KR20100007733A - Method of producing decolored sodium aluminate solution - Google Patents

Abstract

PURPOSE: A method for making decolored sodium aluminate by adding ozon-containing gas to sodium aluminate solution is provided. CONSTITUTION: A method for making decolored sodium aluminate solution comprises: a step of heating slurry over 130°C and isolating solid powder. The slurry contains: solid magnesium oxide and sodium aluminate; solid magnesium oxide, solid aluminium hydroxide and sodium aluminate of low concentration; or solid magnesium, solid aluminum hydroxide, and sodium hydroxide aluminate solution.

Description

METHODS OF PRODUCING DECOLORED SODIUM ALUMINATE SOLUTION}

The present invention relates to a process for the preparation of a decolorized aqueous solution of soda aluminate. Specifically, the present invention relates to a method for producing a decolorized aqueous solution of sodium aluminate using solid magnesium oxide and a method for producing high white aluminum hydroxide using a decolorized aqueous solution of sodium aluminate obtained by the method.

In the process of extracting aluminum contained in bauxite with caustic soda aqueous solution and obtaining an aqueous solution of soda aluminate, after adjusting said aqueous solution of soda aluminate to a suitable concentration, the seed crystal of aluminum hydroxide is added, and the said aluminic acid is added. It is industrially manufactured by the method of depositing aluminum hydroxide by hydrolyzing an aqueous solution of soda (so-called a via method).

As a raw material, bauxite is a natural ore, and since the organic matter contained in the soil contains many coloring substances such as humic acid, which is formed by corrosion, the aqueous solution of sodium aluminate produced in the Bayer process is colored and precipitated from the solution. A coloring substance is introduce | transduced into the aluminum hydroxide which becomes.

However, aluminum hydroxide is widely used for applications such as artificial marble fillers, abrasives such as toothpastes, papermaking fillers and coating agents, and aluminum hydroxides used for such applications are required to have high whiteness.

Thus, a method of producing a relatively high white aluminum hydroxide is known by dissolving a crude aluminum hydroxide containing a coloring substance in an aqueous solution of caustic soda or an aqueous solution of alumina soda having a low aluminum concentration, followed by precipitation again. Japanese Patent Laid-Open No. 2002-241128: Patent Document 2).

However, when there are many coloring substances contained in crude aluminum hydroxide, since a large amount of coloring substance exists in the aqueous sodium aluminate solution which melt | dissolved it, a small amount of coloring substance will introduce | transduce into aluminum hydroxide precipitated from it again. In addition, the aqueous solution of soda aluminate for dissolving and re-precipitating aluminum hydroxide is usually used repeatedly industrially, so that the coloring material in the crude aluminum hydroxide accumulates, so even in such a case, the coloring material is introduced into the aluminum hydroxide which is reprecipitated therefrom. It becomes.

Therefore, in order to obtain aluminum hydroxide with high whiteness, it is fundamentally necessary to remove the coloring material from the aqueous solution of soda aluminate containing the coloring material. For this reason, various methods for reducing the colored substance in the aqueous solution of soda aluminate have been proposed, and a number of adsorptive removal methods of the colored substance by the addition of the third component have been reported.

For example, Japanese Unexamined Patent Application Publication No. 54-163799 (Patent Document 1) discloses one or two or more kinds of alkaline earth metal compounds that are not substantially dissolved in the above solution in the aqueous solution of sodium aluminate and do not react substantially. The method of depositing aluminum hydroxide with high whiteness from the filtrate after adding and stirring is disclosed.

In addition, Japanese Patent Laid-Open No. 2002-241128 (Patent Document 2) adds magnesium hydroxide having a specific BET specific surface area, average particle diameter, and calcium content in an aqueous solution of soda aluminate, and decolorizes in a temperature range of 80 to 150 ° C. After the treatment, a method of solid-liquid separation is disclosed.

In addition, US Pat. No. 4,915,930 (Patent Document 3) discloses a method of synthesizing hydrotalcite by reacting magnesium oxide with an aqueous solution of low concentration alumina soda, and contacting it with a via liquid at 90 to 110 ° C. to remove coloring material. Is disclosed.

However, even in the case of using the above-described method of reducing the colored substance in the aqueous solution of sodium aluminate, when the high whiteness is required, the effect of reducing the colored substance of the aqueous sodium aluminate solution was not necessarily sufficient.

