JP3301126B2 - Production method of high-purity ammonium silicofluoride and high-purity silica - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of adding a Ca component to an ammonium silicofluoride solution containing metal impurities to make the metal component hardly soluble, and recovering the ammonium silicofluoride solution from the slurry by solid-liquid separation. And a method for producing high-purity ammonium silicofluoride.

[0002] The present invention also relates to a process for producing high-purity silica, which comprises reacting the purified ammonium silicofluoride solution obtained by the above method with ammonia in an aqueous medium. High-purity ammonium silicofluoride is a synthetic intermediate of high-purity silica.
It is useful as various functional materials such as paint components, fillers and abrasives.

[0003]

2. Description of the Related Art Conventionally, as a method for producing silica, sodium silicate has been used.
A method of neutralizing with an acid or an ion exchange resin Da (wet method) is generally, this method although a low-cost, Na, Al, metallic impurities and SO ₄ ^2-like such as Fe Since the anion component is mixed, it cannot be used in the field where high purity is required.

On the other hand, there is a method of burning silicon tetrachloride at a high temperature in the presence of oxygen and hydrogen as a dry method. However, a special production apparatus is required, and its use is limited due to high cost. The physical properties of the obtained silica are also different from those of wet-process silica. In addition, regarding the method for producing silica using hydrofluoric acid (hereinafter sometimes abbreviated as silicic acid), silicic acid commercially available as a reagent / industrial chemical is expensive and the content of metal impurities is also compared. High. Silicic acid produced as a by-product in a phosphoric acid plant has an extremely high content of metal impurities and is not suitable as a raw material for producing high-purity silica.

Further, as a method for producing silica using a silicon fluoride as a raw material, US Pat. No. 4,981,664 discloses a purification method by crystallization of ammonium silicofluoride. In order to obtain ammonium, it is necessary to use complicated manufacturing processes such as heating and dissolving, solid-liquid separation, crystallization, re-dissolving, and recrystallization, and various manufacturing equipment such as crystallization purification equipment. It is difficult and disadvantageous in manufacturing cost.

Further, Japanese Patent Publication No. 47-2417 discloses a method for purifying a fluorine-containing solution by removing a phosphoric acid component in an ammonium fluoride solution, an alkali metal fluoride or a mixed solution of both by adding a Ca compound. Although a method is disclosed, the object of the invention is different from that of the present invention, and this method cannot obtain high-purity silica or high-purity ammonium silicofluoride as a raw material thereof.

[0007]

In the prior art, hydrosilicofluoric acid or ammonium silicofluoride is used as a raw material, and when it is reacted with ammonia in an aqueous medium to obtain silica, the raw material hydrosilicofluoric acid is used. Alternatively, most of the metal impurities contained in the ammonium silicofluoride migrate into the product silica as it is, so that it is difficult to obtain high quality silica.

In the method of the present invention, high-purity silica can be produced even from commercially available reagents / industrial chemicals having a high metal impurity content, hydrofluoric acid produced by a phosphoric acid or fertilizer plant, or crude ammonium silicofluoride. It becomes possible. An object of the present invention is to provide a method for producing high-purity silica and high-purity ammonium silicofluoride that is a raw material for synthesizing the same. It is a method that is efficient and advantageous in terms of production cost because a high-purity product can be obtained with a simple process and equipment in good yield without requiring special production equipment.

[0009]

According to the present invention, a Ca component is added to an ammonium silicofluoride solution containing metal impurities to make the metal component hardly soluble, and the ammonium silicofluoride solution is separated from the slurry by solid-liquid separation. A method for producing high-purity ammonium silicofluoride, characterized in that the high-purity ammonium silicofluoride solution obtained by the method is reacted with ammonia in an aqueous medium. A method for producing the same.

