Method for preparing MHP by recycling post-manganese precipitation liquid and application thereof

Abstract

The application provides a method for preparing MHP by recycling post-manganese precipitation liquid and application, and the method comprises the following steps: mixing sodium hydroxide, magnesium oxide and post-manganese precipitation liquid to obtain a compound alkali slurry; mixing the post-iron and aluminum removal liquid of laterite nickel ore and the compound alkali slurry to perform a precipitation reaction to obtain an MHP slurry; performing thickening treatment and solid-liquid separation on the MHP slurry to obtain an MHP filter cake and a filtrate; directly performing manganese precipitation treatment on the filtrate to obtain manganese residue and post-manganese precipitation liquid; and recycling the post-manganese precipitation liquid to preparation of the compound alkali slurry. The compound system of sodium hydroxide and magnesium oxide is used to recycle part of the post-manganese precipitation liquid to the preparation process of alkali, which not only simplifies the MHP precipitation process to one step under the premise of ensuring the quality of MHP, but also greatly reduces the cost of MHP preparation and the cost of wastewater treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrometallurgy, and relates to a method for preparing MHP by recycling manganese precipitation liquid and application. BACKGROUND

[0002] It is known that, for MHP (mixed nickel-cobalt hydroxide precipitate) prepared from laterite nickel ore, the key impurity monitoring element is Mg. If the Mg content is too high, not only will the nickel content in the MHP be reduced, increasing the transportation cost, but also the cost of separating nickel and cobalt by P507 extraction magnesium in the subsequent extraction refining section of the MHP will be significantly increased. Specifically, the main elements in the post-iron and aluminum laterite nickel ore liquid are Ni, Co, Mn and Mg, among which the Mg concentration is about 2-3 times the Ni concentration. In order to prepare high-quality MHP and reduce the content of impurity elements therein, the nickel-cobalt precipitation process is divided into two precipitation procedures. The first precipitation procedure is a product grade, and the MHP prepared in the second precipitation procedure is returned to the previous leaching section except for being used as a seed for the precipitation reaction, so as to leach nickel and cobalt in the MHP by using residual acid in the high-pressure leaching liquid. These nickel and cobalt finally re-enter the next round of nickel-cobalt precipitation process, which significantly increases the consumption of alkali in the nickel-cobalt precipitation process section, thereby increasing the production cost of the MHP. When the nickel-cobalt precipitation is complete, the filtrate in the process section mainly contains manganese and magnesium elements. The manganese is precipitated in the wastewater treatment end, and then the manganese residue is filtered and landfilled. At this time, the main element in the filtrate after the manganese residue is filtered is Mg. Since it is alkaline, it is generally neutralized by sulfuric acid and then re-enters the ocean.

[0003] At present, sodium hydroxide or MgO is used to prepare MHP in the industry. In addition to being expensive, sodium hydroxide is easy to cause local over-alkalization due to its strong alkalinity, so that the amount of alkali used in the MHP preparation process section is significantly greater than the theoretical calculation amount, which is not conducive to reducing the production cost of the MHP. MgO is low in price, but it is difficult to dissolve. Therefore, the MHP prepared by using MgO generally has a high Mg content.

[0004] Generally, new energy batteries are attributed to the processing and manufacturing industry, mainly because the raw material cost for producing the positive electrode material of the new energy battery accounts for a high proportion. Therefore, it is of great significance to optimize the MHP preparation process, significantly reduce the production cost of the MHP, and then reduce the cost of the NCM / NCA new energy battery without affecting the quality of the MHP itself. SUMMARY

[0005] The purpose of the present application is to provide a method for preparing MHP by recycling manganese precipitation liquid and application, which can solve the technical problems of high preparation cost, complicated preparation precipitation process and ineffective resource utilization of manganese precipitation liquid in the preparation of MHP.

