JPH05193931A - Production of aluminum hydroxide from alumina-containing ore - Google Patents

Abstract

PURPOSE:To reduce loss of alkali and alumina and to obtain aluminum hydroxide which is hardly contaminated with silica when a liq. alumina extract from a tube reactor is desilicated and the aluminum hydroxide is deposited by specifying the extracting condition. CONSTITUTION:A concd. alumina-contg. ore is slurryed with a small amt. of an aq. alkali soln., and the slurry and an aq. alkali soln. preheated above the extraction temp. of alumina after being mixed with the slurry are simultaneously or the mixture is charged into a tube reactor. The alumina is extracted from the ore at 120-160 deg.C within 10min, the insolubles are immediately separated from the liq. extract, the extract is then desilicated, and then a seed of aluminum hydroxide is added to deposit aluminum hydroxide. When the extraction temp. and time are increased above the above-mentioned values, the extraction rate of alumina is not enhanced, the elution of reactive silica is suppressed, and loss of alkali is increased.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing aluminum hydroxide from an alumina-containing ore.

[0002] More specifically, aluminum hydroxide ores (hereinafter referred to as bauxite) are dissolved in an alkali to hydrolyze a sodium aluminate solution to precipitate aluminum hydroxide, so as to precipitate aluminum hydroxide. Depending on the production method, even when using low-grade bauxite with a high content of soluble silica as the raw material alumina-containing ore, the amount of alkali loss is low, the yield of alumina is high, the amount of silica pollution is low, and the energy consumption rate is low, making it economical. The present invention relates to a method for producing aluminum hydroxide capable of obtaining aluminum hydroxide.

[0003]

The most commonly used method for producing aluminum hydroxide from bauxite is the Bayer process. In this method, bauxite is treated with an alkaline aqueous solution such as caustic soda or a mixed solution of caustic soda and sodium carbonate to form a slurry, and the alumina content in the bauxite is extracted as sodium aluminate (extraction step), and then the slurry is extracted from the slurry. Insoluble residues such as iron oxide, silicate, and titanium oxide are separated (red mud separation step), and aluminum hydroxide is added as seeds to the clear sodium aluminate solution after separating the insoluble residues. Precipitate aluminum hydroxide at a temperature of ℃, separate the precipitated aluminum hydroxide from the sodium aluminate solution (precipitation step), circulate and use a part of the separated precipitated aluminum hydroxide as seeds, and remove the remaining aluminum hydroxide. On the other hand, the sodium aluminate solution after separation (hereinafter referred to as the decomposition solution) is used as it is, or It is formed of a step of recycling the dissolution step of the bauxite after the condensation.

Usually, bauxite contains alkali-soluble silica (hereinafter referred to as reactive silica or R-SiO ₂ ), although it varies depending on the mining site. Therefore, in the above extraction step, the reactive silica contained in the bauxite is eluted at the same time when the alumina content in the bauxite is extracted. When the extract containing the reactive silica eluted in this solution (sodium aluminate solution) is subjected to a precipitation treatment in order to obtain aluminum hydroxide as it is, the silica in the solution is decomposed and precipitated together with the aluminum hydroxide. However, the quality of aluminum hydroxide is deteriorated. Therefore, the reactive silica in the extract is reacted with alumina and a part of the alkaline solution before being sent to the precipitation step, to be precipitated as alkali-insoluble sodalite or zeolite (desulfurization step), and in the subsequent red mud separation step. Separated and discarded along with other insoluble substances such as iron oxide and titanium oxide. Conventionally, most commonly, the residence time in the extraction process is 30 minutes to 6 minutes.
The time is relatively long, and sufficient elution of reactive silica and conversion and precipitation of the eluted reactive silica into a desiliconized product are performed in this step. However, the method
As described above, the soluble silica in the extract is removed as a desulfurized product using a large amount of alumina and alkali, which is not economical.

As a method of reducing the alkali loss due to the reactive silica in the bauxite, the alumina content is selected by utilizing the difference in the dissolution rate of the alumina in the bauxite and the reactive silica in the caustic alkali solution or sodium aluminate solution. Method to make it possible to utilize bauxite having a high content of reactive silica by dissolving it physically (Japanese Patent Publication No.
No. -8257), a method in which the alumina content is sufficiently dissolved, but the elution of reactive silica is suppressed and the extraction residue is separated using a synthetic organic polymer flocculant (JP-B-48-37678), tubular reaction A method of extracting alumina by a vessel, immediately after extraction, a mixed solution of an extract and a dissolution residue is flash-cooled, the dissolution residue is separated and removed, and the extraction solution is subjected to a silica treatment and then aluminum hydroxide is deposited. 62-230613) and the like are known.

[0006]

However, since Japanese Patent Publication No. 37-8257 uses two types of bauxite, one having a high reactive silica content and the other having a normal content, the extraction is carried out under different conditions. However, this cannot be applied when bauxite having a normal reactive silica content or bauxite having a high reactive silica content is used alone.

[0007] Japanese Patent Publication No. 48-37678 is an excellent invention in terms of high-speed separation of extraction residue, but details of how to efficiently suppress elution of reactive silica during extraction of alumina are described in detail. In addition, a process intended to suppress the decrease in alumina yield is not disclosed.

