A method for preparing ferromanganese oxalate in a cycle

Abstract

The present invention relates to the field of material technology, and in particular to a method for cyclically preparing ferromanganese oxalate. In the method, during the circulation process, the recovered liquid obtained by solid-liquid separation is used to prepare the ferromanganese solution of the next circulation process, and the molar ratio of oxalic acid to manganese and iron ions in the first circulation process and the molar amount of oxalic acid in each circulation process are controlled. On the one hand, the method can greatly improve the recovery rate of manganese and iron ions, thereby greatly improving the output of ferromanganese oxalate, and on the other hand, it can avoid the waste of manganese, iron ions and solvent water, avoid material waste, and save production costs; at the same time, the ferromanganese oxalate prepared by the method has good consistency, and the ferromanganese oxalate is used for sintering to prepare lithium iron manganese phosphate positive electrode material, which can significantly improve the capacity of the positive electrode material, and make the high-voltage discharge capacity ratio of the positive electrode material close to the manganese metal content.

Description

Technical Field

[0001] The invention relates to the technical field of materials, and in particular to a method for cyclically preparing ferromanganese oxalate. Background Art

[0002] Compared with lithium iron phosphate, lithium manganese iron phosphate has a higher energy density, which can increase the voltage platform of the positive electrode material while maintaining the stability of lithium iron phosphate.

[0003] In the related technology, a manganese iron salt precursor is often prepared by co-precipitation, and then the manganese iron salt precursor is mixed with a lithium source to prepare lithium iron manganese phosphate. Common manganese iron salt precursors include ferromanganese oxalate, ferromanganese phosphate, and ferromanganese carbonate. Among them, ferromanganese oxalate is widely used due to its advantages of low cost, simple process, and low sintering difficulty.

[0004] However, in the process of realizing the present invention, the inventors found that in the preparation of ferromanganese oxalate in the related art, there were problems such as low yield of ferromanganese oxalate, more impurities and serious waste of materials. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of low ferromanganese oxalate yield, more impurities and serious material waste in the preparation of ferromanganese oxalate in the prior art, thereby providing a method for cyclically preparing ferromanganese oxalate.

[0006] To this end, the present invention provides a method for cyclically preparing ferromanganese oxalate, comprising the following steps:

[0007] (1) contacting a ferromanganese solution with an oxalic acid solution, adjusting the pH value and maintaining the reaction to obtain a reaction solution; wherein the solvent of the ferromanganese solution is water or a recovered solution from a previous cycle;

[0008] (2) performing solid-liquid separation on the reaction liquid, washing and drying the obtained solid, and using the obtained liquid as a recovered liquid for preparing the ferromanganese solution for the next cycle process;

[0009] Wherein, in the first cycle, the ratio of the molar amount of oxalic acid to the total molar amount of manganese ions and iron ions is not less than 1.1; in the cycle, the molar amount of oxalic acid satisfies: C n =[1-0.02×(n-1)]×C, C represents the molar amount of oxalic acid in the first cycle, n represents the number of cycles and n is an integer greater than 0, C n represents the molar amount of oxalic acid in the nth cycle.

[0010] The chemical formula of the ferromanganese oxalate is Mn x Fe yC2O4, where 0 < x < 1, 0 < y < 1, and x + y = 1. When using the recycled liquid to prepare the manganese-iron solution for the next cycle, the residual iron ion concentration and residual manganese ion concentration in the recycled liquid can be measured separately first, and then based on the preset iron ion concentration and preset manganese ion concentration of the manganese-iron solution, the dosages of the iron source and manganese source can be determined, and then the manganese-iron solution for the next cycle can be prepared.

[0011] Optionally, when n = 1, the cycle process is the first cycle process, and the solvent of the manganese-iron solution in step (1) is water;

[0012] When n > 1, the cycle process is a non-first cycle process, and the solvent of the manganese-iron solution in step (1) is the recycled liquid from the previous cycle.

[0013] Optionally, in the first cycle process, the molar ratio of oxalic acid to the total molar amount of manganese ions and iron ions is not less than 1.3.

[0014] Optionally, in the manganese-iron solution, the concentration of iron ions is 0.8 - 3.2 mol / L, and the concentration of manganese ions is 1 - 2.6 mol / L.

[0015] Optionally, the pH value of the manganese-iron solution is less than 2.5. Controlling the pH value of the manganese-iron solution to be less than 2.5 can prevent divalent iron ions from being oxidized. The pH value of the manganese-iron solution can be adjusted using sulfuric acid solution or hydrochloric acid solution.

