Method for preparing high-purity alumina

1. A method for high-purity alumina, the method comprising:

a mother liquor preparing step of preparing a mother liquor by dissolving and aging aluminum hydroxide;

a refining step of adding pulp to absorb impurities from the prepared mother liquor, after the mother liquor preparing step to form refined mother liquor; and

an obtaining step of obtaining high-purity alumina, after the refining step,

wherein the obtaining step is a step of obtaining the high-purity alumina by adding a seed to the refined mother liquor to form a precipitate, filtering, washing and dissolving the precipitate, recrystallizing the dissolved precipitate by neutralizing the dissolved precipitate, again filtering and washing the recrystallized precipitate, mixing a small amount of aluminum fluoride (AlF 3 ) with the washed recrystallized precipitate, and then calcining the mixed precipitate.

2. The method of claim 1 , wherein the mother liquor preparing step comprising:

a dissolving step of preparing a mother liquor by adding a caustic soda (NaOH) solution and aluminum hydroxide into a dissolution bath and dissolving the aluminum hydroxide; and

an aging step of aging impurities while slowly decreasing a temperature of the mother liquor dissolved through the dissolving step of preparing the mother liquor during a predetermined aging time.

3. A method for high-purity alumina, the method comprising:

a dissolving step of preparing a mother liquor by adding a caustic soda (NaOH) solution and aluminum hydroxide into a dissolution bath and dissolving the aluminum hydroxide;

an aging step of aging impurities while slowly decreasing a temperature of the mother liquor dissolved through the dissolving step during a predetermined aging time;

a refining step of adding and dispersing an absorbent made of pulp into the mother liquor aged through the aging step, thereby absorbing the impurities in the mother liquor into the absorbent;

a first filtering step of separating the pulp having the impurities absorbed thereinto, filtering the mother liquor and then providing the filtered mother liquor to a precipitation bath, after the refining step;

a precipitating step of precipitating aluminum hydroxide by adding an aluminum hydroxide seed into the mother liquor of the precipitation bath, after the first filtering step;

a polarizing step of separating a precipitate having a small particle size and a precipitate having a large particle size, after the precipitating step;

a second filtering step of filtering the mother liquor containing the precipitate having the large particle size in the polarizing step, thereby recycling the filtered mother liquor as the caustic soda solution;

a recrystalizing step of washing the precipitate remaining in the second filtering step, dissolving aluminum hydroxide in an acid and then neutralizing the dissolved aluminum hydroxide using alkali, thereby recrystalizing the precipitate;

a third filtering step of collecting the recrystalized precipitate in the recrystalizing step and filtering and washing the collected precipitate; and

a calcining step of mixing aluminum fluoride (AlF 3 ) with the collected precipitate washed in the third filtering step and then calcining the mixed precipitate at 1050° C. or more for 1 hour or more.

4. The method of claim 2 , wherein, in the dissolving step, the weight ratio of aluminum oxide to sodium carbonate (Al 2 O 3 /Na 2 CO 3 ) in the dissolved mother liquor is 0.68 or more.

5. The method of claim 2 , wherein, in the dissolving step, the concentration of the caustic soda (NaOH) solution is 230 g/1 or more, based on the sodium carbonate (Na 2 CO 3 ).

6. The method of claim 2 , wherein, in the aging step, the aging temperature of the mother liquor is maintained at 90° C. to 130° C.

7. The method of claim 6 , wherein, in the aging step, the aging time for aging the impurities is 1 hour or more.

8. The method of claim 3 , wherein the precipitating step is performed at an initial temperature of 70° C. or more.

9. The method of claim 3 , wherein, in the precipitating step, the precipitation time taken to precipitate the aluminum hydroxide is 72 hours or more.

10. The method of claim 3 , wherein, in the precipitating step, the weight ratio of aluminum oxide to sodium carbonate (Al 2 O 3 /Na 2 CO 3 ) in the aluminum hydroxide finally obtained in the precipitating step is 0.40 or less.

11. The method of claim 3 , wherein the recrystalizing step is a step of dissolving the precipitate precipitated in the precipitating step in an acid compound selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid and acetic acid, and then neutralizing the dissolved precipitate using an alkali compound selected from the group consisting of caustic soda, ammonia and sodium acetate, thereby recrystalizing the precipitate.

12. The method of claim 11 , wherein aluminum fluoride (AlF 3 ) of 0.3% based on the weight of a product is mixed with a cake prepared in the recrystalizing step, and the mixed cake is then calcined.