Method for improving the yield of steel slag magnetic separation powder

Abstract

The application provides a method for improving the yield of steel slag magnetic separation powder, and the method comprises the following steps: S1: adding bauxite into raw steel slag, reducing the alkalinity of the raw steel slag, and reducing the alkalinity of the raw steel slag to below 1.8. The application makes up for the loss of the pressure hot stew steel slag magnetic separation material, can obtain more magnetic separation metal iron, improves the yield of the subsequent magnetic separation powder, and promotes the recycling of solid waste resources such as blast furnace dust, iron tailings and dry desulfurization ash. Before the technology is used, the yield of the magnetic separation powder is 10-15%, and after the technology is used, the yield of the magnetic separation powder is more than 30%.

Description

Methods to improve the yield of steel slag magnetic separation powder Technical Field

[0001] This invention relates to the field of comprehensive utilization of steelmaking slag, specifically to a method for improving the yield of magnetic separation powder from steel slag. Background Technology

[0002] Currently, the main processing technologies for steel slag in China include hot pouring, air quenching, water quenching, shallow pan water quenching, cold disposal, hot braising, and mechanical crushing. After processing, the slag undergoes crushing, sorting, and magnetic separation to obtain slag steel (90% total iron content), magnetic powder (30% total iron content), and tailings products. The slag steel is returned to the steelmaking process, while the magnetic powder is washed, ball-milled to remove steel particles, and then pressed into cakes to be returned to the steelmaking production line. The tailings products mainly flow to cement plants and mixing plants. The higher the total iron content of the magnetic powder, the higher its market value, and the lower the iron content in the tailings products, the more beneficial they are for subsequent processing.

[0003] In the steel slag treatment process, the recovery rate of magnetic separation powder varies significantly among different treatment methods. According to production statistics, the recovery rate of magnetic separation powder from steel slag is approximately 15% with pool-type hot quenching, approximately 10% with pressurized hot quenching, and approximately 25% with hot pouring. This shows that the recovery rate of magnetic separation powder from steel slag is lower with both pool-type and pressurized hot quenching methods than with hot pouring. Hot pouring treatment not only consumes a large amount of water resources but also generates severe dust and creates a harsh environment, which no longer meets current environmental protection requirements and is gradually being phased out.

[0004] In summary, the existing technology has the following problems: the yield of magnetic separation powder products is low after steel slag treatment. Summary of the Invention

[0005] This invention provides a method for improving the yield of magnetically separated steel slag powder, thereby increasing the yield of magnetically separated steel slag powder.

[0006] Therefore, the present invention proposes a method for improving the yield of magnetically separated steel slag powder, the method comprising:

[0007] Step S1: Add bauxite to the high-temperature liquid steel slag to reduce the alkalinity of the raw steel slag to below 1.8.

[0008] Furthermore, the method for improving the yield of magnetic separation powder of steel slag also includes: step S2: adding 10% iron tailings modified steel slag to high-temperature liquid steel slag.

[0009] Furthermore, the method for improving the yield of steel slag magnetic separation powder also includes: step S3: adding carbon and iron-containing blast furnace dust, with an addition amount of 5-15%.

[0010] Furthermore, the method for improving the yield of magnetic separation powder of steel slag also includes: step S41: change the production process of liquid steel slag, when the temperature of liquid high temperature steel slag is higher than 570°C during roller crushing or excavator turning crushing, a small amount of water is sprayed to cool it down. After the roller crushing or excavator turning is completed, the temperature of the steel slag is close to about 570°C during pool-type hot quenching or pressurized hot quenching, and a large amount of water is sprayed to cool it down quickly.

[0011] Furthermore, the method for improving the yield of magnetic separation powder of steel slag also includes: step S42: changing the hot steel slag simmering process, when the temperature of the steel slag is below 570°C, adding a soluble reducing substance to the water.

[0012] Further, in step S1: 5% bauxite is added to the high-temperature liquid steel slag to reduce the basicity of the original steel slag to 1.49.

[0013] Furthermore, the reducing substance is dry desulfurization ash rich in sodium sulfate, sodium sulfite, and sodium carbonate.

