CN105908218B - A kind of high pure rare earth metals and its production and use - Google Patents

Abstract

The invention relates to the field of manufacturing high-quality metal materials, in particular to a high-purity rare earth metal and its preparation method and application. The product feature of the high-purity rare earth metal is that the total content of the rare earth metal is greater than 99.5%, and the oxygen content is O≤0.02% (percentage by weight). The high-purity rare earth is obtained by electrolytic rare earth oxide or rare earth oxide fluoride salt, and solidified in a closed/protective atmosphere. The main rare earth elements of the high-purity rare earth are lanthanum and cerium. The main application fields of this high-purity rare earth cover, but are not limited to, continuous casting or die casting of high-quality steel, high-quality structural steel for equipment manufacturing, special steel, aluminum alloy, magnesium alloy and other metal materials. The invention provides additives for equipment manufacturing and high-quality iron and steel materials, purifies molten steel, refines crystal grains, deteriorates inclusions, stably improves the performance of iron and steel materials, and avoids the negative effects of rare earth additives in iron and steel materials such as coarse inclusions, blockage of nozzles, and deterioration of performance. .

Description

A kind of high-purity rare earth metal and its preparation method and application

technical field

The invention relates to the field of manufacturing high-quality metal materials, in particular to a high-purity rare earth metal and its preparation method and application.

Background technique

my country's research on the application of rare earth elements in steel began in the late 1950s. Research on the application of rare earth elements in steel has made some breakthroughs in theory and practice, and many achievements have been made in the application of rare earth elements in steel. A large number of research and production experience have shown that rare earth elements have an important impact on the structure and mechanical properties of steel and alloys. For example, rare earths have the effect of deep deoxidation and deep desulfurization. Rare earths can modify and refine inclusions. Rare earths can inhibit grain growth, thereby improving the toughness and plasticity, fatigue performance, wear resistance, corrosion resistance and heat resistance of metal materials. sex etc.

However, the biggest problem in the application of rare earth elements in steel is that rare earth elements cannot play a sustainable and stable role, and there are many negative effects. For example, in the 1970s and 1980s, large inclusions gathered during the application of a large number of rare earth steels, which caused the performance of the steel to be unstable or even deteriorated; line, and even lead to serious production accidents.

The reason is that the current domestic rare earth metal implementation standards (such as GB/T 4153-2008, etc.) do not have high requirements on the purity of rare earth metal products, which are relatively broad and cannot meet the quality requirements of rare earth metal additives for metal materials used in equipment manufacturing. This leads to problems such as unstable performance and prominent negative effects. Therefore, it is very important to invent an ultra-high-purity rare earth metal and ensure the stability and reliability of its preparation process.

Specifically, the current national standards for rare earth metal products mainly emphasize the content of impurity elements such as Mg, Zn, Pb, Fe, C, etc., and these trace elements are not very harmful to steel, and some are even the main elements in steel; Conversely, the oxygen element that has a greater impact on metal materials is not specified in the current rare earth metal standards and commercial products, resulting in the purity of rare earth metal products only one-sidedly focusing on the control of impurity elements such as Mg, Fe, C, etc. Oxygen content control is ignored. Moreover, the current commercial rare earth products are completely electrolyzed and solidified in an open environment in contact with the air, so the oxygen content in rare earth metals is often as high as 0.1% or even higher, and oxygen generally combines with rare earths to form rare earth oxides. When this part of rare earth oxide is added to steel, it will exist in the form of inclusions, thereby deteriorating the performance of steel, especially wear resistance, heat resistance, corrosion resistance and low temperature toughness. Therefore, from the perspective of rare earth metal products, how to reduce the oxygen content more effectively is crucial to improving the quality of rare earth metal products.

From the perspective of preparation technology, the existing rare earth metal preparation technology uses rare earth oxides or oxide fluoride salts as raw materials to prepare liquid rare earth metals through electrolysis, and then solidifies the rare earth metals into blocks to be commercialized. During the solidification process of rare earth metals from liquid to solid state, an open pouring and unprotected solidification process is usually adopted, and the whole process is in contact with air, which leads to serious oxidation of rare earth metals and high oxygen content. Therefore, the development of a protective rare earth metal solidification preparation process is the basis and guarantee for obtaining high-purity rare earth metal products.

Contents of the invention

The purpose of the present invention is to provide an ultra-high-purity rare earth metal and its preparation method and application, to provide additives for equipment manufacturing and high-quality steel materials, to purify molten steel, to refine grains, to improve the performance of steel materials, and to avoid rare earth Additives have negative effects such as coarse inclusions, blockage of nozzles, and deterioration of performance in steel materials.

Based on this purpose, technical scheme of the present invention is:

A high-purity rare earth metal, the total content of the rare earth metal is greater than 99.5%, and the oxygen content is O≤0.02%.

The high-purity rare earth metal is lanthanum, cerium or a mixture of lanthanum and cerium.

