A method for stabilizing and solidifying heavy metals in metallurgical slag by phosphide-cement synergy

Abstract

The application discloses a kind of phosphide-cement collaborative metallurgical slag heavy metal stabilization solidification method, it is related to the field of hazardous waste solid waste resource disposal, including metallurgical slag pretreatment, solidification system component design, subsection gradient mixing stirring, phosphide low-temperature stable pre-curing, cement hydration wet heat depth curing, solidification product detection and resource grading utilization;The application is coupled by chemical crystal lattice fixation and physical gel wrapping, completely solve the problem that traditional process heavy metal is easy to secondary dissolution, and the problem of poor durability of solidification, the structure of solidification body is stable, and the anti-leaching, anti-erosion ability is strong;The application is produced at normal temperature and pressure all the way, without high-temperature calcination process, greatly reduce production energy consumption and pollutant emission;Compound system effectively reduces the cost of reagent use, process fault tolerance is high, and the universality is wide, is suitable for various metallurgical hazardous slag disposal.

Description

Technical Field

[0001] This invention relates to the field of hazardous and solid waste resource utilization technology, specifically to a method for stabilizing and solidifying heavy metals in metallurgical slag using a phosphate-cement synergistic approach. Background Technology

[0002] Metallurgical slag is industrial solid waste generated during the production processes of non-ferrous metal smelting, recycled aluminum recycling, and steelmaking. Among them, recycled aluminum slag, copper electrolytic slag, and lead-zinc smelting slag are listed in the National Hazardous Waste List. After melting and impurity removal, recycled aluminum raw materials produce aluminum ash slag, which is enriched with various soluble heavy metals such as lead, cadmium, hexavalent chromium, zinc, and arsenic. Copper pyrometallurgical smelting produces matte slag, in which sulfide-bound heavy metals are easily leached out by rainwater. The oxidation process of converter steel slag generates soluble chromates, and when stored in the open, heavy metals seep into the soil and groundwater with leachate, causing permanent heavy metal pollution of water and soil. According to industry statistics, my country produces over 120 million tons of various types of hazardous metallurgical slag annually. Traditional storage and simple landfill methods pose extremely high environmental risks. Current mainstream hazardous waste disposal technologies are divided into three categories: single cement solidification, single phosphide stabilization, and high-temperature melting solidification, but all have significant shortcomings.

[0003] For example, single cement solidification relies solely on physical encapsulation for curing, resulting in poor durability of the finished product structure and a tendency for secondary leaching of heavy metals with long-term use; single phosphide solidification can achieve chemical fixation of heavy metals, but the solidified body lacks effective mechanical strength and cannot meet the requirements for resource utilization; high-temperature melting solidification processes require high-temperature calcination, leading to high overall energy consumption, significant pollution emissions, and high costs for industrial application; traditional multi-agent compounding processes are prone to antagonistic reactions between different agents, causing the solidification system to fail and its stability to be compromised. Furthermore, traditional processes lack standardized, integrated industrial treatment procedures, resulting in low water resource utilization rates and poor process adaptability in slag pretreatment, reaction, and curing stages, making it difficult to meet the large-scale stable treatment needs of various types of single and mixed metallurgical hazardous slags.

[0004] To address these issues, we propose a phosphate-cement synergistic method for stabilizing and solidifying heavy metals in metallurgical slag. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a phosphate-cement synergistic method for stabilizing and solidifying heavy metals in metallurgical slag. This method can achieve long-term stable solidification of various heavy metals. The core of the method adopts a dual-coupling stabilization mechanism of phosphate lattice chemical fixation and cement hydration gel physical encapsulation, combined with a complete set of industrial processes that operate at room temperature and pressure without high-temperature calcination, to achieve the harmless and resource-based disposal of hazardous metallurgical slag.

[0006] To achieve the above objectives, the present invention employs a phosphide-cement synergistic method for stabilizing and solidifying heavy metals in metallurgical slag, which includes metallurgical slag pretreatment, solidification system component design, segmented gradient mixing, phosphide low-temperature stabilization pre-curing, cement hydration and humid heat deep curing, solidified product testing and resource-based classification and utilization. The operating steps for each process are as follows: S1 metallurgical slag pretreatment: The original metallurgical slag is crushed and screened in two stages to obtain slag material with a particle size of 0.05mm to 5mm, and the coarse and fine particles are reasonably graded. The slag is washed using a three-stage countercurrent clean water system to remove soluble salts such as sodium chloride and sodium sulfate. After washing, the slag is dehydrated to control its moisture content. The washing wastewater is collected in a closed system, purified by phosphate precipitation, and then recycled. S2 curing system composition design: The main base material is pretreated metallurgical slag, compounded with phosphate composite stabilizer, P.O42.5 ordinary Portland cement, and mineral auxiliary setting regulator. The four components work together to construct a dual curing system. The formula comprises, by weight, 70-88 parts metallurgical slag, 3-12 parts phosphide composite stabilizer, 8-20 parts PO 42.5 ordinary Portland cement, and 1-5 parts mineral auxiliary setting-regulating components; the phosphide composite stabilizer is composed of calcium hypophosphite, aluminum dihydrogen phosphate, and magnesium phosphate in a fixed mass ratio and ground into ultrafine powder, which stabilizes the acid-base buffer zone of the system and is suitable for the precipitation reaction of various heavy metal lattice. The mineral-assisted setting agent is a compound powder of equal mass of kaolinite and diatomite, which has the functions of filling pores, adsorbing free heavy metals, and delaying the rapid early hydration of cement. S3 segmented gradient mixing: A horizontal twin-shaft continuous mixer is used for segmented differential mixing. First, the pretreated metallurgical slag, phosphate composite stabilizer and mineral auxiliary setting agent are dry mixed evenly at a constant speed, and micro-wetting and slurry conditioning are carried out simultaneously to form a phosphate premix with uniform agent adhesion. Then, silicate cement is added in batches, and the mixing speed is reduced and low-speed continuous mixing is carried out to avoid the problem of phosphate lattice reaction inhibition caused by rapid hydration heat release of cement and sudden increase of pH in the system, so as to obtain a uniform composite slurry without agglomeration and segregation. S4 Phosphate Low-Temperature Stable Pre-Cure: The composite slurry is sent into a closed constant temperature and humidity curing chamber and pre-cured under constant temperature and humidity in a low temperature and low humidity environment to generate stable and insoluble heavy metal phosphate lattice precipitates, thus completing the chemical fixation of heavy metals. S5 cement hydration and deep curing: After the low temperature pre-curing process is completed, the humidity of the curing chamber is increased and the temperature is kept constant. The curing cycle is set according to different resource utilization application scenarios to ensure that the cement is fully hydrated to generate a dense CSH gel system, which fully encapsulates the stable phosphate grains and forms an integrated dense solidified matrix with physical encapsulation and chemical fixation, thereby enhancing the long-term mechanical properties and leaching resistance of the solidified body. S6 solidified finished product testing and resource-based tiered utilization: After curing, samples are taken and heavy metal leaching toxicity testing and unconfined compressive strength testing are carried out in accordance with national standards. After all indicators meet the standards, the products are tiered according to performance parameters to adapt to different resource utilization engineering scenarios, so as to achieve harmless and efficient resource-based disposal of multiple types of metallurgical hazardous slag.

