A method for producing rare earth ferrosilicon alloy using rare earth slag

Abstract

The present invention proposes a method for producing rare earth ferrosilicon alloy using rare earth slag, which belongs to the technical field of preparing rare earth alloys by pyrometallurgy. Compared with preparing rare earth ferrosilicon alloy using rich rare earth slag as raw material, the method uses rare earth tailings and samarium reduction slag after ore dressing as raw materials, adopts carbon thermal method to smelt rare earth ferrosilicon alloy in electric arc furnace, and comprises the steps of: (1) roasting the tailings, adding coke powder and charcoal powder to grind into mixed powder, adding binder to the mixed powder, adding water to mix and make balls, and drying; (2) adding silica, carbon reducing agent, steel scraps and pellets into electric arc furnace for smelting reduction; (3) pouring the charge out of the furnace to obtain the product rare earth ferrosilicon alloy and harmless glassy tailings. The method of the present invention produces rare earth ferrosilicon alloy and produces harmless glassy tailings, so that tailings resources can be used at a high value and environmental pressure can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of preparing rare earth alloys by pyrometallurgy, and in particular relates to a method for producing rare earth ferrosilicon alloy by using rare earth slag. Background Art

[0002] Rare earth master alloys are widely used in steel production, machinery manufacturing and military production. Most of them are used as additives for steel. Their main functions in steel are dephosphorization, desulfurization, neutralization of the harmful effects of low melting point impurities, grain refinement, and improvement of the mechanical properties of steel. In cast iron, they are mainly used as spheroidizers for ductile iron, vermicular cast iron, and additives for alloy cast iron, which greatly improve the mechanical properties of various cast irons. There are many types of rare earth master alloys, mainly including rare earth ferrosilicon alloys, rare earth magnesium alloys, rare earth aluminum alloys, etc. Rare earth master alloys prepared by thermal reduction method mainly include rare earth ferrosilicon alloys, rare earth ferrosilicon magnesium alloys, rare earth ferrosilicon calcium alloys, rare earth ferrosilicon titanium alloys, etc.

[0003] There are two main thermal reduction methods for the production of rare earth ferrosilicon alloys. One is to use ferrosilicon as a reducing agent and smelt in an electric arc furnace, which is called the silicon thermal reduction method. In 1956, the Shanghai Metallurgical Research Institute of the Chinese Academy of Sciences used 75 ferrosilicon as a reducing agent in an electric arc furnace and used Baotou Iron and Steel Company's ironmaking blast furnace slag containing 4-6% REO as raw material to successfully produce rare earth ferrosilicon alloys. Baotou Steel Rare Earth Plant No. 1 first adopted this process and began to produce rare earth ferrosilicon alloys. In 1966, the Baotou Rare Earth Research Institute of the Ministry of Metallurgy successfully developed a process in which medium-poor iron ore containing rare earths and low-grade rare earth concentrate pellets were directly put into the blast furnace for de-ironization and dephosphorization, and rich slag with REO>10% was produced, and then the silicon thermal reduction method was used to smelt rare earth ferrosilicon alloys, which brought the production of rare earth ferrosilicon alloys in my country into a new stage, and the alloy cost was much lower than similar products abroad. Due to the particularity of my country's rare earth raw materials, my country has always used the silicon thermal method as the main process for producing rare earth ferrosilicon alloys before the 1990s. This process has the advantages of simple operation, high yield rate, and easy control of alloy composition, but it has disadvantages such as low rare earth element recovery rate and high residual rare earth content in the smelting slag.

[0004] Another thermal reduction method for producing rare earth ferrosilicon alloy is to use carbon as a reducing agent and smelt it in an ore-heat furnace, which is called the carbothermal reduction method. This method uses rare earth concentrate, silica, and carbonaceous reducing agent as raw materials to continuously operate in an ore-heat furnace to directly produce rare earth ferrosilicon alloy, so it is also called the "one-step method". Compared with the traditional silicon thermal method, the carbothermal method has the advantages of being able to directly reduce the metal in one step, cheap reducing agent, and less element burnout. This method also has obvious shortcomings, that is, during the alloy smelting process, rare earth carbide furnace nodules are easily formed at the bottom of the ore-heat furnace. This furnace nodule has a high melting point and is not easy to flow. It cannot be discharged from the furnace with the molten iron and is deposited on the bottom of the furnace, causing the bottom of the furnace to rise, making the furnace smelting space smaller and smaller, and the furnace must be stopped for repair.