In the high-purity rare earth metal, the mixture of lanthanum and cerium, the mass ratio of lanthanum and cerium is 1:(1-5).

The preparation method of the high-purity rare earth metal comprises the following steps:

1) Electrolysis step: using rare earth oxides or rare earth oxide fluoride salts as raw materials, and using electrolysis to reduce the rare earth metals to a molten state;

2) Solidification step: solidify the electrolytically molten rare earth metal at a temperature above 800°C in a closed container or in a vacuum container under the protection of electrolyte or inert gas.

In the preparation method of the high-purity rare earth metal, the rare earth metal is solidified in an air-isolated environment.

In the preparation method of the high-purity rare earth metal, when the purity of the rare earth metal needs to be further improved, a vacuum induction melting furnace is used to remelt and further purify the rare earth metal.

In the preparation method of the high-purity rare earth metal, the rare earth metal is lanthanum, cerium or a mixture of lanthanum and cerium.

The use of the high-purity rare earth metal is used as an additive for continuous casting or die casting of high-quality structural steel, alloy steel, special steel, aluminum alloy or magnesium alloy.

Design idea of the present invention is:

First of all, the present invention proposes an industrially achievable high-purity rare earth metal product, whose typical characteristics are: the total content of rare earth metals is greater than 99.5%, the oxygen content is less than 0.02% (percentage by weight), and the rare earth metals are mainly lanthanum, cerium and lanthanum and cerium mixture. This is the premise and foundation to ensure that rare earth metals are used as additives in steel materials and aluminum-magnesium alloys, so that they can fully exert their beneficial effects and avoid their side effects. Secondly, the present invention provides a preparation process for high-purity rare earth metals, that is, using rare earth oxides or rare earth oxide fluoride salts as raw materials, and reducing the metals to elemental molten state by electrolysis. Then, the rare earth metal is solidified in an air-isolated environment to avoid oxidation during the solidification process, resulting in an increase in oxygen content. The way of isolating the air is to use LiF, KCl and other electrolytes for covering protection, using inert gas protection or placing molten rare earth metals in airtight or vacuum containers for solidification. When the purity of rare earth metals needs to be further improved, a vacuum induction melting furnace can be selected for remelting and deep purification of rare earth metals. The final prepared rare earth metals with low oxygen content and high purity are used as continuous casting or die casting high-quality structural steel, alloy steel, special steel (with special chemical composition, produced by special process, special structure and performance, and can meet special needs steel), and additives for metal materials such as aluminum alloys and magnesium alloys.

Advantage of the present invention and beneficial effect are:

1. Compared with the product quality requirements for rare earth metals prepared by traditional electrolytic methods, the present invention places more emphasis on the purity of rare earths, and further controls the oxygen content on the basis of the highest quality requirements for rare earth metals in the GB/T 4153-2008 standard.

2. In the preparation process of the present invention, the traditional extensive rare earth metal casting method is avoided, the liquid rare earth metal is avoided from contacting with the air, and solidified in a closed or protective atmosphere, so as to prevent the increase of rare earth metal impurity elements and the increase of oxygen content. When necessary, high-purity rare earth metals are deeply purified in a vacuum induction melting furnace.

3. The further improvement of the purity of the rare earth in the present invention can improve the quality level of the rare earth application link. For example, when the high-purity rare earth in the present invention is used in battery materials, it can further improve the stability of battery quality; when it is used in metal materials such as aluminum, magnesium, and steel, it can reduce the generation of large non-metallic inclusions and give full play to The performance-enhancing effect of rare earths.

4. When the high-purity rare earth of the present invention is used in iron and steel smelting and pouring processes, it can effectively prevent molten steel from reacting with refractory materials and air to avoid clogging of nozzles and ensure stable and smooth production.

In a word, the present invention proposes high-purity rare earth metal products higher than the requirements of national standards, and realizes the preparation of high-purity rare earth metals by controlling the solidification conditions and environment of electrolytic molten rare earth metals. When this kind of high-purity rare earth is used as an additive in the preparation of metal materials, it can avoid a series of problems such as coarse inclusions, fluctuations in material properties, and blockage of nozzles during production, and ensure the stable improvement of metal material properties.

Description of drawings

Figure 1(a)-Figure 1(b) are high-purity rare earth metals prepared by the present invention. Among them, Fig. 1(b) is an enlarged view of Fig. 1(a).

Figure 2(a)-Figure 2(b) are commercial products of rare earth metals. Wherein, Fig. 2(b) is an enlarged view of Fig. 2(a).

detailed description

In the specific implementation process, the present invention provides a kind of high-purity rare earth metal, and provides a kind of preparation process instructively, the specific content is as follows:

1. Rare earth oxides or rare earth oxide fluoride salts (rare earth oxyfluorides) are used as raw materials.

2. Electrolyze rare earth oxides or rare earth oxide fluoride salts in professional electrolysis equipment to separate and obtain liquid rare earth metals.

