Method for extracting vanadium from steel slag and synergistically recycling waste slag and waste acid

Abstract

The present application relates to the technical field of metallurgical waste resource utilization, in particular to a method for extracting vanadium from steel slag and simultaneously resource utilization of waste slag and waste acid. The method first premixes the iron-removed steel slag powder with the standard reuse water containing saturated calcium sulfate microcrystals to build an isotonic osmotic pressure barrier to inhibit the dissolution of impurities; then gradiently adds the waste raffinate for acid leaching, strictly controls the temperature rise and the final pH value of the acid leaching system to cut off the original silicic acid cross-linking condensation pathway from the kinetics; then introduces homologous seeds in a specific pH critical interval to induce the heterogeneous epitaxial growth and hydrolysis precipitation of vanadium elements; finally, the vanadium precipitation waste liquid is fully returned to the premixing process after neutralization for recycling. The present application solves the engineering dead knot of filtration gelation, the vanadium leaching and precipitation rates are both greater than or equal to 99%, and realizes the internal digestion of waste slag and waste liquid and zero secondary discharge, which has very high industrialization popularization value.

Description

Technical Field

[0001] This invention relates to the field of metallurgical waste resource utilization technology, specifically to a method for extracting vanadium from steel slag and co-utilizing waste slag and waste acid. Background Technology

[0002] Currently, the main processes for extracting vanadium from vanadium-containing steel slag in the industry are divided into two categories: pyrometallurgical processes and hydrometallurgical processes. Pyrometallurgical vanadium extraction typically involves sodium roasting or calcification roasting, followed by water leaching or acid leaching. This process requires operation at extremely high temperatures for extended periods, resulting in high energy consumption, substantial investment in front-end roasting equipment, and the generation of dust containing harmful gases during the roasting process. These drawbacks severely restrict its industrial-scale promotion under the dual carbon targets.

[0004] To reduce energy consumption, ambient temperature wet vanadium extraction technology has gradually become a research hotspot in recent years. Its core involves using strong acids (such as sulfuric acid, hydrochloric acid, or industrial waste acid) as leaching agents to directly leach steel slag, or under conditions with the addition of oxidants, followed by vanadium precipitation by adjusting the pH value. However, existing wet vanadium extraction processes have revealed the following fatal technical bottlenecks during actual engineering scale-up: First, existing processes often lack precise control over reaction kinetics and the physicochemical state of the microstructure during the acid leaching stage. They typically employ a crude, one-time acid addition or a general description of the reaction at room temperature, neglecting the specific control of reaction temperature rise and feed parameters. Steel slag contains a large amount of silicate phase. When directly exposed to localized, high-intensity acid abrupt changes, soluble orthosilicic acid readily undergoes rapid condensation reactions within a short time, generating a large amount of network-like polymeric silica in the system. This silica not only physically encapsulates the unreacted vanadium-containing mineral phase, leading to a significant decrease in vanadium leaching rate, but also drastically increases the viscosity of the leached slurry, making subsequent pressure filtration and solid-liquid separation extremely difficult or even completely ineffective.

[0005] Secondly, in the purification and vanadium precipitation stages of the leachate, existing technologies often employ direct alkali addition to adjust the pH of the system to a broad acid-base range to achieve the hydrolysis and precipitation of vanadate. Due to the lack of an induction mechanism and specific aging temperature constraints, the solution system easily crosses the nucleation energy barrier, resulting in homogeneous nucleation and causing the precipitate to exhibit an amorphous, viscous colloidal state. This colloidal precipitate has poor crystallinity and a large specific surface area, making it highly susceptible to physical entrainment or adsorption of impurity ions such as iron, magnesium, and calcium from the mother liquor during precipitation. This not only severely reduces the purity of the final high-vanadium slag product but also presents challenges in washing and dewatering via pressure filtration.

