Production of MnSO4

Abstract

This invention relates to a process for producing MnSO4, particularly high-purity battery-grade anhydrous MnSO4 having a purity between 99.95% and 99.99%. The invention further extends to the products produced by the above process.

Description

[Technical Field]

[0001] This invention relates to the production of MnSO4. In particular, the invention relates to a process for recovering a high-purity MnSO4 product from a MnSO4 solution. [Background technology]

[0002] MnSO4 is a valuable salt. Aside from its widespread use in the metals and alloys industries, there is also a growing need for MnSO4 in the electrochemical battery industry.

[0003] Most processes for producing battery-grade MnSO4·H2O (manganese sulfate monohydrate) end with a crystallization step. In this crystallization step, MnSO4·H2O crystals are recovered from a saturated solution. However, MnSO4·H2O crystals are too fine (typically less than 45 μm) to be effectively separated from the solution by centrifugation, and therefore a filter press is typically used to recover the MnSO4·H2O crystals. Unfortunately, MnSO4·H2O crystals exhibit thixotropic behavior, resulting in poor recovery when mechanical forces are applied to them. Furthermore, MnSO4·H2O crystals are highly soluble in water (approximately 52 g / 100 ml at 5°C and approximately 70 g / 100 ml at 70°C), leading to high losses when the crystals are washed. The inventors understand that "battery-grade" MnSO4·H2O crystals currently have a purity of approximately 99.00%, while containing at least about 10,000 ppm of impurities in the crystal. This is a significant disadvantage. [Overview of the project] [Problems that the invention aims to solve]

[0004] A process is desired for recovering high-purity MnSO4 products from MnSO4 solutions that is free from, or lesser from, some of the aforementioned difficulties. [Means for solving the problem]

[0005] In this specification, the reference to “high purity” refers to battery-grade MnSO4 crystals having a purity greater than 99.10%. Preferably, it means a purity greater than 99.95%, more preferably between 99.95% and 99.99%.

[0006] In one aspect of the present invention, a process is provided for recovering a high-purity MnSO4 product from a supply of MnSO4 solution containing one or more alkali metal or alkaline earth metal contaminants, the process being: From a first MnSO4 aqueous solution containing one or more alkali metals or alkaline earth metals, a divalent cation Mn 2+ and monovalent cations and SO4 2- A step of recovering crystals of a first double salt with an anion, wherein the recovered double salt crystals have a particle size larger than the particle size of the MnSO4·H2O crystals crystallized from the first aqueous solution without the monovalent cation, A step of redissolving the first double salt in water or an aqueous solution to form a second aqueous solution, A step of crystallizing a second aqueous solution to form crystals of a second double salt in a suspension, A step of recovering the high-purity MnSO4 product from the suspension in an anhydrous form, Includes.

[0007] The monovalent cation is NH4 + It is possible.

[0008] Therefore, the first double salt can be MnSO4·(NH4)2SO4·6H2O, i.e., manganese ammonium sulfate hexahydrate, also written as (NH4)2[Mn(H2O)6](SO4)2. This Tatton salt has a pale pink color and a specific gravity of approximately 1.827. Advantageously, the solubility of MnSO4·(NH4)2SO4·6H2O in water is less than that of MnSO4·H2O at the same temperature, and it acts as a carrier for MnSO4.

[0009] To obtain MnSO4·(NH4)2SO4·6H2O as a double salt, the first aqueous MnSO4 solution must contain (NH4)2SO4. During the concentration of the first aqueous MnSO4 solution (which then contains (NH4)2SO4), the first aqueous MnSO4 solution can be concentrated to a concentration of at least about 10% by mass of (NH4)2SO4, preferably at least about 11% by mass of (NH4)2SO4, more preferably at least about 12% by mass of (NH4)2SO4, for example, about 13% by mass of (NH4)2SO4.

