1. The fluoride-free spherical slag for molten iron desulphurization is characterized by comprising a spherical core and a layer of lime coated outside the spherical core, wherein the spherical core is prepared from aluminum slag and rare earth oxide.

2. The spherical slag for fluorine-free molten iron desulphurization according to claim 1, wherein the spherical core comprises the following components in percentage by weight: al: 40 to 50 percent of Al₂O₃：25％～30％，SiO₂: 7% -10%, MgO: 4% -6%, CaO: 1% -2%, rare earth oxide: 10 to 15 percent.

3. A fluorine-free iron according to claim 2The spherical slag for water desulfurization is characterized in that the rare earth oxide is CeO or La₂O₃。

4. The spherical slag for fluorine-free molten iron desulphurization according to claim 1, wherein the aluminum slag comprises the following components in percentage by mass: al: 45 to 55 percent of Al₂O₃：25％～30％，SiO₂: 9% -12%, MgO: 6-8%, CaO: 2 to 3 percent of the total weight of the composition, and the balance of impurities.

5. The spherical slag for fluorine-free molten iron desulphurization according to claim 1, wherein the rare earth oxide accounts for 10-15% of the weight of the aluminum slag.

6. The method for preparing the fluorine-free molten iron desulfurization spherical slag according to any one of claims 1 to 5, comprising the steps of:

1) melting the aluminum slag in an induction furnace;

2) adding rare earth oxide powder into molten aluminum slag in a spiral electromagnetic stirrer and stirring uniformly;

3) cooling the uniformly stirred mixture of the rare earth oxide and the aluminum slag, and preparing into spherical cores with the granularity of 1-3 mm on a crusher and a nodulizer;

4) mixing the ball cores obtained in the step 3), a binder accounting for 3-5 wt% of the total weight of the raw materials and lime powder with the granularity smaller than 1mm on a pelletizer for pelletizing until the granularity reaches 2-4 mm, and obtaining cold-made spherical slag;

5) and (3) heating the cold spherical slag in a drying oven, keeping the temperature for 30-60 min when the temperature reaches 100-120 ℃, taking out the spherical slag, and cooling the spherical slag to room temperature in an air manner to obtain the fluorine-free spherical slag for molten iron desulphurization.

7. The method of claim 6, wherein the binder is pure alcohol.

8. The method according to claim 6, wherein the spiral electromagnetic stirrer used in step 2) has a current of 250 to 300A and a frequency of 30 to 50 Hz.

9. The method for preparing the spherical slag for fluorine-free molten iron desulphurization according to claim 6, wherein the mass percent of CaO in the lime powder in the step 4) is more than or equal to 88.0%, the balance is impurities, and the activity is more than 270 ml.

Background

The KR mechanical stirring method has become an important technical means for producing high-quality steel in advanced steel mills at home and abroad gradually under the advantages of excellent dynamic conditions, deep desulfurization by adopting cheap lime as a desulfurizing agent, ultra-deep desulfurization and the like. At present, adding fluorite into lime as a catalyst in a steel mill is still a common treatment method because the main component CaF of the fluorite₂Can combine with CaO to form a eutectic melt with a low melting point to promote desulfurization, whereas CaF₂It is very important to develop a suitable desulfurization catalyst to replace fluorite because it erodes the furnace lining, pollutes the environment and is harmful to human health.

Relevant researches at home and abroad show that when molten iron contains a certain amount of Al, the desulfurization efficiency and desulfurization speed of lime can be obviously improved, and in actual production, a certain amount of aluminum slag added into CaO to serve as a catalyst has an obvious promotion effect on molten iron desulfurization. For example, in the document "application of the aluminum slag composite desulfurizer in the KR molten iron desulfurization process" (reported in the academy of iron and steel research, vol 29, No. 1 in 2017), fluorite is completely replaced by 5% by mass of aluminum slag, and the aluminum slag composite desulfurizer can obviously promote desulfurization reaction and replace fluorite to avoid corrosion of a furnace lining and environmental pollution. In addition, the aluminum slag is waste slag in the electrolytic aluminum industry, and the aluminum slag is used for purifying molten iron, so that waste materials are changed into valuable materials, and the reduction of the desulfurization cost is facilitated.

In the steel smelting process, it has been reported that the rare earth metal has a good desulfurization effect on molten iron or molten steel, but the rare metal is expensive and easily oxidized, so that the technology cannot be popularized. The rare earth oxide is also industrial waste residue, so that the problems of rare metals are avoided, and the desulfurization effect is good.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide the fluorine-free spherical slag for molten iron desulphurization and the preparation method thereof.

