A method for preparing lithium iron phosphate precursor from high-iron red mud

Abstract

The present application relates to a method for preparing a lithium iron phosphate precursor from high-iron red mud, which belongs to the technical field of comprehensive utilization of industrial solid wastes; the method comprises: mixing high-iron red mud with acid solution, and then leaching to obtain red mud leachate; mixing red mud leachate with phosphate, and then performing a first homogeneous reaction to obtain a primary homogeneous solution; adjusting the pH value and iron-phosphorus ratio of the primary homogeneous solution, and then performing a second homogeneous reaction to obtain a secondary homogeneous solution; precipitating the secondary homogeneous solution to obtain a lithium iron phosphate precursor; the method separates dihydrate iron phosphate through the characteristics of various substances in phosphate, and does not add exogenous substances such as extractants, inducers, separation agents, and metal capture agents, thereby reducing the amount of added components and reducing the cost. At the same time, the use of red mud to prepare dihydrate iron phosphate shortens the existing process flow, reduces the cost of raw materials, and realizes the high-value utilization of red mud, while also opening up new ways to solve the problem of solid hazardous waste disposal and utilization in the aluminum industry.

Description

Technical Field

[0001] The present application relates to the field of comprehensive utilization of industrial solid waste, and in particular to a method for preparing a lithium iron phosphate precursor from high-iron red mud. Background Art

[0002] Red mud is an industrial solid waste generated during the production of alumina. The iron oxide content is generally 10% to 60%, which is the main component of red mud. Therefore, iron is one of the metal elements in red mud that has recycling value. The iron minerals in red mud are mainly hematite, goethite, etc., which have weak magnetism. The usual magnetic separation method can only recover a small part of the iron minerals, while the strong magnetic separation and magnetic roasting methods have the characteristics of large investment and high energy consumption, especially for high-iron red mud mainly composed of goethite, which is difficult to control during magnetic roasting. In recent years, the output of alumina enterprises in Shandong, Guangxi, Yunnan and other places that use high-iron bauxite as raw materials accounts for nearly 50%, and the proportion of high-iron red mud output will continue to rise. The recovery and high-value utilization of iron in high-iron red mud are of great significance to the sustainable development of alumina enterprises.

[0003] At the same time, the market demand for new energy materials continues to expand, and iron phosphate, as a precursor of new energy material lithium iron phosphate, is in short supply. There is currently an imbalance between supply and demand, and there is a huge market gap. The rich iron element in red mud can be used as a raw material for the preparation of iron phosphate. Its reserve advantage and cost advantage provide favorable conditions for red mud to be used as a source of raw material for new energy materials, and it is also the main way to achieve high added value utilization of red mud.

[0004] At present, the common method for preparing ferric phosphate dihydrate from red mud is to use concentrated acid leaching to convert iron compounds into trivalent iron ions and divalent iron ions to react with phosphoric acid to form ferric phosphate dihydrate precipitate. In the precipitation process, concentrated acid leaching is used, and additives and extractants are added through multiple steps to achieve solid-liquid separation to obtain the final product. The process is complicated and lacks consideration of the characteristics of the iron phosphate material. Summary of the invention

[0005] The present application provides a method for preparing a lithium iron phosphate precursor from high-iron red mud, so as to improve the problem that exogenous substances need to be added when preparing iron phosphate dihydrate from red mud.

[0006] In a first aspect, the present application provides a method for preparing a lithium iron phosphate precursor from high-iron red mud, the method comprising:

[0007] The high iron red mud and the acid solution are mixed and then leached to obtain the red mud leaching solution;

[0008] The red mud leachate and phosphate are mixed, and then subjected to a first homogeneous reaction to obtain a primary homogeneous solution;

[0009] The pH value and the iron-phosphorus ratio of the primary homogeneous solution are adjusted, and then a second homogeneous reaction is performed to obtain a secondary homogeneous solution;

[0010] The secondary homogeneous solution is precipitated to obtain a lithium iron phosphate precursor.

[0011] As an optional embodiment, the acid solution includes hydrochloric acid;

[0012] Optionally, the mass concentration of the hydrochloric acid is 2.5-5.4 mol / L.

[0013] As an optional embodiment, the leaching temperature is 110-230°C; and / or

[0014] The leaching pressure is 0.5-2MPa; and / or

[0015] The leaching time is 3-6h.

[0016] As an optional embodiment, the liquid-to-solid ratio of the mixture of the acid solution and the high-iron red mud is (7-15):1.