[0006] Finally, regarding the large amount of acid leaching residue (mainly calcium sulfate and unreacted residue) and vanadium precipitation wastewater generated during the wet vanadium extraction process, existing technologies often adopt an end-of-pipe treatment approach, i.e., constructing a separate, large wastewater treatment plant for neutralization, precipitation, and discharge, failing to achieve a deep closed-loop process for materials within the process. Even when some processes attempt to reuse wastewater, it is merely used as ordinary makeup water, without fully considering the potential impact of accumulated calcium, magnesium, and sulfate ions in the wastewater on the osmotic pressure and impurity leaching behavior of the upstream acid leaching reaction system. Long-term operation can easily lead to system impurity accumulation and collapse.

[0007] In summary, existing vanadium extraction technologies from steel slag struggle to achieve a balance between low energy consumption, high vanadium extraction rate, high product purity, and systematic synergistic treatment of waste. Therefore, developing a novel process that overcomes the engineering challenges of silica gelation and amorphous precipitation, and enables deep closed-loop resource utilization of waste residue and liquid, has become a critical technical challenge that urgently needs to be addressed by those skilled in the art. Summary of the Invention

[0008] The purpose of this invention is to provide a method for extracting vanadium from steel slag and synergistically utilizing waste slag and waste acid, in order to solve the problems of vanadium extraction and separation difficulties, easy agglomeration of orthosilicic acid leading to filter press failure, amorphous precipitates that easily carry impurities, and difficulty in achieving deep closed-loop synergistic treatment of waste slag and waste liquid in the prior art mentioned in the background.

[0009] To achieve the above objectives, on the one hand, the present invention provides a method for extracting vanadium from steel slag and synergistically utilizing waste slag and waste acid, comprising the following steps: S1. System Activation and Construction of the Same Ion Osmotic Barrier: The raw steel slag is ground to a particle size passing through a 200-mesh sieve, and more than 90% of the metallic iron is separated and recovered by magnetic separation to obtain qualified steel slag powder. The qualified steel slag powder and qualified recycled water containing saturated calcium sulfate microcrystals are added to a premixing tank at a material-to-water ratio of 1:2 for thorough premixing. The premixing time is controlled at 30-45 minutes. By utilizing the free alkalinity of the steel slag itself and the coexisting ions in the qualified recycled water, a same ion osmotic barrier is constructed on the surface of the steel slag particles to obtain activated slurry. S2. Gradient-feed anti-depolymerization acid leaching: Acidic waste leaching liquid is introduced into the activated slurry as a leaching agent, and the acid leaching reaction is carried out by gradient-feeding. The feed rate of the leaching liquid is strictly controlled so that the natural temperature rise rate inside the system does not exceed 1.5℃ / min, and the reaction temperature of the entire acid leaching system is controlled between 25℃ and 35℃. The feed is continued until the material-to-water ratio reaches 1:5, and the reaction is continuously stirred at 25℃-35℃ for 2-4 hours. The pH value at the reaction endpoint is strictly controlled between 2.5 and 3.0. After the reaction, solid-liquid separation is performed to obtain acid leaching filter residue and high-selectivity vanadium leaching solution, respectively. S3. Vanadium precipitation purification induced by homologous seed crystals: The highly selective vanadium leachate obtained from solid-liquid separation is introduced into a mechanically stirred tank, and a 10%-20% sodium hydroxide solution is slowly added at a rate of 5-10 L / min; when the pH of the system is adjusted to 4.2-4.5, the addition of sodium hydroxide solution is stopped, and 0.1%-0.3% of high-purity vanadium pentoxide or sodium metavanadate powder based on the total vanadium mass is added to the system as seed crystals; then the addition of sodium hydroxide solution continues until the pH of the reaction reaches a stable value of 4.8-5.0 at the endpoint; the solution is kept at 20℃-25℃ and stirred at a low speed (60-120 r / min) for aging for 1-2 hours, so that more than 99% of the vanadium elements in the solution undergo hydrolysis and precipitation, resulting in a precipitation system; S4. Closed-loop co-processing of waste residue and waste liquid: The sedimentation system is subjected to pressure filtration for solid-liquid separation to obtain high-vanadium slag and vanadium-precipitated waste liquid respectively; the vanadium-precipitated waste liquid is discharged into the sewage treatment plant, and lime milk is added at 5%-8% of the wastewater mass, and a neutralization and precipitation reaction is carried out for 1-2 hours; the clarified filtrate obtained by separation is returned in whole or in part to S1 as compliant reclaimed water containing saturated calcium sulfate microcrystals; the acid leaching filter residue generated in S2 is washed and then used as a raw material for building materials to achieve resource utilization.