[0010] The high-purity MnSO4 product in its anhydrous form may contain, or may be, a second double salt, 2MnSO4·(NH4)2SO4. Advantageously, impurities such as Mg do not eutectic with 2MnSO4·(NH4)2SO4 and remain in the solution in the second aqueous solution.

[0011] According to a preferred embodiment of the present invention, a process is provided for recovering a high-purity MnSO4 product from a supply of MnSO4 and (NH4)2SO4 solutions containing one or more alkali metal or alkaline earth metal contaminants, the process being: From the first aqueous solution of MnSO4 and (NH4)2SO4 containing one or more alkali metals or alkaline earth metals, a divalent cation Mn 2+ and NH4 + The monovalent cation and SO4 2- A step of recovering crystals of a first double salt with an anion, wherein the recovered crystals of the first double salt have a particle size larger than the particle size of the MnSO4·H2O crystals when crystallized from the first aqueous solution without the monovalent cation, A step of redissolving the first double salt in water or an aqueous solution to form a second aqueous solution, A step of crystallizing the second aqueous solution to form a second double salt in the suspension, A step of recovering the high-purity MnSO4 product in an anhydrous form from the suspension, Includes.

[0012] Typically, a high purity MnSO4 product in anhydrous form is a solid material, e.g., a powder.

[0013] The one or more alkali metal or alkaline earth metal contaminants can be one or more of Li, Na, K, Mg, Ca.

[0014] The first aqueous solution contaminated with one or more alkali metal or alkaline earth metal contaminants can contain other contaminants, e.g., Si, Al, Fe, Co, Ni, Cu, and Zn. Also, some of the contaminants such as, for example, Mg, Co, Fe, Ni, Cu, and Zn form double salts with SO4 2- anions. Therefore, it is expected that the double salts recovered from the first aqueous solution can be contaminated with one or more of these contaminants. However, advantageously, contaminants such as Na and Ca do not form double salts with SO4 2- anions and remain in solution in the first aqueous solution of MnSO4 and (NH4)2SO4.

[0015] Recovering the crystals of the first double salt of divalent cation Mn 2+ and monovalent cation NH4 + which is and SO4 2- anions from the first aqueous solution of MnSO4 and (NH4)2SO4 can include concentrating the first aqueous solution.

[0016] Concentrating the first aqueous solution can include evaporating water from the first solution to provide a concentrated solution.

[0017] Preferably, water is evaporated under vacuum. The vacuum can be an absolute pressure of less than about 50 kPa, preferably less than about 40 kPa, more preferably less than about 25 kPa, e.g., about 10 kPa.

[0018] Water can be evaporated at a temperature of at least about 30 °C, preferably at least about 40 °C, more preferably at least about 45 °C, e.g., about 50 °C. Typically, water is evaporated at a temperature not exceeding about 55 °C.

[0019] The first aqueous solution can be concentrated to a concentration of at least about 10% by mass of MnSO4, preferably at least about 11% by mass of MnSO4, more preferably at least about 12% by mass of MnSO4, for example, about 13% by mass of MnSO4.

[0020] From the first aqueous solution, divalent cation Mn 2+ and NH4 + The monovalent cation and SO4 2- Recovering crystals of the first double salt with the anion may involve crystallizing the first double salt from a concentrated solution.

[0021] Crystallization of the first double salt from a concentrated solution can be achieved at a first temperature T1. The first temperature T1 may be less than about 30°C, preferably less than about 25°C, more preferably less than about 20°C, and most preferably less than about 15°C, for example, about 10°C. Typically, the first temperature T1 is between 5°C and 15°C, rather than less than about 5°C.

[0022] From the first aqueous solution, divalent cation Mn 2+ and NH4 + The monovalent cation and SO4 2- Recovering the crystals of the first double salt with the anion may involve centrifugation to separate the first double salt crystals from the first aqueous solution. Alternatively, or in addition, the first aqueous solution may be subjected to filtration to recover the crystals of the first double salt.