An object of the present invention is to provide a method for producing a decolorized aqueous solution of soda aluminate, and to produce a high-white aluminum hydroxide having high whiteness using an aqueous solution of sodium aluminate obtained by the method.

The present inventors earnestly examined the method for decolorizing the aqueous solution of sodium aluminate, and as a result, a slurry composed of a solid magnesium oxide and an aqueous solution of sodium aluminate, a slurry composed of a solid magnesium oxide, a solid aluminum hydroxide and an aqueous solution of low concentration alumina acid or a solid magnesium oxide And a solid slurry of aluminum hydroxide and a caustic soda solution (hereinafter, collectively referred to as "raw material slurry") at a temperature of 130 ° C or higher, and then the solids are separated to decolorize the aqueous solution of sodium aluminate with high efficiency. I found something. Moreover, it discovered that the decolorization effect is higher than the case where it oxidized by ozone alone by further blowing and oxidizing ozone to the soda aluminate aqueous solution obtained in this way.

In other words, the present invention is a slurry comprising a solid magnesium oxide and an aqueous solution of sodium aluminate, a slurry consisting of a solid magnesium oxide, a solid aluminum hydroxide and a low concentration of aluminate aqueous solution, or a slurry composed of a solid magnesium oxide, a solid aluminum hydroxide and an aqueous solution of caustic soda 130 After heat-processing at the temperature of more than C, it is the manufacturing method of the aqueous decolorized alumina-soda solution which isolate | separates solid content.

In the manufacturing method of this invention, it is preferable to use the slurry which consists of a solid magnesium oxide, solid aluminum hydroxide, and low-concentration sodium aluminate aqueous solution, or the slurry which consists of solid magnesium oxide, solid aluminum hydroxide, and caustic soda aqueous solution among the said raw material slurry. .

The amount of the solid magnesium oxide added is preferably 0.01 to 10 g / L relative to the aqueous sodium aluminate solution, the aqueous sodium aluminate solution or the aqueous sodium hydroxide solution.

It is preferable that the BET specific surface area of the said solid magnesium oxide is 5-50 m <2> / g.

In the said manufacturing method, it is preferable to blow in an ozone containing gas further into the aqueous aluminate solution after separating solid content.

The present invention also relates to a method for producing high white aluminum hydroxide in which aluminum hydroxide is precipitated from a decolorized aqueous solution of sodium aluminate prepared by the above production method.

In this invention, after heat-processing the said raw material slurry at the temperature of 130 degreeC or more, the aqueous alumina-sodium aluminate solution decolorized can be obtained by isolate | separating solid content in a liquid. In addition, aluminum hydroxide having high whiteness can be produced by using the decolorized aqueous solution of sodium aluminate obtained by the production method of the present invention.

Further, in the present invention, by further blowing ozone-containing gas into the aqueous solution of sodium aluminate, an aqueous solution of sodium aluminate decolorized can be obtained as compared with the case of oxidizing alone with ozone.

These and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the invention.

The method for producing the decolorized aqueous solution of sodium aluminate solution of the present invention includes a slurry composed of a solid magnesium oxide solution and a sodium aluminate solution, a slurry composed of a solid magnesium oxide solution, a solid aluminum hydroxide solution and a low-density aqueous solution of sodium aluminate, and a solid aluminum hydroxide solution. It is a manufacturing method including the process of separating solid content after heat-processing the slurry which consists of aqueous solution of caustic soda at 130 degreeC or more.

When the heat treatment is performed, the effect of decolorization is reduced at a temperature of less than 130 ° C. On the other hand, in order to obtain a temperature exceeding 250 degreeC, since a large amount of energy is required, it is not preferable. For this reason, it is preferable to make liquid temperature 130 degreeC or more and 250 degrees C or less. More preferably, they are 140 degreeC or more and 200 degrees C or less. In addition, the time which keeps liquid temperature at 130 degreeC or more is 0.1 to 5 hours normally.

There is no restriction | limiting in particular in the speed | rate which raises liquid temperature, Preferably it is about 0.1 degreeC / min-about 50 degreeC / min. The temperature increase rate is preferable in terms of productivity, but may be appropriately adjusted to balance energy and cost required for temperature increase.

It does not specifically limit as a method of obtaining the slurry which consists of a solid magnesium oxide and the sodium aluminate aqueous solution, For example, what is necessary is just to mix a solid magnesium oxide and the aqueous sodium aluminate solution by a conventionally well-known method.

