A method for recovering a battery cathode material from sludge

Abstract

This invention relates to the field of sludge resource utilization technology, and more particularly to a method for recovering battery cathode materials from sludge. The technical solution provided by this invention involves incinerating dried sludge to obtain sludge incineration ash, then leaching the ash using an organic reducing acid, followed by solid-liquid separation to obtain a phosphorus-containing supernatant. The pH of the phosphorus-containing supernatant is then adjusted, and a Li source, Fe source, Mn source, template agent, and carbon source are added to the pH-adjusted supernatant to obtain a mixed solution. This mixed solution is then subjected to hydrothermal synthesis to obtain the battery cathode material. Therefore, the above technical solution involves direct hydrothermal synthesis of the pH-adjusted mixed solution, thus shortening the process flow for preparing battery cathode materials.

Description

Technical Field

[0001] This invention relates to the field of sludge resource utilization technology, and in particular to a method for recovering battery cathode materials from sludge. Background Technology

[0002] Pollutants and nutrients in wastewater aggregate under the action of rapidly multiplying bacteria and chemical agents, eventually forming sludge. With the rapid development of industries such as new energy vehicles and energy storage batteries, the production of cathode materials (such as lithium iron manganese phosphate) is also constantly increasing, leading to a greater demand for its raw materials (such as phosphorus).

[0003] In related technologies, the main method for recovering phosphorus from sludge and preparing battery cathode materials is a multi-stage synthesis method, but this method has a long process flow.

[0004] Therefore, there is an urgent need for a method to recover battery cathode materials from sludge to solve this technical problem. Summary of the Invention

[0005] This invention provides a method for recovering battery cathode materials from sludge, which can shorten the process flow for preparing battery cathode materials.

[0006] This invention provides a method for recovering battery cathode materials from sludge, comprising:

[0007] The dried sludge is incinerated to obtain sludge incineration ash;

[0008] The sludge incineration ash was leached using an organic reducing acid, and a phosphorus-containing supernatant was obtained after solid-liquid separation.

[0009] The pH of the phosphorus-containing supernatant was adjusted, and a Li source, an Fe source, a Mn source, a template agent, and a carbon source were added to the pH-adjusted phosphorus-containing supernatant to obtain a mixed solution.

[0010] The mixed solution was subjected to hydrothermal synthesis to obtain the battery cathode material.

[0011] As can be seen from the above scheme, the method for recovering battery cathode materials from sludge provided by the present invention involves incinerating dried sludge to obtain sludge incineration ash, leaching the ash with an organic reducing acid, and obtaining a phosphorus-containing supernatant after solid-liquid separation. The pH of the phosphorus-containing supernatant is then adjusted, and a Li source, Fe source, Mn source, template agent, and carbon source are added to the pH-adjusted phosphorus-containing supernatant to obtain a mixed solution. This mixed solution is then subjected to hydrothermal synthesis to obtain the battery cathode material. Therefore, the above technical solution involves direct hydrothermal synthesis of the pH-adjusted mixed solution, thus shortening the process flow for preparing battery cathode materials. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of a method for recovering battery cathode materials from sludge, provided in an embodiment of the present invention. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Please see Figure 1 One embodiment of the present invention provides a method for recovering battery cathode materials from sludge, the method comprising:

[0016] Step 100: Incinerate the dried sludge to obtain sludge incineration ash;

[0017] Step 102: Leach the sludge incineration ash using organic reducing acid, and obtain a phosphorus-containing supernatant after solid-liquid separation;

[0018] Step 104: Adjust the pH of the phosphorus-containing supernatant, and add Li source, Fe source, Mn source, template agent and carbon source to the pH-adjusted phosphorus-containing supernatant to obtain a mixed solution;

[0019] Step 106: Perform hydrothermal synthesis on the mixed solution to obtain the battery cathode material.

[0020] In this embodiment, dried sludge is incinerated to obtain sludge incineration ash. The ash is then leached using an organic reducing acid, followed by solid-liquid separation to obtain a phosphorus-containing supernatant. The pH of the phosphorus-containing supernatant is then adjusted, and a Li source, Fe source, Mn source, template agent, and carbon source are added to the pH-adjusted supernatant to obtain a mixed solution. Finally, the mixed solution is subjected to hydrothermal synthesis to obtain the battery cathode material. Therefore, the above technical solution involves direct hydrothermal synthesis of the pH-adjusted mixed solution, thus shortening the process flow for preparing battery cathode materials.

