A method for recovering manganese from manganese metallurgical slag by low-temperature roasting and water leaching

Abstract

This invention discloses a method for recovering manganese from manganese metallurgical slag through low-temperature roasting and water leaching. The manganese metallurgical slag is dehydrated by pressure filtration, dried, and then mixed uniformly with a flux. Under inert gas protection, the mixture is heated to 180°C in a tubular furnace and roasted at a constant temperature. The temperature is then increased to 280°C and roasted further, followed by a further increase to 620°C and roasting. After roasting, the mixture is naturally cooled to room temperature. A roasted slag sample is taken out, and deionized water is added to leach manganese sulfate at room temperature. The mixture is filtered to separate the manganese sulfate, yielding a crude manganese sulfate solution and a leaching residue. The crude manganese sulfate solution undergoes multi-stage impurity removal, and ammonium bicarbonate is added to convert the manganese sulfate into manganese carbonate. After washing, filtration, and calcination, solid manganese tetroxide is obtained. This method utilizes a pyrometallurgical flux under inert gas protection to efficiently sulfatate the metal in the manganese metallurgical slag, whereby manganese forms soluble MnSO4. This enables the water leaching extraction of MnSO4 from the roasted slag. After graded impurity removal, high-purity manganese tetroxide is prepared, solving the resource waste and environmental pollution problems caused by manganese metallurgical slag.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for recovering manganese by low-temperature roasting and water leaching of manganese metallurgical slag. Background Technology

[0002] Manganese alloys are produced by electric furnace smelting. Raw materials such as manganese ore, quartz, limestone, and coke are added to the furnace in a specific ratio and smelted under electric current. During the smelting process, in addition to obtaining the alloy product, a considerable amount of manganese metallurgical slag is also emitted. This slag typically contains 15%–20% manganese. Currently, manganese metallurgical slag is mainly processed by water quenching to form water slag. Although it can be used as a raw material for cement, slag wool, and agricultural fertilizer, most production enterprises still face technical, economic, and environmental shortcomings in practical applications. Instead, they rely on off-site transportation and landfill disposal, which not only occupies land and causes pollution but also wastes the manganese in the slag.

[0003] The bottlenecks facing the resource utilization of manganese slag have been further amplified, and the drawbacks of traditional technological approaches have become increasingly apparent. Traditional pyrometallurgical processes require the slag to be remelted and reduced at high temperatures, resulting in extremely high energy consumption and significant carbon emissions. With rising energy costs and tightening carbon constraints, its economic viability continues to deteriorate. While wet acid leaching for manganese extraction is technically feasible, its environmental risks are particularly prominent. The leaching process generates massive amounts of complex acidic wastewater, which is difficult and costly to treat, and can easily lead to water pollution incidents if not handled carefully. To overcome the manganese slag dilemma, it is essential to develop economical, green, and efficient integrated utilization technologies. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a method for recovering manganese from manganese metallurgical slag through low-temperature roasting and water leaching. This method utilizes a pyrometallurgical flux under inert gas protection to efficiently sulfatate the metal in the manganese metallurgical slag, thereby forming soluble MnSO4. This allows for the water leaching extraction of MnSO4 from the roasted slag. After graded purification, high-purity manganese tetroxide is prepared, solving the problems of resource waste and environmental pollution caused by manganese metallurgical slag.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a flux, characterized in that it is composed of 88% ammonium sulfate and 12% ammonium formate.

[0006] A method for recovering manganese from manganese metallurgical slag by low-temperature roasting and water leaching is characterized by the following steps: The manganese metallurgical slag is dehydrated by pressure filtration, dried, crushed, and then mixed evenly with the flux. Under inert gas protection, the slag is heated to 180°C in a tubular furnace at a rate of 10–15°C / min, roasted at a constant temperature for 5–10 min, then heated to 280°C at a rate of 10–15°C / min for another 5–10 min, then heated to 620°C at a rate of 20–25°C / min for another 10–20 min. After roasting, the slag is naturally cooled to room temperature. The roasted slag sample is then removed, and deionized water is added to leach manganese sulfate at room temperature. The mixture is filtered to obtain crude manganese sulfate solution and leaching residue. After multi-stage impurity removal, ammonium bicarbonate is added to convert the manganese sulfate solution into manganese carbonate. After washing and filtration, the manganese carbonate solution is calcined to obtain solid manganese tetroxide. The solid manganese tetroxide is then crushed or sand-milled, washed with deionized water, and dried to obtain battery-grade manganese tetroxide.

