Method for harmless treatment of solidified stabilized electrolytic manganese residue

Abstract

This application belongs to the field of solid waste treatment and resource utilization technology, specifically involving a method for the harmless treatment of electrolytic manganese slag based on solidification and stabilization, aiming to solve the environmental pollution problems caused by heavy metal ions and ammonia nitrogen in electrolytic manganese slag. The method includes steps such as pretreatment and modification activation, humic acid pre-chelation, geopolymer in-situ mineralization molding, and low-temperature steam curing and aging. Stable humic acid-metal complexes are generated through chemical chelation reactions between the active functional groups of humic acid molecules and heavy metal and ammonium ions. The geopolymer gel physically encapsulates and fixes the chelates, forming a dual stabilization mechanism of chemical chelation and physical coating. This application can eliminate the risks of ammonia escape and heavy metal leaching, and the treated products can be made into building materials, achieving the dual goals of harmless treatment and resource utilization.

Description

Technical Field

[0001] This application belongs to the field of solid waste treatment and resource utilization technology, specifically involving a method for harmless treatment of electrolytic manganese slag based on solidification and stabilization. Background Technology

[0002] The electrolytic manganese industry is a core pillar of global manganese metal supply, widely serving steel smelting, stainless steel production, and new energy material preparation. In the electrolytic manganese production process, an average of 10 to 12 tons of electrolytic manganese slag are generated for every ton of electrolytic manganese produced. This large-scale emission of industrial solid waste has become a major environmental bottleneck restricting the industry's sustainable development. Electrolytic manganese slag has a complex composition, rich in gypsum minerals and aluminosilicates, as well as high concentrations of sulfates, residual soluble manganese ions, and difficult-to-treat ammonia nitrogen compounds. Improper disposal can cause severe eutrophication of water bodies, accumulation of heavy metals in soil, and atmospheric ammonia emissions, resulting in complex environmental pollution. Currently, the harmless disposal of electrolytic manganese slag is still in the technological exploration stage both domestically and internationally. The industry is undergoing a critical period of transformation from passive stockpiling to harmless and resource-based utilization. Developing economical and efficient manganese slag treatment technologies has become an urgent need to ensure the green development of the electrolytic manganese industry.

[0003] However, existing solidification and stabilization technologies still have insurmountable technical defects. While water washing can remove some soluble ammonia nitrogen, it suffers from high water consumption, high wastewater production, and difficulty in treatment, hindering water resource recycling. Pyrometallurgical roasting, although providing stable treatment, presents significant energy consumption and carbon emissions due to its high-temperature process, resulting in poor economic feasibility and making it difficult to promote its application in large-scale industrial production. Traditional alkaline solidification processes primarily use alkaline activators such as quicklime to increase the pH of the system, promoting the formation of hydroxides or oxides from heavy metal ions and simultaneously decomposing ammonium salts to release ammonia. However, this method has a fatal flaw in practice: the lime alkalization process causes severe ammonia emission, resulting in secondary air pollution, harming workers' health, and exacerbating atmospheric nitrogen deposition. More importantly, the heavy metal hydroxide precipitates formed by lime solidification are highly susceptible to redissolution and leaching under acid rain erosion or acidic soil environments, exhibiting poor long-term environmental stability and posing a significant risk of secondary pollution. Therefore, how to develop a new solidification and stabilization technology that does not require a large amount of water resources, does not produce waste gas emissions, and ensures long-term stability and reliability of heavy metals and ammonia nitrogen while being inexpensive to implement has become an urgent technical problem to be solved in the field of harmless treatment of electrolytic manganese slag. Summary of the Invention

[0004] A method for harmless treatment of electrolytic manganese slag based on solidification and stabilization can effectively solve the problems mentioned in the background technology.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for harmless treatment of electrolytic manganese slag based on solidification and stabilization includes the following steps: S1. Pretreatment and Modification Activation: The electrolytic manganese slag is crushed and screened to remove large impurities, then fed into a high-speed shear mixer, and a composite alkaline activator is sprayed into the manganese slag for modification and activation treatment under predetermined temperature and humidity conditions. S2. Humic acid pre-chelation: The prepared humic acid solution is evenly sprayed into the modified manganese slag and stirred vigorously. The amount of humic acid solution used is a certain proportion of the dry slag mass. S3. Geopolymer in-situ mineralization molding: Add fly ash or metakaolin and calcium formate to the chelated manganese slag, mix and control the moisture content of the material within the preset range, and press into shape. S4. Low-temperature steam curing and aging: The molded body is sent into a low-pressure steam curing chamber and cured at a predetermined temperature for a predetermined time period, and then aged under natural conditions for a predetermined number of days.