Further, JP-A-62-230613 discloses that a mixed liquid of an extract and an extraction residue is flash-cooled immediately after extraction to suppress the elution of soluble silica from bauxite into an alkaline solution, and the dissolved residue is separated and removed. Next, it is a method of removing the extracted silica, and in this method, heating is described as a method in which live steam is directly blown into a mixing header or a tubular reactor, but in this case, the water balance in the system is To take
When it is necessary to install a large evaporator separately, it is not economical, and when heating the mixed slurry of alkaline aqueous solution such as circulating decomposition solution and bauxite to the extraction temperature by using recovered steam and live steam in the mixing header. ,
R-SiO ₂ elution suppression is not sufficient for elution of the R-SiO ₂ is also generated preheating process leading to the extraction temperature. Moreover, since the silica removal treatment is performed at a low temperature of 80 to 110 ° C. after flash cooling, the reaction rate is slow, and it is necessary to install a very large silica removal treatment device in order to avoid silica contamination of the product aluminum hydroxide. There are problems such as. Furthermore, when the silica content is held for a long time to reduce the silica content to a desired concentration in the silica removal step, the alumina content in the extract is simultaneously precipitated as aluminum hydroxide, so the extraction rate of alumina is higher than that in bauxite. The whole process causes the disadvantage that the yield of alumina is reduced.

In view of such circumstances, the present inventors have reduced the amount of caustic soda lost, reduced the yield of alumina, and deposited aluminum hydroxide with less silica contamination without deteriorating the energy consumption rate. The present invention has been completed as a result of intensive research to find an economical method for producing aluminum hydroxide from bauxite.

[0010]

Means for Solving the Problems That is, the present invention relates to a method for producing aluminum hydroxide in which alumina is extracted from an alumina-containing ore with an alkaline aqueous solution, and a high-concentration alumina-containing ore slurried with a small amount of alkaline solution is used. The slurry and an aqueous alkaline solution preheated so that the temperature of the slurry after mixing with the slurry is equal to or higher than the extraction temperature of alumina are mixed with each other or after mixing, and the mixture is charged into an extracting device including a tubular reactor at a temperature of 120 ° C to 160 ° C. After extracting alumina from the alumina-containing ore under extraction conditions within minutes,
The dissolution residue is immediately separated and removed from the extract, and then the extract is subjected to a silica removal treatment, and seed aluminum hydroxide is added to the extract after the removal of the silica removal product to precipitate aluminum hydroxide. A method for producing aluminum hydroxide from an alumina-containing ore is provided.

The method of the present invention will be described in more detail below. In the method of the present invention, the ore-containing ore used as a raw material has a crystal form of alumina of alumina 3
Bauxite or laterite mainly composed of hydrate (usually, the content of alumina trihydrate is about 50% by weight or more, preferably about 70% by weight or more based on the alumina contained in the ore) and containing reactive silica. Ore and the like. Although the content of the reactive silica is not particularly limited, it is usually about 0.5% by weight to about 15% by weight, usually about 0.5% by weight to about 10% by weight, based on the ore. The method of the present invention is particularly economical when using bauxite having a high content of volatile silica as a raw material.

In carrying out the present invention, the raw material bauxite is used as it is or after being roughly crushed, and then made into a slurry using a slurrying solution, as it is, or after wet crushing,
If necessary, it is sent to a preheater.

The particle size of the raw material bauxite sent to the preheater is preferably as small as possible in order to increase the difference in dissolution rate between alumina and reactive silica. Since the larger the value, the easier the separation, it is usually 10 mesh or less, preferably 60 mesh or less.
Used below mesh.

The bauxite slurry solution at the time of preheating may be any amount that makes the bauxite a slurry that can be transported. It depends on the type and particle size of the bauxite, but generally the solid content concentration of the slurry is about 20% by weight. % Or more, preferably 30 to 65% by weight.

The solution used for forming the slurry is not particularly limited, but may be a decomposition solution or a concentrated solution thereof (referred to as a circulation decomposition solution), a dissolution residue cleaning solution or a precipitation aluminum hydroxide cleaning solution. It is possible to use a solution that is circulated in the buyer process. Particularly, the solution for cleaning the dissolution residue has a lower concentration of Na ₂ O than the solution for circulating decomposition, and although it is a small amount, reactive silica is eluted and mixed in during the process of cleaning the dissolution residue. Therefore, elution of the reactive silica during the preheating of the bauxite slurry can be suppressed, and at the same time, the reactive silica contained in the dissolution residue cleaning liquid can be subjected to a silica removal treatment in a subsequent silica removal step, which is preferably used.

The temperature at which the bauxite slurry is preheated depends on the type of bauxite, the concentration of Na ₂ O in the slurry solution, the type of slurry preheating device, etc., but the upper limit is set to about 120 ° C., preferably about 110 ° C. It
If the preheating temperature exceeds about 120 ° C, the reactive silica is eluted during the preheating of the bauxite slurry, which is not preferable. Since the elution of the reactive silica proceeds even during the preheating of the bauxite slurry, the time required for this preheating is set within 10 minutes, preferably within 5 minutes. Preheating of the bauxite slurry is not always necessary, but it is preferable to preheat to about 70 ° C or higher, more preferably about 80 ° C or higher when heat is recovered from the slurry after extraction and the heat is effectively utilized.

