JP2002226206A - Production method for hydrogen fluoride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which produces calcium fluoride from a solution containing silicofluoric acid and hydrogen fluoride and utilizes the calcium fluoride as a manufacturing material for hydrogen fluoride, in the process of manufacturing hydrogen fluoride from a calcium fluoride ore. SOLUTION: As regards the method using recovering calcium fluoride from the solution containing silicofluoric acid and hydrogen fluoride which are released as by-products, hydrogen fluoride and calcium carbonate are reacted in a first reactor 1 and silicofluoric acid and calcium carbonate are reacted in a second reactor 3 after calcium fluoride is separated and recovered in a first thickener 2, and the manufactured calcium fluoride is brought back to the first reactor 1 together with surplus calcium carbonate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing hydrogen fluoride, which comprises recovering calcium fluoride from a wastewater obtained in a step of producing hydrogen fluoride from calcium fluoride ore and utilizing the same. About.

[0002]

2. Description of the Related Art Conventionally, hydrogen fluoride has been industrially produced by reacting calcium fluoride ore and sulfuric acid as shown in the following formula 1. Through this step, hydrogen fluoride is extracted as a gas. At this time, a part of the silica component contained as an impurity in the raw material calcium fluoride ore reacts with the generated hydrogen fluoride to form silicon tetrafluoride gas according to the following formula 2, which is converted into hydrogen fluoride gas. Mixed.

Since the hydrogen fluoride gas taken out contains impurities such as sulfur dioxide, sulfuric acid and dust in addition to the silicon tetrafluoride gas, it is washed with sulfuric acid and then condensed, rectified and stripped. It is purified by performing an operation. At this time, most of the generated silicon tetrafluoride gas is separated from hydrogen fluoride in the rectification step and discharged from the rectification tower as a low-boiling substance.

The low-boiling gas discharged from the top of the rectification column usually contains hydrogen fluoride in an amount equal to or more than the equivalent of the reaction of the formula 2 in order to prevent the blockage due to the formation of silica scale in the gas absorption column. Is operated. Silicon tetrafluoride is absorbed into water together with hydrogen fluoride, and reacts as in the following formula 3 to form silicic acid.

[0005]

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[0006] Therefore, the composition of the stock solution of the aqueous solution in which silicon tetrafluoride is absorbed is usually 30 to 50%
(Mass percentage; the same in the present specification), and hydrogen fluoride is 5 to 20%. Usually, this stock solution is mixed with wastewater from another step, and finally, 1.5 to 2.5% of hydrofluoric acid is obtained.
%, 1.2 to 1.5% hydrogen fluoride. Japanese Patent Laid-Open No. 4-228401 proposes that a solution containing silicic acid and hydrogen fluoride can be used effectively as a raw material for producing hydrogen fluoride by regenerating a fluorine component into calcium fluoride.

The silica introduced as an impurity in the process of producing hydrogen fluoride reacts with the produced hydrogen fluoride to form silicon tetrafluoride, which reacts with the hydrogen fluoride to obtain a solution of hydrofluoric acid. Therefore, the yield of hydrogen fluoride is easily affected. Therefore, it is preferable that the amount of silica contained in calcium fluoride is as small as possible.

[0008]

An object of the present invention is to produce and recover calcium fluoride from a solution containing silicic acid and hydrogen fluoride discharged from a process for producing hydrogen fluoride,
An object of the present invention is to provide a method of utilizing hydrogen fluoride as a raw material.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a method for producing hydrogen fluoride by reacting calcium fluoride ore with sulfuric acid, comprising silicic acid and hydrogen fluoride discharged as by-products. The solution is treated in the following steps A, B, C and D, and the calcium fluoride recovered from step B is
This is a method for producing hydrogen fluoride which is used by being mixed with calcium fluoride ore to be reacted with sulfuric acid. A: The solid calcium fluoride and calcium carbonate (hereinafter simply referred to as calcium fluoride and calcium carbonate) obtained in step D are added to a solution containing silicic acid and hydrogen fluoride, and the calcium carbonate is substantially dissolved. A step of producing a dispersion containing calcium fluoride generated by reaction of the target amount and the calcium fluoride returned from step D; B: a step of separating and recovering calcium fluoride from the dispersion produced in step A C: adding calcium carbonate to the separated mother liquor of step B,
A step of producing a dispersion containing calcium fluoride and unreacted calcium carbonate produced by reaction of substantially all of the silicic acid and hydrogen fluoride in the separated mother liquor; D: from the dispersion produced in step C, Separating a liquid phase containing colloidal silica into calcium fluoride and calcium carbonate.

