Method for producing high-purity phosphoric acid using quantum bonding of phosphoric acid

Abstract

To provide a novel phosphoric acid production method that enables economic and industrial acquisition of high-purity phosphoric acid free of unnecessary metals by separating impurities from a phosphoric acid raw material rich in impurities.SOLUTION: A method for producing high-purity phosphoric acid includes a step (S1) of supplying a phosphoric acid raw material containing impurities to a cooling device at 5 to 50°C and a step (S2) of stirring the phosphoric acid raw material to form phosphoric acid crystals, wherein the cooling device has an internal wall surface whose roughness is adjusted such that a contact angle with respect to water is 50° or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing high-purity phosphoric acid from low-purity phosphoric acid by forming pure phosphoric acid crystals using crystallization purification based on quantum bonds of phosphoric acid. More specifically, the present invention relates to a method for producing high-purity phosphoric acid from low-purity phosphoric acid in an economical and industrial manner by activating quantum bonds of phosphoric acid in a phosphoric acid raw material containing a large amount of impurities at a temperature above zero (0°C) to obtain pure crystals. [Background technology]

[0002] Phosphoric acid is the only substance that can wet etch semiconductor silicon nitride film (Si3N4, SiN) and is an essential chemical material in the semiconductor manufacturing process. In this silicon nitride film etching process, impurities in the phosphoric acid etchant have a direct impact on semiconductor yield and the occurrence of defects, so their concentration is strictly controlled.

[0003] High-purity phosphoric acid suitable for use in semiconductor manufacturing can only be produced by a dry process in which yellow phosphorus (P4) is extracted from high-quality phosphate rock and then oxidized and burned at high temperatures of over 200°C, requiring significant process costs.

[0004] In addition, because reserves of high-quality phosphate rock are limited, there is a problem that the price of high-purity phosphoric acid will continue to rise due to the accelerating depletion of minerals, which will lead to economic problems such as increased semiconductor manufacturing costs.

[0005] Conventionally, various methods have been proposed for purifying phosphoric acid containing a large amount of metal ion impurities, such as membrane separation, ion exchange, and liquid extraction.

[0006] First, the membrane separation method has the advantage of high yield and purity of recovered phosphoric acid, but has the disadvantages of high membrane separation process cost and complicated operation method. Also, the corrosive nature of phosphoric acid can cause stability issues for the membranes used.

[0007] The ion exchange method uses ion exchange resin or calcium zeolite to remove acid. However, the ion exchange resin used here has a low ion exchange capacity and can only treat low-concentration acids. In addition, the ion exchange resin must be continuously replaced after ion exchange is complete, resulting in continuous process costs.

[0008] The liquid extraction method has the advantages of being able to operate the process continuously and requiring inexpensive equipment, but has the disadvantage of not being able to obtain phosphoric acid with the high purity required in semiconductor processes.

[0009] The crystallization method is a method of producing crystals from a saturated solution by controlling the rate of crystal nucleation and crystal growth.

[0010] The crystallization method is divided into a method using phosphoric acid seeds to promote nucleation of crystals and a method without using phosphoric acid seeds. When phosphoric acid seeds are not used, crystallization can only proceed by controlling the crystallization conditions to a temperature of -40°C or less, which results in a problem of high cost and time required to produce crystals.

[0011] Therefore, there is a demand for the development of a new method for producing phosphoric acid that can economically and industrially obtain high-purity phosphoric acid that does not contain unnecessary metals by separating impurities from a phosphoric acid raw material that contains a large amount of impurities. Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a production method that can separate and purify high-purity phosphoric acid from low-grade phosphoric acid by adjusting the quantum binding energy of phosphoric acid.

[0013] According to the present invention, in order to form phosphoric acid crystals without using seeds, the quantum bonds of phosphoric acid must be activated and controlled so that crystallization can proceed at temperatures above zero (0°C or higher).By utilizing the phosphoric acid purification method of the present invention, high-purity phosphoric acid can be obtained economically and industrially. [Means for solving the problem]

[0014] The present invention can provide a method for producing high-purity phosphoric acid, comprising: a step (S1) of supplying a phosphoric acid raw material containing impurities to a cooling device at 5 to 50°C; and a step (S2) of stirring the phosphoric acid raw material to form phosphoric acid crystals, wherein the roughness of the cooling device is adjusted so that the contact angle of the inner wall surface with water is 50° or less.