[0016] Optionally, the preparation process of the manganese-iron solution includes: adding the iron source and manganese source to the solvent and adjusting the pH value, where the iron source includes at least one of ferrous sulfate, ferrous nitrate, and ferrous chloride; the manganese source includes at least one of manganese sulfate, manganese chloride, and manganese nitrate.

[0017] Optionally, the concentration of the oxalic acid solution is 1 - 5 mol / L;

[0018] Optionally, the preparation temperature of the oxalic acid solution is 30 - 60 °C.

[0019] Optionally, in step (1), the pH value is adjusted to 2 - 4;

[0020] Optionally, the reaction conditions in step (1) include at least one of the following a - d:

[0021] a. Pass nitrogen, and the nitrogen flow rate is 0.1 - 10 L / min;

[0022] b. Stir, and the stirring speed is 400 - 1000 rpm;

[0023] c. The reaction temperature is 30-90°C;

[0024] d. The reaction time is 3 to 10 hours.

[0025] Optionally, the pH adjuster used in step (1) to adjust the pH value includes aqueous ammonia with a concentration of 6 to 8 mol / L;

[0026] Optionally, when the iron source is ferrous sulfate and the manganese source is manganese sulfate, n is an integer greater than 0 and less than or equal to 6, and the total concentration of the iron ions and the manganese ions in the ferromanganese solution, the volume of the ferromanganese solution, the volume of the oxalic acid solution, the volume of the ammonia water during the first cycle and the concentration of the saturated ammonium sulfate solution at the lowest reaction temperature during the cycle satisfy the following relationship:

[0027] m[1+V1 / (V1+V2+V3)+V1 2 / (V1+V2+V3) 2 +V1 3 / (V1+V2+V3) 3 +V1 4 / (V1+V2+V3) 4 ] <M,

[0028] Wherein, m represents the total concentration of the iron ions and the manganese ions in the ferromanganese solution, mol / L;

[0029] V1 represents the volume of the ferromanganese solution during the first cycle, L;

[0030] V2 represents the volume of the oxalic acid solution during the first cycle, L;

[0031] V3 represents the volume of the ammonia solution during the first cycle, L;

[0032] M represents the concentration of the saturated ammonium sulfate solution at the lowest reaction temperature during the circulation process, mol / L.

[0033] Optionally, the method further includes: ending the circulation process after the sixth cycle is completed, and using the recovery liquid generated by the sixth cycle to recover ammonium sulfate.

[0034] Optionally, when the ferromanganese solution is contacted with the oxalic acid solution, the method further comprises an operation of adding a surfactant;

[0035] Optionally, when the volume unit of the ferromanganese solution is L and the weight unit of the surfactant is g, the ratio of the weight of the surfactant to the volume of the ferromanganese solution is (1-2):10;

[0036] Optionally, the surfactant includes at least one of sodium dodecyl sulfate, sodium octyl sulfate, sodium dodecylbenzene sulfonate, stearic acid, an amino acid surfactant, glyceryl monostearate and alkyl glucoside.

[0037] Optionally, the washing in step (2) is performed using an ammonium oxalate solution at 60 to 80° C., and the concentration of the ammonium oxalate solution is 0.1 to 1 mol / L. The amount of the ammonium oxalate solution can be determined based on the theoretical yield of ferromanganese oxalate. For example, the amount of the ammonium oxalate solution can be 10 to 20 L relative to 1 kg of ferromanganese oxalate.

[0038] Optionally, the drying conditions in step (2) include: a drying temperature of 80 to 120° C. and a drying time of not less than 12 hours.

[0039] The technical solution of the present invention has the following advantages:

[0040] 1. The method for preparing ferromanganese oxalate by circulation provided by the present invention, in the circulation process, the recovered liquid obtained by solid-liquid separation is used to prepare the ferromanganese solution of the next circulation process, so that the manganese and iron ions in the recovered liquid can be fully utilized, on the one hand, the recovery rate of manganese and iron ions can be greatly improved, and then the output of ferromanganese oxalate can be greatly improved, and on the other hand, the waste of manganese, iron ions and solvent water can be avoided, the waste of materials can be avoided, and the production cost can be saved;