When calcium carbonate is reacted with a solution containing hydrogen fluoride and silicic acid, hydrogen fluoride reacts preferentially. Thus, after substantially all of the hydrogen fluoride has reacted, substantially all of the hydrofluoric acid has reacted.

In the present invention, in step A, hydrogen fluoride reacts with calcium carbonate, and in step C, silicic acid and calcium carbonate react. In the step C, calcium carbonate is supplied in a total amount of equivalents of hydrogen fluoride and silicic acid in the solution. For this reason, in step C, calcium carbonate remains in an amount equivalent to hydrogen fluoride, and this remains together with calcium fluoride generated by the reaction between the silicic acid and calcium carbonate in step A.
Supplied to

[0012] Silica, which is the main impurity produced in steps A to D of the present invention, is separated in step D. In step D, the amount of calcium fluoride generated is small, so the amount of silica adhering to calcium fluoride can be reduced, and silica can be efficiently removed. In the step A, since calcium fluoride is precipitated without the precipitation of silica, high-purity calcium fluoride can be recovered in the step B.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a solution discharged from a process for producing hydrogen fluoride by reacting calcium fluoride ore with sulfuric acid is used as a solution containing silicic acid and hydrogen fluoride. In the present invention, silicic acid reacts with calcium carbonate according to the following formula 4, and hydrogen fluoride reacts with calcium carbonate according to the following formula 5, respectively, to generate calcium fluoride.

[0014]

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In step A of the present invention, the calcium fluoride and calcium carbonate obtained in step D are added.
Calcium fluoride and calcium carbonate may be in the form of a cake or a fluid slurry. The calcium carbonate in this calcium fluoride and calcium carbonate is
It is an unreacted component of calcium carbonate added in step C described later.

The calcium carbonate is supplied to the step A together with the calcium fluoride generated in the step C.
In the step A, substantially all of the calcium carbonate in the calcium fluoride and the calcium carbonate becomes calcium fluoride, and substantially no calcium carbonate is supplied to the next step B. Calcium carbonate reacts selectively with hydrogen fluoride among hydrogen fluoride and silicic acid.

In step A, it is preferable to convert 90% or more of the hydrogen fluoride to calcium fluoride. 90% of the total hydrogen fluoride is converted to calcium fluoride
If it is less than the above, the amount of calcium fluoride generated in step C increases, and the amount of silica mixed into calcium fluoride increases, which is not preferable. Further, it is preferable that 10% or less of the silicic acid reacts with calcium carbonate. If the amount of the reaction with calcium carbonate is more than 10% of the total amount of the hydrofluoric acid, silica is generated, and the silica generated in the step A is not easily separated, so that the purity of calcium fluoride is reduced.

The calcium carbonate supplied to the step A is preferably 90 to 120% of the reaction equivalent of hydrogen fluoride. As a result, substantially the entire amount of calcium carbonate and hydrogen fluoride is precipitated as calcium fluoride, and the hydrofluoric acid does not react and remains in the liquid. For this reason, the dispersion obtained in the step A is subjected to solid-liquid separation in the next step B, and calcium fluoride having a small silica component is obtained. If the added calcium carbonate is less than 90% of the reaction equivalent of hydrogen fluoride, the removal rate of silicic acid and hydrogen fluoride in the solution decreases, and
If it exceeds 20%, unreacted calcium carbonate in calcium fluoride increases.

