JP7220102B2 - Bismuth purification method - Google Patents

Description

The present invention relates to a method for purifying bismuth.

A method of refining bismuth by subjecting crude lead obtained from a blast furnace to electrolytic treatment and chlorination treatment is known (Patent Document 1, etc.).

JP 2012-77343 A

In the chlorination treatment, impurities such as lead are removed by blowing chlorine gas into molten bismuth to refine the bismuth anode. In order to improve the production capacity of bismuth anodes, it is important to increase the reaction efficiency between chlorine gas and molten bismuth in the chlorination process.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for purifying bismuth that can improve reaction efficiency in chlorination.

A method for purifying bismuth according to the present invention includes the step of chlorinating the molten bismuth by blowing chlorine gas into the molten bismuth containing impurities that form chlorides, and the melting temperature of the molten bismuth is 400 ° C. or higher. and then lowering the melting temperature by 30° C. or more to form a solid chloride on the surface of the molten bismuth, and the chlorine gas is supplied to the molten bismuth whose surface is covered with the solid chloride. It is characterized by blowing .

In this case, the chlorine gas may be blown into the bismuth melt whose surface is covered with chloride.

Also, the chloride may cover the location of the chlorine gas blowing.

Also, the chloride may cover 33% or more of the surface area of the bismuth melt.

In addition, the chloride-forming impurity may be at least one of lead, silver, zinc, and magnesium.

Further, the chlorine gas may be blown into the molten bismuth from a depth of 200 mm or more on the basis of the surface of the molten bismuth. A lance is placed in the center of the furnace in which the molten bismuth is stored, the end of the lance is submerged to a depth of 200 mm or more based on the surface of the molten bismuth, and the chlorine gas is blown into the molten bismuth from the lance. It's okay.

According to the method for purifying bismuth according to the present invention, it is possible to improve the reaction efficiency in the chlorination treatment.

FIG. 1 is a diagram illustrating a method for purifying bismuth. FIG. 2(a) is a cross-sectional view illustrating the furnace, and FIG. 2(b) is a plan view illustrating the furnace.

The bismuth molten metal containing impurities that form chlorides in the present invention is not limited as long as it is a raw material containing a large amount of bismuth and contains impurities that form chlorides. The process by which a bismuth melt containing impurities that form chlorides from metals is produced is described below.

FIG. 1 is a diagram illustrating a method for purifying bismuth. As shown in FIG. 1, the method for purifying bismuth includes, in order, a lead electrolysis process, a reduction treatment in a reduction furnace, a volatilization process in a volatilization furnace, a chlorination treatment in a chlorination furnace, a bismuth electrolysis process, and a treatment in a melting furnace. A molten bismuth is obtained by melting for chlorination. The lead electrolytic precipitates contain impurities such as lead that form chlorides by chlorination. An example of the composition of the bismuth melt containing impurities that form chlorides in such a process is bismuth (Bi) 70-95%, other impurities 5-30%, among which lead (Pb) is 5-20%. Impurities that form chlorides in the present invention include lead (Pb), silver (Ag), magnesium (Mg) and zinc (Zn). Molten metal is cast from chlorinated bismuth (Bi), and a product ingot is obtained through an electrolysis process and a melting furnace.

In the lead electrolysis step, lead electrolytic precipitates are obtained by electrolytically treating crude lead obtained from the blast furnace. In general, lead electrolytic precipitates contain lead (Pb), bismuth, antimony (Sb) and precious metals derived from copper ore. A sulfamic acid solution, for example, is used as the electrolytic solution, a crude lead plate is used as the anode electrode, and a SUS plate is used as the cathode electrode.

The lead electrolytic precipitate is dried in a drying oven. The dried lead electrolytic deposits are reduced in a reducing furnace to form metal. As a reduction condition, for example, coke is added to the lead electrolytic precipitate.

The metal is put into a volatilization furnace and treated with soda to remove arsenic in the metal as sodium arsenate (Na ₃ AsO ₄ ). After the soda treatment, the metal is melted at, for example, 630-680.degree. Antimony is volatilized as Sb ₂ O ₃ by blowing air onto the slag on the surface of the molten metal and recovered.

The metal is put into a chlorination furnace, and chlorine gas is blown into the molten bismuth for chlorination.

FIG. 2(a) is a cross-sectional view illustrating the furnace, and FIG. 2(b) is a plan view illustrating the furnace. The chlorination furnace 10 is not limited to this shape, and may have an elliptical or rectangular plane. The size of the chlorination furnace 10 is also not limited. For example, a circular furnace has a diameter of 0.5 m to several meters and a depth of 1 m to several meters. A bismuth melt 12 is stored in the chlorination furnace 10 having such a size.

One end of the lance 14 is submerged in the bismuth melt 12 and chlorine gas is blown into the bismuth melt through the lance 14 . The diameter of the lance 14 is, for example, 7 mm. Lance 14 is located, for example, in the center of chlorination furnace 10 . The position of the end of the lance 14, that is, the chlorine gas blowing position, is at a depth of 200 mm or more and 300 mm or less from the surface of the molten bismuth.

In the chlorination treatment, lead in the molten bismuth reacts with chlorine to generate chloride (lead chloride (PbCl ₂ ) 16). The lead chloride 16 is film-like and covers the surface of the molten bismuth. 33% or more of the surface area (top surface area) of the molten bismuth is covered with lead chloride 16 . Also, the lead chloride 16 is formed around the lance 14 and covers the upper side of the chlorine gas blowing position.

