JPH09271603A - Operation of crystallizer - Google Patents

Abstract

(57) Abstract: It is possible to prevent undesired precipitation, adhesion, deposition and solidification of crystals which may occur inside and outside a crystallizer, and to reduce the residual Fe concentration of an organic solvent after iron extraction. SOLUTION: The neutralization titration analysis of the discharged stripping solution is performed to determine the F concentration a (kg / m ³ ) corresponding to the total HF concentration and the F concentration b (kg / m ³ ) corresponding to the total F ⁻ concentration. And the concentration and composition of the stripping solution discharged from the device are NH.
₄ HF ₂ is adjusted to 150 to 400 kg / m ³ , and the (2a-b) value is adjusted to 0 to -20 (kg / m ³ ) by adjusting the concentration of the stripping solution and the amount of ammonia supplied to the apparatus,
In addition, the temperature of the stripping solution in the crystal growth zone or the cooling zone is maintained at 15 to 30 ° C while the liquid temperature at the time of two-phase mixing of the organic solvent supplied to the apparatus and the stripping solution is maintained at 30 to 50 ° C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the recovery treatment of a nitric hydrofluoric acid waste liquid used for pickling stainless steel sheets,
The present invention relates to a method of operating an apparatus for depositing iron fluoride complex crystals by mixing and contacting an organic solvent after iron extraction with a fluoride-based stripping solution.

[0002]

2. Description of the Related Art As a method for treating and recovering a waste liquid of nitric hydrofluoric acid used for pickling stainless steel sheets, Fe contained in the waste liquid of nitric hydrofluoric acid as disclosed in Japanese Patent Publication No. 56-42674. There is a method of removing ³⁺ ions by solvent extraction. In this method, Fe ³⁺ ions are first selectively extracted and removed from the waste liquid of nitric-fluoric acid by an organic solvent containing alkylphosphoric acid, and the organic solvent containing Fe ³⁺ ions is disclosed in JP-A-57-42545. It is stripped by the method using the indicated fluoride stripper and used repeatedly for the extraction of Fe ³⁺ ions. The nitric-hydrofluoric acid waste liquid from which Fe ³⁺ ions have been extracted and removed contains liberated nitric acid and hydrofluoric acid, so it can either be returned to the pickling tank as it is and reused for pickling stainless steel plates, or even a neutral phosphate ester. Only nitric hydrofluoric acid is recovered and reused by the organic solvent containing.

Here, a process flow of a general method for recovering and treating a waste liquid of nitric hydrofluoric acid according to the present invention and a crystallizer for peeling iron used therein will be described.

FIG. 1 shows a process flow of a general method for recovering and treating a nitric-fluoric acid waste liquid. Where A ₀
Indicates a nitric hydrofluoric acid waste liquid containing Fe ³⁺ ions. Fe ³⁺ ions in A ₀ are extracted at 1 by an ion exchange reaction with an organic solvent S using an alkylphosphoric acid or the like as an extractant. A typical alkylphosphoric acid is D2EHPA (di- (2-ethylhexylphosphoric acid), which can be represented as HR.
Since the form of Fe ³⁺ ions in A ₀ is mainly FeF ₂ ⁺ , the iron extraction reaction of 1 is as shown in equations (1) and (2). FeF ₂ ⁺ + 3HR → FeR ₃ + H ⁺ + 2HF (1) FeF ₂ ⁺ + HR → FeF ₂ R + H ⁺ (2) The aqueous phase after iron extraction is reused as a recovered acid.

