Method for enriching manganese from medium-low-grade manganese carbonate ore and preparing iron-free manganese sulfate solution

Abstract

The invention discloses a method for enriching manganese from medium-low-grade manganese carbonate ore and preparing an iron-free manganese sulfate solution, and belongs to the field of metallurgy and chemical industry. The method mainly comprises the two core steps of sulfuric acid circulation leaching and iron removal of goethite through oxidation-shear enhanced dilution. The method comprises the following steps: firstly, leaching medium-and-low-grade manganese carbonate ore by utilizing sulfuric acid through a designed circulating leaching process to obtain a leaching solution rich in manganese sulfate; then, an oxidizing agent is added into the manganese-rich lixivium, and ferrous ions in the manganese-rich lixivium are oxidized into iron ions; the solution is slowly introduced into an iron-free manganese sulfate solution system, the pH value of the reaction system is accurately controlled, iron ions are selectively precipitated and separated out in the form of goethite in a shear strengthening mode, and therefore efficient iron removal is achieved, and finally the pure iron-free manganese sulfate solution is obtained. And a high-quality precursor solution is provided for subsequent electrolysis or preparation of battery-grade manganese sulfate, and the method has outstanding industrial application potential.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy and chemical engineering, and specifically relates to a method for enriching manganese from low-grade manganese carbonate ore and preparing iron-free manganese sulfate solution. Background Technology

[0002] With the rapid development of the global new energy industry, manganese has become increasingly strategically important, serving as a key component of cathode materials for power batteries. This shift places extremely high demands on the purity of manganese raw materials, driving the need for hydrometallurgical technologies from ore to high-purity manganese compounds (such as battery-grade manganese sulfate). Leaching, as the primary step in hydrometallurgical processes, directly determines the quality and cost of the final product through its efficiency and selectivity. Against this backdrop, my country's manganese carbonate ore resources, known for their low quality, fine texture, and impurities, have become the main targets for processing. Therefore, research on the leaching and impurity removal of manganese carbonate concentrate obtained after beneficiation is particularly important.

[0003] my country's manganese resources are poor, with manganese carbonate ore being the main component. Manganese carbonate ore is characterized by low grade, fine particle size, and close association with impurities such as calcium, magnesium, iron, phosphorus, and silicon. Traditional pyrometallurgical processing methods are energy-intensive and heavily polluting, making them unsuitable for green and low-carbon development requirements. Therefore, atmospheric pressure acid leaching has become the mainstream method, but this process faces significant challenges. On the one hand, the manganese ion concentration and manganese / magnesium ratio in the leaching solution of medium- and low-grade manganese carbonate ore are low, requiring cyclic leaching to increase the manganese ion concentration. On the other hand, the numerous impurities in manganese carbonate concentrate cause a series of problems during acid dissolution: high calcium ion concentration; and iron and other impurity ions severely affecting product performance. How to achieve efficient enrichment and selective leaching of manganese, and control impurities such as iron, calcium, and magnesium at the source, is the core technological bottleneck.

[0004] Battery-grade manganese sulfate is a key high-end product in the manganese resource value chain, and its performance fundamentally depends on the quality of the iron-free manganese sulfate precursor solution at the source. To achieve the high energy density and long cycle life requirements of lithium-ion batteries, the iron (Fe) impurity content in this solution must be deeply removed to the level of 1 ppm or even ppb. Trace amounts of iron impurities not only embed themselves in the cathode material lattice, causing lattice distortion and reducing initial capacity, but also catalyze side reactions during charge and discharge, accelerating electrolyte decomposition and battery performance degradation. If the iron removal task is postponed to the preparation stage of cobalt-manganese, nickel-manganese, and other lithium-ion battery cathode powders, the iron element will be deeply embedded inside the particles because the precursor has already formed a solid solution or co-precipitate. Separating it at this time is not only extremely difficult and costly, but will also seriously damage the chemical homogeneity and phase structure of the cathode material. Therefore, deep iron removal in the solution stage of cathode material precursor preparation is a crucial step to ensure product purity from the source. However, existing hydrometallurgical iron removal technologies (such as conventional neutralization methods and sodium ferrous sulfate methods) often face a series of technical bottlenecks when processing solution systems with extremely high purity requirements, including insufficient iron removal depth, easy formation of colloids leading to filtration difficulties, and significant loss of the main element manganese due to co-precipitation or adsorption.

