A method for preparing metallic cobalt from a mixture of cobalt oxides by liquid-phase reduction

Abstract

This invention belongs to the field of cobalt recovery technology and discloses a method for preparing metallic cobalt from a mixture of cobalt oxides by liquid-phase reduction. The method involves dispersing cobalt oxides in a hydroxyl-containing liquid medium to form a first slurry; adding a transition metal salt to the first slurry and mixing it uniformly at room temperature to obtain a second slurry; heating the second slurry to 50°C~70°C and adding a borohydride solution dropwise at a uniform rate under stirring; and collecting the metallic cobalt by magnetic separation after the reaction is complete. This invention reconstructs the wet cobalt extraction process system, achieving efficient reduction and simple separation of cobalt oxide mixtures in a single step under mild conditions. Under the catalysis of the transition metal salt, the released hydrogen reacts with the cobalt oxides in situ to reduce them to elemental metallic cobalt, thus avoiding traditional high-temperature methods and acid dissolution in wet processes. This method is the first to achieve a one-step liquid-phase reduction of complex solid cobalt oxide mixtures with extremely low energy consumption and safety risks.

Description

Technical Field

[0001] This invention belongs to the field of cobalt recovery technology, and particularly relates to a method for preparing metallic cobalt from a mixture of cobalt oxides by liquid-phase reduction. Background Technology

[0002] With the development of the new energy lithium battery industry, cobalt-based lithium battery waste has become the world's main source of cobalt oxides (currently accounting for more than 50%, and continuing to increase). This type of source is a recycled cobalt oxide, which has the advantages of concentrated raw materials, high cobalt grade, and low extraction cost, and is also the core direction of cobalt resource recycling.

[0003] The main methods for recovering metallic cobalt from cobalt oxides are high-temperature thermal reduction methods, such as hydrogen reduction, carbon monoxide reduction, carbothermal reduction, and precursor conversion-reduction. These methods are highly temperature-dependent (the minimum temperature required for gas reduction is 398℃~650℃) and have high energy consumption.

[0004] In addition, there is a relatively mild wet process for extracting metallic cobalt. The core idea of ​​the wet process is to first acid-dissolve cobalt oxides to convert them into soluble cobalt salts, and then obtain metallic cobalt through separation, purification, and reduction. Although acid dissolution can achieve the conversion of cobalt oxides into soluble cobalt salts, it suffers from five major drawbacks due to limitations in the physical properties of cobalt oxides, the characteristics of acids, the reaction system, and industrial application requirements: inherent shortcomings in raw material compatibility, high acid consumption and costs, co-leaching of impurities and burden on subsequent purification, environmental and safety hazards, and limited process efficiency. These drawbacks directly affect subsequent electrolytic / chemical reduction processes, impacting the overall efficiency, cost, and product quality of cobalt extraction. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing metallic cobalt from a mixture of cobalt oxides by liquid-phase reduction, reconstructing the wet cobalt extraction process system, and achieving efficient reduction and simple separation of the cobalt oxide mixture under mild conditions in a single step.

[0006] This invention employs the following technical solution: a method for preparing metallic cobalt from a cobalt oxide mixture via liquid-phase reduction, comprising the following steps: Cobalt oxide is dispersed in a hydroxyl-containing liquid medium to form a first slurry; A transition metal salt is added to the first slurry and mixed evenly at room temperature to obtain a second slurry; wherein the amount of transition metal salt added is 0.4% to 0.5% of the weight of cobalt oxide. The second slurry is heated to 50℃~70℃, and a borohydride solution is added dropwise at a uniform rate under stirring. After the reaction is complete, metallic cobalt is collected by magnetic separation.

[0007] The beneficial effects of this invention are as follows: This invention achieves for the first time a one-step liquid-phase reduction of complex solid cobalt oxide mixtures, completely skipping the intermediate steps such as acid dissolution and purification required in traditional processes; the reaction is carried out at room temperature and pressure, eliminating the need for high-temperature and high-pressure equipment, significantly reducing energy consumption and safety risks; the amount of reducing agent used is only 0.25 to 0.3 times the theoretical amount, the amount of transition metal salt catalyst is low and recyclable, greatly reducing material costs; the obtained metallic cobalt has high purity and good yield, and magnetic separation is simple and efficient; at the same time, it eliminates environmental problems such as acid mist, acidic solid waste and high-salt wastewater, providing a clean, low-carbon and sustainable technical path for cobalt resource recovery. Attached Figure Description

