A method for recovering manganese from electric furnace ferromanganese slag

Abstract

This invention discloses a method for recovering manganese from electric furnace ferromanganese slag, comprising the following steps: crushing and uniformly mixing the ferromanganese slag, then drying it; uniformly mixing the dried ferromanganese slag with flux, calcining it in a tube furnace until the reaction is complete, and after the temperature drops to room temperature, removing the calcined slag sample, adding deionized water to leach manganese sulfate at room temperature, filtering and separating to obtain crude manganese sulfate solution and leaching residue; adding metallic manganese powder, ammonium sulfide, and flocculant to the crude manganese sulfate solution to further remove impurities, then adjusting the pH, filtering and separating to obtain a four-stage purified manganese sulfate solution. This invention utilizes a mixed flux to sulfatate metal oxides, achieving higher sulfatation efficiency than existing technologies, accelerating the process of extracting manganese from ferromanganese slag to produce high-purity manganese tetroxide, while simultaneously solving the resource waste and environmental pollution problems caused by ferromanganese slag from electric furnaces.

Description

Technical Field

[0001] This invention relates to the field of industrial waste resource utilization, specifically a method for recovering manganese from electric furnace manganese-iron slag. Background Technology

[0002] Electric arc furnace ferromanganese slag is a molten byproduct produced during the smelting of ferromanganese ore or manganese alloys (such as ferrosilicon and low-carbon ferromanganese) in electric arc furnaces or submerged arc furnaces. Compared with blast furnace ferromanganese slag, it has a higher MnO content (10%–25%), and due to the higher smelting temperature (1500–1800℃), its mineral composition and physicochemical properties differ, giving it unique resource potential. Currently, manganese is recovered from ferromanganese ore mining and smelting waste slag using a combined magnetic separation-gravity separation process, but the manganese recovery rate is low (usually 60%–70%). Acid leaching dissolves the manganese in the waste slag to generate manganese sulfate solution, which, after purification, is used to produce electrolytic manganese and manganese sulfate fertilizer, but this process faces significant environmental pressure from the acid leaching wastewater. Adopting a combined pyrometallurgical pretreatment and water leaching process not only reduces material costs but also alleviates environmental pressure, making it a green and low-carbon technology. However, reducing pyrometallurgical energy consumption and improving ferromanganese separation efficiency remain the core areas for improvement in the combined pyrometallurgical pretreatment and water leaching process. Summary of the Invention

[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 recovering manganese from electric furnace ferromanganese slag. This method utilizes a mixed flux to sulfatate metal oxides, achieving higher sulfatation efficiency than existing technologies. This accelerates the process of extracting manganese from electric furnace ferromanganese slag to produce high-purity manganese tetroxide, while simultaneously solving the problems of resource waste and environmental pollution caused by electric furnace ferromanganese slag.

[0004] To achieve the first objective mentioned above, the present invention is implemented through the following technical solution: a flux, characterized in that it is composed of 65% ammonium sulfate and 35% thiourea.

[0005] The second objective of this invention is achieved as follows: a method for recovering manganese from electric furnace ferromanganese slag, characterized by the following steps: crushing and uniformly mixing the electric furnace ferromanganese slag, and drying it; uniformly mixing the dried electric furnace ferromanganese slag with the flux at a mass ratio of 1:1.2-1.5, heating it to 150°C in a tube furnace at a heating rate of 5-10°C / min, calcining it at a constant temperature for 80-90 min, then continuing to heat it to 320°C at a heating rate of 5-10°C / min, calcining it for another 25-30 min, then continuing to heat it to 620°C at a heating rate of 5-10°C / min, calcining it for another 50-60 min until the reaction is complete, and then cooling the temperature to room temperature, taking out the calcined slag sample, adding deionized water to leach manganese sulfate at room temperature, filtering and separating to obtain crude manganese sulfate solution and leaching residue;

[0006] Manganese powder is added to crude manganese sulfate solution, reacts at room temperature, and then separated and filtered to remove heavy metals, yielding a primary purified manganese sulfate solution. Ammonium sulfide is added to the primary purified manganese sulfate solution to further remove heavy metals, and the solution is filtered to obtain a secondary purified manganese sulfate solution. A flocculant is added to remove trace amounts of residual aluminum and silicon from the secondary purified manganese sulfate solution, and the solution is filtered to obtain a tertiary purified manganese sulfate solution. Ammonia is added to the tertiary purified manganese sulfate solution to adjust the pH to 6-7, citric acid is added to complex with magnesium ions in the solution, and the solution is filtered and separated to obtain a quaternary purified manganese sulfate solution. In the above scheme: ammonium bicarbonate is added to the obtained quaternary purified manganese sulfate solution, reacts to obtain manganese carbonate precipitate, and the solution is filtered to obtain manganese carbonate and ammonium sulfate solution. The manganese carbonate precipitate is washed with water and then calcined to obtain manganese tetroxide.