[0023] The crystals of the first double salt are at least about 300 μm, preferably at least about 400 μm, more preferably at least about 450 μm, for example, 480 μm to 530 μm of D 50 The particles may have a certain size. Advantageously, these large double salt particles or crystals are easily separated from the first aqueous solution by centrifugation.

[0024] From the first aqueous solution, divalent cation Mn 2+ and NH4 + The monovalent cation and SO4 2-Recovering the crystals of the first double salt with the anion may involve washing the first double salt crystals obtained from the first aqueous solution. The first double salt crystals obtained from the first aqueous solution can be washed with water.

[0025] Redissolving the first double salt in water or an aqueous solution to form a second aqueous solution may involve dissolving the first double salt in water or an aqueous solution at a temperature of at least about 30°C, preferably at least about 40°C, and more preferably between about 45°C and about 55°C. At higher temperatures, the solubility of the double salt decreases.

[0026] If an aqueous solution is used to redissolve the first double salt, the aqueous solution may be the first aqueous solution from which the first double salt crystals have been removed. This implies that the process may involve heating the first aqueous solution from which the first double salt crystals have been removed before using the heated first aqueous solution from which the first double salt crystals have been removed to redissolve the first double salt.

[0027] Redissolving the first double salt in water or an aqueous solution to form a second aqueous solution may involve stirring the second aqueous solution.

[0028] The second aqueous solution may be subject to crystallization to form a second double salt in the suspension. The second double salt is 2MnSO4·(NH4)2SO4. It is understood that the second double salt is in an anhydrous form.

[0029] Crystallization of the second double salt from the second aqueous solution may involve concentrating the second aqueous solution, for example, by evaporation or vacuum evaporation. As is understood, the relatively high temperature of the second aqueous solution results in a high partial pressure of water, leading to the evaporation of a large amount of water, even in the absence of boiling.

[0030] Crystallization of the second aqueous solution occurs at a second temperature T2. This second temperature T2 may be higher than the first temperature T1.

[0031] The second temperature T2 may be at least about 85°C, preferably at least about 90°C, more preferably at least about 95°C, for example, about 97°C. Typically, the second temperature T2 does not exceed about 110°C.

[0032] Recovery of the crystals of the second double salt from the suspension may involve centrifugation. Alternatively, or in addition, the suspension may be subjected to filtration to recover the crystals of the second double salt.

[0033] The crystals of the second double salt are between approximately 160 μm and approximately 300 μm, preferably between approximately 180 μm and approximately 280 μm, more preferably between approximately 200 μm and approximately 260 μm, for example, D of approximately 220-240 μm. 50 It may have a particle size.

[0034] Recovering the crystals of the second double salt in an anhydrous form from the suspension may involve washing the crystals of the second double salt. The crystals may be washed with water.

[0035] The process may further include decomposing an anhydrous second double salt to produce anhydrous MnSO4. Therefore, the process of the present invention may be a process for producing high-purity anhydrous MnSO4 from MnSO4 and (NH4)2SO4 solutions contaminated with one or more alkali metal or alkaline earth metal contaminants. The anhydrous MnSO4 may be battery-grade MnSO4.

[0036] Decomposition of high-purity MnSO4 products can be achieved by heating an anhydrous second double salt to a temperature of at least about 300°C, preferably at least about 400°C, more preferably at least about 450°C, for example, about 500-550°C, in order to produce anhydrous MnSO4. Typically, the anhydrous second double salt is heated to a temperature not exceeding about 600°C.

[0037] The process may include washing away the off-gas produced by the decomposition of the second double salt with water to produce a recovered (NH4)2SO4 aqueous solution. As understood, the off-gas typically contains SO2, O2, and NH3. The (NH4)2SO4 solution can be recycled to the first step of the process described herein, namely the preparation of the first aqueous solution.

[0038] Therefore, the process may include adding an aqueous (NH4)2SO4 solution to the supply MnSO4 solution to form the first aqueous MnSO4 solution.

[0039] The first aqueous solution may be an leachate or a noble leachate.

