KR100454101B1 - Purification method and equipment for phosphoric acid - Google Patents

Abstract

The present invention relates to a method for purifying phosphoric acid and an apparatus thereof, and more particularly, to concentrate the phosphoric acid raw material containing impurities in a predetermined concentration in an evaporation tank (1), and a crystallization tank (4). In the process of preparing a phosphate crystal of a certain size by cooling crystallization, and by separating the prepared phosphate crystals, the crystallization of the separated phosphate crystals by partial melting in the partial melting apparatus (8) by controlling the temperature control and the heat transfer rate A method of purifying phosphoric acid consisting of melting impurities to remove the impurities attached to the surface of the crystal and removing impurities contained in the crystal, and efficiently removing impurities contained in the phosphate raw material and applying them to semiconductor grades. The present invention relates to a method for purifying phosphoric acid and an apparatus thereof.

Description

Purification method and apparatus for phosphoric acid {Purification method and equipment for phosphoric acid}

The present invention relates to a method for purifying phosphoric acid and an apparatus thereof, and more particularly, a process of concentrating a certain amount of phosphoric acid containing impurities in a predetermined concentration in an evaporation tank (1), and a crystallization tank (4). In the process of preparing a phosphate crystal of a certain size by cooling crystallization, and by separating the prepared phosphate crystals, the crystallization of the separated phosphate crystals by partial melting in the partial melting apparatus (8) by controlling the temperature control and the heat transfer rate A method of purifying phosphoric acid consisting of melting impurities to remove the impurities attached to the surface of the crystal and removing impurities contained in the crystal, and efficiently removing impurities contained in the phosphate raw material and applying them to semiconductor grades. The present invention relates to a method for purifying phosphoric acid and an apparatus thereof.

Recently, due to the rapid development of the electronics industry, semiconductor integrated circuits such as LSI and VLSI for high-speed processing of large-capacity information have been put to practical use. As described above, as the electrodes, lines, and the like forming the transistor unit elements are miniaturized and integrated, the distance between the PN junction portion, which acts as a transistor and the electrode, and the minimum line width between the lines have reached sub-microns. However, in the semiconductor materials, the incorporation of impurities such as metal contamination by Fe, Cu, Al, and Mn, ion contamination by SO ₄ ^2- and NO ₃ ^2- , and particle contamination (<0.1 μm) may cause electrical performance of semiconductor devices. It is known to have a fatal effect on. Therefore, very high purity materials are used in the ppb to ppt level in semiconductor manufacturing.

In particular, phosphoric acid is used as an etching solution of silicon nitride (Si ₃ N ₄ ) used in the gate circuit design in the semiconductor manufacturing process, and industrially ultra-high purity phosphoric acid is also used as an etching solution for optical lenses, ceramic alumina and metal aluminum.

In order to obtain the phosphoric acid used for such a use as a material of high purity, the method of crystallization is used.

Crystallization of phosphoric acid is a phase equilibrium technique in which high-purity phosphoric acid crystals are separated from a mother liquor in which a large amount of impurities are concentrated. In the crystallization process, impurities may be contained in the phosphoric acid crystals. As such, when impurities are present in the phosphate crystal, supersaturation for crystal formation is prevented, which makes it difficult to control the crystallization rate.

On the other hand, the conventional phosphoric acid manufacturing process is divided into a wet process and a dry process according to the method of treating phosphate ore. The dry process is a method of reducing phosphate ore to sulfur phosphorus at a high temperature (> 1000 ° C.), oxidizing it with a large amount of oxygen to obtain phosphorus pentoxide, and hydrolyzing to obtain phosphoric acid. Although it is a method to obtain high purity phosphoric acid, it is a process that is problematic due to excessive energy consumption and high cost as a phosphoric acid manufacturing process for fertilizers. Dry phosphoric acid is largely used for the manufacture of chemicals (sodium tripolyphosphate) and for food. The wet process is a method of producing phosphoric acid by treating phosphate with inorganic acids such as nitric acid, sulfuric acid, and perchloric acid, mainly using sulfuric acid.

