JPS583969B2 - Alumina manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for treating bauxite with a sodium aluminate solution to produce alumina. The present invention relates to a method for separating desiliconization products such as sodalite compositions.

As is well known, a large amount of red mud is discharged in the Bayer process, but only a small amount is currently used as road material.

The reason for this is that red mud is difficult to dehydrate and is inconvenient to handle.As is clear from the representative analysis examples shown in Table 1 below, red mud is composed of various components. This is because it is not possible to take advantage of the characteristics of any of the ingredients.

Among the red mud components shown in Table 1, R-8102 (clay-type silica) is alkali-soluble, and quartz-based SiO2
(The sum of this amount and the amount of R-8102 is T-8102), iron oxide and titanium oxide are substantially insoluble in alkali.

Therefore, if red mud could be skillfully separated into alkali-soluble and alkali-insoluble components, the former could be used as various fillers, lightweight aggregates, adsorbents, etc., while the latter could be used as an auxiliary raw material for cement and steel manufacturing, and as a pigment. Red mud, which previously had various problems when disposed of, will now be used effectively.

The various components in red mud can be easily separated by appropriately treating the discharged red mud using known methods. It is clear that industrial implementation is almost impossible.

On the other hand, since the Bayer process is operated on the alkaline side, if the process of separating the above components can be skillfully incorporated into the process of the process, it should be possible to perform the separation industrially. It is.

R-S as a method to remove Si02 from bauxite in advance
The Lautawerk method is known, in which bauxite with a high iO2 content is calcined at high temperature and removed by elution with a dilute alkaline solution, but it requires a huge amount of thermal energy and specific extraction conditions for alumina, so it cannot be applied to ordinary bauxite. is impossible from an economic point of view.

In the Bayer method, it has been found that the behavior of R-8102 with respect to alumina extract from bauxite is as follows.

That is, it is once eluted into a sodium aluminate solution, but when the silica concentration in the solution exceeds a certain value, nuclei such as sodalite are generated, which exhibits a seed effect, and the silica has a composition whose main component is sodalite. It begins to precipitate as a substance.

The dissolution rate of R-8102 in a sodium aluminate solution is similar to that of alumina, and the higher the extract temperature, soda concentration, and Na20/Al203 molar ratio (hereinafter simply referred to as molar ratio), the higher the dissolution rate of R-8102, but the rate of dissolution of R-8102 in a sodium aluminate solution increases. -81
The critical concentration at which 02 becomes a sodalite compound and precipitates becomes higher as the temperature of the extract is lower, the soda concentration is higher, and the molar ratio is lower, and under these conditions, the precipitation rate also becomes lower.

Therefore, in principle, bauxite is treated with an extract under conditions where R-SiO2 dissolves but does not precipitate, and then filtered (this step is hereinafter referred to as the R-8102 elution step), and the filter cake is sent to the usual Bayer step. In addition, seeds are added to the filtrate as necessary to precipitate the dissolved R-Si02 as a composition such as sodalite, and then filtered (this step is hereinafter referred to as the R-8102 precipitation step, and the above steps are performed). (The entire process including this is called a desiliconization process).If the filtrate is circulated through this process, the R-Si02 component can be separated.

However, in such a process, R-SiO
2. In order to avoid precipitation of R-8102 in the elution step, it is necessary, for example, to increase the soda concentration of the extract or use a large amount of extract.
Precipitation of R-Si02 in the R-SiO2 precipitation step becomes difficult.

In addition, if such a pyrocess is incorporated as a pre-process of the Bayer 1 process and an alkaline solution is circulated in that process, the circulating liquid in this process will immediately become saturated with alumina, and the alumina in the bauxite will no longer be dissolved. gone,
As a result, bauxite particles no longer disintegrate and R-Si
Since the amount of 02 dissolved also decreases, a step for removing alumina from the circulating fluid becomes necessary during this step.

As mentioned above, red mud is made into R-S using the Buyer step.
There are many practical difficulties in separating the i02-containing material and the alkali-insoluble material, and it has not been carried out on an industrial scale so far.