[0005] Rare earth tailings are large-scale symbiotic and associated difficult-to-treat tailings produced after iron and rare earth selection, which contain a large amount of rare earth, fluorite, iron, niobium and other usable mineral components. The long-term stacking and backlog of tailings will cause serious pollution to the surrounding environment. Tailings wastewater aggravates soil salinization and leads to fluorine pollution of pasture; tailings dust particles are fine, causing rare earth elements to accumulate in the soil, causing environmental pollution. Rare earth tailings have considerable utilization value. Research on how to economically, reasonably and effectively recycle the useful resources in rare earth tailings can not only solve the problem of comprehensive utilization of rare earth tailings resources and generate huge economic benefits, but also effectively reduce the increasingly serious resource and environmental pressures. The rare earth raw material used in the preparation method of rare earth ferrosilicon alloy mentioned in patent CN201711024218.0 is fluorocarbon cerium concentrate with REO content greater than 55%, which is a rare earth concentrate. This method cannot be applied to low-grade rare earth tailings resources; in a method for producing rare earth ferrosilicon alloy mentioned in patent CN201810411685.7, 886 kg of smelting slag will be generated for every ton of rare earth ferrosilicon alloy product produced. Long-term stacking and backlog will cause serious pollution to the surrounding environment. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention proposes a method for producing rare earth ferrosilicon alloy using rare earth slag. In view of the comprehensive recovery and high-value utilization of rare earth tailings resources, rare earth slag is used as a low-grade rare earth resource, and a carbonaceous reducing agent, silica, steel scraps, etc. are used to enter an electric arc furnace for smelting to produce rare earth ferrosilicon alloy corresponding to the target composition, and harmless glassy tailings are generated. The present invention aims to provide a more feasible solution and solution for smelting rare earth ferrosilicon alloy using rare earth slag in a furnace, which not only reduces resource and environmental pressures, but also enables the useful elements in the tailings to be efficiently and comprehensively recycled.

[0007] The specific technical solutions of the present invention are as follows:

[0008] A method for producing rare earth ferrosilicon alloy using rare earth slag comprises the following steps:

[0009] (1) roasting rare earth slag, adding coke powder and charcoal powder, grinding into a mixed powder; adding a binder to the mixed powder, adding water and mixing to form pellets, and then drying;

[0010] (2) adding pellets, silica, carbonaceous reducing agent and steel scraps into an electric arc furnace for smelting and reduction to obtain a charge;

[0011] (3) The charge is taken out of the furnace and poured to obtain rare earth ferrosilicon alloy and harmless glassy tailings.

[0012] The rare earth slag in step (1) is rare earth tailings, or rare earth tailings and samarium reduction slag. When the rare earth slag is rare earth tailings and samarium reduction slag, the mass ratio of the rare earth tailings to the samarium reduction slag is 4:(1-1.5);

[0013] The components and mass percentages of the rare earth tailings in step (1) are RE=4%-8%, Ce / RE=50-55%, La / RE=20%-30%, Nd / RE=10%-15%, and Pr / RE=10%-15% respectively;

[0014] The components and mass percentages of the samarium reduction slag in step (1) are Sm=8-12%wt, La=55-65%wt;

[0015] The calcination temperature in step (1) is 500-600° C. and the calcination time is 3-5 h.

[0016] The binder in step (1) is one or a mixture of water glass, bentonite, pulp waste liquid, and plant starch;

[0017] When the rare earth slag is rare earth tailings, the binder is 1-5% of the mass of the mixed powder; when the rare earth slag is rare earth tailings and samarium reduction slag, the binder is 3-5% of the mass of the mixed powder;

[0018] The particle size of the coke powder in step (1) is 5-30 mm, and the fixed carbon content is ≥ 75%;

[0019] The charcoal powder in step (1) has a fixed carbon content of ≥75%, a volatile matter of ≤12%, and an ash content of ≤12%;

[0020] The total mass of the coke powder and the charcoal powder in step (1) is 10-25% of the rare earth slag; the mass ratio of the coke powder to the charcoal powder is 2:1;

[0021] The drying temperature in step (1) is 100-120° C. and the drying time is 1-2 h. The moisture content of the pellets after drying is ≤4%. When the pellets fall freely from a height of 1.5-2 m onto a cement floor, the pellets are not crushed.