[0008] Figure 1 The X-ray analysis spectrum of the product obtained in Example 1 of this invention; Figure 2 This is a schematic diagram of the catalytic technology principle of the present invention. Detailed Implementation

[0009] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0010] In the technology of cobalt recycling from waste batteries, developing a one-step process that can directly process solid mixtures and achieve efficient reduction and simple separation of cobalt oxide mixtures under mild conditions has significant industrial value. This invention provides a method for reducing cobalt oxide mixtures to obtain metallic cobalt powder, which features mild reaction conditions, a simple operating procedure, and ease of industrial implementation.

[0011] This invention discloses a method for preparing metallic cobalt from a mixture of cobalt oxides via liquid-phase reduction, comprising the following steps: dispersing cobalt oxides in a hydroxyl-containing liquid medium to form a first slurry; adding a transition metal salt to the first slurry and mixing it uniformly at room temperature to obtain a second slurry; wherein the amount of transition metal salt added is 0.4% to 0.5% of the weight of the cobalt oxides; heating the second slurry to 50°C to 70°C, and uniformly adding a borohydride solution under stirring conditions; after the reaction is complete, collecting the metallic cobalt using magnetic separation. The preferred reaction temperature is 50°C to 60°C, and the reaction time is generally 0.5 h to 4 h, preferably 1 h to 3 h.

[0012] It should be noted that the slurry of this invention refers to a solid-liquid dispersion system formed by dispersing solid cobalt oxide powder in a liquid medium, wherein the solid particles are suspended in the liquid medium and do not undergo significant sedimentation or only undergo slow sedimentation. In this invention, cobalt oxide is defined broadly, encompassing elemental cobalt and various oxides of cobalt. Those skilled in the art should understand that this description is not limited to oxidized species of cobalt, but covers elemental cobalt. Regarding room temperature, this invention refers to 20°C to 25°C.

[0013] This invention utilizes a clever in-situ reaction design, as shown in the following reaction formula, to slowly release hydrogen from borohydrides in reaction with hydroxyl-containing solvents. Under the catalysis of transition metal salts, the released hydrogen gas is reacted in situ with cobalt oxides to reduce metallic cobalt. This avoids the acid dissolution in traditional high-temperature methods and wet processes, and for the first time achieves a one-step liquid-phase reduction of complex solid cobalt oxide mixtures. It skips all intermediate steps such as dissolution and purification, and the process conditions are extremely mild. The reaction is carried out at room temperature and pressure, without the need for high-temperature and high-pressure equipment, resulting in extremely low energy consumption and safety risks.

[0014]

[0015] Wherein, HO-R is water or a C1-C4 alcohol, and R is H, CH3, C2H5, C3H7 or C4H9.

[0016] After adding a transition metal salt to the first slurry and mixing it uniformly at room temperature, the transition metal salt forms catalytically active sites on the surface of cobalt oxide, promoting the subsequent reduction reaction. Following this, a borohydride solution is added dropwise to the second slurry at a predetermined rate. The borohydride reacts with the hydroxyl-containing liquid medium, slowly releasing hydrogen gas, thus avoiding explosive gas release. Then, during the complete reaction, the hydrogen gas released by the transition metal salt undergoes an in-situ reduction reaction with the cobalt oxide, gradually converting cobalt oxides of different valence states into metallic cobalt. Subsequently, the metallic cobalt is collected by magnetic separation using the ferromagnetic properties of cobalt. This separation mechanism avoids material loss that may occur in traditional solid-liquid separation methods. For magnetic separation, an external permanent magnet or electromagnet can be used.

[0017] Furthermore, this invention improves the material transfer process in the cobalt oxide mixture processing, completing the entire conversion process within a single reactor, achieving a direct transformation from raw material to product. Ultimately, this method solves the problem of process complexity caused by multiple steps in series during cobalt oxide mixture processing, thereby significantly simplifying the process and reducing operational complexity.