[0015] The cooling device may have an inner wall surface with a contact angle with water of 6° or more.

[0016] The phosphoric acid crystal formation step (S2) may be carried out at 0°C or higher.

[0017] The phosphoric acid crystal forming step (S2) may be performed by cooling the cooling device to 0 to 15°C.

[0018] In the step (S2), the cooling rate of the cooling device may be 0.1 to 5°C / min.

[0019] In the phosphoric acid crystal formation step (S2), the stirring speed of the phosphoric acid raw material may be 50 to 600 rpm.

[0020] The cooling device may have an inner wall surface with a roughness adjusted so that the surface area increases by 7 to 29%.

[0021] The cooling device may have a roughness adjusted so that the angle of the apex of the inner wall surface is 23 to 74°.

[0022] The method for producing high-purity phosphoric acid of the present invention may further include, after the phosphoric acid crystal formation step (S2), a step (S3) of raising the temperature of the cooling device to 20 to 35°C to partially melt a part of the crystallized phosphoric acid.

[0023] The method for producing high purity phosphoric acid of the present invention may further include a step (S4) of heating the cooling device to 40°C or higher after separating the partially melted phosphoric acid, thereby obtaining phosphoric acid crystals that are not melted in the partially melting step (S3).

[0024] The concentration of the phosphoric acid raw material may be 88 to 91.6%.

[0025] The phosphoric acid raw material may have a total content of impurities including Al, Ni and Fe of 300 ppb or more.

[0026] The phosphoric acid obtained by the above method may contain Al, Ni and Fe at 1 ppb or less each. [Effects of the Invention]

[0027] When high-purity phosphoric acid is produced by the purification method utilizing the quantum bonding of phosphoric acid provided by the present invention, high-purity phosphoric acid can be produced economically and industrially. DETAILED DESCRIPTION OF THE INVENTION

[0028] Unless otherwise defined herein, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used to describe the present invention are merely for the purpose of effectively describing specific embodiments and are not intended to limit the present invention.

[0029] As used herein, the singular forms "a," "an," and "the" include the plural forms as well, unless the context clearly dictates to the contrary.

[0030] As used herein, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other certain properties, regions, integers, steps, operations, elements, components, and / or groups.

[0031] Although the present invention can be embodied in various forms through various modifications, specific embodiments will be described in detail below by way of example, but it should be understood that this is not intended to limit the present invention to the specific disclosed embodiments, and that the present invention encompasses all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention.

[0032] In this specification, when the positional relationship of two parts is described using, for example, "above," "on top," "below," or "to the side," one or more other parts may be located between the two parts, unless the expressions "directly" or "immediately" are used.

[0033] In this specification, when a temporal relationship is described using, for example, "after," "following," "next," or "before," the expressions "directly" or "immediately" are not used, and therefore non-consecutive cases may also be included.

[0034] As used herein, the term "at least one" should be understood to include all possible combinations of one or more associated items.

[0035] Hereinafter, a method for producing high-purity phosphoric acid according to a specific embodiment of the invention will be described in more detail.

[0036] According to one embodiment of the present invention, there is provided a method for producing high-purity phosphoric acid, comprising: a step (S1) of supplying phosphoric acid raw material containing impurities to a cooling device at 5 to 50°C; and a step (S2) of stirring the phosphoric acid raw material to form phosphoric acid crystals, wherein the roughness of the cooling device is adjusted so that the contact angle of the inner wall surface with water is 50° or less.

[0037] As described above, a conventional method of purifying phosphoric acid by cooling to crystallize it is well known. However, if phosphoric acid seeds are not used, crystallization can only proceed by controlling the crystallization conditions at a temperature of -40°C or lower, which poses a problem of high cost and time required for producing crystals.

