A method for treating manganese slag in centralized utilization of magnesium resources

Abstract

This invention discloses a method for treating manganese slag with centralized utilization of magnesium resources. By using magnesium-rich water as the washing water for manganese slag, ammonia nitrogen and manganese in the manganese slag can be dissolved, while magnesium is retained, improving the subsequent solidification and stabilization effect of the washed slag. It also employs a forward two-stage oxidation process to remove iron and precipitate manganese, achieving resource recovery of multiple valuable metals. Furthermore, it uses the ferrous ammonium sulfite method to remove ammonia nitrogen, achieving a closed-loop, cascaded treatment of sulfur dioxide. The high-magnesium wastewater after ammonia removal is recycled for the washing treatment of electrolytic manganese slag. In other words, this invention achieves zero emissions of waste slag, waste gas, and wastewater through magnesium-rich circulating washing coupled with two-stage oxidation and the ferrous ammonium sulfite method for ammonia nitrogen removal, and also has the advantages of a short process flow and low input cost.

Description

Technical Field

[0001] This invention relates to the resource utilization of electrolytic manganese slag, specifically to a method for the harmless and resource-based treatment of manganese slag for the efficient and centralized utilization of magnesium resources. It belongs to the technical field of manganese-containing solid waste treatment. Background Technology

[0002] Electrolytic manganese slag is a general term for leaching slag, sulfide slag, and iron removal slag generated during the electrolytic manganese production process. It is a dark brown, muddy paste with weak acidity and belongs to Class II general industrial solid waste. Generally, producing 1 ton of electrolytic manganese generates 8-10 tons of electrolytic manganese slag. Due to the lack of universally applicable manganese slag disposal technology, most electrolytic manganese enterprises in my country transport the waste slag to stockpiles. However, electrolytic manganese slag typically contains 3-6% manganese, 2-3% ammonia nitrogen, and 8-10% iron, giving it some resource recovery value. Currently, the common method for removing soluble valuable components from manganese slag produced by the electrolytic manganese process is water washing, followed by further treatment of the washing liquid.

[0003] Current research on the water washing treatment of electrolytic manganese mainly focuses on improving the leaching rate of manganese slag pollutants, the resource utilization of leachate, and the solidification and stabilization of remaining manganese slag. Regarding improving the leaching rate of manganese slag pollutants: Chinese patent CN110551898A, "A Method for Treating Electrolytic Manganese Slag," uses electrolytic manganese anolyte combined with a high-pressure impact method to treat the electrolytic manganese slag. Chinese patent CN 201710755518, "A Method for Microwave Extraction of Manganese from Electrolytic Manganese Slag," uses a 5-15% sulfuric acid solution to slurry the electrolytic manganese slag, and then uses microwaves to promote the dissolution of manganese. Regarding the resource utilization of leachate: Chinese patent CN108483501A, "A Comprehensive Utilization Method for Water Washing Liquid of Electrolytic Manganese Slag," involves adding ammonium bicarbonate to the water washing liquid to convert manganese into manganese carbonate, and then removing impurities and recovering ammonia through precipitation and deammoniation reactions. Chinese patent CN 112408488 A, "A Method for Recovering Soluble Ammonium Manganese from Electrolytic Manganese Slag," describes a method for extracting manganese ions from the washing liquid using an organic phase containing an extractant, followed by back-extraction to obtain high-purity manganese ions. The raffinate is then treated with alkaline stripping to recover ammonia. Regarding the solidification and stabilization of the remaining manganese slag after washing: Chinese patent CN 108262336A, "A Method for Solidifying Electrolytic Manganese Slag," reports mixing electrolytic manganese slag with alkaline industrial waste such as phosphorus slag, slag, high-calcium fly ash, composite alkaline agents, and water, followed by solidification and storage in a slag silo. Chinese patent CN 103320621A, "A Method for Solidifying Heavy Metals in Electrolytic Manganese Slag and Producing Sulfur," describes mixing calcium sulfide with manganese slag to achieve the stabilization and solidification of heavy metals in the slag. Chinese patent CN 104307849 A, "A Method for Solidifying / Stabilizing Electrolytic Manganese Slag," describes adding alkaline agents and sodium hexametaphosphate to solidify the manganese slag. Chinese patent CN104307850 A, "A method for solidifying / stabilizing high concentration water-soluble manganese in manganese slag," describes the addition of active silica and magnesium oxide to solidify the manganese slag.

