Method for reducing RO phase in steel slag

Abstract

The invention belongs to the technical field of steel slag resource utilization, and provides a method for reducing an RO phase in steel slag. The method comprises the following steps: mixing steel slag and carbonate, and grinding to obtain a ground sample; and roasting the ground sample to obtain the modified steel slag containing Fe3O4. The carbonate and the steel slag are mixed and then ground, so that the carbonate is in full contact with the steel slag, and the subsequent roasting efficiency of the carbonate and the steel slag is improved; cO2 gas is generated through chemical reaction of carbonate and all phases in the steel slag, meanwhile, due to changes of the phases of the steel slag, the wrapped RO phase is exposed, then FeO of the RO phase is oxidized into Fe3O4 through the generated CO2, and finally the purpose of reducing the RO phase in the steel slag is achieved. A roasting system is a solid-phase system of carbonate and steel slag, so that pressure control required by taking gas as a reducing agent or an oxidizing agent is avoided, and the operation is simpler.

Description

Technical Field

[0001] This invention relates to the field of steel slag resource utilization technology, and in particular to a method for reducing the RO phase in steel slag. Background Technology

[0002] Effective reuse methods are urgently needed to address the issue of excessive steel slag stockpiles. Currently, steel slag reuse includes internal recycling within steel plants and resource utilization. Internal recycling involves returning steel slag to the steel production process. However, this method tends to lead to the enrichment of phosphorus and sulfur (P and S) during steel production, increasing the burden on steelmaking; therefore, the amount of steel slag consumed in this way is limited. Resource utilization of steel slag is a major research focus. This involves using steel slag treated through oxidation, reduction, and reconstruction to prepare ceramics, building materials, fillers, CO2 scavengers, and fertilizers. Except for its application as fertilizer in agriculture, other methods are related to the cementitious properties of steel slag. Therefore, improving the cementitious properties of steel slag is one of the key issues in solving the resource utilization problem. Existing research shows that the cementitious properties of steel slag originate from the highly reactive silicate phase, while the RO phase (a solid solution composed of FeO, MnO, MgO, etc.), which accounts for the largest proportion of steel slag, is a poorly reactive phase. The key to improving the cementitious properties of steel slag is to reduce the content of the RO phase. The RO phase is predominantly FeO, so reducing the RO phase primarily involves reducing the amount of FeO in the steel slag. Researchers mainly achieve this by reducing FeO in the steel slag to Fe or oxidizing it to Fe3O4, followed by magnetic separation. Common methods include pyrometallurgy and hydrometallurgy. Pyrometallurgy includes high-temperature oxidation methods using oxygen, air, or CO2 as oxidants and reduction methods using coke or CO as reducing agents. Hydrometallurgy uses inorganic or organic acids to leach iron from the steel slag in the form of ferrous ions, thereby separating iron and reducing the RO phase. The two methods mentioned above have achieved certain results in reducing the RO phase in steel slag, but they also have some problems: In pyrometallurgy, it is difficult to control the oxygen partial pressure when using oxygen or air as oxidants, which easily oxidizes FeO to Fe2O3, and Fe2O3 is not conducive to subsequent magnetic separation; using CO2, a weak oxidant, requires high kinetic conditions, which are usually controlled by adjusting the reaction temperature, gas flow rate, and the state of the steel slag raw material (cold steel slag, hot molten steel slag); using coke or CO as a reducing agent easily generates a large amount of CO2 tail gas; in hydrometallurgy, the process is long, and the generation of acidic waste liquid increases the cost of treatment. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a method for reducing the RO phase in steel slag. The method of this invention can effectively reduce the RO phase in steel slag, and is simple to operate, avoiding the problems of pressure control difficulties in pyrometallurgy and the defects of acid-generating waste liquid in hydrometallurgy.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for reducing the RO phase in steel slag, comprising the following steps: Steel slag and carbonates were mixed and then ground to obtain a ground sample. The ground sample was calcined to obtain modified steel slag containing Fe3O4; The steel slag contains an RO phase.

[0005] Preferably, the type of steel slag includes one or more of converter steel slag, electric furnace steel slag, and refining slag; The steel slag also includes one or more of the following: calcium ferrite, calcium silicate, aluminum silicate, calcium aluminosilicate, and calcium oxide.

[0006] Preferably, the steel slag is further subjected to drying treatment before use.

[0007] Preferably, the carbonate includes one or more of sodium carbonate, potassium carbonate, lithium carbonate, and magnesium carbonate.