[0010] The present invention uses ammonium silicofluoride containing metal impurities as a raw material. In the present invention, a commonly available hydrosilicofluoric acid may be added to ammonia and an ammonium salt to prepare an ammonium silicofluoride solution, and then subjected to the Ca component addition purification. In the present invention, adding the Ca component to make the metal component hardly soluble means, in addition to making the metal component a hardly soluble compound, co-precipitating with another hardly soluble compound or adsorbing to a solid phase such as formed sludge. Including the case.

As the ammonium fluoride used in the present invention, commercially available reagents and industrial chemicals can be used. Further, an ammonium silicofluoride solution obtained by the method described in Japanese Patent Application Laid-Open No. 3-218914 of the present applicant may be used as a raw material. The hydrosilicofluoric acid used in the present invention is obtained by adding an ammonium salt such as ammonia or ammonium fluoride to generally available commercially available reagents, industrial chemicals or phosphoric acid plant by-product hydrosilicofluoric acid, or the like. A solution having an ammonium fluoride composition is prepared, and a Ca component is added to the solution.

The commercially available reagent hydrofluoric acid is usually H ₂ Si
F ₆ are provided in a concentration of about 40% as the component 4
F as a metallic impurity in 0% concentration of hydrosilicofluoric acid
e, Al, Ca, Mg, etc., each containing about 5 to 30 ppm (about 10 to 100 ppm in total of metal components). This amount is about 30 to 180 ppm of each metal component in terms of a concentration in terms of SiO ₂ (total of 60
６００600 ppm), and silica products obtained from these raw materials hydrofluoric acid cannot be used for applications requiring high purity.

Further, since phosphoric acid and hydrosilicic acid produced as a by-product in a fertilizer plant have a wide range of hydrofluoric acid concentration (about 5 to 30%), the concentration of metallic impurities in the form of hydrofluoric acid is limited. Although it cannot be expressed uniformly, as a metal impurity concentration in terms of silica, for example, Fe is 1000 ppm or more and contains a considerable amount of other metal components, and silica products obtained from this hydrosilicofluoric acid are extremely impure. It is.

In the present invention, the level of metal impurities in the raw material hydrosilicofluoric acid or ammonium silicofluoride solution is not particularly limited.
% Or less, and usually 3000 ppm or less. The removal rate of metal impurities in the present invention cannot be said unconditionally because it depends on the impurity species, the concentration level, and the amount of the Ca component added to the raw material. The resulting metal impurities in the high-purity ammonium silicofluoride and high-purity silica are usually 100 ppm or less in terms of silica, and 50 pp.
m or 10 pm or less.

The concentration of the ammonium silicofluoride solution used as a raw material is not particularly limited, but the Ca component is usually added at about 1 to 35%, preferably about 5 to 25%.
If the concentration is too low, the volumetric efficiency at the time of treatment is reduced, and if the concentration is too high, precipitation of ammonium silicofluoride or coexisting components is undesirable. The coexisting components in the ammonium silicofluoride solution include ammonium fluoride, ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium phosphate,
Examples thereof include (bi) ammonium carbonate, but are not particularly limited as long as they do not deviate from the object of the present invention of producing high-purity silica and high-purity ammonium silicofluoride as a raw material thereof.

Incidentally, if a large amount of a metal forming a hardly soluble fluoride or silicofluoride, such as a sodium or potassium component, is mixed, the recovery rate of fluorine or silicofluoride decreases or the solid-liquid separation step becomes complicated. It is not desirable. When the raw material ammonium silicofluoride solution contains insoluble impurities, after removing insoluble components by solid-liquid separation in advance,
The component a may be added for purification.

The Ca component to be added includes calcium hydroxide, calcium oxide, calcium sulfate, calcium nitrate, calcium chloride, calcium carbonate and the like. Calcium fluoride tends to have a small purification effect. Of course, the Ca component is not limited to the above examples. These Ca
The components may be added in the form of a solid (powder, granule, coarse particle, etc.) in the form of an anhydride or a hydrated salt, or may be added as a solution or slurry.