[0017] As an optional embodiment, in the first homogeneous reaction, the molar ratio of the phosphate to the aluminum ion in the solution is (3-5):1; and / or

[0018] The temperature of the first homogeneous reaction is 80-100°C.

[0019] As an optional embodiment, the phosphate includes normal salt and acid salt;

[0020] Optionally, the normal salt includes at least one of sodium phosphate and calcium phosphate;

[0021] Optionally, the acid salt includes at least one of sodium dihydrogen phosphate and ammonium dihydrogen phosphate.

[0022] As an optional embodiment, the pH value of the secondary homogeneous reaction is 1.8-6; and / or

[0023] The iron-to-phosphorus ratio of the secondary homogeneous reaction is 0.96-1.02; and / or

[0024] The reaction time of the secondary homogeneous reaction is 30-90 min.

[0025] As an optional implementation manner, the step of precipitating the secondary homogeneous solution to obtain a lithium iron phosphate precursor comprises:

[0026] The secondary homogeneous solution is naturally cooled to room temperature, then diluted with ice water, and then subjected to low-temperature precipitation and aging to obtain a lithium iron phosphate precursor.

[0027] As an optional implementation, in the ice water dilution, the mass amount of ice water used is 2%-8% of the mass of the secondary homogeneous solution.

[0028] As an optional embodiment, the temperature of the low-temperature precipitation aging is 1-9°C; and / or

[0029] The low-temperature precipitation aging time is 12-36h.

[0030] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0031] The method provided in the embodiment of the present application separates ferric phosphate dihydrate by using the characteristics of various phosphate substances, thereby eliminating the need to add a variety of exogenous substances such as extractants, inducers, separation agents, and metal capture agents, thereby reducing the added ingredients and greatly reducing the cost. At the same time, the use of red mud to prepare ferric phosphate dihydrate shortens the existing process flow, reduces the cost of raw materials, and realizes the high-value utilization of red mud, while also opening up new ways to solve the problem of solid hazardous waste disposal and utilization in the aluminum industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0033] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0034] Figure 1 A flowchart of a method provided in an embodiment of the present application;

[0035] Figure 2 A process diagram of the method provided in the embodiment of the present application;

[0036] Figure 3 This is a morphology diagram of iron phosphate dihydrate powder prepared by the method provided in the examples of the present application. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0038] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0039] like Figure 1 and Figure 2 As shown, the embodiment of the present application provides a method for preparing a lithium iron phosphate precursor from high-iron red mud, the method comprising:

[0040] S1. Mixing high iron red mud and acid solution in a certain proportion into slurry, pressurizing and heating for leaching, and obtaining red mud leaching solution after solid-liquid separation;

[0041] In some embodiments, the mass concentration of the hydrochloric acid solution is 2.5 mol / L-5.4 mol / L.

[0042] The reason for controlling the mass concentration of the hydrochloric acid solution to 2.5mol / L-5.4mol / L is that it is beneficial to the leaching of valuable element iron in red mud and the subsequent separation of iron phosphate. The disadvantage of too high a concentration is that inactive substances will also be leached, there are too many impurities, the acid concentration is too high, and the hazard is strong. The disadvantage of too low a concentration is that it is not conducive to the leaching of valuable element iron.

[0043] In some embodiments, the temperature ranges from 110°C to 230°C.

[0044] The reason for controlling the leaching temperature of the red mud slurry to 110℃-230℃ is that it is conducive to the leaching of the valuable element iron in the red mud. If the temperature is too high, it is dangerous and too much insoluble impurities will be dissolved. If the temperature is too low, less iron will be leached. Since the selected acid concentration is medium, high temperature leaching is required.

[0045] S2. mixing the red mud leachate and the phosphate and heating them for a homogeneous reaction to obtain a homogeneous solution;

[0046] In some embodiments, the phosphate includes normal salts and acid salts, the normal salts include sodium phosphate Na3PO4, calcium phosphate Ca3(PO4)2, the acid salts include dihydrogen salts such as sodium dihydrogen phosphate NaH2PO4, ammonium dihydrogen phosphate NH4H2PO4, but phosphoric acid is not used.

[0047] The reason for not using phosphoric acid is that phosphoric acid cannot directly react with trivalent iron ions to form a precipitate, and will further reduce its pH, making it too acidic.

[0048] In some embodiments, the molar ratio of the phosphate to the aluminum ions in the solution is 3-5:1.

