Method for preparing carbon-doped metal catalyst by recycling waste lithium batteries through spinach-assisted acid leaching and application of carbon-doped metal catalyst

Abstract

The invention discloses a method for preparing a carbon-doped metal catalyst by recycling waste lithium batteries through spinach-assisted acid leaching and application, and relates to the field of waste lithium ion battery recycling. The carbon-doped metal catalyst can be obtained and is used for removing multiple flotation reagents in beneficiation wastewater. The method comprises the following steps: premixing waste lithium battery positive electrode powder and dried waste spinach powder through ball milling, leaching the mixture with an oxalic acid solution, and carrying out in-situ low-temperature roasting on solid-phase leaching residues to prepare a carbon-doped metal catalyst in one step; the carbon-doped metal catalyst can efficiently activate peroxymonosulfate, and efficient degradation of various organic flotation reagents such as ammonium dibutyl dithiophosphate, butyl xanthate and N, N-diethyldithiocarbamate is achieved. According to the method, one-step recovery and high-value conversion of the transition metal in the waste lithium battery are realized through spinach-assisted acid leaching and direct roasting of the leaching residues, strong acid dependence and multi-stage separation steps of a traditional lithium battery recovery process are avoided, and a green way is provided for lithium battery recovery and water treatment catalyst co-production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of waste lithium-ion battery recycling, in particular to a method for directly recovering waste lithium battery cathodes by spinach-assisted acid leaching to prepare carbon-doped metal catalysts in one step and applications thereof. BACKGROUND

[0002] With the expansion of the application field of lithium batteries, the amount of scrap lithium batteries has increased dramatically. Fluorine-containing substances, heavy metals and various organic auxiliary materials make waste lithium batteries a complex hazardous pollutant, triggering strong environmental protection demands. Currently, hydrometallurgy has become the main path for the recovery of lithium battery cathodes due to its high metal recovery rate and product purity. Traditional hydrometallurgical processes usually use inorganic acid (H2SO4) and reducing agent (H2O2) in combination. However, sulfuric acid is highly corrosive, and the use of H2O2 also has high explosiveness and instability, which requires strict safety production measures. In addition, the recovery of valuable metals after leaching often relies on methods such as solvent fractional extraction or chemical precipitation, which are limited by problems such as large amounts of chemical reagents, multiple extraction stages, and metal co-precipitation, and there is an urgent need to find more economical and environmentally friendly alternatives.

[0003] Biomass contains abundant natural antioxidant components (vitamins, anthocyanins, flavonoids, etc.), in addition, when heated in an acidic environment, cellulose and hemicellulose in biomass can be converted into reducing sugars and polyhydroxy aldehyde acids. The presence of these active ingredients makes biomass an excellent alternative to green reducing agents. However, although various combinations of biomass and organic acids have good extraction effects on valuable metals in cathode materials, subsequent metal recovery still involves complex purification and separation processes. Therefore, finding a cheap biomass containing abundant natural active ingredients and combining it with an organic acid with strong complexing ability to selectively precipitate high-valence metals can greatly reduce the leaching and recovery process, saving energy and cost.

[0004] In addition, the transition metal elements such as nickel, cobalt, manganese and iron in the waste lithium battery cathode materials (such as lithium cobaltate, lithium manganate, nickel-cobalt-manganese ternary material, etc.) are rich in transition metal elements, which have excellent intrinsic catalytic activity due to their unique d-orbital electron configuration and controllable redox properties, which provides an important way for the high-value utilization of transition metals. If these recovered transition metals (especially single metal or specific combination of multi-metal components) can be directly used to prepare high-performance catalysts, replacing expensive commercial metal salt raw materials, and applied to the catalytic degradation of residual flotation reagents in complex systems such as mineral processing wastewater, a circular path of "waste treatment" can be established. This not only can improve the economic benefits of waste lithium battery recycling, but also provides a more cost-effective and environmentally sustainable solution for mineral processing wastewater treatment, achieving a win-win of resource recovery and pollution control. SUMMARY

