A process for purifying battery-grade manganese pyrophosphate

Abstract

The application relates to the technical field of inorganic functional material preparation, and discloses a battery-grade manganese pyrophosphate purification process, which comprises the following steps: high-temperature leaching of low-purity manganese pyrophosphate by using an inorganic acid solution to drive complete hydrolysis of pyrophosphate, so that an acid solution system containing divalent manganese ions and dihydrogen phosphate ions is obtained; under the synergistic constraint of a high-potential window of 1300 mV to 1550 mV and specific hydrogen ion activity, directional impurity removal and precipitation of monohydrogen manganese phosphate or hydrated manganese phosphate are carried out; the system containing the precipitate is subjected to high-speed grinding shear control to precisely control the particle size of the intermediate body, and the crystal powder is obtained through washing and drying; finally, high-temperature calcination is carried out at 600 DEG C to 800 DEG C, high-phase-purity manganese pyrophosphate is obtained by using solid-phase intermolecular dehydration condensation phase transition, and the problems of coherent impurity wrapping in the process of purifying low-value crude manganese pyrophosphate into high-value battery-grade manganese pyrophosphate and uncontrollable kinetics of a traditional process are solved.

Description

Technical Field

[0001] This invention relates to a purification process for battery-grade manganese pyrophosphate, belonging to the field of inorganic functional material preparation technology. Background Technology

[0002] Manganese pyrophosphate can be used as a precursor material for lithium iron phosphate (LFP), the cathode material of lithium-ion batteries. However, battery-grade manganese pyrophosphate requires extremely high purity, which cannot be met by low-purity manganese pyrophosphate produced in general industrial processes, necessitating purification treatment. However, when processing low-purity manganese pyrophosphate with complex compositions, various anionic and cationic impurities are commonly present in the material. Conventional wet purification processes often intensify specific chemical complexations or multi-stage precipitation. Due to the thermodynamic instability of pyrophosphate ions, strong acid or alkaline environments easily disrupt the coordination state between manganese ions and pyrophosphate ions, leading to uncontrolled crystallization kinetics. This induces disordered physical encapsulation or lattice embedding of impurity ions in the mother liquor by amorphous aggregates, resulting in significant deviations in the phase purity and stoichiometry of the final product.

[0003] In addition, traditional process routes attempt to directly construct pyrophosphate ions with complete crystal lattices in the liquid phase system, but the mass transfer resistance in the liquid phase and the violent fluctuations in local supersaturation make it difficult to remove the impurities of orthophosphate or polyphosphate.

[0004] Therefore, how to drive the directional acid leaching and hydrolysis of pyrophosphate into dihydrogen phosphate ions and specifically transform them into manganese monohydrogen phosphate mediators with well-defined structures, introduce an efficient kinetic blocking mechanism during the crystal building stage to eliminate impurity embedding, and finally output manganese pyrophosphate with extremely high phase purity through precisely controlled solid-phase intermolecular condensation phase transition, is a technical bottleneck that urgently needs to be solved for the high-value-added conversion and utilization of low-purity manganese pyrophosphate. Summary of the Invention

[0005] To address the problems in the background art, the technical solution of the present invention is as follows: A purification process for battery-grade manganese pyrophosphate, comprising the following steps:

[0006] Step S101: Low-purity manganese pyrophosphate is mixed with an inorganic acid solution with a concentration of 1.0 mol / L to 3.0 mol / L at a solid-liquid mass ratio of 1:5 to 1:8. The mixture is then subjected to an acid leaching reaction at 50°C to 90°C with stirring for 2 to 4 hours. After the reaction is completed, the mixture is filtered to remove impurities, and an acid-soluble system containing divalent manganese ions, dihydrogen phosphate ions, and anionic and cationic impurities is obtained. Step S102: Add an oxidant and a pH adjuster to the acid-soluble system to control the redox potential of the acid-soluble system to be stable within the range of 1300mV to 1550mV, and use the pH adjuster to perform segmented pH gradient adjustment: First, keep the acid-soluble system in the first pH range to directionally precipitate and filter out iron impurities to obtain a pure liquid phase; then adjust the pH of the system to 3.8 to 4.5, and react to generate manganese monohydrogen phosphate or hydrated manganese phosphate precipitate to obtain a precipitate-containing system; In step S103, the precipitated system is fed into a grinding device for high-speed grinding and shearing to control the particle size of the precipitated product; after grinding, the system is repeatedly washed and filtered to control the conductivity of the wash water to the range of 150 μS / cm to 420 μS / cm; the filter cake is dried to remove water and obtain dry crystalline powder of manganese monohydrogen phosphate or manganese hydrate phosphate. Step S104: The dried crystalline powder is subjected to high-temperature calcination at a temperature of 600°C to 800°C. The high-temperature thermal energy drives the solid-phase phase transformation and lattice recombination, removing structural water and solid-phase condensation to form a high-purity manganese pyrophosphate powder product.