[0007] As a further optimization of the above scheme, the metallurgical slag is any single slag material selected from recycled aluminum slag, copper smelting slag, converter steel slag, and lead-zinc smelting slag, or a mixture of two or more types of slag materials of equal mass, and the slag body contains Pb, Cd, and Cr. 6+ It contains at least two of the heavy metals Cu, Zn and As, and is suitable for the co-solidification and treatment of various types of metallurgical hazardous solid waste.

[0008] As a further optimization of the above scheme, the moisture content of the slag material after dewatering in S1 is controlled at 12wt% to 22wt%.

[0009] As a further optimization of the above scheme, the phosphide composite stabilizer in S2 is composed of calcium hypophosphite, aluminum dihydrogen phosphate, and magnesium phosphate in a mass ratio of 2:1:1, and the powder is uniformly ground to below 200 mesh. In the mineral-assisted coagulation component, kaolinite and diatomaceous earth are mixed in an equal mass ratio of 1:1, the powder particle size is ≤200 mesh, and each component is uniformly dispersed in the system.

[0010] As a further optimization of the above scheme, in the S3 dry mixing stage, the stirring speed is controlled at 40-60 r / min, and the solid phase material is uniformly mixed by dry mixing at a constant speed for 3 minutes; in the cement blending stage, the stirring speed is reduced to 20-30 r / min, and stirring is continued for 5 minutes.

[0011] As a further optimization of the above scheme, the low-temperature pre-curing environment in S4 is 25-40℃ with a relative humidity of 60%-75% and a curing time of 2 days; the pH of the system is controlled online throughout the process to keep it stable in the reaction range of 7.5-9.5. When the pH is low, it is adjusted with calcium hydroxide to make it alkaline, and when the pH is high, it is neutralized and stabilized with dilute phosphate buffer.

[0012] As a further optimization of the above scheme, the temperature of the wet and hot deep curing environment in S5 is 30-45℃ and the relative humidity is 90%-98%; the curing cycle is set according to the grade of resource utilization: 7 days for roadbed fill, 14 days for conventional building material aggregate, and 28 days for long-term landfill base.

[0013] The present invention provides a phosphide-cement synergistic method for stabilizing and solidifying heavy metals in metallurgical slag, which has the following beneficial effects: The present invention provides a phosphide-cement synergistic method for stabilizing and solidifying heavy metals in metallurgical slag. Through the dual coupling effect of chemical lattice fixation and physical gel encapsulation, it completely solves the problems of easy secondary leaching of heavy metals and poor solidification durability in traditional processes. The solidified body has a stable structure and strong resistance to leaching and erosion. This invention is produced entirely at room temperature and pressure, without a high-temperature calcination process, which significantly reduces production energy consumption and pollutant emissions; the compound system effectively reduces reagent usage costs, has a high process tolerance, wide versatility, and is suitable for the disposal of various metallurgical hazardous slags; This invention enables the complete closed-loop recycling and reuse of production wastewater and water vapor, with no external pollution discharge. The treated metallurgical solid waste can be fully utilized as a resource, truly achieving the synergistic treatment of harmlessness and resource utilization. The mechanical properties and heavy metal curing index of the solidified body of this invention are stable and controllable. It can be adapted to various engineering scenarios such as building material aggregates, roadbed fillers and mine backfills according to the process ratio and curing parameters, and has high batch production stability.

[0014] Specific embodiments of the present invention are disclosed in detail with reference to the following description and accompanying drawings, indicating how the principles of the present invention can be adopted. It should be understood that the embodiments of the present invention are not limited in scope as a result, and that the embodiments of the present invention include many changes, modifications and equivalents within the spirit and scope of the appended claims. Attached Figure Description

[0015] Figure 1 This is a diagram of the phosphide-cement synergistic heavy metal stabilization and solidification method for metallurgical slag according to the present invention.

[0016] Figure 2 This is a connection diagram of the seven functional units of the present invention. Detailed Implementation

[0017] Please refer to the instruction manual appendix. Figure 1-2 This invention provides a technical solution: a phosphide-cement synergistic method for stabilizing and solidifying heavy metals in metallurgical slag, suitable for single slag materials or multiple mixed metallurgical hazardous slags such as recycled aluminum slag, copper smelting slag, converter steel slag, and lead-zinc smelting slag, to solve the problem of Pb, Cd, and Cr in the slag body. 6、 The issue of long-term stability of various easily leached heavy metals such as Cu, Zn, and As.

[0018] This invention utilizes a dual long-term stabilization method of phosphate lattice chemical fixation and cement hydration gel physical encapsulation. It employs a normal temperature and pressure process without high-temperature calcination. Through metallurgical slag graded water washing and desalination pretreatment, solidification system component ratio, segmented gradient stirring reaction, staged temperature, humidity and pH control curing, and a complete closed-loop water resource recycling process, it replaces the problems of poor durability of traditional single cement solidification, lack of mechanical strength of single phosphate solidification, high energy consumption and pollution of high-temperature melting, and the failure of two-phase reaction antagonism in traditional compound processes.

[0019] The complete industrial process of this invention includes six continuous core steps: first, metallurgical slag classification and water washing pretreatment; second, solidification system composition design; third, segmented gradient mixing and stirring; fourth, low-temperature lattice stabilization pre-curing of phosphides; fifth, cement hydration and wet heat deep curing; and sixth, solidified finished product testing and resource-based classification and utilization, which can be continuously and automatically produced.

