Method for producing high-purity phosphoric acid by utilizing phosphoric acid quantum coupling

Abstract

The invention relates to a method for preparing high-purity phosphoric acid from low-purity phosphoric acid by forming pure phosphoric acid crystals through quantum coupling crystallization purification of phosphoric acid. In particular, the present invention relates to a method for producing phosphoric acid by obtaining pure crystals from a phosphoric acid raw material containing a large amount of impurities by activating quantum coupling of phosphoric acid at a temperature above zero (0 DEG C and above), thereby economically and industrially obtaining high purity phosphoric acid from low grade phosphoric acid.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for producing high-purity phosphoric acid from low-purity phosphoric acid by quantum coupling crystallization purification to form pure phosphoric acid crystals. Specifically, it relates to a method for producing phosphoric acid, which can obtain high-purity phosphoric acid at low cost for industrial use by activating quantum coupling of phosphoric acid at a temperature higher than zero degrees (0°C and above) to obtain pure crystals from a raw material of phosphoric acid containing a large amount of impurities. BACKGROUND

[0002] Phosphoric acid is an essential chemical material in semiconductor manufacturing processes and is the only substance that can wet-etch a semiconductor silicon nitride film (Si3N4, SiN). In the silicon nitride film etching process, impurities in the phosphoric acid etching solution directly affect the yield and defect rate of semiconductors, and thus the concentration thereof must be strictly controlled.

[0003] Since high-purity phosphoric acid suitable for semiconductor manufacturing processes can only be prepared by dry method, i.e., extracting yellow phosphorus (P4) from high-quality phosphate ore and producing it by oxidizing and burning yellow phosphorus at a high temperature of 200°C or higher, the process cost is high.

[0004] In addition, since the reserves of high-quality phosphate ore are limited, the depletion rate of its mineral resources is accelerating, which leads to a continuous increase in the price of high-purity phosphoric acid, thereby causing an economic problem of an increase in the cost of semiconductor manufacturing.

[0005] For the purification process of phosphoric acid containing a large amount of metal ion impurities, various methods have been proposed in the prior art, such as membrane separation method, ion exchange method, or liquid extraction method.

[0006] First, the membrane separation method has the advantages of high phosphoric acid yield and high purity, but has the disadvantages of high membrane separation process cost and extremely complex operation method. In addition, due to the corrosive nature of phosphoric acid, there can be safety problems with used membranes.

[0007] The ion exchange method uses ion exchange resins or calcium zeolite to remove acid, but since the ion exchange capacity of the ion exchange resins used is low, it can only handle low-concentration acid, and the ion exchange resins after ion exchange completion need to be continuously replaced, thus having the defect of causing an increase in the cost of continuous processes.

[0008] Although the liquid extraction method has the advantages of continuous process operation and low equipment cost, it has the disadvantage that high-purity phosphoric acid required for semiconductor processes cannot be obtained.

[0009] The crystallization method is a method of forming crystals from a saturated solution by controlling the nucleation rate and growth rate of the 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 present invention aims to provide a method for preparing high-purity phosphoric acid by controlling the quantum coupling energy of phosphoric acid to separate and purify it from low-grade phosphoric acid.

[0014] As described in this invention, forming phosphoric acid crystals without the use of seed crystals requires controlling the crystallization conditions and activating the quantum coupling of phosphoric acid to crystallize at temperatures above zero degrees Celsius (0°C or higher). The method for purifying phosphoric acid as described in this invention enables the economical and industrialized production of high-purity phosphoric acid.

[0015] Technical solution

[0016] One embodiment of the present invention provides a method for preparing high-purity phosphoric acid, the method comprising the following steps:

[0017] The phosphoric acid raw material containing impurities is added to the cooling device (S1) at 5℃-50℃;

[0018] Phosphoric acid crystals (S2) are formed by stirring the raw materials;

[0019] The cooling device has an adjustable roughness such that the contact angle of the inner wall surface with water is 50° or less.

[0020] The contact angle of the inner wall surface of the cooling device with water is 6° or greater.

[0021] The step (S2) of forming phosphate crystals is carried out at 0°C or higher.

[0022] The step (S2) of forming phosphoric acid crystals is carried out while the cooling device cools the temperature to 0 to 15°C.

[0023] In step (S2), the cooling rate is controlled between 0.1 and 5 °C / min.

