Selective leaching-normal pressure mineralization coupled steel slag carbon sequestration method and system

Abstract

The invention relates to the technical field of solid waste resource utilization and carbon dioxide capture and storage, in particular to a selective leaching-normal pressure mineralization coupled steel slag carbon sequestration method and system, and the method comprises the following steps: S1, steel slag pretreatment: pretreating steel slag to obtain pretreated steel slag; s2, selective leaching is conducted, specifically, the pretreated steel slag is placed in an ammonium acetate solution to be subjected to leaching treatment, and first steel slag leaching liquid and filter residues are obtained; then the filter residues are placed in an acetic acid solution to be subjected to leaching treatment, and second steel slag leaching liquid and leaching residues are obtained; and S3, mineralization carbon sequestration: mixing the first steel slag leachate and the second steel slag leachate, and introducing a carbon dioxide source into the mixed leachate for carbon sequestration reaction to obtain carbonate precipitate. According to the method, two-step synergistic leaching of ammonium acetate and acetic acid is adopted, selective efficient leaching of MgO / CaO in the steel slag can be achieved, the impurity ion inhibition rate is high, and the additional value of a product is effectively increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization and carbon dioxide capture and storage, and particularly relates to a selective leaching-atmospheric mineralization coupled steel slag carbon fixation method and system. BACKGROUND

[0002] Carbon capture and storage (CCS) technology is considered as an important carbon reduction approach, and mineral carbon fixation technology is considered as an innovative path with carbon reduction and resourceization potential because of its characteristics of converting CO2 into stable carbonates. Steel slag is the main byproduct of the steel industry, and its comprehensive utilization rate is less than 30%. Land resources are wasted and heavy metal pollution risks are caused by large-scale stacking. Steel slag is rich in calcium, magnesium and other alkaline oxides, so indirect fixation of carbon dioxide using steel slag has potential application prospects. At present, steel slag carbon fixation methods mainly include the following three methods:

[0003] 1) Dry carbon fixation: CO2 is directly adsorbed by steel slag. This process has the advantages of simple process and low energy consumption, but the carbon fixation efficiency is low. Although the carbon fixation efficiency can be improved by increasing the pressure and temperature, it is still difficult to achieve high carbon fixation efficiency;

[0004] 2) Direct wet carbon fixation: CO2 is dissolved in an aqueous solution and then reacts with alkali metals in steel slag. A large amount of water is consumed in this process, and the generated wastewater also needs to be treated to meet the standard before being discharged, so the use range is limited;

[0005] 3) Indirect wet carbon fixation: the effective components in steel slag are leached by a medium (commonly acid, alkali, and ammonium salt), and then the leaching solution absorbs CO2. This process can achieve high carbonation efficiency at a relatively low reaction temperature and gas pressure.

[0006] At present, the wet carbon fixation process generally has the characteristics of long leaching time, low product added value (high impurity content), and poor economic benefit (poor functionality). Therefore, it is necessary to develop a selective leaching-atmospheric mineralization coupled steel slag carbon fixation method and system with high-efficiency leaching, low cost, and high added value. SUMMARY

[0007] The purpose of the present application is to provide a selective leaching-atmospheric mineralization coupled steel slag carbon fixation method and system, which can at least solve some of the defects in the prior art.

[0008] To achieve the above-mentioned purpose, the technical scheme of the present application is a selective leaching-atmospheric mineralization coupled steel slag carbon fixation method, comprising the following steps:

[0009] S1, steel slag pretreatment: pretreating the steel slag to obtain pretreated steel slag;

[0010] S2, selective leaching: first, the pretreated steel slag is placed in an ammonium acetate solution for leaching treatment to obtain a first steel slag leaching solution and a filter residue; then, the filter residue is placed in an acetic acid solution for leaching treatment to obtain a second steel slag leaching solution and a leaching residue;

[0011] S3, mineralization and carbon sequestration: the first steel slag leaching solution and the second steel slag leaching solution are mixed, and a carbon dioxide source is introduced into the mixed leaching solution for carbon sequestration reaction to obtain a carbonate precipitate.

[0012] As one of the embodiments, in step S2, ultrasonic assisted acetic acid leaching treatment is used, and the frequency of the ultrasonic wave is 20-40 kHz.

[0013] As one of the embodiments, in step S2, the concentration of the ammonium acetate solution is 3-5 mol / L, the liquid-solid ratio of the ammonium acetate solution to the pretreated steel slag is 5:1-20:1, the leaching treatment temperature is 50-80℃, and the leaching treatment time is 30-40 min.