[0020] Implementation preparation: 1. Unified raw material pretreatment standards: All metallurgical slags are crushed by a jaw crusher and screened in two stages by a double-layer vibrating screen to control the finished product particle size range of 0.05mm to 5mm; of which coarse particles of 1 to 5mm account for 40% to 60% by mass and fine powder of 0.05 to 1mm account for 40% to 60% by mass.

[0021] A three-stage countercurrent water washing process is adopted, with a solid-liquid ratio of 1:3 in each stage, which fully removes soluble salts such as sodium chloride and sodium sulfate from the slag, eliminating the problem of long-term corrosion and damage to the solidified matrix by salt ions.

[0022] After washing, the residue is dewatered using a plate and frame filter press, and the moisture content of the residue is adjusted to 12wt% to 22wt%. The standard moisture content for this example is 17wt%.

[0023] The washing wastewater is collected in a unified and sealed manner. A trace amount of phosphate stabilizer is added to precipitate free heavy metal ions in the water. The clarified and purified wastewater is all recycled back to the washing process, achieving zero discharge of process wastewater and closed-loop utilization of water resources.

[0024] 2. Standardized Curing System Components: The curing system of this invention consists of four parts, with the following mass ratios: 70-88 parts metallurgical slag, 3-12 parts phosphide composite stabilizer, 8-20 parts PO 42.5 ordinary Portland cement, and 1-5 parts mineral auxiliary setting modifier. The four ratios in parentheses in the title of the example correspond to the mass ratio of [metallurgical slag: phosphide stabilizer: cement: mineral auxiliary component].

[0025] The phosphate composite stabilizer is composed of calcium hypophosphite, aluminum dihydrogen phosphate, and magnesium phosphate in a mass ratio of 2:1:1. The powder is uniformly ground to below 200 mesh, which can adjust the pH buffer of the system between 7.5 and 9.5, perfectly adapting to the precipitation reaction of various heavy metals. The mineral auxiliary setting agent is a powder composed of kaolinite and diatomaceous earth in an equal mass ratio of 1:1, with a particle size ≤200 mesh. It has multiple core functions, including pore filling, adsorption of free heavy metals, and delaying the rapid early hydration of cement. The cementitious component uses P.O42.5 ordinary Portland cement to provide stable mechanical strength for the solidified body.

[0026] 3. Standardized segmented mixing process: A horizontal twin-shaft continuous mixer is used for segmented mixing to avoid antagonistic reactions between reagents; the dry mixing stage has a constant speed of 40-60 r / min, with a standard reference speed of 50 r / min and a dry mixing time of 3 min, to achieve uniform mixing of slag, phosphate stabilizer and mineral additives; the cement blending stage has the speed reduced to 20-30 r / min, with a standard reference speed of 25 r / min, and continuous mixing for 5 min, effectively avoiding the problems of rapid hydration heat release of cement and sudden pH rise in the system inhibiting phosphate lattice precipitation.

[0027] 4. Standardized phased curing process: divided into two phases: low-temperature pre-curing and humid heat deep curing.

[0028] The low-temperature pre-curing stage involves a temperature of 25–40°C and a relative humidity of 60%–75%, with standard reference parameters of 32°C and 68% humidity. The curing is carried out for 2 days to provide sufficient time for heavy metal ions and phosphorus components to undergo a lattice precipitation reaction. The damp-heat deep curing stage involves a temperature of 30–45°C and a relative humidity of 90%–98%, with standard reference parameters of 38°C and 95% humidity. The curing is carried out for 7 days, 14 days, and 28 days according to the resource utilization purpose, with the standard implementation example showing a uniform curing of 14 days.

[0029] The pH of the system is monitored online in real time throughout the process. The optimal reaction range is 7.5 to 9.5. When the pH is too low, calcium hydroxide is added to adjust the alkali, and when the pH is too high, dilute phosphate buffer is added to neutralize and stabilize the pressure. The volatile water vapor generated during the pre-curing process is condensed and recovered and all of it is returned to the pre-treatment water washing section to achieve a closed-loop circulation of water resources.

[0030] 5. Unified Finished Product Testing Standards: Heavy metal leaching toxicity testing and unconfined compressive strength testing are conducted strictly in accordance with national standards; core performance thresholds for cured products: 7-day unconfined compressive strength ≥ 12 MPa, 28-day unconfined compressive strength ≥ 20 MPa; heavy metal leaching limits: Pb ≤ 0.25 mg / L, Cd ≤ 0.05 mg / L, Cr 6、 ≤0.1mg / L, Cu≤1mg / L and Zn≤2mg / L, As≤0.3mg / L.

[0031] 6. Unified Mixed Slag Proportioning Standard: The multiple mixed slag examples of this invention use the original disclosed proportioning standard. Among them, the four types of mixed metallurgical slag are mixed with 25% each of recycled aluminum slag, copper smelting slag, converter steel slag and lead-zinc smelting slag. The two types of mixed slag are mixed with the corresponding single slag material in a 1:1 ratio. There is no additional adulteration or proportional deviation in the mixed slag.

[0032] The entire curing equipment is arranged as a continuous production line, with seven functional units set up sequentially along the material flow direction: Raw material feeding unit: Metallurgical slag is quantitatively fed through a closed silo and processed into 0.05-5mm standard particle size slag material by a jaw crusher and a double-layer grading screen; Pretreatment water washing and screening unit: multi-stage water washing removes soluble salts from the slag, and plate and frame filter press controls the moisture content of the material; the water washing wastewater is collected and purified by phosphate precipitation to achieve water recycling and reuse; Ingredient storage unit: Separately stores pretreated slag, phosphate stabilizer, silicate cement, and mineral setting aids, equipped with a quantitative screw weigher for precise proportioning and feeding; The segmented gradient mixing unit first mixes the dry slag material, stabilizer and mineral additives at high speed and atomizes and wets them, then adds cement in batches at low speed and mixes them to obtain a uniform composite slurry. Dual-stage constant temperature and humidity curing chamber: The interior is divided into a low-temperature pre-curing zone and a high-humidity deep curing zone by a sliding sealed door, which can control the temperature and humidity in the zone and monitor and adjust the pH of the system online; the chamber also includes a condensation and recovery of volatile water vapor and a reflux water washing process. Finished product testing compartment unit: After curing, it automatically samples and tests for heavy metal leaching and compressive strength. Qualified materials are stored in separate compartments, which are suitable for roadbed, building material and landfill base resource utilization scenarios. Water circulation closed-loop system: Unified control of the speed, temperature, humidity, pH of all equipment and the timing of each process to achieve automated continuous production.