[0006] Preferably, the crushing process in S1 adopts a two-stage crushing process of jaw crusher and impact crusher in series, the screening process adopts multi-level vibrating screen for grading, and the speed and stirring temperature of the high-speed shear mixer are controlled within a preset range.

[0007] Preferably, the composite alkaline activator in S1 is mainly composed of finely ground blast furnace slag, steel slag powder and sodium hydroxide, and the mass ratio of each component is within a preset range. The composite alkaline activator is injected by uniformly spraying it onto the surface of manganese slag in the high-speed shear mixer through an atomizing nozzle, and the spraying pressure and spraying time are within a preset range.

[0008] Preferably, the concentration of the humic acid solution in S2 is within a preset range. During preparation, the humic acid powder is mixed with deionized water and placed in a constant temperature stirrer, and stirred and dissolved under a predetermined temperature condition. The humic acid solution is sprayed using a high-pressure atomizing device to evenly cover the surface of the modified manganese slag, and the spraying pressure and stirring speed are within a preset range.

[0009] Preferably, the carboxyl and phenolic hydroxyl functional groups in the humic acid molecule in S2 undergo ammoniation with the ammonium ions in the manganese slag to generate a stable ammonium humic acid complex. At the same time, the active functional groups of humic acid undergo multiple complexation adsorption with heavy metal ions such as divalent manganese ions, trivalent chromium ions, and divalent lead ions in the solution to form a stable five- or six-membered cyclic chelate structure.

[0010] Preferably, the fineness and specific surface area of ​​the fly ash or metakaolin in S3 are within a preset range, and the purity and particle size of the calcium formate are within an appropriate range. The order of adding the fly ash or metakaolin and the calcium formate is as follows: first add the fly ash or metakaolin and dry mix for a predetermined time, then add the calcium formate and continue mixing for a predetermined time, and finally add the alkaline activation solution to adjust the moisture content.

[0011] Preferably, in step S3, the pressing and molding process uses a hydraulic molding machine or a compression molding machine, with the molding pressure and holding time within a preset range. The shape of the molded product includes brick blanks, roadbed materials, or non-fired aggregates. After pressing and molding, the product is left to stand at room temperature for a predetermined period of time before undergoing subsequent curing treatment.

[0012] Preferably, in the S4 low-pressure steam curing chamber, the steam pressure is controlled within a preset pressure range, the relative humidity is maintained above the preset humidity, the heating rate is the preset heating rate, the temperature is raised to the set temperature and then kept warm for curing, and after curing, the temperature is cooled to room temperature by natural cooling. The aging process is carried out in a well-ventilated aging chamber.

[0013] Preferably, the formation process of the geopolymer gel in S3 includes: firstly, under the action of an alkaline activator, the active silica and active alumina in manganese slag, fly ash or metakaolin undergo a depolymerization reaction to generate silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron monomers; subsequently, under the coagulation-promoting action of calcium formate, these monomers undergo a condensation reaction to rearrange and form a three-dimensional network structure geopolymer gel, which physically encapsulates and fixes the humic acid-metal complex formed in the preceding steps, forming a dense microstructure.

[0014] Preferably, the method further includes an environmental stability testing step for the treated product, specifically including: taking samples to prepare a leachate, determining the leaching concentration of heavy metals using the acetic acid buffer solution method, and ensuring that the leaching concentrations of manganese ions and ammonia nitrogen do not exceed the corresponding thresholds; conducting an acid tolerance test, immersing the product in an acidic solution for a predetermined time, and ensuring that the increase in heavy metal leaching concentration does not exceed a preset increment threshold; and conducting a freeze-thaw cycle test, ensuring that after a predetermined number of freeze-thaw cycles, the appearance of the product shows no significant change, and the strength loss does not exceed a preset loss threshold.

[0015] The present invention has the following beneficial effects: This invention uses humic acid as a pre-curing agent to replace the traditional strong alkaline route of quicklime. Through a chemical chelation reaction between the active functional groups in humic acid molecules and ammonium ions and heavy metal ions, stable ammonium humate complexes and heavy metal chelates are generated. This reaction mechanism fundamentally inhibits the volatilization of free ammonium, completely avoiding the secondary air pollution problem caused by ammonia escape in traditional alkaline curing processes. Simultaneously, it significantly reduces the leaching toxicity of heavy metals, achieving in-situ stable fixation of pollutants.