[0005] Therefore, this invention focuses on the leaching and iron removal of low- and medium-grade manganese carbonate ores. It aims to improve the deep iron removal method for goethite while efficiently leaching manganese by optimizing leaching conditions and introducing cyclic leaching techniques, providing theoretical support for solving problems in actual large-scale production. This invention also aims to establish a technological pathway from complex ores to iron-free manganese sulfate solutions, providing high-quality precursor solutions for the preparation of downstream products (such as battery-grade manganese sulfate).

[0006] In conclusion, the efficient circulating leaching technology for medium- and low-grade manganese carbonate ore and the deep iron removal technology from the leaching solution are not only a strategic necessity to ensure the national manganese resource security supply, but also a key link in achieving independent control and green upgrading of the new energy industry chain. Overcoming its technical difficulties is of paramount importance for enhancing the overall competitiveness and sustainable development capability of my country's manganese chemical industry. Summary of the Invention

[0007] To address the problems of lengthy processes, low leaching efficiency, harsh iron removal processes, and high manganese loss rates in the current treatment of low- and medium-grade manganese carbonate ore, this invention provides a novel method for enriching manganese from low- and medium-grade manganese carbonate ore and preparing iron-free manganese sulfate solution. The core of this invention lies in employing a circulating leaching process, which significantly improves the actual utilization rate and manganese recovery rate of low- and medium-grade manganese carbonate ore resources, and substantially reduces the discharge of leaching washing wastewater. Furthermore, this invention innovatively proposes an oxidation-shear-enhanced dilution method for goethite, achieving highly efficient and deep iron removal from the leaching solution with a significant reduction in iron slag. This method can provide high-quality raw materials for high-value downstream products such as battery-grade manganese sulfate and high-purity metallic manganese, and its technological prospects are broad.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for enriching manganese from low- to medium-grade manganese carbonate ore and preparing iron-free manganese sulfate solution includes the following steps:

[0010] S1. Using sulfuric acid as the leaching agent, the leaching reaction is carried out by thoroughly mixing and stirring the medium- and low-grade manganese carbonate ore powder to obtain leaching solution and leaching residue. The leaching operation is repeated, and the leaching solution obtained each time is returned to the next batch of manganese carbonate ore powder for leaching reaction until the leaching solution reaches the leaching limit to obtain manganese-rich leaching solution.

[0011] S2. Add an oxidant to the manganese-rich leachate obtained in S1 to oxidize the ferrous ions to ferric ions, and then filter to obtain an oxidized solution and filter residue.

[0012] S3. The oxidized solution obtained in S2 is slowly added to the iron-free manganese sulfate solution to dilute the iron ion concentration. At the same time, the solution is heated and sheared and stirred, and the pH of the system is controlled. Through shear enhancement, the iron in the oxidized solution is precipitated in the form of goethite. After standing and aging, the iron-free manganese sulfate solution and goethite product are finally obtained.

[0013] This invention involves crushing low- to medium-grade manganese carbonate ore and then leaching it with sulfuric acid under heating and stirring conditions. This process dissolves the manganese carbonate while simultaneously transferring impurities such as iron, magnesium, calcium, and aluminum from the ore into the liquid phase. After filtration, a manganese-containing leachate is obtained. This leachate is then used to leach another batch of manganese carbonate ore, achieving gradual enrichment of manganese sulfate through cyclic leaching to obtain a manganese-rich leachate. Subsequently, an oxidant is added to the manganese-rich leachate to oxidize ferrous ions to ferric ions. Next, the oxidized leachate is diluted with an iron-free manganese sulfate solution to reduce the iron ion concentration to a level that meets the requirements for iron removal using the goethite method. The pH value of the system is controlled in real time under heating and stirring conditions. Iron removal is carried out through an oxidation-shear-enhanced dilution method for goethite, ultimately yielding an iron-free manganese sulfate solution.