[0024] In step (S2) of forming phosphoric acid crystals, the stirring rate of the phosphoric acid feedstock is controlled at 50 to 600 rpm.

[0025] The cooling device has an adjustable roughness, which increases the surface area of ​​the inner wall by 7% to 29%.

[0026] The cooling device has an adjustable roughness such that the apex angle of the inner wall surface is between 23° and 74°.

[0027] The method for producing high-purity phosphoric acid according to the present invention further includes, after the step of forming phosphoric acid crystals (S2), partially melting some of the crystalline phosphoric acid by raising the temperature of the cooling device to 20°C to 35°C (S3).

[0028] The method for producing high-purity phosphoric acid according to the present invention further includes, after separating the partially melted phosphoric acid, obtaining unmelted phosphoric acid crystals (S4) by raising the temperature of the cooling device to 40°C or higher.

[0029] The concentration of the phosphoric acid feedstock is 88% to 91.6%.

[0030] The total content of impurities, including Al, Ni, and Fe, in the phosphoric acid raw material is 300 ppb or more.

[0031] Phosphoric acid obtained using the above method may contain Al, Ni, and Fe, with each metal impurity comprising 1 ppb or less.

[0032] Beneficial effects

[0033] When using the phosphoric acid quantum coupling purification method described in this invention to produce high-purity sulfuric acid, high-purity phosphoric acid can be produced economically and industrially. Detailed Implementation

[0034] 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.

[0035] Unless the context clearly indicates otherwise, the singular form used in this specification also includes the plural form.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] The method for producing high-purity phosphoric acid will now be described in more detail according to the specific embodiments described herein.

[0042] 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 at 5-50°C (S1); and forming phosphoric acid crystals by stirring the phosphoric acid raw material (S2). The cooling device has an adjustable roughness such that the contact angle of its inner wall surface with water is 50° or less.

[0043] As mentioned above, the cooling crystallization method 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 required for the crystal formation process.

[0044] Therefore, the inventors of this invention determined that when the roughness of the inner wall surface of the cooling device is adjusted to a certain level, crystallization can be carried out at a temperature above zero degrees (0°C or higher) without the use of phosphoric acid seed crystals, so as to economically and industrially produce high-purity phosphoric acid, thus completing this invention.

[0045] As described in this invention, the method includes: adding a phosphoric acid raw material containing impurities to a cooling device at 5 to 50°C (S1); forming phosphoric acid crystals by stirring the phosphoric acid raw material (S2); wherein the cooling device has an adjustable roughness such that the contact angle of the inner wall surface with respect to water is 50° or less; changing the quantum coupling energy of phosphoric acid to activate quantum coupling, thereby crystallizing phosphoric acid at a temperature above zero degrees (0°C or higher) to obtain high-purity, high-yield phosphoric acid.

[0046] 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.

[0047] In the method for producing high-purity phosphoric acid described in this invention, phosphoric acid raw material containing a large amount of impurities is added to a cooling device at 5-50°C, and phosphoric acid crystals are formed while the phosphoric acid raw material is stirred; wherein, the cooling device has adjustable roughness so that the contact angle of the inner wall surface with water is 50° or less; the quantum coupling energy of phosphoric acid is changed to activate quantum coupling, and phosphoric acid crystallizes at a temperature above zero degrees (0°C or higher).

[0048] When the surface roughness of the inner wall of the cooling device is adjusted, the surface non-uniformity of the cooling device increases. This increase in non-uniformity leads to a decrease in the apex angle, and consequently, a decrease in the contact angle due to the increase in the surface energy of the cooling device. Firstly, due to the decrease in the apex angle, the contact area between phosphoric acid and the cooling device increases, and correspondingly, the heat exchange area between phosphoric acid and the nucleation site of the phosphoric acid crystal increases, reducing the nucleation energy required for the nucleation process—the initial stage of phosphoric acid crystal formation and growth. Therefore, by activating the quantum coupling of phosphoric acid, phosphoric acid crystals can be formed at temperatures above zero (0°C or higher). With the change in apex angle, the contact angle decreases as the surface energy of the cooling device increases. This decrease in contact angle increases the residence time of phosphoric acid at the nucleation site; as the residence time of phosphoric acid at the nucleation site increases, nucleation proceeds faster, and more nuclei are formed. Furthermore, many phosphoric acid crystals grow rapidly from the numerous nuclei formed above. The increase in the number and rate of nucleation and crystal growth is influenced by the increase in phosphoric acid saturation at the nucleation site. It can be assumed, as described above, that by adjusting the surface roughness of the cooling device, the quantum coupling of phosphoric acid is activated to control the energy required for the formation of phosphoric acid crystal nuclei and crystals, thereby enabling crystallization without lowering the temperature below zero degrees Celsius.