[0033] Example 1: High-cement, low-phosphorus recycled aluminum slag solidification formula (70:3:20:5); In this embodiment, the raw material is a single recycled aluminum slag, which is rich in heavy metals such as Pb, Cd, As and Zn, and has a moderate content of soluble salts, making it suitable for preparing high mechanical strength recycled building aggregates. The proportions of each component by mass are as follows: 70 parts of pretreated recycled aluminum slag, 3 parts of phosphate composite stabilizer, 20 parts of P.O42.5 silicate cement, and 5 parts of kaolinite-diatomite mineral auxiliary components.

[0034] Pretreatment process: The recycled aluminum slag is crushed and screened to control the proportion of coarse particles (1-5mm) to 40% and fine powder (0.05-1mm) to 60%. Soluble salts in the slag are removed by three-stage countercurrent water washing. After dewatering by plate and frame filter press, the moisture content of the slag is adjusted to 17%. The washing wastewater is purified by phosphide precipitation, filtered and clarified, and then completely recycled back to the washing process.

[0035] Segmented mixing process: All pretreated aluminum slag, 3 parts phosphate stabilizer, and 5 parts mineral additives are put into a horizontal twin-shaft mixer and dry-mixed at a constant speed of 50 r / min for 3 minutes. Simultaneously, a small amount of deionized water is sprayed in to wet the powder, ensuring that the agent is evenly attached to the surface of the slag particles. 20 parts silicate cement are added in two equal amounts. After the addition is completed, the mixer speed is reduced to 25 r / min and the mixture is continuously stirred at a uniform speed for 5 minutes to finally obtain a uniform and moist composite slurry without local lumps, dry material agglomeration, agent segregation, or other problems.

[0036] Segmented curing process: The mixed composite slurry is sent into a sealed, constant temperature and humidity curing chamber for standardized low-temperature pre-curing: temperature 32℃, relative humidity 68%, sealed static curing for 2 days, with the pH of the system maintained online throughout the process to ensure that heavy metal ions and phosphorus components react fully to form stable, insoluble phosphate crystals; after the pre-curing process is completed, the curing chamber parameters are adjusted to a constant temperature of 38℃ and relative humidity increased to 95%, and continuous wet and hot deep curing is carried out for 14 days to adapt to the application scenarios of recycled aggregates in construction.

[0037] Finished product performance testing: The cured body has a dense structure, low porosity, and no microcracks; the 7-day unconfined compressive strength is 18.2 MPa, and the 28-day compressive strength is 23.5 MPa; heavy metal leaching test results: Pb 0.21 mg / L, Cd 0.032 mg / L, Cr 6、 The concentrations of Cu, Zn, and As are all below the national standard limits (0.07 mg / L, 0.72 mg / L, 1.45 mg / L, 0.21 mg / L), and can be directly used in the preparation of building materials such as permeable bricks and non-fired bricks.

[0038] Example 2: Low-phosphorus, high-auxiliary-material formulation for recycled aluminum slag (72:4:19:5); The raw material in this embodiment is a single recycled aluminum metallurgical slag. Compared with Example 1, the proportion of slag is slightly increased, the cement content is moderately reduced, and the high mineral auxiliary content is maintained to balance the mechanical strength of the solidified body and the solidification stability of heavy metals. The mass ratio of each component is as follows: 72 parts recycled aluminum slag, 4 parts phosphate stabilizer, 19 parts cement and 5 parts mineral auxiliary components.

[0039] The pretreatment, segmented mixing and staged curing processes use common benchmark parameters. After crushing and screening, the proportion of coarse particles is 42% and the proportion of fine powder is 58%. During the pre-curing stage, the pH of the system is maintained at a stable 8.3. The wet heat deep curing cycle is 14 days. The process parameters of the whole process are standardized and without deviation.

[0040] Finished product performance testing: 7-day compressive strength of the cured body is 17.5 MPa, and 28-day strength is 22.8 MPa; Heavy metal leaching indicators: Pb 0.19 mg / L, Cd 0.030 mg / L, Cr 6、 The concentrations of phosphate crystals in this embodiment are 0.068 mg / L, Cu 0.68 mg / L, Zn 1.38 mg / L, and As 0.19 mg / L. Compared to Example 1, the phosphate crystals in this embodiment are more evenly distributed within the slag, the heavy metal leaching index is further optimized, and the mechanical strength is only slightly reduced. The overall performance is excellent and suitable for high-end recycled building material aggregate production scenarios.

[0041] Example 3: Balanced formulation of recycled aluminum slag (74:5:18:3); This embodiment optimizes the component ratio, balancing the proportions of slag, phosphide agent, cement, and mineral auxiliary materials, aiming for low cost and large-scale production, and is suitable for the large-scale resource utilization of roadbed filler. The mass proportions of each component are as follows: 74 parts recycled aluminum slag, 5 parts phosphide stabilizer, 18 parts cement, and 3 parts mineral auxiliary components.

[0042] After crushing and screening, the slag material has a coarse particle ratio of 45% and a fine powder ratio of 55%. The entire process strictly follows the general benchmark process parameters. During the pre-curing stage, the pH of the system is stable at 8.1, and the standard wet heat curing is carried out for 14 days, resulting in strong process stability.

[0043] Finished product performance testing: 7-day compressive strength of the cured body is 16.8 MPa, and 28-day strength is 22.1 MPa; Heavy metal leaching: Pb 0.18 mg / L, Cd 0.028 mg / L, Cr 6、 The concentrations of phosphates are 0.065 mg / L, Cu 0.65 mg / L, Zn 1.32 mg / L, and As 0.18 mg / L. The moderate increase in phosphate content enhances the lattice fixation of heavy metals, while the slight reduction in mineral additives has a negligible impact on overall mechanical strength. The finished product fully meets the standards for long-term service of roadbed fillers.

[0044] Example 4: High-phosphorus, low-auxiliary-material formulation for recycled aluminum slag (76:6:17:1); This embodiment further increases the dosage of phosphate stabilizer and reduces the proportion of cement and mineral additives, with a core focus on enhancing the stabilization and solidification effect of heavy metals. It is specifically designed for the harmless treatment of recycled aluminum slag with medium to high heavy metal pollution content. The mass ratio of each component is as follows: 76 parts recycled aluminum slag, 6 parts phosphate stabilizer, 17 parts cement, and 1 part mineral auxiliary component.