[0008] Preferably, the mass of the carbonate is 5-40% of the mass of the steel slag.

[0009] Preferably, the grinding speed is 250~500 rpm and the grinding time is 5~12 hours.

[0010] Preferably, the calcination temperature is 500~1200℃ and the time is 0.5~4h, and the calcination is carried out under a protective atmosphere, which is argon.

[0011] Preferably, the roasting is carried out in a tube furnace.

[0012] Preferably, after roasting, the process further includes: sequentially washing and drying the obtained roasting product with water to obtain the modified steel slag containing Fe3O4; The drying temperature is 100~250℃, and the time is 22~26h.

[0013] Preferably, after obtaining the modified steel slag containing Fe3O4, the process further includes: removing Fe3O4 by magnetic separation to obtain steel slag with a low RO phase.

[0014] This invention provides a method for reducing the RO phase in steel slag.

[0015] This invention involves mixing and grinding carbonates and steel slag to ensure sufficient contact between the carbonates and steel slag, thereby improving the subsequent roasting efficiency of the carbonates and steel slag. The chemical reaction between the carbonates and various phases in the steel slag generates CO2 gas. Simultaneously, the phase changes in the steel slag expose the previously encapsulated RO phase, allowing the generated CO2 to oxidize the FeO in the RO phase to Fe3O4, ultimately reducing the RO phase content in the steel slag. The roasting system of this invention is a solid-phase system of carbonates and steel slag, avoiding the complex operations of pyrometallurgical processes involving pressure control using gases as reducing or oxidizing agents, thus simplifying the operation. It also avoids the drawbacks of hydrometallurgical processes, such as the generation of acidic wastewater. Attached Figure Description

[0016] Figure 1 The XRD pattern of the modified steel slag containing Fe3O4 obtained in Example 1 is shown below. Figure 2 The XRD pattern of the modified steel slag containing Fe3O4 obtained in Example 2; Figure 3 The image shows the XRD pattern of the modified steel slag containing Fe3O4 obtained in Example 3. Detailed Implementation

[0017] This invention provides a method for reducing the RO phase in steel slag, comprising the following steps: Steel slag and carbonates were mixed and then ground to obtain a ground sample. The ground sample was calcined to obtain modified steel slag containing Fe3O4; The steel slag contains an RO phase.

[0018] In this invention, unless otherwise specified, all raw materials used are preferably commercially available products.

[0019] This invention involves mixing steel slag and carbonates and then grinding them to obtain a ground sample.

[0020] In this invention, the steel slag comprises an RO phase. In this invention, the RO phase refers to a solid solution formed by FeO, MnO, and MgO. Preferably, the steel slag also comprises one or more of calcium ferrite, calcium silicate, aluminum silicate, calcium aluminosilicate, and calcium oxide.

[0021] In this invention, the type of steel slag preferably includes one or more of converter steel slag, electric arc furnace steel slag, and refining slag. In a specific embodiment of this invention, the steel slag preferably includes the following components: mainly RO phase, Ca2SiO4, and Ca2Al2SiO7, and small amounts of CaO and Ca2Fe2O5.

[0022] In this invention, the steel slag preferably undergoes a drying process before use. The drying temperature is preferably 100-250°C, specifically 100°C, 150°C, 200°C, or 250°C; the drying time is preferably 22-26 hours, more preferably 24 hours; and the drying process is preferably carried out in a heating furnace. This drying process removes moisture and volatile matter from the steel slag, which helps to avoid the influence of water and volatile matter during ball milling and roasting of the modified steel slag.

[0023] In this invention, the carbonate preferably includes one or more of sodium carbonate, potassium carbonate, lithium carbonate, and magnesium carbonate. In this invention, the mass of the carbonate is preferably 5-40% of the mass of the steel slag, specifically preferably 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%. In this invention, the grinding speed is preferably 250-500 rpm, specifically preferably 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or 500 rpm; the grinding time is preferably 5-12 hours, specifically preferably 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours. In this invention, the grinding ensures that the steel slag and carbonate are mixed evenly and in sufficient contact to facilitate the calcination reaction.

[0024] After obtaining the ground sample, the present invention calcines the ground sample to obtain modified steel slag containing Fe3O4.