[0021] In some implementations, the incineration temperature is 750–900°C to ensure the incineration effect of the dried sludge.

[0022] In one embodiment of the present invention, the organic reducing acid includes at least one selected from oxalic acid, ascorbic acid, citric acid, formic acid, glyoxylic acid, and salicylic acid.

[0023] In some embodiments, the solid-liquid ratio of sludge incineration ash to organic reducing acid can be 1:50 to 1:200, the leaching time can be 2 to 4 hours, and the tumbling and shaking speed can be 60 to 120 rpm, to ensure the leaching effect of organic reducing acid on phosphorus in sludge incineration ash.

[0024] In this embodiment, the organic reducing acid can better leach phosphorus from the sludge incineration ash, and at the same time, the reducing property of the organic reducing acid can prevent the ferrous salts in the sludge incineration ash and the ferrous iron in the battery cathode material from being oxidized to ferric iron.

[0025] In related technologies, some leachates typically use high-concentration inorganic acids such as sulfuric acid and nitric acid to leach phosphorus due to their high acidity. However, the preparation of battery cathode materials requires a neutral environment, necessitating the addition of other reagents to achieve neutralization, resulting in significant reagent consumption. In contrast, the organic reducing acid in this embodiment not only provides an acidic environment for phosphorus leaching but also utilizes the reducing properties of the organic reducing acid and the chelating properties of organic acid anions to provide additional driving force for phosphorus leaching from sludge incineration ash.

[0026] Furthermore, Fe / Al bound phosphorus (usually FePO4 or AlPO4) constitutes a significant portion of phosphorus in sludge incineration ash. Organic reducing acids can reduce insoluble FePO4 to more soluble ferrous salts through their own reducing properties, thereby releasing phosphorus in the form of phosphate or hydrogen phosphate ions. This process can be summarized as "reduction dissolution." Simultaneously, the organic acid anions of organic reducing acids, such as C2O4... 2- Citrate ions also have a strong chelating coordination ability, capable of displacing Al from AlPO4 through chelation to generate Al. - Organic acid ligands release phosphorus into the liquid phase; this process can be summarized as "coordinate dissolution." Due to the combined effects of acidity, reducing properties, and chelating properties, organic reducing acids exhibit better phosphorus leaching performance than inorganic acids, leaching more phosphorus at lower concentrations.

[0027] In one embodiment of the present invention, the concentration of the organic reducing acid is 0.04–0.5 mol / L. At this concentration, the leaching effect of the organic reducing acid on phosphorus can be guaranteed.

[0028] In one embodiment of the present invention, the pH of the phosphorus-containing supernatant is adjusted using ammonia.

[0029] In this embodiment, by adding ammonia to the phosphorus-containing supernatant, the effect of not introducing impurities during pH adjustment can be achieved. This is because ammonia will generate ammonia gas and be discharged during subsequent hydrothermal synthesis.

[0030] In one embodiment of the present invention, the pH of the phosphorus-containing supernatant after pH adjustment is 5 to 8.

[0031] In this embodiment, adjusting the pH of the phosphorus-containing supernatant to 5-8 not only helps remove Fe(III) / Al / Ca / Mg / heavy metal impurities that precipitate simultaneously during hydrothermal synthesis, but also retains soluble metal ions (such as Na+) in the leachate. + K + ).

[0032] Typically, battery cathode materials require further carbon coating before use. Currently, the commonly used carbon coating methods are hydrothermal and calcination. The former involves adding a carbon source simultaneously during Li replenishment, which directly yields carbon-coated cathode materials, but the carbon adhesion effect is limited. The latter involves calcining the battery-grade cathode material and carbon source in a high-temperature reducing gaseous environment after Li replenishment. While this method can improve the carbon coating effect to some extent, the distributed steps further lengthen the processing flow, and the uniformity of carbon coating is not as good as the hydrothermal method.

