Method for producing high-purity phosphoric acid through quantum behavior control

Abstract

The present invention relates to a method for producing high-purity phosphoric acid by quantum behavior control, and more particularly, to a method for producing high-purity phosphoric acid, which can produce high-purity phosphoric acid by using a temperature difference between an added phosphoric acid raw material and a cooling device. The growth position and speed of phosphoric acid crystals are controlled by changing the molecular or quantum behaviors of phosphoric acid, water molecules and impurities in the phosphoric acid raw material, the phenomenon that the impurities are wrapped in the phosphoric acid crystals is effectively inhibited, some formed phosphoric acid crystals are melted by additionally adding the high-temperature phosphoric acid raw material to remove the impurities wrapped in the crystals, and the phosphoric acid crystals are obtained. Therefore, high-purity phosphoric acid is economically and industrially produced from low-grade phosphoric acid.

Description

Technical Field

[0001] This invention relates to a method for producing high-purity phosphoric acid through quantum behavior control, and more specifically, to a method for producing high-purity phosphoric acid. This method can control the growth position and rate of phosphoric acid crystals by utilizing the temperature difference between the added phosphoric acid raw material and a cooling device to change the molecular or quantum behavior of phosphoric acid, water molecules, and impurities in the phosphoric acid raw material. This effectively suppresses the phenomenon of impurities being encapsulated within the phosphoric acid crystals. By adding additional high-temperature phosphoric acid raw material to melt some of the formed phosphoric acid crystals to remove impurities encapsulated within the crystals, phosphoric acid crystals are obtained, thereby economically and industrially obtaining high-purity phosphoric acid from low-grade phosphoric acid. Background Technology

[0002] Phosphoric acid is an essential chemical material in semiconductor manufacturing processes and is the only substance capable of wet etching semiconductor silicon nitride films (Si3N4, SiN). In the silicon nitride film etching process, impurities in the phosphoric acid etching solution directly affect the semiconductor yield and defect rate; therefore, its concentration must be strictly controlled.

[0003] Because high-purity phosphoric acid suitable for semiconductor manufacturing processes can only be prepared by dry methods—that is, extracting yellow phosphorus (P4) from high-quality phosphate rock and oxidizing and burning the yellow phosphorus at high temperatures above 200°C—its preparation process is very costly.

[0004] Furthermore, due to the limited reserves of high-quality phosphate rock, the depletion of its mineral resources is accelerating, leading to a continuous rise in the price of high-purity phosphoric acid, which in turn causes economic problems such as increased semiconductor manufacturing costs.

[0005] For the purification process of phosphoric acid containing a large number of metal ion impurities, existing technologies have proposed a variety of methods, such as membrane separation, ion exchange, or liquid extraction.

[0006] First, while membrane separation offers advantages such as high phosphoric acid yield and purity, it also suffers from drawbacks including high processing costs and extremely complex operation. Furthermore, due to the corrosive nature of phosphoric acid, used membranes may pose safety risks.

[0007] Ion exchange uses ion exchange resins or calcium zeolite to remove acid. However, the ion exchange capacity of the ion exchange resins used is low, and they can only treat low concentrations of acid. Furthermore, the ion exchange resins need to be replaced continuously after the ion exchange is completed, which leads to increased costs for continuous processes.

[0008] While liquid extraction has the advantages of continuous operation and low equipment cost, its disadvantage is that it cannot obtain the high-purity phosphoric acid required for semiconductor processes.

[0009] Crystallization is a method of forming crystals from a saturated solution by controlling the nucleation and growth rates of crystals.

[0010] Crystallization methods can be divided into crystallization methods using phosphate seed crystals to promote crystallization nucleation and crystallization methods without using phosphate seed crystals. When phosphate seed crystals are not used, the crystallization conditions need to be controlled at -40°C or lower to carry out crystallization, which has the disadvantages of high energy consumption and long crystallization time.