[0007] Preferably, in step S102, the segmented pH gradient adjustment specifically includes: adding an oxidant to the acid-soluble system to directionally oxidize ferrous ions in the acid-soluble system to ferric ions and generate ferric hydroxide coprecipitate; using a filtration device to filter out the ferric hydroxide coprecipitate in a first pH range, the first pH range being 2.5 to 3.2, to obtain a pure liquid phase rich in ferrous manganese ions and dihydrogen phosphate ions; subsequently adding a first pH adjuster to the pure liquid phase to raise the pH value to the range of 4.0 to 4.2, inducing targeted crystallization of manganese monohydrogen phosphate.

[0008] Preferably, in step S101, the inorganic acid solution is a mixed acid system composed of sulfuric acid solution, phosphoric acid solution, or a combination thereof, and the concentration of the inorganic acid solution is 2.0 mol / L to 2.5 mol / L. During the reaction process in step S101, by setting staggered baffles in the reaction vessel and cooperating with a flat paddle stirring at a speed of 500 rpm, the low-purity manganese pyrophosphate is in a highly dispersed suspension state in the acidic medium, so as to improve the directional hydrolysis conversion efficiency.

[0009] Preferably, in step S102, the first pH adjuster used to adjust the pH value is a sodium hydroxide solution with a mass fraction of 10% to 20% or an ammonia solution with a concentration of 2.0 mol / L to 3.5 mol / L. During the addition of the first pH adjuster, the temperature difference fluctuation range is controlled within 2°C, and the change in hydrogen ion activity of the acid-soluble system is monitored online in real time using a pH meter to ensure that the pH value is kept constant in the deep impurity removal and intermediate crystallization range of 4.0 to 4.2.

[0010] Preferably, in step S103, the high-speed grinding and shearing treatment uses a precision sand mill circulation device to control the solid-liquid mass ratio of the precipitate system to be in the range of 1:6 to 1:7.5, and to control the linear velocity of the grinding media to be in the range of 5.0 m / s to 8.0 m / s. The explosive disordered agglomeration of amorphous precipitate is broken by the flow field shear stress, and the median particle size D50 of manganese monohydrogen phosphate or hydrated manganese phosphate intermediate is controlled to be in the range of 0.3 μm to 2.5 μm.

[0011] Preferably, in step S103, repeated washing and filtration specifically involves: repeatedly rinsing the precipitated product with deionized water with a resistivity of not less than 15 MΩ·cm, using ion exchange during the washing process to remove sodium or potassium ions adsorbed on the particle surface, until the conductivity of the discharged washing liquid stabilizes in the range of 150 μS / cm to 420 μS / cm.

[0012] Preferably, in step S103, the drying and dehydration are carried out in a forced-air drying oven at a temperature of 110°C to 115°C for a time of 6 to 10 hours to remove the physically adsorbed water from the surface of the crystal particles.

[0013] Preferably, in step S104, the high-temperature calcination treatment specifically involves: placing the dry crystalline powder in a tube furnace, and introducing air, high-purity nitrogen, or argon at a flow rate of 200 mL / min to 400 mL / min into the furnace cavity at a temperature of 650°C to 750°C as a sintering atmosphere, and carrying out a high-temperature solid-state sintering reaction for 4 to 8 hours, thereby driving the intermediate to undergo a process of removing structural water and intermolecular dehydration and condensation reaction to form a single-phase anhydrous manganese pyrophosphate powder product.

[0014] Preferably, in the obtained manganese pyrophosphate, the mass content of iron is less than 100 ppm, the mass content of calcium, magnesium, aluminum, nickel and chromium is less than 50 ppm, the mass content of zinc is less than 20 ppm, the mass content of copper is less than 5 ppm, the mass content of sulfur is less than 200 ppm, the mass fraction of the main phase of manganese pyrophosphate is not less than 99.5%, and the measured manganese-phosphorus molar ratio returns to the range of 0.965 to 0.985.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention abandons the traditional approach of directly maintaining the crystal lattice structure of pyrophosphate in the liquid phase, and actively drives the controlled hydrolysis of pyrophosphate in a specific high-temperature inorganic acid system to transform it into a more stable dihydrogen phosphate ion; through a precisely directional mediator transformation mechanism, it provides a single and pure anion precursor environment for the subsequent deep separation of impurities.

