# Patent

## Title
Method for preparing manganese sulfate monohydrate

## Abstract

Provided is a method for preparing manganese sulfate monohydrate, which comprises the following steps: (1) reacting MnO with (NH4)2SO4 solution under heat, and separating solid from liquid after reaction 2) determining the concentration of MnSO4 in the resulting solution of step 1), adding equimolar ammonium sulfide solution thereto to carry out reaction under agitation, separating solid from liquid after reaction, and then washing solid phase: 3) dissolving the solid phase with concentrated sulfuric acid, adding hydrogen peroxide to the obtained solution, heating to boiling, adjusting the pH value of the solution to 5-6, removing the solid phase through precise filtration, evaporating and oven drying the filtrate to obtain MnSO4.H2O product. The impurities are separated away and the amount of byproducts is reduced by this method, and the yield of manganese sulfate monohydrate is improved.

## Background
This is a National Phase Application filed under 35 U.S.C. 371 as a national stage of PCT/CN2010/075312, filed Jul. 20, 2010, an application claiming the benefit under 35 USC 119(e) Chinese Application No. 201010137708.3, filed Mar. 31, 2010, the content of each of which is hereby incorporated by reference in its entirety.
TECHNICAL FIELD
The present invention relates to a method for preparing manganese sulfate monohydrate, especially, relates to a method for preparing manganese sulfate monohydrate by utilizing MnO.
BACKGROUND ART
MnSO4.H2O is usually used to prepare a positive material of an auto power battery. During application process of MnSO4.H2O, there are higher requirements for contents of impurity ions such as K, Na, Ca, Mg, Fe, and various heavy metal ions in MnSO4.H2O. In prior art, in order to separate impurities, a larger amount of by-products such as BaSO4, may be produced at the same time in methods of preparing MnSO4.H2O. These by-products have a certain market capacity. However, comparing with the demand in the auto power battery, the market aggregate demand for these by-products is lower. Therefore, there is urgent need to design a method for preparing MnSO4. H2O product with a higher productivity.
MnO2 ore in nature is usually classified as high grade MnO2 ore and low grade MnO2 ore. High grade MnO2 ore is often used in iron alloy industry. While, the application of low grade MnO2 ore is always a problem to be solved because the grade of MnO prepared from such ore is lower as well. At present, there is no effective utilizing ways for the MnO product with MnO content less than 20 wt % at home or abroad.
SUMMARY OF THE INVENTION
The present invention provides a method for preparing manganese sulfate monohydrate (MnSO4.H2O), and the method utilizes MnO as material to prepare manganese sulfate monohydrate, especially low-grade MnO could be used as material in the method.
Chemical reactions involved in the present invention mainly comprise:

MnO+(NH4)2SO4MnSO4+NH3↑

MnSO4+(NH4)2S→MnS+(NH4)2SO4 

MnS+H2SO4→MnSO4+H2S↑

The method comprises the following steps:
1) Reacting MnO with (NH4)2SO4 solution under heat, and then carrying out solid-liquid separation for the obtained product;
Raw material used in the reaction may be any MnO product, even the MnO product with lower MnO content, such as MnO product with MnO content of 10-20% based on weight percentage, for example MnO product prepared by reacting manganese dioxide ore with reductive sulfide disclosed in the patent application No. 200910157921.8. MnSO4 solution is obtained after the above reaction, and ammonia gas is produced. The end point of the reaction is found when the gas stops generating, at the time of which, the MnSO4 solution comprises part of impurities such as Ca, Mg, K, Na, Fe and so on.
Preferably, ammonia gas produced in said step 1) can be recovered with bubble absorption device. The present invention can be realized by using two-stage bubble absorption devices, and specific operations of it comprise: heating the devices to 100° C. and maintaining the temperature for 30-60 mins, and then stopping heating.
2) Determining the concentration of MnSO4 in the resulting solution of step 1), adding ammonium sulfide solution to carry out equimolar reaction under agitation, carrying out solid-liquid separation for obtained product, and then washing solid phase;
Firstly, the concentration of MnSO4 solution is determined by utilizing chemical method in this reaction step, ammonium sulfide is commercially available and is prepared into a solution having corresponding concentration based on equimolar proportion, then the reaction is carried out. The mixture containing MnS and (NH4)2SO4 is obtained after reaction, wherein MnS mainly remains in solid phase, and (NH4)2SO4 mainly remains in liquid phase. Solid phase and liquid phase further comprise some impurities, and the main purpose of washing solid phase is removing soluble impurity ions in the solid phase, such as K+, Na+, Mg2+, Ca2+ and so on.
Preferably, in the step of washing solid phase after solid-liquid separation in said step 2), hot water with temperature of 60-80° C. could be used for washing the solid, wherein the ratio of slurry to water is generally 1:4-1:5, and washing time is generally 2 hours.
3) Dissolving the solid obtained in step 2) with concentrated sulfuric acid, adding hydrogen peroxide to the resulting solution, heating to boiling, adjusting the pH value of the solution to 5-6, removing the solid phase through precise filtration, evaporating and drying filtrate to obtain MnSO4.H2O product.
Wherein, in step 3), hydrogen peroxide is added for removing impurities such as Fe, on the other hand, a small amount of sulfide is oxidized, and in the same time there is no other impurities be introduced; Precise filtration is used for removing impurities in the form of precipitate, such as colloid of Fe and fine sulfur and so on.
Preferably, compounds which will not introduce new impurities could be chosen in the step of adjusting pH value in step 3), for example basic compounds of manganese, such as Mn(OH)2 or MnCO3 and so on.
Preferably, in said step 3), before adding hydrogen peroxide, pH value of the obtained solution is adjusted between 1-2, which is also preferably carried out by using Mn(OH)2 or MnCO3. The reason of adjusting pH value is that if the acidity of the solution is too strong, after adding appropriate amount of hydrogen peroxide in the solution to remove impurities such as Fe, the step of neutralizing the solution with Mn(OH)2 or MnCO3 will introduce more impurities such as Fe, which will affect the quality of the product.
Preferably, H2S produced in step 3) may be absorbed with NH4OH solution in the second stage of the two-stage bubble absorption devices, and (NH4)2S product obtained by absorbing H2S with said NH4OH solution could be introduced into (NH4)2S solution of step 2) to carry out reaction, so as to reach the effects of recycling raw material. However, the concentration of ammonium sulfide should be determined newly before reacting ammonium sulfide with manganese sulfate so as to insure equimolar reaction.
Preferably, the precise filtration in step 3) could be carried out by using filter membrane with a diameter of 0.24-0.45 tin, and could be realized through filter press.
Wherein, main technical conditions and reaction devices involved in above steps are all conventional in prior art, and are not one of the invention points of the present invention, so that these contents are not described in the description.
The main process flow diagram of the method of the present invention is shown as FIG. 1.
In the present invention, through reacting MnO with (NH4)2SO4, and subjecting the obtained manganese sulfate solution to carry out several treatments such as vulcanizing, the impurities are separated away and the amount of by-product is reduced meanwhile, and the productivity of manganese sulfate is improved, which creates conditions for producing MnSO4.H2O product in large-scale industrial production.
The process route of recycling and purification used in the present invention could make MnSO4 be purified and auxiliary material be recycled meanwhile, so that the problem of limited production efficiency is solved.



BRIEF DESCRIPTION OF THE DRAWINGS
The main process flow diagram of the method of the present invention is shown as FIG. 1.