The method for obtaining a slurry composed of a solid magnesium oxide, a solid aluminum hydroxide, and a low-concentration sodium aluminate aqueous solution is not particularly limited. For example, a solid-state magnesium oxide, a solid aluminum hydroxide, and a low-concentration sodium aluminate aqueous solution may be prepared by a conventionally known method. Mix well.

When obtaining the slurry which consists of a solid magnesium oxide, a solid aluminum hydroxide, and a low-concentration aluminate aqueous solution, you may add a solid magnesium oxide and a solid-state aluminum hydroxide simultaneously to the low-concentration aluminate aqueous solution, and consist of a solid-state aluminum hydroxide and a low-concentration aluminate aqueous solution Solid magnesium oxide may be added to the slurry.

It does not specifically limit as a method of obtaining the slurry which consists of a solid magnesium oxide, a solid aluminum hydroxide, and a caustic soda aqueous solution, For example, what is necessary is just to mix a solid magnesium oxide, a solid aluminum hydroxide, and a caustic soda aqueous solution by a conventionally well-known method.

When obtaining the slurry which consists of a solid magnesium oxide, a solid aluminum hydroxide, and a caustic soda aqueous solution, solid magnesium oxide and a solid aluminum hydroxide may be added simultaneously to a caustic soda aqueous solution, and a solid magnesium oxide is added to the slurry which consists of solid aluminum hydroxide and a caustic soda aqueous solution. You may add.

As said mixing method, the method of mixing using a stirring blade, etc. are mentioned, for example.

In the raw material slurry, for example, it is preferable that the solid aluminum hydroxide in the raw material slurry is dissolved by heat treatment.

The aluminum concentration in the aqueous sodium aluminate solution or the aqueous sodium aluminate solution obtained by dissolving the solid aluminum hydroxide is 60 g / L or more in terms of Al ₂ O ₃ and 200 g / L or less, and the soda concentration is 60 g / L or more in terms of Na ₂ O. It is preferable that it is 200 g / L or less.

It is preferable that the aluminum concentration in the liquid phase in the slurry composed of the solid magnesium oxide, the solid aluminum hydroxide and the low concentration aqueous aluminate solution is 10 g / L or more and 100 g / L or less in terms of Al ₂ O ₃ , and the soda concentration is Na ₂ O equivalent. Therefore, it is preferable that they are 60 g / L or more and 200 g / L or less. On the other hand, soda concentration in the liquid phase in the solid magnesium oxide and the solid phase a slurry consisting of aluminum hydroxide and caustic soda aqueous solution is preferably 60g / L more than 200g / L or less in terms of Na ₂ O.

The solid MgO may be added in various shapes such as powder, granules, or the like, or may be added in a state such as a slurry in which solid MgO fine particles are dispersed in water. It is preferable that the BET specific surface area of solid MgO is 5-50 m <2> / g. When it is smaller than 5 m 2 / g, it may take time for the solid phase MgO to contact aluminum and the coloring material in the liquid during heating, and as a result, the time required for removing the coloring material may be long. It is not preferable at the point of efficiency. If it is larger than 50 m 2 / g, the solid phase MgO to be used may be special and expensive, which is not preferable in view of cost and effectiveness.

The amount of the solid MgO added is preferably 0.01 g / L or more and 10 g / L or less with respect to the aqueous sodium aluminate solution, the aqueous sodium aluminate solution or the aqueous sodium hydroxide solution. When the added amount is less than 0.01 g / L, the desired decoloring effect may not be obtained. Moreover, even if it adds more than 10 g / L, the improvement of the exceptional discoloration effect may not be seen. Moreover, when converting the addition amount into the molar concentration of Mg, Preferably it is 0.25 mmol / L or more and 250 mmol / L or less.

As for the said solid-state MgO, the average particle diameter measured by the laser scattering method is 0.1 micrometer or more and 100 micrometers or less are preferable. When the average particle diameter is less than 0.1 µm, the viscosity of the raw material slurry may be increased. In addition, when the average particle diameter exceeds 100 µm, the reactivity with aluminum in the liquid and the rate of adsorbing the colored substance in the liquid may decrease in the heat treatment step, so that the time for decolorizing the desired color is long. It may become.

