A method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag

Abstract

The invention discloses a method for realizing comprehensive recycling of vanadium, iron, calcium and phosphorus in steel slag, comprising the following steps: S1, the steel slag is crushed and classified and leached under normal pressure with nitric acid, and then solid-liquid separation is performed to obtain filtrate and filter material; S2, the filtrate is iron precipitated, and after solid-liquid separation, iron removal purification liquid and crude iron phosphate are obtained; the iron removal purification liquid is added with sodium hydroxide and hydrogen peroxide for neutralization and oxidation to obtain neutralization oxidation liquid; S3, the neutralization oxidation liquid is subjected to resin adsorption, and after adsorption saturation, it is desorbed with sodium hydroxide solution to obtain resin desorption liquid; S4, the adsorption tail liquid is evaporated and concentrated and cooled and crystallized in sequence to obtain calcium nitrate product; the resin desorption liquid is purified by phosphorus removal and vanadium precipitation by ammonium salt to obtain ammonium metavanadate product and calcium phosphate product. The present invention realizes the comprehensive recycling of vanadium, iron, calcium and phosphorus in steel slag, has high comprehensive resource utilization rate, no new wastewater and waste residue are generated, and has the advantages of good economic benefits and green environmental protection.

Description

Technical Field

[0001] The invention belongs to the field of comprehensive recycling of solid wastes, and in particular relates to a method for realizing comprehensive recycling of vanadium, iron, calcium and phosphorus in steel slag. Background Art

[0002] Steel slag is an industrial waste residue produced during the smelting process of vanadium-titanium magnetite. Due to the difficulty of resource utilization, it is currently mainly treated by direct stockpiling or crushing for use in building materials. The large-scale stockpiling of steel slag will not only occupy a large amount of land, but also pose a risk of environmental pollution; at the same time, since steel slag contains a large amount of calcium, magnesium, iron, vanadium, aluminum, silicon, phosphorus and other elements, direct use of steel slag in building materials will cause a waste of resources. Therefore, the establishment of a set of comprehensive utilization technology for steel slag resources has extremely strong social and economic benefits.

[0003] Researchers have developed a large number of technical processes for recycling steel slag resources, such as: ① secondary smelting to prepare high-grade vanadium slag; ② high-temperature reduction to prepare vanadium-containing pig iron; ③ sodium roasting-leaching vanadium extraction; ④ calcium roasting-leaching vanadium extraction; ⑤ direct leaching vanadium extraction, etc. However, they only recycle one or two of the main elements, such as vanadium and iron, and have disadvantages such as low efficiency of comprehensive recycling of elements, large amounts of wastewater discharge polluting the environment, high consumption of raw materials, and high processing costs. Large-scale application technology is not yet mature.

[0004] CN101121966A discloses a new process for recovering vanadium and iron from high-calcium and high-iron steel slag. The vanadium and iron in the steel slag are recovered through crushing, magnetic separation, roasting, leaching, extraction, stripping, vanadium precipitation and other processes. The recovery rates of vanadium and iron are 50% and 75%. The process flow is relatively long and an extraction process is used. The operation requirements and difficulty are relatively high. At the same time, only vanadium and iron in the steel slag are recovered, and the comprehensive resource recovery rate is not high.

[0005] CN110453025A discloses a method for smelting vanadium-rich pig iron with high-calcium vanadium-containing steel slag, which uses vanadium-containing steel slag as raw material, low-grade carbon as reducing agent, and adopts electric furnace for reduction smelting to finally obtain vanadium-containing pig iron and slag. The process adopts electric furnace for smelting, and finally obtains high-phosphorus pig iron with vanadium content of 2.99%, iron content of 88.13%, and phosphorus content of 2.79%. The product has low added value and consumes a lot of electricity. At the same time, the slag produced during the smelting process creates new processing problems. Summary of the invention

[0006] In view of the problems in the prior art of recovering metals from steel slag, such as long process flow, high operating requirements and difficulty, and low comprehensive recovery rate, the present invention provides a method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag, which can achieve the comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag, not only has a high comprehensive utilization rate of resources and no new wastewater and waste slag is generated, but also has the advantages of good economic benefits and green environmental protection.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] A method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag, the method comprising the following steps:

[0009] S1. The steel slag is crushed and classified and leached with nitric acid at normal pressure, and then solid-liquid separation is performed to obtain a filtrate and a filter material. The filter material is washed with water to obtain a low-phosphorus iron concentrate, and the low-phosphorus iron concentrate can be used for secondary smelting and iron extraction;