[0007] In the above scheme, the manganese metallurgical slag is dried at 100-110℃.

[0008] In the above scheme, manganese metallurgical slag is crushed into particles with a diameter ≤75μm.

[0009] In the above scheme, manganese metallurgical slag and flux are mixed at a mass ratio of 1.5 to 2.5:1.

[0010] In the above scheme: the inert gas is nitrogen, and the flow rate is 1.0 to 2.0 L / min.

[0011] In the above scheme: the amount of deionized water added is 8 to 12 times the mass of manganese metallurgical slag, and the leaching time is 50 to 70 minutes.

[0012] The steps for multi-stage impurity removal from crude manganese sulfate solution are as follows: add metallic 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 water to the filtrate to adjust the pH to 6-7, add citric acid, react at room temperature, and filter to obtain the purified solution.

[0013] In the above scheme, the amount of manganese powder added is 2‰ to 3‰ of the manganese metallurgical slag; the amount of ammonium sulfide added is 1‰ to 2‰ of the mass of the manganese metallurgical slag. The flocculant is polyacrylamide, and the amount added is 1‰ to 2‰ of the mass of the manganese metallurgical slag. The amount of citric acid added is 1.5‰ to 2‰.

[0014] Adding manganese powder reduces trace metal ions such as lead, iron, cobalt, nickel, copper, and zinc remaining in the crude manganese sulfate solution to metals, which are then separated by filtration. Ammonium sulfide is added to the filtrate to further remove residual trace metal ions. Polyacrylamide is added to the filtrate to remove residual aluminum and silicon. Citric acid is then added to the filtrate so that residual magnesium ions in the solution can combine with the citric acid and be removed during the subsequent ammonium bicarbonate precipitation process.

[0015] Most of the manganese in manganese metallurgical slag exists in the form of low valence (+2 valence). A small amount of manganese exists in the form of high valence, such as manganese aluminum oxide, manganese dioxide, and manganese trioxide, due to the influence of air and smelting environment (such as oxygen-enriched blowing). Ensuring the efficient reduction of high valence manganese is the key to improving manganese recovery and leaching rates. The ammonium formate in the mixed flux has a melting point of 120℃. During the heating process, it decomposes to produce NH3 (HCOONH4→NH3+HCOOH). When the temperature reaches 180℃, ammonium formate significantly decomposes to produce NH3 and CO. This means that the mixed roasting material not only has enhanced fluidity (improved mass transfer efficiency), but also that the generation of gas accelerates the exchange of heat with the roasting material (improved heat transfer efficiency). This enhances the efficiency of the subsequent rapid decomposition of ammonium sulfate to produce ammonia and sulfuric acid vapor. Simultaneously, the highly reducing CO converts the high-valence manganese in the manganese metallurgical slag into low-valence manganese. When the temperature reaches the melting point of ammonium sulfate (280℃), ammonium sulfate begins to decompose, producing large amounts of ammonia and ammonium bisulfate. Ammonium bisulfate continues to decompose, producing ammonia and sulfuric acid vapor, causing the metal elements in the manganese metallurgical slag to undergo sulfation reactions to form sulfates. At this point, the low-valence form of manganese (+2) in the manganese metallurgical slag rapidly forms manganese sulfate. The protection of the inert gas prevents the influence of oxygen in the air on the low-valence manganese, ensuring the stability of the manganese sulfate. When the temperature rises to 620℃, some of the generated metal sulfates begin to decompose to form corresponding oxides. In particular, ferric sulfate completely decomposes to form water-insoluble ferric oxide, and nickel sulfate partially decomposes to form water-insoluble nickel oxide. Leaching the insoluble matter with deionized water removes some of the metallic impurities from the manganese sulfate. Then, the manganese sulfate leachate undergoes further impurity removal through fractionation, reacts with ammonium bicarbonate to produce manganese carbonate, and is then calcined to prepare high-purity manganese tetroxide.

[0016] Beneficial effects:

[0017] (1) Compared with the prior art, the present invention reduces the consumption of ammonium sulfate and the calcination reaction time by using inert gas protection, thus shortening the process flow.