By solid-liquid separation of the slurry obtained after heat processing by solid-liquid separation operation, such as pressure filtration and centrifugal separation, the solid content which introduce | transduced the coloring substance and the decolorized aqueous solution of alumina soda can be isolate | separated. The separated and recovered solids are colored in dark brown by adsorbing the coloring material in the liquid, but can be reused for the decolorization treatment of the colored aqueous sodium aluminate solution by removing the organics in the solids by calcination.

In this invention, it is preferable to use the slurry which consists of a solid magnesium oxide, solid aluminum hydroxide, and a low concentration aqueous solution of sodium aluminate, or the slurry which consists of solid magnesium oxide, solid aluminum hydroxide, and caustic soda aqueous solution. Here, the solid aluminum hydroxide may be added in various shapes such as powder, granules, or the like, or may be added in a state such as a slurry in which solid aluminum hydroxide fine particles are dispersed in water.

In addition, when using the slurry which consists of solid-state magnesium oxide, solid-state aluminum hydroxide, and low-concentration sodium aluminate aqueous solution in the said raw material slurry, or the slurry which consists of solid-state magnesium oxide, solid-state aluminum hydroxide, and aqueous solution of caustic soda, solid-state aluminum hydroxide in the said heat processing It is preferable to dissolve. Thereby, it is not necessary to perform the dissolution process which melt | dissolves solid aluminum hydroxide and prepares the crude aqueous solution of sodium aluminate, and a manufacturing process is simplified. Moreover, a high decolorization effect is acquired compared with the method of adding solid-phase MgO with respect to the aqueous sodium aluminate solution after melt | dissolving a solid aluminum hydroxide.

(Combination of discoloration by ozone-containing gas etc.)

In the manufacturing method of the aqueous solution of soda aluminate of the present invention, it is preferable that the ozone-containing gas is further blown into the decolorized aqueous solution of sodium aluminate after separating the solid content. By further decolorizing the decolorized aqueous solution of sodium aluminate with an ozone-containing gas, a higher decolorizing effect can be obtained than when decolorizing with ozone alone. Since the decolorization method using ozone is by oxidative decomposition, it is decomposed first from an organic substance which is easily oxidized regardless of whether it is an uncolored organic substance or a colored organic substance. For this reason, a large amount of ozone is required in order to acquire a desired decolorizing effect. However, the decolorization method using the solid-phase MgO is by adsorption removal of a coloring substance, and a higher decolorization effect can be obtained by combining removal of the coloring substance by this adsorption | action, and oxidative decomposition.

The ozone-containing gas used herein is not particularly limited as long as it is a gas containing ozone, but the ozone concentration in the ozone-containing gas is usually 5 g / m 3 or more and 300 g / m 3 or less, and more preferably 20 g / m 3 or more and 200 g / m 3 or less. If the ozone concentration is less than 5 g / m 3, the amount of ozone blown into the liquid is small, and in order to decompose the colored organic matter contained in the liquid, a large amount of ozone-containing gas must be blown, which may require a long time for discoloration. On the other hand, in order to obtain the ozone containing gas of concentration higher than 300 g / m <3>, an apparatus may become special.

As a raw material used for producing ozone, either oxygen or air may be used, but oxygen is preferably used in view of efficiently obtaining high concentrations of ozone. In particular, it is preferable to use oxygen obtained by separating air using PSA (Pressure Swing Adsorption) method in that a large amount of oxygen can be easily produced. In this regard, the ozone-containing gas is preferably an ozone / oxygen mixed gas.

Ozone can be generated using generally known methods such as a silent discharge method, a creepage discharge method, and an ultraviolet irradiation method, but it is preferable to generate the ozone by a silent discharge type from the viewpoint of high generation efficiency and large amount of ozone. Do.

The temperature of the aqueous solution of soda aluminate at the time of contact with ozone is usually 30 ° C or more and a boiling point or less. In particular, it is preferably 50 ° C. or higher and 90 ° C. or lower in view of the process advantage of being able to move directly to the precipitation process of aluminum hydroxide after contact with ozone.

There is no particular limitation on the method of bringing the ozone-containing gas into contact with the decolorized aqueous solution of soda aluminate, and an ozone contact tank as described in the Ozone Handbook, page 154 of Isao Somiya, can be used. In general, it is known that ozone promotes self decomposition in the high pH region. For this reason, when ozone is blown into a high alkali aqueous solution, such as an aqueous solution of sodium aluminate, it is preferable to use the method which can contact a coloring organic substance immediately after ozone is dissolved in aqueous solution. For example, microbubbling bubbles of ozone-containing gas is also an effective method for dissolving ozone in a decolorized aqueous solution of sodium aluminate.

