JP7074350B2 - Method for manufacturing high-purity silica - Google Patents

Description

The present invention relates to a method for adjusting high-purity silica (for example, an impurity concentration of 0.01 ppm or less), and more specifically, to purify a diatomaceous earth raw material suitable for use in the photovoltaic solar cell industry. Regarding. The gist of the present invention relates to a method for producing high-purity silica at low cost by extracting high-purity silica (for example, 8N) from a low-cost diatomaceous earth raw material.

A global concern for clean solar energy to replace fossil fuels is the conversion efficiency when converting solar thermal energy to low-cost electricity. The main cost of silicon solar cells lies in the high purity silicon (Si) used in PV (photoelectric conversion) cells. Significantly lowering the cost of manufacturing high-purity silicon will lower the price of solar cells and expand their applications, expanding the fields of application that will allow solar cells to compete with traditional traditional power sources. .. An important factor in the cost of high-purity silicon is the inherent cost of the manufacturing process of silica, the source of raw materials. The inherent cost of this manufacturing process is the inherent cost of a method of separating and purifying raw materials to produce high-purity silica for high-purity silicon used in solar cells.

The demand for high-purity silica as a raw material for the production of high-purity silicon will reach its supply limit in the near future. Therefore, there is a demand for an alternative method of supplying a material suitable for manufacturing a solar cell, a filtration process, and an insulator in an electronic component.

The search for efficient methods for producing raw materials for application to silicon photovoltaic batteries has progressed over the last three decades. Raw material sources for these methods are primarily limited to crystalline silica and volatile compounds of silicon. This is due to limited research on other sources of material such as rice husks and diatomaceous earth.

The demand for silica as a functional, optical, or electronic material is growing rapidly, making it increasingly difficult to use natural silica in its purest, shape, or properties. In particular, natural silica is difficult to use as a raw material provided for the production of solar cell grade silicon.

Patent Documents 1 to 7 have been proposed as a method for producing high-purity silica, and Patent Documents 8 to 14 have been proposed as a method for producing high-purity silicon.

Japanese Unexamined Patent Publication No. 63-291808 Japanese Unexamined Patent Publication No. 3-218914 Japanese Unexamined Patent Publication No. 5-36366 Japanese Unexamined Patent Publication No. 5-35086 Japanese Unexamined Patent Publication No. 5-35087 Special Fair 7-106890 Gazette Special Fair 7-57685 Gazette Japanese Unexamined Patent Publication No. 55-67519 Japanese Unexamined Patent Publication No. 56-323319 Special Publication No. 61-27323 Japanese Unexamined Patent Publication No. 10-265214 Japanese Unexamined Patent Publication No. 10-324514 Japanese Unexamined Patent Publication No. 10-324515 Japanese Patent No. 4436904

Further developments in photovoltaic power generation based on silicon solar cells require large amounts of high-grade quartz ore. This usually occurs in "gama" or "pockets" in fully naturally dried quartz veins and superficial deposits. Reserves of ore deposits in the crust are physically limited. In the photovoltaic power generation business, it is necessary to consider other reliable sources.

Conventionally, silica has been produced by purifying sandstone quartz. In this purification step, multiple subs, such as a stone grinding step, to minimize the size of the silica particles below the micrometer scale and improve the efficiency of the chemical treatment during the purification step. Has a process. Further, after that, a step of forming silica gel and forming a silicic acid solution by adding an acid to the final silica having a purity close to 99% (2N) is continued.

However, the purity level of this silica is too low for the production of high purity silicon targeting high conversion efficiency solar cells. To date, no method has been developed to obtain high-purity silica for solar cell applications. The most defective part of the conventional sandstone quartz purification method is the sandstone grinding process. This process consumes time and energy and is not preferred.

The present invention has been made in view of the above problems, and is a method for producing high-purity silica capable of producing high-purity silica suitable for producing high-purity silicon for solar cells with high efficiency and low cost. The purpose is to provide.

The method for producing high- purity silica according to the present invention is
A step of leaching the diatomaceous earth raw material with an acid and washing it with pure water to remove impurities including alkaline earth metal, alkali metal, transition metal or post-transition metal, and obtaining water-soluble silica from the residue after washing. ,
A step of reacting this water-soluble silica with an alkaline aqueous solution composed of a hydroxide of one or more alkali metals selected from the group consisting of lithium, sodium, potassium, rubidium and cesium to obtain a silicate aqueous solution thereof . When,
A boron removing step of passing the aqueous silicate solution through a first column containing an ion chelate specific agent to remove boron in the aqueous silicate solution.
A phosphorus removing step of removing phosphorus in the silicate aqueous solution by passing the silicate aqueous solution from which the boron has been removed through a second column containing an anion chelate specific agent.
A step of recovering silica by centrifuging and filtering the aqueous silicate solution from which phosphorus has been removed.
It is characterized by having.

