JP2013528555A - Method for producing high purity aluminum hydroxide - Google Patents

Abstract

  The present invention relates to a method for producing high-purity aluminum hydroxide, and in particular, after dissolving general aluminum hydroxide under a predetermined condition of a weight ratio of aluminum oxide to aluminum hydroxide as a mother liquor, after aging, To obtain high-purity aluminum hydroxide that adsorbs impurities from the mother liquor prepared by adding pulp, deposits seed crystals into the mother liquor, and then filters, wash, and dry the deposited substance This offers the advantage of producing high purity aluminum hydroxide that is environmentally friendly but low in cost.

Description

  The present invention relates to a method for producing high-purity aluminum hydroxide, and more specifically, prior to the Bayer Process, a general aluminum hydroxide is dissolved in a caustic soda (NaOH) solution, and the dissolved liquid is aged. Then, only impurities in the solution aged using a small amount of adsorbent are selectively removed to produce high-purity aluminum hydroxide, so that water is added before the Bayer process, which is a conventional production method. Can eliminate over-product loss, waste generation and inefficiency due to inefficiency during co-precipitation process in which impurities present in the solution dissolved with aluminum oxide are co-precipitated with aluminum hydroxide However, it is possible to produce high-purity aluminum hydroxide that can produce high-quality, high-purity aluminum hydroxide in an environmentally friendly manner while reducing costs. On.

  In recent years, high-purity aluminum hydroxide is used in special ceramics, high-purity glass for optical production, optical glass, high-purity aluminum compounds, and high-purity alumina raw materials. It is also a compound that has recently attracted attention in connection with LED products such as LED TVs.

  In order to produce such high-purity aluminum hydroxide, a Bayer process is an essential process among the production processes of the compound, and this Bayer process is an aluminum hydroxide present in bauxite ore. In order to extract the product, bauxite is added to a caustic soda (NaOH) solution and heated to elute aluminum hydroxide (dissolution step), and then sludge is discarded and aluminum hydroxide dissolved by the caustic soda is precipitated (precipitation method) Precipitation step).

  Aluminum hydroxide produced in such a Bayer process contains a large amount of impurities due to impurities introduced from bauxite introduced in the melting process and residues of auxiliary materials used in the Bayer process.

  Therefore, high-purity aluminum hydroxide having a predetermined purity or higher cannot be produced only by a general Bayer process. Therefore, conventionally, in order to remove impurities, aluminum hydroxide is dissolved in an acid (Acid), and then a metal ion is removed using an organic solvent such as isodecanol or kerosene. The method of was used. However, such an impurity removal method is difficult to operate, and not only an expensive solvent extractant must be used, but also problems such as environmental pollution have emerged.

  Moreover, although the manufacturing method using an aluminum (Al) metal may be utilized, this is also high manufacturing cost and the possibility of commercialization is unclear, and substantially, manufacture of high purity aluminum hydroxide The actual situation is that the method is commercialized as a private know-how only in one or two companies worldwide.

  The present invention has been devised to solve the technical problems as described above, and after dissolving general aluminum hydroxide with a caustic soda (NaOH) solution, the dissolved liquid is aged ( Among the terms used herein, “ripening” refers to growing particles in a dissolved state) to activate impurities, and then to a solution dissolved using an adsorbent of pulp material. By adsorbing the impurities present and filtering, the dissolved liquid is effectively purified, and the purified liquid is precipitated by using a Bayer process to deposit high-purity aluminum hydroxide. An object of the present invention is to provide a method for producing high-purity aluminum hydroxide capable of mass-producing high-purity aluminum hydroxide at a low cost and in an environmentally friendly manner.

  In addition, the present invention is an important condition required in the production of high-purity aluminum hydroxide, weight ratio of process mother liquor, aging time, amount of adsorbent, stirring speed, adsorption time, precipitation temperature, precipitation time, etc. The object is to provide a method for producing high-purity aluminum hydroxide having a purity of 99.9 or more by developing optimum conditions.

  One preferred embodiment of the method for producing high-purity aluminum hydroxide according to the present invention was prepared by dissolving a general aluminum hydroxide and then aging, and after adding the pulp after the mother liquor preparation step. A purification step for adsorbing impurities from the mother liquor, and after the purification step, seed crystals are added to the mother liquor and precipitated, and then the precipitated material is filtered, washed, and dried to obtain high-purity aluminum hydroxide Obtaining step.