[0014] The low-grade manganese carbonate ore described in this invention has a manganese content of ≤25% and a total content of 1~15wt% for iron, magnesium, calcium and aluminum.

[0015] In step S1, the sulfuric acid concentration is 0.5~12 mol / L; the leaching reaction temperature is 50~80 ℃; the liquid-to-solid ratio of the leaching reaction is 3~6 L / kg; and the particle size of the ore used in the leaching reaction is 100~300 mesh.

[0016] In step S1, the leaching operation is repeated 3 to 6 times; the leaching limit is when the pH of the leachate reaches 2 to 3.

[0017] Preferably, the sulfuric acid concentration is 0.5 ~ 2 mol / L during a single leaching process.

[0018] The inventors discovered that during a single leaching process, the manganese leaching rate initially increases and then stabilizes with increasing sulfuric acid concentration. Based on this, the sulfuric acid concentration was controlled within the aforementioned range, increasing accordingly with increasing manganese ore grade, while ensuring a manganese leaching rate above 98.5% and maintaining the leachate pH between 2 and 3. This optimized scheme aims to achieve two objectives: firstly, to reduce reagent consumption and save costs; and secondly, to facilitate pH control in subsequent goethite iron removal processes.

[0019] The inventors' research confirmed that the average leaching rate of manganese gradually decreases with increasing cycle number. Within the range of 3 to 6 cycles, the number of cycles can be appropriately reduced as the manganese ore grade increases, but it is necessary to ensure that the manganese concentration in the final manganese-rich leachate reaches 100 to 140 g / L, and that the total manganese leaching rate throughout the entire cycle process remains above 98%. The sulfuric acid concentration used in the cyclic leaching, based on the concentration of a single leaching, increases exponentially with the number of cycles, and its range is controlled between 0.5 and 12 mol / L.

[0020] The inventors discovered that during cyclic leaching, the manganese leaching rate initially increases and then stabilizes with rising temperature. On the one hand, increasing the temperature accelerates the reaction and improves the manganese leaching rate; on the other hand, excessively high temperatures lead to increased process costs. Taking all factors into consideration, the specified temperature range effectively avoids excessive energy consumption while ensuring a manganese leaching rate higher than 98%.

[0021] The inventors discovered that, under the premise of a fixed total amount of sulfuric acid and optimal other conditions, the manganese leaching rate showed a trend of first increasing and then decreasing with changes in the liquid-solid ratio or the particle size of the ore.

[0022] Regarding the liquid-to-solid ratio, when it is below 3 L / kg, the leaching system becomes too viscous, resulting in low mass transfer efficiency; while when it is above 6 L / kg, the sulfuric acid concentration is too low, leading to insufficient reaction driving force. Both of these conditions result in poor manganese leaching rates. By optimizing the liquid-to-solid ratio to 3-6 L / kg, the above contradictions are effectively resolved, achieving a manganese leaching rate of over 98% while also possessing the combined advantages of high reagent utilization and low wastewater generation.

[0023] Regarding the particle size of the ore, when it is less than 100 mesh, the specific surface area is insufficient; when it is greater than 300 mesh, the excessively fine particles are prone to agglomeration due to surface tension, which reduces the effective contact area. Limiting the particle size to 100-300 mesh effectively balances the specific surface area and the surface tension of the material, thereby ensuring that the manganese leaching rate is stably maintained above 98%.

[0024] In step S2 of this invention, the oxidant is selected from at least one of manganese dioxide, pyrolusite, oxygen, and air.