Moreover, in the manufacturing method of the soda aluminate aqueous solution of this invention, a well-known adsorbent can be added and the decolorization of a coloring substance can also be performed after the said heat processing. As the adsorbent, known ones such as hydroxides, carbonates, silicates, oxalates, sulfates and quaternary ammonium salts of activated carbon, magnesium and calcium can be used.

(Method for producing aluminum hydroxide)

The present invention also relates to a method for producing high white aluminum hydroxide in which aluminum hydroxide is precipitated from a decolorized aqueous solution of soda aluminate prepared by the above production method. Aluminum hydroxide powder having a high whiteness can be obtained by precipitating aluminum hydroxide using a decolorized aqueous solution of sodium aluminate prepared by the production method of the present invention.

Various well-known methods can be used for the method of depositing aluminum hydroxide using the decolorized aqueous solution of sodium aluminate obtained by the method for producing the aqueous solution of sodium aluminate of the present invention. Specifically, a method of precipitating aluminum hydroxide on the surface of aluminum hydroxide hydroxide by stirring for 1 hour while maintaining the liquid temperature at 30 ° C. to 90 ° C. while adding granular aluminum hydroxide as a seed to the decolorized alumina soda aqueous solution. After adding an acidic aqueous solution to the aqueous solution of sodium aluminate prepared to produce a neutralizing gel, a method of promoting crystallization and obtaining aluminum hydroxide may be exemplified by maintaining the gel at a temperature of 30 ° C. to 90 ° C. for at least 1 hour. .

(Yes)

Although an Example and a comparative example are given to the following and this invention is demonstrated to it in more detail, this invention is not limited at all by these description.

(1) measuring method of liquid color

An aqueous solution of soda aluminate was placed in a glass cell, measured twice using a colorimetric color difference meter ("ZE-2000" manufactured by Nippon Denshoku Industries Co., Ltd.), and the arithmetic mean value of the value was defined as the color of the aqueous solution. The measuring method measured the L value, a value, and b value based on JIS-Z-8729. As an index of the degree of decolorization, a b value indicating that the larger the value in the positive direction is colored in yellow, was used.

(2) the method of measuring the central particle diameter

The particle size distribution curve was calculated | required by the laser scattering type particle size distribution analyzer ("Microtrack HRA" by the Liz & Norrap company), and the average particle diameter was calculated | required as 50 weight% equivalence particle diameter (D50).

(3) Measurement method of BET specific surface area

It calculated | required by the nitrogen adsorption method according to the method prescribed | regulated to JIS-Z-8830.

(Example 1)

Powdered aluminum hydroxide (aluminum hydroxide obtained by Bayer method from bauxite, containing carbon is 0.06%) in 200 mL of caustic soda aqueous solution of Na ₂ O concentration 145 g / L. Center particle diameter 110 micrometers measured by the laser diffraction method ) And a slurry obtained by adding 0.1 g of 47 g of powdered MgO (A) (UC95-C, manufactured by Ube Materials, BET specific surface area: 9 m 2 / g, and a central particle diameter of 3.6 µm measured by laser diffraction). It injected | poured into the autoclave, it heated up to 160 degreeC at the temperature increase rate of 4 degree-C / min, and hold | maintained for 10 minutes. In this process, all aluminum hydroxide was dissolved in an aqueous solution of caustic soda to obtain an aqueous solution of sodium aluminate. Thereafter, the mixture was cooled with water to lower the liquid temperature to room temperature. Solid content in a liquid was removed by pressure filtration in this state, and the decolorized aqueous alumina soda solution was obtained. In addition, the usage-amount of powdery MgO in a slurry is 0.5g per 1L of caustic soda aqueous solution.

(Example 2)

Except for adding 1 g of powdery MgO (A), the same operation as in Example 1 was carried out to obtain a decolorized aqueous aluminate solution.

(Example 3)

The same procedure as in Example 1 was carried out except that 0.1 g of powdered MgO (B) (# 5000, manufactured by Tatehoka Chemical Co., Ltd., BET specific surface area 6 m 2 / g, and the central particle diameter measured by laser diffraction) was added 0.1 g. A decolorized aqueous solution of sodium aluminate was obtained.