Organic solvent S containing Fe ³⁺ ions by extraction
Generates a (NH ₄ ) ₃ FeF ₆ crystal X by a peeling (back extraction) reaction with the aqueous solution D mainly containing NH ₄ HF _{2 in 2} . FeR ₃ + 3NH ₄ HF ₂ → 3HR + (NH ₄ ) ₃ FeF ₆ ↓ (3) FeF ₂ R + 3NH ₄ HF ₂ → HR + (NH ₄ ) ₃ FeF ₆ ↓ + 2HF (4) FeR ₃ + 3NH ₄ HF ₂ + 3NH ₄ F → 3NH ₄ R + (NH ₄ ) ₃ FeF ₆ ↓ + 3HF (5) Since part of the extractant after stripping iron is ammonia type (NH ₄ R) by the reaction as shown in formula (5), the solvent S should be 3 Hydrogen form (HR) by reaction with aqueous phase C containing hydrochloric acid in
Convert to NH ₄ R + HCl → HR + NH ₄ Cl (6)

The stripping solution containing the crystal X discharged from 2 is solid-liquid separated at 5, X is dried at 6, and is decomposed at 7 in air containing water or in a hydrogen stream to produce iron oxide H or It becomes metallic iron I. (NH ₄ ) ₃ FeF ₆ + 3 / 2H ₂ O → 3NH ₄ F + 3HF + 1 / 2Fe ₂ O ₃ (7) (NH ₄ ) ₃ FeF ₆ + 3 / 2H ₂ → 3NH ₄ F + 3HF + Fe (8) 7 Since NH ₄ F and HF are equimolar, they are absorbed and reused as the stripping solution D.

FIG. 2 shows the crystal used in the iron stripping process.
It is an example of the analyzer 10. Fe³⁺Contains ions by extraction
The organic solvent S passes through the temperature controller 11 and NH_FourHF_TwoEtc.
Fluoride-based stripping solution D consisting of
Iron introduced to the mixing zone 13 and expressed by the formulas (3) to (5)
Iron complex (NH_Four)_ThreeFeF ₆
Crystal X forms. After the iron is removed, the solvent remains in the stationary zone 14.
After that, it is discharged from the discharge port 15.

Since the iron complex (NH ₄ ) ₃ FeF ₆ has a relatively low solubility in a stripping solution, it is crystallized and deposited when stripping is continued. Stripping solution containing crystals is downcomer 1.
It descends 6 to a zone 17 called the crystal growth zone or cooling zone. The zone 17 is connected to an external heat exchanger 18 or the like by piping, and the growth of crystals is promoted by cooling the stripping solution that has been heated in the mixing zone 13. Forced circulation zone 1 inside zone 17 if necessary
9 is provided, and by connecting to an external circulation pump, the stripping solution in this area 19 is caused to flow to suppress the adhesion of crystals to the vessel wall and the deposition / solidification on the bottom. The stripping solution passes through the crystal separation zone 20 and is finally discharged from the discharge port 21. The crystals are appropriately discharged as a slurry from the crystal discharge pipe 22 and subjected to solid-liquid separation.

FIGS. 3 and 4 show iron fluoride complexes (N
H_Four)_ThreeFeF₆Each NH_FourHF _TwoConcentration 75kg
/ M^ThreeAnd 150 kg / m^ThreeFluoride-based stripper
2 is a graph of solubility, in which HF is 0 to 20 kg / m
^ThreeThe solubility curve is given in the range of. These solubility songs
From the line, NH which is a component of the stripper_FourHF_TwoThe concentration of
When the HF concentration increases, (NH_Four)_ThreeFeF₆Melting
It can be seen that the temperature gradient of the solution curve increases.

Conventionally, due to the adhesion, deposition and solidification of crystals inside the crystallizer, and the precipitation of crystals by cooling the stripping solution by pipes / pumps other than the main body of the crystallizer, especially during the cold season, and the temperature rise of the organic solvent. In order to prevent deterioration, Japanese Patent Laid-Open No. 58-81402 proposes a crystallizer as shown in FIG. Further, in JP-A-60-206402, in a crystallizer as shown in FIG. 2, the concentration of the stripping liquid discharged from the device is 85 to 115 k for NH ₄ HF ₂ .
The concentration of the stripping solution supplied to the apparatus is adjusted so that g / m ³ and HF are 10 kg / m ³ or less, and the temperature of the organic solvent supplied to the apparatus is 20 to 25 ° C. The temperature of the stripping solution in the crystal growth zone or the cooling zone is 15 to 40 ° C. when the two-phase mixing with the stripping solution is performed.
An operating method of maintaining at 20 ° C was proposed.