[0025] If manganese dioxide or pyrolusite is used as the oxidant, it is added to the manganese-rich leaching solution, where the manganese dioxide oxidizes the ferrous ions to ferric ions. The amount of oxidant used is 1.5 to 2 times the theoretical amount.

[0026] The oxidation reaction temperature is 50~80 ℃, and the reaction time is 0.5~3 h; the particle size of the oxidant is 50~300 mesh.

[0027] Under these conditions, ferrous ions in the manganese-rich leachate can be completely converted into ferric ions. After the reaction, the unreacted oxidant residue can be returned to the circulating leaching process or the oxidation process for reuse.

[0028] If oxygen or air is used as the oxidant, ferrous ions are oxidized to ferric ions by shear strengthening; the shear rate of shear strengthening is 1000~10000 r / min; the reaction temperature is 40~98 ℃; and the reaction time is 2~6 h.

[0029] More preferably, the shearing form includes internal shearing, external shearing, or a combination thereof. In this invention, the shear-enhancing process can significantly improve the oxidation efficiency of ferrous ions, thereby enhancing the iron removal effect of the subsequent goethite iron removal process. Experiments show that without shear-enhancing technology, using only oxygen or air as an oxidant, the oxidation rate of ferrous ions is only 60% to 70%; while with the introduction of shear-enhancing technology, the oxidation rate of ferrous ions can be increased to 90% to 98%, resulting in a significant improvement in oxidation efficiency.

[0030] In step S3, the iron concentration is controlled to be below 1 g / L and the dilution rate is below 100 (ml / min) / L during the dilution process; the temperature of the iron removal process is 75~85 ℃; the reagent used to adjust the pH is selected from at least one of calcium oxide, calcium carbonate, calcium hydroxide, sodium carbonate and sodium hydroxide, and the pH control range is 3.5~3.7; the shear rate during shear strengthening is 1000~10000 r / min.

[0031] In step S3, the iron concentration of the iron-free manganese sulfate solution should be less than 1 ppm.

[0032] Further optimization:

[0033] The leaching residue obtained in step S1 is washed with water to recover the residual manganese in the residue, and the resulting washing liquid is returned to S1 for the preparation of the sulfuric acid leaching agent required for this step.

[0034] The filter residue obtained in step S2 is returned to S1 for sulfuric acid leaching;

[0035] Step S3: Take a portion of the iron-free manganese sulfate solution and return it to the diluent to dilute the oxidizing solution.

[0036] The inventors discovered that during the dilution process, if the iron concentration exceeds 1 g / L, ferric hydroxide colloid is easily formed. This colloid not only hinders the complete conversion of iron into goethite precipitate and its removal from the liquid phase, resulting in a high residual iron ion content in the final solution, but also deteriorates the filtration and washing performance of goethite slag. Specifically, this manifests as increased viscosity of the slag slurry, slower settling speed, and extremely difficult filtration operations; simultaneously, the resulting filter cake has a high water content and carries a large amount of manganese-containing mother liquor, leading to a decrease in manganese recovery rate.

[0037] The inventors' research shows that by controlling the dilution rate to within 100 (mL / min) / L, excessively high local iron concentrations can be effectively avoided, thereby inhibiting the formation of ferric hydroxide colloids.

[0038] During the oxidation-shear-enhanced dilution of goethite for iron removal, the pH of the system must be strictly controlled within the range of 3.5 to 3.7.

[0039] The inventors discovered that the initial pH of the manganese-rich leaching solution is between 2 and 3. During the oxidation-shear-enhanced dilution of goethite for iron removal, as the final pH standard increases, the residual iron content in the solution exhibits a trend of first decreasing, then slightly increasing, and finally stabilizing, with the lowest iron concentration occurring between pH 3.5 and 3.7. When the pH is too low, iron is difficult to fully convert into goethite precipitate, resulting in its residue in the solution; while when the pH is too high, some iron forms ferric hydroxide colloids, which not only remain in the liquid phase but also cause problems such as filtration difficulties and increased manganese loss.

