JPH08175817A - Calcium aluminate hydrate and method for producing aluminum hydroxide using the same - Google Patents

Abstract

(57) [Summary] (Corrected) [Structure] X-ray diffraction analysis of bauxite and slaked lime disappeared due to disappearance of crystal peaks of gibbsite and boehmite-containing compounds contained in bauxite by X-ray diffraction. Dry pulverization until at least the formation of calcium aluminate hydrate is confirmed by the method to form calcium aluminate hydrate, and then an alkali carbonate solution is added to the pulverized product to extract alumina into the solution. An alkali aluminate solution slurry, which is characterized by solid-liquid separating the slurry into a dissolution residue and a solution, and then blowing carbon dioxide gas into the solution to precipitate aluminum hydroxide. Production method. [Effect] The calcium aluminate hydrate can be obtained by simply pulverizing the alumina-containing substance such as bauxite or the like at a high temperature without sinter or sinter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hydrated calcium aluminate and a method for producing aluminum hydroxide using the same. More specifically, the present invention relates to a novel method for producing calcium aluminate hydrate by dry-mixing an alumina-containing substance and slaked lime, and a method for producing aluminum hydroxide using the same. It is a thing.

[0002]

2. Description of the Related Art The elemental aluminum is about 8% in the crust.
There are many alumina-containing substances in nature because it is an element that is present and is the second most abundant element after oxygen and silicon. Among these, those with a high alumina content are bauxite, alumite, gravel shale, white garnet, It is an ore such as nepheline, feldspar, and phosphoric acid. As a technique for producing alumina, a method of separating and refining the alumina content from these alumina-containing ores is various methods corresponding to each ore in the past, for example, a Bayer method using bauxite as a raw material, bauxite or nepheline or shale shale. Known methods include the calcium aluminate method (also referred to as the sodium carbonate method) used, the ammonia-soda method using alumite, the sulfuric acid method using phosphorous earth.

Of these, the calcium aluminate method is
To obtain calcium aluminate by adding limestone to conglomerate shale or bauxite ore and melting it in an electric furnace or sintering with a kiln, and extracting it with an alkali carbonate, for example, sodium carbonate solution, to obtain a sodium aluminate solution, It is a method in which carbon dioxide gas is blown into the solution to obtain aluminum hydroxide. In this method, since the alumina from the alumina-containing ore mainly composed of diaspore and kaolinite, which have various problems in extraction in the Bayer method, is converted into calcium aluminate and then extracted with sodium carbonate or the like, Fe ₂ O ₃ or It is possible to use an alumina-containing substance having a small amount of substances insoluble in an alkaline solution such as TiO ₂ , for example, gravel shale, which has the advantage of being able to reduce the amount of dissolution residue generated after alumina extraction. However, the cost of dissolving or sintering the alumina-containing substance is high, and it is not commercially produced in Japan. Currently, bauxite is used exclusively as the raw material, and this is contacted with an alkaline solution in a high-temperature, high-pressure container to extract the alumina content of the bauxite as a sodium aluminate solution, and then solid-liquid separation to remove the bauxite dissolution residue. Cooling the sodium aluminate solution after separation and precipitating aluminum hydroxide as a product by adding seed aluminum hydroxide, the so-called "Bayer method" is less expensive than other methods, It is carried out industrially.

[0004]