[0006] To achieve the object of the present application, the present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a method for preparing MHP by recycling the post-manganese precipitation liquid, which comprises the following steps:

[0008] (1) mixing sodium hydroxide and magnesium oxide with the post-manganese precipitation liquid to obtain a compounded alkali slurry;

[0009] (2) mixing the post-iron and aluminum removal liquid of laterite nickel ore with the compounded alkali slurry of step (1) to perform a precipitation reaction, thereby obtaining an MHP slurry;

[0010] (3) performing thickening treatment and solid-liquid separation on the MHP slurry of step (2), thereby obtaining an MHP filter cake and a filtrate;

[0011] (4) performing manganese precipitation treatment on the filtrate of step (3), thereby obtaining manganese residue and a post-manganese precipitation liquid;

[0012] (5) recycling the post-manganese precipitation liquid of step (4) for use in the preparation of the compounded alkali slurry of step (1).

[0013] The conventional method for preparing MHP by directly adding a strong alkaline precipitant is prone to cause the formation of local over-alkaline in the precipitation system, thereby affecting the quality of MHP. Therefore, the prior art usually divides the MHP precipitation into two process sections, which not only makes the MHP preparation process cumbersome, but also increases the production cost of MHP. In addition, after the complete precipitation of nickel and cobalt, the manganese in the filtrate is precipitated by a chemical method, and then the post-manganese precipitation liquid is generally further treated and discharged into the ocean by each enterprise.

[0014] In view of this, the present application provides a method for preparing MHP by recycling the post-manganese precipitation liquid, which utilizes a compounded system of sodium hydroxide and magnesium oxide to recycle part of the post-manganese precipitation liquid to the alkali preparation process, which not only simplifies the MHP precipitation process to one step under the premise of ensuring the quality of MHP, but also greatly reduces the cost of MHP preparation and the cost of wastewater treatment.

[0015] Preferably, the molar ratio of sodium hydroxide to magnesium oxide in step (1) is 1:(0.05-2), for example, it can be 1:0.05, 1:0.1, 1:0.5, 1:1, 1:1.5 or 1:2, but is not limited to the listed values, and other values not listed in the value range are also applicable, and preferably 1:(0.1-1.5).

[0016] The molar ratio of sodium hydroxide and magnesium oxide in the present application will affect the quality of MHP. If the amount of magnesium oxide is too small compared to sodium hydroxide, it will cause local over-alkalization, resulting in high manganese and magnesium content and low nickel content in MHP. If the amount of magnesium oxide is too large compared to sodium hydroxide, it will cause excessive magnesium content in the system, resulting in a decrease in nickel content in MHP and affecting the quality of MHP.

[0017] Preferably, the concentration of the compounded alkali slurry in step (1) is 0.5-15 wt%, for example, it can be 0.5 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 11 wt%, 13 wt% or 15 wt%, but is not limited to the listed values, other values not listed within the value range are also applicable, preferably 2-8 wt%.

[0018] Preferably, the concentration of the compounded alkali slurry in step (1) is changed by changing the amount of recycled post-manganese precipitation solution.

[0019] The present application controls the concentration of the compounded alkali slurry by controlling the amount of recycled post-manganese precipitation solution. The quality of MHP is affected by the concentration of the compounded alkali slurry. Within a certain concentration range, appropriately reducing the concentration of the compounded alkali slurry can effectively reduce the content of Mn and Mg in MHP to increase the content of nickel in MHP, i.e., by adjusting the amount of recycled post-manganese precipitation solution to optimize the quality of MHP. However, considering the utilization rate of equipment and the production efficiency of MHP, the concentration of the compounded alkali slurry should not be too low.

[0020] Preferably, the concentration of magnesium ions in the post-manganese precipitation solution in step (1) is below 10 g / L, for example, it can be 10 g / L, 8 g / L, 6 g / L, 4 g / L or 2 g / L, but is not limited to the listed values, other values not listed within the value range are also applicable, preferably 2-10 g / L.

[0021] The concentration of magnesium ions in the post-manganese precipitation solution in step (1) is below a certain concentration, which is beneficial to increasing the content of nickel and cobalt in MHP.

[0022] Preferably, the solution after removing iron and aluminum from the laterite nickel ore in step (2) comprises 2-8 g / L of Ni (referring to Ni ions), such as 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L or 8 g / L, 0.15-0.8 g / L of Co (referring to Co ions), such as 0.15 g / L, 0.25 g / L, 0.35 g / L, 0.45 g / L, 0.55 g / L, 0.65 g / L, 0.75 g / L or 0.8 g / L, 1-6 g / L of Mn (referring to Mn ions), such as 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L or 6 g / L, 5-20 g / L of Mg (referring to Mg ions), such as 5 g / L, 10 g / L, 15 g / L or 20 g / L, but not limited to the listed values, other values not listed within the value range are also applicable.