[0049] In other words, when phosphoric acid raw materials are stirred in a cooling device with adjusted roughness, the contact angle of the inner wall surface relative to water is reduced to 50° or less when the temperature inside the cooling device is lowered. Even at temperatures above zero degrees (0°C or higher), the phosphoric acid crystal nuclei formed can have good contact with the phosphoric acid raw materials, increasing the size of the crystals. Therefore, crystallization can occur even at temperatures above zero degrees.

[0050] The contact angle between the inner wall surface of the cooling device and the water can be 50° or less. When the contact angle between the inner wall surface of the cooling device and the water is greater than 50°, the problem of phosphoric acid not crystallizing at temperatures above zero degrees may occur.

[0051] The contact angle between the inner wall surface of the cooling device and water can be 6° or greater. When the contact angle between the inner wall surface of the cooling device and water is less than 6°, the problem of phosphoric acid not crystallizing at temperatures above zero degrees may occur.

[0052] The contact angle of the inner wall surface of the cooling device with respect to water can be measured using a contact angle measuring device (PhoenixMT, SEO).

[0053] The cooling device may have an adjustable roughness, thereby increasing the surface area of ​​the inner wall surface by 7% to 29%.

[0054] The change in surface area can be determined by measuring the volume change corresponding to the water volume in the cooling device reaching a specific height before and after roughness adjustment.

[0055] The cooling device may have an adjustable roughness, such that the apex angle of the inner wall surface is 23° to 74°.

[0056] The apex angle can be measured using FE-SEM (JEOL JSM-7610F).

[0057] The step (S2) of forming phosphate crystals can be carried out at 0°C or higher.

[0058] Specifically, the step (S2) of forming phosphoric acid crystals can be carried out by adding the phosphoric acid raw material containing impurities to a cooling device at about 5°C to 50°C, and then cooling the cooling device to 0°C to 15°C.

[0059] The cooling rate of the cooling device can be from 0.1℃ / min to 5℃ / min. Cooling at the above rate is suitable for removing impurities from the phosphoric acid raw material to obtain high-purity phosphoric acid.

[0060] In the method for producing high-purity phosphoric acid according to the present invention, phosphoric acid raw material containing impurities is added to a cooling device at a temperature of 5°C to 50°C, and then simultaneously stirred and cooled to form phosphoric acid crystals. The stirring rate of the phosphoric acid raw material can be from 50 rpm to 600 rpm.

[0061] In step (S2) of forming phosphoric acid crystals, the phosphoric acid raw material is stirred at a certain or higher rate to ensure good contact between the cooled crystal nuclei and the phosphoric acid raw material, thereby increasing the size of the crystals and shortening the time required for crystallization.

[0062] When the stirring speed is less than 50 rpm, crystallization may not occur. When the stirring speed is greater than 600 rpm, crystals may not grow, resulting in a decrease in the crystallization rate.

[0063] The method for producing high-purity phosphoric acid according to the present invention may further include, after the step of forming phosphoric acid crystals (S2), partially melting some of the crystalline phosphoric acid by raising the temperature of the cooling device to 20°C to 35°C (S3).

[0064] Phosphoric acid obtained by crystallization can include pure phosphoric acid with almost no impurities inside the crystal and phosphoric acid with impurities mixed on the crystal surface.

[0065] Therefore, by raising the temperature of crystalline phosphoric acid to 20°C to 35°C, some of the phosphoric acid crystals on the surface can be partially melted, and impurities attached to the surface can be removed to obtain phosphoric acid with higher purity.

[0066] Next, the partially melted phosphoric acid is separated, and then the temperature of the cooling device is raised to 40°C or higher to obtain unmelted phosphoric acid crystals (S4) from the partial melting step (S3).

[0067] The phosphoric acid raw material before purification contains a large number of impurities. For example, the total content of impurities, including Al, Ni and Fe, in the phosphoric acid raw material can be above 300 ppb.

[0068] More specifically, the total content of impurities in the phosphoric acid raw material, including aluminum ≥150ppb, nickel ≥20ppb and iron ≥100ppb, can reach 300ppb or higher.