The addition amount of the Ca component cannot be unconditionally defined because it depends on the content of metal impurities in the ammonium silicofluoride solution and the type and content of the coexisting components. 0.0001 ~
It is about 1 and preferably about 0.001 to 0.1. C
When the addition amount of the component a is small, the effect of removing metal impurities becomes insufficient.
The loss for i and the amount of by-product sludge increase, which is disadvantageous.

The addition temperature of the Ca component may be room temperature or under heating conditions, but it is usually in the range of 0 to 100 ° C, preferably in the temperature range of room temperature to about 80 ° C. Not limited. An off-white sludge is generated by the addition of the Ca component. This sludge is mainly composed of calcium fluoride, but the sludge also contains metal impurities dissolved in the solution of silicofluoride or ammonium silicofluoride, which are separated by sedimentation, filtration, centrifugation, etc. , And the purified ammonium silicofluoride solution is recovered as a liquid part.

The recovery of the ammonium silicofluoride solution by the solid-liquid separation is performed by setting the hydrogen ion exponent (pH) in the range of 3 to 7.5 so that the metal impurities including the Ca component to be added are kept in the solid phase. As a result, reliable removal and purification can be performed.
Hydrogen ion exponent (p) of pure ammonium silicofluoride solution
H) is around 4, but the hydrogen ion exponent (pH) fluctuates due to the presence of coexisting components.

When an acid, a base or various salts are added for the purpose of adjusting the hydrogen ion index (pH), the type and amount of addition are selected without departing from the object of the present invention.
In the present invention, the additive components are not particularly limited, but the usually used additive components include hydrosilicofluoric acid and hydrofluoric acid, and inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and carbonic acid, and various organic acids. And a cation exchange resin. Ammonia is usually used as the base component, but other bases and anion exchange resins may be used. Further, various salts are often used usually, typically, ammonium fluoride, ammonium acid fluoride, ammonium (bi) carbonate, etc., but the kind of the salt is not particularly limited.

The temperature conditions for the solid-liquid separation may be low temperature or normal temperature treatment, or heating conditions, for example, 40 to 90 ° C.
It may be filtered by heating at about the temperature. In the case of filtration by heating, the concentration of the ammonium silicofluoride solution can be set high due to the solubility, and the filtrate is cooled to crystallize and purify the ammonium silicofluoride to obtain a higher purity ammonium silicofluoride or silica. Can be manufactured. It is also possible to concentrate ammonium silicofluoride before and after solid-liquid separation.

The mechanism of removal and purification of metal components is not clear, but Fe and Al components dissolved in a solution of silicic acid or ammonium silicofluoride (for example, exist in the form of a solubilized complex salt)
Metal impurities such as metal oxides can be converted into poorly soluble compounds (metal hydroxides, fluorides, silicofluorides, etc.) by adding a Ca component or by adding a Ca component and controlling the pH, or calcium fluoride as a main component. It is considered that it is adsorbed in the generated sludge. Since the Ca component to be added is hardly soluble in the form of calcium fluoride, it is removed by an appropriate solid-liquid separation method to obtain a purified ammonium silicofluoride solution as a liquid portion.

Various additives may be added at the time of adding the Ca component or at the time of solid-liquid separation without departing from the object of the present invention. For example, when a filter aid (coagulant) is added for the purpose of improving the filterability at the time of solid-liquid separation, or when colloidal silica is present in the ammonium silicofluoride solution, the filterability is poor and the filter medium is clogged. Is added with hydrofluoric acid or hydrofluoric acid
While adjusting H, the colloidal silica can be dissolved to improve the filterability. When the ammonium silicofluoride solution contains a coloring component or an odorous component, activated carbon can be added to remove these components. Hereinafter, examples of the present invention will be described.

[0025]

【Example】

Example 1 1K of crude hydrosilicofluoric acid (concentration 8.64% in terms of H ₂ SiF ₆ , solution A) containing metal impurities recovered in a phosphoric acid plant
103 g of 25% ammonia water was added to the g, to obtain a solution B having a pH of about 4 on a pH test paper. The pH of this solution was 3.55 as measured with a pH meter.