However, the prepared phosphoric acid has a large amount of impurities such as chromium, vanadium, iron, manganese, magnesium, aluminum, sulfate, fluorine, constituents of organic or colloidal insolubles and suspended solids due to many side reactions of phosphate and inorganic acid. have. In addition, wet phosphoric acid is called black acid because of coloring by ppm levels of impurities. On the other hand, sulfuric acid, an inorganic acid used in the manufacture of wet phosphoric acid, may form a precipitate such as gypsum after reaction with phosphate ore, but most of it is present as a dissolved ion and affects the shape of phosphate crystals produced. In particular, when the concentration of sulfate ions is high, the resulting crystals have many needle-shaped shapes, and in this case, the surface area of the crystals is large, so that inclusion and aggregation of impurities easily occur.

On the other hand, various documents for removing impurities from the phosphoric acid as described above will be described as an example.

According to U.S. Patent No. 4,299,804, aluminum and magnesium present in phosphoric acid were removed by insoluble crystals in the form of MgAl ₂ F ₈ and MgAlF ₅ by adding a compound capable of giving fluorine ions to wet phosphoric acid. However, the above method has the disadvantage that the removal efficiency of magnesium, aluminum, sodium, and silicon reaches 90%, but the time taken for removing the precipitate is 16 to 20 hours, and other impurities cannot be purified.

U.S. Patent No. 4,169,882 also discloses a method of treating wet phosphoric acid with urea and converting it to urea-phosphate and then decomposing urea-phosphate with oxalic acid to obtain purified phosphoric acid. However, aluminum, magnesium, fluorine, Only 80% of iron was removed.

Japanese Patent No. 14,692 discloses a wet phosphoric acid purification method by a continuous fluidized bed crystallizer. In the above patent, a commercial scale purification process can be developed in the state where impurities are removed using an oxidizing agent suitable for wet phosphoric acid. However, since impurities are contained in phosphoric acid to inhibit the crystallization rate, it is difficult to industrialize.

British Patent 1,436,115 discloses a method for crystallizing and purifying wet phosphoric acid. However, there is a drawback of purifying wet phosphoric acid by solvent extraction, and it is practically impossible to prepare purified phosphoric acid by direct crystallization from wet phosphoric acid, and the same is described in US Patent No. 3,912,803.

Japanese Patent No. 193,614 discloses a method for purifying wet phosphoric acid using film crystallization. Phosphoric acid crystals were grown on a cold surface to produce high purity phosphoric acid for semiconductors through a sweating operation and ultrapure water cleaning, but the disadvantage is that the impurities removed are limited to Fe, Mn and Na.

As a result, a review of the literature on phosphate purification has been focused on the purification of wet phosphoric acid instead of dry phosphoric acid, which can be produced relatively purely. After conversion to a substance, it adopts the method of precipitation and removal by additional chemical reaction. In addition, the type of impurities to be removed shows a considerable variety of phenomena depending on the constituents of phosphorescent ore, there is a disadvantage that is limited to a few elements. In addition, impurities generated in the manufacturing process, which are disadvantages of the fundamental wet phosphoric acid refining process, are solubilized, so that perfect impurities cannot be removed.

As such, the phosphate purification technology developed so far has had to go through additional chemical treatment and pretreatment step, and impurity is limited to a few metals, and the crystallization method requires a multi-stage operation to remove impurities to ppb level. There is.

Thus, the present inventors concentrated on a certain concentration in the evaporation tank (1) in order to efficiently crystallize the phosphate raw material containing impurities in order to solve the above problems, and in the cooling crystallization in the crystallization tank (4) The process of preparing a phosphate crystal of a certain size, and by separating the prepared phosphate crystals by melting the crystals by partial melting in the partial melting apparatus (8) by controlling the temperature and heat transfer rate of the separated phosphate crystals The present invention has been completed by purifying phosphoric acid by removing impurities attached to the crystals and simultaneously removing impurities contained in the crystals.

Accordingly, an object of the present invention is to provide a method and apparatus for purifying phosphoric acid that can be applied to semiconductor grades by efficiently removing impurities contained in the process of growing phosphate crystals by partial melting to obtain high purity phosphoric acid. .

Figure 1 shows a phosphoric acid purification apparatus according to the present invention consisting of an evaporation tank, a crystallization tank and a partial melting apparatus.