[0040] The process may include recycling the recovered (NH4)2SO4 aqueous solution to form part of the first aqueous solution.

[0041] The process may include, for example, removing potassium from the first aqueous solution by a jallocite precipitation step. Unfortunately, it is not possible to prevent potassium from remaining as an unnecessarily high level of contaminant in the high-purity MnSO4 product in anhydrous form by the crystallization step described earlier in this specification.

[0042] The process of the present invention can be carried out in a batch-based, semi-batch-based, or continuous process.

[0043] The present invention extends to high-purity MnSO4 products produced by processes such as those described earlier in this specification.

[0044] The present invention further extends to anhydrous MnSO4 produced by processes such as those described earlier in this specification.

[0045] In a preferred embodiment of the present invention, a process is provided for recovering a high-purity MnSO4 product from a supply of a first aqueous solution of MnSO4 and (NH4)2SO4 containing one or more alkali metal or alkaline earth metal impurities, the process being: (a) From the first aqueous solution of MnSO4 and (NH4)2SO4 containing one or more alkali metals or alkaline earth metals, divalent cation Mn 2+ and NH4 + The monovalent cation and SO4 2- A step of recovering crystals of a first double salt with an anion, wherein the recovered crystals of the first double salt have a particle size larger than the particle size of the MnSO4·H2O crystals when crystallized from the first aqueous solution without the monovalent cation, (b) A step of redissolving the first double salt in water or aqueous solution to form a second aqueous solution, (c) A step of crystallizing the second aqueous solution to form anhydrous crystals of the second double salt in the suspension, (d) A step of recovering a high-purity MnSO4 product in an anhydrous form from the suspension.

[0046] The first aqueous solution is concentrated by evaporation under vacuum so that the first aqueous solution has a MnSO4 concentration selected from the group consisting of at least about 10% by weight of MnSO4, at least about 11% by weight of MnSO4, at least about 12% by weight of MnSO4, and at least about 13% by weight of MnSO4.

[0047] The crystals of the first double salt recovered from the first aqueous solution are selected from the group consisting of at least about 300 μm, at least about 400 μm, at least about 450 μm, and between 480 and 530 μm. 50 It has a particle size. The crystals of the first double salt are recovered from the crystallization of the first aqueous solution. The crystallization of the first aqueous solution is carried out at a temperature between 5°C and 15°C.

[0048] The crystals of the second double salt are selected from the group consisting of at least about 160 μm, at least about 300 μm, at least about 180 μm and about 280 μm, at least about 200 μm and about 260 μm, and at least about 220-240 μm. 50 It has a particle size.

[0049] The crystals of the second double salt are subjected to decomposition with water to produce a high-purity anhydrous MnSO4 product. Decomposition takes place at a temperature of approximately 500°C to 550°C.

[0050] The off-gas produced by the decomposition of the second double salt crystals and water yields a recoverable (NH4)2SO4 aqueous solution. The (NH4)2SO4 aqueous solution is recovered and recycled into the first aqueous solution.

[0051] Herein, the present invention will be described with reference to the following embodiments and individual schematic drawings. [Brief explanation of the drawing]

[0052] [Figure 1] Figure 1 is a process flow diagram of a continuous process for recovering high-purity MnSO4 products in the form of anhydrous manganese sulfate from MnSO4 and (NH4)2SO4 solutions contaminated with one or more alkali metal or alkaline earth metal impurities. [Examples]

[0053] A relatively clean leachate containing 12.09 wt% MnSO4 and 14.43 wt% (NH4)2SO4 was used in the laboratory experiment. This first aqueous solution was concentrated by evaporation at 50°C under vacuum and then cooled to 10°C to produce crystals of the first double salt MnSO4·(NH4)2SO4·6H2O, i.e., 1:1:6 crystals. 480-530 μm D25, which can be easily separated from the leachate by centrifugation, was also used. 50Large crystals containing [the specified compound] were obtained. The crystals of the first double salt showed lower solubility in cold water compared to the solubility of MnSO4·H2O and were stable under mechanical pressure. The crystals of the first double salt were washed in water, and as shown in Table 1 below, the washed crystals had improved purity compared to the leached noble liquor, considering impurities such as Na and Ca that do not form a double salt with (NH4)2SO4.