As a preheating device for the bauxite slurry, a device such as a double-tube heat exchanger or a multi-tube heat exchanger which can preheat in a short time with little backmixing is generally used.

In carrying out the method of the present invention, the other alkaline aqueous solution to be mixed with the preheated bauxite slurry is not particularly limited, but is mainly composed of the circulating decomposition solution, and the other alkaline solution generated in the process. The containing solution is used as it is or after being concentrated.

These alkaline aqueous solutions are generally preheated to 150 ° C. to 170 ° C., in a known manner, so that the temperature after mixing with the bauxite slurry stream reaches the extraction temperature by means of recovered steam and live steam. It As a preheating device for the alkaline aqueous solution, an indirect heating type heat exchanger such as a double tube type heat exchanger, a multi-tube type heat exchanger, a spiral type heat exchanger is generally used.

The bauxite slurry after preheating and the alkaline aqueous solution after preheating are fed to the extraction device separately or after mixing. The mixing ratio of bauxite slurry after preheating and alkaline aqueous solution after preheating is the type of bauxite,
Although it depends on the solid concentration of the bauxite slurry and the composition of the decomposed solution, the liquid composition at the outlet of the extraction device has a molar ratio (Na
₂ O / Al ₂ O ₃ ) 1.30 to 1.60, preferably 1.35 to 1.50. In the present invention, the temperature of the slurry mixed at the inlet of the extractor reaches the target extraction temperature. When extraction at a higher temperature is desired, the preheated alkaline aqueous solution immediately before being supplied to the extraction device, or the bauxite slurry and the preheated alkaline aqueous solution immediately before being supplied to the extraction device are mixed to the extraction device. In the introduction method, a part of live steam may be directly blown into the mixed slurry for heating.

The fact that there is a time difference in the dissolution rate of alumina and reactive silica in bauxite in an aqueous alkali solution and the production rate of desiliconized products is found in JP-B-37-8257 or JP-A-62-230613. It is well known as described in the above. However, when the elution rates of alumina and reactive silica in bauxite were examined in more detail, it was found that the dissolution reaction rate was a first-order reaction for each component, and the reaction rate constant was that of alumina as shown in FIG. Has a higher gradient than that of reactive silica, that is, when the crystalline form of alumina in bauxite is alumina trihydrate (gibbsite), the elution of alumina trihydrate is much higher than that of reactive silica. Since the dissolution equilibrium determined by the Na ₂ O concentration and temperature is reached very quickly, and the temperature dependence is large at a fixed Na ₂ O concentration, the alumina in bauxite is sufficiently dissolved and the elution of reactive silica is suppressed. As a conventional method, an alkaline aqueous solution for extraction is mixed with a high-concentration alumina-containing ore slurry after crushing as is conventionally done, and the mixed slurry is heated. It is ideal that the bauxite slurry and alkaline aqueous solution are preheated separately at the reactor inlet and the temperature is instantly raised to the temperature required for dissolution of alumina by mixing, rather than the method of raising the temperature to the precipitation temperature. Found.

As a result of earnest studies on the method satisfying the above conditions, the present inventors preheated the bauxite slurry and the alkaline aqueous solution with an indirect heating type preheating device, and mixed the preheated slurry with the preheated alkaline aqueous solution. The so-called two-fluid system is used, and the preheating temperature of the bauxite slurry in the two-fluid system is low so that the reactive silica is not eluted as much as possible, but the heat recovery is partially achieved. The present invention has been completed by setting the temperature so high that the preheating temperature of the alkaline aqueous solution that does not cause the elution of silica is set high so as to reach the extraction temperature of alumina immediately after mixing the two fluids after preheating. .. Of course, the bauxite slurry may be unheated if the alkaline aqueous solution can be heated to a sufficiently high temperature.

As a device for extracting alumina, a tubular reactor with less backmixing is used adiabatically. The shape of this reactor is not particularly limited, and for example, if two fluids consisting of preheated bauxite slurry and preheated alkaline aqueous solution are mixed and alumina can be extracted from the bauxite, the following The conduit for transferring the slurry to the separation step can be kept warm to function as a reactor.

It is not necessary for the extractor to have a heating function from the outside, the slurry temperature at the inlet of the extractor is the highest, and only the temperature of the slurry is kept and the heat is not supplied thereafter.
It is recommended that the reaction occur so-called adiabatically. This skillfully utilizes the fact that the dissolution rates of alumina and silica in alkaline solutions are different.When applying the same amount of heat for the same extraction time, it is necessary to keep the slurry temperature constant by the heating function. This is because it is possible to suppress the elution amount of silica and extract the same amount of alumina by adopting a method in which the temperature at the inlet of the apparatus is increased and the temperature is decreased from the inlet of the extraction apparatus to the outlet. Furthermore, by making the extraction device not particularly have a heating function from the outside, there is no problem of reduction of heat transfer rate due to scaling, which is a big problem in the use of a tubular reactor,
It also has a secondary effect of substantially reducing the scaling to the equipment used for preheating the alkaline aqueous solution and the alkali-containing ore slurry.

