METHOD OF MANUFACTURING HIGH-DENSITY BEADS OF HIGH-PURITY ALUMINA

Abstract

A method of manufacturing high-density beads of high-purity alumina, in which general aluminum hydroxide is dissolved in a sodium hydroxide solution. Insoluble impurities are removed to thus manufacture a pure sodium aluminate solution. High-purity aluminum hydroxide is manufactured. The manufactured high-purity aluminum hydroxide is subjected to a hydrothermal reaction, thus removing both crystal water and sodium. Sulfuric acid and ammonia are not used, raw material powder uncontaminated with impurities is manufactured by performing atomization using pulverizing media, and the powder as a raw material and ultrapure water are used to manufacture seeds. While the atomized powder and the ultrapure water are put onto a rotating plate, steps are performed until a desired size is obtained, thus manufacturing highly densified beads. A sintering process is performed in order to maintain a molding shape and to increase a density, followed by a classification process.

Claims

1. A method of manufacturing high-density beads of high-purity alumina, the method comprising: a mother-solution preparation step of putting general aluminum hydroxide and a sodium hydroxide solution into a dissolver and performing heating to thus form a supersaturated liquid; a purification step that includes a first filtration process for filtering a mother solution using a filter cloth to thus remove insoluble impurities and transferring the purified mother solution to a precipitator, a precipitation process for adding high-purity aluminum hydroxide seeds to the mother solution of the precipitator, thus precipitating high-purity aluminum hydroxide, a second filtration process for separating the precipitated high-purity aluminum hydroxide and the sodium hydroxide solution, which includes a part of the aluminum hydroxide dissolved therein, transferring a filtrate back to the process and washing a solid matter, a hydrothermal process for mixing the washed high-purity aluminum hydroxide with distilled water and putting a mixture into a high-pressure reactor, followed by a reaction at 250 to 300 C., thus removing some of the crystal water from Al.sub.2O.sub.3*H.sub.2O, and a third filtration process for separating the water and the solid matter after the hydrothermal process; a heat-treatment step of performing heat treatment and firing at a high temperature in order to remove the crystal water after the third filtration process; and a forming step of the high-density beads of the high-purity alumina, which includes an atomization process for pulverizing particles into fine particulates after the heat-treatment step, a molding process for performing molding into beads having a predetermined size after the atomization process, a sintering process for performing the heat treatment at a high temperature after the molding process, and a classification process for sorting the particles after the sintering process.

2. The method of claim 1, wherein during the mother-solution preparation step, the heating is performed at a temperature condition of 110 to 150 C. for 1 to 4 hours to cause dissolving.

3. The method of claim 1, wherein during the first filtration process, the mother solution is filtered using the filter cloth at a temperature condition of 60 to 80 C. to thus remove the impurities.

4. The method of claim 3, wherein the filter cloth includes a PE or Teflon material and has a breathability of 1 m or less.

5. The method of claim 1, wherein during the precipitation process, a reaction-starting temperature is 55 to 75 C. and a reaction-finishing temperature is 35 to 55 C.

6. The method of claim 5, wherein the precipitation process is performed for 48 to 96 hours.

7. The method of claim 1, wherein the seeds used during the precipitation process have a purity that is identical with or higher than a purity of the high-purity aluminum hydroxide.

8. The method of claim 7, wherein during the precipitation process, the seeds are used in an amount of 3 vol % or more and preferably 5 to 10 vol % based on a purified mother solution.

9. The method of claim 1, wherein during the hydrothermal process, the reaction is performed at a temperature of 200 to 300 C. for a maintenance time of 30 min to 2 hours.

10. The method of claim 1, wherein during a reaction of the third filtration process, ultrapure water is used in an amount that is at least 0.5 times and preferably 1 to 10 times more than a weight of the high-purity aluminum hydroxide.

11. The method of claim 1, wherein the heat-treatment step is performed at a firing temperature of 800 C. or higher and preferably 1,100 to 1,300 C., thus performing pregelatinization.

12. The method of claim 1, wherein the particles are atomized until an average particle diameter of 100 to 900 nm is obtained using a dry pulverizer and pulverizing media, which is directly manufactured with the high-purity alumina, during the atomization process.

13. The method of claim 1, wherein during the molding process, the seeds having a size of 100 m or more and preferably 500 to 1,000 m are formed from an atomized powder using ultrapure water, and while the atomized powder and the ultrapure water are put onto a rotating plate that rotates at 30 to 150 rpm, the molding and classification are repeated in a unit of 500 m until a desired size is obtained, thus molding the beads having a high density.

14. The method of claim 1, wherein during the sintering process, a molded product is heat-treated at 1,400 C. or higher and preferably 1,500 to 1,650 C., thus maintaining a molding shape and increasing a density thereof.

15. The method of claim 1, wherein during the classification process, only particles remaining between two standard sieves having maximum and minimum particle diameters are sorted in order to obtain particles having a desired particle size.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0032] FIG. 1 is a block diagram showing a method of manufacturing high-density beads of high-purity alumina according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0033] While the present invention has been described using terms relating to what is presently considered to be the most practical and preferred embodiment, in certain cases, there may be a term arbitrarily selected by the applicant, in which case the meaning thereof should be understood based not on the name of a simple term but on the meaning of the term described or used in the detailed description of the invention.