[0054] [Table 1]

[0055] To address the problem of impurity inclusion, such as Mg, which also forms double salts, the 1:1:6 crystals of the first double salt were redissolved in hot water to form an aqueous solution, allowing for slight concentration as a result of evaporation, and then crystallized at 97°C to produce crystals of the second double salt, i.e., 2:1 crystals, in the anhydrous form of 2MnSO4·(NH4)2SO4. Residual impurities (other than K), such as Mg, which are provided in undesirably high levels in the first double salt 1:1:6 crystals, did not eutectic with the second double salt 2MnSO4·(NH4)2SO4 crystals and remained in the aqueous solution. The aqueous solution can be recycled by returning it to a fresh MnSO4 leaching solution, and the 1:1:6 crystallization process for the first double salt can be restarted.

[0056] The second double salt crystal, 2MnSO4·(NH4)2SO4, is 220-240 μm in diameter. 50 It crystallized with [unclear] and was easily separated from the aqueous solution by centrifugation. The second double salt, 2MnSO4·(NH4)2SO4 crystals, showed lower solubility in water at temperatures above 90°C compared to the solubility of MnSO4·H2O and were stable under mechanical pressure. The washed second double salt, 2MnSO4·(NH4)2SO4 crystals, showed improved purity compared to the aqueous solutions obtained when considering impurities such as Na, Mg, and Ca, as shown in Table 2 below.

[0057] [Table 2]

[0058] The anhydrous second double salt 2:1 crystals decomposed at 550°C, producing anhydrous battery-grade MnSO4 as well as off-gases containing SO2, O2, and NH3.

[0059] As shown in Tables 1 and 2, potassium (K) cannot be removed from MnSO4 even after two crystallization steps. However, potassium can be removed before these crystallization steps via a known jallocite precipitation process.

[0060] Referring to a single diagram, reference numeral 10 generally refers to a continuous process relating to an invention for recovering a high-purity MnSO4 product (i.e., battery-grade anhydrous MnSO4) from MnSO4 and (NH4)2SO4 solutions containing one or more alkali metal or alkaline earth metal contaminants.

[0061] Process 10 broadly includes vacuum evaporation 12, a condenser 14, a first centrifugation 16, a first washing step 18, a stirring and dissolving step 20, a precipitation step 22, a second centrifugation 24, a second washing step 26, a rotary furnace 28, and a scrubber 30.

[0062] The manganese sulfate (MnSO4) leaching solution supply line 40 and the ammonium sulfate ((NH4)2SO4) solution supply line 42 are connected to the vacuum evaporator 12. The vacuum evaporator 12 is provided with a water vapor extraction line 43 and a heating coil 45.

[0063] The suspension transport line 44 leads from the vacuum evaporator 12 to the cooler 14, and the cooled suspension transport line 46 leads from the cooler 14 to the first centrifugal separator 16.

[0064] The first centrifugal separation 16 provides a solution extraction line 48 and a crystal transport line 50 leading to a first washing step 18.

[0065] The first cleaning stage 18 is provided with a cleaning water supply line 60 and a wastewater discharge line 62.

[0066] A washing crystal line 64 leads from the first washing step 18 to the dissolution step 20, and a solvent supply line 66 is also provided.

[0067] The solution transport line 68 leads from the dissolution stage 20 to the precipitation stage 22, accompanied by a suspension transport line 70 that leads from the precipitation stage 22 to a second centrifugation stage 24. The precipitation stage 22 also provides a steam extraction line 71.

[0068] The ammonium sulfate solution recycling line 72 leads from the second centrifugation 24 to the ammonium sulfate supply line 42, and the crystal transport line 74 leads from the second centrifugation 24 to the second washing stage 26.