[0049] The reason for controlling the molar ratio of phosphate to aluminum ion in the solution to 3-5:1 is that it is beneficial to the generation of aluminum phosphate and other phosphates for impurity removal and subsequent separation of iron phosphate. If the molar ratio is too large, it will lead to excessive impurities in the phosphate, and if it is too small, it will easily lead to excessive aluminum and other impurities, affecting the quality of iron phosphate.

[0050] In some embodiments, the heating temperature is 80°C-100°C.

[0051] Controlling the heating temperature to 80°C-100°C is beneficial for separation according to the different solubility characteristics of phosphates at different temperatures. Too low a value will cause iron phosphate and aluminum phosphate to precipitate together, while too high a value will cause water to evaporate too quickly and affect the concentration of the system. In addition, too high a temperature is unsafe and is not conducive to the safe reaction of the system.

[0052] S3. The pH and iron-phosphorus ratio of the primary homogeneous solution are regulated by phosphate, and after a certain reaction time, the solid-liquid is separated to obtain a secondary homogeneous solution;

[0053] In some embodiments, the phosphate is consistent with step 2.

[0054] Phosphates are used to control pH because phosphates have acidic and alkaline properties. Generally speaking, dihydrogen phosphate is acidic, while monohydrogen phosphate and normal salt are alkaline. Therefore, without adding exogenous substances, phosphates can be used to control the iron-phosphorus ratio and adjust the pH.

[0055] S4. After the secondary homogeneous solution is naturally cooled to room temperature, cold water is added to dilute it and precipitate it at low temperature for a period of time to obtain a precipitate after solid-liquid separation.

[0056] In some embodiments, the aging time is 12h-36h.

[0057] The reason for controlling the aging time to 12h-36h is that the iron phosphate reacts fully, and the newly prepared iron phosphate is still unstable and needs to be aged for a period of time to stabilize its properties. The adverse effect of a shorter aging time will cause the iron phosphate to be unstable.

[0058] S5. The precipitate is washed and dried for multiple times to obtain ferric phosphate dihydrate.

[0059] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods in the following examples without specifying specific conditions are carried out according to general international standards, conventional conditions, or according to the conditions recommended by the manufacturer.

[0060] The chemical composition of the high iron red mud used in the following examples and comparative examples is shown in the following table:

[0061] Main components in high iron red mud / ω%

[0062]

[0063] Example 1

[0064] A method for preparing a lithium iron phosphate precursor from high-iron red mud, the method comprising:

[0065] The red mud was mixed with 5.4 mol / L hydrochloric acid, with a liquid-solid ratio of 15, to form a uniform slurry, and poured into a high-temperature reactor for leaching reaction at 230°C for 6 hours at a pressure of 2MPa. After the leaching reaction, the red mud leachate was obtained after solid-liquid separation. Phosphate was then added to the red mud leachate and slowly heated to 100°C. The amount of phosphate added was 5:1 of the aluminum ion molar ratio, and a primary homogeneous solution was obtained after solid-liquid separation. Phosphate was continued to be added to the primary homogeneous solution to adjust the pH to 1.8, control the iron-phosphorus ratio to 0.96-1.02, and solid-liquid separation was performed after 90 minutes of reaction at 100°C to obtain a secondary homogeneous solution. 8% of the volume of pure water was added to the secondary homogeneous solution for cooling and dilution, and the temperature was rapidly reduced for precipitation. The precipitation temperature was 1°C, and finally a dihydrate iron phosphate product was obtained.

[0066] The ferric phosphate dihydrate product was tested, and the results are shown in the following table:

[0067]

[0068] Example 2

[0069] A method for preparing a lithium iron phosphate precursor from high-iron red mud, the method comprising:

[0070] The red mud was mixed with 2.5 mol / L hydrochloric acid, with a liquid-solid ratio of 7, to form a uniform slurry, and poured into a high-temperature reactor for leaching reaction at 110°C for 3 hours at a pressure of 0.5 MPa. After the leaching reaction, the red mud leachate was obtained after solid-liquid separation. Phosphate was then added to the red mud leachate and slowly heated to 80°C. The amount of phosphate added was 3:1 of the aluminum ion molar ratio, and a primary homogeneous solution was obtained after solid-liquid separation. Phosphate was continued to be added to the primary homogeneous solution to adjust the pH to 6.0, control the iron-phosphorus ratio to 0.96-1.02, and react at 80°C for 30 minutes before solid-liquid separation to obtain a secondary homogeneous solution. 2% of the volume of pure water was added to the secondary homogeneous solution for cooling and dilution, and the temperature was rapidly reduced for precipitation. The precipitation temperature was 9°C, and finally a dihydrate iron phosphate product was obtained.