EMBODIMENT
The MnO-containing rough product obtained by reacting MnO2 ore powder (Guizhou Redstar Developing Co., Ltd) with SrS or BaS solution was used as raw material to carry out the reaction in examples.
Example 1
1500 g of MnO (17.51% based on weight) obtained by combining Ba—Mn (i.e., reacting MnO2 ore powder with BaS solution) was put in a 5000 mL beaker, and 3490 mL of (NH4)2SO4 solution with a concentration of 147 g/L was added into the beaker. Mixture was heated to react under agitation, and generated gas was recovered with two-stage bubble absorption devices. The devices were heated to 100° C. and the temperature was maintained for 60 mins, and then the heating treatment was stopped.
The above solution was separated with suction filtration, and the funnel was spray-cleaned with a small amount of deionized water. Filtrates were combined, and the concentration of MnSO4 solution is determined as 221.8 g/L and the volume of MnSO4 solution is 2443 mL. 2441 mL of (NH4)2S solution with a concentration of 1.47 mol/L was added to carry out equimolar reaction under agitation. Mixture was kept agitating for 30 mins, and then separated by suction filtration. Filtrate was discarded, and filter cake was washed with hot water with a temperature of 60° C. for 2 hours in a ratio of slurry to water of 1:5, and then separated with suction filtration. Filtrate was discarded.
Filter cake was dissolved with 200 ml of concentrated sulfuric acid, and the obtained H2S was absorbed with two-stage NH4OH solution obtained from two-stage absorption devices. 10 ml of industrial-grade hydrogen peroxide with a concentration of 27.5 wt % was added in the filtrate, and the mixture was heated to boiling. The mixture was kept light boiling for 15 mins, and then was precise filtered with filter press, wherein the diameter of the filter membrane is 0.24 μm. Clarification filtrate was evaporated and dried at 85° C. for 16 hours to obtain sample 1# of MnSO4.H2O.
Example 2
1500 g of MnO (9.71% based on weight) obtained by combining Mn—Sr (i.e., reacting MnO2 ore powder with SrS solution) was put in a 5000 mL beaker, and 2084 mL of (NH4)2SO4 solution with a concentration of 130 g/L was added in the beaker. Mixture was heated to react under agitation, and generated gas was recovered with two-stage bubble absorption devices. The devices were heated to 100° C. and the temperature was maintained for 30 mins, and then the heating treatment was stopped.
The above solution was separated with suction filtration, and the funnel was leached with a small amount of deionized water. Filtrates were combined and the concentration of MnSO4 solution is determined as 206.1 g/L and the volume of MnSO4 solution is 1458 mL. 1309 ml of (NH4)2S solution with a concentration of 1.52 mol/L was added to carry out equimolar reaction under agitation. Mixture was kept agitating for 30 mins, and then separated by suction filtration. Filtrate was discarded. Filter cake was washed with hot water with a temperature of 80° C. for 2 hours in the ratio of slurry to water of 1:4, and then separated with suction filtration. Filtrate was discarded.
Filter cake was dissolved with 111 ml of concentrated sulfuric acid, pH value of obtained solution was adjusted to 1, and the obtained H2S was absorbed with NH4OH solution obtained from two-stage absorption devices. (NH4)2S solution obtained from such two-stage NH4OH solution could be introduced into MnSO4 solution to carry out reaction, but the concentration of (NH4)2S solution should be determined newly before the above step. 10 ml of industrial-grade hydrogen peroxide with concentration of 27.5 wt % was added in the filtrate, and the mixture was heated to boiling. The mixture was kept light boiling for 15 mins, and then was precise filtered with filter press, wherein the diameter of the filter membrane is 0.45 μm. Clarification filtrate was evaporated and dried at 85° C. for 16 hours to obtained sample 2# of MnSO4.H2O.
Weight contents of respective component of each sample obtained in examples are shown as followers:














MnSO4•H2O 1#
MnSO4•H2O 2#









MnSO4•H2O content % ≧
99.71
99.42













K
PPm
<10
<10


Na
PPm
<10
<10


Ca
PPm
<50
<50


Mg
PPm
<50
<50


Pb
PPm
<1.0
<1.0


Fe
PPm
<5
<5









It can be concluded from above table, manganese sulfate monohydrate with higher purity could be produced through the method of the present invention, and the content of various metal impurities were reduced remarkably.

## Claims

1. A method for preparing manganese sulfate monohydrate, comprising the following steps:
1) reacting MnO with (NH4)2SO4 solution under heat, and then carrying out solid-liquid separation for obtained product;
2) determining concentration of MnSO4 in the resulting solution of step 1), adding ammonium sulfide solution to carry out equimolar reaction under agitation, carrying out solid-liquid separation for obtained product, and then washing solid phase; and
3) dissolving the solid phase obtained in step 2) with concentrated sulfuric acid, adding hydrogen peroxide to the resulting solution, heating to boiling, adjusting the pH value of the solution to 5-6, removing solid phase through precise filtration, evaporating and drying the filtrate to obtain MnSO4.H2O product.

2. The method according to claim 1, characterized in that, content of MnO in the MnO in said step 1) is 10-20% based on weight percentage.

3. The method according to claim 1, characterized in that, ammonia gas produced in said step 1) is recovered with bubble absorption device.

4. The method according to claim 3, characterized in that, the step of absorbing ammonia gas in said step 1) comprises: heating the bubble absorption device to 100° C. and maintaining the temperature for 30-60 mins, and then stopping heating.

5. The method according to claim 1, characterized in that, the step of washing solid phase after solid-liquid separation in said step 2) comprises washing solid phase with 60-80° C. hot water in the ratio of slurry to water of 1:4-1:5.

6. The method according to claim 1, characterized in that, before adding hydrogen peroxide in said step 3), pH value of the obtained solution is adjusted between 1-2.

7. The method according to claim 1, characterized in that, MnCO3 or Mn(OH)2 is used to adjust pH value in said step 3).

8. The method according to claim 1, characterized in that, H2S produced in step 3) is absorbed with NH4OH solution in the second stage of two-stage bubble absorption device.

9. The method according to claim 8, characterized in further comprising the step of introducing (NH4)2S product obtained by absorbing H2S with the NH4OH solution into (NH4)2S solution of step 2) to carry out reaction.

10. The method according to claim 1, characterized in that, precise filtration in step 3) is carried out by using filter membrane with a diameter of 0.24-0.45 μm.

11. The method according to claim 6, characterized in that, MnCO3 or Mn(OH)2 is used to adjust pH value in said step 3).