[Description of Major Symbols in Drawing]

1: evaporation tank 2: heat medium

3: heat exchanger 4: crystallization tank

5: cooling water 6: thermostat

7: internal stirrer 8: partial melting device

9: melt controller 10: heat medium

The present invention

1) a process of concentrating the concentration of phosphoric acid (P ₂ O ₅ ) to 60 to 80% by supplying a phosphate raw material to the evaporator maintained at 40 ~ 200 ℃,

2) preparing a phosphoric acid crystal by supplying the concentrated phosphoric acid solution of step 1 to a crystallization tank maintained at -70 to 20 ℃, and

3) The phosphate refining method includes supplying the phosphate crystals in the two steps to a partial melting apparatus maintained at 20 to 80 ° C. to partially melt and reflux the crystal grains.

The present invention

An evaporation tank 1 for producing a high concentration of phosphoric acid solution by maintaining a temperature of 40 to 200 ° C. using a heat medium 2 and a heat exchanger 3,

A crystallization tank 4 which maintains -70 to 20 ° C by using a cooling water 5 and a temperature controller 6 for temperature control, and manufactures phosphate crystals by using an internal stirrer 7,

Partial melting apparatus (8) obtained by melting the phosphate crystals partially by refluxing and partly refluxing and partially by high-purity phosphoric acid by using a melt control device (9) and a heat medium (10) for melting the phosphate crystals. It is another feature of a high-purity phosphoric acid production apparatus made, including.

Referring to the present invention in more detail as follows.

The present invention provides a method for concentrating industrial phosphoric acid prepared by a dry or wet method to a certain concentration, growing phosphate crystals by cooling, partially melting the grown phosphate crystals, and purifying the highly purified phosphoric acid for semiconductors by removing impurities in the crystals; and To the device.

Such a manufacturing method of the present invention will be described in detail with reference to FIG. 1 as follows.

1 is a device arrangement diagram applied to the phosphoric acid purification method according to the present invention, an evaporation tank (1) for concentrating phosphate raw materials, a crystallization tank (4) for producing phosphate crystals and a partial melting apparatus (8) for purifying phosphate crystals. It consists of.

The evaporation tank 1 is composed of a heat medium 2 circulating to an outer jacket and a heat exchanger 3 for condensing evaporated water vapor. In particular, the evaporation tank is a process for concentrating the phosphoric acid concentration to a certain concentration in order to more efficiently crystallize the phosphoric acid raw material containing impurities in the present invention. Thus, in order to concentrate the phosphoric acid concentration, the temperature in the evaporation tank is adjusted to 40-200 ° C. with the heat medium 2 circulated to the outer jacket, and the phosphoric acid (P ₂ O ₅ ) concentration of the phosphoric acid raw material passed through the evaporation tank is 60-80. %: has the (83-110% based on H ₃ PO ₄₎ range. If the concentration of phosphoric acid (P ₂ O ₅ ) concentrated through the evaporator is less than 60%, there is a problem that requires additional energy consumption due to concentration, if it exceeds 80% is high viscosity, it is difficult to produce crystals. In addition, when the temperature of the evaporation tank is less than 40 ° C, it takes a long time to concentrate to the desired concentration, and when it exceeds 200 ° C, there is an operational problem. As the phosphate raw material, lower phosphoric acid prepared by phosphate ores by a dry or wet process may be used. The phosphoric acid raw material supplied to the evaporation tank is Al 100ppb, As 20ppb, Au 20ppb, Ag 10ppb, Ba 100ppb, B 100ppb, Ca 100ppb, Cd 100ppb, Co 10ppb, Cu 10ppb, Cr 2ppb, Fe 100ppb, Ga 100ppb, K as impurities. 100ppb, Li 5ppb, Mg 1ppb, Mn 1ppb, Na 100ppb, Ni 20ppb, Pb 20ppb, Si 100ppb, Sn 1000ppb, Sr 10ppb, Zn 40ppb or more are included.