[0018] This invention constructs a stably dispersible cobalt oxide slurry in a hydroxyl-containing liquid medium and introduces a catalytic amount of transition metal salt to activate borohydride for in-situ hydrogen release, enabling selective reduction of active hydrogen on the cobalt oxide surface. Simultaneously, utilizing the ferromagnetism of the generated metallic cobalt, solid-liquid separation is directly achieved within the reaction system. This solves the problems of long processes, high energy consumption, complex equipment, and large wastewater volumes associated with existing technologies that require high-temperature thermal reduction or wet acid leaching. Its advantages include: reduction and separation are completed in one step under mild conditions of atmospheric pressure and 50℃~70℃, avoiding the use of large amounts of strong acids and alkalis and high-pressure gas operations, significantly reducing process safety risks and environmental treatment burdens; the synergistic effect of each step accelerates the reduction reaction kinetics, increases product crystallinity, and improves the magnetic separation recovery rate to over 96.5%.

[0019] Specifically, in this invention, the cobalt oxide includes at least one of CoO, Co2O3, and Co3O4. The hydroxyl-containing liquid medium is water, a C1-C4 alcohol (such as methanol, ethanol, isopropanol, etc.), or a mixture of water and a C1-C4 alcohol.

[0020] In one embodiment, the cobalt oxide may further include elemental cobalt. That is, this method has a broad-spectrum reduction capability for oxides of different valence states, and the elemental cobalt already present in the raw material can act as a nucleus to promote the attachment and growth of the reduction product, thereby improving the yield.

[0021] In this invention, by limiting the cobalt oxide to at least one of CoO, Co2O3, and Co3O4, and using water, lower alcohols (methanol, ethanol, isopropanol), or mixtures thereof as hydroxyl-containing media, borohydrides can be controlled to hydrolyze / alcoholize and release hydrogen gas in different polar environments, and all types of cobalt oxides can be effectively reduced in this system; wherein Co3O4 (containing Co) 2+ / Co 3+ ) and CoO (containing Co) 2+ When mixed, these substances have different reduction potentials and are prone to forming a micro-battery effect to promote electron transfer. The mixed solvent of water and alcohol can synergistically regulate the viscosity of the slurry, interfacial tension and hydrogen diffusion rate, thereby broadening the range of applicable raw materials while improving reaction uniformity and mass transfer efficiency.

[0022] In this invention, pre-existing metallic cobalt is introduced into a cobalt oxide mixture to serve as a heterogeneous nucleation site, adsorbing cobalt atom clusters generated during the reduction process and inducing their directional deposition and growth. This accelerates the reduction reaction process and inhibits excessive agglomeration and colloidalization of nanoscale cobalt particles. This nucleation effect not only improves the crystal integrity and magnetic response intensity of the newly generated cobalt but also enhances the magnetic separation efficiency, resulting in a more concentrated particle size distribution and fewer residual impurities in the final product.

[0023] The transition metal salts used in this invention are non-noble transition metal salts, that is, the transition metal salts are non-noble metal salts, such as Fe. 2+ Ni 2+ or Co 2+ The soluble salt is preferably FeCl2, FeSO4, NiCl2, NiSO4, CoCl2, CoSO4, etc., and its addition amount is 0.4% to 5% of the mass of cobalt oxide.

[0024] This process enables metal ions to form high-density catalytic sites on the surface of cobalt oxide, efficiently promoting the hydrolysis of NaBH4 to generate H2 and further activating it into atomic hydrogen, thereby significantly improving the reduction reaction rate. When the dosage is below 0.4%, the catalytic activity is insufficient; above 5%, it easily triggers localized and intense exothermic reactions and foam overflow. Furthermore, excess metal ions may remain in the product, affecting cobalt purity. The cobalt yields of the products obtained in Examples 1, 4, 5, and 6 were 96.5%, 97.0%, 97.7%, and 96.9%, respectively. XRD analysis showed pure metallic cobalt phase, and ICP purity was ≥99.1%, verifying the dual necessity of this parameter range for ensuring both catalytic efficiency and product quality.