  Here, in the mother liquor preparation step, a general aluminum hydroxide and caustic soda (NaOH) are put in a dissolution tank, and the general aluminum hydroxide is dissolved to make a mother liquor, and the dissolution step dissolves And a maturing step of maturing impurities while slowly lowering the temperature of the mother liquor for a predetermined maturing time.

  In another embodiment of the method for producing high-purity aluminum hydroxide according to the present invention, a caustic soda solution (NaOH) and general aluminum hydroxide are placed in a dissolution tank, and general aluminum hydroxide is dissolved to form a mother liquor. In the mother liquor, the pulp material adsorbent is added and dispersed in the dissolving step, the maturation step in which the temperature of the mother liquor is slowly lowered over a predetermined time after the dissolving step and the impurities are aged, and the mother liquor aged through the aging step A purification step for adsorbing the impurities to the adsorbent, and after the purification step is completed, separating the pulp on which the impurities have been adsorbed, filtering the mother liquor, and then sending it to the precipitation tank; After the first filtration step, a precipitation step in which an aluminum hydroxide seed crystal is administered to the mother liquor in the precipitation tank to precipitate aluminum hydroxide; and after the precipitation step, the particle size is A polarization step for separating the deposits and the precipitates having a large particle size; and a mother liquor containing the precipitates having a large particle in the polarization step is filtered, and the filtrate is recycled to the caustic soda solution. A filtration step, and a drying step of removing moisture after washing the precipitate filtered by the second filtration step.

Here, in the dissolution step, the weight ratio (Al ₂ O ₃ / Na ₂ CO ₃ ) of aluminum oxide to sodium hydroxide in the dissolved mother liquor is 0.68 or more.
In the dissolution step, the concentration of the caustic soda (NaOH) is 270 g / l or more based on sodium carbonate (Na ₂ CO ₃ ).

In the aging step, the aging temperature of the mother liquor can be maintained at 130 ° C. to 90 ° C. for a predetermined time or more.
The aging time for aging impurities in the aging step may be 1 hour or more.
The deposition process may be performed at an initial temperature of 85 ° C. or higher.
In addition, the deposition step may be performed for 72 hours or longer for depositing aluminum hydroxide.
Further, the weight ratio of aluminum oxide to sodium hydroxide finally obtained in the precipitation step (Al ₂ O ₃ / Na ₂ CO ₃ ) may be 0.36 or less.

  The method for producing high-purity aluminum hydroxide according to the present invention has an effect that environmentally friendly high-purity aluminum hydroxide can be produced by adsorbing impurities using an adsorbent such as pulp.

  In addition to the purification process, the method for producing high-purity aluminum hydroxide according to the present invention presents important precipitation conditions accompanying various processes, as well as the coprecipitation process, and is difficult to operate. In addition, by eliminating the expensive process, it is possible to produce high-purity aluminum hydroxide at a low cost.

FIG. 1 is a block diagram showing sequential manufacturing steps of a method for manufacturing high-purity aluminum hydroxide according to the present invention.

Hereinafter, a preferred embodiment of a method for producing high-purity aluminum hydroxide according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing sequential manufacturing steps of a method for manufacturing high-purity aluminum hydroxide according to the present invention.

In general, in order to produce aluminum hydroxide, bauxite is dissolved in a high concentration caustic soda (NaOH) solution in a heated and pressurized state to form a sodium aluminate (NaAlO ₂ ) supersaturated solution.

  The sodium aluminate thus prepared is allowed to stand and filter, and after the purification step (S210) for removing undissolved impurities, the purified sodium aluminate solution is precipitated at a high temperature. The desired aluminum hydroxide is finally produced through a precipitation step by a method of slowly lowering the temperature over a long time so as to start. Here, in order to produce high-purity aluminum hydroxide with high purity, the purification step (S210) for removing impurities is extremely important among the above-mentioned steps. The actual situation is that a certain purification step (S210) is focused.

  A preferred embodiment of the method for producing high-purity aluminum hydroxide according to the present invention provides various and experimental steps for increasing the purity of the finally obtained aluminum hydroxide, as shown in FIG. .

  More specifically, the method for producing high purity aluminum hydroxide according to the present invention uses the adsorbent that adsorbs impurities after aging the sodium aluminate supersaturated solution. The solution is purified to remove a small amount of pulp with adsorbed impurities, and the purified sodium aluminate solution is slowly lowered over a long period of time to complete precipitation at a low temperature so as to start precipitation at a high temperature. As a result, high-purity aluminum hydroxide is produced.