[0011] Therefore, there is an urgent need to develop a new method that can economically and industrially separate impurities from high-impurity phosphoric acid feedstock and prepare high-purity phosphoric acid free of unnecessary metal impurities. Summary of the Invention

[0012] Technical issues

[0013] The purpose of this invention is to provide a method for producing high-purity phosphoric acid through quantum behavior control, which enables the economical and industrialized production of phosphoric acid.

[0014] This invention relates to a method for preparing high-purity phosphoric acid, which enables the economical and industrial production of high-purity phosphoric acid from low-grade phosphoric acid. The method controls the growth position and rate of phosphoric acid crystals by utilizing the temperature difference between the added phosphoric acid raw material and a cooling device to alter the molecular or quantum behavior of phosphoric acid molecules, water molecules, and impurities in the phosphoric acid raw material. This results in the acquisition of phosphoric acid crystals and effectively suppresses the phenomenon of impurities being encapsulated within the phosphoric acid crystals. Furthermore, by adding additional high-temperature phosphoric acid raw material to melt some of the formed phosphoric acid crystals, impurities encapsulated within the crystals are removed, thus obtaining high-purity phosphoric acid from low-grade phosphoric acid in an economical and industrial manner.

[0015] Technical solution

[0016] One embodiment of the present invention provides a method for producing high-purity phosphoric acid, the method comprising the following steps: adding phosphoric acid raw material containing impurities to a cooling device (S1); adding phosphoric acid seed crystals to a cooling device (S2); forming phosphoric acid crystals by stirring the added phosphoric acid raw material and phosphoric acid seed crystals (S3); and additionally adding phosphoric acid raw material containing impurities to a cooling device (S4), wherein the temperature of the phosphoric acid raw material added in steps (S1) and (S4) is 5°C to 35°C higher than the temperature of the cooling device.

[0017] The temperature of the phosphoric acid raw material added in steps (S1) and (S4) can be from 30°C to 50°C.

[0018] The temperature of the cooling device in step (S1) can be from 15°C to 30°C.

[0019] The step of adding additional phosphoric acid (S4) can be performed once or multiple times.

[0020] In the step (S4) of adding additional phosphoric acid raw material, the content of the additional phosphoric acid raw material can be from 10 parts by weight to 90 parts by weight, based on a total content of 100 parts by weight of phosphoric acid raw material.

[0021] The method for producing high-purity phosphoric acid according to the present invention further includes, after the step of adding additional phosphoric acid raw material (S4), cooling the cooling device to 0°C to 15°C to grow phosphoric acid crystals (S5).

[0022] In the step (S5) of growing phosphate crystals, the cooling rate of the cooling device can be from 0.1°C / min to 5°C / min.

[0023] The method for producing high-purity phosphoric acid according to the present invention further includes, after the step of growing phosphoric acid crystals (S5), partially melting some of the crystalline phosphoric acid by raising the temperature of the cooling device to 20°C to 35°C (S6).

[0024] The method for producing high-purity phosphoric acid according to the present invention further includes obtaining unmelted phosphoric acid crystals (S7) in the partial melting step (S6) by raising the temperature of the cooling device to 40°C or higher after separating the partially melted phosphoric acid.

[0025] In the step (S3) of forming phosphate crystals, the stirring rate can be from 50 rpm to 600 rpm.

[0026] The concentration of the phosphoric acid feedstock can be from 80% to 91.6%.

[0027] The total content of Al, K, and Cu impurities in the phosphoric acid raw material can be 300 ppb or higher.

[0028] The phosphoric acid obtained using the above method can contain 1 ppb or less of Al, K, and Cu.

[0029] Beneficial effects

[0030] When the method for producing high-purity phosphoric acid by controlling quantum behavior as described in this invention is used, high-purity phosphoric acid can be produced economically and industrially. Detailed Implementation

[0031] Unless otherwise defined in this specification, all technical and scientific terms have the same meaning as commonly understood by those skilled in the art. The terminology used in the description of this invention is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention.