[0023] Preferably, the sum of 2 times the molar amount of sodium element and the molar amount of magnesium element in the compounded alkali slurry in step (2) is A, and the sum of the molar amounts of nickel and cobalt in the solution after removing iron and aluminum from the laterite nickel ore is B, A:B=(0.9-1):(1-1.1), i.e. (Na x 2+Mg):(Ni+Co)=(0.9-1.1):(1-1.1), such as 0.9:1, 0.95:1.05 or 1:1.1, but not limited to the listed values, other values not listed within the value range are also applicable.

[0024] Preferably, the temperature of the precipitation reaction in step (2) is 55-75°C, such as 55°C, 60°C, 65°C, 70°C or 75°C, and the time is 1-8 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h, but not limited to the listed values, other values not listed within the value range are also applicable.

[0025] Preferably, the solid-liquid separation in step (3) comprises filtration, and distilled water or industrial water is used to wash the MHP filter cake during filtration.

[0026] Preferably, the manganese precipitation treatment in step (4) comprises mixing the filtrate with an alkaline substance to adjust the pH, and then filtering to obtain manganese residue and manganese precipitation solution.

[0027] Preferably, the alkaline substance comprises lime milk.

[0028] Preferably, the pH is adjusted to 8-9, such as 8, 8.5 or 9, but not limited to the listed values, other values not listed within the value range are also applicable.

[0029] Preferably, the concentration of magnesium ions in the manganese precipitation solution of step (5) is less than 10 g / L, for example, it can be 10 g / L, 8 g / L, 6 g / L, 4 g / L or 2 g / L, but is not limited to the listed values, other values not listed in the value range are also applicable, preferably 2-10 g / L.

[0030] As a preferred technical solution of the method of the present application, the method comprises the following steps:

[0031] (1) mixing sodium hydroxide and magnesium oxide with the manganese precipitation solution to obtain a compound alkali slurry;

[0032] The molar ratio of sodium hydroxide to magnesium oxide is 1:(0.1-1.5), and the concentration of the compound alkali slurry is 2-8 wt%;

[0033] (2) mixing the red soil nickel ore iron and aluminum removal solution with the compound alkali slurry, and performing a precipitation reaction at a temperature of 55-75°C for 1-8h to obtain an MHP slurry;

[0034] The red soil nickel ore iron and aluminum removal solution contains 2-8 g / L of Ni, 0.15-0.8 g / L of Co, 1-6 g / L of Mn, and 5-20 g / L of Mg; the sum of 2 times the molar amount of sodium element and the molar amount of magnesium element in the compound alkali slurry is A, and the sum of the molar amounts of nickel and cobalt elements in the red soil nickel ore iron and aluminum removal solution is B, A:B=(0.9-1.1):(1-1.1);

[0035] (3) performing thickening treatment on the MHP slurry to obtain a thickening underflow;

[0036] (4) filtering the thickening underflow while washing the MHP with distilled water or industrial water to obtain an MHP filter cake and a filtrate;

[0037] (5) mixing the filtrate with an alkaline substance to adjust the pH to 8-9, and then filtering to obtain manganese residue and a manganese precipitation solution;

[0038] The concentration of magnesium ions in the manganese precipitation solution is 2-10 g / L;

[0039] (6) recycling the manganese precipitation solution of step (5) to prepare the compound alkali slurry of step (1), and changing the concentration of the compound alkali slurry of step (1) by changing the amount of manganese precipitation solution recycled.

[0040] In a second aspect, the present application provides an MHP obtained by precipitation using the method of the first aspect.