Further, another method for producing high-purity silicon according to the present invention is
A step of leaching the diatomaceous earth raw material with an acid and washing it with pure water to remove impurities including alkaline earth metal, alkali metal, transition metal or post-transition metal, and obtaining water-soluble silica from the residue after washing. ,
A step of obtaining an aqueous solution of sodium silicate or an aqueous solution of potassium silicate by reacting the water-soluble silica with sodium hydroxide or potassium hydroxide.
A boron removing step of passing the sodium silicate aqueous solution or the potassium silicate aqueous solution through the first column containing an ion chelate specific agent to remove boron in the sodium silicate aqueous solution or the potassium silicate aqueous solution.
A phosphorus removing step of removing phosphorus in the sodium silicate aqueous solution or the potassium silicate aqueous solution by passing the sodium silicate aqueous solution or the potassium silicate aqueous solution from which the boron has been removed through a second column containing an anion chelate specifying agent. ,
A step of recovering silica by centrifuging and filtering the sodium silicate aqueous solution or the potassium silicate aqueous solution from which phosphorus has been removed.
It is characterized by having.

In the method for producing these high-purity silicas,
It is possible to supply a part of the aqueous solution that has passed through the first column to the first chelate regeneration tank to regenerate the chelate in the first chelate regeneration tank and supply the chelate to the first column. ..

again,
It is possible to supply a part of the aqueous solution that has passed through the second column to the second chelate regeneration tank to regenerate the chelate in the second chelate regeneration tank and supply the chelate to the second column. ..

According to the present invention, high-purity silica can be produced by wet treatment at a low treatment cost using diatomaceous earth, which is inexpensive and widely available all over the world, and is therefore expensive and expected to be exhausted. High-purity silica suitable for producing high-purity silicon can be stably produced at low cost.

FIG. 1 is a diagram showing a first step of the method of the embodiment of the present invention. In this first step, silica is extracted from diatomaceous earth to produce an aqueous sodium silicate solution. FIG. 2 is a diagram showing a second step of the method of the embodiment of the present invention. In this second step, boron is removed from the aqueous glass solution using the specific ion exchange chelate resin CRB03 / 05. FIG. 3 is a diagram showing a third step of the method of the embodiment of the present invention. In this third step, phosphorus is removed from the aqueous glass solution using the anion exchange chelate resin WA20 / 21J. FIG. 4 is a diagram showing a final fourth step of the method of the embodiment of the present invention. This fourth step recovers silica from the aqueous glass solution by filtering and drying using the present invention.

Hereinafter, embodiments of the present invention will be specifically described with reference to FIGS. 1 to 4. The present invention is a method for producing high-purity silica by purifying diatomaceous earth. This method comprises the steps of acid treatment, water glass formation, removal of boron and phosphorus and recovery of purified silica.

An object of the present invention is to produce high-purity silica of about 8 N or more, which is effective for producing high-purity silicon for solar cell applications. First, silica is extracted from diatomaceous earth into an aqueous solution through a preliminary purification step. The target boron concentration at this time is a low concentration of ppb level, preferably 5 ppb or less, more preferably 1 ppb or less, still more preferably 0.3 ppb or less. This pre-purified silica is preferably obtained in the form of silica dissolved in an aqueous solution as water-soluble silica by a treatment of eluting diatomaceous earth with an acid.

Diatomaceous earth is widely distributed all over the world and mainly exists as diatomaceous earth diatomaceous earth. It consists of a small amount of clay and diatomaceous earth crust (amorphous silica) associated with crushed rock with stalks removed from low cost open pit mining. Lightly colored, soft and fragile rocks are highly absorbent porous and have relatively good chemical stability, and are therefore primarily used for filters, absorbents, fillers and insulators. Will be done.

As described above, the diatom shell has a characteristic that it is easily dissolved in a corrosive alkaline solution. This suggests that high-purity silica can be produced from diatomaceous earth using a water-soluble chemical process. However, a method for producing high-purity silica using this diatomaceous earth as a raw material to obtain high-purity silica has not yet been developed. The present invention provides a low-cost method for producing high-purity silica using this diatomaceous earth as a raw material.

The water-soluble silica is preferably sodium silicate or potassium silicate, and the water-soluble silica is brought into contact with the boron remover in the following steps. This boron remover is an ion exchange resin having a functional group of N-methylglucamine. The aqueous solution containing the water-soluble silica is then treated with a phosphorus remover. The phosphorus remover is preferably an anion exchange resin having a polyamine functional group.

The present invention is a method for producing high-purity silica having an 8N purity level. First, an aqueous solution of silica is prepared from diatomaceous earth by acid leaching, and an aqueous solution of water-soluble silica from which metal impurity components have been removed is extracted by filtering the aqueous solution. do. Further, the filtered aqueous solution is brought into contact with the boron specific ion resin column and the anionic phosphorus specific anion resin column to precipitate silica gel, and the silicate is converted into silica gel in which impurities of boron and phosphorus are reduced to a low concentration level. ..

In other words, the present invention relates to a method for producing high-purity silica having a low B amount and a low P amount. In the method of the present invention, first, the diatomaceous soil is leached with an acid to obtain an aqueous solution of silicate from the diatomaceous soil, and the aqueous solution is filtered to remove metal-based impurities, and the filtered solution is prepared with boron and phosphorus. It has a plurality of steps including a step of contacting with the specific ion and anion resin column of the above and a step of evaporating water. Further, the obtained silica gel is converted into silica.