[0010] Furthermore, the acid mist generated during the acid leaching reaction in S2 is efficiently collected through a gas collection pipe and purified by alkaline spraying before being discharged in compliance with standards. The wastewater generated by the spraying is returned to the leaching tank for recycling.

[0011] Furthermore, in S4, the acid leaching filter residue is rinsed with qualified recycled water generated from the wastewater treatment plant, and lime milk is added to adjust the pH value of the system to 7.0 before pressure filtration. The resulting rinsing liquid is returned to the premixing tank for recycling.

[0012] In S1, this invention intentionally introduces recycled water containing saturated calcium sulfate microcrystals and free calcium ions, returned from a closed-loop wastewater treatment system. During the premixing stage, this recycled water with a specific ionic strength forms a dynamic osmotic pressure barrier on the surface of steel slag particles (rich in calcium, magnesium, and iron ore phases). Due to the common ion effect, the calcium ions and trace amounts of sulfate ions in the recycled water strongly inhibit the explosive and rapid dissolution of matrix elements (especially active impurities such as iron, magnesium, and calcium) in the steel slag during the initial stage of acid leaching. Conversely, vanadate ions, with stronger diffusion capabilities and a special occurrence state, can selectively penetrate this microscopic barrier into the liquid phase, thereby improving the leaching purity of vanadium at the source.

[0013] Steel slag inevitably contains a large amount of silicate materials. Traditional direct acid addition or room-temperature acid leaching without temperature rise control easily leads to local over-acidification and violent exothermic reactions, causing the free orthosilicic acid to instantly cross the isoelectric point and undergo intense dehydration and condensation, forming a large three-dimensional network of silica. This invention, S2, employs a gradient flow leaching method with weak alkaline activation and a limited temperature rise rate (≤1.5℃ / min), resulting in a gradual and uniform decrease in the system's pH value, avoiding microscopic local over-acidification. Within the strictly defined temperature range of 25℃-35℃, silica molecules lose the kinetic conditions for rapid polymerization into a large molecular network, existing mostly in oligomerized form or directly precipitating as particulate silica. This eliminates the problem of solid-liquid separation failure caused by silicalization during pressure filtration and ensures that vanadium ions are not encapsulated and released.

[0014] The hydrolysis precipitation of trace amounts of vanadium at room temperature exhibits a high nucleation energy barrier. Directly crossing this barrier readily leads to homogeneous nucleation, generating amorphous colloidal polyhydrate vanadates that are difficult to filter and have a large surface area. In this invention, S3 introduces a very small amount of homogeneous seed crystals at the pH critical point (4.2-4.5), artificially altering the crystallization kinetics of the system. This allows the system to bypass the energy-intensive homogeneous nucleation stage and directly undergo heterogeneous epitaxial growth using the seed crystals as the core. Combined with aging conditions of 20℃-25℃, the crystallinity and particle size of the vanadium precipitate are significantly improved. This not only drastically shortens the subsequent pressure filtration separation time but also effectively reduces the physical entrainment and adsorption of heavy metals and other impurities from the mother liquor by the precipitate.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: In this method for extracting vanadium from steel slag and co-utilizing waste slag and waste acid, gradient feeding and controlled temperature range (25℃-35℃) suppress the cross-linking of orthosilicic acid into polymers. Combined with the seed-induction mechanism during the vanadium precipitation stage, the materials throughout the process maintain excellent filtration performance. The moisture content of the filter residue is significantly reduced, and the pressure filtration efficiency is several times higher than that of traditional wet processes, demonstrating strong feasibility for industrial-scale production.