[0025] In this invention, the calcination temperature is preferably 500~1200℃, specifically 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, or 1200℃; the heating rate to the calcination temperature is 5~10℃ / min, specifically 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min; the time is preferably 0.5~4h, specifically 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, or 4h. In this invention, the calcination is preferably carried out under a protective atmosphere, preferably argon. In this invention, the calcination pressure is preferably atmospheric pressure. In this invention, the calcination is preferably carried out in a tube furnace.

[0026] In this invention, the preferred specific process of the calcination is as follows: the ground sample is placed in an alumina crucible, the alumina crucible containing the ground sample is placed in a tube furnace, the tube furnace is sealed, the air in the tube furnace is evacuated by a vacuum pump, and a protective atmosphere is introduced to maintain atmospheric pressure. The temperature is raised to the calcination temperature under the protective atmosphere for calcination.

[0027] After roasting, the present invention preferably further includes: cooling the obtained roasted product to room temperature in the furnace, and then sequentially washing and drying it with water to obtain the modified steel slag containing Fe3O4. The present invention does not specifically limit the number of water washes or the amount of washing agent used, as long as the unreacted carbonates are completely removed.

[0028] In this invention, the drying temperature is preferably 100~250℃, specifically 100℃, 150℃, 200℃ or 250℃; the drying time is preferably 22~26h, more preferably 24h. In this invention, the drying is preferably carried out in vacuum drying.

[0029] After obtaining the modified steel slag containing Fe3O4, the present invention preferably further includes: removing Fe3O4 by magnetic separation to obtain steel slag with a low RO phase. The present invention does not specifically limit the method of magnetic separation.

[0030] The method of this invention does not require the addition of an oxidant. It relies solely on the chemical reaction between carbonates and the composite mineral phase in steel slag to induce a phase change in the composite mineral phase, exposing the RO phase encased within the composite mineral phase and producing CO2 gas. The produced CO2 gas oxidizes the FeO in the RO phase to Fe3O4, resulting in a modified steel slag powder containing Fe3O4 but free of the RO phase. During the roasting process, the solid-phase system formed by the carbonates and steel slag of this invention transforms into a multi-component system of gas-solid-liquid phases (the liquid phase refers to the molten carbonate, silicate, etc.).

[0031] The following detailed description of the method for reducing the RO phase in steel slag provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0032] Example 1: Carbonate Type The converter slag (mainly composed of RO phase, Ca2SiO4, Ca2Al2SiO7, and small amounts of CaO and Ca2Fe2O5) was dried in a heating furnace at 200℃ for 24 hours to obtain dried slag for later use.

[0033] 10g of dry steel slag was mixed with different types of carbonates and ball-milled at 400rpm for 10h to obtain ball-milled samples; wherein the carbonates were potassium carbonate or sodium carbonate, and the mass of the carbonates was 15% of the mass of the dry steel slag.

[0034] The ball-milled sample was placed in an alumina crucible, and then the alumina crucible containing the ball-milled sample was placed in a tube furnace. The tube furnace was sealed, and a vacuum pump was used to evacuate the air. Argon gas was introduced to maintain normal pressure. The temperature was increased to 1000℃ at 5℃ / min and calcined for 2 hours in an argon atmosphere. After calcination, the product was cooled to room temperature in the furnace. The calcined product was then taken out and washed with water. It was then placed in a vacuum drying oven and dried at 150℃ for 24 hours to obtain steel slag containing Fe3O4.

[0035] The obtained Fe3O4-containing steel slag was characterized by XRD, and the results are as follows: Figure 1 As shown, Figure 1 In the original text, carbonate 1 is potassium carbonate, and carbonate 2 is sodium carbonate. From... Figure 1 It can be seen that after modification with carbonates, the RO phase of the steel slag disappears, and all FeO in the RO phase is converted into Fe3O4. The Fe3O4 peak of the steel slag modified with potassium carbonate is stronger than that of sodium carbonate, indicating that the type of carbonate has an impact on the modification of steel slag, and potassium carbonate is more effective than sodium carbonate.

[0036] Example 2 Calcination temperature The converter steel slag (same as in Example 1) was dried in a heating furnace at 200°C for 24 hours to obtain dried slag for later use.

[0037] 10g of dried steel slag was mixed with potassium carbonate and ball-milled at 400rpm for 10h to obtain a ball-milled sample; wherein the mass of potassium carbonate was 15% of the mass of dried steel slag.

