Method for leaching red mud modified steel slag and returning red mud modified steel slag to steel mill for utilization

Abstract

The invention is applicable to the technical field of metallurgy, and provides a method for leaching red mud modified steel slag and returning the red mud modified steel slag to a steel mill for utilization, which comprises the following steps: step 1, adding red mud into converter slag for high-temperature modification under the conditions of heat preservation at 1550 DEG C for 1 hour, cooling to 1350 DEG C and heat preservation for 1 hour to generate a high phosphorus-rich phase, the phosphorus content in the high phosphorus-rich phase is 2-3 times of that in the previous phosphorus-rich phase, and 20-200g of red mud is added into 1Kg of converter slag. According to the method for leaching the red mud modified steel slag and returning the red mud modified steel slag to the steel mill for utilization, the problems that converter slag and red mud are large in accumulation amount, large in harm, serious in pollution, high in yield and low in utilization rate can be effectively solved, then reference is provided for iron and steel enterprises to recycle converter slag and red mud resources and obtain phosphate fertilizer products, and cooperative utilization of the red mud and the steel slag is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for leaching red mud modified steel slag and returning it to a steel plant for utilization. Background Art

[0002] Steel slag is a major industrial solid waste produced during the steel smelting process, accounting for about 15% of the total steel production. China produces more than 100 million tons of steel slag each year, but its comprehensive utilization rate is only about 30%. The large-scale storage of steel slag not only occupies land resources, but also damages the natural environment.

[0003] Converter slag is an inevitable byproduct of modern steelmaking in order to remove impurity elements from steel. The increasing accumulation of converter slag will not only occupy a large amount of land, but also pollute the soil and environment after some harmful elements are dissolved, and even affect people's health. It has become a serious problem for society and the steel industry itself. However, converter slag contains a large amount of valuable elements such as P, Fe and Mn. Although phosphorus is a harmful element for most types of steel, it is an important strategic resource for agricultural food production, and phosphorus is one of the three indispensable elements for plant growth. Red mud is a reddish-brown waste produced in the process of alumina production. It contains a certain amount of iron and aluminum oxides and has the characteristics of strong alkalinity and high yield. Due to its strong alkalinity and high salinity, the difficulty and cost of red mud treatment are significantly increased, resulting in its low utilization rate. However, a large amount of iron, aluminum and other substances in red mud can be used as a modifier for steel slag to modify and utilize steel slag, thereby achieving the green environmental protection goal of waste treatment and resource recycling, and realizing the synergistic utilization of red mud and steel slag.

[0004] Therefore, converter slag and red mud have very important recycling value. How to achieve efficient recycling of converter slag and red mud is one of the hot issues that various steel companies and researchers have paid extensive attention to and studied. According to relevant reports, due to the long-term export of phosphate rock, high-grade phosphate rock resources will be exhausted in the future; in particular, with the growth of the global population, the demand for food will increase, and the demand for phosphorus will increase, which will lead to an increase in the price of phosphate rock. In order to change this situation and achieve a sustainable supply of phosphorus, it is urgent to use other methods to obtain phosphorus resources. Summary of the invention

[0005] The present invention provides a method for leaching red mud modified steel slag and returning it to a steel plant for utilization, aiming to solve the problem of low utilization rate of converter slag raised in the above background technology.

[0006] To solve the above problems, the present invention is implemented as follows: a method for leaching red mud modified steel slag and returning it to a steel plant for utilization, comprising the following steps:

[0007] Step 1: Add red mud to the converter slag for high-temperature modification. The conditions for the converter slag modification are: keep it at 1550°C for 1 hour, cool it to 1350°C and keep it for 1 hour, generate a high-phosphorus-rich phase, the phosphorus content in the high-phosphorus-rich phase is 2 to 3 times the phosphorus content in the previous phosphorus-rich phase, and the amount of red mud added is 20 to 200g of red mud for 1Kg of converter slag;

[0008] Step 2: Prepare leaching solution for leaching of phosphorus: 10.5 kg citric acid, 4.2 kg sodium hydroxide, 8 L hydrochloric acid, 500 L deionized water, 20 to 80 g converter slag per liter of leaching solution, leaching time 30 min, the dephosphorization rate of the converter slag can reach 80% to 90%.