The concentrated phosphate solution through the evaporator is transferred to the crystallization tank (4) to cool by a temperature program method to form a phosphate crystal. Crystallization tank (4) is composed of a coolant (5), a temperature controller (6) and an internal stirrer (7) circulating the outer jacket, this crystallization tank uses the cooling water to -70 temperature of the inner tube wall of the crystallization tank The phosphoric acid solution concentrated in an evaporation tank is maintained at ˜20 ° C. to form phosphate crystals in a crystallization tank. At this time, the cooling rate of the crystallization tank using the cooling water is preferably in the range of 0.1 ~ 10 ℃ / min, if the cooling rate is out of the above range it is not possible to obtain a phosphate crystal of the desired size. The temperature controller generates a phosphate crystal by constantly adjusting the supersaturation of the concentrated phosphate solution programmatically. In the crystallization tank, the internal stirrer 7 is rotated at a speed of 10 to 1000 rpm to continuously produce phosphate crystals having a size of 300 to 1000 µm. If the speed of the internal stirrer is less than 10 rpm, the size of the phosphate crystal is too large to settle, and if it exceeds 1000 rpm, the size of the phosphate crystal is too small and the surface area of the crystal increases, so that the adsorption of impurities occurs and the purity decreases. There is a problem. In addition, when the size of the phosphate crystal is out of the above range, stirring is difficult, and there is a problem in that inclusion of impurities is increased. Phosphoric acid crystals produced through the crystallization tank have an impurity total content in the range of 100 to 30,000 ppb.

The phosphate crystals produced in the crystallization tank were separated into phosphate crystals and residual mother liquor through a crystal separation device, and the separated phosphate crystals were heated to a temperature near the melting point of phosphoric acid to melt crystal grains, thereby causing impurities contained in the phosphate crystals. It is transferred to a partial melting apparatus (8) to purify it. As mentioned above, the partial melting apparatus 8 which refine | purifies the phosphate crystal | crystallization produced | generated in the crystallization tank is comprised by the melting regulator 9 and the heat medium 10 for melt | dissolution of a phosphate crystal. The separated phosphate crystals are partially purified by controlling the temperature of the melt control device 8 to be separated from the melt containing impurities and purified. At this time, the temperature of the partial melting apparatus is set to 20 to 80 占 폚 by the heat medium to adjust the degree of melting of the phosphate crystal. If the temperature of the partial melting apparatus is less than 20 ℃ there is a problem that the partial melting does not occur, if it exceeds 80 ℃ there is a problem of low yield due to excessive melting. In addition, the partial melting of the phosphate crystal may be a molten amount of the crystal per minute up to 0.1 to 50%, there is a low yield problem when the partial melting rate is out of the above range. The partial melting apparatus may move impurities attached to the surface of the crystal and impurities contained in the crystal by partial melting of the phosphate crystal using a thermal gradient inside and outside the crystal. Accordingly, the degree of purification of the partially phosphate crystals subjected to partial melting according to the present invention can be obtained by removing 90% or more of impurities with a partition coefficient of <0.1 to obtain high purity phosphoric acid.

In this case, the distribution coefficient is defined as in Equation 1 below.

In Equation 1, when the distribution coefficient is 1, the separation of impurities is not performed at all, and when the distribution coefficient is 0, it means complete separation of impurities.

The high purity phosphoric acid prepared through the evaporation tank, crystallization tank, and partial melting apparatus according to the present invention as described above is Al 30ppb, As 30ppb, Au 3ppb, Ag 19ppb, Ba 10ppb, B1ppb, Ca 10ppb, Cd 3ppb, Co 5ppb, It contains impurities of Cu 1ppb, Cr 10ppb, Fe 25ppb, Ga 1ppb, K 1ppb, Li 10ppb, Mg 10ppb, Mn 1ppb, Na 50ppb, Ni 15ppb, Pb 1ppb, Si 20ppb, Sn 15ppb, Sr 1ppb, Zn 10ppb Applicable to semiconductor grades.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by Examples.

Preparation Example 1

Dry phosphoric acid was placed in a double jacketed, ventilated, stirred 1L evaporator (1), and then heated to 150 ° C. When the density of the phosphate solution reached about 1.74 g / cm ³ (P ₂ O ₅ concentration 64.8%), the solution was transferred to the crystallization tank 4 and cooled to -10 ° C at a rate of 10 ° C / min. Phosphoric acid crystals were prepared. In the cooling process of the crystallization tank 4, phosphate crystals were grown to a cube shape of about 400 μm, and 87 g of phosphate crystals (H ₃ PO ₄ · 1 / 2H ₂ O) was obtained. Impurities in the obtained phosphate crystals were measured using ICP-MS [inductively coupled plasma mass spectrometer], and the impurity contents in the phosphate crystals are shown in Table 1 below. The partition coefficient calculated according to Equation 1 was 0.12.