[0025] In one embodiment, the borohydride can be sodium borohydride or potassium borohydride, and the weight of the borohydride is 0.25 to 0.3 times the theoretical stoichiometric amount required to completely reduce cobalt oxide to elemental cobalt. Based on the "transition metal catalytic in-situ hydrogen release-interfacial hydrogenation" mechanism rather than the traditional electron transfer pathway, the consumption of reducing agent is significantly reduced while ensuring complete reduction. At this ratio, the hydrogen gas generated by the decomposition of NaBH4 can be efficiently captured and used for the stepwise reduction of cobalt oxide (Co3O4→CoO→Co), avoiding excessive hydrogen escape that could cause safety hazards and the accumulation of borate byproducts. A comparison of Example 1 (10g NaBH4, corresponding to 0.28 times the theoretical amount) with Examples 8 (12g NaBH4, corresponding to 0.34 times the theoretical amount) and 9 (11g NaBH4, corresponding to 0.3 times the theoretical amount) shows that the yield of Examples 8 and 9 was not significantly improved (96.6% vs 96.6% vs 96.8%), confirming that 0.25~0.3 times is the optimal range for balancing safety, economy and reduction efficiency.

[0026] like Figure 2As shown, the catalytic principle of transition metal salts in this invention is a two-stage in-situ interface catalysis on the surface of cobalt oxides. The non-noble transition metal ions dissociated from the transition metal salts are first adsorbed on the surface of cobalt oxide particles (adsorption and in situ formation), forming high-density catalytic active sites. Subsequently, they catalyze the hydrolysis or alcoholysis reaction of borohydrides with hydroxyl-containing liquid media (controlled hydrogen release and activation), achieving controlled hydrogen release and activating hydrogen gas H2 into highly active adsorbed atomic hydrogen [H]. At the same time, it mediates the electron transfer between atomic hydrogen and cobalt oxides (electron transfer and stepwise reduction), weakening the cobalt-oxygen bond and promoting the in-situ stepwise reduction of cobalt oxides of different valence states such as Co3O4, CoO, and Co2O3 to metallic cobalt element under mild conditions (cobalt element generation and nucleation growth). Throughout the catalytic process, transition metal salts act only as catalyst promoters, without being consumed or participating in product formation. After completing one catalytic cycle, they retain their original valence and adsorption states, allowing them to continuously exert catalytic effects. Furthermore, the presence of catalytic sites can synergize with the heterogeneous nucleation behavior of elemental cobalt in the raw materials, providing directional deposition and growth sites for cobalt atom clusters. This catalytic mechanism is the core for achieving efficient utilization of borohydrides and complete low-temperature reduction of cobalt oxides. Its adaptability and efficiency also provide key support for the one-step liquid-phase reduction of cobalt oxide mixtures, demonstrating significant technological and industrial value.

[0027] It should be noted that, unless otherwise specified, all materials, reagents, and instruments used in the embodiments of this invention can be obtained through commercial channels. The cobalt oxide mixture is derived from cobalt-rich slag obtained by roasting, acid leaching, precipitation, and calcination of waste lithium-ion battery cathode materials, and its composition was confirmed by XRD.

[0028] Example 1: This embodiment provides a complete process for obtaining high-purity metallic cobalt powder by using waste battery cobalt material as raw material, anhydrous ethanol as medium, FeCl2•4H2O as catalyst, and NaBH4 as reducing agent to complete liquid-phase reduction and magnetic separation at 50°C.

[0029] 100g of cobalt-enriched material obtained from processed waste battery materials (XRD analysis: Co3O4 weight content 40%, Co2O3 weight content 30%, CoO weight content 20%, Co weight content 10%) was ground and passed through a 325-mesh sieve. This was added to a 500ml three-necked flask equipped with a stirrer and a constant-temperature water bath, along with 200ml of anhydrous ethanol, and stirred until evenly dispersed. 0.5g of catalyst FeCl2•4H2O (0.5% of the raw material mass) was weighed and added to the slurry, and stirred at room temperature for 15min to allow the catalyst to fully adsorb onto the solid surface. The water bath temperature of the flask was raised to 50℃. Under vigorous stirring, 50ml of an aqueous solution containing 10g of NaBH4 was slowly added dropwise to the slurry over 1h using a constant-pressure dropping funnel. During the addition, the slurry rapidly turned black and produced a small amount of bubbles. After the addition was complete, the reaction was continued at 50℃ with stirring for 2h. After the reaction was complete, the reaction mixture was transferred to a glass beaker. A strong neodymium iron boron magnet was placed on the outer wall of the beaker, and the black powder was clearly seen to be rapidly attracted to one side of the magnet. The supernatant was discarded, and the magnetic solid was washed twice with 0.1 mol / L dilute hydrochloric acid, and then twice each with deionized water and anhydrous ethanol. The washed black solid was dried in a vacuum drying oven at 60°C for 6 hours to obtain 85.5 g of black magnetic powder. Figure 1 The XRD pattern of the product is shown. The diffraction intensity curve of the sample as a function of 2θ was compared with the standard PDF card for metallic cobalt (Co-PDF#04-002-1029). The results show that the diffraction peak positions of the sample are basically consistent with the standard card, indicating that the main crystalline phase of the sample is metallic cobalt, and it has good crystallinity. ICP analysis shows that the cobalt content of the product is 99.2 wt%. Based on the total cobalt content in the raw material, the total cobalt yield is 96.5%.