[0010] The filtrate obtained in S2 and S1 is added with a precipitant to precipitate iron, and after solid-liquid separation, an iron removal purification liquid and crude ferric phosphate are obtained; sodium hydroxide and hydrogen peroxide are added to the iron removal purification liquid for neutralization and oxidation to obtain a neutralized oxidation liquid;

[0011] S3, subjecting the neutralized oxidizing liquid obtained in S2 to resin adsorption, and desorbing it with sodium hydroxide solution after saturation, to obtain resin desorption liquid; the remaining liquid after resin adsorption is adsorption tail liquid;

[0012] S4, the adsorption tail liquid obtained in S3 is sequentially evaporated and concentrated and cooled and crystallized to obtain a calcium nitrate product; the resin desorption liquid obtained in S3 is purified by dephosphorization and vanadium precipitation by ammonium salt to obtain an ammonium metavanadate product and a calcium phosphate product.

[0013] Preferably, in step S1, the steel slag is industrial waste slag produced in the smelting process of vanadium-titanium magnetite, and its main element contents are: V2O5: 2.0%~5.0%, TiO2: 2.0%~5.0%, TFe: 20.0%~25.0%, MgO: 5.0%~10.0%, CaO: 30%~50%, SiO2: 3%~8%, MnO: 1.0%~2.0%, Al2O3: 2.0%~3.0%.

[0014] Preferably, in step S1, when the steel slag is leached, the mass concentration of nitric acid is 15% to 20%, the amount of nitric acid used is 1 to 1.5 times the mass of the steel slag, the leaching temperature is 20 to 40°C, and the leaching reaction is carried out by slowly adding acid. Appropriate nitric acid dosage, leaching temperature and acid addition method can increase the vanadium leaching rate and improve the slurry filtration performance.

[0015] Preferably, in step S2, iron precipitation should be carried out under low-acid conditions, the pH of the reaction system is controlled to be 0-1, and the precipitant is selected from one or more of phosphoric acid, diammonium dihydrogen phosphate, sodium phosphate, ammonia water, and urea.

[0016] Preferably, in step S2, sodium hydroxide solution is added to the iron removal purification solution to adjust the pH to 1.2-2.0, and then hydrogen peroxide is added to change the solution potential so that the vanadium in the solution is converted into VO3 - 、V 10 O 28 6- 、HV 10 O 28 5- or H2V 10 O 28 4- The vanadium exists in one or more forms, making it easy for the subsequent anion resin to adsorb the vanadium. The amount of hydrogen peroxide added is 1 to 2 times the mass of vanadium in the resin desorption solution. Since the resin desorption solution is produced in step S4, the amount of hydrogen peroxide added in this step can also be calculated by the mass of vanadium in the steel slag. The vanadium leaching rate in the steel slag can reach 98%, and the loss of vanadium in the leaching process can be ignored.

[0017] Preferably, in step S4, the obtained calcium nitrate product is used in the resin desorption liquid phosphorus removal process.

[0018] Preferably, in step S4, when the resin desorption liquid is used for phosphorus removal, the pH is adjusted to 10-12, and calcium nitrate prepared from the S3 adsorption tail liquid is added. In order to achieve the best phosphorus removal effect, the phosphorus content in the resin desorption liquid should be detected in advance, and the amount of calcium nitrate used is 2-3 times the mass of phosphorus in the resin desorption liquid. The calcium nitrate added in this step is the calcium nitrate product produced in the previous step, and no additional addition is required, mainly to save economic costs and achieve the purpose of comprehensive recovery. The obtained calcium phosphate product meets the standards for fertilizer additives.

[0019] The present invention utilizes the vanadium, iron, calcium, phosphorus and other elements in the steel slag as resources, and uses the calcium nitrate produced in the previous step in the next step without producing new waste slag and wastewater. Compared with the prior art, it has the following advantages:

[0020] 1) In step S1, the steel slag is leached using nitric acid and a specific acid addition method to reduce the leaching rate of iron in the steel slag and increase the leaching rate of vanadium, and the oxidizing property of nitric acid is used to achieve the dual purposes of oxidation and leaching.

[0021] 2) In step S2, the slag leachate is subjected to iron precipitation using a suitable precipitant and under relatively low pH conditions to avoid excessive consumption of alkali and achieve separation of iron and calcium.