[0038] The ball-milled sample was placed in an alumina crucible, and then the alumina crucible containing the ball-milled sample was placed in a tube furnace. The tube furnace was sealed, and a vacuum pump was used to evacuate the air. Argon gas was introduced to maintain normal pressure. The temperature was increased to 1000℃ or 1100℃ at 5℃ / min and calcined for 2 hours in an argon atmosphere. After calcination, the product was cooled to room temperature in the furnace. The calcined product was then taken out and washed with water. It was then placed in a vacuum drying oven and dried at 150℃ for 24 hours to obtain steel slag containing Fe3O4.

[0039] The obtained Fe3O4-containing steel slag was characterized by XRD, and the results are as follows: Figure 2 As shown, Figure 2 In the diagram, temperature 1 is a firing temperature of 1100℃, and temperature 2 is a firing temperature of 1000℃. From... Figure 2 It can be seen that the RO phase disappears after potassium carbonate-modified steel slag at different temperatures, and all FeO in the RO phase is converted into Fe3O4. The Fe3O4 peak of the modified steel slag at different temperatures does not differ significantly, indicating that temperatures above 1000℃ have little effect on the modified steel slag.

[0040] Example 3: Amount of carbonate added The converter steel slag (same as in Example 1) was dried in a heating furnace at 200°C for 24 hours to obtain dried slag for later use.

[0041] 10g of dry steel slag was mixed with potassium carbonate and ball-milled at 400rpm for 10h to obtain ball-milled samples; wherein the mass of potassium carbonate was 10%, 15% or 20% of the mass of dry steel slag.

[0042] The ball-milled sample was placed in an alumina crucible, and then the alumina crucible containing the ball-milled sample was placed in a tube furnace. The tube furnace was sealed, and a vacuum pump was used to evacuate the air. Argon gas was introduced to maintain normal pressure. The temperature was increased to 1100℃ at 5℃ / min and calcined for 2 hours in an argon atmosphere. After calcination, the product was cooled to room temperature in the furnace. The calcined product was then taken out and washed with water. It was then placed in a vacuum drying oven and dried at 150℃ for 24 hours to obtain steel slag containing Fe3O4.

[0043] The obtained Fe3O4-containing steel slag was characterized by XRD, and the results are as follows: Figure 3 As shown, Figure 3 In the formula, ratio 1 is 20% of the mass of potassium carbonate by the dry steel slag, ratio 2 is 15% of the mass of potassium carbonate by the dry steel slag, and ratio 3 is 10% of the mass of potassium carbonate by the dry steel slag. Figure 3 It can be seen that the RO phase disappears after potassium carbonate modification of the steel slag, and all FeO in the RO phase is converted into Fe3O4. The Fe3O4 peak of the modified steel slag does not change much under different ratios, indicating that the amount of potassium carbonate has no significant effect on the modified steel slag.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for reducing the RO phase in steel slag, characterized in that, Includes the following steps: Steel slag and carbonates were mixed and then ground to obtain a ground sample. The ground sample was calcined to obtain modified steel slag containing Fe3O4; The steel slag contains an RO phase.

2. The method according to claim 1, characterized in that, The types of steel slag include one or more of converter steel slag, electric furnace steel slag, and refining slag; The steel slag also includes one or more of the following: calcium ferrite, calcium silicate, aluminum silicate, calcium aluminosilicate, and calcium oxide.

3. The method according to claim 1 or 2, characterized in that, The steel slag also undergoes a drying process before use.

4. The method according to claim 1, characterized in that, The carbonates include one or more of sodium carbonate, potassium carbonate, lithium carbonate, and magnesium carbonate.

5. The method according to claim 1 or 4, characterized in that, The mass of the carbonate is 5-40% of the mass of the steel slag.

6. The method according to claim 1, characterized in that, The grinding speed is 250~500 rpm, and the time is 5~12 hours.

7. The method according to claim 1, characterized in that, The calcination temperature is 500~1200℃, and the time is 0.5~4h. The calcination is carried out under a protective atmosphere, which is argon.

8. The method according to claim 1 or 7, characterized in that, The roasting is carried out in a tube furnace.

9. The method according to claim 1, characterized in that, After roasting, the process further includes: washing and drying the roasted product sequentially to obtain the modified steel slag containing Fe3O4. The drying temperature is 100~250℃, and the time is 22~26h.

10. The method according to claim 1 or 9, characterized in that, After obtaining the modified steel slag containing Fe3O4, the process further includes: removing Fe3O4 by magnetic separation to obtain steel slag with a low RO phase.

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