  More generally, a method for producing high-purity aluminum hydroxide according to the present invention will be described. As shown in FIG. 1, the present invention includes a mother liquor preparation step (S100) in which general aluminum hydroxide is dissolved and then aged. ), After the mother liquor preparation step (S100), after the purification step (S200) for adsorbing impurities from the mother liquor prepared by adding pulp, and after the purification step (S200), seed crystals are introduced into the mother liquor and precipitated. Then, an acquisition step (S300) of acquiring high-purity aluminum hydroxide for filtering, washing, and drying the deposited substance is included.

  In particular, the refining step (S200) is unique in that impurities are adsorbed using an adsorbent such as pulp instead of the conventional coprecipitation method in which impurities in the mother liquor are coprecipitated with aluminum hydroxide seed crystals. You can say that.

  Here, the mother liquor preparation step (S100) includes a general aluminum hydroxide and caustic soda (NaOH) in a dissolution tank to dissolve the general aluminum hydroxide to make a mother liquor (S110), An aging step (S120) of aging impurities while slowly lowering the temperature of the mother liquor dissolved in the dissolving step (S110) for a predetermined aging time.

  In the method for producing high-purity aluminum hydroxide according to the present invention, in addition to the purification step (S200), important conditions are presented in the production process. It should be noted that the range is not limited.

  For example, another embodiment of the method for producing high-purity aluminum hydroxide according to the present invention obtains final aluminum hydroxide through a more detailed process than the above-described embodiment under more precise conditions. become able to.

  That is, as shown in FIG. 1, another embodiment of the method for producing high-purity aluminum hydroxide according to the present invention uses the above caustic soda solution (NaOH) and general water to produce a sodium aluminate supersaturated solution. Impurities are matured by slowly lowering the temperature of the mother liquor over a predetermined time after the dissolving step (S110) in which aluminum oxide is placed in a dissolving tank to dissolve general aluminum hydroxide to make a mother liquor, and the dissolving step (S110). An aging step (S120), and a purification step (S210) in which an adsorbent of pulp material is added to and dispersed in the mother liquor aged through the aging step (S120) to adsorb impurities in the mother liquor to the adsorbent. After the refining step (S210) is completed, the pulp on which impurities have been adsorbed is separated and the mother liquor is filtered, and then sent to the precipitation tank. After the step (S310) and the first filtration step (S310), a precipitation step in which aluminum hydroxide seed crystals are administered to the mother liquor in the precipitation tank to precipitate aluminum hydroxide, and the growth is sufficient after the precipitation step. In other words, a precipitate having a small particle size is separated from a precipitate that has grown completely, that is, a particle having a large size, and the precipitate having a small particle size is used as an aluminum hydroxide seed crystal in the precipitation step. A polarization step (S330) to be used, a second filtration step (S340) in which the mother liquor containing precipitates having large particles in the polarization step (S330) is filtered, and the filtrate is recycled to the caustic soda solution; A drying step (S350) for removing moisture after washing the precipitate filtered in the second filtration step (S340).

  It will be as follows if the manufacturing method of the high purity aluminum hydroxide based on this invention comprised as mentioned above is demonstrated in detail.

First, in order to produce a sodium aluminate process mother liquor in a dissolution tank made of a stainless steel (Sus 316L) material capable of raising the temperature, a sodium hydroxide (NaOH) solution is added to sodium carbonate (Na ₂ CO ₂ ). ₃ ) based on 210 to 280 g / l, and a general aluminum hydroxide containing water has a weight ratio (A / C: weight ratio) of Al ₂ O ₃ / Na ₂ CO ₃ of 0.60. After adding general aluminum hydroxide to ˜0.72, in order to disperse aluminum hydroxide, the temperature was raised to 120 to 130 ° C. while stirring at 30 RPM, and then 10 minutes. the extent maintained (lysis step (S110)) is not a result, as can be seen in Table 1 and Table 2, _Al 2 _{O 3} The weight ratio of _{Na 2 CO 3 (A / C} ) is not less 0.68 or more, caustic soda (NaOH) solution 270 g / l and 280 g / l, based on the sodium carbonate _(Na 2 CO _3), i.e. 270 g / l or more In this case, impurities were minimized. More preferably, if the weight ratio (A / C) of Al ₂ O ₃ / Na ₂ CO ₃ is 0.68 to 0.72, based on the results of Table 1 tested by the applicant, It can be seen that the content of Fe is minimized to 5 ppm for Fe and 4 ppm for Na.