[0069] As described above, high-purity phosphoric acid can be obtained economically and industrially using the method for producing high-purity phosphoric acid described in this invention. Specifically, the phosphoric acid obtained using this method may include Al, Ni, and Fe, each in an amount of 1 ppb or less. The concentration of the phosphoric acid feedstock can reach 88% to 91.6%.

[0070] As described above, the high-purity phosphoric acid preparation method of this invention can economically and industrially obtain high-purity phosphoric acid. Specifically, the content of aluminum, nickel, and iron in the phosphoric acid obtained by this method can be controlled below 1 ppb.

[0071] The embodiments of the present invention will be described in detail below with reference to examples. It should be noted that the following examples are only used to illustrate the embodiments of the present invention and do not constitute any limitation on the scope of the present invention.

[0072] <Identification by Crystallization at Room Temperature>

[0073] (1) Example 1

[0074] First, 1000g of 91.6% phosphoric acid raw material containing impurities was added to a cooling device at 35°C. The cooling device was adjusted to have a roughness such that the contact angle of the inner wall surface with water was 6°, the apex angle was 23°, and the surface area increased by 7%.

[0075] Subsequently, while stirring the phosphoric acid feedstock at a rate of 50 rpm, the cooling device was used to cool the feedstock from 35°C to 5°C at a rate of 0.5°C / min, and phosphoric acid crystallization was carried out for 1 hour.

[0076] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0077] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (807g).

[0078] (2) Example 2

[0079] The method for crystallizing phosphoric acid is the same as in Example 1, except that the concentration of the phosphoric acid raw material is 88%.

[0080] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid partially melts and separates.

[0081] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (738g).

[0082] (3) Example 3

[0083] The method for phosphoric acid crystallization is the same as in Example 1, except that the stirring speed of the phosphoric acid feedstock is 600 rpm.

[0084] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0085] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (758g).

[0086] (4) Example 4

[0087] The method for phosphoric acid crystallization was the same as in Example 1, except that the roughness of the cooling device was adjusted to increase its surface area by 29%.

[0088] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0089] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (848g).

[0090] (5) Example 5

[0091] The method for phosphoric acid crystallization is the same as in Example 1, except that the cooling rate is controlled at 0.1°C / min.

[0092] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0093] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (812g).

[0094] (6) Example 6

[0095] The method for phosphoric acid crystallization is the same as in Example 1, except that the cooling rate is controlled at 5°C / min.

[0096] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0097] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (835g).

[0098] (7) Example 7

[0099] The method for phosphoric acid crystallization is the same as in Example 1, except that the temperature of the cooling device is controlled at 50°C when adding the phosphoric acid raw material.

[0100] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0101] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (799g).

[0102] (8) Example 8

[0103] The method for phosphoric acid crystallization is the same as in Example 1, except that the temperature of the cooling device is controlled at 5°C when adding the phosphoric acid raw material.

[0104] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0105] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (863g).

[0106] (9) Example 9

[0107] The method for phosphoric acid crystallization is the same as in Example 1, except that the cooling temperature is controlled at 0°C.

[0108] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0109] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (859g).

[0110] (10) Example 10

[0111] The method for phosphoric acid crystallization is the same as in Example 1, except that the cooling temperature is controlled at 15°C.

[0112] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0113] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (766g).

[0114] (11) Example 11

[0115] The method for phosphoric acid crystallization is the same as in Example 1, except that the contact angle between the inner wall surface of the cooling device and the water is controlled at 50°.

[0116] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0117] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (774g).

[0118] (12) Example 12

[0119] The method for phosphoric acid crystallization is the same as in Example 1, except that the apex angle of the inner wall surface of the cooling device is controlled at 74°.

[0120] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0121] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (751g).

[0122] (13) Comparative Example 1

[0123] 1000g of 91.6% phosphoric acid raw material containing impurities was added to a cooling device at 35°C. The cooling device was adjusted to have a roughness such that the contact angle of the inner wall surface with water was 60°, the apex angle was 23°, and the surface area was increased by 7%.

[0124] Subsequently, the cooling device cooled the phosphoric acid raw material from 35°C to 5°C at a rate of 0.5°C / min, while the phosphoric acid raw material was stirred at a rate of 50 rpm, and then phosphoric acid crystallization was carried out for 1 hour.

[0125] The results of the crystallization experiment showed that the phosphoric acid feedstock did not crystallize.