[0033] However, in this embodiment, soluble metal salts (i.e., the retained sodium and potassium salts) can enhance the reactivity of -OH, -COOH, and -COC- bonds on the carbon source during the hydrothermal process through bridging, altering charge density, or direct catalytic reactions. This promotes deoxygenation polymerization, decarboxylation polymerization, and aromatization between carbon sources, as well as condensation polymerization within the carbon source. The enhanced reactions significantly improve the carbon coating degree on the surface of the battery cathode material compared to traditional hydrothermal processes, thereby improving the conductivity and ion transport capacity of the battery cathode material.

[0034] In some embodiments, the adjusted solution is stirred at a speed of 1 to 200 rpm for a duration of 10 to 240 min to ensure thorough mixing.

[0035] In some implementations, the pH-adjusted phosphorus-containing supernatant can be filtered using a filter head such as 0.22 μm to remove any remaining solid particles.

[0036] In one embodiment of the present invention, the phosphorus-containing supernatant is used for the cyclic leaching of new sludge incineration ash.

[0037] In this embodiment, the phosphorus in the phosphorus-containing supernatant is recycled and leached into the sludge incineration ash, which reduces reagent consumption.

[0038] In one embodiment of the present invention, the hydrothermal synthesis reaction temperature is 120-250°C and the reaction time is 1-24 h.

[0039] In one embodiment of the present invention, the Li source includes at least one of LiOH, LiCl, Li2CO3 and Li2SO4.

[0040] In one embodiment of the present invention, the Fe source includes at least one of FeSO4, FeCl2, Fe(NO3)2 and FeC2O4.

[0041] In one embodiment of the present invention, the Mn source includes at least one of MnSO4, MnCl2, Mn(NO3)2 and MnC2O4.

[0042] In one embodiment of the present invention, the template agent includes at least one selected from polyvinyl alcohol, ethylene glycol, hexadecyltrimethylammonium bromide, and sodium dodecylbenzenesulfonate.

[0043] In one embodiment of the present invention, the carbon source includes at least one selected from sucrose, glucose, furfuryl alcohol, starch, graphene, carbon nanotubes, carbon black, and acetylene black.

[0044] In this embodiment, when the Li source is a soluble lithium salt and its hydrate, the Fe source is a soluble iron salt and its hydrate, and the Mn source is a soluble manganese salt and its hydrate, the mixed solution can have higher ionic conductivity, better thermal stability, and better electrochemical stability.

[0045] In this embodiment, the template agent forms steric hindrance between the battery cathode material particles through coordination during the hydrothermal synthesis process, thereby preventing the battery cathode material particles from becoming too large or sticking together, thus playing a role in regulating the morphology and uniformity of the battery cathode material particles.

[0046] In this embodiment, during the hydrothermal synthesis process, the carbon source generates a carbon-rich structure through the polymerization reaction between organic matter, and then attaches to the surface of the battery cathode material through the bonding reaction between the organic and inorganic material surfaces, ultimately forming a dense carbon layer to increase the conductivity and Li ion transport efficiency of the battery cathode material.

[0047] In one embodiment of the present invention, when the Fe source is an inorganic iron salt and the Mn source is an inorganic manganese salt, the molar ratio of P element in the Li source, Fe source, Mn source and phosphorus-containing supernatant is 3:x:(1-x):1, where x is greater than 0 and less than 1.

[0048] In one embodiment of the present invention, when the Fe source is an organic acid iron salt and the Mn source is an organic acid manganese salt, the molar ratio of P element in the Li source, Fe source, Mn source and phosphorus-containing supernatant is 1:x:(1-x):1, where x is greater than 0 and less than 1.

[0049] In one embodiment of the present invention, the amount of carbon source added is 1 to 10% of the total mass of the battery cathode material.

[0050] In one embodiment of the present invention, the amount of template agent added is 1 to 25% of the total mass of the battery cathode material.

[0051] In some implementations, the total mass is the theoretical yield of the battery cathode material, calculated using the following formula:

[0052] Total mass = (157 + x) * molar amount of phosphorus in the liquid phase.