[0041] In addition, by controlling the molar ratio of oxalic acid to manganese and iron ions in the first cycle, the manganese ions and iron ions in the ferromanganese solution can be precipitated in proportion, thereby further improving the recovery rate of manganese and iron ions; by controlling the molar amount of oxalic acid in each cycle, the molar amount of oxalic acid is gradually reduced as the number of cycles increases, which can avoid the influence of residual manganese ions, iron ions and oxalate in the recovered liquid on the consistency of the product, thereby ensuring the consistency of the product obtained in each cycle. Therefore, the manganese iron oxalate prepared by this method has good consistency. The manganese iron oxalate is used for sintering to prepare lithium iron manganese phosphate positive electrode material, which can significantly improve the capacity of the positive electrode material and make the high-voltage discharge capacity ratio of the positive electrode material close to the manganese metal content.

[0042] 2. The method for cyclically preparing ferromanganese oxalate provided by the present invention, wherein the preparation temperature of the oxalic acid solution is 30-60°C, and the concentration of oxalate in the oxalic acid solution is increased by increasing the preparation temperature of the oxalic acid solution, which can effectively increase the reaction rate of oxalate with metal ions, reduce the impurity content in the lithium manganese oxalate product, and improve the morphology of the ferromanganese oxalate product, making it easy to sinter and the capacity of the lithium iron manganese phosphate obtained by sintering is higher.

[0043] 3. The method for cyclically preparing ferromanganese oxalate provided by the present invention can ensure that ammonium sulfate is dissolved in the 1st to 6th cycles, avoid precipitation of ammonium sulfate in the cycle, and thus greatly reduce the impurity content in the ferromanganese oxalate product by controlling the total concentration of the iron ions and the manganese ions in the ferromanganese solution, the volume of the ferromanganese solution, the volume of the oxalic acid solution, the volume of the ammonia water, and the concentration of the saturated ammonium sulfate solution at the lowest reaction temperature in the cycle during the first cycle to meet a specific relationship.

[0044] 4. The method for cyclically preparing ferromanganese oxalate provided by the present invention ends the circulation process after the sixth cycle is completed, and the recovered liquid generated by the sixth cycle is used to recover ammonium sulfate, thereby realizing the recovery of sulfate radicals and ammonium ions, while producing by-products and reducing the emission of harmful wastewater and waste gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 These are the SEM scanning results and EDS scanning results of the ferromanganese oxalate prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0047] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0048] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0049] Example 1

[0050] Ferromanganese oxalate was prepared as follows:

[0051] (1) preparing 10 L of a solution by taking ferrous sulfate heptahydrate, manganese sulfate monohydrate, and a solvent (water), and adjusting the solution pH to less than 2 with sulfuric acid to obtain a ferromanganese solution, wherein the iron ion concentration is 0.8 mol / L and the manganese ion concentration is 1 mol / L; preparing an oxalic acid solution with a concentration of 1 mol / L at 60° C. with oxalic acid, and keeping the solution warm at 60° C.; and diluting ammonia water to a concentration of 6 mol / L as a pH adjuster;

[0052] (2) adding the above ferromanganese solution into a reaction kettle, heating to 60°C and keeping warm at a stirring speed of 400 rpm, then adding 1 g of sodium octyl sulfate, and passing nitrogen at a flow rate of 0.1 L / min;

[0053] (3) adding the oxalic acid solution to the reactor of step (2), controlling the adding speed and completing the addition within 1 hour, and simultaneously adding the above-mentioned pH adjuster to adjust the pH value of the solution in the reactor to 2;

[0054] (4) The reaction was maintained for 3 h, and the obtained reaction liquid was filtered. The obtained solid was washed with 26 L of 0.1 mol / L oxalic acid ammonia solution at 60 ° C., and the washed material was dried at 120 ° C. for 12 h to obtain ferromanganese oxalate;

[0055] (5) collecting the filtrate obtained by filtration in step (4) as a recovered liquid, detecting the contents of manganese ions and iron ions therein by ICP, chemical titration or the like, and then using the recovered liquid to prepare 10 L of a manganese iron solution having an iron ion concentration of 0.8 mol / L, a manganese ion concentration of 1 mol / L, and a pH value of less than 2;

[0056] (6) After repeating step (2) to step (5) four times, repeat step (2) to step (4) once, then feed the recovered liquid obtained in step (5) into a drum dryer at a rate of 5 L / h, and dry it at 150° C., collect the dried material, and obtain ammonium sulfate.