In order to achieve the purpose, the invention is realized by the following technical scheme:

the fluoride-free spherical slag for molten iron desulphurization is characterized by comprising a spherical core and a layer of lime coated outside the spherical core, wherein the spherical core is prepared from aluminum slag and rare earth oxide.

The core comprises the following components in percentage by weight: al: 40 to 50 percent of Al₂O₃：25％～30％，SiO₂: 7% -10%, MgO: 4% -6%, CaO: 1% -2%, rare earth oxide: 10 to 15 percent.

The rare earth oxide is CeO or La₂O₃。

The aluminum slag comprises the following components in percentage by mass: al: 45 to 55 percent of Al₂O₃：25％～30％，SiO₂: 9% -12%, MgO: 6-8%, CaO: 2 to 3 percent of the total weight of the composition, and the balance of impurities.

The rare earth oxide accounts for 10-15% of the weight of the aluminum slag.

A preparation method of the fluorine-free spherical slag for molten iron desulphurization comprises the following steps:

1) melting the aluminum slag in an induction furnace;

2) adding rare earth oxide powder into molten aluminum slag in a spiral electromagnetic stirrer and stirring uniformly;

3) cooling the uniformly stirred mixture of the rare earth oxide and the aluminum slag, and preparing into spherical cores with the granularity of 1-3 mm on a crusher and a nodulizer;

4) mixing the ball cores obtained in the step 3), a binder accounting for 3-5 wt% of the total weight of the raw materials and lime powder with the granularity smaller than 1mm on a pelletizer for pelletizing until the granularity reaches 2-4 mm, and obtaining cold-made spherical slag;

5) and (3) heating the cold spherical slag in a drying oven, keeping the temperature for 30-60 min when the temperature reaches 100-120 ℃, taking out the spherical slag, and cooling the spherical slag to room temperature in an air manner to obtain the fluorine-free spherical slag for molten iron desulphurization.

The binder is pure alcohol.

The current of the spiral electromagnetic stirrer in the step 2) is 250-300A, and the frequency is 30-50 Hz.

The mass percent of CaO in the lime powder in the step 4) is more than or equal to 88.0 percent, the balance is impurities, and the activity is more than 270 ml.

Compared with the prior art, the invention has the beneficial effects that:

1. the industrial waste aluminum slag and rare earth slag are utilized, the preparation cost is reduced, the good desulfurization effect is realized, the calcium fluoride fluxing agent commonly used in the prior molten iron desulfurization is replaced, and the erosion of a furnace lining and the environmental pollution are avoided.

2. The melting temperature range of the aluminum slag not only can ensure that the rare earth oxide powder is dispersed and distributed in the molten aluminum slag, but also can avoid the burning loss of aluminum in the aluminum slag.

3. The invention adopts the spiral electromagnetic stirrer to enable the melt to generate horizontal, vertical or two-direction simultaneous movement, so that the rare earth oxide powder is dispersed and distributed in the molten aluminum slag, and the efficiency is high and the cost is low.

4. In the invention, pure alcohol is used as a binder, and the main consideration is that CaO in the raw material is easy to absorb water and modify, so that the desulfurization capability of the slag is reduced. Therefore, the use of pure alcohol prevents the slag material from water-absorbing denaturation. In addition, the alcohol has volatility and is volatilized in the subsequent heating process of the slag, and the physical and chemical properties of the slag are not affected.

5. The invention adopts lime powder with the particle size less than 1mm as a raw material for pelletizing, thereby not only avoiding the adsorption of dust removing equipment on lime with small particle size, but also being beneficial to coating lime particles on the surface of a ball core, and further improving the desulfurization efficiency of the lime.

6. The outer calcium oxide layer of the spherical slag has the function of molten iron desulphurization, one of the functions of the aluminum slag in the spherical core is to reduce high-melting calcium silicate formed on the surface of the calcium oxide and form low-melting calcium aluminate, the other of the functions of the aluminum slag is to utilize aluminum in the aluminum slag to generate rare earth cerium for the molten iron deep desulphurization by aluminothermic reaction with the rare earth cerium oxide at the molten iron temperature, and the main purpose of forming the structure of the inner and outer layers is to further remove the sulfur in the rare earth cerium in the inner layer by contacting with the molten iron when the calcium oxide desulphurization is limited in dynamics.