[0004] The above methods each have their advantages and disadvantages, but none of them take into account the entire process of harmless treatment of manganese slag. This leads to problems such as high energy consumption, high cost, lack of closed-loop treatment, and loss of magnesium resources, which have not been fully utilized, resulting in the manganese slag not being effectively treated. Summary of the Invention

[0005] To address the problems of high energy consumption, high cost, lack of closed-loop treatment, and underutilization of magnesium resources in the existing electrolytic manganese slag treatment process, this invention provides a manganese slag treatment method for centralized utilization of magnesium resources. By using magnesium-rich water as the circulating washing water for manganese slag, ammonia nitrogen and manganese in the manganese slag can be dissolved, while magnesium cannot be dissolved. This effectively preserves the magnesium content in the manganese slag while removing ammonia nitrogen and manganese, thus achieving the rational utilization of valuable metals in the manganese slag.

[0006] Furthermore, this invention utilizes a SO2 / O2 mixed gas as an oxidant under acidic conditions to oxidize divalent manganese ions into manganese dioxide precipitate, thereby achieving the separation of manganese ions from the solution. Simultaneously, the remaining sulfur dioxide, after being absorbed by the absorbent, can participate in the ammonia nitrogen precipitation treatment of the ammonia-containing wastewater after manganese precipitation, thus obtaining high-purity ferrous ammonium sulfite with high economic value. A large amount of magnesium ions are retained in the ammonia-removed wastewater, which can be recycled for the washing treatment of electrolytic manganese slag. In other words, the process of this invention achieves closed-loop treatment of wastewater and waste gas while further coupling difficult-to-close-loop elements for resource utilization, improving economic efficiency and reducing treatment costs.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is specifically described as follows:

[0008] A method for treating manganese slag for centralized utilization of magnesium resources, the method comprising the following steps:

[0009] 1) Manganese slag leaching treatment: The manganese slag is washed with magnesium-containing water, and the solid and liquid are separated to obtain leaching solution and leaching residue.

[0010] 2) Oxidation to remove iron: Add hydrogen peroxide to the leaching solution to react, and after solid-liquid separation, obtain iron-removed liquid and iron-containing slag.

[0011] 3) Oxidation precipitation of manganese: A mixed gas containing sulfur dioxide and oxygen is introduced into the iron removal liquid to carry out the reaction. After solid-liquid separation, manganese-rich precipitate and ammonia-containing wastewater are obtained. At the same time, sulfur-containing tail gas overflowing during the oxidation precipitation of manganese is absorbed by an alkaline solution to obtain sulfur-containing absorbent liquid.

[0012] 4) Ammonia nitrogen precipitation treatment: Ammonia-containing wastewater and sulfur-containing absorbent are mixed to obtain mixed wastewater. The mixed wastewater is then adjusted to neutral or weakly acidic, and soluble ferrous salt is added to react. After solid-liquid separation, ferrous ammonium sulfite precipitate and ammonia-removed wastewater are obtained. The ammonia-removed wastewater is returned to step 1) to participate in the manganese slag leaching treatment.

[0013] Preferably, the method further includes:

[0014] 5) Curing treatment: The leaching residue obtained in step 1) is mixed with the mixed curing agent to obtain a cured material. The curing agent is a mixture containing at least calcium oxide, magnesium oxide, sodium carbonate, phosphate, and sodium hypochlorite.

[0015] Preferably, the manganese slag is magnesium-containing electrolytic manganese slag. The magnesium content is 0.5-5% by mass, preferably 1-3%. For example, it is one of the following: 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.5%, 4%, 4.5%, and 5%.

[0016] Preferably, the curing agent comprises: 40-60% calcium oxide, 30-70% magnesium oxide, 2-10% sodium carbonate, 0.5-2% phosphate, and 1-5% sodium hypochlorite. More preferably, it comprises 45-55% calcium oxide, 35-60% magnesium oxide, 3-8% sodium carbonate, 0.8-1.8% phosphate, and 1.5-4.5% sodium hypochlorite.

[0017] Preferably, the phosphate is one or more of calcium dihydrogen phosphate, sodium hydrogen phosphate, and sodium phosphate.

[0018] Preferably, in step 1), the magnesium-containing water is an acidic magnesium-containing water whose pH has been adjusted to 2-6 (preferably 3-5) using an acid. The acid is an aqueous solution of sulfuric acid, hydrochloric acid, nitric acid, and optionally an acidic gas (including but not limited to sulfur dioxide, nitrogen dioxide, hydrogen sulfide, and chlorine).