[0057] This embodiment includes 6 cycles, wherein the solvent used in preparing the ferromanganese solution in the first cycle is water, and the solvent used in preparing the ferromanganese solution in the last five cycles is the recovered liquid obtained in step (5) in the previous cycle. In the first cycle, the molar amount of oxalic acid is 20 mol, the total molar amount of manganese ions and iron ions is 18 mol, and the ratio of the molar amount of oxalic acid to the total molar amount of manganese ions and iron ions is about 1.1 / 1; the molar amount of oxalic acid in the second cycle is 19.6 mol, the molar amount of oxalic acid in the third cycle is 19.2 mol, the molar amount of oxalic acid in the fourth cycle is 18.8 mol, the molar amount of oxalic acid in the fifth cycle is 18.4 mol, and the molar amount of oxalic acid in the sixth cycle is 18 mol.

[0058] Among them, in the first cycle, the total concentration of iron ions and manganese ions in the ferromanganese solution is m=1.8 mol / L, the volume of the ferromanganese solution is V1=10L, the volume of the oxalic acid solution is V2=20L, the volume of the ammonia water is V3=5L, and the concentration of the saturated ammonium sulfate solution at the lowest reaction temperature (25°C) during the cycle is M=4.1 mol / L, then:

[0059] m[1+V1 / (V1+V2+V3)+V1 2 / (V1+V2+V3) 2 +V1 3 / (V1+V2+V3) 3 +V1 4 / (V1+V2+V3) 4 ]=2.5.

[0060] In this embodiment, 12687.8 g of ferrous sulfate heptahydrate and 9634.1 g of manganese sulfate monohydrate were used in 6 cycles. The ferromanganese oxalate obtained in step (4) in 6 cycles was mixed to obtain 14484.6 g of ferromanganese oxalate. The comprehensive yield of metallic ferromanganese was 98%. The ferromanganese oxalate was tested. The test results showed that the ratio of manganese to iron was: Mn / Fe=56% / 44%. The SEM scanning results and EDS scanning results are shown in FIG. Figure 1 shown.

[0061] Example 2

[0062] Ferromanganese oxalate was prepared as follows:

[0063] (1) preparing 10 L of a solution by taking ferrous sulfate heptahydrate, manganese sulfate monohydrate, and a solvent (water), and adjusting the solution pH to less than 2 with sulfuric acid to obtain a ferromanganese solution, wherein the iron ion concentration is 1.6 mol / L and the manganese ion concentration is 1.3 mol / L; preparing an oxalic acid solution with a concentration of 2.5 mol / L at 60° C. with oxalic acid, and keeping the solution warm at 60° C.; and diluting ammonia water to a concentration of 8 mol / L as a pH adjuster;

[0064] (2) adding the above ferromanganese solution into a reaction kettle, heating to 90°C with a stirring speed of 1000 rpm and keeping the temperature, then adding 2 g of sodium octyl sulfate, and passing nitrogen at a flow rate of 10 L / min;

[0065] (3) adding the oxalic acid solution to the reactor of step (2), controlling the addition rate and completing the addition within 1 hour, and simultaneously adding the above-mentioned pH adjuster to adjust the pH of the solution in the reactor to 4;

[0066] (4) The reaction was maintained for 10 h, and the obtained reaction liquid was filtered. The obtained solid was washed with 167 L of 1 mol / L oxalic acid ammonia solution at 80 ° C., and the washed material was dried at 80 ° C. for 24 h to obtain ferromanganese oxalate;

[0067] (5) collecting the filtrate obtained by filtration in step (4) as a recovered liquid, detecting the contents of manganese ions and iron ions therein by ICP, chemical titration or the like, and then using the recovered liquid to prepare 10 L of a manganese-iron solution having an iron ion concentration of 1.6 mol / L, a manganese ion concentration of 1.3 mol / L, and a pH value of less than 2;

[0068] (6) After repeating step (2) to step (5) four times, repeat step (2) to step (4) once, then feed the recovered liquid obtained in step (5) into a drum dryer at a rate of 5 L / h, and dry it at 150° C., collect the dried material, and obtain ammonium sulfate.