[Problems to be Solved by the Invention] 11 for bauxite
Gibbsite that can be dissolved at 0 ° C to 150 ° C, 180 ° C to 2
There are some types that contain a large amount of boehmite, diaspore, and kaolinite in which silica and alumina are bonded, which are difficult to dissolve unless they are at a high temperature of 50 ° C. Conventionally, in the Bayer method in Japan, it is easily dissolved in an alkaline solution mainly consisting of gibbsite. Bauxite with sexual gibbsite has been commonly used. However, recently, even in the Bayer method, the content of alumina soluble in an alkaline solution is high,
The so-called high-grade bauxite having a low silica content soluble in an alkaline solution is reduced, and the use of low-grade bauxite having a high silica concentration and a slightly low alumina concentration is unavoidable. As is well known, when the concentration of silica soluble in an alkaline solution in bauxite is high, the silica component elutes in the sodium aluminate solution during the extraction process of alumina, which reacts with the alumina content and sodium content in the solution. , Produces a desiliconized product mainly composed of sodalite, which deteriorates the soda unit consumption and reduces the yield of alumina. In addition, when low-grade bauxite is used, the alumina content in the bauxite is low, and the desiliconized product produced by elution of soluble silica is mixed in the bauxite dissolution residue (also called red mud). The amount of dissolution residue tends to increase remarkably.

In the Bayer method, a large amount of bauxite dissolution residue after extracting alumina from bauxite is discharged even when easily soluble high-quality bauxite mainly containing gibbsite is used. About 800 kg of these bauxite dissolution residues are discharged per ton of alumina, so if the alumina production amount is 500,000 tons / year, about 400,000 tons / year will be discharged. The composition of these bauxite dissolution residues is not unique depending on the type of bauxite used and operating conditions in the buyer process,
Loss on ignition (LOI): 8 to 12% by weight, Al ₂ O ₃ : 1
8-25 wt%, SiO _2: 15~20 wt%, Fe ₂
O _3: 30 to 40 wt%, Na ₂ O: 8 to 12 wt%,
TiO _2: is about 2 to 8% by weight (both Inuikarada base) ( "Aluminum Industry", Jiro Kitagawa al, MakotobundoShinkosha issue, pp 76).

[0006] As examples of applications in which a large amount of the above-mentioned bauxite dissolution residue generation amount can be collectively utilized, iron-making raw materials, ceramic raw materials, construction materials such as paving materials, etc. are mentioned.
The composition as it is cannot satisfy the requirements of any application and is merely applied as a landfill material. However, these days, even in this landfill treatment,
The number of reclaimed coastlines and inland areas near the factory has decreased, and even if a reclaimable site is found in a remote place, transportation costs will be high, and it will be difficult to produce by the commercial buyer method. It's starting.

Under the circumstances, the inventors of the present invention have diligently studied to find an alternative method of producing alumina by the Bayer method. As a result, slaked lime is added to and mixed with an alumina-containing substance.
When crushing this under specific conditions, it was found that gibbsite, boehmite, etc. in the alumina-containing substance can be transferred to calcium aluminate without melting or sintering the alumina-containing substance, and to complete the present invention. I arrived.

[0008]

That is, the present invention provides a method for producing a calcium aluminate hydrate characterized by dry pulverizing an alumina-containing substance and slaked lime.

Further, according to the present invention, the crystal peak of a compound containing an alumina component contained in the alumina-containing substance disappears in the alumina-containing substance and slaked lime by the X-ray diffraction method, and at least calcium aluminate water is obtained by the X-ray diffraction method. After dry pulverization until the formation of a hydrate is confirmed, an alkali carbonate solution is added to the pulverized product to extract alumina into the solution to form an alumina aluminate solution slurry, and the slurry is solid-liquid separated and dissolved. Another object of the present invention is to provide a method for producing aluminum hydroxide, which comprises separating a residue and a solution, and then blowing carbon dioxide gas into the solution to precipitate aluminum hydroxide.

The present invention will be described in more detail below. The present invention uses an alumina-containing substance as a raw material, mixes it with slaked lime, and dry-mills it. The alumina-containing substance as a raw material is not particularly limited as long as it contains an alumina component, but normally, gibbsite, boehmite, bauxite containing alumina hydrate such as diaspore, gravel shale, and others Alumina-containing substances containing the alumina compound, more specifically, alumite, phosphophosphate, bauxite dissolution residue, sodalite, zeolite, and the like. Among these ores, when an ore having a high alumina content, for example, a shale shale, is used, the amount of residues discharged is small.

