JPS59205424A - Metal purifying method - Google Patents

Abstract

PURPOSE:To obtain a high purity metal, in purifying a metal from an impure molten metal by a fractional crystallization method, by allowing the metal layer which is crystallized on a floor to be present at all times. CONSTITUTION:A molten metal containing impurities is introduced into an apparatus from a molten metal introducing port 11 and stirred by inserting a stirrer 10. In the next step, air or other cooling medium is flowed through a cooling medium flowing pipe 5 to cool a floor 3 and a part of the molten metal is crystallized on the surface of the floor 3. After the residual molten metal is discharged from the apparatus, the crystallized metal 12 on the floor 3 is melted under heating to recover a high purity metal. At this point, the melting of the crystallized metal 12 under heating is performed so that the layer of the crystallized metal 12 remains on the floor 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying metals, and more particularly to a method for obtaining highly pure metals from impure molten metals by fractional crystallization.

It is known that high purity metals can be obtained by fractional crystallization methods. Currently, this technology is most often studied for aluminum (Special Publications Showa Geta No. 3g06, Ta0-2
(See θkJA No. 3g-12328). When the fractional crystallization method is applied to aluminum, impurity elements with smaller fractionation coefficients, such as iron and silicon, are excluded from the crystallized aluminum crystals and remain in the mother liquor.

Therefore, high purity aluminum can be obtained by separating the crystallized aluminum and the mother liquor by an appropriate method. The present inventors also obtained high-purity aluminum by storing molten aluminum in a container with a bed equipped with a cooling means, and cooling the bed while stirring to crystallize aluminum on the bed. proposed a method to
g 2.5- / issue, S7-76777g issue, 37-/
79! ;0g issue, 57-/ggqgg issue). This method allows mass production of high-purity aluminum by using a large container, and is an excellent industrial method. In this method, the vessel floor is usually constructed of a carbonaceous block, similar to an aluminum electrolyzer, and the cooling medium flow pipes are housed in holes drilled in the carbonaceous block. An insulating brick layer is provided below the carbonaceous blocks to prevent heat radiation from the floor. If there is no insulating brick layer, the heat of the molten aluminum will be dissipated through the carbonaceous block, which has good thermal conductivity, making it difficult to maintain the molten aluminum in the container before and after the crystallization operation of the molten aluminum. becomes.

One of the problems with this method is leakage of bath molten aluminum from the floor of the vessel. In other words, the bed made of carbonaceous blocks is integrated by filling the spaces between the carbonaceous blocks with a carbonaceous paste joint material, but if the container is used repeatedly for aluminum purification, the carbonaceous paste will shrink due to firing and the repetition will occur. Cracks and voids occur in the joints due to temperature changes. Molten aluminum then leaks out through these cracks and voids, necessitating floor repairs. In addition, when molten aluminum reaches the insulation brick layer through these cracks and voids, it reacts with silica, titania, iron oxide, etc. in the bricks and reduces them to metals, so the molten aluminum in the container does not contain these metals. contaminated by

The present invention provides a method of inhibiting leakage of molten aluminum from a bed by the constant presence of a layer of crystallized aluminum on the bed.

That is, the gist of the present invention is to store molten metal in a container made of carbonaceous material and equipped with a bed having a cooling medium flow pipe therein, and to supply a cooling medium to the cooling medium flow pipe while stirring the molten metal. A method comprising crystallizing a portion of the metal on the bed by cooling the bed through circulation, then discharging the remaining molten metal from the container, and then recovering the crystallized metal on the bed by heating and melting it, A method for purifying a metal characterized by heating and melting the crystallized metal so that a layer of the crystallized metal remains on the bed.

The present invention will now be described in further detail.

The present invention is characterized in that a layer of crystallized metal is always present on the bed to prevent molten metal from coming into direct contact with the bed.

Although the present invention can be applied to the purification of various metals, it is particularly suitable for the purification of aluminum. The case of aluminum purification will be explained below based on the drawings.

FIG. 7 is a plan view of the lower part of an example of a device suitable for carrying out the method of the present invention, and mainly shows the carbon block constituting the floor surface, the cooling medium flow pipe buried inside the carbon block, and the cooling medium flow pipes installed in the side wall. This figure is for schematically showing a molten aluminum outlet and a fuel combustion device. 2 and 3 are schematic longitudinal cross-sectional views of the apparatus of FIG. 1 along lines AA' and BB', respectively. This device consists of a rectangular shallow steel substructure with a molten aluminum discharge inlet formed on its side wall, an upper structure that covers the upper structure, and a stirring device suspended from this superstructure. .