[0069] The present embodiment includes 6 cycles, wherein the solvent used in preparing the ferromanganese solution in the first cycle is water, and the solvent used in preparing the ferromanganese solution in the last five cycles is the recovered liquid obtained in step (5) in the previous cycle. In the first cycle, the molar amount of oxalic acid is 32 mol, the total molar amount of manganese ions and iron ions is 29 mol, and the ratio of the molar amount of oxalic acid to the total molar amount of manganese ions and iron ions is about 1.1 / 1; the molar amount of oxalic acid in the second cycle is about 31.4 mol, the molar amount of oxalic acid in the third cycle is about 30.7 mol, the molar amount of oxalic acid in the fourth cycle is about 30.1 mol, the molar amount of oxalic acid in the fifth cycle is about 29.4 mol, and the molar amount of oxalic acid in the sixth cycle is about 28.8 mol.

[0070] Among them, in the first cycle, the total concentration of iron ions and manganese ions in the ferromanganese solution is m=2.9 mol / L, the volume of the ferromanganese solution is V1=10L, the volume of the oxalic acid solution is V2=12.8L, the volume of the ammonia water is V3=8L, and the concentration of the saturated ammonium sulfate solution at the lowest reaction temperature (40°C) during the cycle is M=4.3 mol / L, then:

[0071] m[1+V1 / (V1+V2+V3)+V1 2 / (V1+V2+V3) 2 +V1 3 / (V1+V2+V3) 3 +V1 4 / (V1+V2+V3) 4 ]=4.28.

[0072] In this embodiment, 25353.6 g of ferrous sulfate heptahydrate and 12522.9 g of manganese sulfate monohydrate were used in 6 cycles. The ferromanganese oxalate obtained in step (4) in the 6 cycles was mixed to obtain 23565.2 g of ferromanganese oxalate in total, and the comprehensive yield of metallic ferromanganese was 99%. The ferromanganese oxalate was tested, and the test results showed that the ratio of ferromanganese therein was: Mn / Fe=45% / 55%.

[0073] Example 3

[0074] Ferromanganese oxalate was prepared as follows:

[0075] (1) preparing 10 L of a solution by taking ferrous sulfate heptahydrate, manganese sulfate monohydrate, and a solvent (water), and adjusting the solution pH to less than 2 using sulfuric acid to obtain a ferromanganese solution, wherein the iron ion concentration is 1 mol / L and the manganese ion concentration is 1 mol / L; preparing an oxalic acid solution with a concentration of 2 mol / L at 60° C. using oxalic acid, and keeping the solution warm at 60° C.; diluting ammonia water to a concentration of 7 mol / L as a pH adjuster;

[0076] (2) adding the above ferromanganese solution into a reaction kettle, heating to 70°C and keeping the temperature under stirring at 800 rpm, then adding 1.5 g of sodium octyl sulfate, and passing nitrogen at a flow rate of 2 L / min;

[0077] (3) adding the oxalic acid solution to the reactor of step (2), controlling the adding speed and completing the addition within 1 hour, and simultaneously adding the above-mentioned pH adjuster to adjust the pH value of the solution in the reactor to 3;

[0078] (4) Maintaining the reaction for 10 hours, filtering the resulting reaction liquid, washing the resulting solid with 65 L of 1 mol / L oxalic acid ammonia solution at 80° C., and drying the washed material at 120° C. for 24 hours to obtain ferromanganese oxalate;

[0079] (5) collecting the filtrate obtained by filtration in step (4) as a recovered liquid, detecting the contents of manganese ions and iron ions therein by ICP, chemical titration or the like, and then using the recovered liquid to prepare 10 L of a manganese-iron solution having an iron ion concentration of 1 mol / L, a manganese ion concentration of 1 mol / L, and a pH value of <2;

[0080] (6) After repeating step (2) to step (5) four times, repeat step (2) to step (4) once, then feed the recovered liquid obtained in step (5) into a drum dryer at a rate of 10 L / h, and dry it at 250° C., collect the dried material, and obtain ammonium sulfate.

[0081] The present embodiment includes 6 cycles, wherein the solvent used in preparing the ferromanganese solution in the first cycle is water, and the solvent used in preparing the ferromanganese solution in the last five cycles is the recovered liquid obtained in step (5) in the previous cycle. In the first cycle, the molar amount of oxalic acid is 26 mol, the total molar amount of manganese ions and iron ions is 20 mol, and the ratio of the molar amount of oxalic acid to the total molar amount of manganese ions and iron ions is 1.3 / 1; the molar amount of oxalic acid in the second cycle is about 25.5 mol, the molar amount of oxalic acid in the third cycle is about 25 mol, the molar amount of oxalic acid in the fourth cycle is about 24.4 mol, the molar amount of oxalic acid in the fifth cycle is about 23.9 mol, and the molar amount of oxalic acid in the sixth cycle is about 23.4 mol.

