JP3316863B2 - Red mud separation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for separating red mud. More particularly, the present invention relates to a method for rapidly separating red mud from a high-temperature sodium aluminate solution.

[0002]

2. Description of the Related Art As is well known, extraction of alumina content from alumina-containing ore by the Bayer method involves, for example, mixing pulverized bauxite with a casein soda solution and steaming in a tubular reactor or an autoclave to remove the alumina content in the bauxite. The extraction is performed as a sodium aluminate solution. At this time, the alumina component is extracted and the reactive silica contained in the bauxite is also eluted.

When the sodium aluminate solution containing the reactive silica eluted in the liquid is sent to the aluminum hydroxide precipitation step and precipitated, the silica in the liquid is also decomposed and precipitated at the same time, and the aluminum hydroxide is precipitated. Because it is mixed in,
The quality of aluminum hydroxide is deteriorated, which is not preferable.

[0004] Therefore, it is necessary to carry out a desiliconization operation in which the reactive silica in the liquid is reacted with alumina and a part of the alkaline solution to form insoluble sodalite or zeolite before being sent to the aluminum hydroxide precipitation step. . The sodalite or zeolite produced by the desiliconization operation is usually discarded together with the dissolved residue (hereinafter referred to as red mud).

[0005] The higher the content of reactive silica in the bauxite in the raw material, and the higher the rate of reactive silica elution into the liquid during the extraction of alumina from the bauxite, the higher the amount of alumina lost in the desiliconization operation. And the amount of alkaline solution increases and is not economical.

In recent years, it has become difficult to obtain high-quality bauxite mainly containing alumina trihydrate which has a low silica content and a high alumina content and can be extracted at a relatively low temperature. There is a tendency to use high bauxite.

As a method of reducing the loss of the alkaline solution caused by the reactive silica in the bauxite, there is a method of selectively dissolving the alumina by utilizing the difference in the dissolution rate of the alumina in the bauxite and the reactive silica in the alkaline solution. Is taught. (Japanese Patent Publication No. 37-825 or Japanese Patent Publication No. 62-230613)
issue)

In this method, it is usually necessary to separate alumina sodium liquid and red mud as quickly as possible after substantially extracting alumina at a temperature of about 110 to 160 ° C. It is more advantageous than preventing silica elution.
Conventionally, separation of red mud from a sodium aluminate solution has been carried out from a sodium aluminate solution having a temperature below the boiling point after heat is recovered by a flasher or the like. However, considering the post-treatment of removing the silica component dissolved in the sodium aluminate solution after the red mud separation as a silicon removal product, it is considered that the sodium aluminate solution is as high as possible in temperature. However, it is advantageous because the desiliconization equipment can be made compact.

Therefore, the present inventors used a conventionally known red mud coagulant to quickly remove red mud from high-temperature sodium aluminate liquid, and separated red mud from high-temperature sodium aluminate liquid. Tests have shown that in the conventional method, for example, in a sodium aluminate solution having a boiling point or lower (about 60 to 90 ° C.), even a flocculant exhibiting excellent flocculating and separating effects exceeds about 100 ° C. It has been found that the coagulation effect is significantly reduced for sodium aluminate liquid having a boiling point or higher.

[0010]

In view of such circumstances,
The present inventors have intensively studied to find a very effective method for separating red mud from high-temperature sodium aluminate liquid,
Certain coagulants have been found to have a significant effect on the separation of red mud from sodium aluminate liquid at high temperatures,
The present invention has been completed.

[0011]

That is, the present invention relates to the separation of red mud from a sodium aluminate solution obtained by dissolving an alumina-containing ore with an alkaline solution, and the amount of uneluted reactive silica in the red mud. Is present at least 5% by weight or more,
And the temperature is sodium aluminate solution to the average molecular weight 12 million or more and atmospheric pressure boiling point above, from sodium aluminate solution and performing separation by adding ionic 40% to 60% of a synthetic organic polymer flocculant To provide a method for separating red mud.

Hereinafter, the method of the present invention will be described in more detail.
The sodium aluminate solution to be used in the present invention has a boiling point or higher, specifically about 110 ° C. or higher, preferably about 120 ° C. or higher.
C. to about 150.degree. C., and the red mud subjected to separation contains at least 5% by weight or more of uneluted reactive silica.