[0014] As one of the embodiments, in step S2, the concentration of the acetic acid solution is 0.5-3 mol / L, the liquid-solid ratio of the acetic acid solution to the filter residue is 5:1-20:1, the leaching treatment temperature is 50-80℃, and the leaching treatment time is 20-30 min.

[0015] As one of the embodiments, in step S3, the carbon sequestration reaction is carried out at a pressure of normal pressure, a temperature of 50-80℃, and a pH of 8-10.

[0016] As one of the embodiments, in step S3, ultrasonic assisted carbon sequestration reaction is used, and the frequency of the ultrasonic wave is 20-40 kHz.

[0017] As one of the embodiments, in step S1, the method for pretreating the steel slag is as follows: first, the steel slag is crushed, then the crushed steel slag is subjected to magnetic separation treatment, and then the steel slag after the magnetic separation treatment is subjected to high-temperature activation treatment.

[0018] As one of the embodiments, after step S3, the following steps are further included: the obtained carbonate precipitate is calcined at 800-900℃ to prepare a light magnesium carbonate / calcium carbonate product, or the obtained carbonate precipitate is directly used as a building material additive; and the obtained leaching residue is dehydrated and used as a cement admixture or a roadbed material.

[0019] The application also provides a steel slag carbon fixation system coupled with selective leaching and atmospheric mineralization, comprising a steel slag pretreatment unit, a selective leaching unit and a mineralization carbon fixation unit connected in sequence; the selective leaching unit comprises an ammonium acetate leaching device and an acetic acid leaching device, the steel slag outlet of the steel slag pretreatment unit is connected with the steel slag inlet of the ammonium acetate leaching device, the filter residue outlet of the ammonium acetate leaching device is connected with the filter residue inlet of the acetic acid leaching device, and the leaching liquid outlets of the ammonium acetate leaching device and the acetic acid leaching device are both connected with the leaching liquid inlet of the mineralization carbon fixation unit.

[0020] As one of the embodiments, the steel slag pretreatment unit comprises a crusher, a magnetic separator and a first heating furnace connected in sequence.

[0021] Compared with the prior art, the application has the following beneficial effects:

[0022] (1) The application adopts two-step synergistic leaching of ammonium acetate and acetic acid, can realize selective and efficient leaching of MgO / CaO in steel slag, has high impurity ion inhibition rate, and effectively improves the added value of the product;

[0023] (2) The application realizes CO2 mineralization fixation under atmospheric pressure and low temperature conditions, and the energy consumption is reduced by more than 60% compared with the traditional method, thereby greatly reducing the carbon sequestration cost;

[0024] (3) The application realizes graded utilization of each component in the steel slag carbon fixation reaction, realizes resource utilization in the whole process, and no secondary waste is generated, and the carbon fixation rate can reach 15-20 kg CO2 / ton of steel slag;

[0025] (4) The steel slag carbon fixation system of the application has good equipment compatibility, is compatible with the existing hydrometallurgical equipment, and can be applied industrially without large-scale modification. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0027] Figure 1 A flow chart of a selective leaching-atmospheric mineralization coupled steel slag carbon fixation method provided by the embodiment of the application;

[0028] Figure 2 A schematic diagram of a selective leaching-atmospheric mineralization coupled steel slag carbon fixation system provided by the embodiment of the application;

[0029] In the diagram: 1. Crusher; 2. Magnetic separator; 3. First heating furnace; 4. Ammonium acetate leaching device; 5. Acetic acid leaching device; 6. Mineralization reactor; 7. Second heating furnace. Detailed Implementation

[0030] The technical solutions of 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.

[0031] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0032] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0033] like Figure 1 As shown, this embodiment provides a selective leaching-atmospheric pressure mineralization coupled method for steel slag carbon fixation, including the following steps:

[0034] S1. Steel slag pretreatment: Steel slag is pretreated to obtain pretreated steel slag;

[0035] S2. Selective leaching: First, the pretreated steel slag is placed in an ammonium acetate solution for leaching treatment to obtain the first steel slag leachate and filter residue; then, the filter residue is placed in an acetic acid solution for leaching treatment to obtain the second steel slag leachate and leaching residue.