[0022] The silica in step (2) has a particle size of 5-20 mm and a SiO2 content of ≥ 98%;

[0023] The carbonaceous reducing agent in step (2) is one or a mixture of coke, semi-coke, gas coke, petroleum coke, charcoal, and wood blocks, wherein the fixed carbon content is ≥75%;

[0024] The mass percentages of the pellets, silica, carbonaceous reducing agent and steel scraps in step (2) are: pellets (40-50%), silica (20-30%), carbonaceous reducing agent (15-20%), and steel scraps (10-15%);

[0025] The smelting reduction in step (2) is specifically to put the charge into an electric arc furnace for smelting reduction at 1500-2000°C;

[0026] The step (3) of pouring out of the furnace specifically comprises pouring all the molten charge into an ingot mold to separate the slag from the iron;

[0027] In step (3), Si in the rare earth ferrosilicon alloy is 30-40%wt, and the balance is iron, wherein when the rare earth slag is rare earth tailings, Re is 10-15%wt, and when the rare earth slag is rare earth tailings and samarium reduction slag, Re is 15-20%wt;

[0028] The smelting slag separated in step (3) is harmless glassy tailings, and its components and mass contents are SiO2=40-45%wt, Al2O3=30-35%wt, MgO=3-5%wt, Fe=1-3%wt, wherein, when the rare earth slag is rare earth tailings, CaO=25-30%wt, and when the rare earth slag is rare earth tailings and samarium reduction slag, CaO=20-25%wt.

[0029] The technical principle of the present invention is:

[0030] 1. The rare earth content in rare earth tailings is about 4-8%, which can be used as low-grade rare earth raw materials. Carbon thermal reduction smelting can achieve the production of rare earth ferrosilicon alloy with a rare earth content of about 10-15%. As a method for producing rare earth ferrosilicon alloy, carbon thermal method has the advantages of cheaper reducing agent, less element burnout, and can directly reduce metal in one step compared with traditional silicon thermal method.

[0031] 2. The carbon thermal method for producing rare earth ferrosilicon alloy can be mainly described as two processes, namely, silicon dioxide is reduced to silicon by carbon and silicon monoxide is carbonized with rare earth compounds to form carbides and rare earth carbides are reduced to rare earth metals by silicon monoxide.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] 1. Compared with the traditional method of using rare earth concentrate as raw material, the present invention uses rare earth slag (rare earth content is about 4-8%) as smelting raw material, and produces rare earth ferrosilicon alloy with rare earth content of 10-15% and silicon content of 30-40% through the proportion of silica, carbonaceous reducing agent and steel scraps. The use of low-grade rare earth tailings can not only comprehensively recycle the useful elements therein, realize the high-value utilization of tailings, and reduce resource and environmental pressures; but also explore new raw materials and new processes for carbon thermal smelting rare earth ferrosilicon alloys.

[0034] 2. The present invention adopts the carbon thermal reduction method to smelt rare earth ferrosilicon alloy in an electric arc furnace, which can realize direct reduction of metal, reduce element burning loss, and improve rare earth recovery rate.

[0035] 3. The tailings produced in the production process of the present invention are harmless glassy tailings, and the composition thereof is SiO2=40-45%wt, Al2O3=30-35%wt, MgO=3-5%wt, and Fe=1-3%wt. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention provides a process flow chart of a method for producing rare earth ferrosilicon alloy using rare earth tailings. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the embodiments.