[0019] Preferably, in step 1), the concentration of magnesium ions in the magnesium-containing water is not less than 150 g / L, more preferably not less than 200 g / L, and even more preferably not less than 250 g / L.

[0020] Preferably, in step 1), the water washing is a three-stage countercurrent water washing. The liquid-to-solid mass ratio during each stage of water washing is 1.5-8:1, preferably 2-6:1, and more preferably 2.5-5:1.

[0021] Preferably, in step 2), the concentration of hydrogen peroxide is not less than 25 wt%, preferably 25-50 wt%, and more preferably 30-40 wt%. The amount of hydrogen peroxide added is 0.1-0.8 times the total mass of ferrous ions in the dissolution solution, preferably 0.2-0.6 times, and more preferably 0.3-0.4 times.

[0022] Preferably, the reaction time with added hydrogen peroxide is not less than 5 minutes, preferably 0.3-2 hours, and more preferably 0.5-1 hour.

[0023] Preferably, in step 3), the concentration of sulfur dioxide in the mixed gas containing sulfur dioxide and oxygen is not less than 0.5 wt%, and the concentration of oxygen is not less than 5 wt%. More preferably, the concentration of sulfur dioxide is 0.5-5 wt%, and the concentration of oxygen is 5-50 wt%. More preferably, the concentration of sulfur dioxide is 1-3 wt%, and the concentration of oxygen is 10-20 wt%.

[0024] Preferably, the ratio of the total flow rate of the sulfur dioxide and oxygen mixture to the total volume of the iron removal liquid is 20-70:1, more preferably 25-60:1, and even more preferably 30-50:1.

[0025] Preferably, the reaction time after introducing a mixed gas containing sulfur dioxide and oxygen is not less than 10 minutes, preferably 0.5-3 hours, and more preferably 0.8-2 hours.

[0026] Preferably, in step 3), the sulfur-containing tail gas overflowing during the oxidation and precipitation of manganese is absorbed by an alkaline solution in a three-stage countercurrent absorption process. Specifically, the sulfur-containing tail gas passes through a first-stage reaction absorber, a second-stage reaction absorber, and a third-stage reaction absorber in sequence. The pH of the alkaline solution in the first-stage and second-stage reaction absorbers is independently 8-11 (preferably 8.5-10), and the pH of the alkaline solution in the third-stage reaction absorber is 10-14 (preferably 11-12).

[0027] Preferably, the alkali in the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, with sodium hydroxide being the most preferred.

[0028] Preferably, in step 4), adjusting the mixed wastewater to neutral or weakly acidic is done by using an alkali (preferably sodium hydroxide) or an acid (preferably sulfuric acid) to adjust the pH to ≤7, preferably pH 5-7.

[0029] Preferably, in step 4), the soluble ferrous salt is ferrous sulfate and / or ferrous chloride, with ferrous sulfate being the most preferred.

[0030] Preferably, the reaction time for adding soluble ferrous salt is 0.1-2 h, and more preferably 0.3-1.5 h.

[0031] In existing technologies, the resource-based treatment of manganese slag mostly focuses on how to extract as much manganese as possible, such as how to increase the leaching rate of manganese in the manganese slag washing solution, how to reduce the content of impurities in the leachate, and how to improve the extraction rate or precipitation conversion rate of manganese in the leachate. These methods each have their advantages and disadvantages, but none of them consider the entire process of harmless treatment of manganese slag. This leads to problems such as high energy consumption, high cost, lack of closed-loop treatment, and the loss and underutilization of other elements (such as magnesium, sulfur, and ammonia) in the manganese slag treatment process. As a result, the existing manganese slag treatment technology has serious shortcomings, and the manganese slag has not been truly harmlessly treated.