[0045] After crushing and screening, the slag material has a coarse particle ratio of 48% and a fine powder ratio of 52%. The standardized pretreatment and segmented mixing process is strictly implemented. The pH of the pre-curing system is kept stable at 8.4, and the wet heat curing cycle is 14 days.

[0046] Finished product performance testing: 7-day compressive strength of the cured body is 15.6 MPa, and 28-day strength is 21.3 MPa; Heavy metal leaching: Pb 0.16 mg / L, Cd 0.025 mg / L, Cr 6、 The concentrations of heavy metals in the leaching solution are 0.060 mg / L, Cu 0.60 mg / L, Zn 1.25 mg / L, and As 0.16 mg / L. Overall heavy metal leaching indicators are significantly optimized, solidification stability is significantly improved, and only mechanical strength decreases slightly. This method can efficiently achieve deep and harmless treatment of highly polluting recycled aluminum slag.

[0047] This embodiment closely matches the lower limit of cement content in the claims, maximizes the proportion of metallurgical solid waste disposal, significantly reduces hazardous waste disposal costs, and ensures that the finished product meets the minimum performance standards for roadbed fillers. It is a preferred formulation for low-cost industrialization. The mass proportions of each component are as follows: 78 parts recycled aluminum slag, 7 parts phosphate stabilizer, 14 parts cement, and 1 part mineral auxiliary component.

[0048] After crushing and screening, the slag material has a coarse particle ratio of 50% and a fine powder ratio of 50%, with a balanced particle size distribution. The entire process parameters are standardized, the pre-curing pH is stable at 8.3, and the wet heat curing lasts for 14 days.

[0049] Finished product performance testing: The cured body's 7-day compressive strength is 14.2 MPa, and its 28-day strength is 20.1 MPa, consistently meeting the core strength indicators of ≥12 MPa at 7 days and ≥20 MPa at 28 days; Heavy metal leaching: Pb 0.14 mg / L, Cd 0.022 mg / L, Cr 6、 With a concentration of 0.055 mg / L, Cu 0.56 mg / L, Zn 1.18 mg / L, and As 0.14 mg / L, it offers excellent cost-effectiveness and is suitable for large-area roadbed filling projects.

[0050] Example 6: Medium-phosphorus, low-cement copper smelting slag formulation (80:8:11:1). In this embodiment, the raw material is a single copper smelting slag. The core pollutants in the slag are Cu, Zn, Pb, and As. The content of hexavalent chromium and cadmium is relatively low. The finished product is suitable for mining backfill aggregate and simple roadbed resource utilization scenarios in the plant area. The mass ratio of each component is as follows: 80 parts copper smelting slag, 8 parts phosphide stabilizer, 11 parts cement, and 1 part mineral auxiliary component.

[0051] After crushing and screening, the slag material has a coarse particle ratio of 52% and a fine powder ratio of 48%. After three-stage deep water washing and desalination, the moisture content is stabilized at 17%. The standard segmented mixing process is implemented, with low-temperature pre-curing for 2 days, system pH maintained at 8.2, and wet-heat deep curing for 14 days.

[0052] Finished product performance testing: 7-day compressive strength of the cured body is 13.5 MPa, and 28-day strength is 19.4 MPa; Heavy metal leaching: Pb 0.13 mg / L, Cd 0.020 mg / L, Cr 6、 The concentrations of Cu, Zn, and As were 0.052 mg / L, 0.52 mg / L, 1.10 mg / L, and 0.13 mg / L, all met the standards and fully satisfied the requirements for mine solid waste backfilling and resource utilization of plant roadbed.

[0053] Example 7: Boundary formula for high-slag, low-reagent copper smelting slag (82:9:8:1). This embodiment represents the extreme proportion of copper smelting slag disposal, closely approximating the upper limit of metallurgical slag content and the lower limit of cement content in the claims. It is used to verify the extreme adaptability and fault tolerance of the process of this invention. The mass proportions of each component are as follows: 82 parts copper smelting slag, 9 parts phosphate stabilizer, 8 parts cement, and 1 part mineral auxiliary component.

[0054] After crushing and screening, the slag material has a coarse particle ratio of 54% and a fine powder ratio of 46%. The entire process is standardized with pretreatment and mixing. During the pre-curing stage, the pH is kept stable at 8.5, and the material is cured in a humid heat for 14 days.

[0055] Finished product performance testing: The 7-day compressive strength of the cured body is 12.4 MPa, just meeting the minimum strength threshold of the national standard; the 28-day strength is 18.3 MPa; heavy metal leaching: Pb 0.11 mg / L, Cd 0.018 mg / L, Cr 6、 It exhibits excellent heavy metal stabilization effects with concentrations of 0.048 mg / L for Cu, 0.48 mg / L for Zn, 1.02 mg / L for As, and 0.11 mg / L for Zn, making it suitable for simple temporary roadbed filling and temporary backfilling in mines.

[0056] Example 8: High-phosphorus, high-strength converter steel slag formulation (70:12:15:3); In this embodiment, the raw material processed is a single converter steel slag, and the core pollutant of this slag is Cr. 6、 Hexavalent chromium and zinc are the most difficult types of metallurgical slag to solidify. In this embodiment, a high phosphide formulation is used to specifically enhance the stabilizing and solidifying effect of hexavalent chromium and zinc. The mass ratio of each component is as follows: 70 parts of converter steel slag, 12 parts of phosphide stabilizer, 15 parts of cement and 3 parts of mineral auxiliary components.

[0057] After crushing and screening, the slag material has a coarse particle ratio of 40% and a fine powder ratio of 60%. It undergoes three-stage water washing to remove soluble salt ions. During the pre-curing stage, the pH of the system is kept stable at 8.6 to ensure sufficient crystal lattice precipitation of chromate and zinc ions. It is then cured in a humid heat for 14 days.

[0058] Finished product performance testing: 7-day compressive strength of the cured body was 16.3 MPa, and 28-day strength was 21.8 MPa; Heavy metal leaching: Cr 6、 With concentrations of 0.042 mg / L for Zn, 0.95 mg / L for Pb, and 0.10 mg / L for Cd, the curing effect of hexavalent chromium is particularly outstanding, resulting in a finished product with strong resistance to leaching. It can be used to prepare permeable building materials with high environmental protection requirements.