Applicant, among the above-mentioned general conditions, the weight ratio (A / C) of Al ₂ O ₃ / Na ₂ CO ₃ of the process mother liquor is 0.68 and 0 which are the weight ratios described in Table 1 below In order to make a process mother liquor in which the aluminum hydroxide is completely dissolved in a state of 0.69 which is an intermediate value of .70, the caustic soda concentration is set to 270 g / l based on Na ₂ CO _3. It put into the dissolution tank, and after heating up temperature to 125 degreeC, it maintained for 10 minutes in the state.

  Thus, the stirrer is slowly operated at a speed of about 3 RPM in order to age the process mother liquor in a state where the aluminum hydroxide is completely dissolved so that the A / C of the process mother liquor is 0.69. The mother liquor temperature was slowly lowered to 100 ° C. and aged over 1 hour. Here, the reason for aging the process mother liquor is to increase the size of the impurity particles so that the impurities contained in the process mother liquor can be easily removed, as described above. (Aging process (S120))

Effect of product by weight ratio (A / C) of Al ₂ O ₃ / Na ₂ CO ₃ in process mother liquor

Effect of products on caustic soda (NaOH) concentration in process mother liquor

  On the other hand, the applicant understands the content relationship of impurities depending on the aging time in the aging step (S120) from Table 3, A / C of the mother liquor of the process is 0.69, and the concentration of the caustic soda is sodium carbonate. It was found that the most suitable ripening time must be maintained for 1 hour or more under the condition of 270 g / l based on the above. In particular, there is an advantage that it is possible to produce high-purity aluminum hydroxide that can be used for LED products that have recently received intensive attention only when the Fe content is 5 ppm or less. The time is preferably maintained for 1 hour or longer.

Impurity content of high-purity products depending on the aging time of process mother liquor

  Next, in order to remove impurities contained in the process mother liquor, as shown in Tables 4 and 5 in the well-aged process mother liquor, the product production per liter is the largest and the impurity removal rate is Pulp corresponding to 1 g per liter, which is the highest condition, is added, and the speed of the stirrer is increased to 5 RPM as shown in Table 6 to disperse the pulp in the mother liquor and adsorb impurities for 10 minutes. (Purification step (S210))

Effect of process mother liquor on amount of adsorbent pulp for removal of impurities in process mother liquor (mother liquor temperature 100 ° C., stirring speed 5 RPM, stirring time 10 minutes)

Changes in process mother liquor due to stirrer speed (RPM) during 10 min reaction time

Change in process mother liquor due to adsorption time (temperature 95 ° C, pulp usage 1 g / l, stirring speed 5 RPM)

Meanwhile, the pulp impurities adsorbed from the process mother liquor is removed at a first filtration step is the next step (S310), wherein, in order to remove the pulp, the mother liquor 1 m ³ per A beautiful process mother liquor from which impurities have been removed by filtration at a pressure of 2 atm using a filter press with a filter cloth made of polyethylene (Polyethylene) having a filtration area of 25 cm × 25 cm in width and length. Then, the pulp that has been sent to the precipitation tank and adsorbed with impurities for the subsequent precipitation step is treated as recycled waste after washing. (First filtration step (S310))

In this way, the purified process mother liquor from which impurities have been removed then undergoes a precipitation process. At this time, the process mother liquor is in a state where the weight ratio of Al ₂ O ₃ / Na ₂ CO ₃ is 0.69 and the temperature is maintained at 90 ° C. In the precipitation step, the speed of the stirrer is increased to 15 RPM so that the precipitate and the seed crystal can float. As shown in Table 7, precipitation begins at 90 ° C. or higher, and as shown in Table 8, the precipitation time is maintained at 72 hours or longer. (Precipitation process)

Relation of Na% content of precipitates by initial precipitation temperature (precipitation time 72 hours)

After the precipitation, the Na content of the precipitate and the weight ratio of Al ₂ O ₃ / Na ₂ CO _{3 in} the final process liquid (final precipitation temperature 40 ° C., initial precipitation temperature 90 ° C., seed crystal 65 g / l, average particle size 40 μm) )

The precipitate deposited by the deposition step becomes high-purity aluminum hydroxide having a smaller impurity content ratio as the caustic soda (NaOH) content is minimized. Thus, as the deposition conditions that allow the caustic soda content to be minimized, as shown in Tables 7 and 8, the applicant has an initial deposition temperature of 90 ° C., a final deposition temperature of 40 ° C., and a deposition time of It was found that when the time was 72 hours or longer, the weight ratio (A / C) of Al ₂ O ₃ / Na ₂ CO _{3 in} the final precipitate was 0.34 or less. Thus, when the weight ratio (A / C) of the final deposition liquid is 0.34 or less, it becomes a condition for aligning quality and competitiveness.