[0032] Unless the context clearly indicates otherwise, the singular form used in this specification also includes the plural form.

[0033] The term "comprising" as used in this specification specifies a particular feature, region, integer, step, operation, element, and / or component, and does not exclude the presence or addition of other particular features, regions, integers, steps, operations, elements, components, and / or groups.

[0034] This invention can have various applicable modifications and can take many forms, and specific embodiments will be described and detailed below. However, this is not intended to limit the invention to the particular form disclosed, and it should be interpreted as including all modifications, equivalents, and substitutions contained within the stated objectives and scope of the invention.

[0035] In this specification, when the positional relationship between two parts is described as such as “in”, “in the upper half of”, “in the lower half of”, “near”, etc., one or more other parts may be located between the two parts unless an expression such as “directly opposite” or “directly” is used.

[0036] In this specification, when a time relationship is described as, for example, “after,” “after,” “then,” “before,” etc., it may include cases where the operations are not consecutive, unless an expression such as “immediately” or “directly” is used.

[0037] In this specification, the term "at least one" should be interpreted to include all combinations that may be presented by one or more related items.

[0038] The method for producing high-purity phosphoric acid will now be described in more detail according to the specific embodiments described herein.

[0039] According to one embodiment of the present invention, a method for producing high-purity phosphoric acid is provided, the method comprising the following steps: adding phosphoric acid raw material containing impurities to a cooling device (S1); adding phosphoric acid seed crystals to the cooling device (S2); forming phosphoric acid crystals by stirring the phosphoric acid raw material and the phosphoric acid seed crystals (S3); and additionally adding phosphoric acid raw material containing impurities to the cooling device (S4), wherein the temperature of the phosphoric acid raw material added in steps (S1) and (S4) is 5°C to 35°C higher than the temperature of the cooling device.

[0040] As mentioned above, cooling crystallization is a well-known method for purifying phosphoric acid in the relevant field. However, when phosphoric acid seed crystals are not used, the crystallization temperature needs to be controlled at -40°C or lower to initiate crystallization, which results in a high cost and a lot of time for the crystal formation process.

[0041] Therefore, the inventors of this invention have studied a method to further improve purification efficiency while using phosphoric acid seed crystals for crystallization at room temperature. They have determined that by utilizing the temperature difference between the added phosphoric acid raw material and the cooling device to change the molecular or quantum behavior of phosphoric acid, water molecules, and impurities in the phosphoric acid raw material, the growth position and growth rate of the phosphoric acid crystals can be controlled, effectively suppressing the phenomenon of impurities being encapsulated inside the phosphoric acid crystals. Furthermore, by adding additional high-temperature phosphoric acid raw material to melt some of the formed phosphoric acid crystals to remove impurities encapsulated within the crystals, phosphoric acid crystals are obtained, enabling the economical and industrial production of high-purity phosphoric acid. This completes the present invention.

[0042] According to the present invention, when the method includes the following steps, higher purity phosphoric acid can be obtained by improving the impurity purification efficiency: adding phosphoric acid raw material containing impurities to a cooling device (S1); adding phosphoric acid seed crystals to the cooling device (S2); forming phosphoric acid crystals by stirring the phosphoric acid raw material and the phosphoric acid seed crystals (S3); and additionally adding phosphoric acid raw material containing impurities to the cooling device (S4), wherein the temperature of the phosphoric acid raw material added in steps (S1) and (S4) is 5°C to 35°C higher than the temperature of the cooling device.

[0043] Firstly, as a phosphoric acid feedstock, commercially available low-purity (industrial grade) phosphoric acid can be purchased and used, or phosphoric acid used in semiconductor cleaning processes can be collected and used. However, in terms of resource recycling, there is a preference for collecting and using impurity-containing phosphoric acid used in semiconductor processes.