[0009] Step 3: Leachate treatment: After the converter slag and the leachate are separated, the leachate is naturally precipitated. The precipitate contains some phosphates. The precipitate is calcined to become the raw material for making phosphate fertilizer;

[0010] Step 4: The leached residue is used for pre-desiliconization, desulfurization and dephosphorization of molten iron or for slag-making agent and flux for converter steelmaking: the leached residue is mixed with lime, iron oxide, dust removal ash and sintering return ore in different proportions to uniformly prepare pre-desiliconization, desulfurization and dephosphorization agent, and put into molten iron. The temperature of the molten iron is 1380℃, and 30-50kg slag-making agent is added per ton of molten iron;

[0011] Step 5: After the pre-desiliconization, desulfurization and dephosphorization of the molten iron or the converter steelmaking is completed, the slag is taken out for circulation operation.

[0012] Preferably, in the high-temperature reforming of the converter slag in step 1, the converter slag and red mud are evenly mixed and heated to 1550° C. to melt the converter slag, and then cooled to 1350° C. and kept warm for 1 hour to generate a phosphorus-rich phase.

[0013] Preferably, in step 2, the modified converter slag is placed in the prepared leaching solution, 20 to 80 g of slag can be placed per liter of leaching solution, and after reacting for 30 minutes, the converter slag is separated from the leaching solution and dried.

[0014] Preferably, the raw material for phosphate fertilizer described in step three is obtained by allowing the leaching residue to stand or adding adsorbents such as Ca(OH)2 and activated Al2O3 to adsorb and precipitate the phosphorus in the acid leaching solution to obtain a phosphorus-containing precipitate, which can be used as a raw material for phosphate fertilizer after calcination.

[0015] Preferably, the pre-desiliconization, desulfurization and dephosphorization treatment of molten iron described in step four is as follows: the converter slag is dried and evenly mixed with lime, iron oxide scale, dust ash and sintered return ore in different proportions to perform pre-desiliconization, desulfurization and dephosphorization of molten iron as a pre-desiliconization, desulfurization and dephosphorization agent for molten iron. The temperature of the molten iron is 1380°C, 30 to 50 kg of pre-desiliconization, desulfurization and dephosphorization agent is added per ton of molten iron, and the dephosphorization process is continuously stirred for 15 to 30 minutes.

[0016] Preferably, after the pre-desiliconization, desulfurization and dephosphorization in step 4, the carbon content of the molten iron is between 3.2 and 4.09%, the silicon content is between 0.11 and 0.22%, the phosphorus content is between 0.07 and 0.137%, and the sulfur content is between 0.09 and 0.027%.

[0017] Preferably, after the desiliconization, desulfurization and dephosphorization or converter steelmaking reaction described in step five is completed, the pre-desiliconization, desulfurization and dephosphorization slag or converter steelmaking slag is scraped out and continues to be reformed at high temperature - leached - and returned to the factory for utilization.

[0018] Compared with the related art, the method for leaching red mud modified steel slag and returning it to the steel plant for utilization provided by the present invention has the following beneficial effects:

[0019] Compared with the prior art, the method for leaching red mud modified steel slag and returning it to the steel plant for utilization provided in this scheme realizes the comprehensive utilization of converter slag by controlling the reasonable type, addition amount, leaching temperature, time, precipitation effect of leaching residual liquid, and ratio of leaching residue to lime, iron oxide scale, dust removal ash and sintering return ore of the converter slag. Ultimately, the phosphorus in the converter slag is utilized in the field of making phosphate fertilizer, and the remaining residue is returned to the factory for utilization, thereby realizing a process for leaching phosphorus from converter slag to make phosphate fertilizer.

[0020] In summary, the method of leaching red mud modified steel slag and returning it to the steel plant for utilization of the present invention can effectively solve the problems of large accumulation of converter slag and red mud, great harm, serious pollution, high output and low utilization rate, and thus provide a reference for steel enterprises to recycle converter slag resources and obtain phosphate fertilizer products, thereby realizing the coordinated utilization of red mud and steel slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of comprehensive utilization of converter slag in a method of leaching red mud modified steel slag and returning it to a steel plant for utilization provided by the present invention. DETAILED DESCRIPTION

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field of the present application; the terms used in the specification of the application herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "including" and "having" in the specification and claims of the present application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of the present application or the above-mentioned figures are used to distinguish different objects, rather than to describe a specific order; the terms "inside", "outside", "left", and "right" indicate directions or positional relationships based on the directions or positional relationships shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0023] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0024] The embodiment of the present invention provides a method for leaching red mud modified steel slag and returning it to a steel plant for utilization, such as Figure 1 As shown, the method for leaching red mud modified steel slag and returning it to the steel plant for utilization comprises the following steps:

[0025] Step 1: Add red mud to the converter slag for high-temperature modification. The conditions for the converter slag modification are: keep it at 1550°C for 1 hour, cool it to 1350°C and keep it for 1 hour, generate a high-phosphorus-rich phase, the phosphorus content in the high-phosphorus-rich phase is 2 to 3 times the phosphorus content in the previous phosphorus-rich phase, and the amount of red mud added is 20 to 200g of red mud for 1Kg of converter slag;

[0026] Step 2: Prepare leaching solution for leaching of phosphorus: 10.5 kg citric acid, 4.2 kg sodium hydroxide, 8 L hydrochloric acid, 500 L deionized water, 20 to 80 g converter slag per liter of leaching solution, leaching time 30 min, the dephosphorization rate of the converter slag can reach 80% to 90%.

[0027] Step 3: Leachate treatment: After the converter slag and the leachate are separated, the leachate is naturally precipitated. The precipitate contains some phosphates. The precipitate is calcined to become the raw material for making phosphate fertilizer;

[0028] Step 4: The leached residue is used for pre-desiliconization, desulfurization and dephosphorization of molten iron or for slag-making agent and flux for converter steelmaking: the leached residue is mixed with lime, iron oxide, dust removal ash and sintering return ore in different proportions to uniformly prepare pre-desiliconization, desulfurization and dephosphorization agent, and put into molten iron. The temperature of the molten iron is 1380℃, and 30-50kg slag-making agent is added per ton of molten iron;

[0029] Step 5: After the molten iron is pre-desiliconized, desulfurized and dephosphorized, the pre-desiliconized, desulfurized and dephosphorized slag is taken out for circulation operation.

[0030] In this embodiment, converter slag is obtained:

[0031] The components of the converter slag include, by mass percentage, 30% to 55% CaO, 10% to 20% SiO2, 2% to 8% MgO, 10% to 30% FeO2, 2% to 8% MnO, 2% to 8% Al2O3, 2% to 8% and 0.5% to 4% P2O5.

[0032] (ii) Ball milling the converter slag:

[0033] The ball milling treatment includes ball milling the obtained converter slag in a ball mill for 0.5h to 2h to control the particle size of the converter slag.

[0034] (III) High temperature modification of converter slag after ball milling:

[0035] The converter slag with a particle size of ≤0.074 mm after ball milling is mixed with red mud and reformed at a reforming temperature to ensure that a high phosphorus-rich phase is generated in the converter slag;

[0036] The modification temperature is 1000°C to 1500°C, and the modification time is 45min to 150min. The modification temperature is one of 1000°C, 1100°C, 1200°C, 1300°C, 1350°C, 1400°C, 1500°C, 1600°C or any value satisfying the above range value. The modification time is one of 45min, 60min, 90min, 120min, 150min or any value satisfying the above range value.

[0037] Since the solubility of different phases in the converter slag in the leaching solution is different, the converter slag needs to be modified to enrich phosphorus into the phosphorus-rich phase. The phosphorus-rich phase has a higher solubility in the leaching solution, so selective dissolution can be achieved.

[0038] By controlling the reasonable type, addition amount, leaching temperature, time, precipitation effect of leaching residue, and the ratio of leaching residue to lime, iron oxide scale, dust removal ash and sintering return ore, the comprehensive utilization of converter slag can be achieved, and the phosphorus in the converter slag can be finally utilized in the field of making phosphate fertilizer, and the remaining residue can be returned to the factory for utilization, thus realizing a process for leaching phosphorus from converter slag to make phosphate fertilizer.

[0039] In a further preferred embodiment of the present invention, in step 1, the converter slag is subjected to high temperature modification, the converter slag and red mud are evenly mixed and heated to 1550° C. to melt the converter slag, and then cooled to 1350° C. and kept warm for 1 hour to generate a phosphorus-rich phase.

[0040] In a further preferred embodiment of the present invention, the modified converter slag is placed in the prepared leaching solution as described in step 2, and the leaching solution is configured as shown in Table 1. 20 to 80 g of slag can be placed per liter of leaching solution. After reacting for 30 minutes, the converter slag is separated from the leaching solution and dried.

[0041] Table 1

[0042]

[0043]

[0044] In this embodiment, the modified converter slag is leached to obtain leaching waste liquid and leaching residue, the leaching temperature is 20°C ~ 80°C, the modification time is 10min ~ 120min, the leaching temperature is one of 20°C, 40°C, 60°C, 80°C or any value satisfying the above range, the modification time is one of 10min, 30min, 50min, 70min, 90min or any value satisfying the above range.