In the figure, (1) is a heat insulating brick layer, (2j is a refractory brick layer).For the side wall portion of the refractory brick layer that comes into contact with molten aluminum, a material that does not contaminate molten aluminum, such as a high alumina refractory brick, is used. If desired, the side wall portions in contact with the molten aluminum, as well as the bottom surface, may be further lined with a carbonaceous material over the refractory brick layer, in which case the heat can pass through the lining layer. The structure shall be such that there is virtually no leakage to the floor made of carbonaceous material at the bottom. (3) is a floor made of carbonaceous material with high thermal conductivity. Normally, this floor is equipped with an aluminum electrolytic cell (3). Similarly to the cathode part, it is constructed by arranging carbon blocks (4) and filling the gaps between them with a carbonaceous binder. The carbon block (4) is preferably graphite or quasi-graphite having high thermal conductivity. A cooling medium flow pipe (5) is buried in this bed (3) made of carbonaceous material. Preferably, the direction of flow of the cooling medium is reversed in adjacent tubes. (6) and (7) are molten metal outlets projecting outward from the side wall.

The discharge ports (6) and (7) have their bottoms connected to the third side so that when the container is tilted, the molten metal can easily flow out without leaving any residue.
As shown in the figure, it is preferable to have a structure that is inclined upward from the floor surface. (8) is the molten metal outlet (6) and (7).
) is a chimney installed at the top of the chimney. The chimney (8) is normally fixedly attached to the device, but may be removably installed so that it can be removed when tilting the device if desired. (9)
is a burner that burns fuel oil or gas to gently heat the surface of the molten metal in the container during the crystallization operation, and rapidly heats the surface of the molten metal and crystallized metal after the crystallization operation is complete. It is preferable that the amount of heat generated can be changed over several levels to accommodate the needs of the user. α0) is a stirrer, and the part in contact with the molten aluminum is made of a material that does not contaminate the molten aluminum, preferably graphite or quasi-graphitic material. The stirrer is suspended and supported by a drive device (not shown), and is gradually pulled up as the crystallized aluminum surface rises during driving so that the distance from the crystallized aluminum surface is always within a certain range. Furthermore, once the crystallization operation is completed, the stirrer is taken out of the container to prevent damage to the stirrer even if the heat generated by the burner (9) is increased. (Illid is the inlet for molten metal.)

To purify aluminum according to the method of the present invention using the apparatus shown in the figure, first, molten aluminum is introduced into the apparatus from the molten metal inlet 0υ, and stirred by inserting the stirrer 0 (υ) into the apparatus. Air or other cooling medium is circulated through (5) to cool the floor (37), and aluminum (121) is crystallized on the floor surface.The flow rate of the cooling medium is:
The crystallization rate of aluminum, that is, the rate of rise of the aluminum crystallization surface is 70~/! ;0@717 o'clock is preferably selected. Further, the rotational speed of the stirrer 0 is preferably 7 to 10 m7 seconds as the tip speed of the stirring blade.

If a plurality of stirrers are used, it is preferable to arrange them in a row on the center line of the bed and to rotate all the stirrers in the same direction. If the rotation directions of adjacent stirrers are different, a suction side and a discharge side will be formed, and there will be a part on the suction side where the flows of molten aluminum from the left and right join, and there is a risk that the flow of molten aluminum will stagnate here. There is.

During the crystallization operation, the molten aluminum surface is heated by a burner (9) to compensate for heat loss from the surface and side walls and to prevent aluminum from crystallizing out except on the bottom surface. Heating may be continuous or intermittent, but is such that the molten aluminum is maintained at a temperature well above its melting point, typically approximately 1.62°C. Combustion gas is molten metal outlet (6)
, (7) to the outside via the chimney (8). Molten metal outlet (6), (because the force projects outward from the side wall, the flow of molten aluminum is generally worse in this area than in other areas. Therefore, unless some measure is taken
Molten aluminum in this area tends to crystallize due to heat loss from the side walls and surface. However, when high-temperature combustion gas is discharged to the outside through this portion, the peripheral wall and molten aluminum surface of this portion are heated, and crystallization of aluminum in this portion is suppressed.

During the crystallization operation, the stirrer 0 (
υ is raised continuously or intermittently so that the distance between the crystallization surface and the lower end of the stirring blade is always maintained constant at about 11. Typically, this distance is preferably 70 to ioomm. The crystallization plane can be detected directly or indirectly estimated from the amount of cooling heat.

