JPH05170434A - Production of low-sodium red mud - Google Patents

Abstract

PURPOSE:To provide the process which can produce the red mud of insoluble residues produced in a large amt. in a Bayer method as low-sodium red mud effectively utilizable for applications, such as auxiliary raw materials for cement, etc., while the red mud is heretofore compelled to be thrown away as industrial waste even if useful components are contained therein. CONSTITUTION:A specified amt. of bauxite is circulated in a desiliconization stage of extracting 2 reactive silica from the bauxite with an aluminate liquid having the alkali concn. higher than in the case of a Bayer process as far as possible after pulverizing 1 a specified amt. of the bauxite, then separating 3 an extracted liquid and insoluble residues from the extract and crystallizing 4 sodalite from the extracted liquid as the pretreatment stage of the Bayer process. The insoluble residues are treated in exactly the same manner as with the bauxite of the ordinary Bayer stage and the normal Bayer process consisting of alumina extraction 6, discharge 7 of the low-sodium red mud as the insoluble residues, precipitation 8 of aluminum hydroxide from the separated liquid of the low-sodium red mud, etc., is repeated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a method for dissolving bauxite in an alkaline aqueous solution or an alkaline aluminate solution (hereinafter referred to as an aluminate solution) under high pressure and high temperature to extract alumina components and the like from bauxite, and to precipitate aluminum hydroxide by precipitation. The present invention relates to red mud, which is an insoluble residue generated in the so-called buyer process of manufacturing. More specifically, it relates to a method for producing low soda red mud, which is optimal as an inexpensive cement raw material.

[0002]

2. Description of the Related Art As a method for producing aluminum hydroxide / alumina, bauxite is mixed with an aluminate solution, the alumina content is extracted under high pressure and high temperature conditions, and then aluminum hydroxide is added to the aluminate solution from which the insoluble residue is separated. It is generally carried out by a so-called Bayer method in which the solution is added as seeds and the solution is hydrolyzed. What is produced during high-pressure and high-temperature dissolution and discharged as insoluble residue is called red mud, which produces a large amount of about 700 to 800 kg per ton of alumina, so its effective utilization is for companies that employ the buyer method. Although it has been a problem for many years, it is difficult to use it effectively, so there is no choice but to dispose of the entire amount as industrial waste at a large cost. However, as environmental regulations are being tightened, there is an urgent need to establish effective measures to utilize red mud. Bauxite, which is a raw material for the Bayer method, contains aluminum hydroxide as the first component, iron oxide as the second component, and silica, titania, etc. as the other components. When this bauxite is subjected to high pressure and high temperature dissolution treatment, aluminum hydroxide, silica, etc. are partially dissolved in the aluminate solution. The eluted aluminum hydroxide is relatively stable in the aluminate solution until seeds are added and precipitated, and the silica content that can be dissolved in the aluminate solution is reactive silica (R-SiO 2).
₂ ), the reactive silica is likely to be supersaturated in a short time when dissolved, and when the concentration is high, it is not stable in the aluminate solution and is easily crystallized as sodalite.

Sodalite is stable at high temperatures, and Al ₂
O _3, SiO _2, an Na ₂ consisting of O, etc. material, aluminate upon crystallization - capturing silica preparative liquid. That is, sodalite cannot be produced unless silica is present in the liquid.

Therefore, in the usual buyer process, the red mud discharged as an insoluble residue contains iron oxide, which was the second component, and sodalite crystallized during dissolution as the main components. The composition of this red mud is slightly different depending on the composition of the raw bauxite, but Fe ₂ O ₃
40-50% by weight, sodalite 20-50% by weight
Is in the range. In addition, quartz, TiO ₂ , hydrated alumina, and limestone are contained in several% by weight, respectively. Red mud consisting of a single useful component, such as this composition, is dumped because there are too many types of components and the content ratio is too small for effective use. It is technically difficult to separate, and even if it is possible, it is not worth the cost at this time. Therefore, in order to effectively use red mud, it is necessary to search for a use in which each component can be used in a mixed state. Conventionally, a method of utilizing as an auxiliary raw material for cement has been considered for the purpose of utilizing the red mud with each component mixed. Desirable characteristics as an auxiliary raw material for Portland cement, especially as an iron source, are (1) high iron oxide content because the iron content in the cement is 3 to 6% by weight.
(2) Portland cement for general use has an alkaline content (Na
₂ O + 0.658K ₂ O) is 1% or less, and that of low-alkali Portland cement is 0.6% or less, and since it is also mixed from clay used as a raw material, the alkali content is as low as possible. That, (3)
It does not contain metal particles, and (4) does not contain harmful substances such as heavy metals. Red mud complies with the conditions as an iron source except that it contains a large amount of alkali. Since the content of K ₂ O in the red mud is negligible, in order to use it as it is as an auxiliary raw material for cement, the Na ₂ O content in the red mud should be at least 1% by weight from the above (2). Must be:

An extremely effective measure for reducing red mud soda is to prevent red mud from containing sodalite at all. This is because most of Na ₂ O in red mud is present in sodalite. Therefore, various methods have been devised to prevent sodalite from being contained in red mud. For example, silica, which is a constituent of sodalite, is extracted from bauxite in advance and the production of sodalite is suppressed by removing it (Japanese Patent Publication Sho 58-3969). The finer the particle size of ground bauxite, the more reactive silica content There is a method (Japanese Patent Application Laid-Open No. 63-190709) which utilizes the fact that it is high and the difference in elution rate between the alumina content and the silica content is large.

[0006]

However, in these methods, since the conditions were unsuitable for extracting the reactive silica sufficiently, sodalite remained in the red mud, which resulted in the red mud remaining in the red mud. The alkali content was 3% by weight or more, and reduction of the Na ₂ O content was insufficient to use it as an auxiliary raw material for cement as it was. FIG. 1 is a schematic diagram showing how the alumina component, the silica component, and the sodalite are eluted from the bauxite during the high-pressure high-temperature dissolution in the Bayer process. When the mixed slurry of bauxite and aluminate liquid flows into the dissolution reactor, the reactive silica component begins to elute.
Around this time, the alumina content also dissolves out, but this alumina content is dissolved in the solution and remains relatively stable in the aluminate solution until seeds are added and precipitated.

However, the reactive silica elutes, the silica concentration in the liquid rises, and before it is completely extracted, it becomes stable and insoluble, and the tendency to crystallize as sodalite increases. The crystallized sodalite is stable at high temperature and contains Si as an essential constituent, so that the reactive silica in the aluminate solution is taken in during the crystallization, so that the reactive silica concentration is significantly reduced. Therefore, it is necessary to make a commercial selection such that after the reactive silica is completely eluted, the total amount thereof is crystallized as sodalite. That is, it is an object of the present invention to establish a method for producing low-soda red mud that can be used as it is as an auxiliary raw material for cement by completely separating the reactive silica elution reaction and the sodalite crystallization reaction. is there.

[0008]

Means for Solving the Problems As a result of earnest studies on establishment of a method for producing low soda red mud, the present inventors have found that a quality suitable as an auxiliary raw material for cement can be obtained by devising a normal buyer process. The present invention has been completed by finding a method for producing aluminum hydroxide and sodalite having a low level of soda red mud and the quality which is completely the same as that obtained by the conventional buyer process. The gist of the present invention is, as a pretreatment step of the buyer step, extracting as much as possible the reactive silica component among the main components of bauxite using an alkaline aluminate solution having a higher alkali concentration than in the case of the buyer step, and then extracting the extracted solution. Solid-liquid separation into an insoluble residue and a step of circulating a desiliconization step in which seeds are added to the extract to crystallize sodalite, and the insoluble residue is treated in a Bayer step in exactly the same manner as bauxite. And a main step of producing aluminum hydroxide or alumina, which is a method for producing low soda red mud.