7. The molten iron desulfurizer prepared by the invention not only has the advantages of low melting point, high lime activity, good desulfurization effect and the like, but also does not contain fluorine, thereby avoiding erosion of a furnace lining and environmental pollution. The method avoids forming high-melting-point silicate on the surface of lime particles, but forms low-melting-point calcium aluminate on the surface of the lime particles, and in addition, the rare earth cerium generated by thermite reaction is beneficial to deep desulfurization or the maintenance of stable terminal ultra-low sulfur content, so that the method is suitable for the deep desulfurization of molten iron of high-added-value steel such as silicon steel, pipeline steel and the like. And the preparation method is simple, easy and low in cost.

Detailed Description

The present invention is described in detail below, but it should be noted that the practice of the present invention is not limited to the following embodiments.

Example 1:

a preparation method of fluorine-free spherical slag for molten iron desulphurization comprises the following steps:

(1) melting the aluminum slag in a graphite crucible of an induction furnace, wherein the melting temperature is 850 ℃, and the main components of the aluminum slag by weight percentage are as follows: al: 46.2% of Al₂O₃：33.5％，SiO₂: 10.2%, MgO: 7.5%, CaO: 2.4 percent, and the balance of impurities.

(2) Placing the graphite crucible filled with the molten aluminum slag in a spiral electromagnetic stirrer, starting the stirrer, and adding the rare earth cerium oxide powder into the molten aluminum slag to be stirred uniformly. The mass ratio of the rare earth cerium oxide to the aluminum slag is 1: 10. The spiral electromagnetic stirring current is 250A, and the frequency is 30 Hz.

(3) And cooling the uniformly stirred mixture of the rare earth cerium oxide and the aluminum slag, and preparing a spherical core of the desulfurizer with the granularity of 1-3 mm on a crusher and a nodulizer.

(4) Mixing lime powder with the granularity of less than 1mm and ball cores with the granularity of 1-3 mm on a pelletizer for pelletizing, and taking pure alcohol accounting for 4 wt% of the total weight of the raw materials as a binder until the granularity reaches 2-4 mm to obtain the cold-made spherical slag. The mass percent of CaO in the lime is 90 percent, and the balance is impurities, and the activity is 400 ml.

(5) And (2) heating the cold spherical slag in a drying oven, keeping the temperature for 45min when the temperature reaches 120 ℃, taking out the spherical slag, and cooling the spherical slag to room temperature in an air manner to obtain the fluorine-free spherical slag for molten iron desulphurization, wherein the fluorine-free spherical slag comprises the following components in percentage by weight: al: 45.5% of Al₂O₃：26.8％，SiO₂: 8.9%, MgO: 5.3%, CaO: 1.5%, rare earth CeO: 10.2 percent, and the balance of impurities.

Example 2:

a preparation method of fluorine-free spherical slag for molten iron desulphurization comprises the following steps:

(1) melting the aluminum slag in a graphite crucible of an induction furnace, wherein the melting temperature is 870 ℃, and the aluminum slag comprises the following components in percentage by weight: al: 46.2% of Al₂O₃：33.5％，SiO₂: 10.2%, MgO: 7.5%, CaO: 2.4% and the balance impurities.

(2) Placing the graphite crucible filled with the molten aluminum slag in a spiral electromagnetic stirrer, starting the stirrer, and adding the rare earth cerium oxide powder into the molten aluminum slag to be stirred uniformly. The mass ratio of the rare earth cerium oxide to the aluminum slag is 3: 25. the spiral electromagnetic stirring current is 270A, and the frequency is 40 Hz.

(3) And cooling the uniformly stirred mixture of the rare earth cerium oxide and the aluminum slag, and preparing a spherical core of the desulfurizer with the granularity of 1-3 mm on a crusher and a nodulizer.

(4) Mixing lime powder with the granularity of less than 1mm and ball cores with the granularity of 1-3 mm on a pelletizer for pelletizing, and taking pure alcohol accounting for 4 wt% of the total weight of the raw materials as a binder until the granularity reaches 2-4 mm to obtain the cold-made spherical slag. The mass percent of CaO in the lime is 95 percent, the balance is impurities, and the activity is 420 ml.

(5) And (2) heating the cold spherical slag in a drying oven, keeping the temperature for 45min when the temperature reaches 100 ℃, taking out the spherical slag, and cooling the spherical slag to room temperature in an air manner to obtain the fluorine-free spherical slag for molten iron desulphurization, wherein the fluorine-free spherical slag comprises the following components in percentage by weight: al: 45.2% of Al₂O₃：26.2％，SiO₂: 8.3%, MgO: 5.1%, CaO: 1.2%, rare earth CeO: 12.4%, and the balance impurities.