An object of the present invention is to provide a method for producing silica of 8N or more. The present invention is a method for obtaining highly purified silica using inexpensive diatomaceous earth resources as a raw material, and this high-purity silica enables the production of high-purity silicon that can be used for photoelectrostatic applications. do. This method preferably has the following steps.

(1) Preliminary purification step of silica (a) Select a diatomaceous earth material rich in silica.
(B) Step of extracting silica from diatomaceous earth by wet chemical treatment,
In this step, alkaline earth metals (Mg, Ca, Sr and Ba), alkali metals (Na, Li, K and Cs), transition metals (Fe, Ti, Co, Ni, Cu, V,) due to acid leaching, It removes impurities such as Mn and Cr) and post-transition metals (Al, Bi, In, Ga and Zn).
(2) High purification step of silica (a) After obtaining an aqueous solution of water glass (sodium silicate), the solution is filtered.
(B) The filtered water glass solution is brought into contact with specific ions of boron and phosphorus and an anionic resin column, and then the water is dried.
(3) Recovery of silica The obtained silica gel is converted into silica. This silica is preferably a final silica product in which boron (B) is less than 0.3 mass ppb, phosphorus (P) is less than 0.3 mass ppb, and metal impurities are 0.3 mass ppb or less.

Next, an embodiment of the present invention will be specifically described. First, in the first step of the present embodiment shown in FIG. 1, the diatomaceous earth raw material is leached with an acid and washed with pure water to carry out impurities containing an alkaline earth metal, an alkali metal, a transition metal or a post-transition metal. Is removed, and an aqueous sodium silicate solution is obtained from the residue after washing. In this embodiment, diatomaceous earth is used as a raw material. Diatomaceous earth has conventionally been mainly used as a filter material, an absorbent material, a filler and an insulating material, but this diatomaceous earth is present in a large amount all over the world and is used for producing high-purity silica through a water-soluble chemical process. Therefore, it is possible to produce high-purity silica at low cost. That is, pure silica is extracted at low cost, and it does not take time because of its structure. Mainly, it has a natural colloidal structure and fossil diatom shells of diatoms (diatoms) (hard and porous outer layer). Has a high specific surface area resulting from the cell wall).

The method of this embodiment is for producing high-purity grade silicon capable of directly producing a photovoltaic battery having high efficiency and high speed conversion efficiency by treating diatomaceous earth, which is a raw material resource. It is possible to produce high-purity silica as a high-purity raw material used in the above.

Impurities present in the raw material diatomaceous earth are known to prevent the dissolution of silica in an alkaline aqueous solution. For this reason, the leaching process is an important step for the efficient dissolution of silica in alkaline solutions. Silica-related impurities exist as independent minerals and are reorganized into three areas. It has (1) no chemical bonds with the structure of silica found in tightly bonded minerals, and (2) has surface bonds, chemical bonds and physical bonds with respect to the structure of silica, as breaks in the mineral. As can be seen, (3) minerals contained in silica particles or silica particles bonded to each other to form agglomerates in an annular shape, (4) Al ^{+ 3} which replaces Si ^{+ 4} in a SiO ₂ three-dimensional lattice, Like Fe ^{+ 3} , it is reorganized as a substituted interstitial ion in the silica particles themselves. When this occurs, the presence of other ions such as Li ^{+ 4} , K ^{+ 1} , Na ^{+ 1} , or H ^{+ 1} is required to maintain the electrical neutrality of the silica.

These impurities can be removed from the silica using a variety of methods. Conventional methods begin with mechanical treatments such as grinding, grinding, and cleaning and require chemical treatments such as wet chemical treatments. However, in the case of diatomaceous earth, due to its high porosity, no mechanical treatment is required for the size of silica particles in diatomaceous earth. The size of the silica particles averages 15 μm, which is small enough to obtain high reaction efficiency in chemical treatment.

According to the first step of the present invention shown in FIG. 1, a preliminary purification step of extracting silica from diatomaceous earth is shown. The natural structure of diatomaceous earth is preserved. First, a wet chemical treatment of diatomaceous earth for the extraction of silica will be described. Diatomaceous earth is stored in the tank 1, and an inorganic acid or an organic acid is stored in the tank 2. This acid is an inorganic mineral acid such as hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄ ) or nitric acid (HNO ₃ ), or an organic acid. A stirring propeller 4 is installed in the lower part of the acid leaching tank 2. The stirring propeller 4 is magnetically connected to a magnetic drive device (not shown) outside the tank, and is magnetically rotationally driven in the tank 2 by this magnetic drive device. By the rotation of the propeller 4, the diatomaceous earth in the tank 2 and the inorganic acid or the organic acid are stirred and mixed. Further, in this magnetic stirring, the object to be agitated in the tank 2 is heated by the heating device 5. Therefore, the diatomaceous earth and the inorganic acid or organic acid in the tank 2 are stirred and mixed in a state of being heated to a predetermined temperature by the heating device 5.