[0030] Example 2: Under the same preparation conditions as in Example 1, except that the hydroxyl-containing liquid medium was replaced with 200 mL of deionized water instead of anhydrous ethanol, 83.0 g of black magnetic powder was obtained. ICP analysis showed that the cobalt content of the product was 99.3 wt%, and the total cobalt yield was 97.4% based on the total cobalt content in the raw materials. The results indicate that the product can still achieve the technical effects of the present invention, thus proving that the technical solution of the present invention has good feasibility and stability within the range of water, C1-C4 alcohols and their mixtures.

[0031] Example 3: With all other preparation conditions the same as in Example 1, only the reaction temperature was adjusted from 50°C to 70°C, and 87.1 g of black magnetic powder was obtained. The cobalt content was determined by ICP to be 99.3 wt%, and the cobalt yield was 97.4%, which is slightly higher than that in Example 1, confirming that the present invention has good adaptability in the temperature range of 20°C to 80°C.

[0032] Example 4: Under the same preparation conditions as in Example 1, except that the transition metal salt was replaced with NiCl2 instead of FeCl2•4H2O, 86.5 g of black magnetic powder was obtained. ICP analysis showed that the cobalt content was 99.3 wt% and the cobalt yield was 97.0%, proving that non-noble transition metal salts can be used interchangeably within a limited range.

[0033] Example 5: Under the same preparation conditions as in Example 1, except that the transition metal salt was replaced with CoCl2•6H2O instead of FeCl2•4H2O, 87.5 g of black magnetic powder was obtained. ICP analysis showed that the cobalt content of the product was 99.4 wt%. Calculated based on the total cobalt content in the raw materials, the total cobalt yield was 97.7%. This example demonstrates that cobalt-based catalysts can also effectively exert catalytic effects.

[0034] Example 6: Under the same preparation conditions as in Example 1, except that the amount of transition metal salt FeCl2•4H2O was changed to 0.4 g, 86 g of black magnetic powder was obtained. ICP analysis showed that the cobalt content of the product was 99.2 wt%. Calculated based on the total cobalt content in the raw materials, the total cobalt yield was 96.9%. Consistent with the results of Example 1, this example demonstrates that the efficiency of transition metal salts is optimal in the range of 0.4% to 0.5%.

[0035] Example 7: Under the same preparation conditions as in Example 1, except that the borohydride was replaced with KBH4 instead of NaBH4, 87.2 g of black magnetic powder was obtained. ICP analysis showed that the cobalt content was 99.1 wt% and the cobalt yield was 97.3%, confirming that NaBH4 and KBH4 can be used interchangeably as borohydrides.

[0036] Example 8: With all other preparation conditions the same as in Example 1, only the amount of borohydride was adjusted from 10g to 12g, yielding 85.7g of black magnetic powder. ICP analysis showed a cobalt content of 99.1wt% and a cobalt yield of 96.6%, which was basically consistent with Example 1. Adding an additional 2g of borohydride did not significantly improve efficiency.

[0037] Example 9: With all other preparation conditions the same as in Example 1, only the amount of borohydride was adjusted from 10g to 11g, yielding 86.2g of black magnetic powder. ICP analysis showed a cobalt content of 99.3wt% and a cobalt yield of 96.8%, which is basically consistent with Example 1, indicating that the reduction efficiency has reached a plateau within the range of 0.25 to 0.3 times the theoretical amount.

[0038] Comparative Example 1: Without adding FeCl2•4H2O catalyst, all other conditions were exactly the same as in Example 1. The reaction rate was significantly slower, and the slurry was still brownish-brown after 4 hours of reaction. Very little cobalt powder was recovered by magnetic separation, and XRD showed a large amount of unreacted Co3O4.