[0040] Further research shows that by precisely controlling the pH of the system during the iron removal process between 3.5 and 3.7, iron can be fully converted into goethite precipitate, thus achieving efficient iron removal. Under these optimized conditions, the iron concentration in the solution after iron removal can be reduced to below 1 ppm, while the manganese loss rate is less than 2%.

[0041] The inventors discovered that during the iron removal process, as the system temperature gradually increases, the residual iron content in the solution shows a trend of first decreasing and then increasing, reaching its lowest value in the range of 75–85 °C. When the reaction temperature is too low, the iron removal reaction rate is slow, and the generated precipitate is flocculent and loosely structured, resulting in poor sedimentation and filtration performance, a large amount of entrained mother liquor, and incomplete iron removal. Conversely, when the reaction temperature is too high, it is easy to form fine, almost colloidal precipitates, making sedimentation and filtration extremely difficult. At the same time, it is easy to encapsulate manganese ions, leading to a decrease in iron removal rate and an increase in energy consumption.

[0042] The inventors discovered that using shear-enhanced technology during the dilution and iron removal process can increase iron removal efficiency and reduce manganese loss. Shear-enhanced technology ensures rapid and uniform mixing of the high-concentration iron solution with the underflow, effectively eliminating localized supersaturation and preventing the formation of difficult-to-filter colloidal ferric hydroxide, thus promoting iron precipitation in the form of regular goethite crystals. Secondly, this process significantly reduces manganese loss because the adsorption and encapsulation of manganese by regular goethite crystals is far less than that of colloidal precipitation. Finally, shearing also maintains good crystal suspension, promotes crystal growth, and prevents equipment scaling, ensuring continuous and stable production operation. This series of synergistic effects enables the technology to simultaneously achieve multiple objectives: efficient iron removal, reduced valuable metal loss, and optimized production process.

[0043] Preferably, after the goethite precipitation reaction is basically completed, the slurry needs to be allowed to stand and age for 2 to 24 hours while maintaining the original temperature and pH (adjusting the pH with at least one of calcium oxide, calcium carbonate, calcium hydroxide, sodium carbonate and sodium hydroxide) to finally obtain iron-free leaching solution and goethite product.

[0044] The inventors discovered that if the precipitation reaction is not allowed to stand and age after it is basically completed, the iron content in the solution will be too high, and the generated iron precipitate will be a fine, colloidal metastable particle. This type of precipitate has extremely poor settling and filtration performance, making solid-liquid separation difficult. At the same time, it will severely adsorb and encapsulate manganese ions in the solution, leading to increased manganese loss, which in turn affects subsequent process flow and overall economic benefits.

[0045] By implementing a static aging process lasting 2–24 hours, sufficient and suitable thermodynamic and kinetic conditions can be provided for the nucleation and growth of goethite crystals, promoting the transformation of metastable iron precipitates into well-crystallized target goethite products with excellent filtration performance. Under these optimized conditions, the manganese loss rate in the final iron removal process can be controlled below 2%, and goethite and an iron-free manganese sulfate solution with an iron concentration of less than 1 ppm can be obtained.

[0046] Compared with the prior art, the present invention has at least the following advantages:

[0047] (1) Resource efficiency and environmental friendliness: By constructing a closed-loop leaching system, the internal recycling of leaching mother liquor and washing liquid is realized, which not only significantly reduces the amount of process wastewater discharge, but also significantly improves the utilization efficiency of acid. This process is particularly suitable for processing medium and low grade manganese carbonate ore, achieving efficient and high-yield leaching of manganese, with a manganese leaching rate of over 98%.