[0059] Example 9: Balanced formulation of medium-high phosphorus converter steel slag (73:11:14:2). This embodiment optimizes the formulation of converter steel slag, balancing reagent costs and solidification effects, and is suitable for large-scale routine treatment. The mass proportions of each component are: 73 parts converter steel slag, 11 parts phosphate stabilizer, 14 parts cement, and 2 parts mineral auxiliary components. After crushing and screening, the slag material has a coarse particle ratio of 43% and a fine powder ratio of 57%. The entire process follows standard procedures, with pre-curing at pH 8.4 and moist heat curing for 14 days.

[0060] Finished product performance testing: 7-day compressive strength of the cured body is 15.1 MPa, and 28-day strength is 20.6 MPa; Cr 6、 With concentrations of 0.045 mg / L and Zn of 0.98 mg / L, it exhibits good batch production stability, excellent resistance to long-term rainwater leaching and soil erosion, and is suitable for long-term open-air roadbed engineering.

[0061] Example 10: Medium phosphorus medium slag converter steel slag formulation (76:10:12:2). The mass ratio of each component is as follows: 76 parts of converter steel slag, 10 parts of phosphate stabilizer, 12 parts of cement, and 2 parts of mineral auxiliary components. After crushing and screening, the slag material has a coarse particle ratio of 46% and a fine powder ratio of 54%. The entire process follows the general benchmark process parameters without any special adjustments.

[0062] Finished product performance testing: 7-day compressive strength of the cured body is 14.0 MPa, and 28-day strength is 19.7 MPa; Cr 6、 With concentrations of 0.049 mg / L and Zn of 1.05 mg / L, it achieves a balance between harmlessness and resource utilization, making it suitable for large-scale, batch disposal of hazardous steel slag waste by steel enterprises.

[0063] Example 11: Low-phosphorus, high-slag converter steel slag formulation (79:9:11:1). The mass ratio of each component is as follows: 79 parts converter steel slag, 9 parts phosphate stabilizer, 11 parts cement, and 1 part mineral auxiliary component. After crushing and screening, the slag material has a coarse particle ratio of 49% and a fine powder ratio of 51%. The construction process includes standardized pretreatment, mixing, and curing.

[0064] Finished product performance testing: 7-day compressive strength of the cured body is 13.1 MPa, and 28-day strength is 18.9 MPa; Cr 6、 The concentrations of 0.053 mg / L and Zn are 1.12 mg / L, meeting the standards and suitable for use as fill material for non-main roads and temporary storage yards within the plant area.

[0065] Example 12: Low-cost formula for converter steel slag (82:8:9:1). This embodiment represents the lowest-cost boundary formula for steel slag disposal, used to verify the fault tolerance limit and low-cost implementation capability of the process of this invention. The mass proportions of each component are: 82 parts converter steel slag, 8 parts phosphate stabilizer, 9 parts cement, and 1 part mineral auxiliary component. After crushing and screening, the slag material has a coarse particle ratio of 53% and a fine powder ratio of 47%, and is cured for 14 days using standard processes throughout the process.

[0066] Finished product performance testing: The 7-day compressive strength of the cured body is 12.2 MPa, which just meets the minimum strength requirement of the national standard; the 28-day strength is 17.8 MPa; Cr 6、 With a concentration of 0.057 mg / L and Zn of 1.19 mg / L, the heavy metal leaching levels are close to the national standard limits, making it only suitable for short-term temporary landfills and temporary roadbeds, and not for long-term open-air service projects.

[0067] Example 13: Solidification formula for 1:1 mixed aluminum slag and copper slag (70:6:19:5). The entire process adopts standard pretreatment, segmented mixing, and graded curing techniques. The pre-curing pH is stabilized at 8.2, and the wet heat curing lasts for 14 days. The process parameters are standardized.

[0068] Finished product performance testing: 7-day compressive strength of the cured body is 17.9 MPa, and 28-day strength is 23.1 MPa; Pb, Cd, Cr... 6、 The leaching indices of multiple metals, including Cu, Zn, and As, are all below the national standard limits, proving that this process can effectively and synergistically treat complex metallurgical slags without the risk of cross-leaching of heavy metals or antagonistic reactions, demonstrating excellent versatility in the treatment of mixed slags.

[0069] Example 14: Solidification formula for 1:1 mixed aluminum slag and steel slag (74:7:16:3). In this embodiment, the raw materials are recycled aluminum slag and converter steel slag mixed in a 1:1 ratio, and the aluminum slag is high in arsenic and the steel slag is high in hexavalent chromium, two difficult-to-stabilize heavy metals, to verify the synergistic solidification effect of cross-category slag materials. The mass ratio of each component is as follows: 74 parts of mixed slag, 7 parts of phosphide stabilizer, 16 parts of cement and 3 parts of mineral additives, and the standard process is cured for 14 days.

[0070] Finished product performance testing: The solidified body has a 7-day compressive strength of 16.1 MPa and a 28-day strength of 21.5 MPa. It exhibits outstanding stabilization effects on arsenic and hexavalent chromium, and has strong adaptability to composite slag treatment, which can simultaneously solve the problem of harmless treatment of two types of high-risk metallurgical slag.

[0071] Example 15: Copper slag-steel slag 1:1 mixed slag solidification formula (78:8:13:1). In this embodiment, the raw materials are copper smelting slag and converter steel slag mixed in a 1:1 ratio, mainly for the application scenario of resource utilization in mine backfilling; the mass ratio of each component is as follows: 78 parts of mixed slag, 8 parts of phosphide stabilizer, 13 parts of cement and 1 part of mineral additives, and the entire process is standardized and cured for 14 days.

[0072] Finished product performance testing: The 7-day compressive strength of the solidified body is 14.5 MPa, and the 28-day strength is 20.3 MPa. It can simultaneously achieve long-term stability of Cu, Cr and Zn heavy metals, making it the optimal formula for backfilling in mining solid waste scenarios.