Example 3:

a preparation method of fluorine-free spherical slag for molten iron desulphurization comprises the following steps:

(1) melting the aluminum slag in a graphite crucible of an induction furnace, wherein the melting temperature is 870 ℃, and the aluminum slag comprises the following components in percentage by weight: al: 46.2% of Al₂O₃：33.5％，SiO₂: 10.2%, MgO: 7.5%, CaO: 2.4% and the balance impurities.

(2) Placing the graphite crucible filled with the molten aluminum slag in a spiral electromagnetic stirrer, starting the stirrer, and adding the rare earth cerium oxide powder into the molten aluminum slag to be stirred uniformly. The mass ratio of the rare earth cerium oxide to the aluminum slag is 3: 20. the spiral electromagnetic stirring current is 300A, and the frequency is 50 Hz.

(3) And cooling the uniformly stirred mixture of the rare earth cerium oxide and the aluminum slag, and preparing a spherical core of the desulfurizer with the granularity of 1-3 mm on a crusher and a nodulizer.

(4) Mixing lime powder with the granularity of less than 1mm and ball cores with the granularity of 1-3 mm on a pelletizer for pelletizing, and taking pure alcohol accounting for 4 wt% of the total weight of the raw materials as a binder until the granularity reaches 2-4 mm to obtain the cold-made spherical slag. The mass percent of CaO in the lime is 95 percent, the balance is impurities, and the activity is 420 ml.

(5) And (2) heating the cold spherical slag in a drying oven, keeping the temperature for 45min when the temperature reaches 100 ℃, taking out the spherical slag, and cooling the spherical slag to room temperature in an air manner to obtain the fluorine-free spherical slag for molten iron desulphurization, wherein the fluorine-free spherical slag comprises the following components in percentage by weight: al: 44.2% of Al₂O₃：24.2％，SiO₂: 8.8%, MgO: 5.6%, CaO: 1.8%, rare earth CeO: 14.8 percent.

Example 4:

a preparation method of fluorine-free spherical slag for molten iron desulphurization comprises the following steps:

(1) melting the aluminum slag in a graphite crucible of an induction furnace, wherein the melting temperature is 900 ℃, and the aluminum slag comprises the following components in percentage by weight: al: 46.2% of Al₂O₃：33.5％，SiO₂: 10.2%, MgO: 7.5%, CaO: 2.4% and the balance impurities.

(2) Placing the graphite crucible filled with the molten aluminum slag in a spiral electromagnetic stirrer, starting the stirrer, and adding the rare earth cerium oxide powder into the molten aluminum slag to be stirred uniformly. The mass ratio of the rare earth cerium oxide to the aluminum slag is 3: 25. the spiral electromagnetic stirring current is 280A, and the frequency is 45 Hz.

(3) And cooling the uniformly stirred mixture of the rare earth cerium oxide and the aluminum slag, and preparing a spherical core of the desulfurizer with the granularity of 1-3 mm on a crusher and a nodulizer.

(4) Mixing lime powder with the granularity of less than 1mm and ball cores with the granularity of 1-3 mm on a pelletizer for pelletizing, and taking pure alcohol accounting for 4 wt% of the total weight of the raw materials as a binder until the granularity reaches 2-4 mm to obtain the cold-made spherical slag. The mass percent of CaO in the lime is 95 percent, the balance is impurities, and the activity is 420 ml.

(5) And (2) heating the cold spherical slag in a drying oven, keeping the temperature for 45min when the temperature reaches 100 ℃, taking out the spherical slag, and cooling the spherical slag to room temperature in an air manner to obtain the fluorine-free spherical slag for molten iron desulphurization, wherein the fluorine-free spherical slag comprises the following components in percentage by weight: al: 44.8% of Al₂O₃：24.3％，SiO₂: 8.7%, MgO: 5.2%, CaO: 1.5%, rare earth CeO: 14.6 percent.

Example 5:

a preparation method of fluorine-free spherical slag for molten iron desulphurization comprises the following steps:

(1) melting the aluminum slag in a graphite crucible of an induction furnace, wherein the melting temperature is 950 ℃, and the aluminum slag comprises the following components in percentage by weight: al: 46.2% of Al₂O₃：33.5％，SiO₂: 10.2%, MgO: 7.5%, CaO: 2.4% and the balance impurities.

(2) Placing the graphite crucible filled with the molten aluminum slag in a spiral electromagnetic stirrer, starting the stirrer, and adding the rare earth cerium oxide powder into the molten aluminum slag to be stirred uniformly. The mass ratio of the rare earth cerium oxide to the aluminum slag is 3: 25. the spiral electromagnetic stirring current is 250A, and the frequency is 50 Hz.