[0016] Secondly, based on the ambient temperature and pressure acid leaching process, there is no need to provide an external high temperature and high pressure environment, which significantly reduces energy consumption. At the same time, by precisely controlling the pH value at the leaching endpoint to 2.5-3.0 and the pH value at the precipitation endpoint to 4.8-5.0, and by utilizing seed epitaxial growth, the vanadium leaching rate and precipitation rate can both be stably maintained at over 99%. The final high-vanadium slag has a V2O5 content of no less than 21%, and the product quality is high and extremely stable.

[0017] This invention breaks through the traditional end-of-pipe treatment model of fresh water inflow and wastewater outflow. It uses recycled water containing specific components from the wastewater treatment plant as a functional reagent to inhibit impurity leaching, returning it to the premixing process. This not only achieves an extremely high water resource recycling rate but also enhances the impurity separation degree of the upstream process by utilizing the antagonistic effect of common ions. The calcium sulfate filter residue produced by acid leaching is directly used as a building material raw material, and acid mist is efficiently absorbed and purified. Ultimately, the entire system achieves internal digestion of waste residue and wastewater and zero-pollution secondary discharge. Attached Figure Description

[0018] Figure 1 This is an overall flowchart of Embodiment 1 of the present invention. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1: This example provides a method for extracting vanadium from steel slag and co-utilizing waste slag and waste acid. The specific steps are as follows: S1. System Activation and Construction of the Common Ion Osmotic Barrier: Vanadium-containing steel slag produced by Panzhihua Iron and Steel Group was used as raw material. The raw steel slag was sent to a professional grinding equipment and ground to a particle size of 250 mesh (meeting the requirement of passing through a 200-mesh sieve). 92% of the metallic iron was separated and recovered using magnetic separation to obtain qualified steel slag powder. 1000 kg of the qualified steel slag powder and 2000 kg of qualified recycled water containing saturated calcium sulfate microcrystals (from subsequent S4) were added to a premixing tank at a material-to-water ratio of 1:2 for thorough premixing. The premixing time was controlled at 40 minutes, at which point the system was slightly alkaline, and a stable common ion osmotic barrier was constructed on the surface of the steel slag particles, resulting in an activated slurry.

[0021] S2. Gradient-feed anti-depolymerization acid leaching: Waste leaching liquid is introduced into the activated slurry as a leaching agent using a precisely metered feed pump. The feed rate of the leaching liquid is controlled to stabilize the natural temperature rise rate within the system at 1.0℃ / min, and the reaction temperature of the entire acid leaching system is kept constant at 30℃. Feeding continues until the material-to-water ratio reaches 1:5. The reaction is continuously stirred at 30℃ for 3 hours, and the final pH value is strictly controlled at 2.8 (within the 2.5-3.0 range). After the reaction, solid-liquid separation is performed using a filter press. Under these conditions, since no orthosilicic acid condensation occurs, the filter press process is extremely smooth (the filter press time for each batch is controlled within 30 minutes), yielding acid leaching residue and highly selective vanadium leaching solution.

[0022] S3. Homologous seed-induced vanadium precipitation purification: The filtrate is introduced into a mechanically stirred tank, and a 15% sodium hydroxide solution is slowly added at a rate of 8 L / min. When the pH of the system is adjusted to 4.3, the addition of alkali is stopped, and 0.2% of high-purity vanadium pentoxide powder based on the total vanadium mass is added to the system as seed crystals. Then, sodium hydroxide solution is added until the pH of the reaction reaches a stable value of 4.9 at the end of the reaction. The mixture is kept at 22°C and stirred at a low speed of 90 r / min for 1.5 hours to allow the vanadium element in the solution to undergo heterogeneous epitaxial growth and hydrolysis precipitation, resulting in a precipitation system with good crystal structure.