[0014] Furthermore, the method for improving the yield of steel slag magnetic separation powder specifically includes:

[0015] Based on a capacity of 30 tons of liquid steel slag per batch, and considering the addition of approximately 5% bauxite, 10% iron tailings, and 10% blast furnace dust, each batch of steel slag requires the addition of 1.5 tons of bauxite, 3 tons of iron tailings, and 3 tons of carbon-containing blast furnace dust. After the above raw materials are mixed evenly, they are placed at the bottom of the slag pot and then collected in the converter. The impact force of the high-temperature liquid steel slag is used to achieve the purpose of uniform mixing. The heat released by the combustion of some carbon-containing materials can achieve heat preservation and promote the continuous reaction. After reacting for 1-2 hours, the roller crushing or excavator turning of slag is carried out, and the modified high-temperature liquid steel slag production process is followed, namely: 1. When the temperature of the liquid high-temperature steel slag is higher than 570℃ during roller crushing or excavator turning, a small amount of water is sprayed to cool it down. After the roller crushing or excavator turning is completed, the temperature of the steel slag is close to about 570℃ during the pool-type hot quenching or pressurized hot quenching process, and a large amount of water is sprayed to quickly cool it down; 2. During the hot quenching process of hot steel slag, when the temperature of the steel slag is lower than 570℃, dry desulfurization ash rich in sodium sulfate, sodium sulfite and sodium carbonate can be added to the water.

[0016] This invention compensates for the losses in magnetic separation of pressurized hot slag, yielding more magnetic minerals, improving the recovery rate of subsequent magnetic separation powder, and promoting the resource reuse of solid wastes such as blast furnace dust, iron tailings, and dry desulfurization ash. Before adopting this technology, the magnetic separation powder recovery rate was 10-15%; after adopting this technology, the magnetic separation powder recovery rate is over 30%. Detailed Implementation

[0017] To provide a clearer understanding of the technical features, objectives, and effects of this invention, the invention is now described.

[0018] The applicant discovered that both pool-type and pressurized hot slag treatment methods require crushing the liquefied steel slag using roller crushers or excavators while it is still in its liquid state, while continuously turning the slag and applying water for cooling to solidify the surface and prevent caking. Then, pool-type or pressurized hot slag is applied, with intermittent water application to rapidly cool the slag. The slag is slag-treated under pressure or without pressure. Pool-type hot slag treatment requires approximately 12 hours, while pressurized hot slag treatment requires 2 hours. During the roller crushing or excavator slag turning process, the continuous turning and water application expose the liquefied steel slag to air and water vapor, causing oxidation of the iron in the slag and changes in the crystal structure of the minerals, ultimately leading to a decrease in the yield of magnetic separation powder from the steel slag.

[0019] Therefore, this invention mainly combines steel slag modification and changes to the hot slag quenching process to improve the yield of magnetic separation powder products.

[0020] Step 1: Change the basicity of steel slag

[0021] The ratio of basic oxides to acidic oxides in slag is called basicity. Basicity is generally used as a standard for measuring and selecting slag. Although many oxides make up slag, the four most abundant and influential are SiO2, Al2O3, CaO, and MgO. Therefore, slag basicity is often expressed as the weight percentage of basic oxides CaO and MgO to acidic oxides SiO2 and Al2O3.

[0022] Bauxite was added to the (high-temperature) liquid steel slag to increase the alumina content and decrease the basicity of the slag. When the basicity of the original slag decreased from 2.4 to 1.49 and 1.76 respectively, its magnetic permeability increased from 30.6% to 74.04% and 62.5% respectively, while its f-CaO (free calcium oxide) decreased from 5.14% to 0.42% and 1.06% respectively, as shown in Table 1 below:

[0023] Table 1 Chemical composition (wt%) of raw slag and modified slag

[0024] Samples: SiO2, CaO, Al2O3, Fe2O3, MgO, CaO; Raw slag: 17.04, 40.84, 3.19, 27.96, 3.36, 5.14; Modified slag: 123.13, 34.42, 8.56, 21.01, 3.93, 0.42; Modified slag: 221.36, 37.69, 5.47, 23.44, 4.33, 1.06 surface

[0025] Note: Modified slag 1 indicates the addition of 5.37% bauxite, reducing the basicity from 2.4 (original slag) to 1.49; Modified slag 2 indicates the addition of 2.28% bauxite, reducing the basicity from 2.4 (original slag) to 1.76.