[0126] (14) Comparative Example 2

[0127] The method for phosphoric acid crystallization is the same as in Example 1, except that the stirring speed of the phosphoric acid feedstock is 1,000 rpm.

[0128] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0129] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (89g).

[0130] (15) Comparative Example 3

[0131] The method for phosphoric acid crystallization is the same as in Example 1, except that the surface roughness of the cooling device is not adjusted.

[0132] The results of the crystallization experiment showed that the phosphoric acid feedstock did not crystallize.

[0133] (16) Comparative Example 4

[0134] The method for phosphoric acid crystallization is the same as in Example 1, except that the cooling rate of the phosphoric acid raw material is 10°C / min.

[0135] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0136] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (828g).

[0137] (17) Comparative Example 5

[0138] The method for phosphoric acid crystallization is the same as in Example 1, except that the cooling device is controlled at 70°C when adding the phosphoric acid raw material.

[0139] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0140] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (138g).

[0141] (18) Comparative Example 6

[0142] The method for phosphate crystallization is the same as in Example 1, except that the cooling temperature is controlled at 30°C.

[0143] The results of the crystallization experiment showed that the phosphoric acid feedstock did not crystallize.

[0144] (19) Comparative Example 7

[0145] The method for phosphoric acid crystallization is the same as in Example 1, except that the contact angle between the inner wall surface of the cooling device and the water is controlled at 90°.

[0146] The results of the crystallization experiment showed that the phosphoric acid feedstock did not crystallize.

[0147] (20) Comparative Example 8

[0148] The method for phosphoric acid crystallization was the same as in Example 1, except that the roughness of the cooling device was adjusted to increase its surface area by 43%.

[0149] To remove the uncrystallized phosphoric acid, the cooling device is heated to 20°C, and some of the crystalline phosphoric acid is partially melted and separated.

[0150] The temperature was raised to above 40°C to completely melt the remaining unmelted phosphoric acid crystals, finally yielding purified crystalline phosphoric acid (818g).

[0151] Analysis of Metal Impurities in Crystallized Phosphoric Acid

[0152] 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.

[0153] 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.

[0154] Table 1

[0155]

[0156] Table 2

[0157]

[0158] Table 3

[0159]

[0160]

[0161] Table 4

[0162]

[0163] Table 5

[0164]

[0165]

[0166] As can be seen from Tables 1 to 5, when using the method for producing high-purity phosphoric acid described in this invention, high-purity phosphoric acid free of unnecessary metals can be obtained by separating impurities from phosphoric acid raw materials containing a large number of impurities.

Claims

1. A method for preparing high-purity phosphoric acid, the method comprising the steps of: The phosphoric acid raw material containing impurities is added to the cooling device (S1) at 5℃-50℃; Phosphoric acid crystals (S2) are formed by stirring the phosphoric acid raw material; in, The cooling device has an adjustable roughness such that the contact angle of the inner wall surface with water is 50° or less.

2. The method as described in claim 1, characterized in that, The contact angle of the inner wall surface of the cooling device with water is 6° or greater.

3. The method as described in claim 1, characterized in that, The step (S2) of forming phosphate crystals is carried out at 0°C or higher.

4. The method as described in claim 1, characterized in that, The step (S2) of forming phosphoric acid crystals is carried out when the cooling device cools the temperature to 0 to 15°C.

5. The method as described in claim 4, characterized in that, In step (S2), the cooling rate is controlled between 0.1 and 5 °C / min.

6. The method as described in claim 1, characterized in that, In step (S2) of forming phosphoric acid crystals, the stirring rate of the phosphoric acid raw material is 50 to 600 rpm.

7. The method as described in claim 1, characterized in that, The cooling device has an adjustable roughness, which increases the surface area of ​​the inner wall surface by 7% to 29%.

8. The method as described in claim 1, characterized in that, The cooling device has an adjustable roughness such that the apex angle of the inner wall surface is 23° to 74°.

9. The method as described in claim 1, characterized in that, The method further includes raising the temperature of the cooling device to 20°C to 35°C after the step of forming phosphoric acid crystals (S2) to partially melt some of the crystalline phosphoric acid (S3).

10. The method as described in claim 9, characterized in that, The method further includes raising the temperature of the cooling device to 40°C or higher after separating the partially melted phosphoric acid to obtain unmelted phosphoric acid crystals in the partial melting step (S3) (S4).

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, Ni and Fe.

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