The temperature and time required for the extraction are as follows: the type of bauxite, the particle size, the Na ₂ O concentration in the alkaline aqueous solution, the Al ₂
Depending on the O ₃ concentration and the molar ratio charged, the basic unit and unit price of bauxite and caustic soda; set to the economical optimum point based on the equipment cost, the performance of the separation equipment, the performance of the desilvering process, etc. Has a Na ₂ O concentration of about 100 to about 160 g / l and an extraction temperature (extractor outlet temperature).
Is about 120 ° C to about 160 ° C, extraction time is within 10 minutes,
Preferably, the extraction temperature is set to about 125 ° C to about 150 ° C and the extraction time is set to about 5 minutes or less. Above the extraction temperature and the extraction time, it becomes difficult to achieve the object of the present invention to increase the extraction rate of alumina from bauxite to suppress the elution of reactive silica and reduce the caustic soda loss.

In the extraction step, the extraction rate of alumina is higher than that of bauxite and the elution of reactive silica is set as low as possible. Usually, the extraction rate of alumina is about 70% or more, preferably About 80% or more,
The elution of silica may be set to about 70% or less, preferably 50% or less.

The slurry after extraction with alumina is immediately sent to a solid-liquid separation device and separated into an extraction liquid (liquid) and a dissolution residue (solid). This solid-liquid separation is carried out at a temperature substantially equal to the extraction temperature.

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 for the solid liquid, particularly the dissolution residue, and can reduce the amount of the extraction liquid entrained in the dissolution residue, A high-speed separation type thickener and a centrifugal separator (decanter) are used. At the time of separation, it is possible to accelerate the separation by adding a known coagulant to the slurry, for example, a polyacrylic acid polymer coagulant. The addition amount of the aggregating agent may be in a known addition range, and is usually about 0.005% by weight to about 0.1% by weight based on the dissolved residue (dry basis).
Used in a percentage by weight. The separation needs to be carried out in the shortest possible time, and is usually carried out within about 10 minutes, preferably within about 5 minutes after extraction. The separation time mentioned here is the residence time of the dissolved residue in the separation device. In this method, the solid-liquid separation temperature is high, which is almost isothermal to the extraction temperature.
It can be inferred that the solid-liquid separation can be performed at high speed as compared with the conventional method. If the separation time becomes long, the reactive silica in the residue will elute, which is not preferable.

The extract separated in the solid-liquid separation step is sent as it is or after being indirectly heated or cooled if necessary, and then sent to a silica removal reaction tank (silicon removal step).
In the desiliconization step, the extract is as it is, or if necessary, seeds containing a solid silicate material as a main component are added,
The silica dissolved in the extract is sent to a desulfurization reaction tank, and the silica dissolved in the extract is reacted with alumina and a part of the alkaline solution to form an insoluble silicate substance such as sodalite or zeolite.

When the content of reactive silica in the raw material bauxite is large and the silica concentration in the extract is about 10 g / l or more, the silica removal reaction proceeds due to spontaneous nucleation, but the silica removal time is shortened, and For the purpose of improving the solid-liquid separation property of the resulting desulfurized product, it is preferable to add seeds made of a solid silicate material containing sodalite or zeolite as a main component.

The desiliconization reaction tank is not particularly limited in its shape as long as it gives a residence time for precipitating the reactive silica as a desilvered product from the extract, but preferably there is little backmixing. A multi-stage reactor equipped with a stirrer is used.

The silica removal conditions are not unique because they differ depending on whether the heat recovery process from the extract by flash evaporation or the like is performed before or after the silica removal treatment, but the silica removal temperature is about 80 to about 160. C, the processing time is about 15 minutes to about 10 hours, preferably the removal temperature is about 115 to about 160 ° C, the processing time is about 15 minutes to about 5 hours, more preferably the temperature is about 120 ° C.
˜140 ° C., and processing time is about 0.5 hour to about 3 hours. The higher the treatment temperature, the faster the silica removal rate, and the less precipitation of aluminum hydroxide during the silica removal treatment,
When the treatment temperature is high, the pressurizing device is used, and therefore, it is sufficient to select the desilvering condition in consideration of economical efficiency. The extract after the silica removal treatment is cooled, if necessary, and then solid-liquid separated into a silica removal product and a clarified sodium aluminate solution, and the solution is sent to a precipitation step of aluminum hydroxide.

Flash evaporation or an indirect heat exchanger is used for cooling the extract, and the flashed flash is used as a recovery steam to preheat the bauxite slurry or the circulating decomposition liquid, and also for the indirect heat exchanger. Used for preheating bauxite slurry and circulating decomposition liquid. In the present invention, the cooling of the extraction liquid may be carried out immediately after the separation of the extraction liquid and the dissolution residue or after the silica removal treatment.

For separation of the desiliconized product from the extract, a thickener, a centrifuge, a filter, etc. may be used alone or in appropriate combination. When a part of the separated silica removal product is reused as seeds for silica removal treatment, the activity of the seeds should be restored by operations such as crushing, sieving and washing before recycling to the silica removal process. Is recommended. In particular, the desiliconization treatment time can be significantly shortened by crushing the obtained desiliconization product with a ball mill or the like and using it as seeds under the following conditions. The silica removal product used as seeds is not unique depending on the silica removal temperature, the soluble silica concentration in the extract, the silica removal time, etc., but the average particle size is usually about 1 μm.
To about 30 μm, preferably about 5 μm to about 20 μm, seed loading of about 5 g / l to about 150 g / l, preferably about 20
It is carried out in the range of g / l to about 100 g / l.