Then, the diatomaceous earth in the tank 1 is put into the acid leaching tank 2. In ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry) analysis, it is preferable to use this diatomaceous earth powder containing 90% by mass or more of silica and other metal impurities. Next, the raw material diatomaceous earth powder in the tank 2 is treated with a thermal acid by receiving the addition of an inorganic acid or an organic acid from the tank 3. Preferably, the acid for this treatment is a strong inorganic acid such as hydrochloric acid, sulfuric acid and nitric acid. In most cases, the acid can be used as a concentrated acid or an aqueous solution. Therefore, when a strong inorganic acid is used, HCl: 35 to 37% by mass when the acid is hydrochloric acid, H ₂ SO ₄ : 95 to 99% by mass when the acid is sulfuric acid, and HNO ₃ when the acid is nitric acid. : The processing efficiency is high when it is 65 to 75% by mass. Preferably, a concentrated inorganic acid solution diluted with at least 3 times the volume of water is used. Deionized water, i.e. pure water, is preferably used to dilute the acid in order to avoid impurity contamination from other solvents. The solubility of diatomaceous earth is less than 500 g / dm ³ , and it is miscible with acid.

During the acid treatment, acid-soluble impurities in diatomaceous earth dissolve in the acid solution. In this acid leaching step, the contents are heated to a temperature between the dissolution temperature of the acid-soluble impurities and the boiling point of the acid or diluted acid. Then, the contents are stirred by the propeller 4. In this way, under atmospheric pressure, the diatomaceous earth and the acid undergo an acid leaching treatment at a temperature between the dissolution temperature of the impurities and the boiling point of the acid or the diluting acid. Preferably, the acid leaching temperature is close to the boiling point of the acid reagent. In particular, it is preferable to carry out the acid treatment at the boiling point of the acid reagent mixture.

More preferably, ultrasonic waves are radiated to the contents while the raw materials are acid-leached while heating and stirring the contents in the tank 2 by the magnetic rotation propeller 4 and the heating device 5 shown in FIG. This ultrasonic radiation is in an appropriate frequency range of 40 to 50 rpm. Also, the continuous or pulsed ultrasonic power is 60-70 W, and the duration of the thermal acid treatment depends on the efficiency of impurity removal predicted by ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry) analysis. Is optimized.

The choice of inorganic acid used for the diatomaceous earth leaching process depends on the following three key factors: (1) Acid reaction effect on major metal oxides such as alumina and iron oxide present in the raw material diatomaceous soil, (2) Solubility of anions generated after leaching by the metal oxide in water, (3) The optimum amount of the inorganic acid or its diluted solution and the amount added to maintain the structural properties of the diatomaceous soil. It is important to carefully apply acid leaching steps to remove metal-derived impurities associated with alkaline earth metals, alkali metals, transition metals and post-transition metals from diatomaceous soil raw materials.

After that, the acid leaching solution in the tank 2 is transferred into the water glass generation tank 8. During this transfer, the acid leaching solution is filtered and the aqueous solution containing the metal impurities is discharged from the discharge channel 7. On the other hand, the silica after filtration is washed with pure water several times in this transfer path by supplying the pure water stored in the tank 6 to the silica transfer path. Then, the washed silica is sent to the water glass generation tank 8. That is, metal impurities are dissolved in the acid aqueous solution discharged from the tank 2, and silica exists as a solid in the aqueous solution and is supplied to the tank 8. Then, in the middle of the process, the aqueous solution is filtered, so that the filtered solid silica is supplied to the tank 8, and the aqueous solution in which the metal impurities are dissolved is discarded from the discharge passage 7. Although silica is water-soluble, it is charged into the tank 8 in a solid state. Then, sodium hydroxide is added to silica in the tank 8, and an aqueous solution of sodium silicate (water glass) is produced according to Chemical Formula 1.

The latter half of the first step shown in FIG. 1 is a key step for obtaining high-purity silica from water glass which is an aqueous solution. Silica extracted from diatomaceous earth is charged into the water glass generation tank 8. Then, a sodium hydroxide solution is added from the tank 9 to the silica in the tank 8 at a concentration of 2 to 5 mol, and the following reaction (chemical formula 1) occurs between the sodium hydroxide and the silica. Na ₂ SiO ₃ known as sodium silicate or water glass is obtained.

In this reaction, the contents in the tank 8 are agitated by the magnetic rotation propeller 10 while being heated to a predetermined temperature of 65 to 85 ° C. by the heating device 11. In addition, ultrasonic waves are applied to the contents in the tank 8 by an ultrasonic oscillator (not shown). This ultrasonic irradiation is extremely effective in achieving a complete reaction between silica and sodium hydroxide. Continuous stirring at a temperature close to the boiling point of water and slow addition of sodium hydroxide are extremely effective for the reaction to produce water glass (Na ₂ SiO ₃ ).