[0018] (2) Compared with the prior art, the present invention utilizes low-temperature calcination, which reduces energy consumption and extends the service life of the equipment.

[0019] (3) The present invention utilizes ammonium sulfate composite molten salt + water leaching to extract and recover manganese from manganese metallurgical slag, and the recovery rate can reach more than 98%.

[0020] (4) This invention accelerates the process of extracting manganese from manganese metallurgical slag to prepare high-purity manganese tetroxide, while solving the problems of resource waste and environmental pollution caused by manganese metallurgical slag. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments.

[0022] Example 1

[0023] Manganese metallurgical slag (manganese content 10.2%) was dried to constant weight at 110℃, crushed to a particle size ≤75μm, and passed through a 200-mesh sieve to obtain manganese metallurgical slag powder. 100g of manganese metallurgical slag and 50g of mixed flux (composed of 88% ammonium sulfate and 12% ammonium formate by mass) were accurately weighed and mixed evenly. The mixture was then calcined in a tube furnace under nitrogen protection at a nitrogen flow rate of 1.5L / min. The calcination program was as follows: heating rate 10℃ / min, controlled temperature 180℃, constant temperature calcination for 10min; heating rate 10℃ / min, controlled temperature 280℃, constant temperature calcination for 8min; heating rate 20℃ / min, controlled temperature 620℃, constant temperature calcination for 15min. After calcination, the mixture was allowed to cool naturally to room temperature. The calcined slag sample was removed, and 1L of deionized water was added to leach the manganese sulfate solution at room temperature. After leaching for 60min, the solution was filtered to obtain crude manganese sulfate solution. Add 0.2g of metallic manganese powder to the crude manganese sulfate solution, react at room temperature for 30min, filter, add 0.2g of ammonium sulfide to the filtrate, react at room temperature for 15min, filter, add 0.2g of flocculant polyacrylamide to the filtrate, react for 30min, precipitate, filter; add ammonia water to the filtrate to adjust the pH to 6.5, add 0.2g of citric acid, react at room temperature, filter and separate to obtain the purified solution.

[0024] Based on the molar amount of manganese in the manganese metallurgical slag, an excess of 5% ammonium bicarbonate was added to convert manganese sulfate into manganese carbonate precipitate. The manganese carbonate precipitate was washed five times with deionized water and then calcined at 910℃ to obtain solid manganese tetroxide. The solid manganese tetroxide was then crushed or sand-milled, washed with deionized water, and dried to obtain high-purity manganese tetroxide with a purity of 99.88%. The manganese recovery rate reached 98.38%.

[0025] Example 2

[0026] Manganese metallurgical slag (manganese content 13.5%) was dried to constant weight at 105℃, crushed to a particle size ≤75μm, and passed through a 200-mesh sieve to obtain manganese metallurgical slag powder. 100g of manganese metallurgical slag and 40g of mixed flux (composed of 88% ammonium sulfate and 12% ammonium formate by mass) were accurately weighed and mixed evenly. The mixture was then calcined in a tube furnace under nitrogen protection at a nitrogen flow rate of 2L / min. The calcination program was as follows: heating rate 15℃ / min, controlled temperature 180℃, constant temperature calcination for 5min; heating rate 10℃ / min, controlled temperature 280℃, constant temperature calcination for 10min; heating rate 25℃ / min, controlled temperature 620℃, constant temperature calcination for 10min. After calcination, the mixture was allowed to cool naturally to room temperature. The calcined slag sample was removed, and 1.2L of deionized water was added to leach manganese sulfate solution at room temperature. After leaching for 50min, the solution was filtered to obtain crude manganese sulfate solution. Add 0.3g of metallic manganese powder to the crude manganese sulfate solution, react at room temperature for 30min, filter, add 0.1g of ammonium sulfide to the filtrate, react at room temperature for 15min, filter, add 0.2g of flocculant polyacrylamide to the filtrate, react for 30min, precipitate, filter; add ammonia water to the filtrate to adjust the pH to 6.8, add 0.2g of citric acid, react at room temperature, filter and separate to obtain the purified solution.

[0027] Based on the molar amount of manganese in the manganese metallurgical slag, an excess of 5% ammonium bicarbonate was added to convert manganese sulfate into manganese carbonate precipitate. The manganese carbonate precipitate was washed five times with deionized water and then calcined at 880℃ to 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 with a purity of 99.89%. The manganese recovery rate reached 98.26%.