[0022] 3) This method makes full use of the characteristics of steel slag and forms an organic whole series for the comprehensive recycling of its elements. A one-step leaching and step-by-step separation treatment method is adopted to obtain a variety of products. The comprehensive recycling of vanadium, iron, calcium and phosphorus elements in steel slag is achieved, and the recovery rate of each element reaches more than 90%.

[0023] In summary, this method realizes the comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag. It not only has a high comprehensive utilization rate of resources and no new wastewater and waste slag are generated, but also has the advantages of good economic benefits and green environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 The present invention is a flow chart of the method for realizing comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag. DETAILED DESCRIPTION

[0026] The following will describe the technical solutions and technical problems solved in the embodiments of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them.

[0027] Comparative Example 1

[0028] A method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag, specifically comprising the following steps:

[0029] 1) Add 100 g of crushed steel slag with an average particle size of 0.074 mm and 300 ml of 25% nitric acid solution into a beaker and stir to react. The reaction time is 4 hours (the time starts from the mixing of the steel slag and the nitric acid solution). After the reaction, solid-liquid separation is performed. The slurry filtration performance is extremely poor (the filtration time exceeds 24 hours). The vanadium content in the obtained filtrate is 1.05 g / L and the iron content is 30 g / L.

[0030] Since nitric acid was added directly at one time after acid preparation, the vanadium leaching rate was low and the iron leaching rate was too high, so the next step of the experiment was not carried out.

[0031] Comparative Example 2

[0032] 1) Pour 100g of crushed steel slag with an average particle size of 0.074mm and 100ml of water into a beaker and stir to make a slurry for 10min. Then prepare 300ml of 25% nitric acid solution and add it into the beaker with a separatory funnel at a flow rate of 5ml / min. Stir and react in a water bath at 60°C for 4h (the time is counted from the beginning of the addition of nitric acid solution). After the reaction, solid-liquid separation is performed. After the reaction, solid-liquid separation is performed. The slurry filtration performance is extremely poor (the filtration time exceeds 36h).

[0033] Since the temperature of nitric acid was too high, the slurry was difficult to filter and the filtrate could not be sampled and analyzed, so the next step of the experiment was not carried out.

[0034] Comparative Example 3

[0035] A method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag, specifically comprising the following steps:

[0036] 1) Pour 100g of crushed steel slag with an average particle size of 0.074mm and 100ml of water into a beaker and stir to slurry for 10 minutes, then prepare 300ml of nitric acid solution with a concentration of 25% and add it into the beaker with a separatory funnel at a flow rate of 5ml / min for stirring reaction. The reaction time is 4h (the time is counted from the beginning of the addition of nitric acid solution). After the reaction, solid-liquid separation is performed. The obtained filter residue is a low-phosphorus iron enrichment after washing with water, and its iron content is 31.48% and its phosphorus content is 0.07%; the obtained filtrate is a steel slag leachate, in which the vanadium content is 2.67g / L, the calcium content is 60.11g / L, the iron content is 14.32g / L, and the phosphorus content is 3.0g / L;

[0037] 2) Take 200 ml of the slag leachate and pour it into a beaker, then add 80 ml of 5% ammonia water and 50 ml of 15% sodium phosphate solution at a flow rate of 5 ml / min to control the pH of the reaction system to 2.5, react at a temperature of 50°C for 0.5 h, and perform solid-liquid separation after the reaction. The resulting filter residue is crude iron phosphate with an iron-phosphorus ratio of 0.87; the resulting filtrate is the post-iron precipitation liquid, in which the vanadium content is 0.45 g / L, the calcium content is 30.45 g / L, the iron content is 0.075 g / L, and the phosphorus content is 0.21 g / L.

[0038] Since the pH of the reaction system is 2.5 during iron precipitation, the content of impurity elements in the crude ferric phosphate is too high, and more than 60% of the vanadium is lost in the slag phase, and the purpose of separating vanadium and iron is not achieved.

