A method for extracting manganese from low-grade rhodochrosite

Abstract

The application discloses a method for extracting manganese from low-grade rhodochrosite, and the manganese is extracted according to the following method: after low-grade rhodochrosite is dried, crushed and screened, the low-grade rhodochrosite is uniformly mixed with a flux, heated to 165 DEG C under the protection of an inert gas in a tube furnace, baked at constant temperature, heated to 245 DEG C, baked at constant temperature, then heated to 620 DEG C, baked at constant temperature, naturally cooled to room temperature after baking is completed, deionized water is added to leach manganese sulfate from the baked sample at room temperature, filtration separation is conducted, after the filtrate is purified and impurities are removed in stages, ammonium bicarbonate is added to convert the manganese sulfate into manganese carbonate, the manganese carbonate is filtered and washed with deionized water, high-temperature calcination is conducted, and three-manganese tetroxide is obtained. The method utilizes a reducing atmosphere formed by a pyroprocess flux under the protection of an inert gas, fully utilizes manganese sources in low-grade rhodochrosite, reduces high-valence manganese in the low-grade rhodochrosite into low-valence manganese (+2), utilizes the low-valence manganese to carry out a sulfation reaction, and realizes efficient extraction of manganese from the low-grade rhodochrosite by leaching of formed soluble MnSO4 through deionized water.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization of low-grade minerals, specifically relating to a method for extracting manganese from low-grade rhodochrosite. Background Technology

[0002] Manganese ore is an important mineral resource in my country, and metallic manganese produced from it has extremely wide applications in metallurgy, chemical industry, light industry, and electronic materials. my country has abundant manganese reserves, mainly stored in the form of rhodochrosite. However, most of my country's rhodochrosite is of low grade, and the main mineral, MnCO3, is often accompanied by a large amount of other minerals. Furthermore, due to the complex formation of manganese deposits in nature, some mined rhodochrosite contains high-valence manganese. Therefore, reduction methods are used to reduce this high-valence manganese to a lower valence state, which is more conducive to manganese leaching. Because it is easily soluble in acid, the main process for extracting manganese from rhodochrosite in my country is currently the hydrometallurgical process, supplemented by pyrometallurgical methods. Acid leaching is the most widely used method, with roasting-acid leaching being the most common. This involves first roasting the rhodochrosite at low temperature to decompose it into manganese oxide, followed by acid leaching to improve the leaching rate. Pyrometallurgical processes are suitable for high-grade rhodochrosite, converting manganese carbonate into manganese monoxide through reduction roasting, and then smelting it in a blast furnace or electric furnace to obtain ferromanganese alloys. In addition, there is the ammonia leaching method, which uses an ammonia-ammonium carbonate solution to leach manganese, forming soluble complexes, which are then purified and precipitated to obtain manganese compounds. These methods have advantages in terms of cost and resource utilization, but they still face challenges in actual production, including technology optimization, pollution control, and economic viability. Breakthroughs in efficient manganese leaching technology from low-grade rhodochrosite and the construction of a green circular system are crucial for ensuring my country's manganese resource security. (Invention Content)

[0003] To address the aforementioned technical problems, the first objective of this invention is to provide a flux, and the second objective is to provide a method for extracting manganese from low-grade rhodochrosite. This method utilizes a pyrometallurgical flux to create a reducing atmosphere under inert gas protection, fully leveraging the manganese source in the low-grade rhodochrosite to reduce the high-valence manganese in the low-grade rhodochrosite to +2 valence manganese. The low-valence manganese is then used for a sulfation reaction, and the resulting soluble MnSO4 is leached with deionized water, thereby achieving efficient extraction of manganese from the low-grade rhodochrosite.

[0004] To achieve the aforementioned first objective, the present invention provides the following technical solution: a flux, characterized in that it is composed of 78% ammonium sulfate and 22% oxalic acid.

[0005] The second objective of this invention is achieved as follows: a method for extracting manganese from low-grade rhodochrosite, characterized by the following extraction method: the low-grade rhodochrosite is dried, pulverized, and sieved, then mixed evenly with the flux, and heated in a tube furnace under inert gas protection to 165°C at a rate of 15-20°C / min, and roasted at a constant temperature for 5-10 min; then heated to 245°C at a rate of 10-15°C / min, and roasted at a constant temperature for 5-10 min; then heated to 620°C at a rate of 20-25°C / min, and roasted at a constant temperature for 10-20 min; after roasting, it is naturally cooled to room temperature, deionized water is added, and manganese sulfate is leached from the roasted sample at room temperature; the sample is filtered and separated; the filtrate is purified by graded purification to remove impurities; ammonium bicarbonate is added to convert manganese sulfate to manganese carbonate; the sample is filtered, washed with deionized water, and calcined at high temperature to obtain manganese tetroxide; the manganese tetroxide is pulverized or sand-milled, washed with deionized water, and dried to obtain high-purity manganese tetroxide.