[0069] The second cleaning stage 26 is provided with a cleaning water supply line 76 and a wastewater discharge line 78.

[0070] The washing crystal line 80 leads from the second washing stage 26 to the rotary furnace 28, and provides an anhydrous MnSO4 extraction line 90 and an off-gas extraction line 82.

[0071] The off-gas draw line 82 leads into the scrubber 30, which is supplied with a water supply line 84, a vent line 86, and an ammonium sulfate solution recycling line 88.

[0072] In process 10, a manganese sulfate leachate aqueous solution (for example, having a MnSO4 concentration of about 12.1% by mass) is supplied into the vacuum evaporation 12 by the manganese sulfate leachate supply line 40. The leachate contains various impurities such as Na, Mg, and Ca, typically in the ppm range.

[0073] An aqueous solution of ammonium sulfate (for example, having a (NH4)2SO4 concentration of approximately 14.4% by mass) is also supplied into the vacuum evaporator 12 via the ammonium sulfate solution supply line 42. Therefore, manganese sulfate and ammonium sulfate are supplied into the vacuum evaporator 12 in a stoichiometric molar ratio of approximately 1:1, or slightly more than 25%, with a slight excess of ammonium sulfate. As a result of mixing the leached aqueous solution of manganese sulfate and the aqueous solution of ammonium sulfate in the vacuum evaporator 12, the concentrations of MnSO4 and ammonium sulfate are greatly reduced.

[0074] In the vacuum evaporation 12, a mixed solution of ammonium sulfate and manganese sulfate (i.e., a first aqueous solution of MnSO4 and (NH4)2SO4 containing one or more alkali metals or alkaline earth metals) is concentrated under vacuum at an absolute pressure of about 12 kPa and a temperature of about 50°C. The heat for evaporation is provided by a heating coil 45, which may be, for example, a steam heating coil or an electric heating coil. Steam is drawn out of the vacuum evaporation 12 by a steam extraction line 43 and is also used to create a vacuum in the vacuum evaporation 12.

[0075] The mixed solution is concentrated in a vacuum evaporation 12 to a concentration of approximately 13% by mass of MnSO4 and slightly higher (NH4)2SO4, and then transported to a condenser 14 by a suspension transport line 44. In the condenser 14, the mixed solution is cooled to a temperature of approximately 10°C using cold water, leading to the precipitation of saturated and first double salt MnSO4·(NH4)2SO4·6H2O crystals.

[0076] These first double salt crystals hexahydrate (i.e., 1:1:6 crystals) are approximately 480 μm to 530 μm in diameter. 50 With a certain size, the crystals are transported to the first centrifugation 16 by the cooling suspension transport line 46. In the first centrifugation 16, the first double salt crystals of MnSO4·(NH4)2SO4·6H2O are easily separated from the mixed solution and transported to the first washing step 18 by the crystal transport line 50.

[0077] The remaining mixed solution is drawn from the first centrifuge 16 by the solution draw line 48. This drawn mixed solution can be processed in a reverse osmosis plant or stage (not shown) to produce a concentrated MnSO4 / (NH4)2SO4 solution, which can then be recycled to the vacuum concentrator 12 (not shown). However, in the draw line 48, the drawn mixed solution contains impurities such as dissolved Na and Ca, which do not form double salts with ammonium sulfate. A bleed flow (not shown) can be used to prevent the accumulation of these impurities in process 10.

[0078] In the first washing stage 18, the first double salt crystals of MnSO4·(NH4)2SO4·6H2O are washed with clean water at ambient temperature supplied by the washing water supply line 60. The contaminated washing water is drawn out of the first washing stage 18 by the wastewater drawout line 62, and the washed first double salt crystals of MnSO4·(NH4)2SO4·6H2O are transported to the stirring and dissolution stage 20 by the washing crystal line 64. Advantageously, the solubility of the first double salt crystals of MnSO4·(NH4)2SO4·6H2O in water at the operating temperature of the first washing stage 18 is less than the solubility of MnSO4·H2O.