[0048] (2) Optimization of iron removal pathway and reduction of solid waste: The traditional iron removal process for goethite was systematically optimized. By precisely controlling key parameters such as oxidation, dilution, shear enhancement, pH, temperature and aging, efficient and deep iron removal was achieved. The iron content of the final product leachate was less than 1 ppm, and the manganese loss rate could be controlled below 2%. This optimized pathway not only has high iron removal efficiency, but also produces goethite slag with excellent settling and filtration performance, small slag volume and high purity, which can be used as a by-product for resource utilization, realizing the reduction and value-added of solid waste from the source.

[0049] (3) Overall process integration and industrialization prospects: The various units of this process are closely integrated, and the total recovery rate of manganese is high. The final iron-free manganese sulfate solution has a manganese-iron ratio of over 20,000, providing a stable and reliable high-quality raw material for subsequent electrolysis of metallic manganese or preparation of manganese-based fine chemicals. The entire process has sufficient material recycling and controllable energy and material consumption, demonstrating outstanding technical and economic performance and broad prospects for industrial application. Detailed Implementation

[0050] The following examples illustrate the essence of the present invention, but the scope of protection of the present invention is not limited thereto.

[0051] Example 1 (using manganese carbonate ore with a manganese grade of 16.5 wt.% as raw material)

[0052] The main chemical composition of the manganese carbonate ore used was: Mn 16.5 wt.%, Fe 3.86 wt.%, Ca 5.47 wt.%, Al 2.99 wt.%, Mg 1.67 wt.%. Three 2.5 kg portions of manganese carbonate ore were weighed, and 10 L of a 4.4 mol / L sulfuric acid solution was prepared. Leaching was carried out under the conditions of a liquid-to-solid ratio of 4 L / kg, a leaching temperature of 65 ℃, a material particle size of 100–150 mesh, and a single leaching time of 1 h. After the reaction, the solution was filtered and washed to obtain the first manganese leaching solution. The second portion of manganese ore was then leached using the same procedure, and the leaching process was repeated three times. In the final leaching, sulfuric acid or mineral powder was added appropriately to control the final pH between 2 and 3. After filtration, a manganese-rich leaching solution was obtained, and the washing water was reused as the leaching solution for the next cycle.

[0053] Subsequently, manganese dioxide (1.5 times the theoretical amount) was added to the manganese-rich leachate, and the reaction was carried out at 50 °C for 1 h. The resulting oxidized solution was then filtered. Next, the oxidized solution was slowly added to an iron-free manganese sulfate solution (iron concentration less than 1 ppm) at a flow rate of 70 mL / min / L. During the dilution process, the iron concentration was maintained below 1 g / L. The pH of the system was adjusted to 3.5 in real time using a 15% sodium carbonate solution. The temperature was maintained at 80 °C, and shearing was intensified at a rate of 5000 r / min. After all the oxidized solution had been added, the shearing was stopped, and the pH was adjusted to 3.7 using a 15% sodium carbonate solution. The solution was allowed to stand and age for 10 h under the same temperature and pH conditions. Finally, the solution was filtered while hot, and the slag was washed to obtain goethite product and an iron-free manganese sulfate solution.

[0054] Chemical analysis and calculations showed that the average leaching rate of manganese during the cyclic leaching process was 98.3%, and the leaching rate of iron was 36.4%. The resulting manganese-rich leachate had a manganese concentration of 121 g / L and an iron concentration of 11 g / L. After oxidation with manganese dioxide, the Fe concentration in the leachate decreased. 3+ / Fe 2+ The ratio reached 4400, and the ferrous ion concentration was less than 3 ppm. After iron removal via oxidation-shear-enhanced dilution of goethite (the solution volume increased slightly due to the addition of sodium carbonate solution and filtration washing), the overall manganese loss was less than 2%, and the iron removal rate was higher than 99.8%. The final iron-free manganese sulfate solution had an iron concentration of 0.8 ppm and a manganese concentration of 115 g / L.