[0038] Therefore, in the present invention, it was confirmed that when the roughness of the inner wall surface of the cooling device is adjusted to a certain level, crystallization can proceed at a temperature above zero (0°C) without using phosphoric acid seeds, and high-purity phosphoric acid can be obtained economically and on an industrial scale, and thus the present invention was completed.

[0039] According to the present invention, the method includes a step (S1) of supplying phosphoric acid raw material containing impurities to a cooling device at 5 to 50°C, and a step (S2) of stirring the phosphoric acid raw material to form phosphoric acid crystals. When the roughness of the inner wall surface of the cooling device is adjusted so that the contact angle with water is 50° or less, quantum bonding is activated by a change in the quantum bonding energy of phosphoric acid, and phosphoric acid crystallization is promoted at a temperature above zero (0°C or higher), thereby obtaining high-purity phosphoric acid with an excellent yield.

[0040] First, the phosphoric acid raw material may be purchased from the market as low-purity (industrial-grade) phosphoric acid, or may be recovered from a semiconductor cleaning process. However, from the viewpoint of resource recycling, it is preferable to recover and use phosphoric acid containing impurities that has been used in a semiconductor process.

[0041] In the method for producing high purity phosphoric acid of the present invention, phosphoric acid raw material containing a large amount of impurities is supplied to a cooling device at 5 to 50°C, and then the phosphoric acid raw material is stirred to form phosphoric acid crystals. At this time, if the roughness of the inner wall surface of the cooling device is adjusted so that the contact angle with water is 50° or less, quantum bonds of phosphoric acid are activated due to a change in quantum binding energy, and phosphoric acid crystallization can proceed at temperatures above zero (0°C or above).

[0042] Adjusting the roughness of the inner wall surface of a cooling device increases the surface irregularity of the cooling device. This increase in irregularity reduces the apex angle and increases the surface energy of the cooling device, resulting in a decrease in the contact angle. First, a decrease in the apex angle increases the contact surface area between the phosphoric acid and the cooling device, thereby increasing the heat exchange area for phosphoric acid and the number of nucleation sites for phosphate crystals. This decreases the nucleation energy required for the nucleation process, the initial stage of phosphoric acid crystal formation and growth, and activates the quantum bonds of phosphoric acid, allowing phosphoric acid crystals to form at temperatures above zero (0°C). As the apex angle changes, the surface energy of the cooling device surface increases, resulting in a decrease in the contact angle. This decrease in contact angle increases the residence time of phosphoric acid at the nucleation sites. The longer the residence time of phosphoric acid at the nucleation sites, the faster nucleation occurs and the more nuclei are formed. Furthermore, the more nuclei formed, the faster many phosphate crystals grow. The increase in the number and rate of nucleation and crystal growth occurs due to the increase in the degree of phosphoric acid saturation at the nucleation sites. In this way, by adjusting the surface roughness of the cooling device, it is thought that by activating the quantum bonds of phosphoric acid and adjusting the energy required to form phosphoric acid crystal nuclei and crystals, crystallization can proceed without reducing the temperature to below zero.

[0043] In other words, when the temperature inside the cooling device is lowered and the phosphoric acid raw material is stirred using a cooling device with a roughness adjusted so that the contact angle of the inner wall surface with water is 50 degrees or less, the nucleus particles of phosphoric acid crystals generated by cooling can come into good contact with the phosphoric acid raw material even at temperatures above zero (0°C), allowing the crystal size to increase, and crystallization can be achieved even at temperatures above zero (0°C).

[0044] The cooling device may have an inner wall surface with a contact angle to water of 50° or less. However, if the inner wall surface of the cooling device has a contact angle to water of more than 50°, a problem may occur in that phosphoric acid is not crystallized at temperatures above zero degrees.

[0045] The cooling device may have an inner wall surface with a contact angle to water of 6° or more. If the inner wall surface of the cooling device has a contact angle to water of less than 6°, a problem may occur in which phosphoric acid is not crystallized at temperatures above zero degrees.