[0039] Comparative Example 4

[0040] A method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag, specifically comprising the following steps:

[0041] 1) Pour 100g of crushed steel slag with an average particle size of 0.074mm and 100ml of water into a beaker and stir to slurry for 10 minutes, then prepare 300ml of 25% nitric acid solution and add it into the beaker with a separatory funnel at a flow rate of 5ml / min for stirring reaction. The reaction time is 4h (the time is counted from the beginning of the addition of nitric acid solution). After the reaction, solid-liquid separation is performed. The obtained filter residue is a low-phosphorus iron enrichment after washing with water, and its iron content is 34.11% and its phosphorus content is 0.07%; the obtained filtrate is a steel slag leachate, in which the vanadium content is 2.67g / L, the calcium content is 51g / L, the iron content is 16.9g / L, and the phosphorus content is 2.74g / L;

[0042] 2) Take 200ml of slag leaching solution and pour it into a beaker, then add 50ml of 5% ammonia water and 50ml of 15% sodium phosphate solution at a flow rate of 5ml / min to control the pH of the reaction system to 0.3, react at a temperature of 50℃ for 0.5h, and perform solid-liquid separation after the reaction. The obtained filter residue is crude iron phosphate with an iron-phosphorus ratio of 1.05; the obtained filtrate is the post-iron precipitation liquid, in which the vanadium content is 2.01g / L, the calcium content is 50g / L, the iron content is 1.5g / L, and the phosphorus content is 0.21g / L;

[0043] 3) Take 500ml of the liquid after iron precipitation and pour it into a beaker, add 30ml of 30% sodium hydroxide solution to adjust pH=2.1, and then adsorb it through two-stage series adsorption of anion resin. The average vanadium content in the adsorption tail liquid is 1.87g / L, calcium content is 49.5g / L, phosphorus content is 0.04g / L, and iron content is 1.46g / L. Since hydrogen peroxide is not added in this step to change the form of vanadium ions, the resin has a very poor adsorption effect on vanadium, and the experiment is terminated.

[0044] Example 1

[0045] This embodiment discloses a method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag. The experimental process is as follows: Figure 1 As shown, this embodiment specifically includes the following steps:

[0046] 1) Pour 100g of crushed steel slag with an average particle size of 0.074mm and 100ml of water into a beaker and stir to slurry for 10 minutes, then prepare 300ml of 25% nitric acid solution and add it into the beaker with a separatory funnel at a flow rate of 5ml / min for stirring reaction. The reaction time is 4h (the time is counted from the beginning of the addition of nitric acid solution). After the reaction, solid-liquid separation is performed. The obtained filter residue is a low-phosphorus iron enrichment after washing with water, and its iron content is 32.24% and its phosphorus content is 0.05%; the obtained filtrate is a steel slag leachate, in which the vanadium content is 2.5g / L, the calcium content is 55g / L, the iron content is 18g / L, and the phosphorus content is 2.5g / L;

[0047] 2) Take 200ml of slag leaching solution and pour it into a beaker, then add 50ml of 5% ammonia water and 50ml of 15% sodium phosphate solution at a flow rate of 5ml / min to control the pH of the reaction system to 0.3, react at a temperature of 50℃ for 0.5h, and perform solid-liquid separation after the reaction. The obtained filter residue is crude iron phosphate with an iron-phosphorus ratio of 1.05; the obtained filtrate is the post-iron precipitation liquid, in which the vanadium content is 1.78g / L, the calcium content is 49.97g / L, the iron content is 1.2g / L, and the phosphorus content is 0.24g / L;

[0048] 3) Take 500ml of the liquid after iron precipitation and pour it into a beaker, add 30ml of 30% sodium hydroxide solution to adjust the pH to 2.1, then add 20ml of 30% hydrogen peroxide and stir to react for 1h. After the reaction, the resulting solution is a neutralized oxidizing solution. After two-stage series adsorption by anion resin, the average vanadium content in the adsorption tail liquid is 0.08g / L, the calcium content is 48.76g / L, the phosphorus content is 0.04g / L, and the iron content is 1.18g / L. The resin after adsorption is desorbed with 5% sodium hydroxide solution to obtain a desorption liquid with a vanadium content of 18.97g / L and a phosphorus content of 1.47g / L; the adsorption tail liquid is evaporated, concentrated, cooled and crystallized to obtain 85g of solid calcium nitrate;

[0049] 4) Take 100 ml of the resin desorption solution and pour it into a beaker, add 5 ml of 98% sulfuric acid to adjust the solution pH to 9.3, then add 5 g of cooled crystallized calcium nitrate, react at 60 ° C for 1 hour, and perform solid-liquid separation after the reaction. The resulting filter residue is the calcium phosphate product, in which the phosphorus content is 20%; add 20 g of ammonium chloride to the obtained filtrate, react at 45 ° C for 2 hours, let it stand for 1 hour after the reaction, and finally separate the solid and liquid to obtain an ammonium metavanadate product with a vanadium content of 43.11% and a phosphorus content of 0.01%.