(Example 4)

The same operation as in Example 1 was carried out except that 0.1 g of powdered MgO (C) (H-10, manufactured by Tatehoka Chemical Co., Ltd., BET specific surface area 44 m 2 / g, measured by laser diffraction) was added 0.1 g. An aqueous solution of soda aluminate was obtained.

(Example 5)

As a heat treatment after injecting the slurry into the autoclave, the same operation as in Example 1 was carried out except that the temperature was raised to 180 ° C. at a temperature increase rate of 4 ° C./min, and then maintained for 60 minutes to obtain an aqueous sodium aluminate solution.

(Comparative Example 1)

Except not adding powdery MgO, operation similar to Example 1 was performed and the aqueous aluminate soda solution was prepared.

(Comparative Example 2)

The slurry prepared by performing the same operation as Example 1 without adding powdery MgO was injected into an autoclave, and it heated up to 180 degreeC at the temperature increase rate of 4 degree-C / min, and hold | maintained for 60 minutes. Thereafter, the mixture was cooled with water to lower the liquid temperature to room temperature. The resulting aqueous solution of soda aluminate was heated to 90 ° C., 0.1 g of powdered MgO (A) was added, the mixture was kept at 90 ° C. for 10 minutes, and then a solid solution of sodium adamic acid was removed by pressure filtration.

(Comparative Example 3)

The same operation as in Example 1 was carried out except that powdered magnesium hydroxide (Magstar # 30, manufactured by Tate-Hokagaku Co., Ltd., BET specific surface area 26 m 2 / g, and a central particle diameter of 10.5 μm measured by laser diffraction) was used. Aqueous aluminate solution was prepared.

(Example 6)

Na ₂ O concentration of 145g / L powder in the aqueous solution of caustic soda, and 700mL action of an aluminum hydroxide obtained by the Bayer process from aluminum hydroxide (bauxite, containing carbon is being 0.06% center particle diameter measured by a laser diffraction method is 93 165 g of 탆) and 0.35 g of MgO (A) in powder form (12 mmol / L in terms of Mg molar concentration) were added to the autoclave, and the temperature was raised to 160 ° C. at a heating rate of 4 ° C./min and held for 10 minutes. did. Then, after cooling with water again and lowering liquid temperature to room temperature, solid content in a liquid was removed by pressure filtration, and the aqueous solution of sodium aluminate was obtained.

(Example 7)

The aqueous solution of soda aluminate was obtained in the same manner as in Example 6 except that the amount of the powdery MgO (A) added was 0.7 g (25 mmol / L in terms of Mg molar concentration).

(Example 8)

A slurry in which 165 g of powdered aluminum hydroxide (the same as that used in Example 6) was added to 700 mL of an aqueous solution of caustic soda having a concentration of 145 g / L of Na ₂ O was injected into an autoclave, and the temperature was raised to 160 ° C. at a heating rate of 4 ° C./min. Hold for 10 minutes. Thereafter, the mixture was cooled with water to lower the liquid temperature to room temperature. 0.35 g (Mg molar concentration conversion: 12 mmol / L) was added to the obtained aqueous solution of soda aluminate, and the temperature was again raised to 160 ° C and held for 10 minutes. Then, after cooling with water and lowering liquid temperature to room temperature, solid content in a liquid was filtered by pressure filtration, and the aqueous alumina-sodium aluminate solution was obtained.

(Example 9)

The aqueous solution of soda aluminate was obtained in the same manner as in Example 8 except that the amount of MgO added was 0.7 g (Mg molar concentration: 25 mmol / L).

(Comparative Example 4)

The aqueous solution of soda aluminate was obtained in the same manner as in Example 6 except that 0.5 g (Mol molar concentration: 12 mmol / L) was added to Mg (OH) ₂ used in Comparative Example 3 instead of the powdered MgO.

(Comparative Example 5)

The aqueous solution of soda aluminate was obtained in the same manner as in Comparative Example 4 except that the amount of Mg (OH) ₂ added was 1.0 g (Mg molar concentration: 25 mmol / L).