[0055] Example 2 (using manganese carbonate ore with a manganese grade of 10.3 wt.% as raw material)

[0056] The main chemical composition of the manganese carbonate ore used was: Mn 10.3 wt.%, Fe 3.21 wt.%, Ca 3.48 wt.%, Al 5.79 wt.%, Mg 1.25 wt.%. Five 1 kg portions of manganese carbonate ore were weighed, and 4 L of a 5.5 mol / L sulfuric acid solution was prepared. Leaching was carried out under the conditions of a liquid-to-solid ratio of 4 L / kg, a leaching temperature of 70 ℃, a material particle size of 100–150 mesh, and a single leaching time of 1 h. After the reaction, the solution was filtered and washed to obtain the first manganese leaching solution. The second portion of manganese ore was then leached using the same procedure, and the leaching process was repeated five times. In the final leaching, sulfuric acid or mineral powder was added appropriately to control the final pH between 2 and 3. After filtration, a manganese-rich leaching solution was obtained, and the washing water was reused as the leaching solution for the next cycle.

[0057] Subsequently, manganese dioxide (twice the theoretical amount) was added to the manganese-rich leachate, and the reaction was carried out at 50 °C for 1 h. The resulting oxidized solution was obtained by filtration (the filter residue was returned to the sulfuric acid recycling leaching process). The oxidized solution was then slowly added to an iron-free manganese sulfate solution (iron concentration less than 1 ppm) at a flow rate of 60 mL / min / L. During dilution, the iron concentration was maintained below 1 g / L. The pH of the system was continuously adjusted to 3.5 using a 15% sodium carbonate solution, and the temperature was maintained at 80 °C with shear enhancement at a shear rate of 8000 r / min. After all the oxidized solution had been added, shearing was stopped, and the pH was adjusted to 3.7 using a 15% sodium carbonate solution. The solution was then allowed to stand and age for 10 h while maintaining the temperature and pH. Finally, the solution was filtered while hot and the residue was washed to obtain goethite product and an iron-free manganese sulfate solution. A portion of the obtained iron-free manganese sulfate solution was reused for dilution of the oxidized solution.

[0058] Chemical analysis and calculations showed that the average leaching rate of manganese during the cyclic leaching process was 98.1%, and the leaching rate of iron was 39.2%. The resulting manganese-rich leachate had a manganese concentration of 119 g / L and an iron concentration of 14 g / L. After oxidation with manganese dioxide, the Fe concentration in the leachate decreased. 3+ / Fe 2+ The ratio reached 5000, and the ferrous ion concentration was less than 1 ppm. After iron removal via oxidation-shear-enhanced dilution of goethite (the solution volume increased slightly due to the addition of sodium carbonate solution and filtration washing), the overall manganese loss was less than 2%, and the iron removal rate was higher than 99.8%. The final iron-free manganese sulfate solution had an iron concentration of 0.3 ppm and a manganese concentration of 117 g / L.

[0059] Comparative Example 1 (without using circulating leaching)

[0060] Comparative Example 1 used the same process conditions as Example 1, except that the leaching process was not a cyclic leaching process, but a conventional single leaching method was used instead. The results showed that the manganese leaching rate under these conditions was very close to that of Example 1, but the manganese concentration in the resulting leachate was only 22 g / L, and the iron concentration was 4 g / L. After iron removal, the iron concentration was 5 ppm. This method failed to effectively enrich the manganese sulfate solution; if the same amount of manganese needed to be leached as in Example 1, the total water consumption would be three times that of Example 1.

[0061] Comparative Example 2 (no shear strengthening was used during iron removal from goethite)

[0062] Comparative Example 2 used the same process conditions as Example 1, except that shear strengthening technology was not employed in the iron removal process of the oxidation-dilution goethite; instead, conventional mechanical stirring at 400 r / min was used. The results showed that the iron removal efficiency was reduced, with the residual iron concentration in the solution reaching 0.18 g / L. Furthermore, the manganese loss rate was high, reaching 7%, resulting in a final iron-free manganese sulfate solution with a manganese concentration of 111 g / L. This process failed to achieve both efficient and deep iron removal and full utilization of manganese.