[0071] The ferric phosphate dihydrate product was tested, and the results are shown in the following table:

[0072]

[0073] Example 3

[0074] A method for preparing a lithium iron phosphate precursor from high-iron red mud, the method comprising:

[0075] The red mud was mixed with 3.0 mol / L hydrochloric acid, with a liquid-solid ratio of 10, to form a uniform slurry, and poured into a high-temperature reactor for leaching reaction at 150°C for 4 hours at a pressure of 1MPa. After the leaching reaction, the red mud leachate was obtained after solid-liquid separation. Phosphate was then added to the red mud leachate and slowly heated to 85°C. The amount of phosphate added was 3.5:1 of the aluminum ion molar ratio, and a primary homogeneous solution was obtained after solid-liquid separation. Phosphate was continued to be added to the primary homogeneous solution to adjust the pH to 3.0, control the iron-phosphorus ratio to 0.96-1.02, and react at 85°C for 50 minutes before solid-liquid separation to obtain a secondary homogeneous solution. 4% of the volume of pure water was added to the secondary homogeneous solution for cooling and dilution, and the temperature was rapidly reduced for precipitation. The precipitation temperature was 4°C, and finally a dihydrate iron phosphate product was obtained.

[0076] The ferric phosphate dihydrate product was tested, and the results are shown in the following table:

[0077]

[0078] Example 4

[0079] A method for preparing a lithium iron phosphate precursor from high-iron red mud, the method comprising:

[0080] The red mud was mixed with 3.0 mol / L hydrochloric acid with a liquid-solid ratio of 10 to form a uniform slurry, and poured into a high-temperature reactor for leaching reaction at 150°C for 4 hours at a pressure of 1.5 MPa. After the leaching reaction was completed, the red mud leachate was obtained after solid-liquid separation. Phosphate was then added to the red mud leachate and the temperature was slowly raised to 85°C. The amount of phosphate added was 3.5:1 of the aluminum ion molar ratio, and a primary homogeneous solution was obtained after solid-liquid separation. Phosphate was continued to be added to the primary homogeneous solution to adjust the pH to 3.0, and the iron-phosphorus ratio was controlled to 0.96-1.02. After solid-liquid separation at 85°C for 50 minutes, a secondary homogeneous solution was obtained. 4% of the volume of pure water was added to the secondary homogeneous solution for cooling and dilution, and the temperature was rapidly reduced for precipitation. The precipitation temperature was 4°C, and finally a dihydrate ferric phosphate product was obtained. The dihydrate ferric phosphate product was tested, and the results are shown in the following table:

[0081]

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 1 is that acid leaching is not performed, and pure water is used for leaching, and no ferric phosphate dihydrate product is obtained.

[0084] Comparative Example 2

[0085] The difference between this comparative example and Example 1 is that the secondary homogeneous reaction time is shortened to 10 minutes, and the obtained ferric phosphate product meets the standards.

[0086]

[0087]

[0088] Comparative Example 3

[0089] The difference between this comparative example and Example 1 is that the primary homogeneous phase and the secondary homogeneous phase reaction temperature are 50° C., and the obtained ferric phosphate product does not meet the standards.

[0090]

[0091] Comparative Example 4

[0092] The difference between this comparative example and Example 1 is that the precipitation temperature is increased to 15° C., and the obtained ferric phosphate product does not meet the standards.

[0093]

[0094] Comparative Example 5

[0095] The difference between this comparative example and Example 1 is that the pressure during leaching is reduced to 0.2 MPa, and the obtained iron phosphate product meets the standards.

[0096]

[0097] Comparative Example 6

[0098] The difference between this comparative example and Example 1 is that the pH is adjusted to 7 and no iron phosphate product is obtained.

[0099] The control of each parameter and the results of preparing the products in Examples 1 to 4 and Comparative Examples 1 to 6 are shown in the following table:

[0100]

[0101] It can be seen from the above table that the method provided in the embodiment of the present application can be used to produce ferric phosphate dihydrate, and all indicators meet the requirements of the HG / T4701-2021 "Iron Phosphate for Batteries" standard.

[0102] It can be seen from Comparative Examples 1 and 5 in the table that acid leaching is a necessary process for preparing iron phosphate, but the acid leaching process requires parameter optimization to achieve precise selective leaching, laying the foundation for the subsequent preparation of iron phosphate. When the pressure is reduced, iron phosphate can be prepared but the output is low, which is caused by insufficient leaching.