[0082] Among them, in the first cycle, the total concentration of iron ions and manganese ions in the ferromanganese solution is m=2mol / L, the volume of the ferromanganese solution is V1=10L, the volume of the oxalic acid solution is V2=13L, the volume of the ammonia water is V3=6L, and the concentration of the saturated ammonium sulfate solution at the lowest reaction temperature (25°C) during the cycle is M=4.1mol / L, then:

[0083] m[1+V1 / (V1+V2+V3)+V1 2 / (V1+V2+V3) 2 +V1 3 / (V1+V2+V3) 3 +V1 4 / (V1+V2+V3) 4 ]=3.0.

[0084] In this embodiment, 15846 g of ferrous sulfate heptahydrate and 9633 g of manganese sulfate monohydrate were used in 6 cycles. The ferromanganese oxalate obtained in step (4) in the 6 cycles was mixed to obtain 16169.8 g of ferromanganese oxalate in total, and the comprehensive yield of metallic ferromanganese was 99%. The ferromanganese oxalate was tested, and the test results showed that the ratio of ferromanganese therein was: Mn / Fe=50% / 50%.

[0085] Comparative Example 1

[0086] Ferromanganese oxalate was prepared as follows:

[0087] (1) preparing 10 L of a solution by taking ferrous sulfate heptahydrate, manganese sulfate monohydrate, and a solvent (water), and adjusting the solution pH to less than 2 with sulfuric acid to obtain a ferromanganese solution, wherein the iron ion concentration is 0.8 mol / L and the manganese ion concentration is 1 mol / L; preparing 20 L of an oxalic acid solution with a concentration of 1 mol / L at 60° C. with oxalic acid, and keeping the solution warm at 60° C.; and diluting ammonia water to a concentration of 6 mol / L as a pH adjuster;

[0088] (2) adding the above ferromanganese solution into a reaction kettle, heating to 60°C and keeping warm at a stirring speed of 400 rpm, then adding 1 g of sodium octyl sulfate, and passing nitrogen at a flow rate of 0.1 L / min;

[0089] (3) adding the oxalic acid solution to the reactor of step (2), controlling the adding speed and completing the addition within 1 hour, and simultaneously adding the pH adjuster to adjust the pH value of the solution in the reactor to 2;

[0090] (4) The reaction was maintained for 3 h, and the resulting reaction liquid was filtered. The resulting solid was washed with 26 L of 0.1 mol / L oxalic acid ammonia solution at 60° C., and the washed material was dried at 120° C. for 12 h to obtain ferromanganese oxalate.

[0091] In this comparative example, the molar amount of oxalic acid is 20 mol, the total molar amount of manganese ions and iron ions is 18 mol, and the ratio of the molar amount of oxalic acid to the total molar amount of manganese ions and iron ions is 1.1 / 1; 2460 g of ferromanganese oxalate is obtained in step (4), and the comprehensive yield of metallic ferromanganese is 95%; the ferromanganese oxalate is tested, and the test results show that the ratio of manganese to iron is: Mn / Fe=55.6% / 44.4%.

[0092] Comparative Example 2

[0093] Manganese iron oxalate was prepared according to the method of Example 1, except that in this comparative example, the amount of oxalic acid solution in step (3) was controlled so that the ratio of the molar amount of oxalic acid to the total molar amount of manganese ions and iron ions was 1.0.

[0094] In this comparative example, 12131.7 g of ferrous sulfate heptahydrate and 9218.78 g of manganese sulfate monohydrate were used in 6 cycles. The ferromanganese oxalate obtained in step (4) in the 6 cycles was mixed to obtain 13479.6 g of ferromanganese oxalate in total, and the comprehensive yield of metallic ferromanganese was 96%. The ferromanganese oxalate was tested, and the test results showed that the ratio of ferromanganese therein was: Mn / Fe=56% / 44%.

[0095] Comparative Example 3

[0096] Manganese iron oxalate was prepared according to the method of Example 1, except that in this comparative example, the amount of oxalic acid solution in step (3) of each cycle process was controlled so that the molar amount of oxalic acid in the second cycle process was 18 mol, the molar amount of oxalic acid in the third cycle process was 16 mol, the molar amount of oxalic acid in the fourth cycle process was 14 mol, the molar amount of oxalic acid in the fifth cycle process was 12 mol, and the molar amount of oxalic acid in the sixth cycle process was 10 mol.