[0005] The present application aims at the above problems, and provides a method for preparing a carbon-doped metal catalyst from waste lithium batteries by assisting acid leaching of spinach and application thereof. After mechanical ball milling of the waste lithium battery positive material and waste spinach, the mixture is placed in an oxalic acid solution. After the positive material is completely dissolved, simple solid-liquid separation is performed to simultaneously achieve complete dissolution of lithium and selective precipitation of transition metals. The obtained precipitate is air calcined to directly convert into a carbon-doped metal catalyst, which is used for removal of various flotation reagents in mineral processing wastewater.

[0006] The technical scheme of the present application is as follows: waste lithium battery positive powder and dry waste spinach powder are pre-mixed by ball milling, the mixture is leached by an oxalic acid solution, and the solid leaching residue is in-situ low-temperature calcined to obtain a carbon-doped metal catalyst in one step. The specific steps are as follows:

[0007] Step A1, pre-mixing;

[0008] Step A1.1, the waste spinach leaves are washed, dried and ground into powder, and are ready for use;

[0009] Step A1.2, the positive plate of the waste lithium battery is air calcined at 550 DEG C for 4h to remove PVDF, and the aluminum foil is peeled off to obtain waste lithium battery positive powder;

[0010] Step A1.3, the waste lithium battery powder and the waste spinach powder are mixed uniformly at a predetermined mass ratio, and the mixture is put into a planetary ball mill for ball milling;

[0011] Step A2, the ball milling product in step A1 is placed in an oxalic acid solution for heating leaching until the waste lithium battery positive powder is completely dissolved to form a new solid-liquid mixed system;

[0012] Step A3, the solid-liquid mixed system after leaching in step A2 is filtered and separated to obtain a yellow lithium-containing leaching solution and a leaching residue.

[0013] Step A4, the leaching residue in step A3 is dried, ground, air calcined and naturally cooled to obtain a black carbon-doped metal catalyst.

[0014] Specifically, the waste lithium battery positive powder in step A1.2 includes waste lithium cobaltate, a mixture of waste lithium cobaltate and waste lithium manganate, and waste NCM523, and the mass ratio of waste lithium cobaltate and waste lithium manganate is 1:1; the mass ratio of the waste spinach powder and the waste lithium battery positive powder in step A1.3 is 0.6:1;

[0015] Specifically, the concentration of oxalic acid in step A2 is 0.8 mol / L, the leaching temperature is 100 DEG C, and the leaching time is 3h;

[0016] Specifically, the calcination temperature in step A4 is 300℃, the calcination time is 2h, and the heating rate is 2℃ / min.

[0017] Specifically, step A4 prepares carbon-doped single-metal, double-metal and multi-metal catalysts by calcination and leaching, respectively.

[0018] Further, the calculation formula of the leaching rate of metal elements in the positive electrode material is:

[0019]

[0020] In the formula, η i represents the leaching rate of metal (i represents Li / Ni / Co / Mn), C i (mg / L) represents the concentration of metal ions, V(L) represents the volume of the leaching solution, m i (mg) and w i respectively represent the mass of the positive electrode material and the mass proportion of the metal.

[0021] The separation ratio ε of lithium and transition metal in the leaching solution is calculated according to the following formula:

[0022]

[0023] In the formula, η Li represents the leaching rate of lithium, η Co / Mn / Ni represents the leaching rate of cobalt, manganese or nickel.

[0024] The application method is: after mixing the carbon-doped metal catalyst in the organic pollutant solution, adding PMS for catalytic reaction.

[0025] During the test, first configure a certain concentration of organic pollutant solution, then mix the catalyst and the pollutant solution, and magnetically stir for 30min to investigate the adsorption effect. Then add PMS to start the catalytic reaction, take 2mL of the suspension at regular intervals, and quench with 15μL of methanol. After centrifugation, the supernatant is used to determine the concentration of pollutants in the solution by ultraviolet spectrophotometer, and the adsorption and degradation efficiency of organic pollutants is calculated.