[0016] This invention introduces geopolymer in-situ mineralization molding technology. Under the action of an alkaline activator, the active silica and active alumina in manganese slag undergo depolymerization-condensation reactions with an added silicon-aluminum source, forming a three-dimensional network structure of inorganic polymer gel. This gel physically imprisons humic acid-metal complexes, forming a dual stabilization mechanism of chemical chelation and physical coating. The geopolymer structure exhibits excellent acid and alkali resistance and freeze-thaw resistance. Its acid resistance is significantly improved compared to ordinary silicate cement, ensuring the absolute stability of heavy metals under long-term extreme environments and eliminating the risk of redissolution of traditional hydroxide precipitates in acid rain or acidic soil environments.

[0017] This invention does not consume large amounts of water resources, does not generate secondary high-salinity wastewater, and does not require high-temperature pyrometallurgical treatment, thus avoiding high energy consumption and carbon emissions. The treated product can be made into building materials such as brick blanks, roadbed materials, or non-fired aggregates, achieving the dual goals of harmless treatment and resource utilization of electrolytic manganese slag. The treatment cost is significantly reduced compared to traditional pyrometallurgical processes, resulting in significant economic and environmental benefits. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall process flow framework of the harmless treatment method for electrolytic manganese slag based on solidification and stabilization according to an embodiment of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0020] The harmless treatment method for electrolytic manganese slag based on solidification and stabilization involved in this invention fully includes the following four core steps: S1. Pretreatment and Modification / Activation Stage: First, the input electrolytic manganese slag raw material undergoes basic property testing and classification. Generally, the moisture content of freshly discharged electrolytic manganese slag is between 25% and 35%. The contaminants in the raw material, especially residual sulfates, soluble manganese ions, and high concentrations of ammonia nitrogen, are partially encapsulated in the dense gypsum or aluminosilicate mineral structure, increasing the difficulty of treatment.

[0021] The crushing process for electrolytic manganese slag employs a two-stage tandem process. The first stage uses a jaw crusher for coarse crushing, breaking larger manganese slag lumps down to medium particle size. The second stage uses an impact crusher for fine crushing, further reducing the medium-sized manganese slag to smaller particles. This tandem configuration of the two crushing stages allows for cascaded energy utilization. The jaw crusher performs the primary compressive crushing function, while the impact crusher utilizes impact shearing to further refine the particles. The synergistic effect of both processes results in a more uniform particle size distribution after crushing, creating favorable conditions for subsequent processing steps.

[0022] The crushed manganese slag enters the screening process, where it is graded using a three-layer vibrating screen. The upper screen is used to trap large impurities that are not completely crushed and unreacted manganese ore particles; the middle screen is used to separate medium-sized particles; and the lower screen is used to collect fine powder. Through the classification process of screening, impurities can be effectively separated according to particle size, while providing uniformly sized raw materials for subsequent batching processes.

[0023] The screened manganese slag is fed into a high-speed shear mixer for modification and activation. The core components of the high-speed shear mixer include a high-speed rotating rotor and stator assembly. The shearing force generated by the high-speed rotation acts on the manganese slag particles, effectively breaking down the inert coating on the particle surface and exposing the internal active components. The mixing time is set to 15-25 minutes, and the mixing temperature is controlled between 60-80℃ by a jacketed circulating heating system. The circulating heating medium is heat transfer oil or hot water, and the heating power is adjusted according to the processing volume.

[0024] During the high-speed shearing and stirring process, a composite alkaline activator is injected into the manganese slag. This activator mainly consists of three components: finely ground blast furnace slag, steel slag powder, and sodium hydroxide. The blast furnace slag primarily comprises mineral phases such as dicalcium silicate and monocalcium aluminate, exhibiting high pozzolanic activity. The steel slag powder primarily comprises tricalcium silicate, dicalcium silicate, and RO phase (referring to the solid solution of divalent metal oxides such as MgO, FeO, and MnO). The sodium hydroxide is industrial-grade caustic soda flakes with a purity of not less than 96%.