[0007] In the above scheme: the electric furnace manganese iron slag is crushed into particles with a diameter ≤80μm and dried at 100-110℃.

[0008] In the above scheme: during leaching, the amount of deionized water added is 8-12 times the mass of the electric furnace manganese iron slag, and the leaching time is 50-70 minutes.

[0009] In the above scheme: the amount of metallic manganese powder added is 2‰-3‰ of the mass of the electric furnace manganese iron slag; the amount of ammonium sulfide added is 1‰-2‰ of the mass of the electrolytic furnace manganese iron slag.

[0010] In the above scheme: the flocculant is polyacrylamide, and the addition amount is 1‰-2‰ of the mass of the electric furnace manganese iron slag.

[0011] The valence state distribution of manganese in electric arc furnace (EAF) ferromanganese slag is complex, mainly related to the smelting process, slag composition, and cooling conditions. The reducing atmosphere (excess carbon) within the EAF reduces high-valence manganese oxides to low-valence states (MnO). Therefore, manganese in EAF ferromanganese slag primarily exists as manganese monoxide (MnO), with a few cases existing as complex manganese aluminum oxides (manganese trioxide). During slag cooling, contact with air leads to oxidation, or under strongly oxidizing conditions during smelting (such as oxygen-enriched blowing), a very small amount of manganese tetroxide may form. Simultaneously, EAF ferromanganese slag has a high iron content, and high-purity manganese tetroxide has strict limits on impurity iron. Therefore, the key to efficiently recovering manganese from EAF ferromanganese slag to produce high-purity manganese tetroxide lies in the efficient reduction and sulfation of manganese oxides, while simultaneously ensuring efficient separation of ferromanganese and manganese.

[0012] The mixed flux used in this invention has ammonium sulfate with a melting point of 280℃ and thiourea with a melting point of 180℃. Their eutectic point is 150℃, meaning that the melting point of electric furnace ferromanganese slag compared to using ammonium sulfate alone (existing common technology) is lowered by 130℃, and the melting point of thiourea is lowered by 30℃. The electric furnace ferromanganese slag begins to flow and decompose at the low temperature of 150℃, improving the mass and heat transfer efficiency of the reaction process between the mixed flux and the ferromanganese slag. The decomposition temperature of ammonium sulfate is also correspondingly lowered. At the low temperature of 150℃, it decomposes to produce a large amount of ammonia and ammonium bisulfate, while ammonium bisulfate continues to decompose to produce ammonia and sulfuric acid vapor, thus causing the sulfation reaction of valuable metals such as manganese, iron, nickel, and cobalt in the electric furnace ferromanganese slag. When the temperature rises above 320℃, the rate at which sulfuric acid gradually decomposes to form sulfur trioxide accelerates, slowing down the sulfation reaction process. Therefore, this invention controls the first-stage roasting temperature at 320℃. The existing method uses a single ammonium sulfate for roasting at a temperature of 380℃. Since the temperature at which ammonium sulfate completely decomposes into various gases is 350℃, the complete decomposition of ammonium sulfate into gases reduces the sulfation reaction process. Therefore, the existing technology needs to increase the amount of ammonium sulfate (the ratio of ammonium sulfate to manganese slag is as high as 15:1) to compensate for the decomposition loss of ammonium sulfate.