[0097] In this comparative example, 11475.8 g of ferrous sulfate heptahydrate and 8720.4 g of manganese sulfate monohydrate were used in 6 cycles. The ferromanganese oxalate obtained in step (4) in the 6 cycles was mixed to obtain 11335.6 g of ferromanganese oxalate in total, and the comprehensive yield of metallic ferromanganese was 85%. The ferromanganese oxalate was tested, and the test results showed that the ratio of ferromanganese therein was: Mn / Fe=50% / 50%.

[0098] Comparative Example 4

[0099] Manganese iron oxalate was prepared according to the method of Example 1, except that in this comparative example, the amount of oxalic acid solution in step (3) of each cycle process was controlled so that the molar amount of oxalic acid in the second cycle process was 20 mol, the molar amount of oxalic acid in the third cycle process was 20 mol, the molar amount of oxalic acid in the fourth cycle process was 20 mol, the molar amount of oxalic acid in the fifth cycle process was 20 mol, and the molar amount of oxalic acid in the sixth cycle process was 20 mol.

[0100] In this comparative example, 12691.5 g of ferrous sulfate heptahydrate and 9638.2 g of manganese sulfate monohydrate were used in 6 cycles. The ferromanganese oxalate obtained in step (4) in the 6 cycles was mixed to obtain 14491.9 g of ferromanganese oxalate in total. The comprehensive yield of metallic ferromanganese was 98%. The ferromanganese oxalate was tested, and the test results showed that the ratio of manganese to iron was: Mn / Fe=56% / 44%.

[0101] Experimental example

[0102] The ferromanganese oxalate prepared in Examples 1-3 and Comparative Examples 1-4 was used to prepare a lithium ion battery according to the following method:

[0103] (1) Preparation of lithium manganese iron phosphate positive electrode material:

[0104] Manganese iron oxalate and lithium carbonate are mixed in a molar ratio of Li:Me=1:1 (Me represents the total molar amount of manganese ions and iron ions) to obtain a premixed material; then 6% of glucose and 0.3% of carbon nanotubes are added to the premixed material by weight, and sand milling is performed to a particle size of 100-300nm; the sanded product is spray-dried, and the spray-dried material is calcined, and the calcination conditions are: heating to 650°C at a rate of 1-2°C / min and calcining for 10h; after the calcination, the temperature is naturally lowered to obtain a lithium manganese iron phosphate positive electrode material.

[0105] (2) Preparation of positive electrode sheet:

[0106] The lithium manganese iron phosphate positive electrode material prepared by the above method is used as the positive electrode active material, and is slurried according to the weight ratio of positive electrode active material: SP (superconducting carbon black): PVDF (polyvinylidene fluoride) = 90:5:5, and then coated on a 20μm thick aluminum foil, and then dried, rolled, die-cut, and punched to produce a surface density of 8mg / cm 2 The positive electrode.

[0107] (3) Preparation of batteries:

[0108] Use R2032 button battery shell for button battery assembly, use lithium sheet as negative electrode, adopt PE material diaphragm, add 80μmL of electrolyte (the electrolyte uses Xinzhoubang lithium-ion battery electrolyte, model LBC3401A60).

[0109] After the battery preparation is completed, each lithium-ion battery prepared above is subjected to a 1C cycle performance test at 25°C. The test method is as follows:

[0110] The prepared button cells were tested using a blue electric tester. The prepared button cells were placed in a high-temperature oven at 25°C for charge and discharge tests. The voltage range was 2.0V-4.35V. The cells were activated by 0.1C charge and discharge for one cycle. Then, they were charged at 0.5C constant current and constant voltage, with a cut-off current of 0.05C. They were discharged at 1C current for 50 cycles to obtain the first discharge specific capacity and the capacity retention rate at the 50th cycle. The test results are shown in Table 1.