[0046] The contact angle of the inner wall surface of the cooling device with water can be measured using a contact angle measuring instrument (Phoenix MT, SEO).

[0047] The cooling device may have an inner wall surface with a roughness adjusted so that the surface area increases by 7 to 29%.

[0048] The change in the surface area can be measured by the change in the water fill volume up to a certain height of the cooling device before and after the roughness adjustment.

[0049] The cooling device may have a roughness adjusted so that the angle of the apex of the inner wall surface is 23 to 74°.

[0050] The vertex angle can be measured using an FE-SEM (JEOL JSM-7610F).

[0051] The phosphoric acid crystal formation step (S2) may be carried out at 0°C or higher.

[0052] Specifically, the phosphoric acid raw material containing impurities is supplied to a cooling device at about 5 to 50°C, and then the cooling device is cooled to 0 to 15°C.

[0053] The cooling rate of the cooling device may be 0.1°C / min to 5°C / min, and cooling at this rate is suitable for removing impurities in the phosphoric acid raw material and obtaining high-purity phosphoric acid.

[0054] In the method for producing high purity phosphoric acid of the present invention, a phosphoric acid raw material containing impurities is supplied to a cooling device at 5 to 50°C, and then the phosphoric acid raw material is cooled while being stirred to form phosphoric acid crystals, and at this time, the stirring speed of the phosphoric acid raw material may be 50 to 600 rpm.

[0055] By stirring the phosphoric acid raw material at a certain speed or more in the phosphoric acid crystal formation step (S2), the nucleus particles of the crystals generated by cooling can be in good contact with the phosphoric acid raw material, thereby increasing the size of the crystals and simultaneously shortening the crystallization time.

[0056] If the stirring speed is less than 50 rpm, crystallization may not proceed smoothly, and if it exceeds 600 rpm, crystals may not grow, resulting in a low crystallization yield.

[0057] The method for producing high-purity phosphoric acid of the present invention may further include, after the phosphoric acid crystal formation step (S2), a step (S3) of raising the temperature of the cooling device to 20 to 35°C to partially melt a part of the crystallized phosphoric acid.

[0058] The phosphoric acid crystallized by the crystallization process may contain pure phosphoric acid with almost no impurities inside the crystal, and may contain phosphoric acid containing impurities on the surface of the crystal.

[0059] Therefore, by raising the temperature of the crystallized phosphoric acid to 20 to 35°C and partially melting part of the surface of the phosphoric acid crystal, impurities adhering to the surface can be removed to obtain phosphoric acid of higher purity.

[0060] Thereafter, after separating the partially melted phosphoric acid, the cooling device is heated to 40° C. or higher, and unmelted phosphoric acid crystals can be obtained in the partially melting step (S3) (S4).

[0061] The phosphoric acid raw material before purification contains a large amount of impurities, and for example, the phosphoric acid raw material may have a total content of impurities including Al, Ni, and Fe of 300 ppb or more.

[0062] More specifically, the phosphoric acid raw material may have a total impurity content of 300 ppb or more, including Al 150 ppb or more, Ni 20 ppb or more, and Fe 100 ppb or more.

[0063] As described above, the method for producing high-purity phosphoric acid of the present invention can economically and industrially produce high-purity phosphoric acid. Specifically, the phosphoric acid obtained by the method can contain Al, Ni, and Fe at levels of 1 ppb or less, respectively. [Example]

[0064] Hereinafter, the present invention will be described in more detail with reference to the following examples, but the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0065] <Checking for room temperature crystallization> (1) Example 1 First, 1,000 g of 91.6% phosphoric acid raw material containing impurities was fed into a cooling device at 35°C. The cooling device was adjusted so that the contact angle of the inner wall with water was 6°, the apex angle was 23°, and the roughness was increased by 7%.

[0066] Thereafter, the phosphoric acid raw material was stirred at a speed of 50 rpm, and the temperature was cooled from 35° C. to 5° C. at a rate of 0.5° C. / min using a cooling device, and phosphoric acid crystallization was allowed to proceed for 1 hour.