The present invention aims to effectively separate red mud discharged in the normal Bayer process into an alkali-soluble portion and an alkali-insoluble portion while maintaining normal alumina production efficiency. The gist of this method is to provide a desiliconization process before the normal Bayer process, organically link this process with the alumina extraction process, and simultaneously perform the separation of red mud components and the extraction of alumina. .

That is, in the method of the present invention, bauxite is treated with a sodium aluminate solution (hereinafter simply referred to as a solution), the insoluble residue is discharged as red mud, and aluminum hydroxide is precipitated from the solution from which the red mud is separated. In the so-called Bayer process, in which alumina is calcined and the solution after separating aluminum hydroxide is recycled, bauxite is treated with a solution to elute alkali-soluble silica, and the eluted silica is precipitated and separated as a sodalite composition. A desiliconization process and a main process of treating the desiliconized bauxite with a solution to extract alumina are provided, and the solution from which aluminum hydroxide is separated in the main process and the sodalite composition precipitated in the desiliconization process are combined. A mixed solution with at least a part of the separated solution is used as a solution for the desiliconization process, and the remaining solution is used as a solution for the main process.

Although the method of the present invention will be explained in detail based on a batch method, it goes without saying that it can also be implemented in a continuous method.

FIG. 1 is a schematic process diagram showing one embodiment of the method of the present invention, in which the system on the left is the desiliconization process and the system on the right is the main process.

In the R-SiO2 elution tank 1, bauxite A is
-After undergoing the Si02 elution treatment, the filter is separated into a filtrate and a filter cake (i.e., desiliconized bauxite) by a filter 2.

The filtrate is sent to the next R-8102 precipitation tank 3, and if necessary, sodalite seeds are added to precipitate the dissolved silica as a sodalite composition.

The liquid after precipitation is separated into sodalite composition B and a filtrate by a filter 4, a part of the filtrate is branched off, and the remainder is put into a storage tank 12.

The desiliconized bauxite is processed in exactly the same way as the normal Bayer process.

That is, after being subjected to alumina elution treatment in the steamer 5, it is separated by the thickener 6 into a slurry containing a residue with a high iron content and a solution with a high alumina content.

The former is separated into a residue C with a high iron content (lower silica content than conventional red mud) and a filtrate in a filter 7, but the filtrate is circulated to a thickener 6 to collect fine particles therein. be done.

The solution with a high alumina content is prepared by adding aluminum hydroxide seeds in an aluminum hydroxide precipitation tank 8.
Dissolved alumina precipitates as aluminum hydroxide.

After the precipitation, the liquid is separated into slurry containing aluminum hydroxide and clear liquid in the thickener 9, and the former is passed through the filter 10.
After filtering, the aluminum hydroxide is fired in a rotary kiln 11 to become alumina D, and the latter is placed in a storage tank 12 after being subjected to treatments such as evaporation and concentration (not shown) as required.

In this embodiment, the solution is recycled as follows.

That is, a part of the filtrate of the filter 4 in the desiliconization process (hereinafter referred to as the desiliconization process finished liquid) is used as a solution for the main process, and the remaining desiliconization process finished liquid is used for clarification of the thickener 9 in the main process. It is mixed with a liquid (hereinafter referred to as the main process finished liquid) and used as a solution for the desiliconization process.

By recycling in this way, it is possible to obtain a solution with a desired molar ratio in the desiliconization process, and the alumina that is eluted together with silica in the desiliconization process is effective for alumina production in the main process. This has the advantage of being used for

FIG. 2 shows another embodiment.

This embodiment differs from the embodiment shown in FIG. 1 above only in the solution circulation method, so a description of the steps will be omitted.

In this embodiment, the desiliconization process finished liquid and the main process finished liquid are mixed in the storage tank 12, a part of which is used for the main process and the remainder used for the desiliconization process.

This method has the advantage of making it easier to circulate the solution, but it also has the disadvantage of reducing the degree of freedom in the operation of the desiliconization process. All you have to do is extract it and add it to the main process solution.