[0034] Hereinafter, the technical constitution of the present invention will be described in detail with reference to preferred embodiments shown in the accompanying drawings.

[0035] However, the present invention is not limited to the embodiments described herein, but may be embodied in other forms. Like reference numerals denote like elements throughout the specification.

[0036] FIG. 1 is a block diagram showing a method of manufacturing high-density beads of high-purity alumina according to an embodiment of the present invention.

[0037] Referring to FIG. 1, a method of manufacturing high-density beads of high-purity alumina according to an embodiment of the present invention includes (A) a mother-solution preparation step of dissolving general aluminum hydroxide in a sodium hydroxide solution so as to be supersaturated, (B) a purification step of removing insoluble impurities using a filter having low breathability, adding seeds to thus recrystallize aluminum hydroxide, and performing mixing with distilled water and heating at high temperatures, thereby removing some of the crystal water and the impurities, after the mother-solution preparation step (A), (C) a heat-treatment step of calcining the remainder of the crystal water, and (D) a forming step of the high-density beads of the high-purity alumina. In step (D), atomized powder is mixed with ultrapure water to form the seeds, the seeds are subjected to a molding process for each particle size to form a final molded body, sintering is performed to maintain a molding shape and to secure high densification, and a classification process for removing particles having a particle size that is the same as or larger than a maximum particle size or is the same as or smaller than a minimum particle size of a final product is performed, thereby forming the final product.

[0038] Particularly, in the purification step (B), aluminum hydroxide is supersaturated and dissolved so as to completely solve problems such as a loss of products, an increase of waste, and energy consumption, caused by co-precipitation and the adsorbent used in order to remove the impurities from the mother solution in the conventional technology. Accordingly, since other impurities are not dissolved, the impurities are removed using only simple filtration, and the extent of supersaturation is high, so that productivity is at least 20% higher than that of the conventional technology.

[0039] Conventionally, a large amount of organic acid and inorganic acid is used in order to remove a small amount of sodium impurities from the purified aluminum hydroxide obtained during the reaction, which causes an increase in raw-material costs and an environmental problem. However, in an embodiment of the present invention, the sodium impurities contained in the purified aluminum hydroxide are subjected to a hydrothermal reaction so that the crystal water and the sodium impurities are eluted in distilled water without using any organic or inorganic acid, thereby achieving purification.

[0040] Further, the raw material that is used is atomized via the atomization process, which is completely different from the conventional manufacturing method, and only the atomized powder and the ultrapure water are used to thus manufacture a molded body, thereby contributing to the improvement of sphericity and density and also remarkably improving productivity, including filling density or self-filling, compared to a conventional low-density powder.

[0041] Another embodiment of a method of manufacturing high-purity alumina according to an embodiment of the present invention, as shown in FIG. 1, includes (A-1) a dissolving process for putting general aluminum hydroxide and a sodium hydroxide solution into a dissolver to form a mother solution so that a supersaturated solution of sodium aluminate is manufactured, (B-1) a first filtration process for removing insoluble impurities and transferring the purified mother solution to a precipitator after the dissolving process, (B-2) a precipitation process for adding high-purity aluminum hydroxide seeds to the mother solution of the precipitator of the first filtration process, thus re-crystallizing high-purity aluminum hydroxide, (B-3) a second filtration process for filtering a precipitate, transferring a filtrate to the dissolver used to manufacture the mother solution, using a part of the precipitate as the seeds in the precipitator, washing the remainder of the precipitate, and transferring the washed precipitate to a hydrothermal reaction vessel after the precipitation process, (B-4) a hydrothermal reaction for adding distilled water to the hydrothermal reaction vessel and performing heating so that phase transition of aluminum hydroxide to boehmite occurs and thus a small amount of sodium impurities contained in aluminum hydroxide is eluted into the distilled water after the second filtration process, (B-5) a third filtration process for washing solid matter and transferring the washed solid matter to a firing process after the hydrothermal reaction, (C-1) a firing process for calcining high-purity boehmite to thus manufacture high-purity alpha-alumina after the third filtration process, (D-1) an atomization process for performing pulverization into atomized powder using a pulverizer, (D-2) a molding process for manufacturing the seeds using the atomized powder and the ultrapure water and performing molding using the seeds until desired particles are obtained while the atomized powder and the ultrapure water are stepwisely added for each particle size, (D-3) a sintering process for performing heat treatment in order to maintain a molding shape and to improve a density, and (D-4) a classification process for removing particles having a particle size that is the same as or larger than a maximum particle size or is the same as or smaller than a minimum particle size in desired particles by classification.

[0042] Hereinafter, a method of manufacturing high-density beads of high-purity alumina according to an embodiment of the present invention will be described in more detail.