[0044] In the method for producing high-purity phosphoric acid described in this invention, a phosphoric acid raw material containing a large amount of impurities is added to a cooling device, and then phosphoric acid seed crystals are added to the cooling device. The added phosphoric acid raw material and phosphoric acid seed crystals are stirred to form phosphoric acid crystals. The temperature difference between the phosphoric acid raw material and the cooling device can improve the impurity purification efficiency.

[0045] Specifically, by altering the molecular and quantum behavior of phosphoric acid, water molecules, and impurities in the phosphoric acid raw material through the temperature difference between the phosphoric acid raw material and the cooling device, sporadic and rapid crystal formation can be prevented, and metal impurities can be prevented from being encapsulated inside the phosphoric acid crystals, thereby improving the purification efficiency of metal impurities.

[0046] During the process of forming phosphoric acid crystals by adding phosphoric acid seed crystals, when there is no temperature difference or the temperature difference between the phosphoric acid raw material and the cooling device is not significant, phosphoric acid crystallization occurs sporadically and rapidly. Due to the trap phenomenon where impurities are trapped inside the phosphoric acid crystals, the formed phosphoric acid crystals contain a large number of impurities, which reduces the purity of the obtained phosphoric acid.

[0047] In contrast, when the temperature difference between the phosphoric acid raw material and the cooling device is controlled at a certain or higher level, and crystallization is carried out by adding phosphoric acid seed crystals, the growth position and rate of phosphoric acid crystals are controlled by changing the molecular and quantum behavior of phosphoric acid, water molecules and impurities in the phosphoric acid raw material. This avoids the sporadic formation of phosphoric acid crystals and the retention of metal impurities inside the phosphoric acid crystals, thereby improving the purification efficiency and obtaining high-purity phosphoric acid.

[0048] The temperature difference between the phosphoric acid feedstock and the cooling device can be 5°C or higher. When the temperature difference between the phosphoric acid feedstock and the cooling device is less than 5°C, phosphoric acid crystals are generated sporadically and rapidly, leading to a reduction in purification efficiency due to the retention of metal impurities inside the phosphoric acid crystals.

[0049] Furthermore, the temperature difference between the phosphoric acid feedstock and the cooling device should be controlled below 35°C. If the temperature difference exceeds 35°C, insufficient phosphoric acid crystal growth may occur.

[0050] Specifically, the temperature of the phosphoric acid feedstock containing impurities added in steps (S1) and (S4) can be between 30°C and 50°C. The temperature of the cooling device when the phosphoric acid feedstock is added can be between 15°C and 30°C.

[0051] According to the present invention, after adding the phosphoric acid raw material containing impurities to the cooling device (S1), phosphoric acid seed crystals are added to the cooling device (S2); wherein the amount of phosphoric acid seed crystals added can be from 0.01 parts by weight to 10 parts by weight, based on 100 parts by weight of the phosphoric acid raw material.

[0052] When too little phosphate seed crystal is added, it may lead to a slow crystallization rate or even failure to grow crystals; while when too much is added, it may result in sporadic formation of phosphate crystals. Therefore, it is preferable to add phosphate seed crystals within the above-mentioned range.

[0053] According to the present invention, it further includes: after adding the phosphoric acid seed crystal to the cooling device (S2), the added phosphoric acid raw material and the phosphoric acid seed crystal can be stirred to form phosphoric acid crystal (S3).

[0054] In step (S3) of forming phosphate crystals, the stirring rate can be from 50 rpm to 600 rpm.

[0055] In step (S3) of forming phosphoric acid crystals, the phosphoric acid raw material and phosphoric acid seed crystals are stirred at a certain rate or higher to avoid impurities being trapped inside the phosphoric acid crystals and to improve purification efficiency.

[0056] When the stirring speed is less than 50 rpm, it is impossible to avoid the phenomenon of impurities being encapsulated in the phosphate crystals, thus reducing the purification efficiency. When the stirring speed is greater than 600 rpm, when heated phosphate is added, due to the excessive stirring speed, some of the molten phosphate crystals may not grow or disappear sufficiently, resulting in a decrease in the yield of pure phosphate crystals.