[0006] In the above scheme, low-grade rhodochrosite is dried at 100-110℃.

[0007] In the above scheme: the dried low-grade rhodochrosite is crushed to a particle size ≤75μm and sieved through a 200-mesh sieve.

[0008] In the above scheme, the mass ratio of rhodochrosite powder to flux is 2 to 3:1.

[0009] In the above scheme, the inert gas is nitrogen, and the flow rate is 1.5–2.5 L / min. Nitrogen is inexpensive and commonly used.

[0010] In the above scheme: the amount of deionized water added is 8 to 12 times the mass of low-grade rhodochrosite, and the leaching time is 50 to 70 minutes.

[0011] In the above scheme, the steps for filtrate staged purification and impurity removal are as follows: Add manganese powder to the filtrate, react at room temperature, and filter; add ammonium sulfide to the filtrate, react at room temperature, and filter; add flocculant to the filtrate, precipitate, and filter; add ammonia to the filtrate to adjust the pH to 6-7, add citric acid, react at room temperature, and filter to obtain the purified liquid. Adding manganese powder reduces residual trace metal ions such as lead, iron, cobalt, nickel, copper, and zinc in the crude manganese sulfate solution to metals, which are then separated by filtration; adding ammonium sulfide to the filtrate further removes residual trace metal ions; adding polyacrylamide to the filtrate removes residual aluminum and silicon; adding citric acid to the filtrate allows residual magnesium ions in the solution to combine with citric acid, which is then removed during the subsequent ammonium bicarbonate precipitation process.

[0012] The amount of manganese powder added is 2‰ to 3‰ of the low-grade rhodochrosite powder; the amount of ammonium sulfide added is 1‰ to 2‰ of the mass of the low-grade rhodochrosite powder. The flocculant is polyacrylamide, and the amount added is 1‰ to 2‰ of the mass of the low-grade rhodochrosite powder. The amount of citric acid added is 1.5‰ to 2‰.

[0013] The present invention relates to a mixed flux of ammonium sulfate and oxalic acid. Oxalic acid has a melting point of approximately 189°C, while ammonium sulfate has a higher melting point. However, when ammonium sulfate and oxalic acid are mixed in a specific ratio, a eutectic mixture with melting points lower than their respective individual melting points is formed. Oxalic acid decomposes at temperatures far below its theoretical melting point, and ammonium sulfate decomposes prematurely near its melting point. When the temperature is raised to 165°C, oxalic acid decomposes and releases gas, with the products being CO and CO2. CO has reducing properties and can reduce a small amount of high-valence manganese in low-grade rhodochrosite to +2-valence manganese. Simultaneously, the large amount of gas generated and its flow within the low-grade rhodochrosite improves mass and heat transfer efficiency. When the temperature reaches 245℃, ammonium sulfate begins to decompose, producing large amounts of ammonia and ammonium bisulfate. Ammonium bisulfate continues to decompose, producing ammonia and sulfuric acid vapor, thus initiating the sulfation reaction of manganese in the low-grade rhodochrosite. Due to the presence of oxalic acid in the initial stage, the high-valence manganese in the low-grade rhodochrosite also exists in the +2 valence state, meaning all manganese in the low-grade rhodochrosite participates in the sulfation reaction, forming manganese sulfate. Simultaneously, other metals in the low-grade rhodochrosite react similarly to manganese, forming metal sulfates. When the temperature reaches 620℃, some metal sulfates begin to decompose, especially ferric sulfate, which has a low decomposition temperature and can almost completely decompose to form iron oxide. At this temperature, manganese sulfate remains stable. Because manganese sulfate is readily soluble in water, the manganese sulfate in the sample roasted at 620℃ can be completely leached with deionized water. Impurities exist as insoluble substances such as iron oxide, nickel oxide, calcium sulfate, barium sulfate, and lead sulfate in the leaching residue, thus achieving the separation of a large number of impurities from manganese sulfate during the roasting stage.

[0014] Beneficial effects:

[0015] (1) The present invention strengthens the reducing atmosphere by using inert gas to protect the roasting process, which greatly reduces the consumption of ammonium sulfate composite flux and realizes the complete conversion of a small amount of high-valence manganese in low-grade rhodochrosite into low-valence manganese.