On the other hand, the dissolution residue separated in the solid-liquid separation step in the method of the present invention is cooled and washed to recover the extract liquid accompanying the dissolution residue. Flash evaporation and an indirect heat exchanger are used for cooling the dissolution residue. In the flash evaporation, the flashed vapor is used as a recovered vapor for preheating the bauxite slurry and the circulating decomposition liquid, and the indirect heat exchanger is also used for preheating the bauxite slurry and the circulating decomposition liquid. The apparatus used for washing and deliquoring the dissolution residue is not particularly limited, but for washing the dissolution residue having a high soda content, a high-speed thickener capable of preventing elution of R-SiO ₂ from the residue at the time of washing, a centrifugal separation Machines, filters, etc. can be used alone or in appropriate combination.

The present invention will be described in more detail below with reference to the drawings, but the method of the present invention is not limited thereby.

FIG. 1 shows a flow sheet of one embodiment for carrying out the method of the present invention, and FIG. 2 is a flow sheet showing one embodiment of a conventionally known buyer process. In the figure, 50 is a slurry preparation tank comprising a ball mill or the like, 51-56 are preheaters, 57 is an extraction device, 58 is a solid-liquid separation device, 59 is a desiliconization reaction tank, 60-62 is a flash flash can for cooling, and 63 is 63. Solid-liquid separator, 64 is a crusher, 1
Indicates bauxite, 2 indicates a circulating decomposition solution, and 3 to 47 indicate lines (conduits).

In FIG. 1, reference numeral 2 denotes a circulating decomposition liquid, which is divided and supplied to lines 3 and 4. The bauxite is supplied from the line 1 to the ball mill 50, and is crushed and mixed in the ball mill together with a part of the circulating decomposition liquid supplied from the line 3 to form a transportable slurry. It consists of a tube heat exchanger and heat is transferred from the flash flash evaporators 62 and 61 to the line 31,
It is preheated to a predetermined temperature in preheaters 51 and 52 configured to be supplied via 30.

The main flow of the circulating decomposed liquid from the line 4 is normally composed of a multi-tube heat exchanger via the lines 8, 9 and 10 and the heat is supplied from the cooling flash evaporators 62, 61 and 60 to the lines 29, 28 and 27. Preheated in preheaters 53, 54 and 55 which are adapted to be supplied via a line 10, which is usually a shell-and-tube heat exchanger, configured such that the heat is supplied via line 26 by live steam. It is preheated in the heated preheater 56. A part of the live steam from the line 26 may be directly blown into the decomposition liquid, but using it as an indirect heating mode in the preheater 56 balances the water in the system, reduces the steam usage amount, and reduces the evaporation can. It is preferable because the scale can be reduced. The preheating temperature in the preheater 56 is not particularly limited, but it is preheated to a desired extraction temperature of alumina when mixed with the bauxite-containing slurry from the line 7 when being introduced into the extraction device.

The bauxite slurry after preheating and the decomposed liquid after preheating were taken out through lines 7 and 11, respectively, and mixed,
It is introduced into the extraction device 57 via line 12. The extraction apparatus uses a tubular reactor with low backmixing, and the extraction temperature is generally in the range of about 120 ° C to about 160 ° C.

The slurry obtained by extracting the alumina content in the ore as sodium aluminate in the extraction device 57 is immediately taken out through the line 13 and introduced into the solid-liquid separation device 58 to be separated into a dissolution residue and an extraction liquid, and dissolved in the extraction liquid. Prevent the elution of silica from the residue. A known polymer flocculant is added to the slurry introduced into the solid-liquid separator 58 for the purpose of enhancing the separation effect from a part of the line 13. The solid-liquid separation device 58 is not particularly limited in its type as long as it is a device capable of performing solid-liquid separation within a time of residence of the dissolved residue within about 10 minutes in the device, but is usually a high-speed separation type thickener. , A centrifuge is used.

The slurry introduced into the solid-liquid separator 58 is separated into a dissolution residue (red mud) and an extraction liquid, and the dissolution residue (red mud) is sent to a dissolution residue treatment step through a line 15 to recover heat and alkali. After that, it is discharged outside the process. On the other hand, the extract is introduced into the silica removal reaction tank 59 through the line 14 and held until the silica component dissolved in the solution becomes a desired amount of silica removal product. As the desiliconization reaction tank 59, a tank having a stirring function is generally used. At the time of removing silica, a solid silicate substance is added as seeds from a line 25 for the purpose of promoting the reaction. The seed can be used by introducing a commercially available solid silicate substance from outside the process, but generally, the desilica product separated in the subsequent process is used as it is, or as a seed such as washing and crushing. After chemical treatment, it is recycled.
The processing temperature in the desiliconization reaction tank 59 is about 115 ° C to about 16 ° C.
0 ° C., the treatment time is about 15 minutes to about 5 hours, preferably the treatment temperature is about 120 ° C. to about 140 ° C., the treatment time is about 0.5 hours to about 3 hours, and the silica removal product as seeds has an average particle size. About 1
μm to about 30 μm, addition amount about 5 g / l to about 150 g / l
It is carried out in the range of.