[0023] S4. Closed-loop co-processing of waste residue and waste liquid: The sedimentation system is subjected to pressure filtration for solid-liquid separation, yielding high-vanadium slag and vanadium-precipitated waste liquid. The vanadium-precipitated waste liquid is discharged into a wastewater treatment plant, where lime slurry is added at 6% of the wastewater mass for neutralization and precipitation reaction for 1.5 hours. The clarified filtrate containing saturated calcium sulfate microcrystals obtained from the separation is entirely returned to step S1 for recycling. The acid leaching filter residue generated in step S2 is washed with recycled water, the pH is adjusted to 7.0 with lime slurry, and then pressure filtered and sent to a building materials plant as a raw material for building materials, achieving resource utilization. Acid mist is purified by alkaline spraying and discharged in compliance with standards.

[0024] Example 2: The operation steps in this example are basically the same as those in Example 1: In S1, the steel slag is ground to 200 mesh and the premixing time is 30 minutes.

[0025] In S2, the temperature rise rate was controlled at 1.5℃ / min, the acid leaching system temperature was controlled at 25℃, the reaction was carried out for 2 hours, and the final pH of the reaction was controlled at 2.5.

[0026] In S3, the alkali addition rate was 5 L / min, and the sodium hydroxide concentration was 10%. When the pH was adjusted to 4.2, 0.1% of seed crystals were added, and the final pH stabilized at 4.8. The mixture was then aged at 20°C for 1 hour.

[0027] In S4, 5% lime slurry is added to the wastewater.

[0028] Example 3: The operation steps in this example are basically the same as those in Example 1: In S1, the premixing time is 45 minutes.

[0029] In S2, the temperature rise rate was controlled at 0.5℃ / min, the acid leaching system temperature was controlled at 35℃, the reaction time was 4 hours, and the final pH of the reaction was controlled at 3.0.

[0030] In S3, the alkali addition rate was 10 L / min, and the sodium hydroxide concentration was 20%. When the pH was adjusted to 4.5, 0.3% seed crystals were added, and the final pH stabilized at 5.0. The mixture was then aged at 25°C for 2 hours.

[0031] In S4, 8% lime slurry is added to the wastewater.

[0032] Comparative Example 1: Conventional one-time acid leaching (excluding gradient flow and reclaimed water barrier), operating procedures: The same vanadium-containing steel slag as in Example 1 was used, but without premixing and pulping. The raffinate with a material-to-water ratio of 1:5 was directly added to the steel slag for leaching. The natural temperature rise of the reaction system was not controlled (the system temperature rapidly spiked to above 55°C in the initial stage of the reaction). The reaction time was 3 hours, and the final pH value was adjusted to 2.8. The subsequent vanadium precipitation process was the same as in Example 1.

[0033] Comparative Example 2: Conventional direct alkali precipitation of vanadium (without seeding mechanism), operation steps: The acid leaching processes for S1 and S2 are exactly the same as in Example 1. In the vanadium precipitation purification process of S3, 15% sodium hydroxide solution is added continuously at a rate of 8L / min until the pH value at the reaction endpoint is 4.9 (without interruption or addition of vanadium pentoxide seed crystals), and the mixture is aged at 22°C for 1.5 hours.

[0034] Experimental Example: A systematic sampling and testing were conducted on the intermediate materials and final products generated in the examples and comparative examples. The specific testing methods and evaluation standards for each key technical indicator are as follows: (1) Solid-liquid separation performance (filtration time) evaluation: To ensure the comparability of engineering data, solid-liquid separation of all batches was carried out using the same specifications of laboratory-grade chamber filter press (filtration area 0.5m²). 2 A constant pressure filtration test was conducted. During the test, the feed pressure of the feed pump was kept constant at 0.6 MPa. The time from the start of feeding until the filtrate no longer flowed continuously (only dripping) from the outlet pipe was recorded as the filtration time for a single batch. If the filtration time exceeded 240 minutes without completion, or if the feed pressure increased abnormally to the point of being unable to feed, it was determined to be a filter blockage or colloid formation failure.