[0039] Comparative Example 2: After the reaction was complete, centrifugation was attempted instead of magnetic separation. The solid obtained after centrifugation was muddy, difficult to completely separate and wash, and the final product contained a large number of non-magnetic impurities, with a cobalt purity of only 91.3%.

[0040] In summary, this invention fundamentally eliminates the inherent defects in cost, environmental protection, process, and efficiency caused by the acid dissolution process, achieving a fundamental optimization of the entire wet cobalt extraction process, rather than a partial improvement. At the same time, it reconstructs the wet cobalt extraction process system, significantly improving the economic efficiency, environmental protection, and industrial adaptability of cobalt resource recovery. Its greatest benefits can be divided into two main aspects: direct core benefits and derived process value, with direct benefits being the most core and significant advantage.

[0041] This invention eliminates the four inherent defects of acid dissolution at its source, achieving a triple improvement in cost reduction, environmental protection, and safety. This is the core value of skipping the acid dissolution process, directly solving the current industry pain points of wet cobalt extraction, and achieving effects that existing acid dissolution optimization methods (such as low acid leaching and high-efficiency stirring) cannot achieve.

[0042] The acid dissolution process is the core link in the wet cobalt extraction process, which involves material consumption and equipment investment. Removing this process can directly eliminate core reagents such as acid agents, reducing agents, and neutralizing alkali solutions, while also eliminating corrosion-resistant equipment, resulting in significant and direct cost reduction.

[0043] The process eliminates the need for reducing agents such as sulfuric acid / hydrochloric acid (theoretical reaction amount 1.2~2.0 times excess), sodium sulfite / SO2, and NaOH / Na2CO3 for subsequent neutralization of free acid. The cost of these three types of reagents alone accounts for 30%~50% of the current cost of wet cobalt extraction materials. The cost reduction effect of low-grade cobalt oxide raw materials is even greater, completely solving the industry problem that "the lower the raw material grade, the higher the acid consumption and the higher the cost".

[0044] It significantly reduces equipment investment and maintenance costs. There is no need to use acid-resistant reactors and pipelines made of titanium, fiberglass, etc., nor is there a need for acid mist absorption towers and exhaust gas treatment systems. Ordinary carbon steel equipment can meet the process requirements, reducing the initial equipment investment by 60% to 80%. At the same time, it eliminates the corrosion of equipment by acid, greatly reducing the frequency and cost of equipment maintenance and extending the service life of the equipment.

[0045] Acid dissolution is the main source of environmental pollution in wet cobalt extraction. Acid mist, acidic solid waste, and high-salt wastewater are all directly generated by the use of acid agents. Removing acid dissolution will essentially eliminate these pollutants, significantly reducing environmental treatment costs and environmental risks.

[0046] No acid mist / toxic exhaust gas, zero air pollution in the workshop, no more high-temperature acid mist volatilization of sulfuric acid / hydrochloric acid, no need to use toxic reducing agents such as SO2, no need for the workshop to be equipped with exhaust gas treatment system, solving air pollution and occupational health risks to operators at the source.

[0047] With no acidic solid waste or high-salt wastewater, end-of-pipe treatment costs are drastically reduced. No acidic leaching residue is produced, and there is no need to generate large amounts of high-salt wastewater (sulfates / chlorides) due to acid neutralization and impurity removal. The environmental protection treatment cost of wet cobalt extraction is directly reduced by 80% to 90%. At the same time, it completely solves the industry problem of high-salt wastewater treatment, eliminating the need for expensive wastewater treatment equipment such as membrane filtration and evaporation crystallization. Process wastewater can be simply treated and recycled, achieving a closed-loop water cycle.

[0048] Environmental compliance risks are significantly reduced, as it no longer involves the storage, transportation, or use of acid agents, nor does it involve the discharge of high-salt wastewater or acidic solid waste, thus meeting the industry development requirements for green manufacturing.

[0049] Safety risks such as acid splashing, localized boiling, and corrosion leakage caused by acid dissolution are all determined by the strong corrosiveness of the acid and the exothermic solid-liquid reaction characteristics. These risks will completely disappear after acid dissolution is removed. There is no need to handle strong acid reagents, completely avoiding the risks of leakage and splashing during acid storage, transportation, and feeding; the reaction system is no longer strongly acidic, eliminating concerns about slurry boiling caused by sudden local temperature rises. The process operation is more gentle and controllable, the safety protection requirements for operators are greatly reduced, and the difficulty of workshop safety management is significantly reduced.