In the method of the present invention, the alumina-containing ore used as a raw material is mainly composed of alumina trihydrate having a crystal form of alumina (usually, the content of alumina trihydrate is about 10% of that contained in the ore. 50% by weight or more, preferably about 70% by weight or more), and bauxite and laterite ore containing reactive silica. Although the content of the reactive silica is not particularly limited,
Usually from about 0.5% to about 15%, usually from about 0.5% to about 10% by weight of the ore.

In carrying out the method of the present invention, the raw material bauxite, as it is, or after crushing, is mixed with an alkali-containing solution and is sent to a slurry-less extraction device.

[0015] The particle size of the raw material bauxite in the slurry sent to the extraction device is more advantageous as the particle size becomes smaller in order to increase the dissolution rate difference between alumina and reactive silica. In the process, the larger the particle size is, the easier the separation becomes. Generally, it is used at 20 mesh or less, preferably at 60 mesh or less.

The amount of the bauxite slurry-forming solution may be any amount as long as the bauxite can be transported, and the smaller the amount, the better. The solution varies depending on the type and particle size of the bauxite, but generally the solid concentration of the slurry is about 5% by weight or more. It is adjusted so as to be preferably 10 to 30% by weight.

Elution of alumina in bauxite is very rapid when the crystal form of alumina is alumina trihydrate (gibbsite) is very temperature-dependent at the same Na ₂ O concentration. Therefore, as an extraction method of alumina in which alumina in bauxite is sufficiently dissolved and elution of reactive silica is suppressed, it is ideal to instantaneously raise the temperature to a temperature necessary for dissolving alumina. Therefore, when using bauxite having a large content of reactive silica, a tubular heat exchanger, such as a double heat exchanger or a multi-tube heat exchanger, capable of rapid heating with a small backmixing and a large heat exchange capacity is used as an extraction device. The use of a reactor is recommended.

The temperature and time required for the extraction depend on the type of bauxite, the particle size, the concentration of Na ₂ O in the aqueous alkali solution, the concentration of Al ₂
It depends on the O ₃ concentration, the molar ratio of the charge, etc., and is set at the economically optimum point according to the basic unit and unit price of bauxite and caustic soda; the equipment cost, the performance of the separation equipment, and the performance of the desiliconization process. Na ₂ O concentration of about 100 to about 1
60 g / l, extraction temperature (refers to extraction device outlet temperature)
Is set at about 110 to about 160 ° C., the extraction time is set within 10 minutes, preferably the extraction temperature is set at about 120 to about 150 ° C., and the extraction time is set within 5 minutes. Above the extraction temperature and extraction time, it becomes difficult to increase the extraction rate of alumina from bauxite, suppress the elution of reactive silica, and reduce the amount of caustic soda loss.

In the extraction step, the extraction rate of alumina trihydrate from bauxite is set as high as possible, and the elution of reactive silica is set as low as possible.
Usually, the extraction ratio of alumina is about 80% or more, preferably about 8%.
The concentration may be set to 5% or more, and the elution of silica to about 70% by weight or less, preferably about 50% by weight or less.

The slurry after the alumina extraction is immediately sent to a solid-liquid separator, where it is separated into a sodium aluminate solution and red mud. In the method of the present invention, the solid-liquid separation is carried out at substantially the same temperature as the extraction temperature.

In the method of the present invention, a synthetic organic polymer flocculant having an average molecular weight of about 12 million or more and an ionicity of about 40 to about 60% in a sodium aluminate solution upon solid-liquid separation, more specifically, an average molecular weight of about 1200 10,000 or more, preferably about 14
A synthetic organic polymer flocculant comprising a copolymer of sodium acrylate and acrylamide having a ionicity of about 40 to about 60%, preferably about 45 to about 55%, is preferably red mud (dry basis). About 0.005 to about 0.1% by weight, preferably about 0.02 to about 0.06% by weight.