[0025] The three components are mixed according to the following mass ratio: blast furnace slag, steel slag powder, and sodium hydroxide are in the following mass ratios: 6-8 parts, 2-4 parts, and 0.5-1.5 parts, respectively. The total ratio can be adjusted appropriately according to the properties of the raw materials. The total amount of the composite alkaline activator injected accounts for 0.5%-1% of the dry weight of the manganese slag. It is injected by uniformly spraying it onto the surface of the manganese slag in a high-speed shear mixer through an atomizing nozzle. The atomizing nozzle uses a pressure atomization structure, with the spraying pressure controlled within the range of 0.3-0.5 MPa, and the spraying time lasting 3-5 minutes. The atomized activator forms fine droplets with a particle size of 50-150 μm, which fully contact and mix with the high-speed stirred manganese slag particles. The sodium hydroxide component in the activator provides a strongly alkaline environment, which is beneficial for breaking down the aluminosilicate structure on the surface of the manganese slag. The active aluminosilicate components in the blast furnace slag and steel slag powder begin to dissolve under alkaline activation, providing the necessary raw material source for the subsequent geopolymer reaction. Under temperature and humidity conditions of 60-80℃, the alkaline substances in the activator react chemically with the inert coating layer on the surface of the manganese slag. The silicon-oxygen bonds and aluminum-oxygen bonds break under the strongly alkaline environment, and the surface coating layer gradually becomes loose and porous, exposing and releasing the internal active silicon-aluminum components. This process lays the foundation for the geopolymer mineralization reaction that occurs in subsequent steps.

[0026] S2. Humic Acid Pre-chelation Stage: Environmentally friendly humic acid is used as a pre-curing agent to achieve the first-stage stabilization treatment of ammonia nitrogen and heavy metal ions. The humic acid can be waste generated in new energy lithium extraction processes, or it can be a product obtained from low-quality carbonaceous raw materials such as lignite and weathered coal after appropriate treatment. Regardless of the source, the humic acid used should meet the following basic requirements: total humic acid content not less than 50%, fulvic acid content not less than 15%, moisture content not more than 15%, pH value within a weakly acidic range of 5-7, and particle size with a residue of not more than 10% passing through an 80-mesh standard sieve.

[0027] The humic acid solution is prepared in a dedicated mixing tank. First, add 70%-80% of the required amount of deionized water to the tank, start the stirrer, and control the stirring speed at 300-500 rpm. Slowly add the calculated amount of humic acid powder to the tank, continuing the addition process for 10-15 minutes while maintaining stirring to prevent powder agglomeration. After all the humic acid powder has been added, heat the mixture in the tank to 40-50°C and continue stirring at this temperature for 40-60 minutes to ensure the humic acid powder is fully dissolved and forms a uniform brownish-red solution. After the solution is prepared, adjust its concentration to the target value, controlling the humic acid solution concentration within the range of 5-10 g / L. At this concentration, the pH value of the solution is approximately 5.5-6.5, and the conductivity is approximately 1-3 mS / cm. The prepared humic acid solution should be used as soon as possible and should not be stored for more than 24 hours to prevent oxidative degradation and performance decline caused by prolonged storage.

[0028] The humic acid solution is sprayed using a high-pressure atomizing device to evenly cover the surface of the modified manganese slag. The spraying pressure of the high-pressure atomizing device is controlled within the range of 0.4-0.6 MPa, and the atomization angle of the nozzle is adjusted to 45-60° to ensure that the atomized solution is evenly distributed on the surface of the manganese slag in the mixer. The amount of humic acid solution used is 2%-4% of the dry slag mass, and the specific amount is adjusted according to the actual content of ammonia nitrogen and heavy metals in the manganese slag. After the solution is sprayed, the high-speed shear mixer continues to operate for strong stirring, maintaining the stirring speed within the aforementioned range of 3000-5000 r / min, and the stirring time is maintained for 8-15 minutes to ensure that the humic acid and manganese slag particles are in full contact and react.

[0029] The active functional groups in humic acid molecules undergo two important types of chemical reactions with pollutants in manganese slag. The first type of reaction involves the reaction of the carboxyl groups (-COOH) and phenolic hydroxyl groups (-OH) in humic acid molecules with ammonium ions (NH4+). + The ammoniation reaction occurs between the carboxyl and phenolic hydroxyl groups. Under appropriate pH conditions, the carboxyl and phenolic hydroxyl groups undergo deprotonation to form negatively charged -COO. - and -O- Forms, these anionic functional groups with positively charged NH4 + Ions approach each other through electrostatic attraction, subsequently forming stable coordinate bonds, ultimately generating ammonium humate complexes (R-COO-NH4 and RO-NH4). These ammonium humate complexes exhibit high stability constants, reaching up to 10. 3 Up to 10 5 The stability is orders of magnitude higher than that of simple ammonium salts. The pH of the ammoniation reaction should be controlled within the range of 6.5 to 7.5, the reaction temperature maintained at 30 to 50°C, and the reaction time controlled at 10 to 20 minutes. Too low a pH will inhibit the deprotonation of carboxyl and phenolic hydroxyl groups, reducing the reactivity; too high a pH may lead to the formation of NH4+. + Converting ammonia to NH3 and evaporating it actually exacerbates the ammonia escape problem. By precisely controlling the reaction conditions, the maximum degree of ammonia nitrogen fixation can be achieved.