[0045] Each liter of leachate can leach 20 to 80 g of slag, and the mass of slag in each liter of leachate is one of 20 g, 40 g, 60 g, 80 g or any value that meets the above range. The leachate is composed of citric acid, sodium hydroxide, hydrochloric acid, and deionized water. Other leachates can be hydrochloric acid, nitric acid, or citric acid alone, which can be selected according to actual conditions.

[0046] In a further preferred embodiment of the present invention, the raw material for phosphate fertilizer described in step three is obtained by allowing the leaching residue to stand or adding adsorbents such as Ca(OH)2 and active Al2O3 to adsorb and precipitate the phosphorus in the acid leaching solution to obtain a phosphorus-containing precipitate, which can be used as a raw material for phosphate fertilizer after calcination.

[0047] In this embodiment, the phosphorus element in the leaching solution is obtained:

[0048] The phosphate in the solution can be precipitated by standing, or by adding Ca(OH)2, active Al2O3, or zeolite for adsorption precipitation. The choice can be made according to the actual situation.

[0049] The temperature is 20°C ~ 80°C, the adsorption precipitation time is 10min ~ 120min, the adsorption temperature is one of 20°C, 40°C, 60°C, 80°C or any value satisfying the above range, the adsorption precipitation time is one of 10min, 30min, 50min, 70min, 90min or any value satisfying the above range.

[0050] In a further preferred embodiment of the present invention, the molten iron pre-desiliconization, desulfurization and dephosphorization treatment described in step four is as follows: the converter slag is dried and evenly mixed with lime, iron oxide, dust ash and sintered return ore in different proportions to perform pre-desiliconization, desulfurization and dephosphorization of molten iron as a molten iron pre-desiliconization, desulfurization and dephosphorization agent. The molten iron temperature is 1380°C, 30 to 50 kg of pre-desiliconization, desulfurization and dephosphorization agent is added per ton of molten iron, and the pre-desiliconization, desulfurization and dephosphorization process is continuously stirred for 15 to 30 minutes.

[0051] In this embodiment, the leached residue is used for pre-desiliconization, desulfurization and dephosphorization of molten iron or slag-making agent and flux for converter steelmaking:

[0052] The mass percentage of lime in the pre-desiliconization, desulfurization and dephosphorization agent is 50%, the mass percentage of leaching residue is 0-50%, the mass percentage of iron oxide scale is 0-50%, the mass percentage of dust removal ash is 0-50%, and the mass percentage of sintered pellets is 0-50%;

[0053] The ratio of the pre-desiliconization, desulfurization and dephosphorization agent is 50% by mass of lime, 0% by mass of leaching residue, 50% by mass of iron oxide, 10% by mass of leaching residue, 40% by mass of iron oxide, 20% by mass of leaching residue, 30% by mass of iron oxide, 30% by mass of leaching residue, 20% by mass of iron oxide, 40% by mass of leaching residue, 10% by mass of iron oxide, 50% by mass of leaching residue, and 0% by mass of iron oxide. The iron oxide can be replaced by dust removal ash and sintered return ore, or any value within the above range can be met;

[0054] Smelting the pre-desiliconization, desulfurization and dephosphorization agent and steel materials:

[0055] The steel materials are molten iron and scrap steel, wherein the scrap steel ratio is 0-20%, which can be selected according to actual conditions.

[0056] The addition amounts of molten iron and scrap steel are 740kg / t~1060kg / t and 100kg / t~370kg / t respectively.

[0057] The scrap steel ratio is one of 1%, 3%, 5%, 7%, 10%, 12%, 14%, 16%, 18%, 20% or any value satisfying the above range.

[0058] Conditions of molten iron entering the furnace: Conditions of molten iron entering the furnace: C 3.74% ~ 5.19%, Si 0.08% ~ 1.04%, Mn 0.4% ~ 0.76%, P 0.084% ~ 1.85%, S 0.023% ~ 0.082%, Ti 0.02% ~ 0.4%, Cr 0.063% ~ 0.134%, V 0.022% ~ 0.103%.

[0059] Control the oxygen supply intensity during the converter process to 2.7Nm 3 / (t·min)~6Nm 3 / (t·min), oxygen supply time is 10min~15min.