Extraction liquid containing silica removal product in which silica dissolved in the extraction liquid in the desiliconization reaction tank 59 is precipitated as a silica removal product and the silica concentration in the extraction liquid is reduced to a desired concentration. Are derived by line 16 and are respectively lines 17, 1
It is sent to the solid-liquid separation device 63 which separates the desiliconized product through line 8 after being cooled by the flash flash evaporators 60, 61 and 62 for cooling. Flash evaporator for cooling 60, 61
The vapors recovered in and 62 are used as the main stream of the circulating decomposition solution, which is the above-mentioned alkaline aqueous solution, and the preheat source of the bauxite-containing slurry.

The slurry sent from the line 19 to the solid-liquid separation device 63 for separating the desilvered product is separated into the desilvered product and a clear extract (sodium aluminate solution), and the desilvered product is line 21. It is recovered from the line 23 through the. The desiliconized product thus obtained has a small content of impurities such as iron oxide and titanium oxide, and therefore can be taken out through the line 23 and effectively used for existing applications such as catalysts and inorganic fillers. In addition, a part of the desiliconized product passes through the line 22 and the crusher 6
4 and crushed to a desired seed particle size to be used in the desiliconization reaction tank 59. The clear extract separated by the solid-liquid separator 63 is sent through a line 20 to an aluminum hydroxide precipitation step (not shown), seeds are added to precipitate aluminum hydroxide, and then the precipitated aluminum hydroxide is separated. On the other hand, the decomposition liquid after the aluminum hydroxide is separated is used in the line 2 in a circulating manner.

FIG. 2 shows an example of a Bayer method for extracting alumina from conventionally known bauxite. In FIG. 2, the circulating decomposition solution is introduced into the slurry preparation tank 50 from line 2 and the bauxite introduced from line 1. Is crushed and made into a slurry, and sent to the preheaters 51, 52 and the extraction device 57 via the lines 32, 33 and 34. As in the case of FIG. 1, the preheaters 51, 52 and the extraction device 57 are equipped with flash evaporation cans 62, 61 and 6 for cooling from the slurry after extraction.
The heat recovered at 0 is introduced through lines 47, 46 and 45, live steam is introduced into the extraction device 57 through line 44 and heated to a desired alumina extraction temperature, and alumina is extracted from the bauxite. The slurry after the extraction process is led out via the line 35. After the extraction, the slurry is subjected to heat recovery in the cooling flash evaporators 60, 61 and 62 and then introduced into the solid-liquid separation device 58 through the line 38.
Separated into extract and dissolution residue. The extraction liquid is introduced from a line 40 into a silica removal reaction tank 59 and subjected to a silica removal treatment, followed by a line 41.
And is introduced into the solid-liquid separation device 63 and separated into a clear sodium aluminate solution and a desulfurized product. The desulfurized product is led out of the system through a line 42, and a part of the product is recycled as seeds. Although a specific number of cooling flash evaporators, decomposition liquid preheaters, and slurry preheaters are shown in FIGS. 1 and 2, these may of course be constituted by arbitrary numbers.

[0046]

According to the present invention, when extracting alumina from bauxite, the elution of reactive silica can be remarkably suppressed without substantially lowering the extraction rate of alumina as compared with the conventional method. It is possible to significantly reduce the loss of caustic soda and alumina caused by removing the volatile silica as a desilvering product. Also,
The slurry is preheated by a two-fluid system with indirect heating, and by adopting the alumina extraction method using an adiabatic reactor (reactor without heating function), heating by blowing raw steam of the conventional method, and further the reactor Compared with the method of extracting alumina while heating it to the alumina extraction temperature in the interior, caustic soda and It is possible to greatly reduce the loss of alumina. Further, in the present invention, when the silica removal treatment is carried out immediately after the dissolution residue is separated, that is, when the extraction silica treatment is carried out at a high temperature before cooling the extraction liquid, the removal speed is higher than that in the conventional method. Since the silica device can be downsized and the precipitation of alumina in the step can be reduced, as a result, the decrease in the yield of alumina can be significantly reduced. As described above, according to the method of the present invention, it is possible to provide a method for producing aluminum hydroxide economically from an alumina-containing ore having a high reactive silica content, which has been conventionally difficult to use, and having less silica pollution. , Its industrial value is enormous.

[0047]

EXAMPLES The method of the present invention will be described in more detail with reference to the following examples, but the method of the present invention is not limited thereto. [Example 1] Alumina was extracted from bauxite having the analytical values (unit is% by weight) shown in Table 1 using an apparatus as shown in FIG.

[0048]

[Table 1]

The feed from line 1 as bauxite, line 3 from the concentration of Na ₂ O 152 g / l, bauxite concentration in the slurry preparation tank 50 of a ball mill circulation decomposing solution of Al ₂ O ₃ 82g / l a 600 g / l And crushed. Next, 1.7 m of crushed bauxite slurry
Pipe diameter 25 mm, total length 360 m (51 + 5
Preheated from 70 ° C. to 95 ° C. at a temperature rising rate of 7 ° C./min using the recovered steam of the extracted slurry introduced from the lines 31 and 30 in the double-tube heat exchangers 51 and 52 of 2). The preheat time of the slurry was 3.5 minutes. On the other hand, the circulating decomposition liquid from the line 4 is the lines 29, 28 and 2
104 ℃ with the recovery steam of the slurry after extraction introduced from 7.
Was preheated up to 160 ° C. by indirect heating by injecting live steam into the outer tube of the double pipe through line 26. The bauxite slurry discharged from the double-tube heat exchanger 52 is introduced through line 7 into the line 12 together with the circulating decomposition liquid preheated by the multi-tube heat exchanger in line 11 and mixed, and this mixed solution is mixed into 2 Pipe diameter 40 mm, length 290 at a flow rate of 1 m / sec.
m was introduced into the extraction step 57 consisting of a tubular reactor, where alumina was extracted adiabatically (without heating) for a short time. The slurry outlet temperature in the extraction step 57 is 130 ° C,
The extraction time was 2.3 minutes. Immediately after quenching at flasher taken out of the slurry from a sample outlet provided at the outlet of the extraction step 57 from the purpose of examining the extraction rate and elution rate of R-SiO ₂ of alumina from bauxite separating bauxite residue, bauxite residue chemistry From the analytical values, the extraction rate of Al ₂ O ₃ and the elution rate of R-SiO ₂ were calculated. The results are shown in Table 2.