  Next, when the precipitation step is finished, the polarization step (S330) is started. In the polarization step (S330), precipitates with insufficient growth are separately separated from precipitates having an average particle size of 30 μm or less using a cyclone polarizer, and hydroxylated administered during the deposition step. A precipitate (average particle size of 60 μm), which is used as an aluminum seed crystal and has well-grown particles, undergoes a subsequent second filtration step (S340). (Polarization process (S330))

  After the polarization step (S330), the well-grown precipitate having an average particle size of 60 μm is separated into a solid and a filtrate using a filter, and then the filtrate is further added to the caustic soda solution necessary for the dissolution step (S110). The precipitate, which is high purity aluminum hydroxide, is sent for recirculation and washed with clean water at 80 ° C or higher, and then subjected to phase transition in a fluidizing blower type dryer that can minimize contamination. Dry at 130 ° C. within 60 minutes to remove moisture without waking up. (Second filtration step (S340) and drying step (S340))

  The high-purity aluminum hydroxide obtained by drying in this way is finally packaged and completed in the packaging step (S360). (Packaging process (S360))

Comparison of high-purity aluminum hydroxide produced by the production method according to the present invention and conventional aluminum hydroxide

  The preferred embodiment of the method for producing high-purity aluminum hydroxide according to the present invention and other embodiments have been described in detail with reference to the accompanying drawings. However, the embodiment of the present invention is not necessarily limited to this, and various modifications or other embodiments belonging to the scope equivalent to the present invention can be obtained by a person having ordinary knowledge in the technical field to which the present invention belongs. It is natural that it can be realized. Accordingly, the true scope of the present invention should be determined by the following claims.

Claims (8)

A dissolving step in which a caustic soda solution (NaOH) and general aluminum hydroxide are placed in a dissolution tank to dissolve the general aluminum hydroxide to form a mother liquor;
After the dissolution step, an aging step of aging impurities by slowly lowering the temperature of the mother liquor over a predetermined time;
A purification step of adsorbing impurities in the mother liquor to the adsorbent by adding and dispersing an adsorbent of pulp material to the mother liquor aged through the aging step;
After the purification step is completed, the pulp that has adsorbed impurities is separated, the mother liquor is filtered, and then sent to the precipitation tank;
After the first filtration step, a precipitation step of precipitating aluminum hydroxide by administering an aluminum hydroxide seed crystal to the mother liquor in the precipitation tank;
After the precipitation step, a polarization step for separating a precipitate having a small particle size and a precipitate having a large particle size;
Filtering the mother liquor containing precipitates with large particles in the polarization step, the filtrate being recycled to the caustic soda solution;
A drying step of removing moisture after washing the precipitate filtered by the second filtration step,
The dissolving step includes
A method for producing high-purity aluminum hydroxide, wherein the weight ratio (Al ₂ O ₃ / Na ₂ CO ₃ ) of aluminum oxide to sodium hydroxide in the dissolved mother liquor is 0.68 or more. _{2. The} method for producing high-purity aluminum hydroxide according to claim 1, wherein the concentration of the caustic soda (NaOH) in the dissolving step is 270 g / l or more based on sodium carbonate (Na ₂ CO ₃ ).   The method for producing high-purity aluminum hydroxide according to claim 1, wherein the aging temperature of the mother liquor is maintained at 130 ° C to 90 ° C for a predetermined time or more in the aging step.   The method for producing high-purity aluminum hydroxide according to claim 3, wherein an aging time for aging the impurities in the aging step is 1 hour or more.   The method for producing high-purity aluminum hydroxide according to claim 1, wherein the precipitation step is performed at an initial temperature of 85 ° C or higher.   2. The method for producing high-purity aluminum hydroxide according to claim 1, wherein the precipitation step is performed for 72 hours or more for precipitation of aluminum hydroxide. _2. The high purity according to claim 1, wherein a weight ratio (Al ₂ O ₃ / Na ₂ CO ₃ ) of aluminum oxide to sodium hydroxide finally obtained in the precipitation step is 0.36 or less. A method for producing aluminum hydroxide. The dissolving step includes
_2. The high-purity water according to claim 1, wherein the weight ratio (Al ₂ O ₃ / Na ₂ CO ₃ ) of aluminum oxide to sodium hydroxide in the dissolved mother liquor is 0.68 to 0.72. A method for producing aluminum oxide.