[0060] Oxygen supply intensity is 2.7Nm 3 / (t·min), 3Nm 3 / (t·min),4Nm 3 / (t·min), 5Nm 3 / (t·min), 6Nm 3 / (t·min) or any value satisfying the above range, the oxygen supply time is one of 10min, 11min, 12min, 13min, 14min, 15min or any value satisfying the above range;

[0061] The temperature of pre-desiliconization, desulfurization and dephosphorization is 1350°C to 1700°C. After pre-desiliconization, desulfurization and dephosphorization, the carbon content of the molten iron is between 3.2% and 4.09%, the silicon content is between 0.11% and 0.22%, the phosphorus content is between 0.07% and 0.137%, and the sulfur content is between 0.09% and 0.027%. The pre-desiliconization, desulfurization and dephosphorization temperature is one of 1350°C, 1500°C, 1600°C, 1700°C or any value satisfying the above range.

[0062] In a further preferred embodiment of the present invention, the carbon content of the molten iron after the pre-desiliconization, desulfurization and dephosphorization described in step four is between 3.2 and 4.09%, the silicon content is between 0.11 and 0.22%, the phosphorus content is between 0.07 and 0.137%, and the sulfur content is between 0.09 and 0.027%.

[0063] In this embodiment, the temperature of pre-desiliconization, desulfurization and dephosphorization is 1350°C ~ 1700°C, the carbon content of molten iron after pre-desiliconization, desulfurization and dephosphorization is between 3.2% and 4.09%, the silicon content is between 0.11% and 0.22%, the phosphorus content is between 0.07% and 0.137%, and the sulfur content is between 0.09% and 0.027%. The pre-desiliconization, desulfurization and dephosphorization temperature is one of 1350°C, 1500°C, 1600°C, 1700°C or any value that meets the above range values.

[0064] In a further preferred embodiment of the present invention, after the pre-desiliconization, desulfurization and dephosphorization reaction described in step 4 is completed, the pre-desiliconization, desulfurization and dephosphorization slag is scraped out and further subjected to high-temperature reforming, leaching and return to the factory for utilization.

[0065] In a further preferred embodiment of the present invention, the process flow of comprehensive utilization of converter slag described in step 1 is: high-temperature modification of converter slag - preparation of leaching solution - leaching and dephosphorization of converter slag - separation of converter slag and leaching solution - precipitation of phosphate fertilizer raw materials with the leaching residue - preparation of pre-desiliconization, desulfurization and dephosphorization of the leaching residue - use of the leaching residue for pre-desiliconization, desulfurization and dephosphorization of molten iron or as a slag-making agent and flux for converter steelmaking - continue to modify the converter slag at high temperature after slagging.

[0066] The chemical composition percentages of the iron oxide scale, dust removal ash and sintered return ore are shown in Table 2:

[0067] Table 2

[0068]

[0069] In this embodiment, by adopting the above preferred scheme, the problems of large accumulation, great harm, serious pollution, high output and low utilization rate of converter slag and red mud can be effectively solved, and the types of reasonable converter slag high temperature modifiers, addition amount, leaching temperature, time, leaching residual liquid precipitation effect, and the ratio of leaching residue to lime, iron oxide, dust removal ash and sintering return ore can be controlled to achieve comprehensive utilization of converter slag and red mud, and finally the phosphorus in the converter slag can be used in the field of making phosphate fertilizer, and the remaining residue can be returned to the factory for utilization, so as to realize a process of leaching and extracting phosphorus from converter slag to make phosphate fertilizer, provide a reference for steel enterprises to recycle converter slag resources and obtain phosphate fertilizer products, and realize the coordinated utilization of red mud and steel slag.

[0070] In a further preferred embodiment of the present invention, the mass percentage of the red mud modifier described in step one is 2% to 20%, and the mass percentage of the red mud modifier is one of 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20% or any value that meets the above range.

[0071] In this embodiment, the modifier is red mud of different components, which can be selected according to actual conditions. Red mud can be used in different proportions with other modifiers such as SiO2, Al2O3, Na2O, CaF2, calcium ferrite, blast furnace slag, etc.

[0072] In summary, compared with related technologies, this method can effectively solve the problems of large accumulation of converter slag and red mud, great harm, serious pollution, high output and low utilization rate, and thus provide a reference for steel enterprises to recycle converter slag resources and obtain phosphate fertilizer products, and provide a reference for steel enterprises to recycle converter slag resources and obtain phosphate fertilizer products, thereby realizing the coordinated utilization of red mud and steel slag.

[0073] In the several embodiments provided in this application, it should be understood that the disclosed device can be implemented in other ways.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the scope of protection of the invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on these embodiments, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in this field can still combine, add, delete or make other adjustments to the features in the various embodiments of the present invention according to the circumstances without conflict, without making creative work, so as to obtain different other technical solutions that do not deviate from the concept of the present invention in essence, and these technical solutions also belong to the scope of protection of the present invention.