[0041] Preferably, in the MHP, the Ni content is 40-44wt%, for example, it can be 40wt%, 40.5wt%, 41wt%, 41.5wt%, 42wt%, 43wt% or 44wt%, the Co content is 3.0-6.0wt%, for example, it can be 3wt%, 4wt%, 5wt% or 6wt%, the Mn content is 3.5-8.0wt%, for example, it can be 3.5wt%, 4.5wt%, 5.5wt%, 6.5wt%, 7.5wt% or 8wt%, the Mg content is 0.2-3wt%, for example, it can be 0.2wt%, 1.2wt%, 1.5wt%, 2.0wt% or 2.0wt% or 3.0wt%, but not limited to the listed values, other values not listed in the value range are also applicable.

[0042] The MHP described in the application can be used to prepare ternary precursor materials.

[0043] Compared with the prior art, the application has the following beneficial effects:

[0044] The application can simplify the MHP precipitation process to one step by using a sodium hydroxide and magnesium oxide compound system as a precipitant; meanwhile, part of the manganese precipitation liquid is recycled to the MHP precipitation process section, reducing the cost of wastewater treatment, and by controlling the recycling amount of the manganese precipitation liquid, the magnesium content in the MHP can be reduced, and the cost of subsequent MHP refining treatment can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 The flow chart of the method for preparing MHP by recycling the manganese precipitation liquid according to Example 1 of the application is shown in the figure. DETAILED DESCRIPTION

[0046] The technical solutions of the application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the application and should not be regarded as specific limitations on the application.

[0047] The source of the laterite nickel ore solution after removing iron and aluminum is as follows: the solution after removing iron and aluminum from the laterite nickel ore after high-pressure acid leaching, the main components are as follows: nickel ions are 3.45g / L, cobalt ions are 0.38g / L, manganese ions are 2.59g / L, and magnesium ions are 7.85g / L.

[0048] Example 1

[0049] The embodiment provides a method for preparing MHP by recycling manganese precipitation liquid, and a flow chart of the method is shown in the figure. Figure 1 The method comprises the following steps:

[0050] (1) mixed sodium hydroxide and magnesium oxide according to a molar ratio of 1:1 with the manganese precipitation solution (magnesium ion concentration of 7 g / L) to obtain a complex alkali slurry with a concentration of 7 wt%;

[0051] (2) mixed the complex alkali slurry with the laterite nickel ore iron and aluminum removal solution, and reacted at a temperature of 65°C for 5 h to obtain an MHP slurry; wherein the ratio of the sum of the molar amounts of sodium and magnesium elements in the complex alkali slurry to the sum of the molar amounts of nickel and cobalt elements in the laterite nickel ore iron and aluminum removal solution satisfies: (Na*2+Mg) / (Ni+Co) = 1;

[0052] (3) concentrated the MHP slurry to separate supernatant and MHP underflow;

[0053] (4) filtered the MHP underflow while washing the MHP with industrial water to obtain a filtrate and an MHP filter cake;

[0054] (5) added lime milk to the filtrate obtained in step (4) to adjust the pH to 8.5 for manganese precipitation, and obtained manganese residue and manganese precipitation solution after filtration;

[0055] (6) recycled the manganese precipitation solution to the complex alkali slurry preparation process in step (1).

[0056] Example 2

[0057] The present embodiment provides a method for preparing MHP by recycling manganese precipitation solution, which is the same as example 1 except that the molar ratio of sodium hydroxide and magnesium oxide in step (1) is 1:0.3.

[0058] Example 3

[0059] The present embodiment provides a method for preparing MHP by recycling manganese precipitation solution, which is the same as example 1 except that the molar ratio of sodium hydroxide and magnesium oxide in step (1) is 1:1.5.

[0060] Example 4

[0061] The present embodiment provides a method for preparing MHP by recycling manganese precipitation solution, which is the same as example 1 except that the concentration of the complex alkali slurry is changed to 4.5 wt% by changing the recycling amount of the manganese precipitation solution in step (5).

[0062] Example 5

[0063] The present embodiment provides a method for preparing MHP by recycling manganese precipitation solution, which is the same as example 1 except that the concentration of the complex alkali slurry is changed to 3 wt% by changing the recycling amount of the manganese precipitation solution in step (5).

[0064] Comparative Example 1

[0065] The present comparative example provides a method for preparing MHP, which is the same as that of Example 1 except that in step (1) a post-manganese precipitation solution is used to prepare a compounded alkali slurry only with sodium hydroxide as a precipitant.