[0067] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0068] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 807 g of final purified crystallized phosphoric acid.

[0069] (2) Example 2 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the concentration of the phosphoric acid raw material was 88%.

[0070] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0071] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 738 g of final purified crystallized phosphoric acid.

[0072] (3) Example 3 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the phosphoric acid raw material was stirred at a speed of 600 rpm.

[0073] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0074] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 758 g of final purified crystallized phosphoric acid.

[0075] (4) Example 4 Phosphoric acid crystallization was carried out as in Example 1, except that the roughness of the cooling device was controlled so that the surface area was increased by 29%.

[0076] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0077] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 848 g of final purified crystallized phosphoric acid.

[0078] (5) Example 5 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the cooling rate was controlled to 0.1° C. / min.

[0079] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0080] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 812 g of final purified crystallized phosphoric acid.

[0081] (6) Example 6 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the cooling rate was controlled to 5° C. / min.

[0082] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0083] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 835 g of final purified crystallized phosphoric acid.

[0084] (7) Example 7 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the temperature of the cooling device was controlled to 50°C when the phosphoric acid raw material was introduced.

[0085] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0086] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 799 g of final purified crystallized phosphoric acid.

[0087] (8) Example 8 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the temperature of the cooling device was controlled to 5°C when the phosphoric acid raw material was introduced.

[0088] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0089] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 863 g of final purified crystallized phosphoric acid.

[0090] (9) Example 9 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the cooling temperature was controlled to 0°C.

[0091] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0092] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 859 g of final purified crystallized phosphoric acid.

[0093] (10) Example 10 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the cooling temperature was controlled to 15°C.

[0094] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0095] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 766 g of final purified crystallized phosphoric acid.

[0096] (11) Example 11 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the contact angle of the inner wall surface of the cooling device with water was controlled to 50°.

[0097] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0098] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 774 g of final purified crystallized phosphoric acid.

[0099] (12) Example 12 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the angle of the apex of the inner wall surface of the cooling device was controlled to 74°.

[0100] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0101] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 751 g of final purified crystallized phosphoric acid.

[0102] (13) Comparative Example 1 1,000 g of 91.6% phosphoric acid raw material containing impurities was fed into a cooling device at 35°C. The cooling device was adjusted so that the contact angle of the inner wall with water was 60°, the apex angle was 23°, and the surface area was increased by 7%.

[0103] Thereafter, the phosphoric acid raw material was stirred at a speed of 50 rpm, and the temperature was cooled from 35° C. to 5° C. at a rate of 0.5° C. / min using a cooling device, and phosphoric acid crystallization was allowed to proceed for 1 hour.

[0104] As a result of the progress of crystallization, the raw material phosphoric acid was not crystallized.

[0105] (14) Comparative Example 2 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the phosphoric acid raw material was stirred at a speed of 1,000 rpm.

[0106] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0107] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 89 g of final purified crystallized phosphoric acid.

[0108] (15) Comparative Example 3 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the surface roughness of the cooling device was not adjusted.

[0109] As a result of the progress of crystallization, the raw material phosphoric acid was not crystallized.

[0110] (16) Comparative Example 4 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the cooling rate of the phosphoric acid raw material was set to 10° C. / min.

[0111] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0112] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 828 g of final purified crystallized phosphoric acid.

[0113] (17) Comparative Example 5 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the temperature of the cooling device was controlled to 70°C when the phosphoric acid raw material was introduced.

[0114] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0115] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 138 g of final purified crystallized phosphoric acid.

[0116] (18) Comparative Example 6 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the cooling temperature was controlled to 30°C.

[0117] As a result of the progress of crystallization, the raw material phosphoric acid was not crystallized.

[0118] (19) Comparative Example 7 Crystallization of phosphoric acid was carried out in the same manner as in Example 1, except that the contact angle of the inner wall surface of the cooling device with water was controlled to 90°.

[0119] As a result of the progress of crystallization, the raw material phosphoric acid was not crystallized.