[0013] Thiourea in the mixed flux begins to decompose at a low temperature of 150℃, initially producing cyanamide and hydrogen sulfide (SC(NH4)2→NH2CN+H2S). The cyanamide further decomposes to produce ammonia, dicyandiamide, melamine, etc. Hydrogen sulfide reduces the high-valence manganese oxides in the electric furnace ferromanganese slag to low-valence manganese oxide, which then reacts with sulfuric acid vapor to form manganese sulfate. When the temperature rises to 320℃, the main products of thiourea are sulfur dioxide, ammonia, and nitrogen. Sulfur dioxide, in conjunction with hydrogen sulfide, further reacts manganese dioxide to low-valence manganese, accelerating the sulfation process of manganese oxide through sulfur dioxide generation. The release of ammonia creates a reducing atmosphere at the high-temperature stage (620℃), keeping manganese in a low-valence state. Nitrogen generated through thermal decomposition acts as a protective agent, slowing the rapid decomposition of ammonium sulfate to sulfur trioxide and enhancing the sulfation reaction process. When the temperature rises to 620℃, the manganese in the electric furnace ferromanganese slag is completely converted into manganese sulfate, while some other metal sulfates (ferric sulfate, nickel sulfate, etc.) decompose to form corresponding oxides. In particular, ferric sulfate completely decomposes to form water-insoluble iron oxide. Leaching the insoluble matter with deionized water removes some of the metallic impurities from the manganese sulfate. Further impurities are removed by adding manganese powder, ammonium sulfide, and flocculants, resulting in a high-purity manganese sulfate purified solution. This achieves the goal of manganese recovery. The obtained manganese sulfate purified solution can be further reacted to form manganese carbonate, which can then be calcined to produce high-purity battery-grade manganese tetroxide.

[0014] Beneficial effects:

[0015] (1) The present invention utilizes the low eutectic point to reduce the calcination temperature of ammonium sulfate and thiourea to 150°C, thereby reducing energy consumption and extending the service life of the equipment.

[0016] (2) The present invention utilizes molten salt + water leaching to remove impurities, and the recovery rate of manganese extracted from electric furnace manganese iron slag can reach more than 99.3%.

[0017] (3) Compared with the prior art, the present invention removes impurities more thoroughly. The iron content of impurities in manganese tetroxide prepared according to the method of the present invention is much less than 10 ppm, which can be used as a raw material for preparing high-end battery cathode materials.

[0018] (4) The present invention utilizes a mixed flux to sulfatate metal oxides, which is more efficient than the existing sulfatation technology, accelerates the process of extracting manganese from electric furnace manganese iron slag to produce high-purity manganese tetroxide, and solves the problems of resource waste and environmental pollution caused by electric furnace manganese iron slag. Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments.

[0020] Example 1

[0021] The main chemical composition of the electric furnace manganese iron slag sample is: manganese 10.2%, magnesium 3.6%, iron 2.8%, aluminum 6.5%, calcium 25.7%, silicon 17.2%, and heavy metal elements such as zinc, copper, nickel, and lead are in trace amounts.

[0022] After crushing and mixing the electric furnace manganese-iron slag with a particle size ≤80μm, dry it at 100-110℃ to constant weight.

[0023] Accurately weigh 100g of electric furnace ferromanganese slag and 120g of mixed flux (65% ammonium sulfate and 35% thiourea by mass), mix thoroughly, and then perform gradient calcination in a tube furnace. First, heat to 150℃ in the tube furnace at a heating rate of 10℃ / min and calcine at this temperature for 90min; then, continue heating to 320℃ at a heating rate of 10℃ / min and calcine for another 30min; finally, continue heating to 620℃ at a heating rate of 10℃ / min and calcine for another 60min. After the reaction is complete, let the temperature drop to room temperature, remove the calcined slag sample, add 1L of deionized water to leach manganese sulfate at a constant room temperature, leach for 60min, and then filter to obtain crude manganese sulfate solution. At room temperature, 2‰ metallic manganese powder was added to crude manganese sulfate solution. After reacting at room temperature for 30 minutes, the solution was separated and filtered to remove heavy metals such as zinc, nickel, and cobalt, yielding a primary purified manganese sulfate solution. 1‰ ammonium sulfide was added to the primary purified manganese sulfate solution to further remove heavy metals, followed by filtration to obtain a secondary purified manganese sulfate solution. 1‰ polyacrylamide was added to the secondary purified manganese sulfate solution to remove trace amounts of residual aluminum and silicon, followed by filtration to obtain a tertiary purified manganese sulfate solution. Ammonia was added to the tertiary purified manganese sulfate solution to adjust the pH to 6.3, and 19g of citric acid was added to complex with magnesium ions in the solution. After filtration and separation, a quaternary purified manganese sulfate solution was obtained. An excess of ammonium bicarbonate (5% excess based on the molar excess of manganese in the electric furnace manganese-iron slag) was added to the quaternary purified manganese sulfate solution to obtain manganese carbonate precipitate. Manganese carbonate precipitate was washed five times with deionized water and then calcined at 890℃ using a suspension low-temperature instantaneous calcination system (ZL 201110100752.1) to decompose and obtain solid manganese tetroxide. The solid manganese tetroxide was then pulverized or sand-milled, washed with deionized water, and dried to obtain high-purity manganese tetroxide. The manganese recovery rate reached 99.4%.