[0032] In this invention, based on the characteristic that manganese slag also contains a certain amount of magnesium and sulfur elements, a low-cost treatment solution with integrated closed-loop, zero-waste disposal is formed by coupling water washing, aqueous solution resource utilization, and water washing slag solidification. This mainly includes circulating water washing with a magnesium-rich solution, which reduces the leaching of magnesium from the manganese slag, allowing it to remain in the water washing slag and effectively ensuring the feasibility of subsequent water washing slag solidification; the manganese-containing leaching solution after water washing undergoes two-stage oxidation to remove iron, precipitate manganese, and remove ammonia, achieving high-value recovery of manganese elements while also realizing high-value recovery of sulfur and iron resources and the tiered closed-loop utilization of the gaseous oxidant through the use of a specific gaseous oxidant; the water washing slag is reacted with a specially formulated solidifying agent, which, while retaining magnesium in the slag, reacts with residual ammonia nitrogen and manganese to achieve stable fixation. The solidified material meets the landfill pollution control technical requirements of the "Technical Specification for Pollution Control of Manganese Slag (HJ1241—2022)".

[0033] Generally, when manganese slag is directly washed with industrial water, the washing solution mainly contains Mn. 2+ Mg 2+ NH4 + SO4 2- And so on. Regarding the subsequent resource recovery of the washing liquid, Mg... 2+ NH4 + SO4 2- These are all low-value resources, generally treated as impurities and removed unnecessarily, increasing processing costs and difficulty, and potentially affecting the quality of recovered manganese products and generating additional waste residue that pollutes the environment. Therefore, controlling their leaching can significantly reduce the difficulty of subsequent resource recovery and disposal of the washing liquid. This invention, through a rational design, uses a magnesium-rich aqueous solution (with a magnesium ion concentration of not less than 150 g / L, preferably not less than 200 g / L, more preferably not less than 250 g / L, with saturation or near-saturation being even better) to circulate and wash the manganese slag. This reduces the leaching of magnesium from the manganese slag, allowing it to remain in the washed slag, while selectively leaching only manganese and ammonia nitrogen. Unlike conventionally washed manganese slag, the washed slag after the above treatment is mainly low in manganese and ammonia, but high in magnesium. This invention effectively retains magnesium in the manganese slag, and magnesium promotes the formation of stable gels, facilitating efficient solidification of the subsequent washed slag.

[0034] In this invention, the washing liquid (i.e., the leaching solution) after washing manganese slag mainly contains manganese ions, ammonia nitrogen, ferrous ions, magnesium ions, and sulfate ions. The general operation in the prior art involves pretreatment to remove Mg... 2+After removal, manganese recovery and subsequent ammonia nitrogen removal are required, resulting in high processing costs. This invention first uses hydrogen peroxide as an oxidant to oxidize ferrous ions to ferric ions. Ferric ions precipitate at a low pH, typically forming in solutions with a pH of 3-5, thus achieving removal. However, hydrogen peroxide has limited oxidizing power and cannot oxidize manganese ions. Therefore, this invention also utilizes a mixed gas of SO2 and O2 as an oxidant, selectively precipitating manganese under acidic conditions. Since the SO2 / O2 mixed gas forms strongly oxidizing SO5 under acidic conditions... - The group will oxidize divalent manganese ions to MnO2 precipitate, thereby achieving separation from the solution. Since magnesium precipitation mainly occurs under alkaline conditions, and the iron removal and manganese precipitation in this invention are both carried out in an acidic environment, magnesium will not precipitate. This allows for efficient separation of iron, manganese, and magnesium, ultimately achieving forward extraction of manganese and reducing disposal costs. The sulfur-containing tail gas overflowing during the manganese precipitation process is absorbed by alkaline solution to obtain an absorbent containing sodium sulfite, which can be used for subsequent ammonia removal treatment, eliminating wastewater and waste gas emissions.

[0035] In this invention, the solution after iron and manganese precipitation still contains a certain concentration of ammonia nitrogen (ammonia-containing wastewater, generally with an ammonia nitrogen concentration of 10-30 g / L). Conventional methods involve adjusting the solution to alkaline for stripping or ammonia stripping, but this consumes a large amount of alkaline solution. This invention, based on the ferrous ammonium sulfite method and the characteristics of manganese precipitation byproducts, induces a precipitation reaction by adding ferrous sulfate and an absorbent containing sodium sulfite. Specifically, through the ferrous ammonium sulfite method: under a solution pH of 5-7, ammonia nitrogen combines with ferrous and sulfite ions to form ferrous ammonium sulfite precipitate. The sulfite solution originates from the absorbent of sulfur-containing tail gas after manganese precipitation, achieving the cascade utilization of sulfur. The entire ammonia nitrogen precipitation process is weakly acidic, preventing magnesium precipitation in the solution. This effectively achieves the open-loop and resource utilization of ammonia nitrogen. The wastewater after ammonia removal also mainly contains magnesium ions; therefore, this magnesium-containing wastewater can be recycled for the washing treatment of electrolytic manganese slag, truly achieving zero wastewater discharge.