[0043] For the manufacture of a sodium aluminate mother solution, a sodium hydroxide solution was diluted to 320 g/L based on sodium carbonate, and was put into a 300 L dissolver which was made of SUS316 and which was equipped with a stirrer. General aluminum hydroxide containing the impurities shown in Table 1 was then added until a weight ratio of Al.sub.2O.sub.3/Na.sub.2CO.sub.3 (represented by A/C) was 0.78, was stirred, was heated to 140 C. and was then maintained for 1 hour, thus manufacturing the sodium aluminate mother solution (dissolving process, A-1). Thereafter, the temperature was reduced, the temperature of the mother solution was maintained at 72 C., and filtration was performed using a linear filter provided with a filter cloth having a breathability of 1 m or less (filter cloth material: PE, housing: SUS316), thus removing insoluble impurities and transferring the purified filtrate to a precipitator (first filtration process, B-1).

[0044] The process mother solution from which the impurities were removed was maintained in a precipitator so that an A/C value was 0.78, a C value was 320 g/L, and the temperature was 65 C. In order to accelerate precipitation, 3 wt % of the high-purity aluminum hydroxide was added all at once to the mother solution, and the temperature was reduced to 45 C. with slow stirring for 72 hours, thereby inducing precipitation. When the precipitation was completed, a slurry having an A/C value of 0.28 and a C value of 340 g/L was manufactured (precipitation process, B-2).

[0045] After the precipitation process is completed, the filtration was performed using a second filter. The filtrate was transferred to the dissolver in order to manufacture the mother solution, part of the solid matter was used as seeds, the remainder of the solid matter was washed using warm water and filtered, and the filtered solid matter having the purity shown in Table 1 was transferred to a hydrothermal reaction vessel (second filtration process, B-3).

[0046] The slurry in which the washed solid matter and the ultrapure water were mixed was heated to 270 C. for 2 hours in the hydrothermal reaction vessel, was maintained for 1 hour, was cooled to 80 C., and was then filtered using a third filter (hydrothermal process, B-4).

[0047] The filtered solid matter in the hydrothermal reaction vessel was again washed with warm water and filtered, thus manufacturing the purified high-purity boehmite cake containing 20% of water shown in Table 1 (third filtration process, B-5).

[0048] The high-purity boehmite manufactured during the third filtration process was put into a high-purity alumina crucible and was placed in a high-temperature firing furnace. Subsequently, the temperature was raised at 2 C./min and was maintained at 1200 C. for 2 hours. Cooling to room temperature was performed, thereby manufacturing high-purity alumina powder having a purity of 99.999% or more shown in Table 1 (firing process, C-1).

[0049] The granules manufactured during the firing process were put into a dry pulverizer, and were rotated at 120 rpm for 1 hour so as to be pulverized until a particle size thereof was 1 m or less, thus manufacturing atomized powder (atomization process, D-1).

[0050] The seeds having a size of 0.5 m were manufactured using the atomized powder and the ultrapure water, and were put onto a rotating plate rotating at 90 rpm to rotate the same. While the atomized powder and the ultrapure water were added, molding was performed until an average particle diameter of 1.0 m was obtained, followed by discharging and classification. Further addition was performed, and molding was performed until 1.5 m was obtained, followed by discharging and classification, thereby manufacturing particles having a desired particle diameter shown in Table 2 (molding process, D-2).

TABLE-US-00001 TABLE 1 Content of impurities in each process according to an embodiment of the present invention (unit: ppm) High-purity Purified alumina aluminum High-purity manufactured by General hydroxide boehmite after an embodiment aluminum after hydrothermal of the present Classification hydroxide precipitation reaction invention Na content 4,000 1,000 2 2 Si content 120 3 2 2 Fe content 95 0.5 0.5 0.5 Ti content 37 0.2 0.1 0.1 Ca content 104 1.7 0.3 0.3

TABLE-US-00002 TABLE 2 Particle size for each step according to an embodiment of the present invention (unit: m) First Second Third Fourth Classification Seed molding molding molding molding Average particle 0.5 1.0 1.5 2.0 2.5 diameter

[0051] Sintering was performed at 1,600 C. in order to maintain the shape of the molded beads and to increase the density thereof. Since a sintering shrinkage ratio is determined to be 10 to 35% according to a sintering temperature, in the molding process, a molding size must be determined in advance so as to be suitable for the sintering shrinkage. The sintering temperature was maintained at 1,600 C., which was a temperature before the surfaces of the particles were fused due to overheating for 1 hour, thus manufacturing the beads (sintering process, D-3).

[0052] The sintered beads were passed through a surface-treated standard sieve in order to separate inferior products including particles having a particle size larger than a maximum particle size or smaller than a minimum particle size, thus preventing the particles from being fused and also preventing over-sintering. In the surface treatment, all surfaces that may come into direct contact with the molded beads must be coated in order to fundamentally prevent the incorporation of impurities. A PE, PP, Teflon, alumina spray coating or nylon material, which was a liquid or powder surface-treating material, was spun using various methods, thus manufacturing the standard sieve (classification process, D-4).

[0053] Although the exemplary embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that the present invention is not limited to the disclosed embodiments but that various modifications and additions are possible without departing from the spirit of the invention as disclosed in the accompanying claims.