[0026] Therefore, it is generally appropriate to choose an amount of bauxite added of 5% of the mass of (high-temperature liquid) steel slag, which will have a better effect on reducing f-CaO.

[0027] Step 2: Add iron tailings modified steel slag

[0028] When the temperature of liquid steel slag exceeds 1250℃, the modified steel slag with 10% iron tailings mainly consists of dicalcium silicate (C2S), tricalcium silicate (C3S), and Fe3O4-based magnetite solid solution. When the iron tailings content is increased to 20%, columnar or polygonal distributions of magnesian feldspar (C2MS2) appear, with C2S and C3S distributed between C2MS2, resulting in improved microstructure and enhanced cementing properties.

[0029] With the increase of iron tailings content, silicate mineral phases such as magnesium rhodochrosite (C3MS2), magnesium feldspar (C2MS2), and calcium magnesium pyroxene (CMS2) gradually appear in the modified steel slag. The modification process promotes the decomposition of the RO phase, in which FeO is converted into magnetite Fe3O4, which compensates for the loss of magnetic separation products in pressurized hot slag, resulting in more magnetic minerals, improving the yield of subsequent magnetic separation powder, and promoting the resource utilization of iron tailings solid waste.

[0030] Step 3: Add blast furnace dust

[0031] In addition to being rich in carbon sources, blast furnace dust also contains some iron. Adding it during the treatment of liquid steel slag utilizes the residual heat of the slag for reduction and magnetization roasting. This enhances the reducing atmosphere during slag treatment, protecting the iron in the slag from oxidation. Simultaneously, it reduces iron oxides in the blast furnace dust, yielding more magnetically separable materials. This also facilitates the resource utilization of blast furnace dust as solid waste, and is cost-effective. The recommended addition amount is approximately 5-15%.

[0032] Step 4: Modify the hot-quenching process for steel slag

[0033] FeO in steel slag is an unstable phase below 570℃, decomposing into α-Fe and Fe3O4. However, rapid cooling at 570℃ can inhibit this decomposition reaction. Therefore, even if FeO is formed at this reaction temperature, if cooling is not timely, the products will contain α-Fe and Fe3O4. The presence of α-Fe reduces the magnetic separation properties of the steel slag, affecting the yield of magnetically separated powder.

[0034] Under a reducing atmosphere, α-Fe₂O₃ can be converted to γ-Fe₂O₃ at 400-600℃, and the color of the steel slag changes from dark red to brown, becoming magnetic. Therefore, the production process should be adjusted as follows: 1. When the temperature of the high-temperature steel slag is above 570℃ during roller crushing or excavator turning, a small amount of water should be sprayed to cool it down. After the roller crushing or excavator turning is completed, during pool-type hot curing or pressurized hot curing, when the steel slag temperature approaches around 570℃, a large amount of water should be sprayed to rapidly cool it down, reducing the formation of α-Fe; 2. During the hot curing process of steel slag, when the steel slag temperature is below 570℃, dry desulfurization ash can be added to the water. Desulfurization ash is rich in sodium sulfate, sodium sulfite, sodium carbonate, etc., which can effectively promote the conversion of the already formed α-Fe₂O₃ to γ-Fe₂O₃.

[0035] The above process adjustments can be made individually or simultaneously.

[0036] Example 1:

[0037] Based on a capacity of 30 tons of liquid steel slag per batch, and considering the addition of approximately 5% bauxite, 10% iron tailings, and 10% blast furnace dust, each batch of steel slag requires the addition of 1.5 tons of bauxite, 3 tons of iron tailings, and 3 tons of carbon-containing blast furnace dust.