Claims

1. A method for enriching manganese from low- to medium-grade manganese carbonate ore and preparing iron-free manganese sulfate solution, characterized in that, Includes the following steps: S1. Using sulfuric acid as the leaching agent, the leaching reaction is carried out by thoroughly mixing and stirring the medium- and low-grade manganese carbonate ore powder to obtain leaching solution and leaching residue. The leaching operation is repeated, and the leaching solution obtained each time is returned to the next batch of manganese carbonate ore powder for leaching reaction until the leaching solution reaches the leaching limit to obtain manganese-rich leaching solution. S2. Add an oxidant to the manganese-rich leachate obtained in S1 to oxidize the ferrous ions to ferric ions, and then filter to obtain an oxidized solution and filter residue. S3. The oxidized solution obtained in S2 is slowly added to the iron-free manganese sulfate solution to dilute the iron ion concentration. At the same time, the solution is heated and sheared and stirred, and the pH of the system is controlled. Through shear enhancement, the iron in the oxidized solution is precipitated in the form of goethite. After standing and aging, the iron-free manganese sulfate solution and goethite product are finally obtained.

2. The method according to claim 1, characterized in that: The medium- and low-grade manganese carbonate ore contains ≤25% manganese and 1~15wt% total iron, magnesium, calcium and aluminum.

3. The method according to claim 1, characterized in that: In step S1, the sulfuric acid concentration is 0.5~12 mol / L; the leaching reaction temperature is 50~80℃; the liquid-to-solid ratio of the leaching reaction is 3~6 L / kg; and the particle size of the ore used in the leaching reaction is 100~300 mesh.

4. The method according to claim 1 or 3, characterized in that: In step S1, the leaching operation is repeated 3 to 6 times; the leaching limit is when the pH of the leachate reaches 2 to 3.

5. The method according to claim 1, characterized in that: In step S2, the oxidant is selected from at least one of manganese dioxide, pyrolusite, oxygen, and air.

6. The method according to claim 5, characterized in that: If manganese dioxide or pyrolusite is selected as the oxidant, it is added to the manganese-rich leaching solution, and the ferrous ions are oxidized to ferric ions by manganese dioxide. The oxidation reaction temperature is 50~80 ℃, and the reaction time is 0.5~3 h; the particle size of the oxidant is 50~300 mesh. If oxygen or air is used as the oxidant, ferrous ions are oxidized to ferric ions through shear strengthening; the shear rate of shear strengthening is 1000~10000 r / min; the reaction temperature is 40~98 ℃; and the reaction time is 2~6 h. The amount of oxidant used is 1.5 to 2 times the theoretical amount.

7. The method according to claim 1, characterized in that: In step S3, the iron concentration is controlled to be below 1 g / L and the dilution rate is below 100 (ml / min) / L during the dilution process; the temperature of the iron removal process is 75~85℃; the reagent used to adjust the pH is selected from at least one of calcium oxide, calcium carbonate, calcium hydroxide, sodium carbonate and sodium hydroxide, and the pH control range is 3.5~3.7; the shear rate during shear strengthening is 1000~10000 r / min.

8. The method according to claim 1 or 7, characterized in that: In step S3, the iron concentration of the iron-free manganese sulfate solution should be less than 1 ppm.

9. The method according to claim 1, characterized in that: In step S3, the settling and aging time is 2 to 24 hours.

10. The method according to claim 1, characterized in that: The leaching residue obtained in step S1 is washed with water to recover the residual manganese in the residue, and the resulting washing liquid is returned to S1 for the preparation of the sulfuric acid leaching agent required for this step. The filter residue obtained in step S2 is returned to S1 for sulfuric acid leaching; In step S3, a portion of the iron-free manganese sulfate solution is returned to the diluted oxidizing solution.