[0016] 2. By constructing a high redox potential window of 1300mV to 1550mV and a hydrogen ion activity gradient of pH 3.8 to 4.5 in step S102, the present invention achieves a strong selective repulsion effect. Under this coupling window, high-valence associated impurity ions such as iron and aluminum are directionally masked or transformed into soluble complexes and retained in the mother liquor, while manganese is selectively precipitated as a high-purity manganese hydrogen phosphate crystal phase, which greatly improves the purification depth.

[0017] 3. The present invention constructs a unique intermediate particle size dynamics control mechanism; in step S103, the mechanical shear force generated by high-speed grinding is used to block the explosive disordered agglomeration of manganese monohydrogen phosphate during the precipitation process, and its particle size is precisely controlled within the preset working window; this not only isolates the lattice impurities mixed in the particles, but also significantly reduces the mass transfer diffusion distance and activation energy in the subsequent solid-state sintering process.

[0018] 4. In the subsequent processing, by precisely limiting the conductivity of the washing water to between 150 μS / cm and 420 μS / cm, the physical impurity ions adsorbed on the particle surface are perfectly removed, while the loss of manganese due to the solubility product effect is effectively suppressed. Finally, combined with high-temperature solid-phase polycondensation calcination at 600℃ to 800℃, the intermediate is driven to smoothly complete the dehydration and conversion to manganese pyrophosphate. The manganese-phosphorus molar ratio of the product accurately returns to the theoretical value, and the phase purity is extremely high. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a purification process for battery-grade manganese pyrophosphate according to the present invention. Figure 2 This is the XRD diffraction pattern of the high-purity manganese pyrophosphate product of this invention.

[0020] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0022] A purification process for battery-grade manganese pyrophosphate includes the following steps: Step S101: Low-purity manganese pyrophosphate is mixed with an inorganic acid solution with a concentration of 1.0 mol / L to 3.0 mol / L at a solid-liquid mass ratio of 1:5 to 1:8. The mixture is subjected to acid leaching reaction at an environment of 50°C to 90°C and a stirring speed of 500 rpm for 2 to 4 hours. After the reaction is completed, the mixture is filtered to remove impurities and obtain an acid-soluble system containing divalent manganese ions, dihydrogen phosphate ions, and anionic and cationic impurities. Step S102: Add an oxidant and a pH adjuster to the acid-soluble system to control the redox potential of the acid-soluble system to be stable within the range of 1300mV to 1550mV, and use the pH adjuster to perform segmented pH gradient adjustment: First, keep the acid-soluble system in the first pH range to directionally precipitate and filter out iron impurities to obtain a pure liquid phase; then adjust the pH of the system to 3.8 to 4.5, and react to generate manganese monohydrogen phosphate or hydrated manganese phosphate precipitate to obtain a precipitate-containing system; Step S103: The precipitated system is fed into a grinding device for high-speed grinding and shearing to control the particle size of the precipitated product. After grinding, the system is repeatedly washed and filtered to control the conductivity of the wash water to the range of 150 μS / cm to 420 μS / cm. The filter cake is dried to remove water, resulting in dry crystalline powder of manganese monohydrogen phosphate or hydrated manganese phosphate. Step S104: The dry crystalline powder is placed in a high-temperature calcination environment at 600℃ to 800℃ to drive solid-phase phase transformation and lattice recombination, removing structural water and solid-phase condensation to form a high-purity manganese pyrophosphate powder product.

[0023] Preferably, in step S102, the segmented pH gradient adjustment specifically includes: adding an oxidant to the acid-soluble system to directionally oxidize ferrous ions in the acid-soluble system to ferric ions and generate ferric hydroxide coprecipitate; using a filtration device to filter out the ferric hydroxide coprecipitate within a first pH range, the first pH range being 2.5 to 3.2, to obtain a pure liquid phase rich in ferrous manganese ions and dihydrogen phosphate ions; subsequently adding a first pH adjuster to the pure liquid phase to raise the pH value to the range of 4.0 to 4.2, initiating targeted crystallization precipitation of manganese monohydrogen phosphate. Preferably, in step S101, the inorganic acid solution is a mixed acid system composed of sulfuric acid solution, phosphoric acid solution, or a combination thereof, and the concentration of the inorganic acid solution is 2.0 mol / L to 2.5 mol / L; during the reaction process in step S101, by setting staggered baffles in the reaction vessel and cooperating with a flat paddle stirring at a speed of 500 rpm, the low-purity manganese pyrophosphate is kept in a highly dispersed suspension state in the acidic medium to improve the efficiency of directional hydrolysis conversion.

