JP2002180145A - Method for producing high purity metallic vanadium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new method for obtaining high purity vanadium and the powder thereof at a low cost. SOLUTION: In the method for obtaining metallic vanadium by reducing vanadium pentoxide, at first, vanadium pentoxide as the raw material is heated in the coexistence of hydrogen and is reduced into lower oxide such as vanadium trioxide and vanadium monoxide. The obtained lower oxide is mixed with calcium or magnesium, and the mixture is heated at <=690 deg.C to cause a reduction reaction, and, from the obtained reduced product, metallic vanadium is separated and recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-purity vanadium used as a raw material of a hydrogen storage alloy and a method for producing the powder at a low cost.

[0002]

2. Description of the Related Art Hydrogen storage alloys are currently being studied by many organizations as storage tanks for hydrogen energy, which are attracting attention as an alternative to petroleum energy, and as anode materials for nickel-metal hydride batteries for automobiles. Of these, vanadium has a very high theoretical hydrogen storage capacity of 3.8 wt% and can absorb and release hydrogen at room temperature, and is therefore expected to be an alloy system that can be replaced with the current mainstream LaNi5 alloy.

[0003] When vanadium is used as a hydrogen storage alloy, its impurity becomes a problem. That is, it is known that oxygen and aluminum in vanadium greatly reduce the hydrogen storage capacity. Therefore, when vanadium is used as the hydrogen storage alloy, high-purity metal vanadium is required. However, it is well known that metal vanadium is one of the most difficult to purify.

Conventionally, vanadium metal has been prepared by first mixing vanadium pentoxide and aluminum, placing the resulting mixture in a refractory crucible, heating the entire crucible in a heating furnace, igniting the mixture from the outside, and performing a thermite reaction. To get it up. Since the obtained metal vanadium contains many impurities such as aluminum and oxygen used in the thermite reaction, the metal vanadium was repeatedly purified by repeatedly dissolving and solidifying the metal vanadium by an electron beam melting method or the like. Since high-purity vanadium can be obtained in this way, it must be very expensive. In order to obtain a hydrogen storage alloy using the metal vanadium thus obtained, it is necessary to make the metal vanadium into a powder, which also increases the price.

[0005] As a means of improving these problems to some extent, the use of calcium or magnesium instead of aluminum has been studied. However, these metals have a higher vapor pressure than aluminum and are more likely to bump, and are open to the atmosphere. If the reduction operation is performed under the following conditions, steam will be scattered by the reduction heat and cannot be reduced, and if performed in an airtight container, the inside of the container will be at a high pressure and there is a danger of explosion. Was very difficult to reduce.

It is already known that even if V205 is reduced by heating in hydrogen gas, only V20 is reduced and the target metal vanadium cannot be obtained.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel method for obtaining high-purity vanadium and its powder at low cost.

[0008]

The inventors of the present invention have made various investigations to solve the above-mentioned problems of the prior art, and as a result, it was possible to obtain a high-purity metal vanadium at a lower cost by dividing the reduction into two stages. The present invention has been found.

[0009] That is, the present invention for solving the above-mentioned problems,
In the method of reducing vanadium pentoxide to obtain metal vanadium, first, vanadium pentoxide as a raw material is heated in the presence of hydrogen to reduce it to a lower oxide such as divanadium trioxide or vanadium monoxide. The oxide is mixed with calcium or magnesium, heated to cause a reduction reaction, and metal vanadium is separated and recovered from the obtained reduction product.

In the present invention, when the vanadium pentoxide is reduced by heating in the coexistence of hydrogen, it is preferable that the vanadium pentoxide is heated to 690 ° C. or less to convert the vanadium pentoxide to divanadium trioxide.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The purity of vanadium pentoxide used in the present invention is not particularly limited, but is preferably as high as possible in consideration of the purity when used as a hydrogen storage alloy. The temperature for heating in a hydrogen stream is not particularly limited, but it is preferable to heat at a melting point of 690 ° C. or less of vanadium pentoxide in order to obtain powdery high-purity vanadium. However, once vanadium pentoxide has been reduced to divanadium trioxide, the reaction can be promoted by heating to above this temperature. This is because the melting point of vanadium trioxide is as high as 1970 ° C.

In the present invention, the two-stage reduction reaction is performed by obtaining a lower oxide having a higher melting point than vanadium pentoxide in the first stage reduction, and using this to form a vanadium by a thermite reaction using calcium or magnesium. This is because by reducing, vanadium pentoxide can be more efficiently reduced to metal vanadium than by directly reducing the vanadium pentoxide with calcium or magnesium by a thermite reaction.

After completion of the reaction, the reaction products calcium oxide and magnesium oxide and unreacted calcium and magnesium can be efficiently removed by washing with water or a weakly acidic solution. As a result, high-purity metal vanadium powder can be obtained more easily than in the case of using aluminum, and it is not necessary to perform the refining process of repeating melting and solidification using an electron beam, and the crushing process of the coagulated material obtained in the refining process. Become.

[0014]

EXAMPLES (Example 1) 100 g of vanadium pentoxide powder
Was reduced at a temperature and for a time shown in Table 1 in a hydrogen stream flowing at 100 ml / min, and a sample was taken out.
0 g and placed in a magnetic crucible.