[0050] Example 2

[0051] This embodiment discloses a method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag, which specifically comprises the following steps:

[0052] 1) Pour 100g of crushed steel slag with an average particle size of 0.045mm and 100ml of water into a beaker and stir to slurry for 10 minutes, then prepare 400ml of nitric acid solution with a concentration of 25% and add it into the beaker with a separatory funnel at a flow rate of 5ml / min for stirring reaction. The reaction time is 4h (the time is counted from the beginning of the addition of nitric acid solution). After the reaction, solid-liquid separation is performed. The obtained filter residue is a low-phosphorus iron enrichment after washing with water, and its iron content is 25.11% and its phosphorus content is 0.04%; the obtained filtrate is a steel slag leachate, in which the vanadium content is 2.78g / L, the calcium content is 74.5g / L, the iron content is 26g / L, and the phosphorus content is 2.75g / L;

[0053] 2) Take 200ml of steel slag leaching liquid and pour it into a beaker, then add 40ml of 10% ammonium dihydrogen phosphate at a flow rate of 5ml / min to control the pH of the reaction system to 1.0, react at a temperature of 50℃ for 1h, and perform solid-liquid separation after the reaction. The obtained filter residue is crude iron phosphate, and its iron-phosphorus ratio is 1.24; the obtained filtrate is the post-iron precipitation liquid, in which the vanadium content is 1.28g / L, the calcium content is 64.11g / L, the iron content is 3.87g / L, and the phosphorus content is 1.2g / L;

[0054] 3) Take 500ml of the liquid after iron precipitation and pour it into a beaker, add 30ml of 30% sodium hydroxide solution to adjust the pH to 1.8, then add 25ml of 30% hydrogen peroxide and stir to react for 1h. After the reaction, the resulting solution is a neutralized oxidizing solution. After three-stage series adsorption by anion resin, the average vanadium content in the adsorption tail liquid is 0.07g / L, the calcium content is 58.97g / L, the phosphorus content is 0.09g / L, and the iron content is 3.51g / L. The resin after adsorption is desorbed with 5% sodium hydroxide solution to obtain a desorption liquid with a vanadium content of 20.01g / L and a phosphorus content of 2.10g / L; the adsorption tail liquid is evaporated, concentrated, cooled and crystallized to obtain 110g of solid calcium nitrate;

[0055] 4) Take 100 ml of the resin desorption solution and pour it into a beaker, add 7 ml of 98% sulfuric acid to adjust the solution pH to 10.0, then add 10 g of cooled crystallized calcium nitrate, react at 60 ° C for 1 hour, and perform solid-liquid separation after the reaction. The resulting filter residue is the calcium phosphate product, in which the phosphorus content is 18.54%; add 30 g of ammonium chloride to the obtained filtrate, react at 45 ° C for 2 hours, stand and age for 1 hour after the reaction, and finally perform solid-liquid separation to obtain an ammonium metavanadate product with a vanadium content of 42.58% and a phosphorus content of 0.02%.

[0056] Example 3

[0057] This embodiment discloses a method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag, which specifically comprises the following steps:

[0058] 1) Pour 100g of crushed steel slag with an average particle size of 0.074mm and 100ml of water into a beaker and stir to slurry for 10 minutes, then prepare 300ml of nitric acid solution with a concentration of 25% and add it into the beaker with a separatory funnel at a flow rate of 5ml / min for stirring reaction. The reaction time is 3h (the time is counted from the beginning of the addition of nitric acid solution). After the reaction, solid-liquid separation is performed. The obtained filter residue is a low-phosphorus iron enrichment after washing with water, and its iron content is 33.01% and its phosphorus content is 0.1%; the obtained filtrate is a steel slag leaching solution, in which the vanadium content is 2.07g / L, the calcium content is 58g / L, the iron content is 17.26g / L, and the phosphorus content is 2.01g / L;

[0059] 2) Take 200ml of slag leaching solution and pour it into a beaker, then add 50ml of 5% ammonia water and 20ml of 30% phosphoric acid solution at a flow rate of 5ml / min to control the pH of the reaction system to 0.4, react at 50℃ for 0.5h, and perform solid-liquid separation after the reaction. The obtained filter residue is crude iron phosphate with an iron-phosphorus ratio of 1.01; the obtained filtrate is the post-iron precipitation liquid, in which the vanadium content is 1.66g / L, the calcium content is 54.36g / L, the iron content is 3.18g / L, and the phosphorus content is 0.17g / L;