It is clear that if such a method is adopted, the same effect as the method shown in FIG. 1 can be achieved.

As can be seen from the above, when using the method of the present invention, not only can ordinary red mud be easily separated into a sodalite composition and a component with a high iron content, but also the equipment added to the bayer step can be easily separated. It is simple and has the advantage of not affecting the alumina production efficiency in any way.

Preferred operating conditions for the desiliconization step in the method of the present invention are as follows.

1. R-8102 elution conditions (1) Eluate Na20 concentration 90-200g/INa20/A
1203 Molar ratio 2.0 to 4.0 (2) Ratio of solution to bauxite 5 to 30 m3/t (3) Reaction temperature
60-110℃ (4) Reaction time
0.5-10hr2, Sodalite composition precipitation conditions (1) Temperature 90-2oooC (2) Reaction time 0.1-1ohr In the above, the molar ratio of the solution and the ratio of solution/bauxite are preferably as large as possible. If it is too large, it becomes difficult to balance the entire process, so it may be determined as appropriate within the above range, taking into account the type of alumina to be produced or the production efficiency.

In addition, in the method of the present invention, R-Si in bauxite
A part of 02 enters the main process undissolved and is eluted with alumina in the steamer, but because the silica concentration is low, it is difficult to precipitate as a sodalite composition, so this part precipitates with aluminum hydroxide. and contaminate the product alumina.

If it is necessary to remove such silica, add a solution to the desiliconized bauxite before the main process.
For example, slurry concentration 6oog/1, Na20 concentration 130g/1
If treated for 1 to 20 hours at a l1 temperature of 90 to 140°C, undissolved R-Si02 will be dissolved and then precipitated as a sodalite composition, which will not dissolve even by steaming, so it will not dissolve even by steaming. It is discharged along with red mud.

An example in which the method of the present invention was carried out in a batch manner will be shown below.

Example 1 Alumina was produced using trihydrate bauxite (sheba ore) according to the process diagram shown in FIG. 1 (however, calcination of aluminum hydroxide was not performed).

R-81 2 tons of bauxite crushed to 9 mesh or less
02 elution tank, and add Na20:135, g/x,
Add 28 m3 of a solution with a molar ratio of 2.40 and heat at 100°C for 2 hours.
Immediately after filtration using a pressurized leaf filter, the product was separated into a desiliconized bauxite filtrate.

28 m3 of the filtrate with a molar ratio of 2.0 was sent to the R-Si02 precipitation tank, and sodalite seeds with a size of 350 mesh or less were added.
After adding 00 kg and performing lhr treatment at 140°C,
Filtered with a pressurized leaf filter to obtain a net sodalite composition (
Amount excluding the amount of seeds added.

Same hereafter) Obtained 152k9.

Of this filtrate (molar ratio 2.00) 28 m', 14 m'.
The mixture was branched into the main process, treated with lhr at 150°C in a steamer together with the desiliconized bauxite, and separated into a filtrate with a molar ratio of 1.50 and red mud with a high iron content using a thickener and a vacuum rotary filter.

The above filtrate was put into a precipitation tank, and 1,400 kg of aluminum hydroxide seeds of 150 mesh or less were added thereto.
The precipitation treatment was carried out for 48 hours while allowing natural cooling from .degree. C. to 50.degree.

After the precipitation was completed, the mixture was separated into 14 m3 of filtrate with a molar ratio of 3.00 and a net weight of 1,506 kg of aluminum hydroxide (985 kg in terms of alumina) using a thickener and a vacuum rotary filter.

The filtrate obtained from the thickener and 14 m3 of the remaining liquid after the desiliconization process (molar ratio 2.00) were mixed in a storage tank to obtain 28 m3 of a solution with a molar ratio of 2.40.

The composition of the high-iron red mud obtained in this example (which becomes a solution for the desiliconization process) is shown in Table 1.
The compositions of the sodalite compositions are shown in Table 2.