The details of the present invention will be described below. First, the silicon removal process, which is the pre-treatment process of the buyer process, will be described. In this desiliconization process, an aluminum liquor having a higher alkali concentration, that is, typically a higher NaOH concentration, is circulated and used than in the Bayer process. This is because, as described above, the reactive silica is the only major component in the main component of bauxite, and the optimum concentration is set so that as much as possible can be extracted. The higher the NaOH concentration of this circulating aluminate solution, the higher the solubility of reactive silica. For example, as shown in FIG. 2, the maximum solubility of silica (indicates the maximum amount of silica that can be dissolved regardless of the state of the solution) is 150 g / l in NaOH concentration.
Then, the SiO ₂ concentration is about 4 g / l, but 200 g / l
When it is 1, it is about 8 g / l, and when it is 250 g / l, it increases to about 12 g / l. If the silica-dissolving ability of the aluminate solution is increased, the silica-dissolving stability (indicating the degree of staying in the dissolved state without being crystallized) is also increased, and it becomes difficult to crystallize as sodalite. Therefore, only the silica content can be extracted. Therefore, it is better that the concentration of the circulating aluminate solution NaOH is higher.

However, there is a problem that when the NaOH concentration becomes high, the liquid viscosity increases and it takes time for solid-liquid separation. Therefore, the concentration of NaOH in the circulating aluminate solution is 1
80g / l to 500g / l, preferably 200g / l
To 300 g / l is recommended. Once this liquid concentration is determined,
The bauxite charging amount is defined by the following formula (1).

[0011]

[Equation 2]

The bauxite charging amount is preferably expressed by the formula (1).
The range of 50% to 95% of the bauxite amount obtained in 1. is preferable. The extraction temperature at that time is 90 ° C to 150 ° C, preferably 100 ° C to 120 ° C. If the extraction temperature is less than 90 ° C, it takes time for the reactive silica to elute, which is not practical. On the other hand, when the temperature is 150 ° C. or higher, the production of sodalite is accelerated, which is not preferable. The extraction time is also within ± 30% of the time calculated based on FIG. 3, and preferably within ± 15%, although it depends on the NaOH concentration of the circulating aluminum liquor and the extraction temperature. Alumina is also eluted from bauxite at the same time as silica, but the effect is basically not a problem.

Next, the sodalite crystallization conditions will be described. In order to sufficiently elute silica, an alumina solution having a higher NaOH concentration than that used in the Bayer process was used.
Therefore, the stability of dissolved silica is remarkably increased, but sodalite is less likely to be produced. Therefore, in the sodalite crystallization step, it is desirable to add silicate minerals as seeds to induce the desulfurization reaction. As seeds, synthetic sodalite or scale zeolite in the Bayer process is preferable. Seed addition rate is from 5 m ² / l at a specific surface area of 200m ² / l, preferably 80 m ² from 30 m ² / l
Add so that it falls within the range of 1 / l. The temperature at that time is 1
10 ° C to 200 ° C, preferably 120 ° C to 180 ° C
Is. The crystallization time is related to the NaOH concentration of the solution, but basically the desalting time obtained from FIG. 4 is good. This time does not have to be controlled as strictly as the silica elution time, but it is better to lower the silica concentration in the liquid as much as possible.

If the desilvering process is illustrated, for example, a process as shown in FIG. 5 can be considered. That is, the bauxite is crushed 1 with a crusher and sent to the silica extraction tank 2. Here, after sufficient elution of silica under the above-mentioned conditions, solid-liquid separation 3 is performed. An ordinary Kelly filter, filter press or the like may be used for this separation. The undissolved residue of the silica removal step is sent to the alumina extraction reaction step of the Buyer main step, the extract is sent to the sodalite crystallization step 4, and the soluble silica is discharged out of the system as sodalite. In the aluminum solution used in this pretreatment step, Na
The OH concentration is high and the processing temperature and processing time are strictly controlled. Further, the amount of the aluminate solution taken out from the pretreatment step is limited to the amount adhering to the bauxite insoluble residue during the soluble silica elution treatment. The liquid shortage due to this carry-out can be used by boiling the circulating aluminum solution used in the buyer's process.

The alumina content of the bauxite insoluble residue sent to the buyer is extracted 6 and the insoluble residue at that time is discharged as low soda red mud, followed by the low soda red mud separation liquid. Aluminum hydroxide is crystallized. The low-soda red mud thus produced has a Na ₂ O content of 1% by weight or less after sufficient washing with water. As described above, according to the present invention in which sodalite is not contained in red mud, unnecessary red mud is not generated, and contamination in the aluminate solution is not generated, which is a very effective method.