[0026] The method comprises the following steps:

[0027] Step B1, 50mL of butyl xanthate, butylamine black and ethylthiourea solutions with concentrations of 100mg / L, 160mg / L and 134mg / L respectively are configured, and the catalyst is added to each pollutant solution at a solid-liquid ratio of 0.4g / L, and the adsorption-desorption balance is reached after magnetic stirring for 30min;

[0028] The adsorption rate A of the pollutant is calculated according to formula (1):

[0029]

[0030] wherein, C0and C e respectively represent the concentration of pollutants in the initial solution and the solution at the adsorption equilibrium (mg / L).

[0031] Step B2, continue to add 0.8 mM PMS (persulfate) to the reaction system to start the catalytic reaction.

[0032] Step B3, during the degradation process, 2 mL of the solution is periodically sampled, and then 15 μL of methanol is injected into the water sample to terminate the oxidation reaction. The supernatant is obtained after using a high-speed centrifuge to centrifuge the sample solution at 4500 rpm for 3 min, and immediately determine the concentration of pollutants in the supernatant using a UV-vis spectrophotometer (UV-vis). The concentrations of xanthate, black drug and ethion are determined using UV-vis at the maximum absorption wavelengths of 301 nm, 230 nm and 282 nm, respectively.

[0033] The degradation efficiency (η t ) of the pollutants is calculated according to formula (2):

[0034]

[0035] wherein, C t and C0respectively represent the concentration of pollutants in the solution at a certain time point and the initial solution (mg / L).

[0036] The present application realizes one-step recovery and high-value conversion of transition metals in waste lithium batteries by spinach assisted acid leaching and direct roasting of leaching residue, avoids the strong acid dependence and multi-stage separation steps of traditional lithium battery recovery process, and provides a green approach for lithium battery recovery and water treatment catalyst co-production; compared with the prior art, the beneficial effects of the present application are:

[0037] Firstly, the present application realizes the dissolution of all components of the positive material of the waste lithium battery under mild conditions by synergistic leaching of waste spinach and oxalic acid, and preferentially releases lithium in a soluble state to the liquid phase, while nickel / cobalt / manganese is directly enriched in the solid phase in the form of insoluble salt. After solid-liquid separation, high-concentration lithium leaching solution and transition metal precipitation residue can be obtained simultaneously, without the need for acid concentration adjustment, multi-stage extraction or step-by-step precipitation and other metal separation steps in the traditional process.

[0038] Secondly, the present application uses the natural active ingredients in waste spinach and the thermal conversion products of cellulose as green reducing agents, and combines degradable oxalic acid to construct a green and safe leaching system. The waste liquid after reaction can be directly biologically treated, avoiding the storage, transportation and operation risks of strong acid and unstable reducing agents, and greatly reducing the safety management cost.

[0039] Thirdly, the carbon-doped metal catalyst is constructed by directly roasting the leaching residue recovered from the waste lithium battery, and one-step conversion of the positive electrode of the waste lithium battery to a high-performance metal catalyst is directly realized, and the raw material and preparation cost of the catalyst is effectively reduced.

[0040] Fourthly, the co-precipitation system of spinach and metal oxalate is constructed to provide conditions for in-situ doping of carbon and transition metals in the metal catalyst. The functional groups and porous structure in the biochar can promote the adsorption of PMS, and the multi-metal active components can synergistically activate PMS, thereby greatly improving the degradation performance of the catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 A flow chart for preparing a carbon-doped metal catalyst by directly recovering the positive electrode of a waste lithium battery with spinach-assisted acid leaching;

[0042] Figure 2 The pictures of the leaching solution and the leaching residue after the waste lithium cobaltate is separately leached (a), the waste lithium cobaltate and the waste lithium manganate are mixed and leached (b), and the waste NCM523 is separately leached (c) using the spinach-oxalic acid combination;