[0038] The components and mass percentages in the rare earth tailings in the embodiment of the present invention are RE=4%-8%, Ce / RE=50-55%, La / RE=20%-30%, Nd / RE=10%-15%, Pr / RE=10%-15%; the components and mass percentages in the samarium reduction slag are Sm=8-12%wt, La=55-65%wt;

[0039] The binder is one or a mixture of water glass, bentonite, pulp waste liquid, and plant starch;

[0040] The silica particle size is 5-20mm, and the SiO2 content is ≥98%;

[0041] The carbonaceous reducing agent is one or a mixture of coke, semi-coke, gas coke, petroleum coke, charcoal, and wood blocks, wherein the fixed carbon content is ≥ 75%;

[0042] The rare earth ferrosilicon alloy prepared in this embodiment contains Si=30-40%wt, and the balance is iron. When the rare earth slag is rare earth tailings, Re=10-15%wt, and when the rare earth slag is rare earth tailings and samarium reduction slag, Re=15-20%wt. The smelting slag obtained by separation is harmless glassy tailings, and its components and mass contents are SiO2=40-45%wt, Al2O3=30-35%wt, MgO=3-5%wt, and Fe=1-3%wt. When the rare earth slag is rare earth tailings, CaO=25-30%wt, and when the rare earth slag is rare earth tailings and samarium reduction slag, CaO=20-25%wt.

[0043] Example 1

[0044] Process flow chart Figure 1As shown, the charge for alloy smelting is: rare earth tailings, carbonaceous reducing agent, silica, steel scraps. The total weight of the charge is 100%, and the charge composition is: rare earth tailings about 68%, carbonaceous reducing agent about 11% (fixed carbon content ≥ 75%), silica about 12% (SiO2 ≥ 98%), steel scraps about 9%. The binder water glass is about 5%.

[0045] The following steps are involved:

[0046] (1) The rare earth tailings are roasted at 550° C. for 3 h, and then 10% of the weight of the rare earth tailings is added with coke powder and charcoal powder to grind into a mixed powder, and then a binder accounting for 5% of the total weight of the mixed powder is added to the mixed powder, and then water is added to mix and make balls, and then dried at 100° C. for 2 h;

[0047] (2) adding silica, coke, steel scraps and pellets into an electric arc furnace for smelting reduction at 1500°C;

[0048] (3) The charge is taken out of the furnace and poured to obtain the product rare earth ferrosilicon alloy and harmless glassy tailings.

[0049] Example 2

[0050] The charge for alloy smelting is: rare earth tailings, carbonaceous reducing agent, silica, steel scraps. The total weight of the charge is 100%, and the charge composition is: rare earth pellets are about 66%, carbonaceous reducing agent is about 13% (fixed carbon content ≥ 75%), silica is about 14% (SiO2 ≥ 98%), steel scraps are about 7%, and the binder water glass is about 2%.

[0051] The following steps are involved:

[0052] (1) The rare earth tailings are roasted at 500° C. for 4 h, and then 15% of the weight of the rare earth tailings is added with coke powder and charcoal powder to grind into a mixed powder, and then a binder accounting for 5% of the total weight of the mixed powder is added to the mixed powder, and then water is added to mix and make balls, and then dried at 110° C. for 1 h;

[0053] (2) adding silica, charcoal, steel scraps and pellets together into an electric arc furnace for smelting reduction at 2000°C;

[0054] (3) The charge is taken out of the furnace and poured to obtain the product rare earth ferrosilicon alloy and harmless glassy tailings.

[0055] Example 3

[0056] The charge for alloy smelting is: rare earth tailings, carbonaceous reducing agent, silica, and steel scraps. The total weight of the charge is 100%, and the charge composition is: rare earth pellets are about 64%, carbonaceous reducing agent is about 14% (fixed carbon content ≥ 75%), silica is about 17% (SiO2 ≥ 98%), and steel scraps are about 5%. Among them, the rare earth tailings in the rare earth pellets are about 85%, coke is about 10% (fixed carbon content ≥ 75%), and the binder water glass is about 5%.

[0057] The following steps are involved:

[0058] (1) The rare earth tailings are roasted at 600°C for 4 hours, and then coke powder and charcoal powder accounting for 20% of the weight of the rare earth tailings are added and ground into a mixed powder. A binder accounting for 5% of the total weight of the mixed powder is added to the mixed powder, and then water is added to mix and make balls, and the mixture is dried at 100°C for 2 hours;

[0059] (2) adding silica, coke and charcoal, steel scraps and pellets into an electric arc furnace for smelting and reduction at 1800°C;

[0060] (3) The charge is taken out of the furnace and poured to obtain the product rare earth ferrosilicon alloy and harmless glassy tailings.