If the amount of the coagulant added to the sodium aluminate solution is less than the above range, a sufficient separation speed cannot be obtained, and even if the amount exceeds the above range, an effect commensurate with the added amount will be exhibited. Not only, it is not preferable because it remains as an organic substance in the sodium aluminate solution and causes coloring of precipitated aluminum hydroxide.

Further, in the method of the present invention, the addition of the flocculant is carried out in the presence of at least about 5% by weight, preferably about 7% by weight, of unresolved reactive silica in red mud in a sodium aluminate solution. It is done. When this condition is satisfied, as described in JP-B-48-37678, 5% by weight
The separation rate is significantly improved as compared with red mud containing less than less reactive silica.

The solid-liquid separation device used in the method of the present invention may be any device as long as it has a short residence time of solid-liquid, particularly red mud, and can reduce the amount of sodium aluminate solution entrained in the red mud. A high-speed separation type thickener, a centrifugal separator (decanter) and the like are typically used.

The sodium aluminate solution separated in the solid-liquid separation step is indirectly heated as it is or, if necessary, indirectly heated or by injecting live steam.
Next, it is sent to the desiliconization reaction tank (silicon denitrification process). In the desiliconization step, the sodium aluminate solution is used as it is, or if necessary, seeds containing a solid silicate substance as a main component are added, and sent to the desiliconization reaction tank to remove the silica dissolved in the extract. It reacts with alumina and a part of the alkaline solution and precipitates as a silicate material such as insoluble sodalite or zeolite.

The desiliconization reaction tank is not particularly limited in its shape as long as it provides a residence time for precipitating the reactive silica as a desiliconization product from the extract. A multi-stage reactor with a stirrer is used.

As the silicon removal conditions, the silicon removal reaction temperature is determined by the temperature of the previous step, but is usually about 115 to about 160 ° C., and the processing time is about 15 minutes to about 5 hours, preferably about 120 ° C. to about 1 hour.
The temperature is set at 40 ° C. and the processing time is about 0.5 hours to about 3 hours. After the silicon removal treatment, the extract is cooled and then solid-liquid separated into a silicon removal product and a clarified sodium aluminate solution, and the solution is sent to an aluminum hydroxide precipitation step.

The sodium aluminate solution sent to the precipitation step is prepared by adding fine aluminum hydroxide seeds to precipitate aluminum hydroxide, and then separating the precipitated aluminum hydroxide from the sodium aluminate solution, After being washed with water and filtered, the sodium aluminate solution after separation of aluminum hydroxide is recycled and used as an alkaline solution for extracting alumina from bauxite. The precipitation temperature of aluminum hydroxide from the sodium aluminate solution is not particularly limited as long as it is within a conventionally known range, and is usually carried out at about 50 ° C. to about 70 ° C.

A flash evaporation or an indirect heat exchanger is used for cooling the sodium aluminate solution. In the flash evaporation, the flashed steam is used as recovered steam for preheating the bauxite slurry or the circulating sodium aluminate solution, and for indirect heat exchange. The vessel is also used for preheating the bauxite slurry and the circulating sodium aluminate solution.

[0030]

According to the method of the present invention described in detail above, since the sedimentation speed of red mud from a high-temperature sodium aluminate solution is high, rapid solid-liquid separation at a high temperature is made possible.
When applied to an improved buyer process, its industrial value is very large.

[0031]

EXAMPLES The method of the present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples. Incidentally, the non-eluted reactive silica% (R) in the red mud according to the present invention is defined as follows. R = A-1.613B where: R: ratio of uneluted reactive silica in red mud (% by weight) A: total reactivity in red mud determined based on JIS-M-8361 (1963) Silica ratio (% by weight) B: Ratio of bound soda in red mud (% by weight) determined based on JIS-R-3101 (1963)

[0032] Separation performance test of flocculant (solid recovery)
Was performed as follows. 150 mm inner diameter shown in FIG.
Using a solid-liquid separator having a cylindrical shape (internal cavity) made of stainless steel and having a conical lower part with a length of 600 mm, slurry is continuously fed from a slurry supply port 1 located at a height of about 1/3 from the lower end of the container. Is supplied and concentrated by gravity in a cylindrical container, and the supernatant liquid is taken out continuously from the upper part 2 and the concentrated slurry is taken out from the lower part 3, and the concentration and amount of the supplied slurry for a predetermined time and the concentrated slurry taken out from the lower part of the solid-liquid separator The solid recovery was determined from the concentration and amount.