[0036] In this invention, the washed slag obtained after water washing is a low-manganese, low-ammonia, high-magnesium slag, in which magnesium mainly exists as magnesium sulfate, a core raw material for preparing basic magnesium sulfate cement. Based on the characteristics of this washed slag, this invention specifically develops an ion-curing agent with calcium oxide, magnesium oxide, sodium carbonate, phosphate, and sodium hypochlorite as its core components. After mixing with the washed slag, complex physicochemical reactions occur in the presence of magnesium ions, fully utilizing the magnesium in the washed slag and promoting the stable immobilization of residual ammonia nitrogen and manganese in the slag. The cured material meets the landfill pollution control technical requirements of the "Technical Specification for Pollution Control of Manganese Slag (HJ 1241—2022)". It can be directly used for resource utilization in road construction, backfilling, and non-fired bricks. This effectively achieves zero discharge of washed waste slag.

[0037] In this invention, experimental studies have revealed that the curing agent comprises: 40-60% calcium oxide, 30-70% magnesium oxide, 2-10% sodium carbonate, 0.5-2% phosphate, and 1-5% sodium hypochlorite; preferably, 45-55% calcium oxide, 35-60% magnesium oxide, 3-8% sodium carbonate, 0.8-1.8% phosphate, and 1.5-4.5% sodium hypochlorite. This mixed curing agent with the above-mentioned special components exhibits excellent curing and stabilizing effects on low-manganese, low-ammonia, and high-magnesium water-washed slag.

[0038] In this invention, the absorption process of sulfur-containing tail gas during the oxidation and precipitation of manganese is as follows: the SO2-containing tail gas is reacted with an alkaline solution using a three-stage countercurrent absorption device. The alkaline solution can be sodium carbonate or sodium hydroxide, preferably sodium hydroxide. The SO2-containing tail gas sequentially passes through a primary reaction absorber, a secondary reaction absorber, and a tertiary reaction absorber. The pH in the primary and secondary reaction absorbers is independently controlled at 8-11 (preferably 8.5-10), and the pH in the tertiary reaction absorber is controlled at 10-14 (preferably 11-12). Through this regulation, sodium sulfite is primarily formed in the primary reaction absorber.

[0039] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0040] 1. This invention uses magnesium-rich water to wash electrolytic manganese slag, which effectively retains magnesium while leaching manganese and ammonia nitrogen from the slag. Furthermore, a mixed curing agent was specifically developed to address the high magnesium content in the washed slag, achieving efficient and stable curing of the electrolytic manganese slag and meeting the landfill pollution control requirements of the "Technical Specification for Pollution Control of Manganese Slag (HJ 1241—2022)".

[0041] 2. In this invention, targeting the high magnesium content in the washing solution, a forward two-stage oxidation process is adopted to remove iron and precipitate manganese for manganese recovery. This approach can recover manganese without consuming the magnesium content in the washing solution, while simultaneously obtaining iron products and high-quality manganese dioxide products. This achieves the resource recovery of multiple valuable metals.

[0042] 3: This invention is based on the high ammonia nitrogen wastewater and high sulfur content absorbent generated by the two-stage oxidation iron removal and manganese precipitation process. It uses the ferrous ammonium sulfite method to remove ammonia nitrogen. Only the addition of ferrous ions is needed to achieve the coupled treatment of high ammonia nitrogen wastewater and high sulfur content absorbent, and obtain high-value ferrous ammonium sulfite products. It realizes the cascade closed-loop treatment of sulfur dioxide. The high magnesium wastewater after ammonia removal is recycled for the water washing treatment of electrolytic manganese slag, realizing zero discharge of waste gas and wastewater. Attached Figure Description

[0043] Figure 1 This is a process flow diagram of the manganese slag treatment method for centralized utilization of magnesium resources according to the present invention. Detailed Implementation

[0044] The technical solution of the present invention will be illustrated below with examples. The scope of protection sought by the present invention includes, but is not limited to, the following embodiments.