[0043] Figure 3 The XRD patterns of the leaching residue after the waste lithium cobaltate is separately leached and the carbon-doped cobalt-based catalyst Co3O4@C;

[0044] Figure 4 The degradation efficiency of several floatation reagents by the carbon-doped cobalt-based single metal catalyst (a), the carbon-doped cobalt-manganese bimetallic catalyst (b), and the carbon-doped nickel-cobalt-manganese multi-metal catalyst (c). DETAILED DESCRIPTION

[0045] In order to clearly illustrate the technical features of the present application, the present application will be described in detail below with specific embodiments, and in conjunction with the accompanying drawings.

[0046] The leaching and recovery of metals in the positive electrode of the waste lithium battery are as follows:

[0047] The spinach was washed and dried, then ground into powder. The waste lithium cobalt oxide, waste lithium manganese oxide and waste NCM523 positive electrode sheet were air calcined at 550-600°C for 4h to remove PVDF, and the aluminum foil was peeled off to obtain waste lithium cobalt oxide, waste lithium manganese oxide and waste NCM523 positive electrode powder. 0.3g of spinach powder and waste positive electrode powder (0.5g of waste lithium cobalt oxide, 0.25g of a mixture of waste lithium cobalt oxide and lithium manganese oxide, and 0.25g of waste lithium manganese oxide, 0.5g of waste NCM523) were mixed and placed in a agate ball mill jar, and ball milled at a speed of 500r / min for 2h to form a black mixed powder; the black powder was placed in a sealed container, 20mL of 0.8mol / L oxalic acid solution was added, and leaching was carried out at 100°C for 3h. After the reaction was completed, solid-liquid separation was carried out to obtain a lithium-containing leaching solution and a transition metal leaching residue.

[0048] The ICP-OES test results of the leaching solution of the waste lithium cobalt oxide positive electrode material are shown in Table 1. After leaching with 0.8mol / L oxalic acid, the cobalt content in the leaching solution is very low due to the coordination precipitation of cobalt with oxalic acid during the leaching process, and the leaching rate of cobalt is only 0.16%, and the separation ratio of Li and Co is as high as 615. Figure 2 a and Figure 3 The pictures of the leaching solution and the leaching residue after leaching of the waste lithium cobalt oxide are clearly shown, and the XRD patterns thereof can be seen. The XRD of the leaching residue matches the cobalt oxalate completely, and no lithium component is detected in the leaching residue, indicating that the lithium and cobalt in the waste lithium cobalt oxide after leaching have been completely separated into liquid and solid phases; Figure 2 b and c respectively show the leaching solution and the leaching residue of the mixture of waste lithium cobalt oxide and lithium manganese oxide and waste NCM523 using spinach-oxalic acid combined leaching, similar to the results of leaching waste lithium cobalt oxide, yellow lithium-containing leaching solution and transition metal leaching residue are obtained; Figure 1 The flowchart of spinach-oxalic acid leaching of waste lithium battery is shown.

[0049] Table 1 Leaching efficiency and separation coefficient of metal elements in the leaching solution.

[0050] Oxalic acid concentration Li ]]> ​ Co ]]> ​ ε 0.8 mol / L 99.30％ 0.16％ 615.15

[0051] The preparation of single metal / dual metal / multi-metal catalysts is as follows:

[0052] The leaching residues of the above waste lithium cobalt oxide, mixture of waste lithium cobalt oxide and lithium manganese oxide, and waste NCM523 were dried at 45°C for 12h, then ground into powder. 0.5g of the above powder was placed in a muffle furnace and air calcined at 300°C with a heating rate of 2°C / min for 2h, and then taken out after natural cooling to room temperature, to obtain carbon-doped cobalt-based single metal catalyst Co3O4@C, carbon-doped cobalt-manganese dual metal catalyst and carbon-doped nickel-cobalt-manganese multi-metal catalyst.