[0073] Example 16: High-phosphorus formulation for high-heavy-metal aluminum slag (75:12:10:3); This embodiment is specifically designed for heavily polluted recycled aluminum slag with high cadmium and high arsenic content. It adopts the formula with the maximum phosphate content as claimed in the claims to maximize the deep stabilization effect of heavy metals and solve the problem of disposal of highly polluting hazardous slag. The mass ratio of each component is as follows: 75 parts recycled aluminum slag, 12 parts phosphate stabilizer, 10 parts cement and 3 parts mineral additives.

[0074] Finished product performance testing: The 7-day compressive strength of the solidified body is 13.8 MPa, and the 28-day strength is 19.2 MPa; the Cd leaching is as low as 0.014 mg / L, the arsenic and lead leaching indicators are significantly optimized, the stability effect is good, and it is specially adapted for the deep harmless treatment of highly polluting metallurgical slag.

[0075] Example 17: Low-pollution aluminum slag, low-cost, high-cement formulation (75:3:20:2). This embodiment targets recycled aluminum slag with low heavy metal content and low pollution. It adopts the lowest phosphide dosage and high cement ratio as claimed in the claims to maximize the reduction of disposal costs and improve the mechanical strength of the solidified body while ensuring that the harmlessness standard is met. The mass ratio of each component is as follows: 75 parts recycled aluminum slag, 3 parts phosphide stabilizer, 20 parts cement and 2 parts mineral additives.

[0076] Finished product performance testing: The 7-day compressive strength of the cured body is 18.7 MPa, and the 28-day strength is 24.1 MPa. This is the formulation with the highest mechanical strength and the lowest cost of phosphide reagents in the examples, which is suitable for the large-scale, low-cost, and harmless treatment of low-pollution metallurgical slag.

[0077] Example 18: Special medium-ratio formula for lead-zinc smelting slag (77:8:13:2). In this embodiment, the raw material is lead-zinc smelting slag. The core pollutants of this slag are high concentrations of Pb and Cd, which is one of the categories with the highest risk of heavy metal leaching among existing metallurgical slags. Traditional solidification methods are prone to secondary leaching. The mass ratio of each component is as follows: 77 parts lead-zinc slag, 8 parts phosphide stabilizer, 13 parts cement, and 2 parts mineral additives.

[0078] After three-stage deep water washing and desalination, segmented gradient reaction, and temperature and humidity curing, the finished product has a 7-day compressive strength of 14.8 MPa; heavy metal leaching results in Pb 0.12 mg / L and Cd 0.019 mg / L, with a stabilization effect more than 4 times better than traditional single cement curing, solving the problems of easy leaching of heavy metals and poor long-term stability in lead-zinc slag.

[0079] Example 19: Extremely high slag cost formula for lead-zinc slag (88:3:8:1). This embodiment is a formula with extreme limits of the proportions claimed, reaching the upper limit of the metallurgical slag content and the lower limit of the phosphide and cement reagent content, used to verify the adaptability of the process of the present invention and the lowest disposal cost; the mass proportions of each component are: 88 parts of lead-zinc smelting slag, 3 parts of phosphide stabilizer, 8 parts of cement and 1 part of mineral additives.

[0080] Finished product performance testing: The 7-day compressive strength of the cured body is 12.1 MPa, which just meets the minimum strength threshold of the national standard; the heavy metal leaching Pb is 0.24 mg / L and Cd is 0.048 mg / L, which is close to the upper limit of the national standard. It is only suitable for temporary and short-term resource utilization scenarios and is strictly prohibited for engineering scenarios involving long-term open-air service and contact with groundwater.

[0081] Example 20: General formulation for four types of mixed metallurgical slag (80:10:9:1); This embodiment simulates the actual working conditions of mixed disposal of multiple types of hazardous slag in a comprehensive smelting enterprise. The raw materials are four types of slag materials: recycled aluminum slag, copper slag, converter steel slag, and lead-zinc slag, mixed in equal proportions (25% each), without any additional components added, which fully verifies the universality and adaptability of the process of this invention. The mass proportions of each component are as follows: 80 parts of mixed slag, 10 parts of phosphate stabilizer, 9 parts of cement, and 1 part of mineral additives.

[0082] Finished product performance testing: 7-day compressive strength of the cured body is 13.3 MPa, and 28-day strength is 18.5 MPa; Pb, Cd, Cr... 6、 The leaching indicators for six heavy metals—Cu, Zn, and As—all consistently met the standards, with no risk of exceeding the limits. This fully demonstrates that the process of this invention does not require specific parameter adjustments or adaptation to different slag materials, and is universally applicable to mainstream metallurgical hazardous slags, exhibiting strong industrial adaptability and versatility.

[0083] In summary, the present invention has excellent dual stabilization mechanism and long-term anti-leaching effect: all embodiments stably achieve phosphate lattice chemical fixation, cement gel physical encapsulation and dual long-term stabilization mechanism. After 5 years of acid rain accelerated leaching simulation test, there is no secondary leaching of heavy metals inside the solidified body, the structure is intact without cracking or pore expansion problems, and the durability is far superior to the traditional single curing process.

[0084] Low energy consumption and strong industrial applicability: The entire process is carried out at normal temperature and pressure without high-temperature calcination. The comprehensive power consumption per ton of slag is ≤35kWh, which is more than 88% lower than the energy consumption of traditional high-temperature melting and solidification processes. The synergistic combination of phosphate and cement reduces the cost of reagents by 55% compared to pure phosphate solidification processes, significantly reducing the hazardous waste disposal costs for enterprises.

[0085] The entire process is closed-loop environmentally friendly with zero pollution emissions: all process washing wastewater and curing condensate volatilization water vapor are collected, purified and recycled, achieving zero discharge of process wastewater; there are no high-temperature toxic fumes and no fugitive dust emissions, and the treated metallurgical solid waste is 100% resource-based, truly achieving harmless treatment of hazardous waste and zero pollution in disposal.

[0086] The product has stable performance and is suitable for multiple application scenarios: the finished products in the compliant implementation examples all meet the national standard heavy metal leaching limit and mechanical strength requirements. It can be adapted to multiple application scenarios such as roadbed filler, high-end building material aggregate, mine backfill and landfill base according to the mixing ratio parameters and maintenance cycle. The performance fluctuation deviation of industrial production batches is <8%, and the product has strong stability.

[0087] High process tolerance and full versatility: The process of this invention can be adapted to single, two-type mixed and four-type mixed metallurgical hazardous slags with unified parameters. At the same time, no specific equipment modification is required. It solves the problems of poor slag material adaptability, reaction antagonism, parameter ambiguity and difficulty in implementation and replication of traditional processes, and has the conditions for large-scale industrial continuous production.