[0024] Preferably, in step S102, the first pH adjuster used to adjust the pH value is a sodium hydroxide solution with a mass fraction of 10% to 20% or an ammonia solution with a concentration of 2.0 mol / L to 3.5 mol / L. During the addition of the first pH adjuster, the temperature difference fluctuation range is controlled within 2°C, and the change in hydrogen ion activity of the acid-soluble system is monitored online in real time using a pH meter to ensure that the pH value is kept constant in the deep impurity removal and intermediate crystallization range of 4.0 to 4.2.

[0025] Preferably, in step S103, the high-speed grinding and shearing treatment uses a precision sand mill circulation device to control the solid-liquid mass ratio of the precipitate system to be in the range of 1:6 to 1:7.5, and to control the linear velocity of the grinding media to be in the range of 5.0 m / s to 8.0 m / s. The explosive disordered agglomeration of amorphous precipitate is broken by the flow field shear stress, and the median particle size D50 of manganese monohydrogen phosphate or hydrated manganese phosphate intermediate is controlled to be in the range of 0.3 μm to 2.5 μm.

[0026] Preferably, in step S103, repeated washing and filtration specifically involves: repeatedly rinsing the precipitated product with deionized water with a resistivity of not less than 15 MΩ·cm, using ion exchange during the washing process to remove sodium or potassium ions adsorbed on the particle surface, until the conductivity of the discharged washing liquid stabilizes in the range of 150 μS / cm to 420 μS / cm.

[0027] Preferably, in step S103, the drying and dehydration are carried out in a forced-air drying oven at a temperature of 110°C to 115°C for a time of 6 to 10 hours to remove the physically adsorbed water from the surface of the crystal particles.

[0028] Preferably, in step S104, the high-temperature calcination treatment specifically involves: placing the dry crystalline powder in a tube furnace, and introducing air, high-purity nitrogen, or argon at a flow rate of 200 mL / min to 400 mL / min into the furnace cavity at a temperature of 650°C to 750°C as a sintering atmosphere, and carrying out a high-temperature solid-state sintering reaction for 4 to 8 hours, thereby driving the intermediate to undergo a process of removing structural water and intermolecular dehydration and condensation reaction to form a single-phase anhydrous manganese pyrophosphate powder product.

[0029] Preferably, in the obtained manganese pyrophosphate, the mass content of iron is less than 100 ppm, the mass content of calcium, magnesium, aluminum, nickel and chromium is less than 50 ppm, the mass content of zinc is less than 20 ppm, the mass content of copper is less than 5 ppm, the mass content of sulfur is less than 200 ppm, the mass fraction of the main phase of manganese pyrophosphate is not less than 99.5%, and the measured manganese-phosphorus molar ratio returns to the range of 0.965 to 0.985.