3. The liquid rare earth metal is poured into the mold under the protection of electrolyte or inert gas, and the liquid rare earth metal is in the electrolyte protection state (specifically covered with LiF, KCl and other electrolytes in the electrolytic cell), or inert gas protection solidification in a sealed container or in a vacuum container to create a non-polluting, non-oxidizing solidification environment for rare earth metals. In order to further improve the cleanliness of rare earth metals, the solidified high-purity rare earths can be remelted in a vacuum induction furnace for deep purification.

4. After the high-purity rare earth metal is solidified, the surface oxide skin is removed, shot blasting and sandblasting are performed, and the packaging is inspected.

5. High-purity rare earth metals can be used as additives in the preparation of aluminum, magnesium, steel and other metal materials.

In order to make the technical solutions and advantages of the present invention clearer, the following will describe in detail with reference to specific embodiments and accompanying drawings.

Example 1——Preparation of high-purity rare earth

In this embodiment, rare earth oxides (lanthanum oxide and cerium oxide) are used as raw materials, and electrolysis is carried out in a graphite electrolytic cell with an electrolysis voltage of 120V, a current of 800A, and an electrolysis time of 2 hours, to reduce the rare earth metals to a molten state at 900°C. After the electrolysis process, the molten rare earth metal is solidified under the cover of chloride salt (such as: KCl), and the obtained rare earth metal is shown in Figure 1(a)-Figure 1(b).

After analysis and detection, the contents of rare earth elements and main impurity elements are shown in Table 1.

Table 1 The main components of the high-purity rare earth metals prepared by the embodiments of the present invention (the balance is other impurity elements)

element La Ce Zn Pb o Content (wt%) 33.23 66.69 0.011 0.0095 0.0086

Comparative Example 1 - National Standard Comparison

Compared with the highest quality grade (GB/T 4153-2008 mixed rare earth metal or XB/T 216-1995 battery grade mixed rare earth metal) of the high-purity rare earth metal in the present invention, the purity is further improved, The specific comparison items are shown in Table 2.

Table 2 High-purity rare earth metal of the present invention and national standard product quality index contrast

Comparative example 2——Comparison of high-purity rare earth products

Rare earth metal commercial products are shown in Figure 2 (a)-Figure 2 (b), and Table 3 is the composition analysis and detection results of the high-purity rare earth metal components prepared by the embodiment of the present invention and existing commercial rare earth metal products. It can be seen that the product purity of this embodiment is much higher than the existing commercial product quality level.

Table 3 Comparison of high-purity rare earth metals of the present invention and commercialized rare earth metals (the balance is other impurity elements)

Example 2——Preparation of high-purity rare earth

In this example, rare earth oxide fluoride salts (lanthanum oxyfluoride and cerium oxyfluoride) were used as raw materials, and electrolysis was carried out in a graphite electrolytic cell with an electrolysis voltage of 150V, a current of 850A, and an electrolysis time of 3 hours to reduce the rare earth metal to a molten state at 1000°C. After the electrolysis process, the molten rare earth metal is solidified under the cover of fluorine salt (such as: LiF).

After analysis and detection, its rare earth element content and main impurity element content are shown in Table 4.

Table 4 The main components of the high-purity rare earth metals prepared by the embodiments of the present invention (the balance is other impurity elements)

As can be seen from the table, the product purity of this embodiment is much higher than the existing commercial product quality level.

Claims (4)

1. A preparation method for high-purity rare earth metals, characterized in that: the rare earth metals used as additives for continuous casting or die casting of high-quality structural steel, alloy steel, special steel, aluminum alloys or magnesium alloys, by weight percentage, rare earth metals The total content is greater than 99.5%, the oxygen content is O≤0.0050%, and the rare earth metal is lanthanum, cerium or a mixture of lanthanum and cerium; the preparation method of the high-purity rare earth metal includes the following steps: 1) Electrolysis step: use lanthanum, cerium rare earth oxides or lanthanum, cerium rare earth oxide fluorine salts as raw materials, and use electrolysis to reduce the rare earth metals to a molten state. The electrolysis parameters are as follows: electrolysis voltage 120V, current 800A; or, electrolysis voltage 150V, current 850A; 2) Solidification step: solidify the rare earth metal in the electrolytic molten state with a temperature above 800°C in a closed container or in a vacuum container under the protection of the electrolyte or the protection of the inert gas; finally, the oxygen content O ≤0.0050% high-purity rare earth metals. 2. The method for preparing high-purity rare earth metals according to claim 1, characterized in that: in the mixture of lanthanum and cerium, the mass ratio of lanthanum and cerium is 1:(1-5). 3. The method for preparing high-purity rare earth metals according to claim 1, characterized in that: the rare earth metals are solidified in an air-isolated environment. 4. The method for preparing high-purity rare earth metals according to claim 1, characterized in that: when the purity of the rare earth metals needs to be further improved, a vacuum induction melting furnace is used to remelt and further purify the rare earth metals.