[0024] Example 2

[0025] The main chemical composition of the electric furnace manganese iron slag sample is: manganese 10.2%, magnesium 3.6%, iron 2.8%, aluminum 6.5%, calcium 25.7%, silicon 17.2%, and heavy metal elements such as zinc, copper, nickel, and lead are in trace amounts.

[0026] After crushing and mixing the electric furnace manganese-iron slag with a particle size ≤80μm, dry it at 100-110℃ to constant weight.

[0027] 100g of electric furnace ferromanganese slag and 150g of mixed flux (65% ammonium sulfate and 35% thiourea by mass) were accurately weighed and mixed evenly, then subjected to gradient calcination in a tube furnace. First, the temperature was increased to 150℃ at a rate of 5℃ / min and calcined at this temperature for 80min. Then, the temperature was increased to 320℃ at a rate of 5℃ / min and calcined for another 25min. Finally, the temperature was increased to 620℃ at a rate of 5℃ / min and calcined for another 50min. After the reaction was complete, the temperature was allowed to drop to room temperature. The calcined slag sample was removed, and 1.2L of deionized water was added to leach manganese sulfate at a constant room temperature. After leaching for 50min, the mixture was filtered to obtain crude manganese sulfate solution. The main components of the leaching residue were calcium sulfate, barium sulfate, and ferric oxide. At room temperature, 3‰ metallic manganese powder was added to crude manganese sulfate solution. After reacting at room temperature for 30 minutes, the solution was separated and filtered to remove heavy metals such as zinc, nickel, and cobalt, yielding a primary purified manganese sulfate solution. 1‰ ammonium sulfide was added to the primary purified manganese sulfate solution to further remove heavy metals, followed by filtration to obtain a secondary purified manganese sulfate solution. 2‰ polyacrylamide was added to the secondary purified manganese sulfate solution to remove trace amounts of residual aluminum and silicon, followed by filtration to obtain a tertiary purified manganese sulfate solution. Ammonia was added to the tertiary purified manganese sulfate solution to adjust the pH to 7, and 19g of citric acid was added to complex with magnesium ions in the solution. After filtration and separation, a quaternary purified manganese sulfate solution was obtained. An excess of ammonium bicarbonate (5% excess based on the molar excess of manganese in the electric furnace manganese-iron slag) was added to the quaternary purified manganese sulfate solution to obtain manganese carbonate precipitate. Manganese carbonate precipitate was washed five times with deionized water and then calcined at 890℃ using a suspension low-temperature instantaneous calcination system (ZL201110100752.1) to decompose and obtain solid manganese tetroxide. The solid manganese tetroxide was then pulverized or sand-milled, washed with deionized water, and dried to obtain high-purity manganese tetroxide. The manganese recovery rate reached 99.42%.

[0028] Example 3

[0029] The main chemical composition of the electric furnace manganese iron slag sample is: manganese 10.2%, magnesium 3.6%, iron 2.8%, aluminum 6.5%, calcium 25.7%, silicon 17.2%, and heavy metal elements such as zinc, copper, nickel, and lead are in trace amounts.

[0030] After crushing and mixing the electric furnace manganese-iron slag with a particle size ≤80μm, dry it at 100-110℃ to constant weight.