[0057] According to the present invention, the method further includes: after the phosphoric acid raw material and phosphoric acid seed crystals are stirred and added to form phosphoric acid crystals (S3), additional phosphoric acid raw material containing impurities is added to the cooling device (S4).

[0058] First, the initially added phosphoric acid raw material is brought into contact with phosphoric acid seed crystals to form phosphoric acid crystals. Subsequently, as the phosphoric acid crystals grow, crystallization occurs. During the crystallization process, the interior of the crystal contains pure phosphoric acid with almost no impurities, while the number of impurities increases towards the crystal surface.

[0059] In this invention, when additional phosphoric acid raw material containing impurities is added to the cooling device, the impurities present on the crystal surface can be melted and removed by the additional high-temperature phosphoric acid raw material, and the crystal growth rate increases due to the added phosphoric acid raw material, thereby obtaining phosphoric acid with higher purity.

[0060] For example, the phosphoric acid crystals obtained from the initially added phosphoric acid raw material are called primary phosphoric acid crystals. Subsequently, when additional phosphoric acid raw material containing impurities is added to the cooling device, the surface of the primary phosphoric acid crystals formed first is partially melted by the additional high-temperature phosphoric acid raw material, and the impurities contained on the surface are melted together and removed, resulting in phosphoric acid with higher purity.

[0061] The step of adding additional phosphoric acid raw material (S4) is carried out after adding phosphoric acid raw material and phosphoric acid seed crystals into the cooling device and stirring to form phosphoric acid crystals, that is, after step (S3) and before the phosphoric acid crystal growth step (S5) of cooling the cooling device to 0°C to 15°C, regardless of time and frequency.

[0062] Specifically, the step of adding additional phosphoric acid raw material (S4) can be performed once or multiple times. It can be performed immediately after the step of forming phosphoric acid crystals (S3) or after a predetermined time. It can also be performed twice or multiple times consecutively, or it can be performed once and then performed additionally after a certain time.

[0063] In the method for producing high-purity phosphoric acid, the amount of additional phosphoric acid raw material added in step (S4) can be from 10 parts by weight to 90 parts by weight, based on a total content of 100 parts by weight of phosphoric acid raw material.

[0064] For example, when the initial amount of phosphoric acid raw material added is 20 parts by weight, the remaining 80 parts by weight of phosphoric acid raw material can be added in one or more additional steps, and there is no limit to the frequency of additional addition or the amount added each time.

[0065] According to this disclosure, the method may further include, after the step of adding additional phosphoric acid raw material (S4), cooling the cooling device to 0°C to 15°C while growing phosphoric acid crystals (S5).

[0066] In the step (S5) of growing phosphoric acid crystals, the cooling rate of the cooling device can be from 0.1°C / min to 5°C / min. Cooling at the above-mentioned cooling rate is suitable for removing impurities from the phosphoric acid raw material to obtain high-purity phosphoric acid.

[0067] The method for producing high-purity phosphoric acid according to the present invention further includes: after the step of growing phosphoric acid crystals (S5), partially melting some of the crystalline phosphoric acid by raising the temperature of the cooling device to 20°C to 35°C (S6).

[0068] As described above, the crystalline phosphoric acid grown through the crystallization process comprises pure phosphoric acid with almost no impurities inside the crystal, and the number of impurities increases towards the crystal surface.

[0069] Therefore, after the phosphoric acid crystals have grown sufficiently, by raising the temperature of the cooling device to 20℃~35℃, the surface of the phosphoric acid crystals can be partially melted, and impurities attached to the surface can be removed to obtain phosphoric acid with higher purity.

[0070] Subsequently, after separating the partially melted phosphoric acid, the unmelted phosphoric acid crystals from the partial melting step (S6) are obtained (S7) by raising the temperature of the cooling device to 40°C or higher.

[0071] Phosphoric acid raw materials before purification contain a large number of impurities. Specifically, the total content of impurities, including Al, K, and Cu, in the phosphoric acid raw materials can be above 300 ppb.