This was further placed in a stainless steel container with a lid, and heated in an Ar gas stream under the conditions shown in Table 1. The obtained reduced product was washed with water until the washing liquid became neutral. After solid-liquid separation, impurities of metallic vanadium, which is a reduction product, were analyzed. The results are shown in Table 1 together with the product morphology.

Example 2 Instead of Ca, 49 g of Mg
Was used and a vanadium metal was obtained in the same manner as in Example 1 except that the obtained reduced product was washed with a 1N hydrochloric acid solution until the washing solution became neutral. After solid-liquid separation, impurities of metallic vanadium, which is a reduction product, were analyzed. The results are shown in Table 1 together with the product morphology.

(Example 3) As shown in Table 1, the hydrogen reduction conditions were as follows: heating at 650 ° C. for 1 hour, then heating at 800 ° C. for 2 hours, and heating in Ar at 1000 ° C. for 2 hours.
Metal vanadium was obtained in the same manner as in Example 1 except that the above conditions were used. After solid-liquid separation, impurities of metallic vanadium, which is a reduction product, were analyzed. Table 1 shows the results together with the product morphology.
It was shown to.

Example 4 As shown in Table 1, the hydrogen reduction conditions were heating at 600 ° C. for 3 hours, and 40 g of Ca and Mg
Metal vanadium was obtained in the same manner as in Example 2 except that 25 g was used as a reducing agent, and the heating conditions in Ar were changed to 1000 ° C. and 2 hours. After solid-liquid separation, impurities of metallic vanadium, which is a reduction product, were analyzed. The results are shown in Table 1 together with the product morphology.

Example 5 As shown in Table 1, the hydrogen reduction conditions were heating at 650 ° C. for 1 hour, 100 g of Mg was used as a reducing agent, and the heating conditions in Ar were 1000
A metal vanadium was obtained in the same manner as in Example 2 except that the temperature was set to 6 ° C. After solid-liquid separation, impurities of metallic vanadium, which is a reduction product, were analyzed. The results are shown in Table 1 together with the product morphology.

(Example 6) Mg 49 g instead of Ca
Is used as steam, the hydrogen reduced product is placed in a stainless steel container, and M
g was prepared separately from the magnesia container, and the obtained reduced product was washed with a 1N hydrochloric acid solution until the washing liquid became neutral, in the same manner as in Example 1 to obtain metal vanadium. After solid-liquid separation, impurities of metallic vanadium, which is a reduction product, were analyzed. Table 1 shows the results together with the product morphology.
It was shown to.

(Comparative Example 1) Ca without hydrogen reduction
A reaction product was obtained in the same manner as in Example 1 except that 110 g and 100 g of vanadium pentoxide were mixed and externally ignited to carry out a thermite reaction. When the reduction product was examined after solid-liquid separation, no metal vanadium was produced.

Comparative Example 2 Al was reduced without performing hydrogen reduction.
75 g and 100 g of vanadium pentoxide were mixed and externally ignited to perform a thermite reaction. Thereafter, the obtained reaction product was washed with a 1N hydrochloric acid solution to obtain a massive metal vanadium. The impurity analysis of this metal vanadium was performed.
The results are shown in Table 1 together with the product morphology.

Table 1 Metal reduction Impurity concentration / wt% Hydrogen reduction condition Element weight / g Heating temperature Oxygen reduced metal Product form Example 1 650 ° C. × 1 hr Ca 80 1200 ° C. × 3 hr 0.05 <0.01 Powder Example 2 650 ° C. × 1hr Mg 49 1200 ° C × 3hr 0.05 0.02〃 Example 3 650 ° C × 1hr Ca 50 1000 ° C × 2hr 0.04 <0.01〃 → 800 ° C × 2hr Example 4 600 ° C × 3hr Ca 40 1150 ° C × 2hr 0.05 0.02〃 Mg 25 Example 5 650 ° C. × 1 hr Mg 100 1000 ° C. × 6 hr 0.07 0.02 powder Example 6 650 ° C. × 1 hr Mg 50 1200 ° C. × 6 hr 0.06 0.01 Powder (steam) Comparative Example 1 None Ca 110 External ignition Metal vanadium not generated Compare Example 2 None A1 75 External ignition 1.00 0.10 lump

[0024]

As described above, high-purity vanadium metal can be obtained by using hydrogen and reduction of Ca and Mg together. In addition, since a subsequent purification step by electron beam melting as in the case of A1 reduction is not required, the conventional 1/1
It became possible to produce high-purity vanadium and its powder at a cost of 20.

Claims (2)

[Claims] In a method for obtaining metal vanadium by reducing vanadium pentoxide, first, vanadium pentoxide as a raw material is heated in the presence of hydrogen to reduce it to a lower oxide such as divanadium trioxide or monadium monoxide. A method for producing high-purity metal vanadium, comprising mixing the obtained lower oxide with calcium or magnesium, heating to cause a reduction reaction, and separating and recovering metal vanadium from the obtained reduction product. 2. The method according to claim 1, wherein the vanadium pentoxide is heated and reduced at 690 ° C. or less to convert the vanadium pentoxide to divanadium trioxide in the presence of hydrogen.