[0036] S3, mineralization and carbon fixation: The first steel slag leaching solution and the second steel slag leaching solution are mixed, and a carbon dioxide source is introduced into the mixed leaching solution to carry out a carbon fixation reaction, resulting in carbonate precipitate.

[0037] This embodiment employs a two-step selective leaching process of ammonium acetate and acetic acid, which enables selective and efficient leaching of MgO / CaO with an impurity ion suppression rate of up to 95%, effectively enhancing the added value of the product.

[0038] In some embodiments, in step S2, the ultrasonic-assisted acetic acid leaching treatment is used, and the frequency of the ultrasonic wave is 20-40 kHz. Through the ultrasonic-assisted acetic acid selective leaching process, the leaching rate and leaching rate of MgO / CaO can be improved, the leaching time can be shortened, and the production cost can be reduced.

[0039] Further, in step S2, the concentration of the ammonium acetate solution is 3-5 mol / L, the liquid-solid ratio of the ammonium acetate solution to the pretreated steel slag is 5:1-20:1, the temperature of the leaching treatment is 50-80℃, and the time is 30-40 min.

[0040] Further, in step S2, the concentration of the acetic acid solution is 0.5-3 mol / L, the liquid-solid ratio of the acetic acid solution to the filter residue is 5:1-20:1, the temperature of the leaching treatment is 50-80℃, and the time is 20-30 min.

[0041] Further, in step S3, the carbon fixation reaction is carried out at a pressure of normal pressure, a temperature of 50-80℃, and a pH of 8-10. By controlling the solution temperature, PH value, etc., the reaction process can be regulated.

[0042] In some embodiments, in step S3, the ultrasonic-assisted carbon fixation reaction is used, and the frequency of the ultrasonic wave is 20-40 kHz. Through the ultrasonic-assisted carbon fixation reaction, the mass transfer of CO2 and the crystal nucleation can be accelerated, thereby improving the generation amount of carbonate precipitation.

[0043] In the above embodiments, in step S3, the carbon dioxide source is the sintering flue gas or the blast furnace flue gas in the enterprise. Since the sintering flue gas in the enterprise is generated in the sintering process of steel production, and the blast furnace flue gas is generated in the blast furnace ironmaking process, both of which contain a certain amount of carbon dioxide, using them as the carbon dioxide source for the carbon fixation reaction can not only fully utilize the waste generated in the enterprise, realize the maximum recycling of resources, and reduce the production cost, but also help to reduce the overall waste gas emission of the enterprise and reduce the negative impact on the environment.

[0044] In some embodiments, in step S1, the method for pretreating the steel slag is as follows: first, the steel slag is crushed, then the crushed steel slag is subjected to magnetic separation, and then the steel slag after the magnetic separation is subjected to high-temperature activation. The crushing is performed by a crusher 1 to increase the specific surface area of the steel slag, thereby increasing the contact area of the steel slag with ammonium acetate / acetic acid, and preferably, the crushing is performed to a particle size of ≤2 mm. The magnetic separation is performed by a magnetic separator 2 to remove the magnetic iron-rich phase in the crushed steel slag to avoid pollution of the leaching solution, and preferably, the iron removal rate of the magnetic separator 2 is ≥98%. The high-temperature activation is performed by a first heating furnace 3 to destroy the lattice structure of the steel slag, thereby improving the leaching activity of MgO / CaO, and preferably, the high-temperature activation is performed at a temperature of 500-700°C for 2-4 h.

[0045] In some embodiments, after step S3, the method further comprises the following steps: calcining the obtained carbonate precipitate at 800-900°C to prepare a light magnesium carbonate / calcium carbonate product, or directly using the obtained carbonate precipitate as a building material additive; and using the obtained leaching residue as a cement admixture or roadbed material after dehydration. In this embodiment, the carbonate precipitate obtained in step S3 has two processing methods: one is calcination at 800-900°C, which causes a series of complex physical and chemical changes in the carbonate precipitate, and finally a light magnesium carbonate / calcium carbonate product is prepared, which can be used as a functional filler; and the other is directly used as a building material additive without further processing such as calcination, which can improve the strength and other indicators of the building material. For the leaching residue obtained in step S3, after dehydration to remove excess water, the main component is silicate phase, which can be used as a cement admixture or roadbed material. Through the graded utilization of the components in the steel slag carbon sequestration method, maximum resource utilization can be achieved, and no secondary waste is generated, and the carbon sequestration rate can reach 15-20 kg CO2 / ton of steel slag.