22 g of ammonium fluoride (special grade reagent, manufactured by Kanto Chemical Co.) was added to solution B at room temperature to obtain solution C having a test paper pH of about 6 (6.55 in the pH meter). Liquid A, B
6 g of gypsum dihydrate (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd.) was added to each of the solution and the solution C at room temperature with stirring, and the mixture was further stirred for 30 minutes. After standing overnight, each supernatant was filtered through a 0.2 μm filter to obtain A ^/ solution, B ^/ solution, and C ^/ solution (Example 1) as Ca-treated filtrates. The metal impurity content in the raw material solution and the Ca-treated filtrate was determined by ICP emission spectrometry. First result
It is shown in the table.

[0027]

[Table 1]

According to the above table, the pH to which the Ca component was added was 6.
Liquid 36 (C 3 ^/ liquid) was purified by removing 90% or more of metal impurities, and an ammonium silicofluoride solution having good purity was obtained. Example 2 1667 g of crude hydrosilicofluoric acid containing metal impurities used in Example 1 (concentration in terms of H ₂ SiF ₆ 8.64%, solution A)
Was added with 170 g of 25% aqueous ammonia to obtain a solution D having a pH of about 6 on a pH test paper. The pH of this solution was 6.1 as measured by a pH meter.

Solution D contains 25% aqueous ammonium fluoride solution 7
4 g was added and the value measured by the pH meter was 6.6. Since this preparation was cloudy and poor in filterability, 46% hydrofluoric acid 2
4 g was added to obtain a solution E having a hydrogen ion index of 6.0 with a pH meter. When 10.3 g of gypsum dihydrate (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd.) was added to this E solution at room temperature with stirring, white sludge was formed. After stirring at room temperature for another 30 minutes, the pH of the slurry
Was 5.9 when measured with a pH meter.

The supernatant liquid obtained by allowing the formed sludge to stand was filtered under reduced pressure (using a filter paper having an aperture of 5 μm) to obtain 1941 g of a purified aqueous ammonium fluoride solution (E ^/ liquid). 340 g of 25% aqueous ammonia was added to the E ^/ liquid at 40 ° C. for 30 minutes with stirring to obtain a silica slurry (pH = 9.1). The silica cake obtained by filtering the silica slurry under reduced pressure was washed with pure water and then redispersed in water to obtain a silica slurry (pH = 9) having a SiO ₂ concentration of 10%. After adding 10% sulfuric acid to the slurry to adjust the pH of the slurry to 4, the slurry was washed again with pure water to obtain 285 g of a hydrated silica cake. This was dried by heating at 110 ° C. to obtain 56 g of silica powder.

The metal impurity contents of the solutions A, E and E ^/ were determined by ICP analysis. For silica powder, the content of metal impurities was determined by ICP analysis of an acid solution of the residue obtained by hydrofluoric acid decomposition in a platinum dish. The results are shown in Table 2.

[0032]

[Table 2]

Example 3 The same procedure as in Example 2 was repeated except that the amount of added gypsum was changed to 30.9 g, and the purified ammonium fluoride solution (F ^/ solution,
Example 3-1) and a silica powder (Example 3-2) were obtained. The content of metal impurities in terms of SiO ₂ in the obtained solution and powder was 10 ppm or less for Fe and 2 ppm or less for all other metals. Example 4 360 g of commercially available 40% hydrosilicofluoric acid (manufactured by Morita Chemical) was diluted with 600 g of pure water to prepare a 15% hydrofluoric acid (solution G). To this, 150 g of 25% aqueous ammonia was added to obtain an H solution having a pH of about 2 on test paper. 37 g of ammonium fluoride (special grade reagent, manufactured by Kanto Kagaku) was added to the solution H at room temperature, and the pH of the test paper was about 6 (6.6 with a pH meter).
A liquid was obtained.