[0028] Example 3

[0029] Manganese metallurgical slag (manganese content 15.2%) was dried to constant weight at 105℃ and crushed to a particle size ≤75μm. 100g of manganese metallurgical slag and 67g of mixed flux (composed of 88% ammonium sulfate and 12% ammonium formate by mass) were accurately weighed and mixed thoroughly. The mixture was then calcined in a tube furnace under nitrogen protection at a nitrogen flow rate of 1L / min. The calcination program was as follows: heating rate 12℃ / min, controlled temperature 180℃, constant temperature calcination for 8 min; heating rate 15℃ / min, controlled temperature 280℃, constant temperature calcination for 5 min; heating rate 25℃ / min, controlled temperature 620℃, constant temperature calcination for 20 min. After calcination, the mixture was allowed to cool naturally to room temperature. The calcined slag sample was removed, and 0.8L of deionized water was added to leach the manganese sulfate solution at room temperature. After leaching for 70 min, the solution was filtered to obtain crude manganese sulfate solution. Add 0.25g of metallic manganese powder to the crude manganese sulfate solution, react at room temperature for 30min, filter, add 0.18g of ammonium sulfide to the filtrate, react at room temperature for 15min, filter, add 0.2g of flocculant polyacrylamide to the filtrate, react for 30min, precipitate, filter; add ammonia water to the filtrate to adjust the pH to 6.2, add 0.15g of citric acid, react at room temperature, filter and separate to obtain the purified solution.

[0030] Based on the molar amount of manganese in the manganese metallurgical slag, an excess of 5% ammonium bicarbonate was added to convert manganese sulfate into manganese carbonate precipitate. The manganese carbonate precipitate was washed five times with deionized water and then calcined at 900℃ to obtain solid manganese tetroxide. The solid manganese tetroxide was then crushed or sand-milled, washed with deionized water, and dried to obtain high-purity manganese tetroxide with a purity of 99.88%. The manganese recovery rate reached 98.70%.

[0031] 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 recovering manganese from a low-temperature roasted water leaching of a manganese metallurgical slag, characterized in that, The following steps are performed: Manganese metallurgical slag is dehydrated by pressure filtration, dried, crushed, and then mixed evenly with flux. The flux consists of 88% ammonium sulfate and 12% ammonium formate. Under inert gas protection, the temperature is raised to 180°C in a tube furnace at a rate of 10–15°C / min, and calcined at a constant temperature for 5–10 min. Then, the temperature is raised to 280°C at a rate of 10–15°C / min and calcined for another 5–10 min. Finally, the temperature is raised to 620°C at a rate of 20–25°C / min and calcined for another 10–20 min. After calcination, the slag is allowed to cool naturally to room temperature. The calcined slag sample is then removed, and deionized water is added to leach manganese sulfate at room temperature. The mixture is filtered to separate the manganese sulfate crude solution and the leaching residue. After multi-stage impurity removal, ammonium bicarbonate is added to convert the manganese sulfate into manganese carbonate. After washing and filtration, the manganese carbonate is calcined to obtain solid manganese tetroxide. The solid manganese tetroxide is then crushed or sand-milled, washed with deionized water, and dried to obtain battery-grade manganese tetroxide.

2. The process for recovery of manganese from low temperature roasted metallurgical manganese slag by water leaching as claimed in claim 1 wherein: Manganese metallurgical slag is dried at 100-110℃.

3. The method for recovering manganese by low-temperature roasting and water leaching of manganese metallurgical slag according to claim 2, characterized in that: Manganese metallurgical slag is crushed to a particle size ≤75 μm.

4. The method for recovering manganese from manganese metallurgical slag by low-temperature roasting and water leaching according to any one of claims 1-3, characterized in that: Manganese metallurgical slag and flux are mixed at a mass ratio of 1.5 to 2.5:

1.

5. The method for recovering manganese by low-temperature roasting and water leaching of manganese metallurgical slag according to claim 4, characterized in that: The inert gas is nitrogen, and the flow rate is 1.0–2.0 L / min.

6. The method for recovering manganese by low-temperature roasting and water leaching of manganese metallurgical slag according to claim 5, characterized in that: The amount of deionized water added is 8 to 12 times the mass of manganese metallurgical slag, and the leaching time is 50 to 70 minutes.