[0053] Figure 1 The preparation process of carbon-doped metal catalyst is shown. Figure 3 The XRD pattern of carbon-doped cobalt-based single-metal catalyst Co3O4@C is clearly shown. The peak position and peak intensity of the characteristic peaks in Co3O4@C are highly consistent with Co3O4, indicating that the main component of Co3O4@C is Co3O4, which is also the key active species in the catalytic process. Due to the loss of spinach during the leaching and calcination processes, the carbon content of the material is relatively low, so the carbon peak of Co3O4@C is not shown in the XRD pattern.

[0054] The specific implementation process of the catalyst degrading black medicine is as follows:

[0055] All degradation experiments were carried out in conical flasks containing 50 mL of butyl xanthate (100 mg / L), ammonium black medicine (160 mg / L), and ethion (134 mg / L) solutions. To each pollutant solution, 0.02 g of catalyst (0.4 g / L) was added, and magnetic stirring was performed for 30 min to achieve adsorption-desorption equilibrium. Then, 0.0123 g of PMS (0.8 mM) was added to the reaction system to initiate catalysis, and 2 mL of periodic sampling was performed on the solution, followed by the injection of 15 μL of methanol into the water sample to terminate the oxidation reaction. A high-speed centrifuge was used to centrifuge the sample solution at 4500 rpm for 3 min, and immediately the concentration of pollutants in the supernatant was determined using a UV-vis spectrophotometer (UV-vis). Among them, the concentrations of xanthate, black medicine, and ethion were determined at the maximum absorption wavelengths of 301 nm, 230 nm, and 282 nm, respectively.

[0056] Figure 4 The degradation efficiency of carbon-doped cobalt-based single-metal catalyst Co3O4@C (a), carbon-doped cobalt-manganese bimetallic catalyst (b), and carbon-doped nickel-cobalt-manganese multi-metal catalyst (c) on each pollutant with time is shown respectively. It can be seen that:

[0057] The degradation efficiency of carbon-doped cobalt-based single-metal catalyst Co3O4@C on the three flotation reagents is in the order of butyl xanthate BX (99.5%, of which 51% is adsorption) > black medicine ADD (96.7%) > ethion DDTC (78%).

[0058] The degradation efficiency of carbon-doped cobalt-manganese bimetallic catalyst on the three flotation reagents is in the order of butyl xanthate BX (99.7%, of which 84% is adsorption) > black medicine ADD (93.1%) > ethion DDTC (89.9%).

[0059] The degradation efficiency of carbon-doped nickel-cobalt-manganese multi-metal catalyst on the three flotation reagents is in the order of butyl xanthate BX (99.9%, of which 84% is adsorption) > ethion DDTC (95.1%) > black medicine ADD (90%).

[0060] It can be seen that the oxygen-containing functional groups and porous structure in the biochar can promote the adsorption of pollutants, and the combination of the multi-metal active component and the synergistic activation of PMS greatly improves the degradation efficiency of the pollutants. The carbon-doped metal catalyst prepared in the case has a significant advantage in the degradation of butyl xanthate BX, and the degradation efficiency of sodium cyanide ADD is also more than 90%. Among them, the carbon-doped cobalt-manganese bimetallic and nickel-cobalt-manganese multi-metal catalysts have a degradation efficiency close to and more than 90% for ethylthiuram DDTC, which is very suitable for removing various flotation reagents in mineral processing wastewater, and can realize efficient degradation of various organic flotation reagents such as ammonium black drug, butyl xanthate and ethylthiuram.

[0061] The present application has many specific implementation ways, and the above description is only the preferred embodiment of the present application. It should be pointed out that for ordinary skilled persons in the art, some improvements can be made without departing from the principles of the present application, and these improvements should also be regarded as the protection scope of the present application.