The amount of slaked lime mixed with the alumina-containing substance may be in the vicinity of the stoichiometric amount for forming calcium aluminate hydrate.
l ₂ O ₃ and slaked lime as CaO,
Usually, the molar ratio of CaO / Al ₂ O ₃ may be in the range of 2.8 to 3.6, preferably 2.9 to 3.1. In the present invention, it is essential that the mixture of the alumina-containing substance and slaked lime is dry-ground. Normally, calcium aluminate hydrate is not formed by mechanically mixing the alumina-containing substance and slaked lime. However, by dry milling the mixture, calcium aluminate 6
A hydrated calcium aluminate hydrate is formed.

It is sufficient that the slaked lime used as a raw material in the present invention is slaked lime at the time of dry crushing. During dry crushing, it is necessary to subject the dry lime to dry crushing in the presence of quick lime and water in an amount capable of converting this to slaked lime. It belongs to the category of dry pulverizing a mixture of an alumina-containing substance and slaked lime as referred to in the invention.

The alumina-containing substance and slaked lime are dry pulverized using a planetary ball mill or the like, and the time course of the alumina crystals such as gibbsite and kaolinite in the alumina-containing substance is traced by X-ray diffraction. The characteristic endothermic peaks of gibbsite and kaolinite disappear. Along with this, from the material identification by X-ray diffraction, the diffraction peaks of gibbsite, kaolinite and slaked lime gradually disappeared, on the contrary, the peak of calcium aluminate hydrate appeared strongly, and finally the peaks of gibbsite, kaolinite and slaked lime Not observed, only peak of calcium aluminate hydrate. This calcium aluminate hydrate is a hexahydrate mainly composed of 3CaO.Al ₂ O ₃ .6H ₂ O, but a part thereof is amorphous calcium aluminate hydrate (3CaO.Al ₂ O ₃ -NH ₂ O), alumina gel, etc. are presumed to exist.

The time required for conversion into calcium aluminate hydrates such as gibbsite, boehmite, diaspore and kaolinite by dry pulverization depends on the type of the material containing alumina, the type of pulverization equipment used, the pulverization conditions, etc. Therefore, in industrial practice, preliminary dry crushing was performed, and the production of calcium aluminate hydrate was confirmed by referring to the results of X-ray diffraction and differential thermal analysis, and the optimum crushing time was determined. Just decide. The International Center for
Diffraction data (INTERNATIONAL CENTER F
OR DIFFRACTION DATA) Powder Diffraction File 1991 issued by the United States
File No. 24-217 calcium aluminum
Hydroxide (Calcium Aluminum Hydroxide: C
The main peak position (interplanar spacing) and peak intensity of a ₃ Al ₂ (OH) ₁₂ ) are almost the same as those of the crushed product, and the peak intensity of the crushed product does not change with the crushing time, that is, becomes constant. The formation of the calcium aluminate hydrate may be completed in the first time.

The formation of the calcium aluminate hydrate is presumed to be caused by a mechanochemical reaction of alumina species such as gibbsite and boehmite and slaked lime by the energy at the time of pulverization, and a pulverizer which gives friction to the powder, for example, Planetary ball mills and shear mills produce calcium aluminate hydrate more efficiently than ordinary conical ball mills. When a planetary ball mill, a vibration mill, a rolling mill, a shearing mill, a fluidized bed type counter jet mill or the like is used as a pulverizer, it is roughly 1 hour to 50 hours, usually 5 hours to 24 hours. The peaks of boehmite, kaolinite, etc. disappear and substantially calcium aluminate hydrate is produced. However, the type of the crusher used is not limited as long as the calcium aluminate hydrate is produced by dry crushing. In the case of wet grinding,
There is no formation of calcium aluminate hydrate.