The pH of the water glass solution is considered to be about 11.2. Thus, most of the metals that are not removed in the acid leaching step due to their low solubility in high pH solutions, such as iron, magnesium, cobalt, zinc, and nickel, are removed in the filtration step. The water glass solution is a metal ion-removing chelate resin (type DIAION CR11 (ion exchange resin manufactured by Mitsubishi Chemical), etc.) developed by Mitsubishi Chemical, for example, in order to suppress ionic metals such as A ^{+ 3} and Fe ^{+ 3} . Purification columns containing the above can be used for additional purification treatments. The water glass generated in the water glass generation tank 8 is transferred toward the pH adjusting tank 13. In the process of this transfer, the water glass is detected by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) 12 at the final impurity levels of boron and phosphorus. This ICP-MS measures the purity of a high-purity substance. Boron and phosphorus are two major impurities that affect the electronic functionality of silicon materials, and it is necessary to know the levels of these impurities prior to the next purification step.

Sulfuric acid is stored in the tank 14, and the sulfuric acid in the tank 14 can be supplied to the pH adjusting tank 13. A stirring propeller 15 is installed in the tank 13, and the pH of the water glass is adjusted by supplying sulfuric acid from the tank 14 to the water glass supplied in the pH adjusting tank 13. In the tank 13, sulfuric acid is added to the water glass and the mixture is stirred by the magnetically coupled rotary propeller 15 to adjust the pH. Then, the pH-adjusted water glass is supplied to the next step after the pH is measured by the pH meter 16.

Boron in a water glass solution having a pH of 11 or higher exists in the form of borate. In this form, boron can be removed by using a boron selective chelate ion exchange resin. This resin is a specific removal chelate resin for borate and contains a functional group of N-methylglucamine such as CRB03 / 05 sold by Mitsubishi Chemical. The pH of the solution plays a crucial role in determining the efficiency of borate removal by the chelating resin. Therefore, it is necessary to optimize the pH of the water glass solution before submitting the solution to the ion exchange purification process. Therefore, in order to adjust the pH of the water glass solution, sulfuric acid is supplied from the tank 14 into the pH adjustment tank 13, and the pH of the solution is gradually controlled to an appropriate range for the most efficient execution of the chelate resin. do. Therefore, while detecting the pH of the contents in the tank 13 with the pH meter 16, the amount of sulfuric acid added is adjusted so that this pH becomes the optimum pH value. Finally, the water glass having the optimum pH value is supplied to the purification step of the next step. The water glass is sent from the pH adjusting tank 13 in FIG. 1 to the next step shown in FIG. 2 (label A).

Next, in the second step of the present embodiment shown in FIG. 2, the sodium silicate aqueous solution is passed through a first column (deboron column 18) containing an ion chelate specifying agent, and the sodium silicate aqueous solution is passed. Remove the boron inside. According to the second step of the present embodiment, the water glass solution from which the metal component has been removed is subjected to the ion exchange purification step shown in FIG. In this second step, the deboron column 18, the pH adjusting tank 25, and the chelate regeneration tank 31 are arranged. Further, the CRB03 / 05 ion exchange chelate specific agent is supplied to the deboron column 18 from the tank 19, and the contents in the deboron column 18 pass through the ion exchange chelate agent to remove the CRB03 / 05 ion exchange chelate. Boron processed. Water glass is supplied into the pH adjusting tank 25, and sulfuric acid is added from the tank 26 into the tank 25. In the tank 25, a stirring propeller 27 that is magnetically connected to an external drive device and is rotationally driven is arranged, and the contents in the tank 25 are stirred by the stirring propeller 27, and the pH thereof is a pH meter. It is designed to be detected by 28.

The water glass from the first step is pumped up to the deboron column 18 by the pump 17, and the water glass from the deboron column 18 is supplied to the pH adjustment tank 25 by the pump 21. A part of the water glass in the deboron column 18 is supplied to the chelate regeneration tank 31 by the pump 30, hydrochloric acid is added to the contents in the chelate regeneration tank 31 from the tank 32, and the chelate is regenerated by the hydrochloric acid. The regenerated chelating agent is filtered and then supplied to the tank 19 of the ion exchange chelate specifying agent for reuse, and impurities are removed from the waste channel 33.

An ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) 22 for detecting the concentration of boron and phosphorus in the water glass passing through this path is installed in the path from the pump 21 to the pH adjusting tank 25. A return path 24 is provided from the middle of the path from the ICP-MS22 to the tank 25 to the middle of the path from the pump 17 to the deboron column 18, and the pump 23 provided in the return path 24 provides. , A part of the water glass supplied to the pH adjusting tank 25 is returned to the route supplied to the deboron column 18.

In this second step, first, the water glass aqueous solution is pumped up to the deboron column 18 by the pump 17. From the tank 19, the CRB03 / 05 ion exchange chelate specific agent is charged into the column 18 until it reaches the label 20 indicating the optimum effect level of the chelate resin. This chelate resin has a high affinity for borate removal without affecting the silica structure and properties in any way. The boron concentration of the water glass aqueous solution sample after deboronation is measured by ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry) 22 and its purity is analyzed. This ICP-OES measures the purity of a medium purity substance. If the analysis result of ICP-OES22 shows below the desired purity level of boron, the deboronized water glass aqueous solution is pumped toward the pH adjustment tank 25 using the pump 21. If the ion exchange purification in the deboron column 18 does not reach the desired regulation level of boron, the aqueous glass solution is pumped back towards the deboron column 18 and again deboroned by the ion exchange chelating agent. It is processed. Then, this boron removal cycle by ion exchange is repeated until the boron concentration in the aqueous glass solution supplied to the pH adjustment tank 25 reaches a desired low value.