[0030] Example 1: In the purification of crude manganese pyrophosphate in industrial applications, the low-purity manganese pyrophosphate contains magnetic material with a mass fraction of 2535.7 ppm and impurities such as Ca, Mg, Al, Ni, Gr, Zn and Cu with mass fractions of 1656 ppm, 1143 ppm, 856 ppm, 385 ppm, 269 ppm, 150 ppm and 35 ppm respectively. To obtain high-value purification of the low-purity manganese pyrophosphate, 8000g of the low-purity manganese pyrophosphate to be treated was added to 50kg of a 2.2mol / L sulfuric acid solution and a phosphoric acid solution. The mixture was vigorously acid-leached and dissolved at 90℃ and 500rpm for 2.5h under stirring. This process drove the pyrophosphate ions to undergo complete acid leaching and hydrolysis in a high-temperature, strong acid system, converting them into structurally defined dihydrogen phosphate ions. After the reaction, the insoluble residue was filtered out using a solid-liquid separation device, and the clear liquid phase was collected. At this point, the liquid phase contained trace amounts of impurity ions such as Fe, Al, Ca, Mg, Ni, Gr, Zn, and Cu. Subsequently, a 30% (w / w) hydrogen peroxide solution was added dropwise to the clarified liquid phase. The redox potential of the system was forcibly increased and stabilized at 1450 mV using an online potential monitoring unit. At this high potential, ferrous ions were directionally oxidized to ferric ions. A 15% (w / w) sodium hydroxide solution was added to precisely adjust the pH of the system to 2.8. Under the coupling window of this high potential and hydrogen ion activity, ferric ions were converted into insoluble ferric hydroxide precipitate, while high-valence impurities such as aluminum were directionally masked and retained in the mother liquor. After filtering to remove co-precipitates, the pH was adjusted to specifically induce the precipitation of manganese, generating a high-purity manganese hydrogen phosphate crystalline precipitate. To address the disordered physical contamination of mother liquor impurity ions by amorphous aggregates caused by explosive liquid-phase crystallization, the precipitate-containing system was pumped into a sand mill. A grinding linear velocity of 6.5 m / s was set, utilizing specific kinetic mechanical shear stress to inhibit the disordered agglomeration of manganese hydrogen phosphate crystal nuclei. The median diameter (D50) of the intermediate particles was precisely stabilized at 0.8 μm, effectively removing lattice impurities trapped within the aggregates. The discharged slurry was then repeatedly washed and filtered with deionized water until the conductivity of the filtrate decreased to 300 μS / cm. The filter cake was then dried in a forced-air drying oven at 110°C for 8 hours to obtain dried manganese hydrogen phosphate crystalline powder. Finally, this powder was sent to… The medium was placed in a tube furnace and heated steadily to 700℃ at a heating rate of 2℃ / min under air atmosphere and calcined for 6 hours. Within this temperature range, the intermediate particles steadily removed structural water and underwent intermolecular dehydration and condensation reactions. The final manganese pyrophosphate product was pinkish-white in color, and its measured Mn / P molar ratio returned to 0.978. The magnetic material content decreased to 14.1 ppm, and the contents of Fe, Al, Ca, Mg, Ni, Gr, Zn and Cu impurities decreased significantly to 85 ppm, 23 ppm, 45 ppm, 25 ppm, 32 ppm, 18 ppm, 18 ppm and 1 ppm, respectively. The crystal phase of the product was perfectly mirror-aligned with the standard card.

[0031] Example 2: In the experimental scenario verifying the stability of the low-purity manganese pyrophosphate regeneration method under different impurity loads, an experimental platform equipped with an online redox potential monitoring unit and a precision grinding circulation device was used as the verification environment. This platform employed a potential sensor with a measurement accuracy of 0.01mV and a flow meter with a sampling frequency of 100Hz to collect physical parameters in real time; the grinding linear velocity was a key process parameter. The design logic lies in balancing the contradiction between the depolymerization efficiency of the explosive, disordered agglomerates of amorphous precipitates and the morphological regularity of the resulting intermediate particles. Furthermore, boundary verification was performed by adjusting the washing endpoint conductivity. When the washing solution conductivity was controlled at 420 μS / cm, the total amount of sodium and potassium ions remaining on the precursor surface increased slightly, but the final product phase purity remained above 99.5%. When the washing solution conductivity further decreased to the lower limit of 150 μS / cm, trace amounts of free divalent manganese ions were detected in the washing solution, indicating that the solubility product effect was triggered. At this point, the manganese loss rate was controlled within 0.5%, and the theoretical stoichiometric ratio of the product did not deviate significantly. If washing was performed beyond the range to 80 μS / cm, the manganese loss rate increased sharply to 3.2%, leading to an uncontrolled manganese-phosphorus molar ratio in the final product. The data verified the scientific validity of the washing water conductivity range.

[0032] During the experiment, a constant grinding linear velocity of 6.5 m / s was applied to the precipitate-containing systems of sample groups A and B. The recorded data showed that, under the action of strong flow field shear stress, the manganese monohydrogen phosphate crystal nuclei in sample group A effectively broke the disordered aggregation of explosive crystallization, precisely stabilizing the median diameter D50 of its particles at 0.8 μm, and controlling the variance of local liquid phase supersaturation fluctuations to around 0.012. In contrast, the control group C, which adopted direct static precipitation without introducing high-speed grinding shear, saw its amorphous precipitate undergo explosive disordered aggregation within 3 minutes, forming amorphous large aggregates with an average particle size exceeding 35 μm. This triggered local liquid phase encapsulation, forcibly capturing and embedding iron, aluminum, calcium, magnesium and other impurity ions associated with the mother liquor into the crystal lattice. The precursor of sample group A was detected by inductively coupled plasma atomic emission spectrometry, and its Fe capture amount was only 42 ppm, while the Fe capture amount of control group C deteriorated to 1420 ppm, confirming the role of high-speed grinding shear mechanism in regulating the particle size dynamics of the intermediate and repelling and isolating impurities. Empirical verification of parameter boundaries, adjusting the grinding line speed A wide-range comparison revealed that when the grinding line speed decreased to 2 m / s below the lower limit, the flow field shear force could not overcome the intrinsic deagglomeration yield stress of the agglomerates, and the median diameter D50 of the intermediate particles increased to 5.5 μm. This led to an increase in the mass transfer diffusion distance during subsequent solid-state sintering, and the final calcined product phase purity decreased to 94.2%. When the grinding line speed increased to 15 m / s above the upper limit, the excessive mechanical shear force caused the already formed manganese hydrogen phosphate crystal structure to physically break down. The proportion of ultrafine powder with a particle size of less than 0.3 μm in the powder increased from 3% to 28%, making it easy for particles to undergo local over-sintering and agglomeration during subsequent high-temperature calcination, resulting in an increase in the content of orthophosphate impurities in the final product. The appearance of the performance inflection point defined the rationality of the grinding line speed parameter range.