[0035] (2) Determination of vanadium content: The vanadium concentration in liquid samples such as leachate and vanadium precipitation mother liquor was quantitatively determined by inductively coupled plasma atomic emission spectrometry (ICP-OES, model: Agilent 5110); For solid samples such as steel slag raw materials and the final high-vanadium slag, the ferrous ammonium sulfate titration method specified in metallurgical industry standard YB / T5304-2011 "Vanadium Pentoxide" was used for high-precision determination.

[0036] (3) Calculation formula for critical conversion rate Based on the above measurement results, the critical conversion rate of vanadium in the system is calculated according to the following formula: Vanadium leaching rate (%) = (absolute mass of vanadium in the leachate / total absolute mass of vanadium in the steel slag raw material) × 100%.

[0037] Vanadium precipitation rate (%) = (absolute mass of vanadium in high vanadium slag / absolute mass of vanadium in leachate) × 100%.

[0038] (4) Determination of the purity of high-vanadium slag: The high-vanadium slag obtained by vanadium precipitation and filtration is dried to constant weight at 110℃, and its V2O5 mass percentage is tested. The qualified judgment standard set by this invention is that the V2O5 content in the high-vanadium slag is ≥21%. The test results are shown in the table below: Example 1 25 30 99.5 99.6 23.5 Example 2 32 35 99.1 99.2 21.8 Example 3 28 32 99.3 99.4 22.6 Comparative Example 1 Filter press clogging, time >240 120 76.4 98.1 16.5 Comparative Example 2 26 150 (colloidalized) 99.4 88.5 18.2 As shown in the table above, Comparative Example 1, due to the direct one-time addition of acid without the construction of an osmotic pressure barrier, experienced intense acid-base neutralization and exothermic reaction, leading to localized temperature runaway. A large amount of orthosilicic acid instantly crossed its isoelectric point and underwent cross-linking and condensation, generating a high-viscosity three-dimensional silica network. Experimental phenomena showed that this group experienced rapid filter cloth clogging during the leaching hydraulic filtration stage, resulting in solid-liquid separation failure after more than 240 minutes. Simultaneously, the dense silica physically encapsulated some of the vanadium-containing mineral phase, causing the vanadium leaching rate to sharply decrease to 76.4%. Example 1, by strictly limiting the feed temperature rise (1.0℃ / min) and reaction temperature zone (30℃), combined with the impurity leaching inhibition effect of recycled water, completely eliminated the polymer condensation pathway of silica formation. A single batch of pressure filtration took only 25 minutes, with a vanadium leaching rate as high as 99.5%, demonstrating that this gradient feed temperature control method has the ability to overcome existing engineering pain points.

[0039] Secondly, in Comparative Example 2, the lack of heterogeneous inducing nuclei during the vanadium hydrolysis precipitation stage resulted in homogeneous nucleation with a high energy barrier. The macroscopic manifestation was an extremely viscous amorphous, polyhydrated vanadate colloid as the precipitate. This morphology not only made pressure filtration extremely difficult (time soared to 150 minutes), but its large specific surface area also severely adsorbed and physically entrained residual impurity ions (such as Fe and Mg) from the mother liquor, resulting in the final product's high-vanadium slag purity failing to meet standards, at only 18.2%. In Example 1, by introducing homologous seeds at a specific pH window (4.3), the system was artificially guided into a low-energy epitaxial growth path. The product crystallinity increased significantly, and the particle coarsening not only reduced the pressure filtration time to 30 minutes but also, by avoiding physical entrainment, caused the high-vanadium slag purity to surge to 23.5%.