The borate present in the water glass solution after deboron purification with the CRB03 / 05 ion exchange chelate specific agent is regulated as boric acid. The purified water glass solution should have a low boron content of about 10 ppb or less, more preferably about 5 ppb or less, still more preferably about 1 ppb or less, still more preferably 0.3 ppb or less.

In order to achieve such a low boron amount, it is preferable to perform a plurality of filtration treatments with the CRB03 / 05 ion exchange chelate specific agent via the return route 24.

The ion exchange filtration step is performed within a specific column 18 designed to suppress boron leaching. At this time, the water glass supplied from the first step is supplied to the deboron column 18 by the pump 17, and the flow rate and the flow velocity of the water glass by the pump 17 are extremely important factors in the purification step. The column 18 is supplied by the manufacturer of the ion exchange resin and is easily available.

After achieving the desired amount of boron, the desired amount of phosphorus will be achieved by the anion exchange chelate resin in the third step described later. However, in order to remove phosphorus with high efficiency using an anion exchange resin, the pH of the purified water glass solution needs to be reduced. Therefore, sulfuric acid in the tank 26 is added into the pH adjusting tank 25 to lower the pH of the water glass in the tank 25. At this time, in order to obtain an optimized pH suitable for removing phosphorus with high efficiency by the anion exchange resin in the third step, the pH of the water glass solution was monitored by the pH meter 28 from the tank 26. Add sulfuric acid to the water glass. In this way, a boron-free water glass solution at a low pH optimum for dephosphorization in the third step is finally supplied to the purification step by anion exchange in the following order shown in FIG.

The CRB03 / 05 ion exchange chelate specific agent has a high affinity for the removal of borate and can remove borate without causing any change or modification in the structure of silica. On the other hand, the chelate specific agent is reusable. The aqueous solution discharged from the deboron column 18 is supplied to the chelate regeneration tank 31, and can be easily regenerated in the chelate regeneration tank 31 by undergoing an acid leaching / cleaning treatment. In this case, the ion-exchange chelate resin is sent out to the chelate regeneration tank 31 by the pump 30, and then the ion-exchange chelate resin is leached and washed in the tank 32. The regenerated chelate resin is then supplied to the tank 19 containing the ion exchange chelate specific agent, and is again supplied to the deboron column 18 as an ion exchange resin. The label B of FIG. 2 is connected to the label B of FIG. 3, and the water glass after deboronation is sent from the pH adjustment tank 25 of FIG. 2 to the next step shown in FIG. 3 (label B).

Next, in the third step of the present embodiment shown in FIG. 3, the aqueous solution from which the boron has been removed is passed through a second column (dephosphorus column 35) containing an anion chelate specificizing agent, and phosphorus in the aqueous solution is passed. To remove. According to the third step of the present embodiment, the water glass solution containing no metal and boron undergoes an anion exchange purification step as shown in FIG. In the anion exchange purification step shown in FIG. 3, a dephosphorization column 35, a pH adjustment tank 42, and a chelate regeneration tank 48 are arranged. Further, the WA20 / 21J anion exchange chelate specific agent is supplied to the dephosphorization column 35 from the tank 36, and the contained material in the dephosphorization column 35 passes through the anion exchange chelate agent to dephosphorize. It is treated with phosphorus. Water glass is supplied into the pH adjusting tank 42, and sulfuric acid is added from the tank 43 into the tank 42. A stirring propeller 44 that is rotationally driven by a magnetically connected drive device is arranged in the tank 42, and the contents in the tank 42 are stirred by the propeller 44, and the pH of the contents in the tank 42 is adjusted. Is detected by the pH meter 45.

The water glass from the second step is pumped up to the dephosphorization column 35 by the pump 34, and the water glass from the dephosphorization column 35 is supplied to the pH adjustment tank 42 by the pump 38. A part of the water glass in the dephosphorization column 35 is supplied to the chelate regeneration tank 48 by the pump 47, sodium hydroxide is added to the contents in the chelate regeneration tank 48 from the tank 49, and the chelate is regenerated by the sodium hydroxide. Will be done. The regenerated chelating agent is filtered and then supplied to the tank 36 of the ion exchange chelate specifying agent for reuse, and impurities are removed from the waste channel 50.

An ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry) 39 for detecting the concentration of phosphorus in the water glass passing through this path is installed in the path from the pump 38 to the pH adjusting tank 42. A return path 41 is provided from the middle of the path from the ICP-OES 39 to the tank 42 to the middle of the path from the pump 34 to the dephosphorization column 35, and the pump 40 provided in the return path 41 provides a return path 41. , A part of the water glass supplied to the pH adjustment tank 42 is returned to the supply path for the dephosphorization column 35.