[0046] As Figure 2As shown, the embodiment also provides a selective leaching-atmospheric mineralization coupled steel slag carbon fixation system, which comprises a steel slag pretreatment unit, a selective leaching unit and a mineralization carbon fixation unit connected in sequence. The selective leaching unit comprises an ammonium acetate leaching device 4 and an acetic acid leaching device 5. The steel slag outlet of the steel slag pretreatment unit is connected with the steel slag inlet of the ammonium acetate leaching device 4. The filter residue outlet of the ammonium acetate leaching device 4 is connected with the filter residue inlet of the acetic acid leaching device 5. The leaching liquid outlet of the ammonium acetate leaching device 4 and the leaching liquid outlet of the acetic acid leaching device 5 are both connected with the mineralization carbon fixation unit. In this embodiment, the steel slag is pretreated by the steel slag pretreatment unit, then the pretreated steel slag is subjected to ammonium acetate leaching treatment by the ammonium acetate leaching device 4, and then the filter residue after the ammonium acetate leaching treatment is subjected to acetic acid leaching treatment by the acetic acid leaching device 5. The two-step selective leaching process of ammonium acetate-acetic acid is adopted to improve the leaching rate of MgO / CaO and the inhibition rate of impurity ions. Then, the first steel slag leaching liquid after the ammonium acetate leaching treatment and the second steel slag leaching liquid after the acetic acid leaching treatment are subjected to carbon fixation reaction by the mineralization carbon fixation unit, which not only can fix carbon dioxide, but also can convert part of the components in the steel slag into high-value carbonates.

[0047] Further, the ammonium acetate leaching device 4 is configured with ammonium acetate solution, and the acetic acid leaching device 5 is configured with acetic acid solution. The pretreated steel slag is subjected to leaching treatment by the ammonium acetate solution, and the filter residue after the ammonium acetate leaching treatment is subjected to leaching treatment by the acetic acid solution, so as to realize the two-step selective leaching of ammonium acetate-acetic acid.

[0048] In some embodiments, the acetic acid leaching device 5 is provided with a first ultrasonic transducer, and the acetic acid leaching device 5 is provided with a first ultrasonic generator, and the first ultrasonic transducer is connected with the first ultrasonic generator. The high-frequency electric signal generated by the first ultrasonic generator is transmitted to the first ultrasonic transducer. After receiving the electric signal, the first ultrasonic transducer rapidly converts it into ultrasonic mechanical vibration, and transmits this vibration to the acetic acid solution in the acetic acid leaching device 5, so as to promote the chemical reaction between acetic acid and steel slag, thereby improving the leaching rate and leaching rate of MgO / CaO.

[0049] In some embodiments, the steel slag pretreatment unit comprises a crusher 1 and a magnetic separator 2, and the steel slag outlet of the crusher 1 is connected with the steel slag inlet of the magnetic separator 2. The steel slag enters the crusher 1 through the steel slag inlet of the crusher 1 for crushing treatment, which can increase the specific surface area of the steel slag to increase the contact area of the steel slag with ammonium acetate / acetic acid. The steel slag after the crushing treatment is discharged from the steel slag outlet of the crusher 1 and enters the magnetic separator 2 through the steel slag inlet of the magnetic separator 2 for magnetic separation treatment, which can remove the magnetic iron-rich phase in the crushed steel slag to avoid pollution to the leaching liquid. The steel slag after the magnetic separation treatment is discharged from the steel slag outlet of the magnetic separator 2.

[0050] Further, the steel slag pretreatment unit further comprises a first heating furnace 3, a steel slag outlet of the magnetic separator 2 is connected with a steel slag inlet of the first heating furnace 3, and a steel slag outlet of the first heating furnace 3 is connected with a steel slag inlet of the ammonium acetate leaching device 4. The steel slag after the magnetic separation treatment is discharged from the steel slag outlet of the magnetic separator 2, enters the first heating furnace 3 through the steel slag inlet of the first heating furnace 3, and is subjected to an activation treatment, so that the lattice structure of the steel slag is destroyed, thereby improving the leaching activity of MgO / CaO; the steel slag after the activation treatment is discharged from the steel slag outlet of the first heating furnace 3, enters the ammonium acetate leaching device 4 through the steel slag inlet of the ammonium acetate leaching device 4, and is subjected to a leaching treatment.

[0051] Further, the crusher 1 is a jaw crusher, the magnetic separator 2 is a belt magnetic separator, and the first heating furnace 3 is a rotary kiln.

