JPH022935B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying aluminum, and more specifically, from impure molten aluminum,
The present invention relates to a method for obtaining high purity aluminum by a fractional crystallization method.

Several methods have been proposed for producing high-purity aluminum by fractional crystallization. (Tokuko Showa 49
-5806, 50-20536, JP-A-55-89439, 56-
55530 and 56-112429). In these methods, impurity elements having a distribution coefficient of less than 1, such as iron and silicon, are excluded from the crystallized aluminum crystals and remain in the mother liquor. Therefore, by separating the crystallized aluminum and the mother liquor by an appropriate method, highly pure aluminum can be obtained. The present inventors have also previously developed a method for obtaining high-purity aluminum by storing molten aluminum in a container with a horizontal bed, cooling the bed while stirring, and crystallizing aluminum on the bed. (See patent application No. 56-201181). Although this method is industrially excellent, when a large container with a large floor area is used, special care is required to ensure uniform flow of molten aluminum in each part of the bed. This is because when the floor area is large, it is almost impossible to stir the entire area with one stirrer, so multiple stirrs are used, but the flow caused by each stirrer is mutually dependent. This is because the flow of molten aluminum tends to become non-uniform in each part of the floor surface due to the mutual influence of the above. If the flow is non-uniform, impurities will not be sufficiently released from the crystallized aluminum in areas where the flow rate is low, resulting in a decrease in the purity of the crystallized aluminum.

The present invention proposes a method that can obtain high-purity aluminum even when using a large container by stirring molten aluminum using multiple stirrs so that the flow is uniform. .

According to the present invention, there is provided a horizontal floor having a rectangular or similar shape with a ratio of the length of the long axis to the short axis of 2 or more, and 2 horizontal floors suspended in a row along the long axis. Molten aluminum is stored in a container equipped with at least one stirrer, and all the stirrers are rotated in the same direction to cool the bed while stirring the molten aluminum to crystallize high-purity aluminum on the bed surface. Then, by separating the aluminum crystallized on the bed from the remaining molten aluminum, high purity aluminum can be obtained.

To explain the present invention in more detail, in the present invention,
The stirrers are arranged in a row and all rotate in the same direction so that they do not interact with each other and create stagnant areas of flow on the bed. In addition, the shape of the bed is rectangular or similar so that sufficient fluidity can be generated over the entire bed with one row of stirrers.

To explain the present invention based on the drawings, FIG. 1 is a plan view of the lower part of an example of an apparatus suitable for carrying out the method of the present invention, mainly showing a carbon block constituting the floor surface and its interior. This is to schematically show the pipe connection with the cooling medium distribution pipes buried in the pipes. 2 and 3 are longitudinal cross-sectional views, respectively, of the apparatus of FIG. 1 along lines A-A' and B-B'. This device consists of a rectangular shallow pot-shaped lower structure with a molten aluminum discharge inlet formed in its side wall, an upper structure covering the upper structure, and a stirring device installed on the upper structure. In the figure, 1 is a heat insulating brick layer and 2 is a fireproof 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 sidewall portions in contact with the molten aluminum, as well as the bottom surface, may be further lined with carbonaceous material over the refractory brick layer. In this case, in order to avoid crystallization of aluminum onto the lining layer, the structure is such that heat does not flow through the lining layer to the carbonaceous material layer on the bottom surface. 3 is a layer of carbonaceous material constituting the surface layer of the bed. usually,
Similar to the cathode of an aluminum electrolytic cell, this layer is constructed by arranging carbon blocks 4 and filling the gaps between them with a carbonaceous binder. The carbonaceous block 4 is preferably made of graphite or quasi-graphite, which has a high thermal conductivity. If desired, the upper surface of the carbon block 4 can be further coated with a carbonaceous material, such as the carbonaceous binder described above, to prevent the carbon block from being worn away by the flow of aluminum. Reference numeral 5 denotes a cooling medium flow pipe buried in the carbonaceous material layer 3. When crystallizing aluminum, the heat of molten aluminum is transferred to the cooling medium in the cooling medium flow pipe through the carbonaceous material layer 3. Therefore, it is preferable that the carbonaceous material has a high thermal conductivity, and in order to uniformly cool the bed, the direction of flow of the cooling medium is preferably reversed in adjacent tubes. Carbonaceous material layer 3
shall be a rectangle or a similar shape with a ratio of the length of the major axis to the minor axis of 2 or more, for example, a shape with rounded corners. The length of the short axis is determined from the length that allows uniform stirring with one stirrer. On the other hand, the length of the major axis is determined from the required surface area of the carbonaceous material layer 3, that is, the production capacity required for one device. Typically, the ratio of the lengths of the major and minor axes is between 3:1 and 7:1.