Bauxite and slaked lime (dry matter) containing alumina in the form of gibbsite and kaolinite
On a planetary ball mill for about 30 minutes to 10 hours, usually about 1
When dry milled for hours to 5 hours, slaked lime reacts preferentially with gibbsite and kaolinite to form calcium aluminate hydrate. It is presumed that the silica content in kaolinite is liberated from kaolinite and becomes amorphous silica gel. In order to separate calcium aluminate and silica gel, silica may be extracted with, for example, an alkali. It can be confirmed by X-ray that other minerals constituting bauxite such as hematite, goethite, and anatase are left as they are, and these minerals gradually become amorphous as the milling time becomes longer. Therefore, it can be seen that if the milling is terminated when gibbsite and kaolinite complete the mechanochemical reaction with slaked lime, a mixture of calcium aluminate hydrate, silica gel, hematite, goethite, anatase and the like is obtained.

Various known methods are known for separating and purifying alumina from a mixture containing calcium aluminate. For example, at least 80% by weight or more of Al ₂ O ₃ in the generated calcium aluminate is added with an amount of an alkali carbonate solution capable of converting into alkali aluminate to form an alkali aluminate solution, and then solid-liquid separation is performed,
The solution residue may be separated from the solution, and then carbon dioxide gas may be blown into the solution to precipitate aluminum hydroxide. The reaction conditions such as the amount of the alkali carbonate solution or the carbon dioxide gas used, temperature, pressure and the like may be carried out according to a commonly known method for extracting aluminum hydroxide from calcium aluminate. In this case, in order to prevent the elution of silica into the alkaline aluminate solution, the alumina-containing substance after the pulverization treatment should be treated with an alkaline solution such as caustic soda beforehand to elute the silica content into the solution, and then solid-liquid separation should be performed. Can be removed by. The conditions for removing the silica component are not particularly limited, but Na ₂ O may be added to Si in the silica to be eluted.
Using 30g / l to 250g / l of caustic soda in conversion,
It may be contacted at room temperature to a boiling point of atmospheric pressure or lower for about 10 to 60 minutes. Use the solution after treatment as water glass,
Alternatively, it can be applied as a raw material for obtaining silica gel by neutralization.

As the alumina-containing substance applicable to the present invention, in addition to the above-described bauxite ore, diaspore, gibbsite, and gravel shale containing a high concentration of boehmite, nepheline, and further generated during the buyer process using bauxite. Desulfurized products (sodalite and a substance mainly composed of sodium aluminosilicate having a similar composition to sodalite), bauxite dissolution residue (dry matter) in which the desalted products are mixed, zeolite, and the like are also included. It is possible to convert the alumina content into calcium aluminate by mixing these with slaked lime and dry pulverizing in the same manner as in the case of using the above-mentioned bauxite ore.

The calcium aluminate hydrate obtained after pulverization can be obtained as aluminum hydroxide by extracting the alumina component as an alkali aluminate solution with an alkali carbonate solution and treating this with carbon dioxide gas in the same manner as above. it can. In addition, since calcium aluminate hydrate produced by crushing has hydraulic properties in this state,
In the case of a desulfurized product generated in the buyer process using bauxite ore as an alumina-containing substance, a bauxite dissolution residue mixed with the desulfurized product, etc., water is added to this to dissolve the desulfurized product or bauxite. It is also possible to apply it as a binder for solidifying the residue.

[0020]

As described above in detail, in the method of the present invention, the alumina-containing substance and slaked lime are simply dry pulverized at room temperature to obtain calcium aluminate hydrate without sintering or sintering at high temperature as in the conventional case. It has been found that aluminum hydroxide can be obtained from this calcium aluminate by a known method, and alumina having a high silica content, which has been difficult to use in the conventional Bayer method and the like. The content of ore and alumina ore mainly composed of diaspore (alumina monohydrate), which has been difficult to dissolve at low temperature, is similar to the content of alumina containing ore mainly composed of gibbsite. It can be used with a reduced amount of silica, and since it is easy to separate and recover the silica content, it is possible to use a high-grade bauxite ore. In the near future it is difficult, its industrial utility value is extremely large.

[0021]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited thereto.