The temperature of the molten bismuth is controlled in the chlorination process. For example, after the lead chloride 16 solid is generated, the temperature is raised to above the melting point of the lead chloride 16, such as 400° C. or above, as the melting temperature. This causes the lead chloride 16 to liquefy and form a film on the surface of the molten bismuth 12 . Thereafter, by lowering the temperature from the melting temperature by 30° C. or more, film-like solid lead chloride 16 is formed on the surface of the molten bismuth as shown in FIGS. 2(a) and 2(b). Since the lead chloride 16 functions as a lid covering the molten bismuth, chlorine gas is less likely to diffuse from the molten bismuth 12 to the outside, improving the reaction efficiency of the chlorination treatment.

The chlorination treatment yields slag and a bismuth (Bi) anode. Chloride slag contains lead, silver, etc., and is removed from the Bi anode. By subjecting the Bi anode to the Bi electrolysis step, an electrodeposit of Bi and precipitates of Ag are obtained.

The electrodeposit is put into a melting furnace to produce a Bi ingot. Bismuth can be purified by the above steps. Also, precipitates are recovered as valuable metals by a known method.

According to this embodiment, in the chlorination treatment, the molten bismuth 12 is heated to a melting temperature of 400° C. or higher, and then lowered from the melting temperature by 30° C. or higher. This forms lead chloride 16 covering the surface of the molten bismuth 12 . The lead chloride 16 serves as a lid, and the chlorine gas remains in the molten bismuth 12, thereby improving the reaction efficiency of the chlorination treatment.

The lead chloride 16 preferably covers the chlorine gas blowing position. For example, lead chloride 16 covers the circumference of the lance 14 for a width of 45 mm. As a result, diffusion of chlorine gas blown from the lance 14 is suppressed by the lead chloride 16, and the reaction efficiency is further increased.

The lead chloride 16 preferably covers 33% or more of the surface area of the molten bismuth 12 . Chlorine gas becomes difficult to separate from the bismuth molten metal 12, and the reaction efficiency is improved. By covering the entire surface of the molten bismuth 12 with lead chloride 16, the reaction efficiency is further increased.

A plurality of lead chlorides 16 may float on the surface of the molten bismuth 12, or one lead chloride 16 may be formed. As shown in FIGS. 2(a) and 2(b), it is preferable to form lead chloride 16 which is large and has few holes. Desorption of chlorine gas is more effectively suppressed, and reaction efficiency is further improved. By changing the temperature of the molten bismuth 12 in the chlorination treatment from 500° C. or more to less than 500° C., lead chloride 16 as shown in FIGS. 2(a) and 2(b) can be formed. In order to maintain the molten state of the molten bismuth 12, the temperature is maintained at 330° C. or higher.

The chlorine gas injection position, that is, the end of the lance 14 is preferably positioned at a depth of, for example, 200 mm or more with respect to the surface of the molten bismuth 12 . The contact between the chlorine gas and the molten bismuth 12 is promoted, and the reaction efficiency is increased.

The molten bismuth 12 contains components such as lead in addition to bismuth. For example, the molten bismuth 12 contains lead remaining in the process from the lead electrolysis treatment to the volatilization treatment. In addition to lead, the molten bismuth 12 may contain, for example, silver, zinc (Zn) and magnesium (Mg). These impurities are removed as chloride slag and the like.

The raw material of the molten bismuth 12 may be other than lead electrolytic precipitates. Lead may be added to the bismuth melt 12 if the bismuth melt 12 has a low lead content or does not contain lead. These lead react with chlorine gas to form lead chloride 16 .

As an example of the present invention, an example of a bismuth melt obtained from a lead electrolytic precipitate will be described. The bismuth melt used in this example had a composition of 80% bismuth, 19% lead, and 1% other.

In the chlorination treatment, the molten bismuth 12 was heated to 510 to 530.degree. C. and then heated to 490.degree. The lead chloride 16 serves as a lid, and the chlorine gas remains in the molten bismuth 12, thereby improving the reaction efficiency of the chlorination treatment. The chlorine gas blowing position, that is, the end of the lance 14 was positioned at a depth of 300 mm with respect to the surface of the molten bismuth metal 12 .

The lead chloride 16 covered a width of 45 mm around the lance 14 above the chlorine gas blowing position. As a result, diffusion of chlorine gas blown from the lance 14 is suppressed by the lead chloride 16, and the reaction efficiency is further increased.

Also, the lead chloride 16 covered about 50% of the surface area of the molten bismuth 12 . As a result, it became difficult for chlorine gas to escape from the molten bismuth 12, and the reaction efficiency was improved by about 20% compared to the operation without cover.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention described in the scope of claims. Change is possible.

10 Chlorination Furnace 12 Molten Bismuth 14 Lance 16 Lead Chloride

Claims (6)

A step of chlorinating the molten bismuth by blowing chlorine gas into the molten bismuth containing impurities that form chlorides;
After heating the molten bismuth to a melting temperature of 400° C. or higher, the melting temperature is lowered by 30° C. or higher to form a solid chloride on the surface of the molten bismuth,
A method for purifying bismuth, wherein the chlorine gas is blown into the molten bismuth having a surface covered with the solid chloride . 2. The method for purifying bismuth according to claim 1 , wherein said chloride covers the position where said chlorine gas is blown. 3. The method for purifying bismuth according to claim 1 , wherein the chloride covers 33% or more of the surface area of the molten bismuth. 4. The method for purifying bismuth according to any one of claims 1 to 3 , wherein the chloride-forming impurity is at least one of lead, silver, zinc, and magnesium. The method for purifying bismuth according to any one of claims 1 to 4 , wherein the chlorine gas is blown into the molten bismuth from a depth of 200 mm or more with respect to the surface of the molten bismuth. placing a lance in the center of the furnace in which the molten bismuth is stored;
immersing the end of the lance to a depth of 200 mm or more based on the surface of the molten bismuth;
The method for purifying bismuth according to any one of claims 1 to 5, wherein the chlorine gas is blown into the molten bismuth from the lance.

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