[0111] Table 1 Test results of button batteries

[0112]

[0113]

[0114] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing ferromanganese oxalate in a cycle, characterized in that: The steps include: (1) contacting a ferromanganese solution with an oxalic acid solution, adjusting the pH value and maintaining the reaction to obtain a reaction solution; wherein the solvent of the ferromanganese solution is water or a recovered solution from a previous cycle; (2) performing solid-liquid separation on the reaction liquid, washing and drying the obtained solid, and using the obtained liquid as a recovery liquid for preparing the ferromanganese solution for the next cycle process; the pH adjusting agent used in step (1) for adjusting the pH value includes aqueous ammonia with a concentration of 6 to 8 mol / L; Wherein, in the first cycle, the ratio of the molar amount of oxalic acid to the total molar amount of manganese ions and iron ions is not less than 1.1; in the cycle, the molar amount of oxalic acid satisfies: C n =[1-0.02×(n-1)]×C, where C represents the molar amount of oxalic acid in the first cycle, n represents the number of cycles and n is an integer greater than 0, and C n represents the molar amount of oxalic acid in the nth cycle, and the total concentration of the iron ions and the manganese ions in the ferromanganese solution, the volume of the ferromanganese solution, the volume of the oxalic acid solution, the volume of the ammonia water, and the concentration of the saturated ammonium sulfate solution at the lowest reaction temperature in the cycle process during the first cycle satisfy the following relationship: m[1+V1 / (V1+V2+V3)+V1 2 / (V1+V2+V3) 2 +V1 3 / (V1+V2+V3) 3 +V1 4 / (V1+V2+V3) 4 ] <M; Wherein, m represents the total concentration of the iron ions and the manganese ions in the ferromanganese solution, mol / L; V1 represents the volume of the ferromanganese solution during the first cycle, L; V2 represents the volume of the oxalic acid solution during the first cycle, L; V3 represents the volume of the aqueous ammonia during the first cycle, L; M represents the concentration of the saturated ammonium sulfate solution at the lowest reaction temperature during the cycle, mol / L; The preparation temperature of the oxalic acid solution is 30-60°C.

2. The method according to claim 1, characterized in that When n=1, the cycle process is the first cycle process, and the solvent of the ferromanganese solution in step (1) is water; When n>1, the circulation process is not the first circulation process, and the solvent of the ferromanganese solution in step (1) is the recovered liquid in the previous circulation process.

3. The method according to claim 1 or 2, characterized in that: During the first cycle, the ratio of the molar amount of the oxalic acid to the total molar amount of the manganese ions and the iron ions is not less than 1.

3.

4. The method according to claim 1 or 2, characterized in that: In the ferromanganese solution, the concentration of the iron ions is 0.8 to 3.2 mol / L, and the concentration of the manganese ions is 1 to 2.6 mol / L; Optionally, the pH value of the ferromanganese solution is less than 2.5; Optionally, the preparation process of the ferromanganese solution includes: adding an iron source and a manganese source to the solvent and adjusting the pH value, wherein the iron source includes at least one of ferrous sulfate, ferrous nitrate, and ferrous chloride; and the manganese source includes at least one of manganese sulfate, manganese chloride, and manganese nitrate.

5. The method according to claim 1 or 2, characterized in that: The concentration of the oxalic acid solution is 1-5 mol / L.

6. The method according to claim 1 or 2, characterized in that: In step (1), the pH value is adjusted to 2-4; Optionally, the reaction conditions in step (1) include at least one of the following a to d: a. Nitrogen flow rate is 0.1~10L / min; b. Stirring at a speed of 400-1000 rpm; c. The reaction temperature is 30-90°C; d. The reaction time is 3 to 10 hours.

7. The method according to claim 4, characterized in that When the iron source is ferrous sulfate and the manganese source is manganese sulfate, n is an integer greater than 0 and less than or equal to 6.

8. The method according to claim 1 or 2, characterized in that: The method further comprises: ending the circulation process after the sixth circulation is completed, and using the recovery liquid generated in the sixth circulation to recover ammonium sulfate.

9. The method according to claim 1 or 2, characterized in that: When the ferromanganese solution is contacted with the oxalic acid solution, the method further comprises the operation of adding a surfactant; Optionally, when the volume unit of the ferromanganese solution is L and the weight unit of the surfactant is g, the ratio of the weight of the surfactant to the volume of the ferromanganese solution is (1-2):10; Optionally, the surfactant includes at least one of sodium dodecyl sulfate, sodium octyl sulfate, sodium dodecylbenzene sulfonate, stearic acid, an amino acid surfactant, glyceryl monostearate and alkyl glucoside.

10. The method according to claim 1 or 2, characterized in that: The washing in step (2) is performed by washing with an ammonium oxalate solution at 60 to 80° C., wherein the concentration of the ammonium oxalate solution is 0.1 to 1 mol / L; Optionally, the drying conditions in step (2) include: a drying temperature of 80 to 120° C. and a drying time of not less than 12 hours.

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