[0016] (2) The low-temperature roasting process proposed in this invention, combined with water leaching to extract manganese, reduces energy consumption and extends the service life of the equipment, which is a green and environmentally friendly process.

[0017] (3) Compared with the prior art, the present invention improves the sulfation efficiency of manganese in the roasting stage, so that the recovery rate of manganese in low-grade rhodochrosite is above 98.50%. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments.

[0019] Example 1

[0020] Low-grade rhodochrosite (containing 18.6% Mn) was obtained from a smelter in Guizhou Province. The rhodochrosite was dried at 105±5℃, pulverized to a particle size ≤75μm, and sieved through a 200-mesh sieve to obtain a rhodochrosite sample. 100 g of the sample was mixed evenly with 40 g of a composite flux consisting of 78% ammonium sulfate and 22% oxalic acid. The mixture was then staged roasted in a tube furnace under nitrogen protection at a nitrogen flow rate of 1.8 L / min. First, the temperature was increased to 165℃ at a rate of 15℃ / min and roasted at this temperature for 10 min. Then, the temperature was increased to 245℃ at a rate of 10℃ / min and roasted at this temperature for 8 min. Finally, the temperature was increased to 620℃ at a rate of 25℃ / min and roasted at this temperature for 15 min. After roasting, the sample was allowed to cool naturally to room temperature. The roasted sample was then removed, and 1 L of deionized water was added to leach 55 μm at room temperature. The sample was then filtered for separation. 0.2 g of metallic manganese powder was added to the crude manganese sulfate solution, and the reaction was carried out at room temperature for 30 min. After filtration, 0.15 g of ammonium sulfide was added to the filtrate, and the reaction was carried out at room temperature for 15 min. After filtration, 0.1 g of flocculant polyacrylamide was added to the filtrate, and the reaction was carried out for 30 min. After precipitation, the filtrate was filtered. Ammonia water was added to the filtrate to adjust the pH to 6.8, and 0.2 g of citric acid was added. The reaction was carried out at room temperature, and the filtrate was filtered to obtain the purified solution. Ammonium bicarbonate was added to convert manganese sulfate to manganese carbonate. The solution was washed three times with deionized water and calcined at 936℃ to obtain manganese tetroxide. After crushing or sand milling, the solution was washed three times with deionized water and dried to obtain high-purity manganese tetroxide. The manganese recovery rate in low-grade rhodochrosite was 98.67%, and the purity of manganese tetroxide was 99.86%.

[0021] Example 2

[0022] Low-grade rhodochrosite (containing 18.6% Mn) was obtained from a smelter in Guizhou Province. The rhodochrosite was dried at 105℃, pulverized to a particle size ≤75μm, and sieved through a 200-mesh sieve to obtain a rhodochrosite sample. 100 g of the sample was mixed evenly with 33.3 g of a composite flux consisting of 78% ammonium sulfate and 22% oxalic acid. The mixture was then staged roasted in a tube furnace under nitrogen protection at a nitrogen flow rate of 1.5 L / min. First, the temperature was increased to 165℃ at a rate of 20℃ / min and roasted at a constant temperature for 5 min; then, the temperature was increased to 245℃ at a rate of 15℃ / min and roasted at a constant temperature for 10 min; finally, the temperature was increased to 620℃ at a rate of 20℃ / min and roasted at a constant temperature for 20 min. After roasting, the sample was allowed to cool naturally to room temperature. The roasted sample was then removed, and 1.2 L of deionized water was added to leach 50 μm at room temperature, followed by filtration. 0.3 g of metallic manganese powder was added to the crude manganese sulfate solution, and the reaction was carried out at room temperature for 30 min. After filtration, 0.1 g of ammonium sulfide was added to the filtrate, and the reaction was carried out at room temperature for 15 min. After filtration, 0.2 g of flocculant polyacrylamide was added to the filtrate, and the reaction was carried out for 30 min. After precipitation, the filtrate was filtered. Ammonia water was added to the filtrate to adjust the pH to 6.5, and 0.15 g of citric acid was added. The reaction was carried out at room temperature, and the purified solution was obtained by filtration. Ammonium bicarbonate was added to convert manganese sulfate to manganese carbonate. The solution was washed three times with deionized water and calcined at 936℃ to obtain manganese tetroxide. After crushing or sand milling, the solution was washed three times with deionized water and dried to obtain high-purity manganese tetroxide. The manganese recovery rate in low-grade rhodochrosite was 98.96%, and the purity of manganese tetroxide was 99.75%.