[0033] Example 3: This example combines Figures 1 to 2 A purification process for battery-grade manganese pyrophosphate is described, such as... Figure 1 As shown, low-purity manganese pyrophosphate and an inorganic acid solution with a concentration of 1.0 to 3.0 mol / L are introduced into the acid-soluble system preparation process. The mixture is stirred at 50°C to 90°C and 500 rpm for 2 to 4 hours at a solid-liquid mass ratio of 1:5 to 1:8, and impurities are removed. This yields an acid-soluble system containing divalent manganese ions and dihydrogen phosphate ions. Hydrogen peroxide oxidant and a first pH adjuster are added to the acid-soluble system. This process is controlled by a redox potential monitoring unit to stabilize the potential within the range of 1300 mV to 1550 mV, and the pH of the acid-soluble system is adjusted to 3.8 to 4.5 by a hydrogen ion activity adjustment module. Under this coupling window, iron impurities are first precipitated and filtered out, and high-valence metal impurities such as aluminum are masked. Then, the pH is increased to induce the targeted generation of pure monohydrogen phosphate or hydrated manganese phosphate precipitate in the liquid phase. Finally, the system containing the precipitate is fed into… High-speed grinding and shearing are performed in the grinding equipment. By controlling the shear stress of the flow field, the particle size of the precipitated intermediate is controlled within the target window. After grinding, deionized water is used to perform repeated washing and filtration processes. The conductivity of the discharged wash water is monitored in real time by an online sensor, and the final conductivity of the wash water is controlled to be constant within the range of 150 μS / cm to 420 μS / cm. The filter cake obtained by filtration is dried at 110℃ to remove water, and dry manganese monohydrogen phosphate crystalline powder with a moisture content of less than 2.0% is obtained. Finally, the dry crystalline powder is placed in a tube furnace and calcined at 600℃ to 800℃ for 4 to 8 hours. The high temperature heat energy drives the solid-phase removal of structural water and intermolecular dehydration and condensation reaction, overcoming the bottleneck of lattice recombination technology, and finally obtaining anhydrous manganese pyrophosphate powder product with low impurities, high phase purity and stable theoretical stoichiometry.

[0034] like Figure 2 As shown, the vertical axis of this XRD diffraction pattern is labeled with intensity (count) and marked with x10 at the beginning of the scale.3 The magnitude is indicated by the horizontal axis. (degrees), the spectral curve shows multiple diffraction peaks reflecting lattice characteristics within the scanning range of 10 degrees to 80 degrees, with the highest intensity diffraction peaks located near 29 degrees and 30 degrees. The angular position, and the standard reference area below the atlas displays the corresponding standard card number 97-004-7137. -The standard spectral information of Manganese Diphosphate was obtained by comparing the peak position and relative intensity of each characteristic peak on the measured curve with the standard spectral line. The peak position distribution of the measured curve and the standard spectral line showed a mirror-like consistency, thus confirming at the phase level that the obtained product is high-purity manganese pyrophosphate.

[0035] Example 4: In the scenario of recovering low-purity manganese pyrophosphate with large fluctuations in initial impurity load, the reaction system faces the risk of electrochemical performance deterioration due to residual anions and cations on the surface of the intermediate. In order to avoid the loss of manganese solubility product while removing surface physically adsorbed impurities, the system introduces the washing solution endpoint conductivity. The dynamic determination model, with the specific calculation formula as follows: Among them, the various physical parameters and logical constraints are defined as follows: The target washing solution's endpoint conductivity command value has a valid range of 150 μS / cm to 420 μS / cm. This represents the initial mass concentration of total residual soluble cations in the reaction mother liquor as determined online by ICP. This represents the total volume of deionized water introduced in a single rinse. This represents the estimated total mass on a dry basis, calculated based on the wet cake output from the filter press. This represents the dynamic moisture content of the filter cake at a specific current temperature. The washing efficiency correction factor is set to 0.88. The intrinsic conductivity background compensation constant for deionized water is set to 15.5.