(Comparative Example 6)

A slurry in which 165 g of powdered aluminum hydroxide (the same as that used in Example 6) was added to 700 mL of an aqueous solution of caustic soda having a concentration of 145 g / L of Na ₂ O was injected into an autoclave, and the temperature was raised to 160 ° C. at a heating rate of 4 ° C./min. Hold for 10 minutes. Thereafter, the mixture was cooled with water to lower the liquid temperature to room temperature. 0.35 g (Mg molar concentration conversion: 12 mmol / L) was added to the obtained aqueous solution of soda aluminate, and the temperature was again raised to 110 ° C and held for 10 minutes. Then, after cooling with water again and lowering liquid temperature to room temperature, solid content in a liquid was removed by pressure filtration, and the aqueous solution of sodium aluminate was obtained.

(Comparative Example 7)

The aqueous solution of sodium aluminate was obtained in the same manner as in Comparative Example 6 except that the amount of powdered MgO added was 1.0 g / L (Mg molar concentration: 25 mmol / L).

(Measurement of the liquid color)

The liquid color of the aqueous solution of soda aluminate obtained in the Examples and Comparative Examples was measured in accordance with the measuring method of the liquid color. The result of Examples 1-5 and Comparative Examples 1-3 is shown in Table 1, and the result of Examples 6-9 and Comparative Examples 4-7 is shown in Table 2. In the case of "addition" in the table, when an additive compound such as solid MgO is added to the liquid together with the solid aluminum hydroxide at the stage before dissolving the solid aluminum hydroxide, the additive compound is dissolved in the solid aluminum hydroxide. When added to the subsequent aqueous solution of alumina soda, it is indicated as "after dissolution". In addition, "dissolution temperature" in a table | surface shows the temperature of the process of melt | dissolving solid aluminum hydroxide before adding MgO, and "processing temperature" shows the temperature of the heat processing after adding solid MgO. In addition, "holding time" shows the time holding process temperature.

(Example 10)

A slurry obtained by adding 165 g of powdered aluminum hydroxide (the same as that of Example 1) and 0.07 g of powdered MgO (A) to 700 mL of an aqueous solution of caustic soda at a concentration of 145 g / L of Na ₂ O was injected into an autoclave. It was maintained for 10 minutes after heating up to 160 degreeC / min. Thereafter, the mixture was cooled with water to lower the liquid temperature to room temperature. After filtering the obtained aqueous solution of soda aluminate, 250 g of the aqueous solution of soda aluminate was heated to 41 ° C, and an ozone / oxygen mixed gas having an ozone concentration of 45 g / m 3 was flown at a flow rate of 0.5 L / min using a high density polyethylene porous ball filter. Blown for a minute to give a decolorized aqueous aluminate solution. Table 3 shows the results of measuring the color of the obtained aqueous solution of soda aluminate according to the measurement method of the liquid color.

In addition, it is apparent that aluminum hydroxide having high whiteness is obtained by a conventional manufacturing method by using the decolorized alumina soda aqueous solution obtained by the method of the present invention as shown in the above examples.

Although the present invention has been described in detail and is for purposes of illustration only, it is to be understood that the scope of the invention is to be interpreted by the appended claims.

Claims (6)

Slurry composed of solid magnesium oxide and aqueous sodium aluminate solution, slurry composed of solid magnesium oxide, solid aluminum hydroxide and low concentration aluminate aqueous solution, or slurry composed of solid magnesium oxide, solid aluminum hydroxide and aqueous sodium hydroxide solution at a temperature of 130 ° C. or higher A process for producing a decolorized alumina soda aqueous solution characterized by separating the solids after the treatment. 2. The slurry according to claim 1, wherein the slurry comprising the solid magnesium oxide, the solid aluminum hydroxide and the low concentration aqueous aluminate solution or the slurry of the solid magnesium oxide, the solid aluminum hydroxide and the aqueous solution of caustic soda is heated at a temperature of 130 DEG C or higher, A process for producing a decolorized aqueous solution of soda aluminate, characterized by separating solid content. The method of claim 1, wherein the amount of the solid magnesium oxide added is 0.01 to 10 g / L based on the aqueous solution of sodium aluminate, the aqueous solution of low concentration aluminate or the aqueous solution of caustic soda. The method of claim 1, wherein the solid magnesium oxide has a BET specific surface area of 5 to 50 m 2 / g. The method for producing a decolorized alumina soda aqueous solution according to claim 1, wherein an ozone-containing gas is further blown into the aqueous solution of soda aluminate after the solids are separated. A method for producing high-white aluminum hydroxide, comprising: depositing aluminum hydroxide from the aqueous solution of sodium aluminate prepared by the method for producing the decolorized aqueous solution of sodium aluminate according to claim 1.