[0016]

EXAMPLES The contents of the present invention will now be specifically described with reference to examples, but the method of the present invention is not limited thereto. (Example 1) About 300 g of ground australian bauxite (reactive silica content 2.8% by weight) was added to Na.
Add 105 cc of aluminate solution having a composition of 250 g / l OH concentration and 180 g / l Al ₂ O ₃ concentration to give 105
It heat-processed, stirring at (degree C). After about 90 minutes, this slurry was immediately subjected to solid-liquid separation by pressure filtration, and separated into an extract and an insoluble residue. A pulverized bauxite dissolution process pipe scale or the like is added to the extract, and sodalite is precipitated at 130 ° C., solid-liquid separation is performed, and S is used as sodalite.
iO ₂ was removed. On the other hand, the undissolved residue is sent to the buyer process, where the NaOH concentration is 150 g / l and the Al ₂ O ₃ concentration is 60 g.
Al ₂ O ₃ after extraction into an aluminate solution with a composition of 1 / l
Concentration / NaOH concentration of 0.8, 140
Extraction of the alumina component was carried out at ℃ for about 1 hour. After extracting this, the insoluble residue and the liquid were separated, and the liquid was used for precipitation of aluminum hydroxide. The SiO ₂ concentration of this solution is 0.5 g /
It was 1, which was a level that did not hinder the precipitation of aluminum hydroxide. When the red mud discharged as an insoluble residue was washed with water and subjected to wet analysis, it contained only 0.9% by weight of Na ₂ O.

(Example 2) About 200 crushed Indonesian bauxite (reactive silica content 3.7% by weight)
g, NaOH concentration 200 g / l, Al ₂ O ₃ concentration 14
It was added to 1000 cc of an aluminate solution having a composition of 0 g / l, and heat-treated while stirring at 105 ° C. About an hour later,
Immediately, this slurry is subjected to solid-liquid separation by pressure filtration,
Separated into extract and insoluble residue. To the extract, add a crushed bauxite dissolution process pipe scale, etc.
Sodalite was precipitated at ℃, solid-liquid separation was performed, and SiO ₂ was removed as sodalite. On the other hand, the undissolved residue is sent to the buyer process, where the NaOH concentration is 150 g / l and Al ₂ O.
_The aluminate solution having a composition of ₃ g of 60 g / l was added so that the Al ₂ O ₃ concentration / NaOH concentration after extraction would be 0.8, and the alumina component was extracted at 140 ° C. for about 1 hour. After extracting this, it was separated into an insoluble residue and an extract, and the extract was used for precipitation of aluminum hydroxide. S of this liquid
The iO ₂ concentration was 0.6 g / l, which was a level that did not hinder the precipitation of aluminum hydroxide. The red mud discharged as an insoluble residue was washed with water and wet-analyzed.
_{The 2} O content was only 0.8% by weight.

Example 3 300 parts by weight of red mud containing low soda obtained in Example 1 and 10 parts of ordinary Portland cement
Mortar cement obtained by adding 0 parts by weight and 50 parts by weight of water (water cement ratio 0.5) to a mixer and kneading for about 3 minutes was poured into a mold of 10 mm × 10 mm × 40 mm.
This was vibrated for 1 minute with a vibrator to carry out compaction. After that, it was left in a room at room temperature for several hours. Then 20 ±
It was put in a constant temperature humid box at 1 ° C. and a relative humidity of 90% or more and cured for 20 hours. This molded body is deframed and left for 20 days ± 1
Standard curing was performed in water at ℃. The molded body thus obtained is crushed and passed through a sieve with an opening of 300 μm to obtain 150 μm.
A sample powder was obtained which did not pass through. This sample powder is AST
An elution test was performed according to the method of MC 289, and the relationship between the amount of dissolved silica (Sc) and the amount of alkali concentration decrease (Rc) was examined. Sc = 80.1 mMol / l, Rc =
It was 106.5 mMol / l, and it was found that low soda red mud is an aggregate that does not cause an alkaline aggregate reaction.