[0066] Comparative Example 2

[0067] The present comparative example provides a method for preparing MHP, which is the same as that of Example 1 except that in step (1) a post-manganese precipitation solution is used to prepare a compounded alkali slurry only with magnesium oxide as a precipitant.

[0068] Comparative Example 3

[0069] The present example provides a method for preparing MHP by recycling a post-manganese precipitation solution, which is the same as that of Example 1 except that in step (5) the amount of recycling the post-manganese precipitation solution is changed to make the concentration of the compounded alkali slurry 15 wt%.

[0070] The MHP obtained in the above examples and comparative examples is tested for its composition by ICP method, and the test results are shown in Table 1.

[0071] Table 1

[0072]

[0073]

[0074] From Table 1, it can be seen that:

[0075] (1) Comparative Example 1 and Comparative Example 1 show that using a strong alkaline precipitant, the precipitation rate of magnesium (manganese) is high due to local over-alkalinity, which leads to high magnesium (manganese) content and low nickel content in MHP, and accordingly reduces the precipitation rate of nickel and cobalt.

[0076] (2) Comparative Example 1 and Comparative Example 2 show that using magnesium oxide alone as a precipitant, the precipitation rate of Ni, Co, Mn and Mg is controlled to make the precipitation more tend to the order of the equilibrium reaction, thereby reducing the manganese content in MHP, and the precipitation rate of nickel and cobalt is high, but the Mg content in MHP is over-standard due to incomplete dissolution of MgO in the precipitation reaction, thereby reducing the nickel content in MHP.

[0077] (3) Comparative Examples 1-3 show that increasing the content of magnesium oxide in the compounded alkali system will increase the magnesium content in MHP, which leads to a significant decrease in the nickel content in MHP, affecting the quality of MHP, but the content of magnesium oxide in the compounded alkali system should not be too low to avoid the problem of increasing the precipitation rate of manganese and magnesium due to local over-alkalinity, therefore, the content of sodium hydroxide and magnesium oxide in the compounded alkali system is preferably within a certain molar ratio range.

[0078] (4) From Comparative Example 1 and Examples 4 and 5, it can be seen that the quality of MHP is very sensitive to the concentration of the compounded alkali slurry, and appropriately reducing the concentration of the sodium hydroxide and magnesium oxide slurry can very effectively reduce the content of magnesium (manganese) in MHP, and the precipitation rate of nickel and cobalt also increases. When the circulation amount of the manganese-removed liquid is increased and the concentration of the compounded alkali slurry is reduced to 3 wt%, the precipitation rate of nickel and cobalt both reaches 98%, the content of Mg in MHP can be reduced by about 0.5 wt%, the content of nickel is as high as 42.76 wt%, and at this time the quality of the MHP product is excellent. However, the concentration of the compounded alkali slurry should not be too low, because if it is too low, on the one hand it is not conducive to the increase of the precipitation rate of nickel and cobalt, and on the other hand the utilization rate of the equipment and the production efficiency will be reduced.

[0079] (5) From Comparative Examples 1-5, from the two aspects of the precipitation rate of nickel and cobalt and the quality of MHP, it can be seen that the present application optimizes the quality of MHP product by optimizing the ratio of sodium hydroxide to magnesium oxide in the compounded system and the concentration of the alkali slurry in the compounded system, and under the premise of ensuring the quality of MHP, the MHP precipitation process can be shortened to one step, which not only greatly simplifies the process of the MHP preparation process section, but also reduces the alkali consumption during the preparation of MHP. In addition, the alkali in the manganese-removed liquid is reused in the configuration process section of the alkali slurry for MHP, which reduces the cost of wastewater treatment.

[0080] In summary, the present application provides a method and application for preparing MHP by recycling the manganese-removed liquid, which can solve the technical problems of high cost, complicated preparation precipitation process and ineffective resource utilization of the manganese-removed liquid in the preparation of MHP.