Example 1 Bauxite having the composition shown in Table 1 as an alumina-containing substance (bintan ore, apparent density: 2.7 g / cm ³ , average particle size:
30 μm) and slaked lime (Ca (OH) ₂ , manufactured by Wako Pure Chemical Industries, density: 2.24 g / cm ³ , center particle size: 22.2 μm) were thoroughly dried, and then bauxite: slaked lime = 1: 2
(Weight ratio), dry-mixed so that the total amount of both becomes 3.0 g, and a planetary ball mill (trade name; Fritsch, pu
lverizette-7, stainless steel pot, content: 50 cm ³ , 5 mmφ steel ball 7
60 pieces at 1350 rpm
Dry milled for minutes. Before crushing, during crushing 15 minutes, 30 minutes,
The X-ray diffraction pattern of the ground product at 60 minutes was examined. The result is shown in FIG. As is clear from FIG. 1, the peaks of gibbsite and kaolinite in bauxite disappeared about 30 minutes after the start of pulverization, and calcium aluminate hexahydrate was formed.

The same bauxite and slaked lime (total amount 3 g) as described above were used for pulverization for 30 minutes to obtain 3 batches of 8.4 g of a pulverized product. This was added to 500 ml of an 8N caustic soda solution, stirred at 90 ° C. for 20 minutes, and then solid-liquid separated, and silica and alumina eluted in the separated solution were analyzed. As a result, the elution rate of SiO ₂ was 87% by weight and the elution rate of Al ₂ O ₃ was 3% by weight. From this result, after bauxite and slaked lime were dry pulverized to produce calcium aluminate hexahydrate,
In producing aluminum hydroxide, when the pulverized product is previously treated with alkali, the elution of alumina is substantially suppressed, and silica in bauxite is substantially extracted,
It turns out that it can be removed.

Then, a sodium carbonate solution was added to the solid substance obtained by solid-liquid separation after treatment with the above caustic soda solution, and the mixture was stirred at room temperature for 1 hour, followed by solid-liquid separation. Carbon dioxide gas was blown into the obtained solution to obtain a white precipitate. The obtained precipitate was chemically analyzed. The results are shown in Table 2.

[0025]

[Table 1]

[0026]

[Table 2] The ignition loss is a value determined by weight loss due to firing at 1100 ° C.

[Brief description of drawings]

FIG. 1 shows an X-ray diffraction pattern of a mixture of bauxite and slaked lime at each grinding time.

Claims (5)

[Claims] 1. A method for producing a calcium aluminate hydrate, which comprises dry pulverizing an alumina-containing substance and slaked lime. 2. Dry pulverization of an alumina-containing substance and slaked lime eliminates a peak of a crystal of a compound containing an alumina component contained in the alumina-containing substance, which is observed by an X-ray diffraction method, and at least an X-ray diffraction method is performed. The method for producing a calcium aluminate hydrate according to claim 1, wherein the pulverization is performed until a peak of the calcium aluminate hydrate occurs. 3. Dry milling is a planetary ball mill, a vibration mill,
The method for producing a calcium aluminate hydrate according to claim 1 or 2, wherein the pulverization is performed by a rolling mill or a fluidized bed type counter jet mill. 4. The method for producing a calcium aluminate hydrate according to claim 1 or 2, wherein the alumina-containing substance is at least one of bauxite, gravel shale, sodalite, red mud and zeolite. . 5. Alumina-containing substance and slaked lime, the crystal peak of a compound containing an alumina component contained in the alumina-containing substance disappears by the X-ray diffraction method, and at least calcium aluminate hydrate by the X-ray diffraction method. After dry pulverization until the formation of was confirmed, an alkali carbonate solution was added to the pulverized product to extract alumina into the solution to form an alumina aluminate solution slurry, and the slurry was subjected to solid-liquid separation to obtain a dissolution residue. A method for producing aluminum hydroxide, which comprises separating into a solution and then blowing carbon dioxide gas into the solution to precipitate aluminum hydroxide.