[0030] The second type of reaction is the complexation adsorption reaction between the active functional groups of humic acid and heavy metal ions in solution. The main heavy metal pollutants in electrolytic manganese slag include divalent manganese ions (Mn). 2+ ), trivalent chromium ions (Cr 3+ ), divalent lead ions (Pb) 2+ These heavy metal ions undergo coordination reactions with functional groups such as carboxyl, phenolic hydroxyl, and amino groups on humic acid molecules, forming stable five- or six-membered cyclic chelate structures. (Mn...) 2+ For example, its outer electron configuration is 3d. 5 It can form a σ-coordinate bond with the oxygen atom in the carboxyl group, and the oxygen atom in the carboxyl group can also donate lone pair electrons and Mn. 2+ π-coordinate bonds are formed, resulting in a stable five-membered ring structure. Cr 3+ Due to its higher charge number, Pb has a stronger ability to complex with humic acid, forming a more stable six-membered ring structure. 2+ Its large ionic radius makes it suitable for simultaneous coordination with multiple functional groups to form bridging multidentate complexes.

[0031] The mechanism of this type of chelation reaction can be described by the following chemical equation. Taking the complexation reaction of catechol in humic acid with heavy metal ions as an example:

[0032] in This represents the molecular skeleton of humic acid. This represents heavy metal ions. The reaction is a reversible process, and the equilibrium constant depends on the structural characteristics of humic acid and the type of heavy metal ions. In practical applications, due to the large molecular weight and complex structure of humic acid, the formed chelates exhibit extremely high stability, effectively preventing the leaching of heavy metal ions during subsequent use. The pH value of the chelation reaction should be controlled within the range of 6.0-8.0, the reaction temperature within 25-40℃, and the reaction time within 15-25 minutes. Under these conditions, the complexation efficiency of humic acid for heavy metal ions can reach 80%-95%, significantly reducing the leaching toxicity of heavy metals.

[0033] The completion of step 2 marks the basic end of the first-stage stabilization treatment. Through the pre-chelation effect of humic acid, ammonia nitrogen and heavy metal ions in the manganese slag are firmly locked within the three-dimensional network structure formed by humic acid, effectively inhibiting the volatilization of free ammonium and the migration activity of heavy metal ions. This treatment process completely avoids the ammonia gas emission problem caused by the addition of quicklime in traditional alkaline solidification processes, fundamentally eliminating the potential for secondary air pollution. Furthermore, humic acid, as a natural organic substance, possesses excellent biocompatibility and environmental friendliness, and no new pollutants are introduced during the treatment process.

[0034] S3. In-situ mineralization and forming stage of geopolymer: The goal of this stage is to achieve resource utilization of waste and construct a long-term stable protection system. Supplementary silica-alumina sources and early-strength accelerators need to be added to the chelated manganese slag. The supplementary silica-alumina sources are fly ash or metakaolin, with a fineness controlled within the range of 45 to 80 μm and a specific surface area controlled within the range of 250 to 400 m². 2 Within the range of / Kg. Fly ash, as an industrial solid waste, mainly originates from the electrostatic precipitators collected in coal-fired power plants. Its main components include glass microspheres, mullite, and quartz, with an active SiO2 content of approximately 40% to 55% and an active Al2O3 content of approximately 20% to 35%. Metakaolin is an anhydrous aluminosilicate obtained by calcining kaolin at 600-900℃, with an active SiO2 content of approximately 45% to 55% and an active Al2O3 content of approximately 35% to 45%. The selection of these two silicon and aluminum sources should be based on a comprehensive consideration of local resource endowment and cost factors. The comprehensive utilization of fly ash also has environmental benefits of treating waste with waste.