[0045] Example 1

[0046] Magnesium-containing water with a magnesium content of 165 g / L (with sulfuric acid to adjust its pH to around 4) was used to treat magnesium-containing electrolytic manganese slag (magnesium-containing electrolytic manganese slag produced by an electrolytic manganese metal plant in Guizhou, whose magnesium content was found to be approximately 2.06% after drying to constant weight) in a three-stage countercurrent water washing process (the liquid-to-solid ratio during each stage of water washing was 3:1, and the water washing solution was recycled). Finally, solid-liquid separation was performed to obtain leaching solution (the discharge volume was approximately 1 times that of the manganese slag) and leaching residue.

[0047] Add 35% hydrogen peroxide (0.3 times the total mass of ferrous ions in the leaching solution) to the leaching solution and react for 40 minutes. Then, after solid-liquid separation, iron-removed liquid and iron-containing slag are obtained.

[0048] A mixed gas containing sulfur dioxide and oxygen (the concentration of sulfur dioxide in the mixed gas is 1.5 wt% and the concentration of oxygen is 7.5 wt%) is introduced into the iron removal liquid and reacted for 1 hour. After solid-liquid separation, manganese-rich precipitate and ammonia-containing wastewater are obtained. At the same time, a three-stage countercurrent absorption reactor is used to absorb and treat the overflow sulfur-containing tail gas to obtain sulfur-containing absorbent liquid.

[0049] Ammonia-containing wastewater and sulfur-containing absorbent were mixed to obtain mixed wastewater. The pH of the mixed wastewater was then adjusted to approximately 6, followed by the addition of ferrous sulfate (23 g / L) and a reaction for 1 hour. After solid-liquid separation, ferrous ammonium sulfite precipitate and ammonia-removed wastewater were obtained. The ammonia-removed wastewater with high magnesium content was returned to step 1) as water for washing manganese slag.

[0050] The leaching residue (with a magnesium content of approximately 3.71% on a dry basis) was mixed with a mixed curing agent (comprising 49% calcium oxide, 40% magnesium oxide, 6% sodium carbonate, 1.5% sodium phosphate, and 3.5% sodium hypochlorite) to obtain a cured material. The cured material exhibited leaching toxicity of 0.022 mg / L for manganese, 4.06 mg / L for ammonia nitrogen, and 1.73% for soluble salts, meeting the landfill pollution control technical requirements of the "Technical Specification for Pollution Control of Manganese Slag (HJ 1241—2022)".

[0051] Example 2

[0052] Magnesium-containing water with a magnesium content of 200 g / L (with the pH adjusted to about 4 using sulfuric acid) was used to perform a three-stage countercurrent water washing treatment on magnesium-containing electrolytic manganese slag (with a dry basis magnesium content of about 2.06%). The liquid-to-solid ratio during each stage of water washing was 3:1, and the water washing liquid was recycled. Finally, solid-liquid separation was performed to obtain leaching liquid (the discharge volume was about 1 times that of manganese slag) and leaching residue.

[0053] Add 35% hydrogen peroxide (0.3 times the total mass of ferrous ions in the leaching solution) to the leaching solution and react for 40 minutes. Then, after solid-liquid separation, iron-removed liquid and iron-containing slag are obtained.

[0054] A mixed gas containing sulfur dioxide and oxygen (the concentration of sulfur dioxide in the mixed gas is 1.5 wt% and the concentration of oxygen is 7.5 wt%) is introduced into the iron removal liquid and reacted for 1.2 hours. After solid-liquid separation, manganese-rich precipitate and ammonia-containing wastewater are obtained. At the same time, a three-stage countercurrent absorption reactor is used to absorb and treat the overflow sulfur-containing tail gas to obtain sulfur-containing absorbent liquid.

[0055] Ammonia-containing wastewater and sulfur-containing absorbent were mixed to obtain mixed wastewater. The pH of the mixed wastewater was then adjusted to approximately 5, followed by the addition of ferrous sulfate (25 g / L) and a reaction for 1 hour. After solid-liquid separation, ferrous ammonium sulfite precipitate and ammonia-removed wastewater were obtained. The ammonia-removed wastewater with high magnesium content was returned to step 1) as water for washing manganese slag.

[0056] The leaching residue (with a dry basis magnesium content of approximately 4.41%) was mixed with a mixed curing agent (the curing agent consisted of 49% calcium oxide, 40% magnesium oxide, 6% sodium carbonate, 1.5% sodium phosphate, and 3.5% sodium hypochlorite) to obtain a cured material. The cured material exhibited leaching toxicity of 0.018 mg / L for manganese, 3.62 mg / L for ammonia nitrogen, and 1.82% for soluble salts, meeting the landfill pollution control technical requirements of the "Technical Specification for Pollution Control of Manganese Slag (HJ 1241—2022)".