A predetermined amount of aluminum, usually a 30 to 7 θ ratio of the charged aluminum, preferably 30 to 7θ. The crystallization operation is stopped when the amount of aluminum is crystallized, and the apparatus is tilted to allow the remaining molten aluminum to flow out from the discharge port (6). Before discharging the remaining molten aluminum, the stirrer 00) is pulled out of the apparatus, and the amount of heat supplied from the burner (9) is increased to rapidly heat the molten aluminum.
It is advantageous to reduce its viscosity. Usually Haru Otsusa~
It is heated to 7° C. to cause the molten aluminum to flow out, but it may be heated to a higher temperature if it is possible to heat rapidly enough to avoid excessive melting of the crystallized aluminum. After the remaining molten aluminum has been discharged, the apparatus is returned to a horizontal position and the crystallized aluminum is heated and melted using a burner. At this time, it is necessary to heat so that a layer of crystallized aluminum remains on the bed without completely melting the crystallized aluminum. Heating is done from the surface, so by heating while measuring the depth of the molten aluminum produced and stopping heating when a predetermined depth is reached, a layer of crystallized aluminum of the desired thickness can be deposited on the floor. The residual heat is removed while cooling the bed by flowing a cooling medium through the cooling medium distribution pipe. By doing so, the temperature difference between the upper surface of the floor and the surface of the molten aluminum increases, and the upper surface of the floor can be reliably maintained at a temperature below the melting point of aluminum. The thickness of the crystallized aluminum layer left on the floor may be about 3θ to 100 mm. If the layer thickness is too thin, there is a risk that the crystallized aluminum layer will dissolve when molten aluminum is charged into the apparatus for the next purification operation. Also, if the layer is too thick, it is disadvantageous because it reduces the effective volume of the device.

When the remaining crystallized aluminum layer on the bed reaches a predetermined thickness, heating is discontinued and the apparatus is tilted in the opposite direction to that for the remaining mother liquor to drain the purified molten aluminum to the outlet (
7) and cast into a predetermined shape to produce a product.

When the discharge of the molten aluminum is completed, the apparatus is returned to the horizontal position, the raw material molten aluminum is introduced through the molten metal inlet (1υ), and the crystallization operation is started again.

According to the method of the present invention, even when using a large-sized apparatus, it is possible to easily obtain high-purity aluminum by preventing leakage of molten aluminum from the floor and contamination of purified aluminum.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the Examples below unless it exceeds the gist thereof.

Example/ As shown in Fig. 1, raw material molten aluminum (Sj, 1g Op
(containing Fe 2 Oppm) was placed in the graphite block, and cooling air was passed through the cooling medium flow pipe in the graphite block while stirring with a stirrer to cause crystallization of aluminum. Approximately When S-0% crystallized, the crystallization operation was stopped and the remaining mother liquor l-5 was discharged.Then, the crystallized aluminum layer was heated and melted from the surface and recovered.

If the crystallized aluminum layer was not left on the surface of the graphite block, Si in the recovered aluminum
It contained 7099 m of Fe.

On the other hand, about s of aluminum crystallized in the previous operation
When the aluminum was left at a thickness of 0 mm, the recovered aluminum contained 7 θ ppm of Si and 0 ppm of Fe.

[Brief explanation of the drawing]

FIG. 1 is a plan view of the lower part of an example of a device suitable for carrying out the invention, in which the arrows indicate the direction of flow of the cooling medium. FIG. 1 is a longitudinal cross-sectional view of the device shown in FIG. 1 taken along line A-A'. FIG. 3 is a longitudinal sectional view of the device of FIG. 1 taken along line B-B'. Note that the support mechanism for the stirrer is omitted in FIGS. 2 and 3. (1) Insulating brick layer, (2) Fireproof brick layer, (3
) floor made of carbonaceous material, (4) carbon block, (5) cooling medium flow pipe, (6), (7) molten metal outlet, (8)
) Chimney, (9) Burner, (1 (〃 Stirring silver, θ
1) Molten metal inlet, (12) Crystallized metal patent applicant
Naoetsuyo Kasei Co., Ltd. Patent attorney Haseyo - 7 others 131 -

Claims (1)

[Claims] (1) Molten metal is placed in a container that is made of carbonaceous material and has a bed with a cooling medium flow pipe inside, and the bed is made by flowing a cooling medium through the cooling medium flow pipe while stirring the molten metal. A method for purifying metals, characterized in that a part of the metal is crystallized on a bed by cooling, and then the remaining molten metal is discharged from the container. (2. A method for purifying a metal according to claim 1, characterized in that the crystallized metal is heated and melted while a cooling medium is passed through a cooling medium flow pipe.