In the present invention, the silica contained in the calcium fluoride separated in the step B is preferably not more than 1.0% of calcium fluoride in terms of SiO ₂ . If the content of silica is more than 1.0%, the purity of the obtained hydrogen fluoride decreases when hydrogen fluoride is produced, which is not preferable.

The concentration of the solution containing silica hydrofluoric acid and hydrogen fluoride supplied to the step A is as follows.
Preferably, the concentration is 5 to 2.5% and the concentration of hydrogen fluoride is 1.2 to 1.5%.

When the concentration of silicic acid is less than 1.5%,
At the same time, the amount of liquid to be treated increases and the apparatus becomes unnecessarily large, and at the same time, the amount of fluorine that escapes out of the system together with the mother liquor increases, and the recovery rate of calcium fluoride decreases. If the concentration of silicic acid exceeds 2.5%, the concentration of SiO ₂ in the reaction solution increases, the gelation of SiO ₂ is promoted, and the amount of silica mixed in the recovered calcium fluoride increases.

If the concentration of hydrogen fluoride is less than 1.2%, the amount of liquid to be treated increases and the apparatus becomes unnecessarily large. At the same time, the amount of fluorine that escapes out of the system together with the mother liquor increases. When the recovery rate of calcium iodide decreases and the concentration exceeds 1.5%, the concentration of the resulting calcium fluoride dispersion increases, and handling becomes difficult.

In step B, calcium fluoride is separated and recovered from the dispersion produced in step A. The separated mother liquor contains dissolved silicic acid and hydrogen fluoride which have not reacted in step A. Hydrogen fluoride in the separated mother liquor accounts for 10% of the total hydrogen fluoride in the solution containing silicic acid and hydrogen fluoride discharged to the step A.
% Is preferable. 10% of all hydrogen fluoride
If it is more than that, the amount of calcium fluoride generated in step C increases, and the amount of silica mixed in calcium fluoride increases. This separated mother liquor is directly transferred to Step C.

In the present invention, in the step B, which is a separation step of calcium fluoride, since the hydrofluoric acid in the solution is dissolved without being reacted, the advantage that silica is hardly mixed into the calcium fluoride is provided. is there. The calcium fluoride recovered from step B is preferably obtained as a slurry having a water content of 70% or more, and is preferably dehydrated by a centrifuge, a decanter, a belt filter, or the like, to a solid content of 40 to 60%.

After the slurry obtained from the step B is dehydrated, the pH of the slurry is adjusted to 8 to 12 by adding an alkali.
Preferably, it is used as calcium fluoride. When the slurry has a pH of 8 to 12, slightly remaining SiO ₂ becomes a stable colloid solution, which facilitates separation, which is preferable. When calcium fluoride is used when the slurry is less than pH 8, the material of the reactor and the like is corroded when calcium fluoride is used. When the pH is more than 12, an unnecessary alkali is mixed into the recovered calcium fluoride. It is not preferable. The pH of the slurry is particularly preferably from 8 to 10.

When an alkali is added to the slurry obtained from the step B, the alkali is preferably sodium hydroxide, calcium hydroxide or the like, and particularly preferably calcium hydroxide. When calcium hydroxide is used, when unreacted fluorine is present in the reaction mother liquor, it can be collected as calcium fluoride. The alkali can be used in the form of a powder, a solution or the like when added to the slurry.

In the step C, the separated mother liquor obtained in the step B is mixed with calcium carbonate of 90 to 120% of the equivalent of the hydrofluoric acid and hydrogen fluoride in the solution containing the hydrofluoric acid and hydrogen fluoride of the step A. Added. Calcium carbonate reacts with silicic acid and hydrogen fluoride to produce calcium fluoride and SiO ₂ . In the dispersion supplied to the step C, substantially the entire amount of hydrogen fluoride in the solution supplied to the step A is separated as calcium fluoride. In the step C, calcium carbonate equivalent to the equivalent amount is used. Unreacted. At this time, unreacted calcium carbonate remains in the dispersion. If the calcium carbonate is less than 90% of the reaction equivalent of the hydrofluoric acid and hydrogen fluoride, the removal rate of the hydrofluoric acid and hydrogen fluoride from the solution containing the hydrofluoric acid and hydrogen fluoride is reduced, and the calcium carbonate and the hydrogen fluoride are removed at a rate of more than 120% If there,
Unreacted calcium carbonate increases in calcium fluoride.