[0035] The amount of silicon-aluminum source added accounts for 3%-5% of the dry slag mass, and the specific amount is adjusted according to the chemical composition of the manganese slag and the strength requirements of the target product. Calcium formate, as an early-strength accelerator, should have a purity of not less than 90%, preferably not less than 95%, and a particle size controlled within the range of 0.1-0.5 mm. The amount of calcium formate added accounts for 1%-2% of the dry slag mass, and its main function is to provide a calcium source and promote the rapid formation of geopolymer gel. During the stirring process, the order of adding fly ash or metakaolin and calcium formate needs to be precisely controlled: First, add fly ash or metakaolin and dry mix it with manganese slag for 5-10 minutes at a speed of 500-800 r / min to ensure that the fly ash particles and manganese slag particles are fully mixed and initially contacted; second, add calcium formate and continue mixing for 5-8 minutes to ensure that calcium formate is evenly distributed in the material; third, add an appropriate amount of alkaline activation solution to adjust the moisture content to the target range of 18%-22%. The concentration of the alkaline activation solution is controlled between 5-15 g / L. The main components are a mixed solution of sodium hydroxide and sodium silicate, and its modulus (molar ratio of SiO2 to Na2O) is controlled within the range of 1.5-2.5.

[0036] In the formation of geopolymer gels, the active SiO2 and Al2O3 in manganese slag, fly ash, or metakaolin first undergo a depolymerization reaction under the action of an alkaline activator. The active SiO2 then reacts with OH- in a strongly alkaline solution. - The reaction produces silicon-oxygen tetrahedral SiO4. 4- Monomer; active Al2O3 and OH - The reaction produces aluminum-oxygen tetrahedron AlO4. 5- Monomers. These tetrahedral monomers approach each other in solution and undergo condensation polymerization by sharing oxygen atoms. The mechanism of condensation polymerization can be described by the following equation:

[0037] During the formation of geopolymer gels, silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra are connected by oxygen bridges to form a three-dimensional network structure. Sodium and calcium ions, as cations balancing the charge, fill the gaps in the network structure. The resulting inorganic polymer gel is called NASH gel (Na2O-Al2O3-SiO2-H2O system) or CASH gel (CaO-Al2O3-SiO2-H2O system), and its microstructure exhibits a three-dimensional network morphology, possessing extremely high strength and durability.

[0038] Calcium formate plays a crucial role in promoting coagulation and strengthening gel formation. Calcium formate (Ca(HCOO)2) ionizes upon dissolving in water to form Ca... 2+ and formate ions (HCOO) - Ca 2+The ions coordinate with the aforementioned tetrahedral monomers, accelerating the polycondensation reaction. Simultaneously, the heat generated by the decomposition of calcium formate helps to accelerate the temperature rise of the system, further promoting the gelation reaction. With the coagulating effect of calcium formate, the initial setting time of the geopolymer gel can be shortened to 30-60 minutes, and the final setting time can be controlled within the range of 2-4 hours, showing a significant improvement compared to the control group without calcium formate.

[0039] Geopolymer gels physically encapsulate and immobilize the humic acid-metal complexes formed in the preceding steps, creating a dense microstructure. The gel's three-dimensional network structure acts like countless tiny "cages," firmly trapping humic acid molecules and their complexed heavy metal ions within. This dual stabilizing mechanism of chemical chelation and physical encapsulation ensures that heavy metal ions are firmly locked within the solid matrix, making migration and escape difficult even under extreme environmental conditions. Geopolymer structures exhibit excellent acid and alkali resistance, with significantly improved acid resistance compared to ordinary silicate cement. In acidic environments with a pH of 3-5, ordinary silicate cement undergoes significant acid corrosion, while geopolymers, due to the large number of Si-O-Al and Si-O-Si bonds in their network structure, exhibit far greater stability in acidic environments than the Ca-O and Ca-Si bonds found in cement hydration products.

[0040] The moisture content of the mixed materials is controlled between 18% and 22%, at which point the material presents a loose, moist powder state with good molding properties. Compression molding is performed using a hydraulic molding machine or a compression molding machine. The rated pressure of the hydraulic molding machine is determined based on the product size and target strength, generally ranging from 500 to 2000 tons, with the molding pressure controlled within the range of 20-60 MPa and the holding time set at 30-60 seconds. The compression molding machine applies pressure to the material through a mechanically driven pressure head, with the downward speed of the pressure head controlled within the range of 10-30 mm per second, and the molding pressure controlled within the range of 15-50 MPa. The shape of the molded product is determined according to actual application requirements; it can be standard-sized building brick blanks (e.g., 240mm × 115mm × 53mm), roadbed materials for road base (e.g., block or granular), or non-fired aggregates used as concrete admixtures (e.g., 5-25mm graded particles).