[0057] Examples 3-8 and Comparative Examples 1-12 were performed using the same processes as Examples 1 and 2. The specific parameters of each example and comparative example are compared in the table below:

[0058]

[0059]

[0060]

[0061]

Claims

1. A method for treating manganese slag for centralized utilization of magnesium resources, characterized in that: The method includes the following steps: 1) Manganese slag leaching treatment: The manganese slag is washed with magnesium-containing water, and solid-liquid separation is performed to obtain leaching solution and leaching residue; 2) Oxidative iron removal treatment: Hydrogen peroxide is added to the leaching solution to carry out the reaction. After solid-liquid separation, iron removal solution and iron-containing slag are obtained. 3) Oxidation precipitation of manganese: A mixed gas containing sulfur dioxide and oxygen is introduced into the iron removal liquid to react. After solid-liquid separation, manganese-rich precipitate and ammonia-containing wastewater are obtained. At the same time, sulfur-containing tail gas overflowing during the oxidation precipitation of manganese is absorbed by alkaline solution to obtain sulfur-containing absorbent liquid. 4) Ammonia nitrogen precipitation treatment: Mix ammonia-containing wastewater and sulfur-containing absorbent to obtain mixed wastewater, then adjust the mixed wastewater to neutral or weakly acidic, then add soluble ferrous salt to react, and after solid-liquid separation, ferrous ammonium sulfite precipitate and ammonia-removed wastewater are obtained; the ammonia-removed wastewater is returned to step 1) to participate in manganese slag leaching treatment.

2. The manganese slag treatment method according to claim 1, characterized in that: The method also includes: 5) Curing treatment: The leaching residue obtained in step 1) is mixed with a mixed curing agent to obtain a cured material; wherein: the curing agent is a mixture containing at least calcium oxide, magnesium oxide, sodium carbonate, phosphate, and sodium hypochlorite; and / or The manganese slag is magnesium-containing electrolytic manganese slag, wherein the magnesium content is 0.5-5% by mass.

3. The manganese slag treatment method according to claim 2, characterized in that: The magnesium content in the manganese slag is 1-3% by mass.

4. The manganese slag treatment method according to claim 2, characterized in that: The curing agent is composed of: 40-60% calcium oxide, 30-70% magnesium oxide, 2-10% sodium carbonate, 0.5-2% phosphate, and 1-5% sodium hypochlorite.

5. The manganese slag treatment method according to claim 4, characterized in that: The curing agent is composed of: 45-55% calcium oxide, 35-60% magnesium oxide, 3-8% sodium carbonate, 0.8-1.8% phosphate, and 1.5-4.5% sodium hypochlorite; wherein the phosphate is one or more of calcium dihydrogen phosphate, sodium hydrogen phosphate, and sodium phosphate.

6. The method for treating manganese slag according to any one of claims 1-5, characterized in that: In step 1), the magnesium-containing water is an acidic magnesium-containing water whose pH has been adjusted to 2-6 by acid; the acid is an aqueous solution of sulfuric acid, hydrochloric acid, nitric acid, or optionally an acidic gas.

7. The manganese slag treatment method according to claim 6, characterized in that: The acidic gases include sulfur dioxide, nitrogen dioxide, hydrogen sulfide, or chlorine.

8. The method for treating manganese slag according to any one of claims 1-5, characterized in that: In step 1), the concentration of magnesium ions in the magnesium-containing water is not less than 150 g / L.

9. The manganese slag treatment method according to claim 8, characterized in that: In step 1), the concentration of magnesium ions in the magnesium-containing water is not less than 200 g / L.

10. The manganese slag treatment method according to claim 9, characterized in that: In step 1), the concentration of magnesium ions in the magnesium-containing water is not less than 250 g / L.

11. The method for treating manganese slag according to any one of claims 1-5, characterized in that: In step 1), the water washing is a three-stage countercurrent water washing; the liquid-solid mass ratio during each stage of water washing is 1.5-8:

1.

12. The manganese slag treatment method according to claim 11, characterized in that: In step 1), the water washing is a three-stage countercurrent water washing; the liquid-solid mass ratio during each stage of water washing is 2-6:

1.