Claims

1. A method for stabilizing and solidifying heavy metals in metallurgical slag using a phosphate-cement synergistic approach, characterized in that, This includes metallurgical slag pretreatment, solidification system composition design, segmented gradient mixing, low-temperature stable pre-curing of phosphides, deep curing of cement hydration under humid heat, and testing and resource-based utilization of solidified finished products. The operating steps for each process are as follows: S1 metallurgical slag pretreatment: The original metallurgical slag is crushed and screened in two stages to obtain slag material with a particle size of 0.05mm to 5mm, and the coarse and fine particles are reasonably graded. The slag is washed using a three-stage countercurrent clean water system to remove soluble salts such as sodium chloride and sodium sulfate. After washing, the slag is dehydrated to control its moisture content. The washing wastewater is collected in a closed system, purified by phosphate precipitation, and then recycled. S2 curing system composition design: The main base material is pretreated metallurgical slag, compounded with phosphate composite stabilizer, PO 42.5 ordinary Portland cement, and mineral auxiliary setting regulator. The four components work together to construct a dual curing system. The formula comprises, by weight, 70-88 parts metallurgical slag, 3-12 parts phosphide composite stabilizer, 8-20 parts PO 42.5 ordinary Portland cement, and 1-5 parts mineral auxiliary setting-regulating components; the phosphide composite stabilizer is composed of calcium hypophosphite, aluminum dihydrogen phosphate, and magnesium phosphate in a fixed mass ratio and ground into ultrafine powder, which stabilizes the acid-base buffer zone of the system and is suitable for the precipitation reaction of various heavy metal lattice. The mineral-assisted setting component is a compound powder of equal mass of kaolinite and diatomite, which has the functions of filling pores, adsorbing free heavy metals, and delaying the rapid early hydration of cement. S3 segmented gradient mixing: A horizontal twin-shaft continuous mixer is used for segmented differential mixing. First, the pretreated metallurgical slag, phosphate composite stabilizer and mineral auxiliary setting agent are dry mixed evenly at a constant speed, and micro-wetting and slurry conditioning are carried out simultaneously to form a phosphate premix with uniform agent adhesion. Then, silicate cement is added in batches, and the mixing speed is reduced and low-speed continuous mixing is carried out to avoid the problem of phosphate lattice reaction inhibition caused by rapid hydration heat release of cement and sudden increase of pH in the system, so as to obtain a uniform composite slurry without agglomeration and segregation. S4 Phosphate Low-Temperature Stable Pre-Cure: The composite slurry is sent into a closed constant temperature and humidity curing chamber and pre-cured under constant temperature and humidity in a low temperature and low humidity environment to generate stable and insoluble heavy metal phosphate lattice precipitates, thus completing the chemical fixation of heavy metals. S5 cement hydration and deep curing: After the low temperature pre-curing process is completed, the humidity of the curing chamber is increased and the temperature is kept constant. The curing cycle is set according to different resource utilization application scenarios to ensure that the cement is fully hydrated to generate a dense CSH gel system, which fully encapsulates the stable phosphate grains and forms an integrated dense solidified matrix with physical encapsulation and chemical fixation, thereby enhancing the long-term mechanical properties and leaching resistance of the solidified body. S6 solidified finished product testing and resource-based tiered utilization: After curing, samples are taken and heavy metal leaching toxicity testing and unconfined compressive strength testing are carried out in accordance with national standards. After all indicators meet the standards, the products are tiered according to performance parameters to adapt to different resource utilization engineering scenarios, so as to achieve harmless and efficient resource-based disposal of multiple types of metallurgical hazardous slag.

2. The method for stabilizing and solidifying heavy metals in metallurgical slag using a phosphide-cement synergistic approach according to claim 1, characterized in that: The metallurgical slag is any single slag material selected from recycled aluminum slag, copper smelting slag, converter steel slag, and lead-zinc smelting slag, or a mixture of two or more types of slag materials of equal mass, and the slag body contains Pb, Cd, and Cr. 6+ It contains at least two of the heavy metals Cu, Zn and As, and is suitable for the co-solidification and treatment of various types of metallurgical hazardous solid waste.

3. The method for stabilizing and solidifying heavy metals in metallurgical slag using a phosphide-cement synergistic approach according to claim 1, characterized in that: The moisture content of the slag material in S1 after dewatering is controlled between 12wt% and 22wt%.

4. The method for stabilizing and solidifying heavy metals in metallurgical slag using a phosphate-cement synergistic approach according to claim 1, characterized in that: The phosphide composite stabilizer in S2 is a mixture of calcium hypophosphite, aluminum dihydrogen phosphate, and magnesium phosphate in a mass ratio of 2:1:1, and the powder is uniformly ground to below 200 mesh. In the mineral-assisted coagulation component, kaolinite and diatomaceous earth are mixed in an equal mass ratio of 1:1, the powder particle size is ≤200 mesh, and each component is uniformly dispersed in the system.

5. The method for stabilizing and solidifying heavy metals in metallurgical slag using a phosphide-cement synergistic approach according to claim 1, characterized in that: In the S3 dry mixing stage, the stirring speed is controlled at 40-60 r / min, and the solid materials are uniformly mixed by dry mixing at a constant speed for 3 minutes; in the cement blending stage, the speed is reduced to 20-30 r / min, and stirring is continued for 5 minutes.

6. The method for stabilizing and solidifying heavy metals in metallurgical slag using a phosphide-cement synergistic approach according to claim 1, characterized in that: The S4 low-temperature pre-curing environment has a temperature of 25-40℃ and a relative humidity of 60%-75%, and a curing time of 2 days. The pH of the system is maintained online throughout the process, in the reaction range of 7.5-9.

5. When the pH is low, it is adjusted with calcium hydroxide to make it alkaline, and when the pH is high, it is neutralized and stabilized with dilute phosphate buffer.

7. The method for stabilizing and solidifying heavy metals in metallurgical slag using a phosphide-cement synergistic approach according to claim 1, characterized in that: The S5 deep curing environment temperature is 30-45℃ and the relative humidity is 90%-98%; the curing cycle is set according to the grade of resource utilization: 7 days for roadbed fill, 14 days for conventional building material aggregate, and 28 days for long-term landfill base.

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