Preparation Example 2

Dry phosphoric acid was placed in a double jacketed, ventilated, stirred 1 L evaporator (1), and then heated to 150 ° C. When the density of the phosphoric acid solution reached about 1.8 g / cm ³ (69% P ₂ O ₅ concentration), the solution was transferred to the crystallization tank (4) and cooled to -12 ℃ at a rate of 10 ℃ / min Phosphoric acid crystals were prepared. In the cooling process of the crystallization tank 4, phosphate crystals were grown to a cube shape of about 400 µm, and 164 g of phosphate crystals (H ₃ PO ₄ · 1 / 2H ₂ O) were obtained. Impurities in the obtained phosphate crystals were measured as in Preparation Example 1, and the impurity content in the phosphate crystals is shown in Table 1 below. The partition coefficient calculated according to Equation 1 was 0.15.

Example 1

87 g of the phosphate crystal obtained in Preparation Example 1 was transferred to the partial melting apparatus 8 to partially melt the phosphate crystal at 40 ° C. for 30 minutes to melt 20% of the crystal, thereby purifying the phosphate crystal to obtain liquid high purity phosphoric acid. . The obtained high purity purified phosphoric acid was 42 g, the H ₃ PO ₄ content in phosphoric acid was 82.8%, the content of impurities in phosphoric acid is shown in Table 1 below. In addition, the partition coefficient calculated according to Equation 1 was 0.019 to confirm that impurities contained in the phosphate crystal of Preparation Example 1 were removed.

Example 2

164 g of the phosphate crystal obtained in Preparation Example 2 was transferred to the partial melting apparatus (8) to partially melt the phosphate crystal at 60 ° C. for 30 minutes to melt 40% of the crystal, thereby purifying the phosphate crystal to obtain liquid high purity phosphoric acid. . The obtained high purity purified phosphoric acid amount was 32 g, the H ₃ PO ₄ content in phosphoric acid was 85.3%, the content of impurities in phosphoric acid is shown in Table 1 below. In addition, the partition coefficient calculated according to Equation 1 was 0.022 to confirm that impurities contained in the phosphate crystal of Preparation Example 2 were removed.

Preparation Example 3

The wet phosphoric acid was put into 400 g of a double jacketed, ventilated, stirred 1 L evaporator (1), and then heated to 150 ° C. When the density of the phosphate solution reached about 1.74 g / cm ³ (P ₂ O ₅ concentration 64.8%), the solution was transferred to the crystallization tank 4 and cooled to -23 ° C at a rate of 10 ° C / min. Phosphoric acid crystals were prepared. In the cooling process of the crystallization tank (4), phosphate crystals were grown to a cube shape of about 400 μm, and 73 g of phosphate crystals (H ₃ PO ₄ · 1 / 2H ₂ O) were obtained. Impurities in the obtained phosphate crystals were measured as in Preparation Example 1, and the impurity contents in the phosphate crystals are shown in Table 2 below. The partition coefficient calculated according to Equation 1 was 0.14.

Example 3

73 g of the phosphate crystal obtained in Preparation Example 3 was transferred to the partial melting apparatus (8) to partially melt the phosphate crystal at 30 ° C. for 30 minutes to melt 20% of the crystal, thereby purifying the phosphate crystal to obtain liquid high purity phosphoric acid. . The obtained high purity purified phosphoric acid amount was 58 g, the H ₃ PO ₄ content in phosphoric acid was 85.3%, the content of impurities in phosphoric acid is shown in Table 2 below. In addition, the partition coefficient calculated according to Equation 1 was 0.017 to confirm that impurities contained in the phosphate crystal of Preparation Example 3 were removed.

Preparation Example 4

400 g of purified phosphoric acid was placed in a double jacketed, ventilated, stirred 1 L evaporator (1), and then heated to 150 ° C. When the density of the phosphate solution reached about 1.74 g / cm ³ (P ₂ O ₅ concentration 64.8%), the solution was transferred to the crystallization tank 4 and cooled to -30 ° C at a rate of 10 ° C / min. Phosphoric acid crystals were prepared. In the cooling process of the crystallization tank 4, phosphate crystals were grown to a cube shape of about 400 μm, and 92 g of phosphate crystals (H ₃ PO ₄ 1/2 H ₂ O) were obtained. Impurities in the obtained phosphate crystals were measured as in Preparation Example 1, and the impurity content in the phosphate crystals is shown in Table 3 below. The partition coefficient calculated according to Equation 1 was 0.10.