13. The manganese slag treatment method according to claim 12, characterized in that: In step 1), the water washing is a three-stage countercurrent water washing; the liquid-solid mass ratio during each stage of water washing is 2.5-5:

1.

14. The manganese slag treatment method according to any one of claims 1-5, characterized in that: In step 2), the concentration of hydrogen peroxide is not less than 25 wt%; the amount of hydrogen peroxide added is 0.1-0.8 times the total mass of ferrous ions in the leaching solution.

15. The manganese slag treatment method according to claim 14, characterized in that: In step 2), the concentration of hydrogen peroxide is 25-50 wt%; the amount of hydrogen peroxide added is 0.2-0.6 times the total mass of ferrous ions in the leaching solution.

16. The manganese slag treatment method according to claim 15, characterized in that: In step 2), the concentration of hydrogen peroxide is 30-40 wt%; the amount of hydrogen peroxide added is 0.3-0.4 times the total mass of ferrous ions in the leaching solution.

17. The manganese slag treatment method according to claim 14, characterized in that: The reaction time after adding hydrogen peroxide should not be less than 5 minutes.

18. The manganese slag treatment method according to claim 17, characterized in that: The reaction time after adding hydrogen peroxide is 0.3-2 hours.

19. The manganese slag treatment method according to claim 18, characterized in that: The reaction time after adding hydrogen peroxide is 0.5-1 hour.

20. The method for treating manganese slag according to any one of claims 1-5, characterized in that: In step 3), the concentration of sulfur dioxide in the mixed gas containing sulfur dioxide and oxygen is not less than 0.5 wt%, and the concentration of oxygen is not less than 5 wt%.

21. The manganese slag treatment method according to claim 20, characterized in that: In a mixture of sulfur dioxide and oxygen, the concentration of sulfur dioxide is 0.5-5 wt% and the concentration of oxygen is 5-50 wt%.

22. The manganese slag treatment method according to claim 21, characterized in that: In a mixture of sulfur dioxide and oxygen, the concentration of sulfur dioxide is 1-3 wt% and the concentration of oxygen is 10-20 wt%.

23. The manganese slag treatment method according to claim 20, characterized in that: The ratio of the total flow rate of the sulfur dioxide and oxygen mixture to the total volume of the iron removal liquid is 20-70:1; and / or The reaction time after introducing a mixed gas containing sulfur dioxide and oxygen shall not be less than 10 minutes.

24. The manganese slag treatment method according to claim 23, characterized in that: The ratio of the total flow rate of the sulfur dioxide and oxygen mixture to the total volume of the iron removal liquid is 25-60:1; and / or The reaction time after introducing a mixed gas containing sulfur dioxide and oxygen is 0.5-3 hours.

25. The manganese slag treatment method according to claim 24, characterized in that: The ratio of the total flow rate of the sulfur dioxide and oxygen mixture to the total volume of the iron removal liquid is 30-50:1; and / or The reaction time after introducing a mixed gas containing sulfur dioxide and oxygen is 0.8-2 hours.

26. The method for treating manganese slag according to any one of claims 1-5, characterized in that: In step 3), the sulfur-containing tail gas overflowing during the oxidation and precipitation of manganese is absorbed by an alkaline solution in a three-stage countercurrent absorption process. Specifically, the sulfur-containing tail gas passes through a first-stage reaction absorber, a second-stage reaction absorber, and a third-stage reaction absorber in sequence. The pH of the alkaline solution in the first-stage and second-stage reaction absorbers is 8-11, respectively, and the pH of the alkaline solution in the third-stage reaction absorber is 10-14.

27. The manganese slag treatment method according to claim 26, characterized in that: The alkali in the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

28. The method for treating manganese slag according to any one of claims 1-5, characterized in that: In step 4), the mixed wastewater is adjusted to neutral or weakly acidic by using an alkali or acid to adjust the pH to ≤7; and / or In step 4), the soluble ferrous salt is ferrous sulfate and / or ferrous chloride.

29. The manganese slag treatment method according to claim 28, characterized in that: The base is sodium hydroxide; the acid is sulfuric acid; the pH is adjusted to 5-7.

30. The manganese slag treatment method according to claim 28, characterized in that: The reaction time for adding soluble ferrous salt is 0.1-2 hours.

31. The manganese slag treatment method according to claim 30, characterized in that: The reaction time for adding soluble ferrous salt is 0.3-1.5 h.

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