[0072] As described above, the method for producing high-purity phosphoric acid according to the present invention can economically and industrially obtain high-purity phosphoric acid. Specifically, the content of Al, K and Cu in the phosphoric acid obtained by the method can be controlled at 1 ppb or lower.

[0073] The embodiments of the present invention will be described in more detail below with reference to examples. However, it should be noted that the following examples are only used to illustrate the embodiments of the present invention, and the scope of the present invention is not limited to the following examples.

[0074] (1) Example 1

[0075] 200g of 91.6% phosphoric acid raw material containing impurities is heated to 30°C and then added to a cooling device with the temperature set at 15°C.

[0076] Add 1g of phosphate seed crystals to the cooling device and stir at 50rpm to crystallize phosphate.

[0077] Five minutes into the crystallization process, an additional 100g of 91.6% phosphoric acid raw material containing impurities was added, and the mixture was heated to 30°C.

[0078] After 1 minute, repeat the process 7 times by adding an additional 100g of 91.6% phosphoric acid raw material containing impurities and heating to 30°C, for a total of 1000g of phosphoric acid raw material added (with 1 minute interval between each addition).

[0079] Subsequently, the cooling device cooled the sample to 5°C at a cooling rate of 0.1°C / min to grow phosphate crystals.

[0080] The uncrystallized phosphoric acid is removed, and then some of the crystalline phosphoric acid is melted and separated by raising the temperature of the cooling device to 20°C.

[0081] By raising the temperature of the cooling device to above 40°C, all the remaining unmelted phosphoric acid crystals were melted, and finally purified crystalline phosphoric acid (794g) was obtained.

[0082] (2) Example 2

[0083] Crystalline phosphoric acid (650g) was obtained using the same method as in Example 1, except that the concentration of the phosphoric acid raw material used was changed to 80%.

[0084] (3) Example 3

[0085] Phosphoric acid (726g) was obtained using the same method as in Example 1, except that the stirring speed was changed from 50 rpm to 600 rpm.

[0086] (4) Example 4

[0087] 200g of 91.6% phosphoric acid raw material containing impurities is heated to 30°C and then added to a cooling device with the temperature set at 15°C.

[0088] Add 1g of phosphate seed crystals to the cooling device and stir at 50rpm to crystallize phosphate.

[0089] After 5 minutes of crystallization, add 100g of 91.6% phosphoric acid raw material containing impurities and heat to 30°C.

[0090] After 10 minutes, repeat the process 7 times by adding an additional 100g of 91.6% phosphoric acid raw material containing impurities and heating to 30°C, for a total of 1000g of phosphoric acid raw material added (each addition was 10 minutes apart).

[0091] Subsequently, the cooling device cooled the sample to 5°C at a cooling rate of 0.1°C / min to grow phosphate crystals.

[0092] The uncrystallized phosphoric acid is removed, and then some of the crystalline phosphoric acid is melted and separated by raising the temperature of the cooling device to 20°C.

[0093] By raising the temperature of the cooling device to above 40°C, all the remaining unmelted phosphoric acid crystals were melted, and finally purified crystalline phosphoric acid (837g) was obtained.

[0094] (5) Example 5

[0095] Crystallized phosphoric acid (801g) was obtained using the same method as in Example 1, except that the cooling rate of the cooling device was changed from 0.1°C / min to 5°C / min.

[0096] (6) Example 6

[0097] Crystalline phosphoric acid (688g) was obtained using the same method as in Example 1, except that the cooling temperature of the cooling device was changed from 5°C to 10°C.

[0098] (7) Example 7

[0099] Crystallized phosphoric acid (713g) was obtained using the same method as in Example 1, except that phosphoric acid feedstock heated to 50°C was used instead of phosphoric acid feedstock heated to 30°C.