Comparative Example 1 Using the apparatus shown in FIG. 2, alumina was extracted using the same circulating decomposition solution and bauxite as in Example 1. The circulating decomposition solution was added so that the bauxite concentration would be 600 g / l, and the mixture was crushed with a ball mill to 60 mesh. The remaining circulating decomposition solution was mixed with the crushed bauxite slurry, and the preheaters 51, 52 and the extraction device 57 consisting of a double-tube heat exchanger with a tube diameter of 40 mm and a total length of 1070 m (51 + 52 + 57) were mixed at a flow rate of 2.1 m / sec. From the lines 47, 46 and 45, and the live steam from the line 44 from 70 ° C to 130 ° C at 7 ° C
Al ₂ O ₃ in bauxite was extracted by heating at a temperature rising rate of 1 / min. In the same manner as in Example 1, the extraction rate of alumina from bauxite and the elution rate of R-SiO ₂ were examined. The results are shown in Table 2.

Comparative Example 2 Using the same process as in Comparative Example 1, the total length of the double-tube heat exchanger was set to 730 m, and the bauxite was heated by heating the slurry in the preheater and the reactor to 5.8 minutes. Extraction rate of alumina and R-SiO
The dissolution rate of ₂ was investigated. The results are shown in Table 2.

Comparative Example 3 The same stock solution as in Example 1,
Bauxite, bauxite amount, the extraction with the extraction temperature is performed 60 minutes using an autoclave, were examined alumina extraction rate and elution rate of R-SiO ₂ from bauxite in the slurry. The results are shown in Table 2.

[0053]

[Table 2] The extraction time in the table shows the temperature rise time of the bauxite slurry and the residence time in the extraction device provided after that. Al ₂ O ₃
"Extraction" in the extraction rate column indicates the extraction rate (extr
acted alumina), "effective" is R-S eluted in the extract
Extraction rate of Al ₂ O ₃ (available alumina) in which iO ₂ was converted to desiliconized product and alumina loss due to this was corrected
Is shown. The loss of Na ₂ O is calculated by converting R-SiO ₂ eluted in the extract into a desiliconized product and calculating the soda loss by the unit of (kg / t-Al ₂ O ₃ ).

Example 2 The tubular reactor shown in Example 1
Polymer coagulant is dissolved in the slurry from 57
Introduced into high-speed thickener 58 after adding 0.04% by weight
Then, the bauxite residue was immediately separated. R in the extract
-SiO₂The concentration was 3 g / l. This liquid is desilvered
It was introduced into the tank 59 and the particle size was adjusted in advance to an average particle size of 10 μm.
The desilvered product was added as seeds in an amount of 50 g / l and the temperature was 126 ° C.
It was removed for 20 minutes. Remove the desulfurized slurry from the cooling
Shu Evaporating can 60-62 led to a temperature of 1 by flash
Decrease to 00 ° C and generate with a gravity type solid-liquid separator 63
Separated. Part of the desilvered product is divided into seeds and balls
The particle size is adjusted with a mill 64 to give seeds of 50 g / l.
It was recycled to the desilvering reactor. Fast removal of remaining amount
Derived from line 15 separated by thickener and shown
With bauxite residue cooled by not cooling system
Mix and wash in a multi-stage countercurrent washer (not shown)
The sodium aluminate solution adhering to the residue was collected. Solid-liquid content
The extract separated by the separator 63 is shown via a line 20.
After performing fine filtration with a clarification filter that has not been
Then, aluminum hydroxide was deposited. Solid-liquid separator 63
R-SiO in the extracted liquid ₂The concentration is 0.6 g /
It was completely removed with l.