In the present invention, calcium carbonate can be used in the form of a powder, but is preferably used in the form of a dispersion having a concentration of 5 to 15%. If the concentration of the calcium carbonate dispersion is less than 5%, the amount of wastewater increases, and if the concentration is more than 15%, the viscosity of the dispersion increases, which is not preferable in the process. When the calcium carbonate is a powder, it is not preferable because it is foamed by carbon dioxide generated in the reactor in the step C.

In step D, the dispersion obtained in step C
Is preferably adjusted to a pH of 1.5 to 4.0.
And the SiO generated in step C_TwoIs the state of the sol (hereinafter S
iO_Two(Referred to as sol) in the dispersion. Solidify the dispersion
By liquid separation, SiO _TwoIs the sol-containing liquid a dispersion?
Is discharged, calcium fluoride and unreacted calcium carbonate
Cium is separated and recovered. Calcium fluoride and uncoated
The equivalent calcium carbonate may be in the form of a cake,
It may be in a certain slurry form. The obtained calcium fluoride and
Unreacted calcium carbonate is used in the reaction of step A.
You.

By adjusting the pH of the dispersion in step D to 1.5 to 4, the gelation time of the formed SiO ₂ sol is increased, and the SiO ₂ sol is present in a colloidal state in the dispersion. When the pH of the dispersion is less than 1.5, SiO ₂ is not present as a sol, which is not preferable. If the pH of the dispersion is more than 4, SiO ₂ is gelled, which is not preferable because filter paper or the like tends to be clogged during filtration. The dispersion has a pH of 2.5 to
It is particularly preferably 3.0.

The calcium fluoride and calcium carbonate obtained by the solid-liquid separation in the step D are dehydrated by a centrifugal separator or the like in order to avoid an increase in the flow rate of the treatment wastewater and the size of the equipment, and a water content of 70 to 90%. % Is preferable. When the water content is less than 70%, handling becomes difficult. When the water content is more than 90%, the ratio of silica contained in water mixed into calcium fluoride increases. Since the separated solution contains an active ingredient such as silica hydrofluoric acid, the solution is preferably returned to the step D.

In the solid-liquid separation operation in the steps B and D, a coagulation precipitation method is generally employed. In this case, it is preferable to use a polymer flocculant effective in a low pH range in order to increase the flocculation efficiency. Examples of the coagulant include an acrylamide polymer coagulant (trade name: Cliffloc PN-161, manufactured by Kurita Water Industries Ltd.). An apparatus such as a complete mixing tank can be used as a reaction apparatus for performing this reaction. Preferably, the inside of the device is rubber-lined.

Step A is preferably a continuous reaction. A continuous reaction facilitates control of the reaction. The residence time of the reaction in step A is preferably from 10 to 40 minutes, particularly preferably from 20 to 30 minutes. Residence time 1
If the time is less than 0 minutes, the reaction rate between hydrogen fluoride and calcium carbonate decreases, which is not preferable. If the time is more than 40 minutes, the amount of liquid to be treated increases, so that the apparatus needs to be enlarged, which is not preferable.

The residence time of the reaction in step C is as follows:
It is preferably from 50 to 120 minutes, particularly preferably from 60 to 90 minutes. If the residence time is less than 50 minutes, the reaction rate between the silicic acid and calcium carbonate decreases, which is not preferable.
If the time exceeds 0 minutes, the amount of the liquid to be treated increases, so that it is necessary to increase the size of the apparatus, which is not preferable.

Hereinafter, the present invention will be described with reference to the flowchart of FIG. 1 as a specific example, but the present invention is not limited thereto. In FIG. 1, reference numeral 1 denotes a first reactor (step A).
2) a first thickener (corresponding to step B), 3 a second reactor (corresponding to step C), 4 a second thickener (corresponding to step D).
).