Claims

1. A method for leaching red mud modified steel slag and returning it to a steel plant for utilization, characterized in that: The steps include: Step 1: Add red mud to the converter slag for high-temperature modification. The conditions for the converter slag modification are: keep it at 1550°C for 1 hour, cool it to 1350°C and keep it for 1 hour, generate a high-phosphorus-rich phase, the phosphorus content in the high-phosphorus-rich phase is 2 to 3 times the phosphorus content in the previous phosphorus-rich phase, and the amount of red mud added is 20 to 200g of red mud for 1Kg of converter slag; Step 2: Prepare leaching solution for leaching of phosphorus: 10.5 kg citric acid, 4.2 kg sodium hydroxide, 8 L hydrochloric acid, 500 L deionized water, 20 to 80 g converter slag per liter of leaching solution, leaching time 30 min, the dephosphorization rate of the converter slag can reach 80% to 90%. Step 3: Leachate treatment: After the converter slag and the leachate are separated, the leachate is naturally precipitated. The precipitate contains some phosphates. The precipitate is calcined to become the raw material for making phosphate fertilizer; Step 4: The leached residue is used for pre-desiliconization, desulfurization and dephosphorization of molten iron or for slag-making agent and flux for converter steelmaking: the leached residue is mixed with lime, iron oxide, dust removal ash and sintering return ore in different proportions to uniformly prepare pre-desiliconization, desulfurization and dephosphorization agent, and put into molten iron. The temperature of the molten iron is 1380℃, and 30-50kg slag-making agent is added per ton of molten iron; Step 5: After the pre-desiliconization, desulfurization and dephosphorization of the molten iron or the converter steelmaking is completed, the pre-desiliconization, desulfurization and dephosphorization slag is taken out for circulation operation.

2. The method for leaching red mud modified steel slag and returning it to a steel plant for utilization as claimed in claim 1, characterized in that: High temperature modification of converter slag in step 1: the converter slag and red mud are evenly mixed and heated to 1550°C to melt the converter slag, and then cooled to 1350°C and kept warm for 1 hour to generate a phosphorus-rich phase.

3. The method for leaching red mud modified steel slag and returning it to a steel plant for utilization as claimed in claim 1, characterized in that: The leaching experiment is as follows: the reformed converter slag is put into the prepared leaching solution, 20 to 80 g of slag can be put into each liter of leaching solution, and after reacting for 30 minutes, the converter slag is separated from the leaching solution and dried.

4. The method for leaching red mud modified steel slag and returning it to a steel plant for utilization as claimed in claim 1, characterized in that: Obtaining the raw materials for phosphate fertilizer described in step three: Allow the leaching residue to stand or add adsorbents such as Ca(OH)2 and active Al2O3 to adsorb and precipitate the phosphorus in the acid leaching solution to obtain a phosphorus-containing precipitate, which can be used as a raw material for phosphate fertilizer after calcination.

5. The method for leaching red mud modified steel slag and returning it to a steel plant for utilization as claimed in claim 1, characterized in that: Step 4: Pre-desiliconization, desulfurization and dephosphorization treatment of molten iron: dry the converter slag and mix it evenly with lime, iron oxide scale, dust ash and sintered return ore in different proportions to use it as a pre-desiliconization, desulfurization and dephosphorization agent for molten iron. The molten iron temperature is 1380°C, 30 to 50 kg of pre-desiliconization, desulfurization and dephosphorization agent is added per ton of molten iron, and the pre-desiliconization, desulfurization and dephosphorization process is continuously stirred for 15 to 30 minutes.

6. The method for leaching red mud modified steel slag and returning it to a steel plant for utilization as claimed in claim 1, characterized in that: After the desiliconization, desulfurization and dephosphorization in step 4, the carbon content of the molten iron is between 3.2 and 4.09%, the silicon content is between 0.11 and 0.22%, the phosphorus content is between 0.07 and 0.137%, and the sulfur content is between 0.009 and 0.027%.

7. The method for leaching red mud modified steel slag and returning it to a steel plant for utilization as claimed in claim 1, characterized in that: After the desiliconization, desulfurization and dephosphorization or converter steelmaking reaction described in step five is completed, the pre-desiliconization, desulfurization and dephosphorization slag or converter steelmaking slag is scraped out for further high-temperature reforming - leaching - and returned to the factory for utilization.

Images