[0038] After the above raw materials (bauxite + iron tailings + blast furnace dust) are evenly mixed, they are placed at the bottom of the slag pot and then collected in the converter. The impact force of the high-temperature liquid steel slag is used to achieve uniform mixing. The combustion of some carbon-containing materials can achieve the purpose of heat preservation and promote the continuous reaction. After reacting for 1-2 hours, the process is carried out by roller crushing or excavator turning of slag, and the modified high-temperature liquid steel slag production process is followed, namely: 1. When the temperature of the liquid high-temperature steel slag is higher than 570℃ during roller crushing or excavator turning, a small amount of water is added to cool it down. After the roller crushing or excavator turning is completed, a large amount of water is added to rapidly cool the steel slag when the temperature approaches 570℃ during pool-type hot curing or pressurized hot curing; 2. During the hot curing process of hot steel slag, when the temperature of the steel slag is lower than 570℃, soluble reducing substances such as ferrous sulfate and sodium sulfite can be added to the water. Adding a small amount of water means reducing the amount of water by 40-60% compared to the original production process, for example, by 50%. In the original hot slag turning process of the pool-type hot slag turning machine, the water-slag ratio was 1, and in the pressurized hot slag turning process of the roller crusher, the water-slag ratio was 0.5. Using the method of this invention, the water ratio is reduced to 0.5 and 0.4 respectively by reducing the amount of water added. After the roller crusher or the excavator turns the slag, when the temperature of the steel slag is close to about 570°C during the pool-type hot slag turning or pressurized hot slag turning process, a large amount of water is added to quickly cool it down and reduce the formation of α-Fe. 2. During the hot slag turning process of hot steel slag, when the temperature of the steel slag is lower than 570°C, dry desulfurization ash can be added to the water. Sodium sulfate, sodium sulfite, and sodium carbonate in the desulfurization ash play different roles. Sodium sulfate solution helps to protect the metallic iron in the steel slag from oxidation and rusting, and sulfate helps to improve the activity of the steel slag tailings. Sodium carbonate decomposes in a high-temperature environment to produce carbon dioxide. Carbon dioxide reacts with carbon in the blast furnace ash to produce carbon monoxide, which has reducing properties. It reacts with the metal oxides of iron to produce more metallic iron. Sodium sulfite has reducing properties and promotes the conversion of the generated α-Fe2O3 into γ-Fe2O3. The amount added should be approximately 20% of the water used for slag removal, i.e., 200 kg of desulfurization ash should be added to 1 ton of water to effectively promote the conversion of the generated α-Fe₂O₃ into γ-Fe₂O₃. Before using this invention: the magnetic separation powder yield was 10-15%; after using this invention: the magnetic separation powder yield is 30%.

[0039] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. The various components of the present invention can be combined with each other without conflict. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for improving the yield of magnetic separation powder for steel slag, characterized in that, The method for improving the yield of magnetic separation powder of steel slag includes: Step S1: Adding bauxite to the high-temperature liquid steel slag raw slag to reduce the basicity of the raw steel slag to below 1.8; The specific method for improving the yield of magnetic separation powder of steel slag is as follows: Based on 30 tons of liquid steel slag per batch, and based on the addition of 5% bauxite, 10% iron tailings, and 10% blast furnace dust, each batch of steel slag needs to be mixed with 1.5 tons of bauxite, 3 tons of iron tailings, and 3 tons of carbon-containing blast furnace dust; After the above raw materials are evenly mixed, they are placed at the bottom of the slag pot and then collected in the converter. The impact force of the high-temperature liquid steel slag is used to achieve the purpose of even mixing. The heat released by the combustion of some carbon-containing materials can achieve heat preservation and promote the continuous reaction. After the reaction is carried out for 1-2 hours, The process involves roller crushing or excavator turning over the slag, following a modified hot-quenching process for steel slag: a) When the temperature of the liquid high-temperature steel slag exceeds 570℃ during roller crushing or excavator turning, a small amount of water is applied to lower the temperature. After the roller crushing or excavator turning is completed, a large amount of water is applied to rapidly cool the slag as it approaches 570℃ during pool-type or pressurized hot-quenching; b) During the hot-quenching process of hot steel slag, when the slag temperature is below 570℃, dry desulfurization ash rich in sodium sulfate, sodium sulfite, and sodium carbonate is added to the water. The amount added is 20% of the water used for quenching, i.e., 200 kg of desulfurization ash is added to 1 ton of water to effectively promote the conversion of the generated α-Fe2O3 to γ-Fe2O3; the magnetic separation powder yield is 30%.

2. The method for improving the yield of magnetic separation powder for steel slag as described in claim 1, characterized in that, The dry desulfurization ash contains more than 80% sodium sulfate, more than 10% sodium sulfite, and more than 5% sodium carbonate.