[0036] According to the model calculation, when the moisture meter measures the dynamic moisture content of the current batch of filter cake... When fluctuations occur, the system automatically calculates... This is converted into a control command to close the automatic rinsing valve. Experimental data shows that through the dynamic control of this model, the final conductivity of the washing solution is precisely locked at 300 μS / cm. This not only ensures that the residual sodium and potassium ions adsorbed on the surface of the final manganese pyrophosphate product are less than 15 ppm, but also perfectly avoids the loss of manganese ions due to excessive washing when the conductivity of the washing water is less than 100 μS / cm. The median diameter D50 of the product is 0.8 μm, and the measured manganese-phosphorus molar ratio converges very stably to 0.979, eliminating the risk of phase inconsistency of the technical solution under different physical scales of mass production.

[0037] The prepared precursor slurry was introduced into a centrifuge and the solid product was separated at 3000 rpm. The product was then washed with deionized water until the conductivity of the washing liquid stabilized within the range of 150 μS / cm to 420 μS / cm. The filter cake was then collected and sent to an electrically heated atmosphere furnace. During the solid-state sintering stage, to ensure the stable release of structural water within the manganese hydrogen phosphate intermediate lattice through diffusion channels and to guide its complete intermolecular dehydration and condensation reaction to the pyrophosphate phase within the sensitive temperature range of 400℃ to 500℃, the overall heating procedure of the atmosphere furnace was controlled as follows: After the furnace temperature rose from room temperature to 250℃, the heating rate was reduced to 1.5℃ / min to match the structural water removal equilibrium, and this rate was maintained until the furnace temperature stably crossed 450℃. The furnace was heated in a sensitive temperature zone for polycondensation, and then heated at a constant rate of 2℃ / min until the furnace temperature reached 700℃, which was maintained in this isothermal zone for 6 hours. By physically constraining the heating gradient, this method effectively avoided local over-sintering caused by local mass transfer resistance oscillations and suppressed the side reaction pathways that evolved into polyphosphate impurities. The physical characterization data of the final product showed that the average particle size D50 of the generated manganese pyrophosphate particles was 0.8μm, the measured manganese-phosphorus molar ratio converged very stably to 0.979, the Al impurity mass fraction decreased from the initial 856ppm to 45ppm, and the crystal phase structure of the product was mirror-image aligned with the standard card, confirming the effectiveness of the synergistic effect of the washing solution endpoint conductivity model control and solid-phase polycondensation thermodynamic intervention.

[0038] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A purification process for battery-grade manganese pyrophosphate, characterized in that, Includes the following steps: Step S101: Low-purity manganese pyrophosphate is mixed with an inorganic acid solution with a concentration of 1.0 mol / L to 3.0 mol / L at a solid-liquid mass ratio of 1:5 to 1:

8. The mixture is then subjected to an acid leaching reaction at 50°C to 90°C with stirring for 2 to 4 hours. After the reaction is completed, the mixture is filtered to remove impurities, and an acid-soluble system containing divalent manganese ions, dihydrogen phosphate ions, and anionic and cationic impurities is obtained. Step S102: Add an oxidant and a pH adjuster to the acid-soluble system to control the redox potential of the acid-soluble system to be stable within the range of 1300mV to 1550mV, and use the pH adjuster to perform segmented pH gradient adjustment: First, keep the acid-soluble system in the first pH range to directionally precipitate and filter out iron impurities to obtain a pure liquid phase; then adjust the pH of the system to 3.8 to 4.5, and react to generate manganese monohydrogen phosphate or hydrated manganese phosphate precipitate to obtain a precipitate-containing system; Step S103: The precipitate-containing system is fed into a grinding device for high-speed grinding and shearing treatment to control the particle size of the precipitate product. After grinding, the material is repeatedly washed and filtered, with the conductivity of the wash water controlled within the range of 150 μS / cm to 420 μS / cm. The filter cake is then dried to remove water, yielding dry crystalline powder of manganese monohydrogen phosphate or hydrated manganese phosphate. Step S104: The dried crystalline powder is subjected to high-temperature calcination at a temperature of 600°C to 800°C. The high-temperature thermal energy drives the solid-phase phase transformation and lattice recombination, removing structural water and solid-phase condensation to form a high-purity manganese pyrophosphate powder product.