[0079] In the stirring and dissolution stage 20, the washed first double salt MnSO4·(NH4)2SO4·6H2O crystals are redissolved in hot water supplied to the stirring and dissolution stage 20 by the solvent supply line 66. The hot water is at almost boiling point.

[0080] The solution formed inside the stirring and dissolution stage 20 (i.e., the second aqueous solution) is transported to the precipitation stage 22 by the solution transport line 68, where the solution is made slightly concentrated as a result of water evaporation to saturate. Concentration can be achieved at atmospheric pressure or, if desired, under a slight vacuum produced by the extraction of water vapor through the water vapor extraction line 71. The concentration of the second aqueous solution in the precipitation stage 22 leads to crystallization at a temperature of approximately 97°C. The precipitate of 2MnSO4·(NH4)2SO4 second double salt crystals (i.e., second double salt 1:2 crystals) from the saturated solution and the suspension of the second 2MnSO4·(NH4)2SO4 double salt crystals are transported to the second centrifugation stage 24 by the suspension transport line 70. The second 2MnSO4·(NH4)2SO4 double salt crystals are approximately 220 μm to 240 μm in diameter. 50 It holds.

[0081] In the second centrifugation 24, the crystals of the second double salt 2MnSO4·(NH4)2SO4 are readily separated from the remaining ammonium sulfate solution, accompanied by the ammonium sulfate solution being recycled to vacuum evaporation 12 by means of the ammonium sulfate solution recycling line 72. The recycled ammonium sulfate solution contains inclusions or impurities such as dissolved Mg that form a double salt with ammonium sulfate but do not eutectic with the second double salt 2MnSO4·(NH4)2SO4 crystals. A bleed stream 73, which is to be contaminated, is used in process 10 to prevent the accumulation of inclusions or impurities such as magnesium.

[0082] Advantageously, the second double salt 2MnSO4·(NH4)2SO4 crystals, which have lower solubility in water than MnSO4·H2O at the operating temperature of the second washing stage 26, are transported from the second centrifugation stage 24 to the second washing stage 26 by the crystal transport line 74. In the second washing stage 26, the second double salt 2MnSO4·(NH4)2SO4 crystals are washed with clean washing water at a temperature of approximately 90-95°C supplied by the washing water supply line 76. The contaminated washing water is drawn out by the wastewater draw-out line 78, and the washed second double salt 2MnSO4·(NH4)2SO4 crystals are transported to the rotary furnace 28 by the washing crystal line 80. It is understood that the second washing stage 26 is an optional process feature.

[0083] In the rotary furnace 28, the washed, anhydrous second double salt 2MnSO4·(NH4)2SO4 crystals are decomposed at a temperature of approximately 550°C, thereby producing anhydrous battery-grade MnSO4, which is drawn out by the anhydrous MnSO4 drawout line 90. The off-gas from the rotary furnace 28 is drawn out by the off-gas drawout line 82 and supplied to the scrubber 30. The scrubber 30 is also supplied with water by the water supply line 84. The off-gas from the rotary furnace 28 contains NH3 and SO2, and these components are washed away from the off-gas using water in the scrubber 30, producing washed off-gas that is recycled to vacuum evaporation 12 by the ammonium sulfate solution recycling line 88 and released into the atmosphere by the vent line 86.