[0081] The above description is merely a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing MHP by recycling of post-manganese precipitation liquor, characterized in that, The method comprises the following steps: (1) mixing sodium hydroxide, magnesium oxide and manganese precipitation liquid to obtain a compound alkali slurry; (2) mixing the laterite nickel ore iron and aluminum removal liquid with the compound alkali slurry of step (1) to carry out a precipitation reaction to obtain an MHP slurry; (3) carrying out thickening treatment and solid-liquid separation on the MHP slurry of step (2) to obtain an MHP filter cake and a filtrate; (4) carrying out manganese precipitation treatment on the filtrate of step (3) to obtain manganese residue and manganese precipitation liquid; (5) recycling the manganese precipitation liquid of step (4) to the preparation of the compound alkali slurry of step (1); In step (1), the molar ratio of sodium hydroxide to magnesium oxide is 1:(1.5-2); the concentration of the compound alkali slurry in step (1) is 2-8 wt%, and the concentration of the compound alkali slurry in step (1) can be changed by changing the recycling amount of the manganese precipitation liquid; in the manganese precipitation liquid in step (1), the concentration of magnesium ions is 2-10 g / L.

2. The method of claim 1, wherein, In step (2), the laterite nickel ore iron and aluminum removal liquid contains 2-8 g / L of Ni, 0.15-0.8 g / L of Co, 1-6 g / L of Mn, and 5-20 g / L of Mg.

3. The method of claim 1, wherein, In step (2), the sum of 2 times the molar amount of sodium element and the molar amount of magnesium element in the compound alkali slurry is A, and the sum of the molar amounts of nickel and cobalt elements in the laterite nickel ore iron and aluminum removal liquid is B, A:B=(0.9-1.1):(1-1.1).

4. The method of claim 1, wherein, In step (2), the temperature of the precipitation reaction is 55-75 ℃, and the time is 1-8 h.

5. The method of claim 1, wherein, In step (3), the solid-liquid separation comprises filtration, and the MHP filter cake is washed with distilled water or industrial water during filtration.

6. The method of claim 1, wherein, In step (4), the manganese precipitation treatment comprises mixing the filtrate with an alkaline substance to adjust the pH, and then filtering to obtain manganese residue and manganese precipitation liquid.

7. The method of claim 6, wherein, The alkaline substance comprises lime milk.

8. The method of claim 6, wherein, The pH is adjusted to 8-9.

9. The method of claim 1, wherein, In step (5), the concentration of magnesium ions in the manganese precipitation liquid is less than 10 g / L.

10. The method of claim 9, wherein, In step (5), the concentration of magnesium ions in the manganese precipitation liquid is 2-10 g / L.

11. The method of claim 1, wherein, The method comprises the following steps: (1) mixing sodium hydroxide, magnesium oxide and manganese precipitation liquid to obtain a compound alkali slurry; The molar ratio of sodium hydroxide to magnesium oxide is 1:(1.5-2), and the concentration of the compound alkali slurry is 2-8 wt%; (2) mixing the laterite nickel ore iron and aluminum removal liquid with the compound alkali slurry to carry out a precipitation reaction at a temperature of 55-75 ℃ for 1-8 h to obtain an MHP slurry; In the laterite nickel ore iron and aluminum removal liquid, there are 2-8 g / L of Ni, 0.15-0.8 g / L of Co, 1-6 g / L of Mn, and 5-20 g / L of Mg; the sum of 2 times the molar amount of sodium element and the molar amount of magnesium element in the compound alkali slurry is A, and the sum of the molar amounts of nickel and cobalt elements in the laterite nickel ore iron and aluminum removal liquid is B, A:B=(0.9-1.1):(1-1.1); (3) carrying out thickening treatment on the MHP slurry to obtain a thickening underflow; (4) filtering the thickening underflow while washing the MHP with distilled water or industrial water to obtain an MHP filter cake and a filtrate; (5) the filtrate is mixed with a basic substance to adjust the pH to 8-9, and then filtered to obtain manganese residue and a post-manganese precipitation solution; In the post-manganese precipitation solution, the concentration of magnesium ions is 2-10 g / L; (6) the post-manganese precipitation solution in step (5) is reused in the preparation of the compound alkali slurry in step (1), and the concentration of the compound alkali slurry in step (1) is changed by changing the amount of the post-manganese precipitation solution.

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