The solution containing hydrofluoric acid and hydrogen fluoride is
It is introduced into the first reactor 1. Next, calcium carbonate is introduced into the first reactor 1, and hydrogen fluoride in a solution containing silicic acid and hydrogen fluoride reacts with calcium carbonate to generate calcium fluoride.

In the first reactor 1, hydrogen fluoride selectively reacts with calcium carbonate, and 90% of hydrogen fluoride
The above converts to calcium fluoride. Further, only 10% or less of the silicic acid reacts with calcium carbonate, and most of the silicic acid passes through the first thickener 2 together with unreacted hydrogen fluoride in a state of silicic acid.

In the second reactor 3, an aqueous solution of calcium carbonate is added to the hydrofluoric acid that has flowed in from the first thickener 2 on the upstream side and hydrogen fluoride that has not been reacted in the first reactor 1.
Silicic acid is converted to calcium fluoride. The reaction solution is
The whole amount flows into the second thickener 4.

In the second thickener 4, the reaction solution is adjusted to pH
The solution is adjusted to 1.5 to 4.0, separated into solid and liquid, and the SiO ₂ sol-containing solution is discharged out of the system. By performing solid-liquid separation on the reaction solution, a slurry containing calcium fluoride can be obtained.

Thereafter, although not shown in the flow chart, the obtained slurry is drained with a centrifugal separator or the like to reduce the water content to 70 to 90% in order to avoid an increase in the amount of treated wastewater and an increase in equipment. It is preferable that the dehydrated water is added to the first reactor 1 as a raw material. Since the solution separated by a centrifuge or the like contains an active ingredient such as silica hydrofluoric acid, it is preferable to return the solution to the second thickener 4.

Calcium fluoride and calcium carbonate generated in the second reactor 3 are added to the first reactor 1, and the calcium carbonate reacts with hydrogen fluoride to form calcium fluoride. It flows into the thickener 2 and is separated into solid and liquid. In the first thickener 2, calcium fluoride having a low SiO ₂ component is taken out in a state containing an aqueous solution.

The calcium fluoride recovered from the first thickener 2 is dehydrated by a centrifugal separator or the like, and has a solid content of 40 to 40%.
Obtained as a 60% slurry. The pH is adjusted by adding an alkali to the obtained slurry to separate calcium fluoride.

As a result, calcium fluoride 95-97
%, An SiO ₂ component of 0.8-1.0% and a calcium carbonate of 1.0-1.5% are obtained. This solid mixture can be supplied and used as a raw material for hydrogen fluoride to a hydrogen fluoride production facility.

Carbon dioxide gas is generated due to the reaction in the first reactor 1 and the second reactor 3, and a small amount of silicic acid and hydrofluoric acid are generated due to the vapor pressure of the hydrofluoric acid and hydrogen fluoride in the raw wastewater, physical scattering, and the like. Hydrogen is generated as exhaust gas. For this reason,
These exhaust gases can be removed with a scrubber that sucks a blower or the like and circulates the calcium carbonate solution, or a scrubber with ordinary water.

Optimum operating conditions can be achieved by monitoring the outlet of the solution of the first thickener 2 in the range of pH 2.5 to 3.0. That is, when the decomposition of the silicic acid starts, fluorine ions are released and the pH decreases. Therefore, the amount of calcium carbonate to be put into the second reactor 3 is adjusted so as to be the same as the pH of the mixed waste water.

[0046]

EXAMPLES Example 1 (Example) 1.83% of hydrofluoric acid and 0.59% of hydrogen fluoride according to the flow chart of FIG.
Was supplied to the first reactor 1 having a volume of 1100 L at a flow rate of 1200 kg / h. An 8% aqueous solution of calcium carbonate (purity: 99.3%) was supplied to the second reactor 3 having a volume of 2570 L at a flow rate of 790 kg / h to cause a reaction. The reaction solution in the second reactor 3 was transported to the second thickener and separated into solid and liquid. The slurry subjected to solid-liquid separation is fed from the bottom of the second thickener 4 to the first reactor 1 with solid contents of 78.7% of calcium fluoride and 20.9% of calcium carbonate.
It was returned at a flow rate of 640 L / h. The liquid separated from the second thickener 4 was discarded as a 0.36% concentration aqueous silica sol solution. The residence time in each reactor was 37 minutes in the first reactor 1 and 58 minutes in the second reactor 3. A coagulant (Kurita Kogyo Co., Ltd., trade name: Cliffloc PN-161) was added to the entrance of each thickener to promote 10 ppm slurry settling.