[0103] From Comparative Example 2, it can be seen that the secondary homogeneous phase controls a certain reaction time in order to fully react and leach the iron phosphate to form a stable chemical state. However, shortening the secondary homogeneous phase reaction time will lead to a decrease in output and the iron phosphate will be unstable.

[0104] It can be seen from Comparative Example 6 that pH is a key factor affecting the synthesis of ferric phosphate, and ferric phosphate can only be generated within a strict pH range.

[0105] From Comparative Examples 3 and 4, it can be seen that the primary and secondary homogeneous reaction temperatures and the subsequent precipitation temperature are key factors in the separation and removal of impurities from ferric phosphate. On the one hand, it is to quickly generate the target product, and on the other hand, it is to achieve the regulation of impurities and crystallization of the target product by different dynamic temperature fields in the continuous homogeneous reaction, mainly for impurity removal. The control of the precipitation temperature is also for the purpose of separating and removing impurities and finally obtaining the target precipitate and the separation liquid to obtain dihydrated ferric phosphate.

[0106] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0107] In this application, unless otherwise specified, directional words such as "upper" and "lower" used refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the specification of this application, the terms "include", "comprise", etc. mean "including but not limited to".

[0108] In this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that there can be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A, B can be singular or plural. In this article, "at least one" refers to one or more, and "multiple" refers to two or more. "At least one", "the following at least one (individual)" or similar expressions refer to any combination of these items, including any combination of single (individual) or plural (individual). For example, "at least one (individual) of a, b, or c", or "at least one (individual) of a, b, and c", can all represent: a, b, c, ab (i.e. a and b), ac, bc, or abc, wherein a, b, c can be single or multiple respectively.

[0109] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing lithium iron phosphate precursor from high-iron red mud, characterized in that: The method comprises: Mix high iron red mud and hydrochloric acid, then leaching to obtain red mud leaching solution, the mass concentration of hydrochloric acid is 2.5-5.4 mol / L, the leaching temperature is 110-230°C, and the leaching pressure is 0.5-2MPa; The red mud leachate and phosphate are mixed, and then subjected to a first homogeneous reaction to obtain a primary homogeneous solution; adjusting the pH value and the iron-phosphorus ratio of the primary homogeneous solution, and then performing a second homogeneous reaction to obtain a secondary homogeneous solution; Precipitating the secondary homogeneous solution to obtain a lithium iron phosphate precursor; In the first homogeneous reaction, the molar ratio of the phosphate to the aluminum ion in the solution is (3-5):1; the temperature of the first homogeneous reaction is 80-100°C; The pH value of the secondary homogeneous reaction is 1.8-6; the iron-phosphorus ratio of the secondary homogeneous reaction is 0.96-1.02; the reaction time of the secondary homogeneous reaction is 30-90 minutes; The temperature of low temperature precipitation aging is 1-9°C; The method does not require the addition of an extractant.

2. The method for preparing a lithium iron phosphate precursor from high-iron red mud according to claim 1, characterized in that: The leaching time is 3-6h.

3. The method for preparing lithium iron phosphate precursor from high-iron red mud according to claim 1, characterized in that: The liquid-to-solid ratio of the mixture of the hydrochloric acid and the high-iron red mud is (7-15):

1.

4. The method for preparing lithium iron phosphate precursor from high-iron red mud according to claim 1, characterized in that: The phosphates include normal salts and acid salts; The normal salt includes at least one of sodium phosphate and calcium phosphate; The acid salt includes at least one of sodium dihydrogen phosphate and ammonium dihydrogen phosphate.

5. The method for preparing lithium iron phosphate precursor from high-iron red mud according to claim 1, characterized in that: The step of precipitating the secondary homogeneous solution to obtain a lithium iron phosphate precursor comprises: The secondary homogeneous solution is naturally cooled to room temperature, then diluted with ice water, and then subjected to low-temperature precipitation and aging to obtain a lithium iron phosphate precursor.

6. The method for preparing lithium iron phosphate precursor from high-iron red mud according to claim 5, characterized in that: In the ice water dilution, the mass amount of ice water used is 2%-8% of the mass of the secondary homogeneous solution.

7. The method for preparing lithium iron phosphate precursor from high-iron red mud according to claim 1, characterized in that: The low-temperature precipitation aging time is 12-36h.

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