[0052] In some embodiments, the mineralization carbon fixation unit comprises a mineralization reactor 6, the mineralization reactor 6 has a leaching liquid inlet, a CO2 inlet and a precipitation outlet, the leaching liquid outlet of the ammonium acetate leaching device 4 and the leaching liquid outlet of the acetic acid leaching device 5 are connected with the leaching liquid inlet, and the CO2 inlet is connected with a carbon dioxide source. The first steel slag leaching liquid after the ammonium acetate leaching treatment and the second steel slag leaching liquid after the acetic acid leaching treatment are transported to the mineralization reactor 6 to perform a carbon fixation reaction with CO2, so as to realize the fixation of carbon dioxide by the steel slag.

[0053] Further, the mineralization reactor 6 is provided with a second ultrasonic transducer, the mineralization reactor 6 is provided with a second ultrasonic generator outside, and the second ultrasonic transducer is connected with the second ultrasonic generator. High-frequency electric signals generated by the second ultrasonic generator are transmitted to the second ultrasonic transducer, the second ultrasonic transducer rapidly converts the electric signals into ultrasonic mechanical vibrations after receiving the electric signals, and transmits the vibrations to the steel slag leaching liquid in the mineralization reactor 6, so as to promote the steel slag leaching liquid to perform a sufficient carbon fixation reaction with CO2, thereby improving the generation amount of carbonate precipitates.

[0054] Further, the mineralization carbon fixation unit further comprises a second heating furnace 7, and the precipitation outlet is connected with a feeding port of the second heating furnace 7. The carbonate precipitates generated by the carbon fixation reaction can be subjected to a high-temperature calcination treatment by the second heating furnace 7, so as to prepare a high-value-added light magnesium carbonate / calcium carbonate product.

[0055] The method of the present application will be described in detail below through a specific embodiment.

[0056] A selective leaching-atmospheric mineralization coupled steel slag carbon fixation method, comprising the following steps:

[0057] 1) Steel slag pretreatment:

[0058] The steel slag after primary treatment is selected in the steel enterprise, first transported to the crusher 1 for crushing treatment, crushed to a particle size of ≤2 mm, which can increase the specific surface area of the steel slag, thereby increasing the contact area of the steel slag with ammonium acetate / acetic acid;

[0059] Then the crushed steel slag is transported to the magnetic separator 2 for magnetic separation treatment, and the iron removal rate of the magnetic separator 2 is ≥98%, which removes the magnetic iron-rich phase in the crushed steel slag to avoid pollution to the leaching solution;

[0060] Then the magnetic separation steel slag is transported to the first heating furnace kiln 3, heated to 650℃, calcined for 3h, and high-temperature activated to destroy the lattice structure of the steel slag to improve the leaching activity of MgO / CaO;

[0061] 2) Selective leaching:

[0062] 5 mol / L ammonium acetate solution and 3 mol / L acetic acid solution are respectively configured, and a continuous countercurrent leaching device composed of ammonium acetate leaching device 4 and acetic acid leaching device 5 is adopted, the high-temperature activated steel slag is first transported to the ammonium acetate leaching device 4, the liquid-solid ratio is 10:1, the temperature is 75℃, and the residence time is 35min, then the ammonium acetate leaching treated filter residue is transported to the acetic acid leaching device 5, the liquid-solid ratio is 10:1, the temperature is 75℃, and the residence time is 25min, and the MgO / CaO comprehensive leaching rate is ≥89%;

[0063] The leaching residue after acetic acid leaching treatment is dehydrated to remove excess water in the residue, and then used as a cement admixture or roadbed material;

[0064] 3) Mineralization:

[0065] The first steel slag leaching solution after ammonium acetate leaching treatment and the second steel slag leaching solution after acetic acid leaching treatment are transported to the mineralization reactor 6, the sintering flue gas or the blast furnace flue gas in the enterprise is transported to the mineralization reactor 6 as the carbon dioxide source, and the steel slag leaching solution and the carbon dioxide are fully carbonated under the conditions of normal pressure, 60℃, pH=8 and 28kHz ultrasonic assistance, to obtain carbonate precipitate, and the carbonation amount can reach 18.7kgCO2 / ton of steel slag, and the purity of the carbonate product is ≥98%;

[0066] The obtained carbonate precipitate is transported to the second heating furnace kiln 7, calcined at 800~900℃ to prepare light magnesium carbonate / calcium carbonate products, and XRD analysis shows The purity is 98.2%, The purity is 97.5%, and the 28-day compressive strength reaches 35MPa, meeting the cement admixture standard.