[0050] This invention significantly lowers the industry barriers for cobalt oxide extraction: equipment investment, environmental costs, and process complexity are all greatly reduced, enabling small and medium-sized enterprises to achieve efficient cobalt resource recovery. This breaks the traditional high-investment, high-barrier-to-entry industry structure of hydrometallurgical cobalt extraction. It also enhances the utilization value of low-grade cobalt resources, making traditionally unusable cobalt resources such as metallurgical slag, low-grade cobalt ore, and spent cobalt-based catalysts economically viable, thus significantly expanding the supply sources of cobalt resources and improving the overall utilization rate of cobalt resources.

[0051] Promote the upgrading of wet cobalt extraction technology: from "acid-dissolution-dominated high-pollution, high-cost process" to "acid-free, clean, low-cost process", driving the entire cobalt resource recycling industry towards green, efficient, and intelligent development, and leading the industry's technological transformation.

[0052] In summary, this invention reconstructs the wet cobalt extraction process, not simply by "omitting a step," but by fundamentally eliminating all problems caused by the use of acid agents. It achieves essential optimization of the wet cobalt extraction process in four core dimensions: cost, environmental protection, safety, and efficiency. At the same time, it reconstructs the wet cobalt extraction process system, significantly improving raw material adaptability and industrialization potential, ultimately achieving clean, low-cost, efficient, and large-scale production of cobalt oxides. This is also the current goal of wet cobalt extraction technology research and development.

Claims

1. A method for preparing metallic cobalt from a mixture of cobalt oxides by liquid-phase reduction, characterized in that, Includes the following steps: Cobalt oxide is dispersed in a hydroxyl-containing liquid medium to form a first slurry; A transition metal salt is added to the first slurry and mixed evenly at room temperature to obtain a second slurry; wherein the amount of the transition metal salt added is 0.4% to 0.5% of the weight of the cobalt oxide; The second slurry is heated to 50℃~70℃, and a borohydride solution is added dropwise at a uniform rate under stirring. After the reaction is complete, metallic cobalt is collected by magnetic separation.

2. The method for preparing metallic cobalt from a mixture of cobalt oxides by liquid-phase reduction as described in claim 1, characterized in that, The cobalt oxide includes at least one of CoO, Co2O3, and Co3O4; The hydroxyl-containing liquid medium is water, a C1-C4 alcohol, or a mixture of water and a C1-C4 alcohol.

3. The method for preparing metallic cobalt from a cobalt oxide mixture by liquid-phase reduction as described in claim 2, characterized in that, The cobalt oxide also includes elemental cobalt.

4. A method for preparing metallic cobalt from a mixture of cobalt oxides by liquid-phase reduction as described in claim 2 or 3, characterized in that, The transition metal salt is a non-noble transition metal salt.

5. The method for preparing metallic cobalt from a cobalt oxide mixture by liquid-phase reduction as described in claim 4, characterized in that, The weight of the borohydride is 0.25 to 0.3 times the theoretical stoichiometric amount required to completely reduce the cobalt oxide to elemental cobalt.

6. The method for preparing metallic cobalt from a cobalt oxide mixture by liquid-phase reduction as described in claim 5, characterized in that, Includes the following steps: Take 100g of cobalt oxide obtained after processing waste battery materials, wherein the cobalt oxide contains 40% Co3O4 by weight, 30% Co2O3 by weight, 20% CoO by weight, and 10% elemental cobalt by weight. The cobalt oxide is ground, sieved, and then added to a flask equipped with stirring and a constant temperature water bath; Add 200 ml of anhydrous ethanol to the flask, stir and disperse evenly to obtain the first slurry; Weigh 0.5g FeCl2•4H2O and add it to the first slurry. Stir at room temperature for 15 minutes to obtain the second slurry. The water bath temperature of the flask was raised to 50°C. Under stirring, 50 ml of aqueous solution containing 10 g NaBH4 was added dropwise to the second slurry over 1 hour using a constant pressure dropping funnel. After the addition is complete, continue to keep the mixture at 50°C and stir for 2 hours. After the reaction was completed, the reaction mixture was transferred to a glass beaker for magnetic separation to obtain a magnetic solid; The magnetic fixative is washed to obtain metallic cobalt.

Images