[0060] 3) Take 500ml of the liquid after iron precipitation and pour it into a beaker, add 30ml of 30% sodium hydroxide solution to adjust the pH to 2.1, then add 20ml of 30% hydrogen peroxide and stir to react for 1h. After the reaction, the resulting solution is a neutralized oxidizing solution. After three-stage series adsorption by anion resin, the average vanadium content in the adsorption tail liquid is 0.03g / L, the calcium content is 53.56g / L, the phosphorus content is 0.02g / L, and the iron content is 3.1g / L. The resin after adsorption is desorbed with 5% sodium hydroxide solution to obtain a desorption liquid with a vanadium content of 20.41g / L and a phosphorus content of 0.97g / L; the adsorption tail liquid is evaporated, concentrated, cooled and crystallized to obtain 100g of solid calcium nitrate;

[0061] 4) Take 100 ml of the resin desorption solution and pour it into a beaker, add 5 ml of 98% sulfuric acid to adjust the solution pH to 9.5, then add 4.5 g of cooled crystallized calcium nitrate, react at 60 ° C for 1 hour, and perform solid-liquid separation after the reaction. The resulting filter residue is the calcium phosphate product, in which the phosphorus content is 19.79%; add 25 g of ammonium chloride to the obtained filtrate, react at 45 ° C for 2 hours, stand and age for 1 hour after the reaction, and finally perform solid-liquid separation to obtain an ammonium metavanadate product with a vanadium content of 43.24% and a phosphorus content of 0.008%.

[0062] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag, characterized in that: The method comprises the following steps: S1. The steel slag is crushed and classified and leached with nitric acid at normal pressure, and then solid-liquid separation is performed to obtain a filtrate and a filter material. The filter material is washed with water to obtain a low-phosphorus iron concentrate, and the low-phosphorus iron concentrate can be used for secondary smelting and iron extraction; In step S1, when the steel slag is leached, the mass concentration of nitric acid is 15% to 20%, the amount of nitric acid used is 1 to 1.5 times the mass of the steel slag, the leaching temperature is 20 to 40° C., and the leaching reaction is carried out by slowly adding acid; The filtrate obtained in S2 and S1 is added with a precipitant to precipitate iron, and after solid-liquid separation, an iron removal purification liquid and crude ferric phosphate are obtained; sodium hydroxide and hydrogen peroxide are added to the iron removal purification liquid for neutralization and oxidation to obtain a neutralized oxidation liquid; In step S2, the pH of the reaction system is controlled to be 0-1 by precipitation of iron, and the precipitant is selected from one or more of phosphoric acid, diammonium phosphate, sodium phosphate, ammonia water, and urea; Add sodium hydroxide solution to the iron removal purification liquid to adjust the pH to 1.2-2.0, and then add hydrogen peroxide, the amount of hydrogen peroxide added is 1-2 times the mass of vanadium in the resin desorption liquid; S3, subjecting the neutralized oxidizing liquid obtained in S2 to resin adsorption, and desorbing it with sodium hydroxide solution after saturation, to obtain resin desorption liquid; the remaining liquid after resin adsorption is adsorption tail liquid; S4, the adsorption tail liquid obtained in S3 is sequentially evaporated and concentrated and cooled and crystallized to obtain a calcium nitrate product; the resin desorption liquid obtained in S3 is purified by dephosphorization and vanadium precipitation by ammonium salt to obtain an ammonium metavanadate product and a calcium phosphate product.

2. The method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag according to claim 1, characterized in that: In step S1, the steel slag is industrial waste slag produced during the smelting process of vanadium-titanium magnetite, and its main element contents are: V2O5: 2.0%~5.0%, TiO2: 2.0%~5.0%, TFe: 20.0%~25.0%, MgO: 5.0%~10.0%, CaO: 30%~50%, SiO2: 3%~8%, MnO: 1.0%~2.0%, Al2O3: 2.0%~3.0%.

3. The method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag according to claim 1, characterized in that: In step S4, the obtained calcium nitrate product is used in the phosphorus removal process of the resin desorption liquid.

4. The method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag according to claim 3, characterized in that: In step S4, when the resin desorption liquid is used for phosphorus removal, the pH is adjusted to 10-12, and calcium nitrate prepared from the adsorption tail liquid of S3 is added.

5. The method for comprehensive recovery and utilization of vanadium, iron, calcium and phosphorus in steel slag according to claim 4, characterized in that: The amount of calcium nitrate used is 2 to 3 times the mass of phosphorus in the resin desorption solution.

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