Example 4

92 g of the phosphate crystal obtained in Preparation Example 4 was transferred to the partial melting apparatus (8) to partially melt the phosphate crystal at 20 ° C. for 30 minutes to melt 20% of the crystal, thereby purifying the phosphate crystal to obtain liquid high purity phosphoric acid. . The obtained high purity purified phosphoric acid was 73 g, the H ₃ PO ₄ content in phosphoric acid was 85%, the content of impurities in phosphoric acid is shown in Table 3 below. In addition, the partition coefficient calculated according to Equation 1 was 0.013 to confirm that impurities contained in the phosphate crystal of Preparation Example 4 were removed.

As described above, the production method of phosphoric acid according to the present invention can efficiently remove impurities of heavy metals contained in the phosphate raw material by drastically reducing the content of impurities by partial melting of the phosphate crystal containing impurities, The purified phosphoric acid is very high, the purification time is short, and the purification method and apparatus are relatively simple and economical. Therefore, phosphoric acid according to the present invention can be usefully used for semiconductors such as etching solution for removing silicon nitride film (Si ₃ N ₄ ), various phosphate preparations, metal surface treatment, and the like.

Claims (8)

1) a process of concentrating the concentration of phosphoric acid (P ₂ O ₅ ) to 60 to 80% by supplying a phosphate raw material to the evaporator maintained at 40 ~ 200 ℃, 2) preparing a phosphoric acid crystal by supplying the concentrated phosphoric acid solution of step 1 to a crystallization tank maintained at -70 to 20 ℃, and 3) The process of supplying the two-step phosphate crystals to the partial melting apparatus maintained at 20 ~ 80 ℃ to partially melt and reflux the crystal grains to purify Phosphoric acid purification method characterized in that it is included. According to claim 1, wherein the phosphate raw material of the first step is a phosphate refining method, characterized in that using a lower phosphoric acid prepared by the dry or wet process. The method of claim 1, wherein the phosphate crystal of the second step is a phosphate purification method, characterized in that the total content of impurities in the range of 100 to 30,000 ppb. The method of claim 1, wherein the crystallization tank agitation speed of the two stages is characterized in that the range of 10 to 1000 rpm. The method of claim 1, wherein the crystallization tank cooling rate of the two steps is 0.1 to 10 ℃ / min. According to claim 1, The impurity contained in the phosphate raw material is Al 100ppb, As 20ppb, Au 20ppb, Ag 10ppb, Ba 100ppb, B 100ppb, Ca 100ppb, Cd 100ppb, Co 10ppb, Cu 10ppb, Cr 2ppb, Fe 100ppb, Ga 100ppb, K 100ppb, Li 5ppb, Mg 1ppb, Mn 1ppb, Na 100ppb, Ni 20ppb, Pb 20ppb, Si 100ppb, Sn 1000ppb, Sr 10ppb, Zn 40ppb characterized in that it contains at least 40ppb. The method of claim 1, wherein the high-purity phosphoric acid obtained by the method is Al 30ppb, As 30ppb, Au 3ppb, Ag 19ppb, Ba 10ppb, B 1ppb, Ca 10ppb, Cd 3ppb, Co 5ppb, Cu 1ppb, Cr 10ppb, Fe 25ppb Ga 1ppb, K 1ppb, Li 10ppb, Mg 10ppb, Mn 1ppb, Na 50ppb, Ni 15ppb, Pb 1ppb, Si 20ppb, Sn 15ppb, Sr 1ppb, Zn 10ppb or less. An evaporation tank 1 for producing a high concentration of phosphoric acid solution by maintaining a temperature of 40 to 200 ° C. using a heat medium 2 and a heat exchanger 3, A crystallization tank 4 which maintains -70 to 20 ° C by using a cooling water 5 and a temperature controller 6 for temperature control, and manufactures phosphate crystals by using an internal stirrer 7, Partial melting apparatus (8) obtained by melting the phosphate crystals partially by refluxing and partly refluxing and partially by high-purity phosphoric acid by using a melt control device (9) and a heat medium (10) for melting the phosphate crystals. To High purity phosphoric acid production apparatus, characterized in that made.