[0053] In one embodiment of the present invention, step 106 may specifically include:

[0054] The mixed solution was subjected to hydrothermal synthesis to obtain the hydrothermal synthesis product;

[0055] The hydrothermal synthesis product was subjected to solid-liquid separation to obtain a solid product;

[0056] The solid product was washed alternately with deionized water and ethanol solution, and then freeze-dried.

[0057] The freeze-dried solid product was calcined under an inert atmosphere to obtain the battery cathode material.

[0058] In this embodiment, vacuum filtration can be used to separate the hydrothermal synthesis products into solid and liquid components, so as to achieve better separation of the solid and liquid components of the hydrothermal synthesis products.

[0059] Alternating washing can remove impurity ions from the solid product, and freeze-drying the washed solid product can remove moisture from the solid product.

[0060] In some embodiments, the calcination temperature can be 500–800°C to ensure that the freeze-dried solid product is fully calcined, thereby obtaining the battery cathode material.

[0061] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering battery cathode materials from sludge, characterized in that, include: The dried sludge is incinerated to obtain sludge incineration ash; The sludge incineration ash was leached using an organic reducing acid, and a phosphorus-containing supernatant was obtained after solid-liquid separation. The pH of the phosphorus-containing supernatant was adjusted, and a Li source, an Fe source, a Mn source, a template agent, and a carbon source were added to the pH-adjusted phosphorus-containing supernatant to obtain a mixed solution. The mixed solution was subjected to hydrothermal synthesis to obtain the battery cathode material; The carbon source includes at least one of sucrose, glucose, furfuryl alcohol, and starch.

2. The method according to claim 1, characterized in that, The organic reducing acid includes at least one of oxalic acid, ascorbic acid, citric acid, formic acid, glyoxylic acid, and salicylic acid.

3. The method according to claim 1, characterized in that, The concentration of the organic reducing acid is 0.04~0.5 mol / L.

4. The method according to claim 1, characterized in that, The phosphorus-containing supernatant was pH-adjusted using ammonia.

5. The method according to claim 1, characterized in that, The pH of the phosphorus-containing supernatant after pH adjustment is 5-8.

6. The method according to claim 1, characterized in that, The phosphorus-containing supernatant is used for the cyclic leaching of new sludge incineration ash.

7. The method according to claim 1, characterized in that, The hydrothermal synthesis reaction temperature is 120~250℃, and the reaction time is 0~24h.

8. The method according to claim 1, characterized in that, The Li source includes at least one of LiOH, LiCl, Li₂CO₃, and Li₂SO₄; and / or, The Fe source includes at least one selected from FeSO4, FeCl2, Fe(NO3)2, and FeC2O4; and / or, The Mn source includes at least one selected from MnSO4, MnCl2, Mn(NO3)2, and MnC2O4; and / or, The template agent includes at least one of polyvinyl alcohol, ethylene glycol, hexadecyltrimethylammonium bromide, and sodium dodecylbenzenesulfonate.

9. The method according to claim 1, characterized in that, When the Fe source is an inorganic iron salt and the Mn source is an inorganic manganese salt, the molar ratio of P in the Li source, the Fe source, the Mn source, and the phosphorus-containing supernatant is 3:x:(1-x):1, where x is greater than 0 and less than 1; and / or, When the Fe source is an organic iron salt and the Mn source is an organic manganese salt, the molar ratio of P in the Li source, the Fe source, the Mn source, and the phosphorus-containing supernatant is 1:x:(1-x):1, where x is greater than 0 and less than 1; and / or, The amount of carbon source added is 1-10% of the total mass of the battery cathode material; The amount of template agent added is 1 to 25% of the total mass of the battery cathode material.

10. The method according to any one of claims 1-9, characterized in that, The hydrothermal synthesis of the mixed solution to obtain the battery cathode material includes: The mixed solution was subjected to hydrothermal synthesis to obtain the hydrothermal synthesis product; The hydrothermal synthesis product was subjected to solid-liquid separation to obtain a solid product; The solid product was washed alternately with deionized water and ethanol solution, and the washed solid product was freeze-dried. The freeze-dried solid product was calcined under an inert atmosphere to obtain the battery cathode material.

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