[0023] Example 3

[0024] Low-grade rhodochrosite (containing 18.6% Mn) was obtained from a smelter in Guizhou Province. The rhodochrosite was dried at 105℃, pulverized to a particle size ≤75μm, and sieved through a 200-mesh sieve to obtain a rhodochrosite sample. 100 g of the sample was mixed evenly with 50 g of a composite flux consisting of 78% ammonium sulfate and 22% oxalic acid. The mixture was then staged roasted in a tubular furnace under nitrogen protection at a nitrogen flow rate of 2.5 L / min. First, the temperature was increased to 165℃ at a rate of 15℃ / min and roasted at this temperature for 10 min. Then, the temperature was increased to 245℃ at a rate of 10℃ / min and roasted at this temperature for 8 min. Finally, the temperature was increased to 620℃ at a rate of 25℃ / min and roasted at this temperature for 10 min. After roasting, the sample was allowed to cool naturally to room temperature. The roasted sample was then removed, and 0.8 L of deionized water was added to leach 70 μm at room temperature. The leaching was then filtered to obtain crude manganese sulfate solution. 0.3 g of metallic manganese powder was added to the crude manganese sulfate solution, and the reaction was carried out at room temperature for 30 min. After filtration, 0.1 g of ammonium sulfide was added to the filtrate, and the reaction was carried out at room temperature for 15 min. After filtration, 0.2 g of flocculant polyacrylamide was added to the filtrate, and the reaction was carried out for 30 min. After precipitation, the filtrate was filtered. Ammonia water was added to the filtrate to adjust the pH to 6.6, and 0.15 g of citric acid was added. The reaction was carried out at room temperature, and the filtrate was filtered to obtain the purified solution. Ammonium bicarbonate was added to convert manganese sulfate to manganese carbonate. The solution was washed three times with deionized water and calcined at 936℃ to obtain manganese tetroxide. After crushing or sand milling, the solution was washed three times with deionized water and dried to obtain high-purity manganese tetroxide. The manganese recovery rate in low-grade rhodochrosite was 99.06%, and the purity of manganese tetroxide was 99.82%.

[0025] This invention is not limited to the above embodiments. Those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this invention. The scope of this invention is defined by the claims and their equivalents.

Claims

1. A method for extracting manganese from low-grade rhodochrosite, characterized in that, Extraction was performed as follows: Low-grade rhodochrosite was dried, pulverized, and sieved, then mixed evenly with a flux consisting of 78% ammonium sulfate and 22% oxalic acid. Under inert gas protection, the mixture was heated in a tube furnace at a rate of 15–20 °C / min to 165 °C and roasted at a constant temperature for 5–10 min. Then, the temperature was increased to 245 °C at a rate of 10–15 °C / min and roasted at a constant temperature for 5–10 min. After roasting, the temperature was naturally cooled to room temperature. Deionized water was added to leach manganese sulfate from the roasted sample at room temperature. The mixture was filtered and separated. The filtrate was purified by graded purification to remove impurities. Ammonium bicarbonate was added to convert manganese sulfate to manganese carbonate. The mixture was filtered, washed with deionized water, and calcined at high temperature to obtain manganese tetroxide. The manganese tetroxide was pulverized or sand-milled, washed with deionized water, and dried to obtain high-purity manganese tetroxide.

2. The method for extracting manganese from low-grade rhodochrosite according to claim 1, characterized in that: Low-grade rhodochrosite is dried at 100–110°C.

3. The method for extracting manganese from low-grade rhodochrosite according to claim 2, characterized in that: The dried low-grade rhodochrosite is crushed into particles with a diameter of ≤75 μm.

4. The method for extracting manganese from low-grade rhodochrosite according to any one of claims 1-3, characterized in that: The mass ratio of rhodochrosite powder to flux is 2 to 3:

1.

5. The method for extracting manganese from low-grade rhodochrosite according to claim 4, characterized in that: The inert gas is nitrogen, and the flow rate is 1.5–2.5 L / min.

6. The method for extracting manganese from low-grade rhodochrosite according to claim 5, characterized in that: The amount of deionized water added is 8 to 12 times the mass of low-grade rhodochrosite, and the leaching time is 50 to 70 minutes.

7. The method for extracting manganese from low-grade rhodochrosite according to claim 6, characterized in that: The steps for filtrate classification, purification, and impurity removal are as follows: add manganese powder to the filtrate, react at room temperature, and filter; add ammonium sulfide to the filtrate, react at room temperature, and filter; add flocculant to the filtrate, precipitate, and filter; add ammonia to the filtrate to adjust the pH to 6-7, add citric acid, react at room temperature, and filter to obtain the purified liquid.