[0067] The embodiment breaks through the technical bottleneck of high-value utilization of steel slag and carbon dioxide mineralization through a two-step leaching system combined with ultrasonic auxiliary technology, and provides a replicable technical solution for low-carbon transformation of the steel industry. Compared with the prior art, the application has significant advantages in leaching efficiency, mineralization rate and resource utilization degree, and has a broad industrial application prospect.

[0068] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A selective leaching-atmospheric pressure mineralization coupled method for carbon fixation of steel slag, characterized in that, Includes the following steps: S1. Steel slag pretreatment: Steel slag is pretreated to obtain pretreated steel slag; S2. Selective leaching: First, the pretreated steel slag is placed in an ammonium acetate solution for leaching treatment to obtain the first steel slag leachate and filter residue; then, the filter residue is placed in an acetic acid solution for leaching treatment to obtain the second steel slag leachate and leaching residue. S3, mineralization and carbon fixation: The first steel slag leaching solution and the second steel slag leaching solution are mixed, and a carbon dioxide source is introduced into the mixed leaching solution to carry out a carbon fixation reaction, resulting in carbonate precipitate.

2. The selective leaching-atmospheric pressure mineralization coupled steel slag carbon fixation method as described in claim 1, characterized in that: In step S2, ultrasonic-assisted acetic acid leaching is performed, with the frequency of the ultrasonic waves being 20~40kHz.

3. The selective leaching-atmospheric pressure mineralization coupled steel slag carbon fixation method as described in claim 1, characterized in that: In step S2, the concentration of ammonium acetate solution is 3~5 mol / L, the liquid-solid ratio of ammonium acetate solution to pretreated steel slag is 5:1~20:1, the leaching temperature is 50~80℃, and the time is 30~40min.

4. The selective leaching-atmospheric pressure mineralization coupled steel slag carbon fixation method as described in claim 1, characterized in that: In step S2, the concentration of the acetic acid solution is 0.5~3 mol / L, the liquid-solid ratio of the acetic acid solution to the filter residue is 5:1~20:1, the leaching temperature is 50~80℃, and the time is 20~30 min.

5. The selective leaching-atmospheric pressure mineralization coupled steel slag carbon fixation method as described in claim 1, characterized in that: In step S3, the carbon fixation reaction is carried out at atmospheric pressure, temperature of 50~80℃, and pH of 8~10.

6. The selective leaching-atmospheric pressure mineralization coupled steel slag carbon fixation method as described in claim 1, characterized in that: In step S3, ultrasonic-assisted carbon fixation reaction is used, with the frequency of the ultrasonic waves being 20~40kHz.

7. The selective leaching-atmospheric pressure mineralization coupled steel slag carbon fixation method as described in claim 1, characterized in that: In step S1, the method for pretreating steel slag is as follows: first, the steel slag is crushed; then, the crushed steel slag is magnetically separated; and finally, the magnetically separated steel slag is activated at high temperature.

8. The selective leaching-atmospheric pressure mineralization coupled steel slag carbon fixation method as described in claim 1, characterized in that: After step S3, the following steps are also included: calcining the obtained carbonate precipitate at 800~900℃ to prepare a light magnesium carbonate / calcium carbonate product, or directly using the obtained carbonate precipitate as a building material additive; and using the obtained leaching residue as a cement admixture or roadbed material after dehydration.

9. A selective leaching-atmospheric pressure mineralization coupled steel slag carbon fixation system, characterized in that: The system includes a steel slag pretreatment unit, a selective leaching unit, and a mineralization and carbon fixation unit connected in sequence. The selective leaching unit includes an ammonium acetate leaching device and an acetic acid leaching device. The steel slag outlet of the steel slag pretreatment unit is connected to the steel slag inlet of the ammonium acetate leaching device, the filter residue outlet of the ammonium acetate leaching device is connected to the filter residue inlet of the acetic acid leaching device, and the leachate outlets of the ammonium acetate leaching device and the acetic acid leaching device are both connected to the leachate inlet of the mineralization and carbon fixation unit.

10. The selective leaching-atmospheric pressure mineralization coupled steel slag carbon fixation system as described in claim 9, characterized in that: The steel slag pretreatment unit includes a crusher, a magnetic separator, and a first heating furnace connected in sequence.

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