for the synthesis of NiFe-LDH, the NiFe-LDH products of each group were characterized by SEM and XRD. The SEM results are as follows: Figure 3 The XRD results show layered / lamellar stacking with no obvious impurities / agglomerates; Figure 4As shown, all exhibit typical hydrotalcite structures (003 / 006 / 012 peaks), with lamellar / sheet-like / layered morphologies, demonstrating the formation of layered structures and indicating that the method of this invention is applicable to various Ni:Fe ratios.

[0017] 3. Nickel recovery rate determination Samples were taken from the supernatant before the reaction (before adding catalyst + NaClO) and after the reaction, and Ni was determined by ICP-OES (or AAS). 2+ concentration( Figure 5 Example result: Ni 2+ The concentration decreased from ~349.3 mg / L to <10 mg / L, corresponding to a Ni recovery rate of approximately 97-99%. This indicates that using α-Ni(OH)2 + NaClO oxidation to break the complex and alkaline sedimentation conditions, Ni in EDTA-Ni in waste liquid can be efficiently released and recovered as Ni(OH)2 with controllable morphology / crystallinity.

[0018] 4. NiFe-LDH and lithium polysulfides (Li2S) x Adsorption / catalytic conversion test of composite materials NiFe-LDH powder was mixed with pre-prepared lithium polysulfide (Li2S) x A mixture of solutions with x=4~8 (experimental group) and a blank (without NiFe-LDH) was used as the control group. Both groups were treated under the same conditions (e.g., 25℃, stirring / standing) for fixed times (e.g., 15, 30, 60 min), and then samples were taken for electrochemical reduction / oxidation (CV and other methods) to evaluate their effect on the conversion of lithium polysulfides (Li₂S₂). x →Catalytic ability of Li2S / Li2S2).

[0019] The results are as follows Figure 6 As shown, compared with the control group (without catalyst), lithium polysulfides exhibit more pronounced redox peaks under the same conditions, indicating that NiFe-LDH has good catalytic conversion ability.

[0020] 5. Rate and cycle testing of NiFe-LDH cathode composite material in lithium-sulfur batteries NiFe-LDH was mixed with sulfur (S) and a conductive agent (CNT or carbon black) at a mass ratio of 2:40:10, and a composite cathode material (NiFe-LDH / C / S) was prepared by melting sulfur (155-160℃, 6-12 h). Electrodes were fabricated, and lithium-sulfur batteries (Li anode + conventional electrolyte + separator) were assembled. The control group consisted of a conventional SC cathode. Charge-discharge cycles were performed at 2C (100-500 cycles), and the capacity vs. the number of cycles was recorded. Figure 7 ).

[0021] The experimental group exhibited significantly higher initial discharge capacity (e.g., ≥900-1000 mAh / g) and maintained a high capacity (≥80-90% capacity retention) even after long cycling (e.g., 500 cycles), while the control group showed rapid capacity decay (≤50%). Performance testing of NiFe-LDH as a cathode catalyst in lithium-sulfur batteries. The above lithium polysulfide catalytic experiments and lithium-sulfur battery cycle tests ( Figure 6-7 The results jointly demonstrate that the NiFe-LDH prepared in this invention has excellent catalytic and stable cycling performance, which can significantly improve the kinetics and cycle life of lithium-sulfur batteries.

Claims

1. A method for preparing NiFe-LDH based on α-nickel hydroxide catalytic decomplexing regeneration, characterized in that, Includes the following steps: 1) Oxidative decomposition of EDTA-Ni complex α-Nickel hydroxide was added as a catalyst to waste liquid containing EDTA-Ni complex, followed by the addition of sodium hypochlorite. An oxidation reaction was carried out under alkaline conditions, causing the EDTA skeleton to undergo ring-opening and breakage, releasing Ni. 2+ And new nickel hydroxide precipitate is generated in situ during the catalytic cycle; 2) Separation of nickel and iron by acid dissolution The precipitate obtained in step 1) was dissolved in hydrochloric acid, and Fe was introduced. 3+ Ni-containing 2+ with Fe 3+ Chloride solution; 3) Co-precipitation preparation of NiFe-LDH precursor Add an alkaline mixture of NaOH and Na2CO3 solution dropwise to the solution obtained in step 2) to maintain the pH of the system at 7.5-10, forming a NiFe-LDH hydrotalcite precursor precipitate; 4) Aging and Collection The precipitate was aged at 60-120℃ for 2-24 h, and then washed and dried to obtain NiFe-LDH solid powder.

2. The preparation method of NiFe-LDH based on α-nickel hydroxide catalytic decomplexing regeneration according to claim 1, characterized in that, The amount of α-nickel hydroxide used is 0.5-1 g / L of waste liquid.

3. The preparation method of NiFe-LDH based on α-nickel hydroxide catalytic decomplexing regeneration according to claim 1, characterized in that, The concentration of sodium hypochlorite is 0.05~1 mol / L.

4. The preparation method of NiFe-LDH based on α-nickel hydroxide catalytic decomplexing regeneration according to claim 1, characterized in that, The oxidation reaction is carried out at a temperature of 20-60 °C and a pH of 8-12.

5. The preparation method of NiFe-LDH based on α-nickel hydroxide catalytic decomplexing regeneration according to claim 1, characterized in that, The concentration of the hydrochloric acid is 0.1-2 mol / L, and the dissolution time is 5-60 min.

6. The preparation method of NiFe-LDH based on α-nickel hydroxide catalytic decomplexing regeneration according to claim 1, characterized in that, Ni in chloride solution 2+ with Fe 3+ The molar ratio is (2~4):

1.

7. The preparation method of NiFe-LDH based on α-nickel hydroxide catalytic decomplexing regeneration according to claim 1, characterized in that, The concentration of the NaOH solution is 0.5-3 mol / L.

8. The preparation method of NiFe-LDH based on α-nickel hydroxide catalytic decomplexing regeneration according to claim 1, characterized in that, The concentration of the Na2CO3 solution is 0.05-0.5 mol / L.

9. A NiFe-LDH material obtained by the preparation method according to any one of claims 1 to 8, characterized in that, The NiFe-LDH has a typical layered hydrotalcite structure with a layer thickness of 5-30 nm and a sheet diameter of 50-300 nm, and contains a small number of surface carboxyl / hydroxyl defect sites induced by EDTA oxidation residues.

10. The application of the NiFe-LDH material according to claim 9 in the preparation of battery electrode materials, characterized in that, The battery electrode material includes lithium battery cathode material; The NiFe-LDH material is used as an electrode catalyst.

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