[0084] As described, process 10 advantageously produces battery-grade anhydrous MnSO4 with low concentrations of sodium, magnesium, and calcium. The crystals formed in the condenser 14 and precipitation stage 22 are conveniently relatively large in size compared to the size of MnSO4·H2O, providing easy separation from the solution in the first centrifugation 16 and the second centrifugation 24. These crystals also have lower solubility in water compared to MnSO4·H2O at the appropriate operating temperature of process 10, which reduces losses during washing. Furthermore, the crystals are stable under mechanical force and do not exhibit thixotropic behavior, which allows the crystals to be separated from the solution by a filter press if desired. [Explanation of Symbols]

[0085] 10 processes 12 Vacuum Evaporation 14 Cooler 16. First Centrifugal Separation 18. First washing stage 20. Stirring and dissolving stage 22. Precipitation stage 24. Second centrifugation 26. Second cleaning stage 28 Rotary Furnaces 30 Scrubber 40. Manganese sulfate leaching solution supply line 42. Ammonium sulfate solution supply line 43. Steam extraction line 44 Suspension transport line 45 Heating coil 46 Cooling suspension transport line 48 Solution extraction line 50 Crystal transport line 60 Wash water supply line 62 Wastewater draw-out line 64 Washing Crystal Line 66 Solvent supply line 68 Solution transport line 70 Suspension transport line 71 Steam extraction line 72 Ammonium Sulfate Solution Recycling Line 73 Breeding Style 74 Crystal transport line 76 Washing water supply line 78 Wastewater drain line 80 Washing Crystal Line 82 Off-gas drawer line 84 Water supply lines 86 Ventline 88 Ammonium Sulfate Solution Recycling Line 90 Anhydrous MnSO4 Drawer Line

Claims

1. MnSO4 containing one or more alkali metals or alkaline earth metals ４ and (NH ４ ) ２ SO ４ From the supply of the first aqueous solution, high-purity MnSO ４ A process for recovering a product, wherein the process is (a) MnSO4 mixed with one or more of the above alkali metals or alkaline earth metals ４ and (NH ４ ) ２ SO ４ A step of recovering crystals of a first double salt of divalent cation Mn ２＋ and NH ４ ＋ monovalent cation which is and SO ４ ２－ an anion, wherein the recovered crystals of the first double salt are MnSO ４ ·H ２ having a particle size larger than the particle size of the crystals of O, a step; (b) A step of redissolving the first double salt in water or an aqueous solution to form a second aqueous solution, (c) A step of crystallizing the second aqueous solution to form anhydrous crystals of the second double salt in the suspension, (d) High-purity MnSO4 in anhydrous form obtained from the suspension ４ A process that includes the step of recalling the product.

2. The first aqueous solution contains at least about 10% by mass of MnSO4. ４ , at least about 11 mass% MnSO ４ , at least about 12 mass% MnSO ４ , and at least about 13 mass% of MnSO ４ MnSO selected from the group consisting of ４ The process according to claim 1, wherein the concentration is obtained by evaporation under vacuum to obtain a concentration.

3. The process according to claim 1, wherein the crystals of the first double salt are recovered from the crystallization of the first aqueous solution.

4. The process according to claim 3, wherein the crystallization of the first aqueous solution is carried out at a temperature between 5°C and 15°C.

5. The recovered crystals of the first double salt from the first aqueous solution are selected from the group consisting of at least about 300 μm, at least about 400 μm, at least about 450 μm, and between 480 and 530 μm. ５０ The process according to claim 1, wherein the particle size is...

6. The crystals of the second double salt are selected from the group consisting of at least about 160 μm, at least about 300 μm, at least about 180 μm and about 280 μm, at least about 200 μm and about 260 μm, and at least about 220 to 240 μm. ５０ The process according to claim 1, wherein the particle size is...

7. The crystals of the second double salt are subject to decomposition with water, resulting in high-purity anhydrous MnSO4. ４ The process according to claim 1 for producing a product.

8. The process according to claim 7, wherein the decomposition is carried out at a temperature of about 500°C to 550°C.

9. The off-gas produced by the decomposition of the second double salt crystal with water is recoverable (NH ４ ) ２ SO ４ The process according to claim 7 for producing an aqueous solution.

10. Said (NH ４ ) ２ SO ４ The process according to claim 8, wherein the aqueous solution is recovered and recycled into the first aqueous solution.

11. High-purity anhydrous MnSO4 produced by the process described in claim 1 ４ .

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