Claims

1. A method for preparing carbon-doped metal catalysts from waste lithium batteries by acid leaching with spinach as an auxiliary agent, characterized in that, Waste lithium battery cathode powder and dried waste spinach powder were premixed by ball milling. After leaching the mixture with oxalic acid solution, the solid leaching residue was subjected to in-situ low-temperature calcination to obtain a carbon-doped metal catalyst in one step. The specific steps are as follows: Step A1: Premixing; Step A1.1: Wash and dry the waste spinach leaves, then grind them into powder for later use; Step A1.2: The positive electrode of the waste lithium battery is air-calcined at 550℃ for 4 hours to remove PVDF. After peeling off the aluminum foil, waste lithium battery positive electrode powder is obtained. Step A1.3: Mix waste lithium battery powder and waste spinach powder evenly at a predetermined mass ratio, and put the mixture into a planetary ball mill for ball milling; Step A2: Place the ball milling product from step A1 in an oxalic acid solution and heat to leach until the waste lithium battery cathode powder is completely dissolved, forming a new solid-liquid mixture system. Step A3: Filter and separate the solid-liquid mixture after leaching in step A2 to obtain a yellow lithium-containing leachate and leaching residue. Step A4: After drying and grinding the leaching residue from step A3, the residue is calcined in air and then naturally cooled to obtain a black carbon-doped metal catalyst.

2. The method for preparing carbon-doped metal catalysts from waste lithium batteries by spinach-assisted acid leaching according to claim 1, characterized in that, The waste lithium battery cathode powder mentioned in step A1.2 includes waste lithium cobalt oxide, a mixed cathode of waste lithium cobalt oxide and lithium manganese oxide, and waste NCM523, wherein the mass ratio of waste lithium cobalt oxide to waste lithium manganese oxide is 1:1; the mass ratio of waste spinach powder to waste lithium battery cathode powder in step A1.3 is 0.6:

1.

3. The method for preparing carbon-doped metal catalysts from waste lithium batteries using spinach-assisted acid leaching according to claim 1, characterized in that, The oxalic acid concentration in step A2 is 0.8 mol / L, the leaching temperature is 100℃, and the leaching time is 3 h.

4. The method for preparing carbon-doped metal catalysts from waste lithium batteries by acid leaching with spinach as described in claim 1, characterized in that, The calcination temperature in step A4 is 300℃, the calcination time is 2h, and the heating rate is 2℃ / min.

5. The method for preparing carbon-doped metal catalysts from waste lithium batteries by acid leaching with spinach as described in claim 1, characterized in that, Step A4 involves preparing carbon-doped monometallic, bimetallic, and polymetallic catalysts through leaching and calcination.

6. A method for applying the carbon-doped metal catalyst prepared according to claim 1, characterized in that, A carbon-doped metal catalyst is mixed with an organic pollutant solution, followed by the addition of persulfate (PMS) to catalyze the reaction; the steps include: Step B1: Prepare an organic pollutant solution including butyl xanthate, butylammonium black powder or ethyl thiocyanate, add carbon-doped metal catalyst according to a predetermined solid-liquid ratio and stir magnetically for 30 min to achieve adsorption-desorption equilibrium; Step B2: Add a predetermined amount of PMS to the solution from Step B1 to initiate the catalytic reaction; Step B3: Take periodic samples of the reaction solution from step B2, and then inject methanol into the water sample to terminate the oxidation reaction.

7. The application method of spinach-assisted acid leaching for the recovery of waste lithium batteries and the preparation of carbon-doped metal catalysts according to claim 6, characterized in that, In step B1, the concentrations of butyl xanthate, butylammonium black powder, and ethyl thiocyanate in the organic pollutants are 100 mg / L, 160 mg / L, and 134 mg / L, respectively; the solid-liquid ratio of the carbon-doped metal catalyst and the pollutant solution is 0.4 g / L.

8. The application method of spinach-assisted acid leaching for the recovery of waste lithium batteries and the preparation of carbon-doped metal catalysts according to claim 6, characterized in that, In step B2, the PMS concentration is 0.8 mM.

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