After the liquid I was divided into 10 parts, 46 g
2.2 g of hydrofluoric acid was added, and the pH of the mixture was adjusted to 5.2 with a pH meter.
J solution was obtained. Similarly, 13 g of 46% hydrofluoric acid was added to solution I.
Was added to obtain a K liquid having a pH of 3.7 with a pH meter. Above tone
Gypsum dihydrate at room temperature (reagent grade, Wako Pure Chemical) at room temperature
Add 0.42 g or 0.18 g of calcium hydroxide,
Stir for an additional 30 minutes. After settling, the supernatant was
The mixture was filtered through a filter to give a filtrate treated with gypsum dihydrate.^/
(Example 4-1), J^/(Example 4-2), K ^/(Implementation
Example 4-3) was converted to a filtrate treated with calcium hydroxide by adding I
^{/ /}(Example 4-4), J^{/ /}(Example 4-5), K
^{/ /}(Example 4-5) was obtained. Raw material liquid and Ca component addition
Determine the metal impurity content of the treated filtrate by ICP analysis
Was. The results are shown in Table 3.

[0035]

[Table 3]

Example 5 Ammonium silicofluoride solution (NH ₄ ) ₂ SiF ₆ 409 g NH ₄ F 127 g NH ₃ 7 g Fe 10.12 mg Al having a hydrogen ion index (pH) of 6.82 on a pH meter 1.66 mg Ca 0.22 mg Mg 3.31 mg Ni 19.96 mg Cr 7.78 mg Balance Solvent (water) 1942 g in total

1942 g was collected in a 2 L-poly container and 31 g of powdered gypsum powder was added at 70 ° C. with stirring over 75 minutes. After stirring for 30 minutes after the addition, the total amount of the slurry was reduced to 65%.
The solution was filtered under reduced pressure while hot using a filter paper having an aperture of 4 μm at ℃ to obtain 1928 g of ammonium silicofluoride solution and 28 g of wet filter cake. The wet cake is dried by heating and dried as a dry powder.
g was obtained. X-ray diffraction showed that the main component of the powder was calcium fluoride.

Of the resulting ammonium silicofluoride solution, 8
31 g of 25% aqueous ammonia was stirred at 340 g at 40 ° C.
Over 30 minutes. The obtained silica slurry was treated in the same manner as in Example 2 to obtain 165 g of a hydrated silica cake. This was dried by heating to obtain 58 g of silica powder. C
Metal impurities were quantified by ICP emission spectrometry in the same manner as in Example 2 for the ammonium silicofluoride solution (L (pH 6.82), L ^/ liquid, respectively) and the product silica powder before and after the addition of the component a. The results are shown in Table 4.

[0039]

[Table 4]

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01B 33/08-33/193 CA (STN) JICST file (JOIS)

Claims (6)

(57) [Claims] 1. A method comprising adding a Ca component to an ammonium silicofluoride solution containing metal impurities to make the metal component hardly soluble, and recovering the ammonium silicofluoride solution from the slurry by solid-liquid separation. A method for producing high-purity ammonium silicofluoride. 2. The method for producing high-purity ammonium silicofluoride according to claim 1, wherein the recovery of the ammonium silicofluoride solution by solid-liquid separation is performed with a hydrogen ion index (pH) in the range of 3 to 7.5. 3. The method for producing high-purity ammonium silicofluoride according to claim 1, wherein a Ca component is added to the ammonium silicofluoride solution in the presence of ammonium fluoride. 4. A purified ammonium silicofluoride solution obtained by adding a Ca component to an ammonium silicofluoride solution containing metal impurities to make the metal component hardly soluble and recovering the slurry by solid-liquid separation in an aqueous medium. And producing ammonia with high purity. 5. The method for producing high-purity silica according to claim 4, wherein the recovery of the ammonium silicofluoride solution by solid-liquid separation is performed at a hydrogen ion index (pH) in the range of 3 to 7.5. 6. The method for producing high-purity silica according to claim 4, wherein a Ca component is added to the ammonium silicofluoride solution in the presence of ammonium fluoride.