[0041] After pressing and molding, the product is left to stand at room temperature for 2-4 hours to allow the particle arrangement inside the material to stabilize and reduce the risk of deformation during subsequent curing. After standing, the product enters the low-temperature steam curing process.

[0042] S4. Low-Temperature Steam Curing and Aging Stage: The molded preform is placed in a low-pressure steam curing chamber for accelerated stabilization. The steam pressure in the low-pressure steam curing chamber is controlled within the range of 0.1-0.3 MPa, corresponding to a saturated steam temperature of 100-130℃. The relative humidity in the curing chamber is maintained above 90%, preferably above 95%, to ensure that the product undergoes hydration and hardening reactions in a humid environment. The heating rate in the curing chamber is controlled at 10-20℃ per hour to prevent excessively rapid heating from causing excessive temperature gradients inside the product, which could lead to cracking. After heating to the set temperature of 60-80℃, the preform is held for curing for 8-12 hours, with temperature fluctuations controlled within ±3℃ during the holding period.

[0043] Low-temperature steam curing can significantly accelerate the polycondensation reaction process of geopolymer gels. At temperatures of 60-80℃, the polycondensation rate of aluminosilicate tetrahedra is 3-5 times higher than at room temperature, with a significant acceleration in gel formation and strength development. Simultaneously, moisture in the steam environment can penetrate into the product, promoting the continued participation of residual active aluminosilicate components in the reaction, further improving the product's density and strength. Humidity control during the curing process is crucial; excessively low humidity can cause the product surface to dry too quickly, leading to cracks, while excessively high humidity may affect heating efficiency. After curing, the product should be cooled to room temperature naturally at a rate of 15-25℃ / h to prevent thermal stress cracking caused by sudden temperature drops.

[0044] Products cooled to room temperature are transferred to a well-ventilated aging chamber for aging. The temperature in the aging chamber is controlled within the range of 20-30℃, and the relative humidity is maintained between 60%-80%. The aging time is set at 3-7 days, with the specific time determined based on the target strength and usage requirements of the product. During the aging process, the strength of the product continues to increase, and the compressive strength can reach 70%-85% of the final strength after 28 days. The ventilation system of the aging chamber is designed as a combination of forced ventilation and natural ventilation, with an air exchange rate controlled at 3-5 times / hour to ensure that moisture and reaction byproducts in the aging environment can be removed in a timely manner.

[0045] The final product after processing is a solid material with certain strength and geometry. Its microstructure exhibits a dense morphology of geopolymer gel encapsulating humic acid-metal complexes. The product can be used directly as a building material, for the production of non-fired bricks, roadbed materials, or as aggregate in concrete admixtures.

[0046] The technical solution of this invention achieves effective fixation of ammonia nitrogen and heavy metals in electrolytic manganese slag through a dual stabilization mechanism combining humic acid pre-chelation and geopolymer in-situ mineralization. The product can be used as a building material for resource utilization. The entire treatment process does not require the consumption of a large amount of water resources, does not generate secondary high-salt wastewater, and does not require high-temperature pyrometallurgical treatment, thus having significant environmental and economic benefits.

[0047] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the scope of protection of the present invention is not limited in any way to the specific parameter values ​​of the specific embodiments. The present invention covers equivalent substitutions or modifications to the specific parameters within the scope of the described technical concept, and all such substitutions and modifications fall within the scope of protection of the present invention.

Claims

1. A method for harmless treatment of electrolytic manganese slag based on solidification and stabilization, characterized in that, Includes the following steps: S1. Pretreatment and Modification Activation: The electrolytic manganese slag is crushed and screened to remove large impurities, then fed into a high-speed shear mixer, and a composite alkaline activator is sprayed into the manganese slag for modification and activation treatment under predetermined temperature and humidity conditions. S2. Humic acid pre-chelation: The prepared humic acid solution is evenly sprayed into the modified manganese slag and stirred vigorously. The amount of humic acid solution used is a certain proportion of the dry slag mass. S3. Geopolymer in-situ mineralization molding: Add fly ash or metakaolin and calcium formate to the chelated manganese slag, mix and control the moisture content of the material within the preset range, and press into shape. S4. Low-temperature steam curing and aging: The molded body is sent into a low-pressure steam curing chamber and cured at a predetermined temperature for a predetermined time period, and then aged under natural conditions for a predetermined number of days.