6 and 7 are outlets for molten aluminum provided in the longitudinal side walls. 8 is a stirrer, and two or more, usually three to ten, are arranged in a row in the center along the long axis of the bed. The portion of this stirrer that comes into contact with the molten aluminum is also made of a material that contaminates the molten aluminum, preferably graphite. The length of the stirrer blades is preferably 0.3 to 0.9 times the short axis of the bed. The stirrer is attached to a drive (not shown). The stirrer is gradually raised during driving as the crystallized aluminum surface rises so that the distance from the crystallized aluminum surface is always within a certain range. Further, once the crystallization operation is completed, the stirrer is taken out of the container to prevent damage to the stirrer due to heating during re-dissolving the crystallized aluminum. Therefore, the stirrer is installed so that it can be raised and lowered in this manner. Reference numeral 9 denotes an inlet for molten aluminum provided on the short side wall. 10 is a burner that heats the surface of the molten aluminum during the crystallization operation to prevent aluminum from crystallizing anywhere other than the bottom surface, and after the crystallization is completed, the remaining mother liquor is discharged and the crystallized aluminum is heated and remelted. It is for the purpose of

In order to purify aluminum according to the method of the present invention using the apparatus shown in the figure, molten aluminum is first introduced into the apparatus through the molten aluminum inlet 9, and stirred by inserting the stirrer 8 into the apparatus. Next, air or other cooling medium is passed through the cooling medium distribution pipe 5 to cool the bed 3, and aluminum 11 is crystallized on the bed surface. The flow rate of the cooling medium is preferably selected such that the crystallization rate of aluminum, that is, the rate of rise of the aluminum crystallization surface is 10 to 150 mm/hour. Further, the rotational speed of the stirrer 8 is preferably 1 to 10 m/sec as the tip speed of the stirring blade. It is necessary that all the stirrers 8 rotate in the same direction. If the rotation directions of two adjacent stirrers 8 are different, a suction side and a discharge side will be formed, and the flow of molten aluminum will stagnate on the suction side. Therefore,
In this stagnation zone, dendrites are likely to form,
Further, impurities removed during crystallization remain between crystals, reducing the purity of crystallized aluminum.

During the crystallization operation, burner 10 heats the molten aluminum surface to compensate for heat loss from the surface and sidewalls and to prevent aluminum from crystallizing anywhere other than the bottom surface. Heating may be continuous or intermittent, but is such that the molten aluminum is maintained at a temperature slightly above its melting point, typically around 662°C. Further, as the aluminum crystallizes, the stirrer 8 is pulled up continuously or intermittently so that the distance between the crystallization surface and the lower end of the stirring blade is always approximately constant. Typically, this distance is preferably between 10 and 100 mm.
The crystallization plane can be detected directly or indirectly estimated from the amount of cooling heat.

When a predetermined amount of aluminum, usually 30 to 70%, preferably 40 to 50%, of the charged aluminum has crystallized, the crystallization is stopped, and the apparatus is tilted to allow the remaining molten aluminum to flow out from the outlet 6. let Although it is not impossible to supply and discharge molten aluminum to and from the apparatus during the crystallization operation, it is not a preferred method because temperature control is difficult. Note that, prior to discharging the molten aluminum, it is advantageous to pull the stirrer 8 out of the apparatus and to rapidly heat the molten aluminum with a burner to reduce its viscosity. Normally, the molten aluminum is heated to 665-667°C to flow out, but if it is possible to heat rapidly to avoid excessive melting of the crystallized aluminum, heating to higher temperatures is possible. good. Once the remaining molten aluminum has been discharged, the apparatus is returned to the horizontal position, the crystallized aluminum is heated and melted with a burner, and the apparatus is tilted in the opposite direction to flow out the purified molten aluminum from the discharge port 7, and the predetermined amount is The product is made by casting into the shape of .

According to the method of the present invention, aluminum can be efficiently purified using a large-sized device.

[Brief explanation of drawings]

FIG. 1 is a plan view of the lower part of a device suitable for carrying out the invention, with arrows indicating the direction of flow of the cooling medium. Figure 2 shows A- of the apparatus shown in Figure 1.
It is a longitudinal cross-sectional view along A'. FIG. 3 is a longitudinal cross-sectional view of the device of FIG. 1 taken along line B-B'. In addition, the second
In the figures and FIG. 3, the support mechanism for the stirrer is omitted. 1...Insulating brick layer, 2...Fireproof brick layer, 3
...Carbonaceous material layer, 4...Carbon block, 5...
Cooling medium flow pipe, 6, 7... Molten aluminum outlet, 8... Stirrer, 9... Molten aluminum inlet, 10... Burner, 11... Crystallized aluminum layer.

Claims (1)

[Scope of Claims] 1. A horizontal floor having a rectangular or similar shape with a ratio of the length of the long axis to the short axis of 2 or more, and a horizontal floor suspended in a row along the long axis. Molten aluminum is stored in a container equipped with two or more stirrers, and all the stirrers are rotated in the same direction to cool the bed while stirring the molten aluminum to crystallize high-purity aluminum on the bed surface. 1. A method for purifying aluminum, which comprises: separating the aluminum crystallized on the bed from the remaining molten aluminum; 2. Claim 1, wherein the horizontal floor is made of a carbonaceous material with high thermal conductivity and has a cooling medium flow pipe therein.
The method described in section. 3. Claim 1 or 3, characterized in that the stirrer is pulled upward as the aluminum crystallizes on the bed, and the distance between the crystallized aluminum surface and the stirrer is maintained substantially constant during the crystallization. The method described in Section 2. 4. The method according to any one of claims 1 to 3, characterized in that the surface of the molten aluminum is heated continuously or intermittently during aluminum crystallization onto the bed.