[0120] (20) Comparative Example 8 Phosphoric acid crystallization was carried out in the same manner as in Example 1, except that the surface area of ​​the cooling device was increased by 43% by roughness control.

[0121] The uncrystallized phosphoric acid was removed, and the temperature of the cooling device was raised to 20°C to partially melt and separate part of the crystallized phosphoric acid.

[0122] The remaining unmelted phosphoric acid crystals were heated to 40°C or higher until they were all melted, yielding 818 g of final purified crystallized phosphoric acid.

[0123] <Analysis of Metal Impurities in Crystallized Phosphoric Acid> The metal impurity contents in the phosphoric acid raw material, amorphous phosphoric acid and phosphoric acid separated by partial melting, and crystallized phosphoric acid obtained by heating to 40°C or higher were analyzed using ICP-MS.

[0124] Specifically, using an Agilent ICP-MS 8900, non-crystallized phosphoric acid, partially molten phosphoric acid, and crystallized phosphoric acid were diluted with DIW or 3% nitric acid to analyze the content of metal impurities in the samples.

[0125] [Table 1]

[0126] [Table 2]

[0127] [Table 3]

[0128] [Table 4]

[0129] [Table 5]

[0130] From Tables 1 to 5, it was confirmed that when the method for producing high-purity phosphoric acid of the present invention is used, impurities can be separated from a phosphoric acid raw material containing a large amount of impurities, and high-purity phosphoric acid free from unnecessary metals can be obtained.

Claims

1. A step (S1) of supplying impurity-containing phosphoric acid raw material to a cooling device at 5 to 50°C; and (S2) a step of stirring the phosphoric acid raw material to form phosphoric acid crystals, The roughness of the inner wall surface of the cooling device is adjusted so that the contact angle with water is 50° or less. A method for producing high-purity phosphoric acid.

2. 2. The method for producing high-purity phosphoric acid according to claim 1, wherein the cooling device has an inner wall surface with a contact angle with water of 6 degrees or more.

3. The method for producing high-purity phosphoric acid according to claim 1, wherein the phosphoric acid crystal formation step (S2) is carried out at 0°C or higher.

4. 2. The method for producing high-purity phosphoric acid according to claim 1, wherein the phosphoric acid crystal formation step (S2) is performed by cooling the cooling device to 0 to 15°C.

5. 5. The method for producing high-purity phosphoric acid according to claim 4, wherein in the step (S2), the cooling rate of the cooling device is 0.1 to 5° C. / min.

6. 2. The method for producing high-purity phosphoric acid according to claim 1, wherein in the phosphoric acid crystal formation step (S2), a stirring speed of the phosphoric acid raw material is 50 to 600 rpm.

7. 2. The method for producing high-purity phosphoric acid according to claim 1, wherein the roughness of the cooling device is adjusted so that the surface area of ​​the inner wall surface increases by 7 to 29%.

8. 2. The method for producing high-purity phosphoric acid according to claim 1, wherein the roughness of the cooling device is adjusted so that the angle of the apex of the inner wall surface is 23 to 74 degrees.

9. After the phosphoric acid crystal formation step (S2), The method for producing high-purity phosphoric acid according to claim 1, further comprising a step (S3) of raising the temperature of the cooling device to 20 to 35°C to partially melt a part of the crystallized phosphoric acid.

10. 10. The method for producing high-purity phosphoric acid according to claim 9, further comprising: a step (S4) of raising the temperature of the cooling device to 40°C or higher after separating the partially melted phosphoric acid, thereby obtaining phosphoric acid crystals that are not melted in the partial melting step (S3).

11. 2. The method for producing high purity phosphoric acid according to claim 1, wherein the concentration of the phosphoric acid raw material is 88 to 91.6%.

12. 2. The method for producing high-purity phosphoric acid according to claim 1, wherein the phosphoric acid raw material has a total content of impurities including Al, Ni, and Fe of 300 ppb or more.

13. 2. The method for producing high-purity phosphoric acid according to claim 1, wherein the phosphoric acid obtained by the method contains Al, Ni and Fe each at 1 ppb or less.

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