2. The method for harmless treatment of electrolytic manganese slag based on solidification and stabilization according to claim 1, characterized in that, The crushing process in S1 adopts a two-stage crushing process of jaw crusher and impact crusher in series, and the screening process adopts multi-level vibrating screen for grading. The speed and stirring temperature of the high-speed shear mixer are controlled within a preset range.

3. The method for harmless treatment of electrolytic manganese slag based on solidification and stabilization according to claim 1, characterized in that, The composite alkaline activator in S1 is mainly composed of finely ground blast furnace slag, steel slag powder and sodium hydroxide. The mass ratio of each component is within a preset range. The composite alkaline activator is injected by uniformly spraying it onto the surface of manganese slag in the high-speed shear mixer through an atomizing nozzle. The spraying pressure and spraying time are within a preset range.

4. The method for harmless treatment of electrolytic manganese slag based on solidification and stabilization according to claim 1, characterized in that, The concentration of the humic acid solution in S2 is within a preset range. During preparation, the humic acid powder is mixed with deionized water and placed in a constant temperature stirrer. The mixture is stirred and dissolved under a predetermined temperature condition. The humic acid solution is sprayed using a high-pressure atomizing device to evenly cover the surface of the modified manganese slag. The spraying pressure and stirring speed are within a preset range.

5. The method for harmless treatment of electrolytic manganese slag based on solidification and stabilization according to claim 1, characterized in that, In S2, the carboxyl and phenolic hydroxyl functional groups in the humic acid molecule undergo ammoniation with the ammonium ions in the manganese slag to generate a stable ammonium humic acid complex. At the same time, the active functional groups of humic acid undergo multiple complexation adsorption with heavy metal ions such as divalent manganese ions, trivalent chromium ions, and divalent lead ions in the solution to form a stable five- or six-membered cyclic chelate structure.

6. The method for harmless treatment of electrolytic manganese slag based on solidification and stabilization according to claim 1, characterized in that, The fineness and specific surface area of ​​the fly ash or metakaolin in S3 are within a preset range, and the purity and particle size of the calcium formate are within a suitable range. The order of adding the fly ash or metakaolin and the calcium formate is as follows: first add the fly ash or metakaolin and dry mix for a predetermined time, then add the calcium formate and continue mixing for a predetermined time, and finally add the alkaline activation solution to adjust the moisture content.

7. The method for harmless treatment of electrolytic manganese slag based on solidification and stabilization according to claim 1, characterized in that, In S3, the pressing and molding process uses a hydraulic molding machine or a compression molding machine. The molding pressure and holding time are within a preset range. The shape of the molded product includes brick blanks, roadbed materials, or non-fired aggregates. After pressing and molding, the product is left to stand at room temperature for a predetermined period of time before subsequent curing treatment.

8. The method for harmless treatment of electrolytic manganese slag based on solidification and stabilization according to claim 1, characterized in that, The steam pressure in the low-pressure steam curing chamber of S4 is controlled within a preset pressure range, the relative humidity is maintained above the preset humidity, the heating rate is the preset heating rate, and after heating to the set temperature, it is kept warm for curing. After curing, it is cooled to room temperature by natural cooling. The aging process is carried out in a well-ventilated aging chamber.

9. The method for harmless treatment of electrolytic manganese slag based on solidification and stabilization according to claim 1, characterized in that, The formation process of the geopolymer gel in S3 includes: firstly, under the action of an alkaline activator, the active silica and active alumina in manganese slag, fly ash or metakaolin undergo a depolymerization reaction to generate silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron monomers; subsequently, under the coagulation-promoting action of calcium formate, these monomers undergo a condensation reaction and rearrange to form a three-dimensional network structure geopolymer gel, which physically encapsulates and fixes the humic acid-metal complex formed in the previous step, forming a dense microstructure.

10. The method for harmless treatment of electrolytic manganese slag based on solidification and stabilization according to claim 1, characterized in that, It also includes environmental stability testing steps for the treated products, specifically including: taking samples to prepare leachate, using the acetic acid buffer solution method to determine the leaching concentration of heavy metals, and ensuring that the leaching concentrations of manganese ions and ammonia nitrogen do not exceed the corresponding thresholds; conducting acid tolerance tests, immersing the products in an acidic solution for a predetermined time, and ensuring that the increase in heavy metal leaching concentration does not exceed the preset increment threshold; and conducting freeze-thaw cycle tests, ensuring that after a predetermined number of freeze-thaw cycles, the appearance of the products does not change significantly, and the strength loss does not exceed the preset loss threshold.

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