[0040] 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 present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for extracting vanadium from steel slag and co-utilizing waste slag and waste acid, characterized in that, Includes the following steps: S1. Grind the raw steel slag to a particle size that passes through a 200-mesh sieve, and obtain qualified steel slag powder after magnetic separation to remove iron; add the qualified steel slag powder and qualified recycled water containing saturated calcium sulfate microcrystals into a premixing tank at a material-to-water ratio of 1:2 for thorough premixing, and control the premixing time to 30-45 minutes to build a common ion osmotic pressure barrier on the surface of the steel slag particles to obtain activated slurry; S2. Acidic waste extraction liquor is introduced into the activated slurry as a leaching agent. The acid leaching reaction is carried out by gradient feeding. The feeding rate of the waste extraction liquor is controlled so that the natural temperature rise rate of the acid leaching system does not exceed 1.5℃ / min. The reaction temperature of the entire acid leaching system is controlled between 25℃ and 35℃. The feeding continues until the material-to-water ratio reaches 1:

5. The reaction is continuously stirred at 25℃-35℃ for 2-4 hours. The pH value at the reaction endpoint is controlled between 2.5 and 3.

0. After the reaction is completed, solid-liquid separation is performed to obtain acid leaching filter residue and high-selectivity vanadium leaching solution, respectively. S3. The highly selective vanadium leaching solution is introduced into a mechanically stirred tank, and a sodium hydroxide solution with a mass concentration of 10%-20% is slowly added at a rate of 5-10 L / min. When the pH value of the system is adjusted to 4.2-4.5, the addition of the sodium hydroxide solution is stopped, and 0.1%-0.3% of vanadium pentoxide or sodium metavanadate powder based on the total vanadium mass is added to the system as seed crystals. Then, the sodium hydroxide solution is added until the pH value at the reaction endpoint stabilizes at 4.8-5.

0. The mixture is then aged at a temperature of 20℃-25℃ and a speed of 60-120 r / min for 1-2 hours to complete the hydrolysis precipitation and obtain the precipitation system. S4. The precipitation system is subjected to pressure filtration to separate solid and liquid, resulting in high-vanadium slag and vanadium-precipitated wastewater. The vanadium-precipitated wastewater is discharged into the sewage treatment plant, and lime milk is added at 5%-8% of the mass of the vanadium-precipitated wastewater for neutralization and precipitation reaction for 1-2 hours. The clear filtrate obtained from the separation is returned to S1 as qualified reclaimed water containing saturated calcium sulfate microcrystals for recycling.

2. The method for extracting vanadium from steel slag and co-utilizing waste slag and waste acid according to claim 1, characterized in that, The acid mist generated during the acid leaching reaction in S2 is efficiently collected through a gas collection pipe and purified by alkaline spraying. The wastewater generated by spraying is returned to the acid leaching reaction in S2 for recycling.

3. The method for extracting vanadium from steel slag and co-utilizing waste slag and waste acid according to claim 1, characterized in that, In S4, the acid leaching filter residue is rinsed with qualified recycled water from the wastewater treatment plant, and lime milk is added to adjust the pH value of the system to 7.0 before pressure filtration. The resulting pressure filter residue is sent out as a raw material for building materials, and the resulting rinsing liquid is returned to the premixing tank in S1 for recycling.

4. The method for extracting vanadium from steel slag and co-utilizing waste slag and waste acid according to claim 1, characterized in that, In step S1, magnetic separation is used to separate and recover more than 90% of the metallic iron in the raw steel slag.

5. The method for extracting vanadium from steel slag and co-utilizing waste slag and waste acid according to claim 1, characterized in that, In S2, the reaction temperature of the entire acid leaching system is controlled at 30°C, and the flow rate of the waste extract is controlled so that the natural temperature rise rate of the acid leaching system is stabilized at 1.0°C / min.

6. The method for extracting vanadium from steel slag and co-utilizing waste slag and waste acid according to claim 1, characterized in that, In step S3, when the pH of the system is adjusted to 4.3, the addition of sodium hydroxide solution is paused and the inducing seed crystals are added.

7. The method for extracting vanadium from steel slag and co-utilizing waste slag and waste acid according to claim 1, characterized in that, In S3, the aging time is 1.5 hours, and the stirring speed during the aging process is 90 r / min.

8. The method for extracting vanadium from steel slag and co-utilizing waste slag and waste acid according to claim 1, characterized in that, In S4, during the neutralization precipitation reaction, at a concentration of 2-5m 3 Oxygen-enriched air is introduced at a flow rate of / h.

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