(Comparative Example 1) About 130 crushed bauxite from Indonesia (reactive silica content 3.7% by weight)
g, NaOH concentration 150 g / l, Al ₂ O ₃ concentration 60
It was added to 1000 cc of aluminate liquid having a composition of g / l, and heat-treated while stirring at 140 ° C. About an hour later,
Immediately, this slurry is subjected to solid-liquid separation by pressure filtration,
Separated into extract and insoluble residue. The extract was used for the precipitation of aluminum hydroxide. The SiO ₂ concentration of this solution was 0.5 g / l, which was the same as before the bauxite treatment, and was at a level that did not hinder the precipitation of aluminum hydroxide. The red mud discharged as an insoluble residue was washed with water and wet-analyzed, and as a result, it contained about 8% by weight of Na ₂ O.

(Comparative Example 2) 300 parts by weight of the normal red mud obtained in Comparative Example 1, 100 parts by weight of ordinary Portland cement and 50 parts by weight of water (water cement ratio 0.5) were charged into a mixer, and about 1 mortar cement obtained by kneading for 3 minutes
It was poured into a mold of 0 mm × 10 mm × 40 mm. This was vibrated for 1 minute with a vibrator to carry out compaction. This was left in a room at room temperature for several hours. After that, it was placed in a constant temperature humid box at 20 ± 1 ° C. and a relative humidity of 90% or more and cured for 20 hours. This molded body was deframed and subjected to standard curing in water at 20 ± 1 ° C. for 28 days. The molded body thus obtained was crushed and passed through a sieve having an opening of 300 μm to obtain a sample powder having a size not passing through 150 μm. This sample powder is designated as ASTM C
According to the method of 289, an elution test was conducted to examine the relationship between the amount of dissolved silica (Sc) and the amount of decrease in alkali concentration (Rc). Sc = 235.3 mMol / l, Rc = 7
It was 0.5 mMol / l, and it was found that ordinary red mud is a reactive aggregate that causes an alkaline aggregate reaction.

[0021]

Industrial Applicability According to the present invention, since the red mud that is dumped at a large cost can be used commercially, it has been a long-standing problem for companies that employ the buyer method, and environmental regulations have been tightened. Therefore, the red mud countermeasure, which has been a big cancer in the future, can be established. In addition, sodalite that had been dumped with red mud is recovered as a by-product and can be effectively used as a raw material for zeolite and the like, which is a great effect in improving the economic efficiency of the buyer process.

[Brief description of drawings]

FIG. 1 schematically shows the state of elution of reactive silica and alumina in bauxite into a liquid and the reaction of sodalite formation in the Bayer method bauxite dissolution step.

FIG. 2 shows the ability of an aluminate solution to dissolve silica with respect to the NaOH concentration.

FIG. 3 shows the time required for silica elution with respect to the NaOH concentration of an aluminate solution.

FIG. 4 shows the time required for crystallization of sodalite.

FIG. 5 shows a typical low soda red mud production process.

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[Procedure amendment]

[Submission date] April 8, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Explanation of code

[Correction method] Added

[Correction content]

[Explanation of symbols] 1 Bauxite grinding 2 Reactive silica extraction 3 Solid-liquid separation 4 Sodalite crystallization 5 Solid-liquid separation 6 Alumina extraction 7 Solid-liquid separation 8 Aluminum hydroxide precipitation 9 Solid-liquid separation

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

[Figure 5]

Claims (3)

[Claims] 1. A buyer process for dissolving bauxite in an alkaline aluminate solution, discharging red mud as an insoluble residue, precipitating aluminum hydroxide from the red mud separation solution, and calcining this to produce alumina. , Bauxite is treated with an alkaline aluminate solution having a higher alkali concentration than in the Bayer process to extract soluble silica as much as possible, solid-liquid separation is performed into an extract and an insoluble residue, and seeds are added to the extract. Production of low-soda red mud, characterized in that it comprises a pretreatment step of circulating a silica removal step of crystallization and separation as sodalite, and a main step of treating the insoluble residue in a buyer step just like bauxite. Method. 2. The method for producing low soda red mud according to claim 1, wherein the alkali aluminate solution used in the silica removing step has a NaOH concentration of 180 g / l to 550 g / l. 3. The method for producing low-soda red mud according to claim 1, wherein the amount of bauxite charged in the silica removing step is 40% to 100% of the amount calculated by the following formula (1). [Equation 1]