2. The purification process for battery-grade manganese pyrophosphate according to claim 1, characterized in that, In step S102, the segmented pH gradient adjustment specifically includes: adding an oxidant to the acid-soluble system to directionally oxidize ferrous ions in the acid-soluble system to ferric ions and generate ferric hydroxide coprecipitate; using a filtration device to filter out the ferric hydroxide coprecipitate in the first pH range, which is 2.5 to 3.2, to obtain a pure liquid phase rich in ferrous manganese ions and dihydrogen phosphate ions; subsequently adding a first pH adjuster to the pure liquid phase to raise the pH value to the range of 4.0 to 4.2, initiating targeted crystallization of manganese monohydrogen phosphate.

3. The purification process for battery-grade manganese pyrophosphate according to claim 1, characterized in that, In step S101, the inorganic acid solution is a mixed acid system consisting of sulfuric acid solution, phosphoric acid solution, or a combination thereof, and the concentration of the inorganic acid solution is 2.0 mol / L to 2.5 mol / L. During the reaction process in step S101, by setting staggered baffles in the reaction vessel and rotating the stirring blades at a speed of 500 rpm, the low-purity manganese pyrophosphate is kept in a highly dispersed suspension state in the acidic medium, thereby improving the directional hydrolysis conversion efficiency.

4. The purification process for battery-grade manganese pyrophosphate according to claim 1, characterized in that, In step S102, the first pH adjuster used to adjust the pH value is a sodium hydroxide solution with a mass fraction of 10% to 20% or an ammonia solution with a concentration of 2.0 mol / L to 3.5 mol / L. During the addition of the first pH adjuster, the temperature difference fluctuation range is controlled within 2°C, and the hydrogen ion activity change of the acid-soluble system is monitored online in real time using a pH meter to ensure that the pH value is kept constant in the deep impurity removal and intermediate crystallization range of 4.0 to 4.

2.

5. The purification process for battery-grade manganese pyrophosphate according to claim 1, characterized in that, In step S103, the high-speed grinding and shearing process uses a precision sand mill circulation device to control the solid-liquid mass ratio of the precipitate system to be within the range of 1:6 to 1:7.5, and to control the linear velocity of the grinding media to be within the range of 5.0 m / s to 8.0 m / s. The explosive disordered agglomeration of amorphous precipitates is broken by the flow field shear stress, and the median particle size D50 of manganese monohydrogen phosphate or hydrated manganese phosphate intermediate is controlled within the range of 0.3 μm to 2.5 μm.

6. The purification process for battery-grade manganese pyrophosphate according to claim 1, characterized in that, In step S103, the repeated washing and filtration specifically involves repeatedly rinsing the precipitated product with deionized water with a resistivity of not less than 15 MΩ·cm, using ion exchange during the washing process to remove sodium ions, potassium ions, sulfate ions, or phosphate ions adsorbed on the particle surface, until the conductivity of the discharged washing liquid stabilizes in the range of 150 μS / cm to 420 μS / cm.

7. The purification process for battery-grade manganese pyrophosphate according to claim 1, characterized in that, In step S103, the drying and dehydration are carried out in a forced-air drying oven at a temperature of 110°C to 115°C for 6 to 10 hours to remove the physically adsorbed water from the surface of the crystal particles.

8. The purification process for battery-grade manganese pyrophosphate according to claim 1, characterized in that, In step S104, the high-temperature calcination treatment specifically involves: placing the dry crystalline powder in a tube furnace, and introducing air, high-purity nitrogen, or argon at a flow rate of 200 mL / min to 400 mL / min into the furnace cavity at a temperature of 650°C to 750°C as a sintering atmosphere, and carrying out a high-temperature solid-state sintering reaction for 4 to 8 hours, thereby driving the intermediate to undergo a process of removing structural water and intermolecular dehydration and condensation reaction to form a single-phase anhydrous manganese pyrophosphate powder product.

9. The purification process for battery-grade manganese pyrophosphate according to claim 1, characterized in that, The obtained manganese pyrophosphate contains less than 100 ppm of iron, less than 50 ppm of calcium, magnesium, aluminum, nickel, and chromium, less than 20 ppm of zinc, less than 5 ppm of copper, and less than 200 ppm of sulfur. The main phase mass fraction of the manganese pyrophosphate is not less than 99.5%, and the measured manganese-phosphorus molar ratio returns to the range of 0.965 to 0.985.

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