The slurry obtained from the first thickener was dehydrated by centrifugation, and treated by adding calcium hydroxide to pH 8, and the components were 98.65% of calcium fluoride, 0.94% of silica, and 1% of calcium carbonate. A solid mixture of .41% was obtained. The fluorine recovery was 99.0%. The obtained solid mixture can be used as a raw material for calcium fluoride in a process for producing hydrogen fluoride.

Example 2 (Comparative Example) The same mixed waste water and calcium carbonate as in Example 1 were supplied to a single reactor having a volume of 2000 L as in Example 1. The generated calcium fluoride was concentrated in a thickener downstream of the reactor, washed with slaked lime slurry, and then taken out. The residence time in the fluorine-containing wastewater reactor was 60 minutes. The obtained slurry was treated in the same manner as in Example 1 to obtain a solid mixture containing 94.9% of calcium fluoride, 2.8% of silica, and 2.3% of calcium carbonate. The fluorine recovery was 93.4%.

[0049]

According to the present invention, in the process of producing hydrogen fluoride from calcium fluoride ore, calcium fluoride can be efficiently recovered from a solution containing silicic acid and hydrogen fluoride.

[Brief description of the drawings]

FIG. 1 is a flowchart of one embodiment of the present invention.

[Explanation of symbols]

 1: first reactor 2: first thickener 3: second reactor 4: second thickener

Claims (6)

[Claims] 1. A method for producing hydrogen fluoride by reacting calcium fluoride ore with sulfuric acid, comprising: a solution containing silicic acid and hydrogen fluoride discharged as by-products;
A method for producing hydrogen fluoride, wherein calcium fluoride recovered in the following steps A, B, C, and D and mixed with calcium fluoride ore to be reacted with sulfuric acid is used. A: The solid calcium fluoride and calcium carbonate obtained in step D are added to a solution containing silicic acid and hydrogen fluoride, and substantially all of the calcium carbonate is reacted to form calcium fluoride and calcium fluoride. A step of producing a dispersion containing the calcium fluoride returned from the step D; a step of separating and recovering calcium fluoride from the dispersion produced in the step A; And add
A step of producing a dispersion containing calcium fluoride and unreacted calcium carbonate produced by reaction of substantially all of the silicic acid and hydrogen fluoride in the separated mother liquor; D: from the dispersion produced in step C, A step of separating into a liquid phase containing colloidal silica and solid calcium fluoride and calcium carbonate. 2. In the solution containing the hydrofluoric acid and hydrogen fluoride in the step A, the hydrofluoric acid has a concentration of 1.5 to 1.5.
The method for producing hydrogen fluoride according to claim 1, wherein the concentration of hydrogen fluoride is 2.5 to 1.5%. 3. The method for producing hydrogen fluoride according to claim 1, wherein the silica contained in the calcium fluoride recovered from the step B is not more than 1.0% of calcium fluoride in terms of SiO _2. . 4. In the reaction of the step C, the amount of calcium carbonate to be added is 90 to 120% of the equivalent of the hydrofluoric acid and hydrogen fluoride in the solution containing the hydrofluoric acid and hydrogen fluoride of the step A. The method for producing hydrogen fluoride according to claim 1. 5. The process for producing hydrogen fluoride according to claim 1, wherein the dispersion produced in the step C in the step D is separated at a pH of 1.5 to 4.0. 6. The hydrogen fluoride according to claim 1, wherein, in the continuous reaction in the step A, the reaction residence time between the solution containing silicic acid and hydrogen fluoride and calcium carbonate is 10 to 40 minutes. Manufacturing method.