[0031] Accurately weigh 100g of electric furnace ferromanganese slag and 120g of mixed flux (65% ammonium sulfate and 35% thiourea by mass), mix thoroughly, and then perform gradient calcination in a tube furnace. First, heat to 150℃ in the tube furnace at a heating rate of 10℃ / min and calcine at this temperature for 90min; then, continue heating to 320℃ at a heating rate of 10℃ / min and calcine for another 30min; finally, continue heating to 620℃ at a heating rate of 10℃ / min and calcine for another 60min. After the reaction is complete, let the temperature drop to room temperature, remove the calcined slag sample, add 0.8L of deionized water to leach manganese sulfate at a constant room temperature, leach for 70min, and then filter to obtain crude manganese sulfate solution. At room temperature, 2‰ metallic manganese powder was added to crude manganese sulfate solution. After reacting at room temperature for 30 minutes, the solution was separated and filtered to remove heavy metals such as zinc, nickel, and cobalt, yielding a primary purified manganese sulfate solution. 2‰ ammonium sulfide was added to the primary purified manganese sulfate solution to further remove heavy metals, followed by filtration to obtain a secondary purified manganese sulfate solution. 2‰ polyacrylamide was added to the secondary purified manganese sulfate solution to remove trace amounts of residual aluminum and silicon, followed by filtration to obtain a tertiary purified manganese sulfate solution. Ammonia was added to the tertiary purified manganese sulfate solution to adjust the pH to 6, and 19g of citric acid was added to complex with magnesium ions in the solution. After filtration and separation, a quaternary purified manganese sulfate solution was obtained. An excess of ammonium bicarbonate (5% excess based on the molar excess of manganese in the electric furnace manganese-iron slag) was added to the quaternary purified manganese sulfate solution to obtain manganese carbonate precipitate. Manganese carbonate precipitate was washed five times with deionized water and then calcined at 890℃ using a suspension low-temperature instantaneous calcination system (ZL 201110100752.1) to decompose and obtain solid manganese tetroxide. The solid manganese tetroxide was then pulverized or sand-milled, washed with deionized water, and dried to obtain high-purity manganese tetroxide. The manganese recovery rate reached 99.37%.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for recovering manganese from electric furnace ferromanganese slag, characterized in that, The following steps are performed: The electric furnace ferromanganese slag is crushed, mixed evenly, and dried. The dried ferromanganese slag is mixed evenly with a flux at a mass ratio of 1:1.2-1.

5. The flux consists of 65% ammonium sulfate and 35% thiourea. The mixture is heated to 150°C in a tube furnace at a heating rate of 5-10°C / min, and calcined at a constant temperature for 80-90 min. Then, the temperature is increased to 320°C at a heating rate of 5-10°C / min, and calcined for another 25-30 min. Finally, the temperature is increased to 620°C at a heating rate of 5-10°C / min, and calcined for another 50-60 min until the reaction is complete. After the temperature drops to room temperature, the calcined slag sample is removed, and deionized water is added to leach manganese sulfate at room temperature. The mixture is then filtered to separate the manganese sulfate crude solution and the leaching residue. Manganese powder was added to the crude manganese sulfate solution, and after reacting at room temperature, the solution was separated and filtered to remove heavy metals, yielding a primary purified manganese sulfate solution. Ammonium sulfide was added to the primary purified manganese sulfate solution to further remove heavy metals, and the solution was filtered to obtain a secondary purified manganese sulfate solution. A flocculant was added to remove a small amount of residual aluminum and silicon from the secondary purified manganese sulfate solution, and the solution was filtered to obtain a tertiary purified manganese sulfate solution. Ammonia was added to the tertiary purified manganese sulfate solution to adjust the pH to 6-7, and citric acid was added to complex with magnesium ions in the solution. After filtration and separation, a quaternary purified manganese sulfate solution was obtained.

2. The method for recovering manganese from electric furnace ferromanganese slag according to claim 1, characterized in that: The obtained manganese sulfate solution after four purifications was added to ammonium bicarbonate, and the reaction produced manganese carbonate precipitate. After filtration, manganese carbonate and ammonium sulfate solution were obtained. The manganese carbonate precipitate was washed with water and then calcined to obtain manganese tetroxide.

3. The method for recovering manganese from electric furnace ferromanganese slag according to claim 1 or 2, characterized in that: The electric furnace manganese-iron slag is crushed to a particle size ≤80μm and dried at 100-110℃.

4. The method for recovering manganese from electric furnace ferromanganese slag according to claim 3, characterized in that: During leaching, the amount of deionized water added is 8-12 times the mass of the electric furnace manganese iron slag, and the leaching time is 50-70 minutes.

5. The method for recovering manganese from electric furnace ferromanganese slag according to claim 4, characterized in that: The amount of metallic manganese powder added is 2‰-3‰ of the mass of the electric furnace manganese ferroalloy slag; the amount of ammonium sulfide added is 1‰-2‰ of the mass of the electric furnace manganese ferroalloy slag.

6. The method for recovering manganese from electric furnace ferromanganese slag according to claim 5, characterized in that: The flocculant is polyacrylamide, and the addition amount is 1‰-2‰ of the mass of the electric furnace manganese iron slag.