Example 1 A slurry obtained by dispersing and mixing 170 g of bauxite having the composition shown in Table 1 and ground to 100 mesh with 1 liter of a sodium aluminate solution containing 145 g / l of Na ₂ O and 77 g / l of Al ₂ O _3. Pipe diameter 10mm, length 220m
Was continuously supplied to the tubular reactor at a flow rate of 2.1 m / sec, and the slurry was heated so that the reactor outlet temperature became 130 ° C. to extract alumina from bauxite. The sodium aluminate solution forming the slurry obtained from the slurry outlet of the reactor was Na ₂ O 130 g / l, Al
_{The amount of 2} O _{3 was} 147 g / l, and the amount of unreacted silica in the red mud was 9.7% by weight. Next, while maintaining a part of the dissolved slurry at the same temperature (130 ° C.), 0.04% by weight of a polymer flocculant (trade name PA-372:
Kurita Water Industries Ltd., molecular weight 14 million, ionic 50
%, A copolymer of sodium polyacrylate and polyacrylamide), and the solid-liquid separation ability was measured by the solid-liquid separation device shown in FIG. Table 2 shows the results. After cooling the temperature of the sodium aluminate solution to which the polymer flocculant was added to 95 ° C., the solid-liquid separation ability of the flocculant at that temperature was measured.
Table 2 shows the results.

Comparative Examples 1 and 2 A polymer flocculant having a molecular weight of 10 million and an ionicity of 80% (trade name: P) was used in place of the polymer flocculant PA-372 as a flocculant.
A-318: manufactured by Kurita Industry Co., Ltd.) and a molecular weight of 600
100% ionic polymer flocculant (trade name PA-3)
12: manufactured by Kurita Water Industries Ltd.) except that solid-liquid separation ability was measured in the same manner as in Example 1. Table 2 shows the results.

Comparative Example 3 The same sodium aluminate solution and bauxite as in Example 1 were introduced into an autoclave and heated at a temperature of about 140.degree.
The mixture was stirred for 0 minute and an alumina extraction treatment was performed from bauxite. The sodium aluminate solution in the slurry after the extraction treatment was 130 g / l of Na ₂ O and 144 g / l of Al ₂ O ₃ , and the unreacted silica in the red mud was 0.5% by weight or less. Next, this slurry was measured for solid-liquid separation ability of the flocculant by the same method using the same polymer flocculant as in Example 1.
Table 2 shows the results.

[0036]

[Table 1]

[0037]

[Table 2]

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a solid-liquid separation device used for a solid-liquid separation performance test of a flocculant.

[Explanation of symbols]

1 is a slurry supply port, 2 is an upper part of the container, and 3 is a lower part of the container.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshio Kumagai 5-1, Sokai-cho, Niihama-shi, Ehime Sumitomo Chemical Industries, Ltd. (72) Inventor Michikazu Inami 5-1, Sokai-cho, Niihama-shi, Ehime Sumitomo Inside Kagaku Kogyo Co., Ltd. (72) Inventor Kazuhisa Ishibashi 5-1 Sokaicho, Niihama-shi, Ehime Prefecture Sumitomo Kagaku Kogyo Co., Ltd. (56) References JP-A-57-51117 (JP, A) JP-A-63 -248717 (JP, A) JP 48-37678 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01F 7/06 B01D 21/01

Claims (2)

(57) [Claims] In the separation of red mud from a sodium aluminate solution obtained by dissolving an alumina-containing ore with an alkaline solution, the amount of uneluted reactive silica in the red mud is at least 5%.
There above wt%, and the temperature is sodium aluminate solution to the average molecular weight 12 million or more and atmospheric pressure boiling point above, and characterized in that the separation by adding a ionic 40% to 60% of a synthetic organic polymer flocculant Of red mud from sodium aluminate solution. 2. The method for separating red mud according to claim 1, wherein the synthetic organic polymer flocculant is a copolymer of sodium acrylate and acrylamide.