Example 2 Using the same bauxite as in Example 1, alumina production was carried out according to the process diagram shown in FIG. 2 (however, calcination of aluminum hydroxide was not performed).

2 tons of bauxite crushed to 9 mesh or less is made into R-Si
Put it in an O2 elution tank and add 28ml of a solution with a molar ratio of 2.25 to it.
3 was added thereto and treated at IQO°C for 2 hours, and immediately filtered using a pressurized leaf filter to separate the desiliconized bauxite and the filtrate.

28 m3 of the filtrate with a molar ratio of 2.00 was sent to the R-8102 precipitation tank, and 2 sodalite seeds of 350 mesh or less were sent to the R-8102 precipitation tank.
00 kg was added and subjected to lhr treatment at 140°C, and then filtered with a pressurized leaf filter to obtain a sodalite composition net of 144 kg.
I got k9.

28 m of this solution (molar ratio 2.00) and molar ratio 3. 14 m3 of DO main process finished liquid was mixed in a storage tank, and the molar ratio was 2.
．． A 42 mm solution of No. 25 was obtained.

The remaining 14 m3 of the solution used in the desiliconization process was put into a steamer together with the desiliconized bauxite, and heated at 140°C for lhr.
After treatment, it was separated into a filtrate with a molar ratio of 1.50 and a red mud with a high iron content using a thickener and a vacuum rotary filter.

The above filtrate was put into a precipitation tank, 400 kg of aluminum hydroxide seeds L of 150 mesh or less were added thereto, and the mixture was heated to 60°C.
The precipitation treatment was carried out for 48 hours while cooling naturally from to 50°C.

After the precipitation, the mixture was separated into 14 m3 of filtrate with a molar ratio of 3.00 and 1,502 kg of aluminum hydroxide (982 kg in terms of alumina) using a thickener and a vacuum rotary filter.

The composition of the high iron content red mud obtained in this example is shown in Table 1.
Further, the compositions of the sodalite compositions are shown in Table 2.

As can be seen from the above examples, according to the method of the present invention, so-called red mud can be easily separated into a sodalite composition and a component with a high iron content by simply adding simple equipment to the conventional buyer process. Moreover, since the ratio of the net amount of aluminum hydroxide precipitated to the amount of bauxite obtained in the examples is almost the same as that of the usual Bayer method, it is clear that there is no problem in terms of productivity.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are schematic process diagrams each showing an embodiment of the method of the present invention. In the figure, 1: R-Sin2 elution tank, 3: R-SIO2 precipitation tank, 5: steaming can, 8: aluminum hydroxide precipitation tank, respectively.

Claims (1)

[Claims] 1. Treating bauxite with a sodium aluminate solution and discharging the undissolved residue as red mud, while precipitating aluminum hydroxide from the solution from which the red mud was separated, and baking this to produce alumina. In the method, bauxite is treated with a sodium aluminate solution,
The main process consists of a desiliconization process in which alkali-soluble silica is eluted and the eluted silica is precipitated and separated as a sodalite composition, and a main process in which the desiliconized bauxite is treated with a sodium aluminate solution to extract alumina. A mixed solution of at least a portion of the solution from which aluminum hydroxide precipitated in the process was separated and the solution from which the precipitated sodalite composition was separated from the desiliconization process is used as the solution for the desiliconization process, and the remaining solution is used in the main process. An alumina manufacturing method characterized by making it into a solution for use. 2 A mixed solution of the solution from which precipitated aluminum hydroxide was separated in the main process and a part of the solution from which the precipitated sodalite composition was separated from the desiliconization process was used as the solution for the desiliconization process, and the remaining solution from the latter was used as the solution for the desiliconization process. 2. The alumina manufacturing method according to claim 1, wherein the alumina is used as a solution for the main process. 3. Mix the solution in which precipitated aluminum hydroxide in the main process was separated and the solution in which the precipitated sodalite composition in the desiliconization process was separated, and use a portion of the solution for the desiliconization process and the remainder for the main process. 2. The method for producing alumina according to claim 1, wherein the alumina production method is made into a solution.