(3) And cooling the uniformly stirred mixture of the rare earth cerium oxide and the aluminum slag, and preparing a spherical core of the desulfurizer with the granularity of 1-3 mm on a crusher and a nodulizer.

(4) Mixing lime powder with the granularity of less than 1mm and ball cores with the granularity of 1-3 mm on a pelletizer for pelletizing, and taking pure alcohol accounting for 4 wt% of the total weight of the raw materials as a binder until the granularity reaches 2-4 mm to obtain the cold-made spherical slag. The mass percent of CaO in the lime is 95 percent, the balance is impurities, and the activity is 420 ml.

(5) And (2) heating the cold spherical slag in a drying oven, keeping the temperature for 45min when the temperature reaches 100 ℃, taking out the spherical slag, and cooling the spherical slag to room temperature in an air manner to obtain the fluorine-free spherical slag for molten iron desulphurization, wherein the fluorine-free spherical slag comprises the following components in percentage by weight: al: 45.1% of Al₂O₃：24.5％，SiO₂: 8.5%, MgO: 5.6%, CaO: 1.3%, rare earth CeO: 14.5 percent.

Example 6:

a preparation method of fluorine-free spherical slag for molten iron desulphurization comprises the following steps:

(1) melting the aluminum slag in a graphite crucible of an induction furnace, wherein the melting temperature is 950 ℃, and the aluminum slag comprises the following components in percentage by weight: al: 46.2% of Al₂O₃：33.5％，SiO₂: 10.2%, MgO: 7.5%, CaO: 2.4% and the balance impurities.

(2) And (3) placing the graphite crucible filled with the molten aluminum slag into a spiral electromagnetic stirrer, starting the stirrer, and adding the rare earth lanthanum oxide powder into the molten aluminum slag to be stirred uniformly. The mass ratio of the rare earth lanthanum oxide to the aluminum slag is 3: 25. the spiral electromagnetic stirring current is 250A, and the frequency is 50 Hz.

(3) And cooling the uniformly stirred mixture of the rare earth lanthanum oxide and the aluminum slag, and preparing a spherical core of the desulfurizer with the granularity of 1-3 mm on a crusher and a nodulizer.

(4) Mixing lime powder with the granularity of less than 1mm and ball cores with the granularity of 1-3 mm on a pelletizer for pelletizing, and taking pure alcohol accounting for 4 wt% of the total weight of the raw materials as a binder until the granularity reaches 2-4 mm to obtain the cold-made spherical slag. The mass percent of CaO in the lime is 95 percent, the balance is impurities, and the activity is 420 ml.

(5) And (2) heating the cold spherical slag in a drying oven, keeping the temperature for 45min when the temperature reaches 100 ℃, taking out the spherical slag, and cooling the spherical slag to room temperature in an air manner to obtain the fluorine-free spherical slag for molten iron desulphurization, wherein the fluorine-free spherical slag comprises the following components in percentage by weight: al: 45.1% of Al₂O₃：24.5％，SiO₂：8.5％，MgO：5.6％，CaO：1.3％，La₂O₃：14.3％。

The sulfur contents before and after desulfurization of molten iron in the process of using fluorine-free spherical slag of examples 1 to 6 in the KR molten iron pretreatment are shown in Table 1. As can be seen from Table 1, the final sulfur content of the molten iron is less than 10ppm, which meets the requirements of high-grade steel such as silicon steel or pipeline steel on deep desulfurization of molten iron pretreatment. In addition, the spherical slag does not contain fluorine, and has no pollution and corrosion to the environment and equipment.

TABLE 1 desulfurization effect of spherical desulfurization slag of the present invention

Type of desulfurizing agent	S before desulfurization of molten iron%	After desulfurization with desulfurization slag, percent
			Example 1	0.023	0.00089
Example 2	0.025	0.00086
			Example 3	0.028	0.00079
Example 4	0.024	0.00082
			Example 5	0.025	0.00086
Example 6	0.026	0.00076

The molten iron desulfurizer prepared by the invention not only has the advantages of low melting point, high lime activity, good desulfurization effect and the like, but also does not contain fluorine, thereby avoiding erosion of a furnace lining and environmental pollution. The method avoids forming high-melting-point silicate on the surface of lime particles, but forms low-melting-point calcium aluminate on the surface of the lime particles, and in addition, the rare earth cerium generated by thermite reaction is beneficial to deep desulfurization or the maintenance of stable terminal ultra-low sulfur content, so that the method is suitable for the deep desulfurization of molten iron of high-added-value steel such as silicon steel, pipeline steel and the like. The preparation method is simple, easy and low in cost.