[0100] (8) Comparative Example 1

[0101] The method for phosphoric acid crystallization was the same as in Example 1, except that phosphoric acid feedstock heated to 70°C was used instead of phosphoric acid feedstock heated to 30°C. However, the result of the crystallization experiment was that the phosphoric acid feedstock did not crystallize.

[0102] (9) Comparative Example 2

[0103] The method for phosphoric acid crystallization was the same as in Example 1, except that a cooling device set to 30°C was used instead of a cooling device set to 15°C. However, the result of the crystallization experiment was that the phosphoric acid feedstock did not crystallize.

[0104] Analysis of Metal Impurities in Crystallized Phosphoric Acid

[0105] The content of metal impurities in each of the following was analyzed by ICP-MS: phosphoric acid raw material, amorphous phosphoric acid, partially melted and separated phosphoric acid, and crystalline phosphoric acid obtained by heating to above 40°C.

[0106] Specifically, non-crystalline phosphoric acid, partially molten phosphoric acid, and crystalline phosphoric acid were diluted with DIW or 3% nitric acid, respectively, and the metal impurity content in the samples was analyzed using an Agilent ICP-MS 8900.

[0107] Table 1

[0108]

[0109] Table 2

[0110]

[0111]

[0112] Table 3

[0113]

[0114] As can be seen from Tables 1 to 3, compared with phosphoric acid raw materials, the metal content in phosphoric acid obtained by the preparation method of the present invention is significantly reduced, and high-purity phosphoric acid can be obtained.

Claims

1. A method for preparing high-purity phosphoric acid, characterized in that, The method includes the following steps: Phosphoric acid raw material containing impurities is added to the cooling device (S1); Phosphate seed crystals are added to the cooling device (S2); Phosphoric acid crystals (S3) are formed by stirring the added phosphoric acid raw material and phosphoric acid seed crystals; and Additional phosphoric acid feedstock containing impurities is added to the cooling device (S4); The temperature of the phosphoric acid raw material added in steps (S1) and (S4) is 5°C to 35°C higher than the temperature of the cooling device.

2. The method as described in claim 1, characterized in that, The temperature of the phosphoric acid raw material added in steps (S1) and (S4) is 30°C to 50°C.

3. The method as described in claim 1, characterized in that, In step (S1), the temperature of the cooling device is 15°C to 30°C.

4. The method as described in claim 1, characterized in that, The step of adding additional phosphoric acid (S4) is performed once or multiple times.

5. The method as described in claim 1, characterized in that, In the step (S4) of adding additional phosphoric acid raw material, the content of the additional phosphoric acid raw material is from 10 parts by weight to 90 parts by weight, based on a total content of 100 parts by weight of phosphoric acid raw material.

6. The method as described in claim 1, characterized in that, Also includes: After the step of adding additional phosphoric acid raw material (S4), the cooling device is cooled to 0°C to 15°C to grow phosphoric acid crystals (S5).

7. The method as described in claim 6, characterized in that, In step (S5) of growing phosphate crystals, the cooling rate of the cooling device can be from 0.1°C / min to 5°C / min.

8. The method as described in claim 6, characterized in that, The method further includes: after the step of growing phosphoric acid crystals (S5), partially melting some of the crystalline phosphoric acid by raising the temperature of the cooling device to 20°C to 35°C (S6).

9. The method as described in claim 8, characterized in that, The method further includes obtaining unmelted phosphoric acid crystals (S7) in the partial melting step (S6) by raising the temperature of the cooling device to 40°C or higher after separating the partially melted phosphoric acid.

10. The method as described in claim 1, characterized in that, In step (S3) of forming phosphate crystals, the stirring rate is 50 rpm to 600 rpm.

11. The method as described in claim 1, characterized in that, The concentration of the phosphoric acid feedstock is 88% to 91.6%.

12. The method as described in claim 1, characterized in that, The total content of impurities such as Al, Ni, and Fe in the phosphoric acid raw material is 300 ppb or more.

13. The method as described in claim 1, characterized in that, The phosphoric acid obtained by the method contains 1 ppb or less of Al, K and Cu.

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