[0061] Example 4

[0062] The charge for alloy smelting is: rare earth tailings, carbonaceous reducing agent, silica, and steel scraps. The total weight of the charge is 100%, and the charge composition is: rare earth pellets are about 64%, carbonaceous reducing agent is about 14% (fixed carbon content ≥ 75%), silica is about 17% (SiO2 ≥ 98%), and steel scraps are about 5%. Among them, the rare earth tailings in the rare earth pellets are about 85%, coke is about 10% (fixed carbon content ≥ 75%), and the binder water glass is about 5%.

[0063] The following steps are involved:

[0064] (1) The rare earth tailings are roasted at 550° C. for 4 h, and then 15% of the weight of the rare earth tailings is added with coke powder and charcoal powder, and ground into a mixed powder. A binder accounting for 3% of the total weight of the mixed powder is added to the mixed powder, and then water is added to mix and make balls, and the mixture is dried at 110° C. for 1 h;

[0065] (2) adding silica, charcoal, steel scraps and pellets together into an electric arc furnace for smelting reduction at 2000°C;

[0066] (3) The charge is taken out of the furnace and poured to obtain the product rare earth ferrosilicon alloy and harmless glassy tailings.

[0067] Example 5

[0068] The charge for alloy smelting is: rare earth tailings and samarium reduction slag, carbonaceous reducing agent, silica, and steel scraps. The total weight of the charge is 100%, and the charge composition is: rare earth pellets are about 43% (the weight ratio of rare earth tailings to samarium reduction slag is 4:1), carbonaceous reducing agent is about 17% (fixed carbon content ≥75%), silica is about 24% (SiO2 ≥98%), and steel scraps are about 15%. The rare earth pellets contain about 75% rare earth raw materials, about 20% coke (fixed carbon content ≥75%), and about 5% binder water glass. The specific steps are the same as in Example 1.

[0069] Example 6

[0070] The charge for alloy smelting is: rare earth tailings and samarium reduction slag, carbonaceous reducing agent, silica, and steel scraps. The total weight of the charge is 100% for batching, and the charge composition is: rare earth pellets are about 46% (the weight ratio of rare earth tailings to samarium reduction slag in Bayan Obo is 4:1), carbonaceous reducing agent is about 16% (fixed carbon content ≥75%), silica is about 27% (SiO2 ≥98%), and steel scraps are about 11%. The rare earth pellets contain about 75% rare earth raw materials, about 20% coke (fixed carbon content ≥75%), and about 5% binder water glass. The specific steps are the same as in Example 2.

[0071] Example 7

[0072] The charge for alloy smelting is: rare earth tailings and samarium reduction slag, carbonaceous reducing agent, silica, and steel scraps. The total weight of the charge is 100% for batching, and the charge composition is: rare earth pellets are about 50% (the weight ratio of rare earth tailings to samarium reduction slag in Bayan Obo is 4:1), carbonaceous reducing agent is about 16% (fixed carbon content ≥75%), silica is about 21% (SiO2 ≥98%), and steel scraps are about 13%. The rare earth pellets contain about 75% rare earth raw materials, about 20% coke (fixed carbon content ≥75%), and about 5% binder water glass. The specific steps are the same as in Example 3.

[0073] Example 8

[0074] The charge for alloy smelting is: rare earth tailings and samarium reduction slag, carbonaceous reducing agent, silica, and steel scraps. The total weight of the charge is 100% for batching, and the charge composition is: rare earth pellets are about 50% (the weight ratio of rare earth tailings to samarium reduction slag in Bayan Obo is 4:1), carbonaceous reducing agent is about 16% (fixed carbon content ≥75%), silica is about 21% (SiO2 ≥98%), and steel scraps are about 13%. The rare earth pellets contain about 75% rare earth raw materials, about 20% coke (fixed carbon content ≥75%), and about 5% binder water glass. The specific steps are the same as in Example 3. The specific steps are the same as in Example 4.