In this third step, first, the water glass aqueous solution after deboronation is pumped up in the dephosphorus compound generation column (dephosphorus column) 35 by using the pump 34. The WA20 / 21J anion exchange chelate specific agent is added from the tank 36 to the dephosphorus column 35 until the label 37, which indicates the optimum level of effectiveness of the chelate resin, is reached. This anion exchange chelate resin has a high affinity for phosphorus removal without affecting the structure and properties of silica. The phosphorus concentration of the sample of the water glass water-soluble solution after dephosphorization is measured by ICP-OES39, and its purity is analyzed. If the analysis result of ICP-OES39 shows the desired purity level of phosphorus, the dephosphorized water glass aqueous solution is pumped toward the pH adjustment tank 42 using the pump 38. If the anion exchange purification in the dephosphorus column 35 does not reach the desired regulation level of phosphorus, the aqueous glass solution is pumped back towards the dephosphorus column 35 and again dephosphorused with an anion exchange chelating agent. It is processed. Then, this phosphorus removal cycle by anion exchange is repeated until the phosphorus concentration in the water glass aqueous solution supplied to the pH adjustment tank 42 reaches a desired low value.

The phosphorus present in the water glass solution after dephosphorus purification with the WA20 / 21J anion exchange chelate specific agent is regulated as phosphoric acid. The purified water glass solution should have a low boron content of about 10 ppb or less, more preferably about 5 ppb or less, still more preferably about 1 ppb or less, still more preferably 0.3 ppb or less. .. For phosphorus, the amount of phosphorus should be as low as about 10 ppb or less, more preferably about 5 ppb or less, still more preferably about 1 ppb or less, still more preferably 0.3 ppb or less. be.

In order to achieve such a low phosphorus content, it is preferable to carry out a plurality of filtration treatments with a WA20 / 21J anion exchange chelate specific agent via the return route 41.

The ion exchange filtration step is performed within a specific column 35 designed to suppress phosphorus leaching. At this time, the water glass supplied from the second step is supplied to the dephosphorization column 35 by the pump 34, and the flow rate and the flow velocity of the water glass by the pump 34 are extremely important factors in the purification step. The column 35 is supplied by the manufacturer of the ion exchange resin and is easily available.

The WA20 / 21J anion exchange chelate specific agent has a high affinity for phosphoric acid and can remove phosphoric acid without causing any change or modification to the structure of silica. On the other hand, the anion exchange chelate specific agent is reusable. The aqueous solution discharged from the dephosphorization column 35 is supplied to the chelate regeneration tank 48, and can be easily regenerated in the chelate regeneration tank 48 by undergoing an alkali leaching / cleaning treatment. In this case, the anion exchange chelate resin is sent out to the chelate regeneration tank 48 by the pump 47, and then the anion exchange chelate resin is leached and washed in the tank 48. The regenerated chelate resin is then supplied to the tank 36 containing the anion exchange chelate specific agent, and is again supplied to the dephosphorization column 35 as an anion exchange resin.

In the pH adjustment tank 42, 2 to 5 M sulfuric acid is added from the tank 43 to the water glass solution and titrated. In this case, sulfuric acid is used to precipitate pure silica particles as silica gel (H ₂ SiO ₃ ). Then, in order to avoid aggregation at room temperature, the following reaction 2 is allowed to proceed with continuous stirring.

Further treatment is possible to obtain a highly purified water glass solution. This treatment involves a second acid leaching using HCl to remove impurities generated during the treatment via NaOH or other acid material.

Silica gel [Si (OH) ₄ ] is obtained as the final product of acid titration and continuous stirring, and is sent to the fourth step shown in FIG. 4 via the label C.

Next, in the fourth step of the present embodiment shown in FIG. 4, silica is recovered by centrifuging and filtering the aqueous solution from which phosphorus has been removed. In the fourth step of the present embodiment, conventional devices such as a centrifuge 51, a deionized water washer 52, and a squeeze filter 53 are used to wash the metal, boron, and phosphorus-free silica. And dried. Then, as shown in FIG. 4, the silica is dried by holding it in a heating furnace 54 at 90 to 120 ° C. for 4 to 6 hours. The recovered and dried silica has a boron and phosphorus content detected by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) 55, and the detection result is a desired impurity level of 10 ppb (8N) or less. Is finally confirmed and then supplied to the silica reduction step (label D).

Next, a comparative example outside the scope of the present invention will be described with respect to the embodiment of the present invention. 10-30 g of diatomaceous earth raw material from Algeria or Japan is leached in a solution of 2 to 2.5 M inorganic acid HCl, H ₂ SO ₄ , or HNO ₃ . In this leaching step, the volume of the diatomaceous earth raw material is 200 to 500 ml, and the mixture is continuously stirred at 70 to 80 ° C. for 3 to 4 hours and at a frequency of 1000 to 1200 rpm. The acid solution is added slowly to allow complete dispersion and leaching of metal contaminants.