[Comparative Example 4] The slurry discharged from the multi-tube reactor shown in Comparative Example 1 was cooled with flash evaporators 60 to 6
It was led to 2 and quenched to 100 ° C. After adding the same amount of coagulant as in Example 2 to the cooled slurry, the extract and bauxite residue were immediately separated by a high-speed thickener 58, and the extract was introduced into a desiliconization reaction tank 59, and the average particle size was previously calculated. Diameter 10
Add 50 g / l of seeds of the desulfurized material with particle size adjusted to μm 1
A silica removal operation was performed at 00 ° C. for 750 minutes. Next, the extracted liquid after the silica removal process is passed through a line 41 and a gravity type solid-liquid separation device 6
The desilvered product was separated at 3. A part of the desulfurized product was divided, the particle size was adjusted with a ball mill, and the seeds were recycled to the desilication reaction tank 59. The remaining silica removal mixture is mixed with the bauxite separated by the high-speed thickener 58 drawn out from the line 42 and drawn out from the line 39, washed with a multistage countercurrent washing machine (not shown), and attached to the residue sodium aluminate solution. Was recovered. The extraction liquid separated by the solid-liquid separation device 63 is line 4
After microfiltration through a clarification filter (not shown) through step 3, the solution was introduced into the precipitation step to precipitate aluminum hydroxide. R-SiO ₂ in the extract liquid derived from the solid-liquid separator 63
The concentration was 0.6 g / l and it was sufficiently desilvered. (In the conventional method shown in FIG. 2, an example of using a high-speed thickener in the solid-liquid separation device 58 and an example of activation of the desilvered product by ball milling were given. This application was used to justify the comparison of the effect with Example 1, and a high-speed thickener was conventionally used as the solid-liquid separator 58, and further, it was activated by ball milling of the desiliconized seeds as seeds. Is not admitted that was done).

The operating conditions in each step of Example 2 and Comparative Example 4 are shown in Table 3, and from the chemical analysis values of the dissolution residue sampled from the outlet of the tubular reactor 57 and the bauxite residue at the outlet of the residue washer, Al Table 4 shows the calculation results of the extraction rate of ₂ O ₃ and the elution rate of R-SiO ₂ .

[0057]

[Table 3]

[0058]

[Table 4]

In Table 4, Comparative Example 4 is compared with Example 2.
4% of alumina extraction rate at the outlet of multi-stage countercurrent washer
Is a loss due to the precipitation of alumina in the silica removal step.

[Example 3] In Example 2, a part of the desulfurized product was divided as seeds, pulverized by a ball mill 64, and recycled to a desulfurization reaction tank. We examined the change of R-SiO ₂ concentration in.
The results are shown in Table 5.

[Comparative Example 5] In Example 2, a part of the desulfurized product was divided as seeds, but it was recycled into the desulfurization reaction tank without crushing as in Example 3, and the recycling frequency and seeds investigating changes in the R-SiO ₂ concentration of the particle size and extracts. The results are shown in Table 5.

[0062]

[Table 5]

[Brief description of drawings]

FIG. 1 is a flow sheet of one embodiment for carrying out the method of the present invention,

FIG. 2 is a flow sheet showing an embodiment of a conventionally known buyer process,

FIG. 3 is a diagram showing the temperature dependence of the dissolution rate coefficient of alumina and reactive silica in bauxite in an aqueous alkaline solution.

[Explanation of symbols]

1 and 2, 50 is a slurry preparation tank, 51
˜56 is a preheater, 57 is an extraction device, 58 is a solid-liquid separation device, 59 is a desiliconization reaction tank, 60-62 are flash evaporation cans for cooling, 63 is a solid-liquid separation device, 64 is a crusher, and 1 is bauxite. 2 is a circulating decomposition solution, 3 to 47 are lines (conduit)
Indicates.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Dowa 5-1 Sokai-cho, Niihama-shi, Ehime Prefecture Sumitomo Chemical Co., Ltd. (72) Inventor Kazuhisa Ishibashi 5-5 Sokai-cho, Niihama-shi Ehime Prefecture Sumitomo Chemical Kogyo Co., Ltd. (72) Inventor Mitsuaki Murakami 5-1 Sokai-cho, Niihama-shi, Ehime Sumitomo Chemical Co., Ltd.

Claims (5)

[Claims] 1. A method for producing aluminum hydroxide in which alumina is extracted from an alumina-containing ore with an alkaline aqueous solution, which comprises a high-concentration alumina-containing ore slurry slurried with a small amount of an alkaline solution, and a slurry after mixing with the slurry. An alkaline aqueous solution preheated so that the slurry temperature becomes equal to or higher than the extraction temperature of alumina is added at the same time or after mixing, and the mixture is charged into an extraction device composed of a tubular reactor at a temperature of 120 ° C to 1 ° C.
After extracting alumina from the alumina-containing ore under extraction conditions of 60 ° C. for 10 minutes or less, the dissolved residue is immediately separated and removed from the extract, the extract is desiliconized, and then the desiliconized product is extracted. A method for producing aluminum hydroxide from an alumina-containing ore, which comprises adding seed aluminum hydroxide to and precipitating aluminum hydroxide. 2. The method according to claim 1, wherein the alumina form in the alumina-containing ore is mainly alumina trihydrate. 3. A solution residue is separated and removed from the extract, and then the extract is desiliconized at a temperature of 115 ° C. to 160 ° C., followed by flash cooling, and the extract after separation of the desiliconized product is seed hydroxylated. The method according to claim 1, wherein aluminum hydroxide is added to precipitate aluminum hydroxide. 4. A high-concentration alumina-containing ore slurry slurried with a small amount of an alkaline solution at 80 ° C. to 110 ° C.
2. The method according to claim 1, wherein the alkali aqueous solution is preheated to 0.degree. C. and the alkaline aqueous solution mixed with the high-concentration alumina-containing ore slurry is mixed so that the slurry temperature becomes equal to or higher than the extraction temperature of alumina. 5. The method according to claim 1, wherein the separated silica removal product is pulverized and used as a seed during the silica removal treatment.