Claims

1. A method for producing rare earth ferrosilicon alloy using rare earth slag, characterized in that: The steps include: (1) The rare earth slag is roasted, and then coke powder and charcoal powder are added and ground into a mixed powder; a binder is added to the mixed powder to form a pellet, and then dried; (2) adding pellets, silica, carbonaceous reducing agent and steel scraps into an electric arc furnace for smelting and reduction to obtain furnace charge; (3) The charge is taken out of the furnace and poured to obtain rare earth ferrosilicon alloy and harmless glassy tailings; In the step (1), the rare earth slag is rare earth tailings, or rare earth tailings and samarium reduction slag; when the rare earth slag is rare earth tailings and samarium reduction slag, the mass ratio of the rare earth tailings to the samarium reduction slag is 4:(1-1.5); In the step (3), Si in the rare earth ferrosilicon alloy composition is 30-40%wt, and the balance is iron, wherein, when the rare earth slag is rare earth tailings, Re is 10-15%wt, and when the rare earth slag is rare earth tailings and samarium reduction slag, Re is 15-20%wt; the components and mass contents of the harmless glassy tailings are, SiO2=40-45%wt, Al2O3=30-35%wt, MgO=3-5%wt, Fe=1-3%wt, wherein, when the rare earth slag is rare earth tailings, CaO=25-30%wt, and when the rare earth slag is rare earth tailings and samarium reduction slag, CaO=20-25%wt.

2. The method for producing rare earth ferrosilicon alloy using rare earth slag according to claim 1, characterized in that: The components and mass percentages in the rare earth tailings in step (1) are RE=4%-8%, Ce / RE=50-55%, La / RE=20%-30%, Nd / RE=10%-15%, and Pr / RE=10%-15%; the components and mass percentages in the samarium reduction slag are Sm=8-12%wt, La=55-65%wt.

3. The method for producing rare earth ferrosilicon alloy using rare earth slag according to claim 1, characterized in that: The calcination temperature of the calcination in step (1) is 500-600°C, and the calcination time is 3-5h; the total mass of the coke powder and the charcoal powder is 10-25% of the rare earth slag, and the mass ratio of the coke powder to the charcoal powder is 2:1; the particle size of the coke powder is 5-30mm, and the fixed carbon content is ≥75%; the fixed carbon content of the charcoal powder is ≥75%, the volatile matter is ≤12%, and the ash content is ≤12%.

4. The method for producing rare earth ferrosilicon alloy using rare earth slag according to claim 1, characterized in that: The binder in step (1) is one or a mixture of water glass, bentonite, pulp waste liquid, and plant starch; when the rare earth slag is rare earth tailings, the binder is 1-5% of the mass of the mixed powder; when the rare earth slag is rare earth tailings and samarium reduction slag, the binder is 3-5% of the mass of the mixed powder.

5. The method for producing rare earth ferrosilicon alloy using rare earth slag according to claim 1, characterized in that: The drying temperature in step (1) is 100-120° C. and the drying time is 1-2 hours. The moisture content of the pellets after drying is ≤4%. The pellets are not crushed when they fall freely from a height of 1.5-2 meters to a cement floor.

6. The method for producing rare earth ferrosilicon alloy using rare earth slag according to claim 1, characterized in that: The silica particle size in step (2) is 5-20 mm, wherein the SiO2 content is ≥ 98%; the carbonaceous reducing agent is one or a mixture of coke, semi-coke, gas coke, petroleum coke, charcoal, and wood blocks, wherein the fixed carbon content is ≥ 75%; the mass percentages of the pellets, silica, carbonaceous reducing agent, and steel chips are as follows: pellets 40-50%, silica 20-30%, carbonaceous reducing agent 15-20%, and steel chips 10-15%.

7. The method for producing rare earth ferrosilicon alloy using rare earth slag according to claim 1, characterized in that: The smelting reduction in step (2) specifically involves placing the charge into an electric arc furnace for smelting reduction at 1500-2000°C.

8. The method for producing rare earth ferrosilicon alloy using rare earth slag according to claim 1, characterized in that: The step (3) of pouring out of the furnace is specifically to pour all the molten charge into the ingot mold to separate the slag and iron.

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