The solution is then filtered through a lamb opening filter (699/470) and the diatomaceous earth residue is washed 4-5 times with deionized water to remove the effects of acid leaching during the separation of metal impurities. 8-25 g of silica is extracted from the washed residue and placed in a plexiglass baker containing 2.2-2.7 M NaOH solvent in a volume of 100-300 ml and placed at 150-200 ° C. for 2-. Continuously stir at a frequency of 1000-1200 rpm for 3 hours. This makes it possible to completely dissolve silica and sodium hydroxide in deionized water to produce sodium silicate (water glass).

The pH of the produced water glass solution is about 11. The pH of the sample is adjusted to 10-10.5 with sulfuric acid. Metal-free solutions are analyzed for boron and phosphorus using an inductively coupled plasma mass spectrometer (ICP-MS). The initial amount of boron and phosphorus is 5 ppb or less. A metal-free, optimal pH water glass solution was passed through a 50-150 ml resin column containing the CRB03 / 05 chelate resin. This resin is extremely compatible with boron via its glucamine functional group and does not affect or absorb silica or sodium ions. The amount of boron was analyzed for a sample having a volume of 30 ml.

This amount of boron decreased from 100 ppm to 10 ppb or less. In addition, the pH of the sample was adjusted to 6-7 with sulfuric acid for subsequent anion exchange purification. An optimized pH water glass solution free of metal and boron was passed through a resin column containing 50-150 ml of WA20 / 21J chelate resin. This resin has a high affinity for phosphoric acid due to the polyamine functional group, does not affect silica or sodium ions, and does not absorb them. The amount of phosphorus was analyzed for a sample having a volume of 30 ml. The amount of phosphorus decreased from 1000 ppm to 10 ppb or less. The solution from the column is treated by adding sulfuric acid until the standard value of pH = 7. After normalization of the water glass solution, silica gel is purified, then filtered and dried at 1200 ° C. After the drying step, the silica powder is recovered and a final ICP-MS check is performed.

The silica powder thus obtained has a purity of 8N.

According to the present invention, high-purity silica can be produced from inexpensive diatomaceous earth by wet treatment. Therefore, by reducing this high-purity silica, high-purity silicon can be easily produced, and a solar cell can be produced. It is extremely useful for the field of application of high-purity silicon such as.

1,3,6,9,14,26,32,43,49: Tank 2: Acid leaching tank 4,10,15,27,44: Propeller 8: Water glass generation tank 12,32,39,55: ICP -MS
13, 25, 42: pH adjustment tank 16, 28, 45: pH meter 17, 21, 23, 30, 34, 38, 40, 47
18: Deboron column 19: CRB03 / 05 Ion exchange chelate specific agent 31, 48: Chelate regeneration tank 35: Dephosphorization column 51: Centrifuge 52: Washer 54: Heating furnace

Claims (4)

A step of leaching the diatomaceous earth raw material with an acid and washing it with pure water to remove impurities including alkaline earth metal, alkali metal, transition metal or post-transition metal, and obtaining water-soluble silica from the residue after washing. ,
A step of reacting this water-soluble silica with an alkaline aqueous solution composed of a hydroxide of one or more alkali metals selected from the group consisting of lithium, sodium, potassium, rubidium and cesium to obtain a silicate aqueous solution thereof . When,
A boron removing step of passing the aqueous silicate solution through a first column containing an ion chelate specific agent to remove boron in the aqueous silicate solution.
A phosphorus removing step of removing phosphorus in the silicate aqueous solution by passing the silicate aqueous solution from which the boron has been removed through a second column containing an anion chelate specific agent.
A step of recovering silica by centrifuging and filtering the aqueous silicate solution from which phosphorus has been removed.
A method for producing high-purity silica, which comprises. A step of leaching the diatomaceous earth raw material with an acid and washing it with pure water to remove impurities including alkaline earth metal, alkali metal, transition metal or post-transition metal, and obtaining water-soluble silica from the residue after washing. ,
A step of obtaining an aqueous solution of sodium silicate or an aqueous solution of potassium silicate by reacting the water-soluble silica with sodium hydroxide or potassium hydroxide.
A boron removing step of passing the sodium silicate aqueous solution or the potassium silicate aqueous solution through the first column containing an ion chelate specific agent to remove boron in the sodium silicate aqueous solution or the potassium silicate aqueous solution.
A phosphorus removing step of removing phosphorus in the sodium silicate aqueous solution or the potassium silicate aqueous solution by passing the sodium silicate aqueous solution or the potassium silicate aqueous solution from which the boron has been removed through a second column containing an anion chelate specifying agent. ,
A step of recovering silica by centrifuging and filtering the sodium silicate aqueous solution or the potassium silicate aqueous solution from which phosphorus has been removed.
A method for producing high-purity silica, which comprises. The claim is characterized in that a part of the aqueous solution that has passed through the first column is supplied to the first chelate regeneration tank, the chelate is regenerated in the first chelate regeneration tank, and the chelate is supplied to the first column. The method for producing high-purity silica according to 1 or 2 . The claim is characterized in that a part of the aqueous solution that has passed through the second column is supplied to the second chelate regeneration tank, the chelate is regenerated in the second chelate regeneration tank, and the chelate is supplied to the second column. The method for producing high-purity silica according to 1 or 2 .

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