[0011]

However, when continuous operation is carried out with the above-described crystallizer and method, iron fluoride complex crystal adhesion, deposition and solidification in the mixing zone 13 and downcomer 16 of the crystallizer are carried out. It was necessary to stop the operation of the device once a month to clean the mixing zone and the downcomer. Also, the iron peeling of the organic solvent is not sufficient,
Therefore, there is also a problem that the next iron extraction rate decreases.
As a result, the long-term continuous stable operation of the wastewater treatment facility for nitric-hydrofluoric acid could not be carried out, the treatment capacity of the facility declined, and the recovery treatment cost was high. The object of the present invention is to solve the problem of operation stop due to the adhesion and deposition / solidification of iron fluoride complex crystals in the crystallizer in the recovery process of the nitric-fluoric acid waste liquid by the solvent extraction method, and the running cost is small and efficient. To provide a driving method.

[0012]

[Means for Solving the Problems] The above problems are solved.
For this reason, the present inventors have investigated the concentration and composition of the stripper and the temperature of the stripper.
Precipitation state of iron fluoride complex crystals and residual organic solvent after exfoliation
Focusing on the relationship with the Fe concentration etc., the composition of the fluoride-based stripping solution
To NH_FourHF_TwoAnd NH_FourNH composed of F _FourHF_Two
When the concentration is high and the two-phase mixture of organic solvent and stripper is
Solution temperature and crystal growth zone or cooling zone
If the temperature is kept high, undesirable crystals may precipitate or
Adhesion, accumulation and solidification can be prevented, and the residual Fe concentration of the organic solvent can be
It was found that the degree of the degree could be lowered, and the present invention was completed.
It is.

According to the present invention, Fe ³⁺ ions in a nitric-fluoric acid waste liquid used for pickling stainless steel are removed by solvent extraction, and then a mixing zone, a standing zone, a crystal separation zone, and a In operating a device for precipitating iron complex crystals by contacting an organic solvent containing Fe ³⁺ ions extracted with a fluoride-based stripping solution in the mixing zone in a crystallizer having a crystal growth zone or a cooling zone, Neutralization titration analysis of the stripping solution discharged from the device was performed to find the F concentration a (kg / m ³ ) corresponding to the total HF concentration.
And the F concentration b (kg / m ³ ) corresponding to the total F ⁻ concentration, the NH ₄ HF ₂ concentration and composition of the stripping solution discharged from the apparatus is 150 to 400 kg / m ³ , (2a
-B) The concentration of the stripping solution and the amount of ammonia supplied to the apparatus are adjusted so that the value is 0 to -20 (kg / m ³ ), and the organic solvent and the stripping solution are supplied to the apparatus. The liquid temperature during the two-phase mixing is 30 to 50 ° C., and the temperature of the stripping liquid in the crystal growth zone or the cooling zone is 15 to 30 ° C.
The present invention provides a method for operating a crystallizer, which is characterized in that

Hereinafter, the present invention will be described in more detail. In the present invention, first, neutralization titration analysis of the stripping solution discharged from the crystallizer is performed. FIG. 5 shows an example of the neutralization titration curve.
The titration amount from the start to the first peak is the F concentration a (kg / m ³ ) corresponding to the total HF concentration in the stripper, and the second from the start.
The titer up to the peak is the F concentration b (kg / m ³ ) corresponding to the total F ^- concentration in the stripper, and the titer from the first to the second peak is the total NH ₄ F concentration in the stripper. Equivalent F
It corresponds to the concentration (ba) (kg / m ³ ), respectively.
The neutralization titration reaction is shown below. From the beginning to the first peak: HF + NaOH → NaF + H ₂ O (9) From the first to the second peak: NH ₄ F + NaOH → NaF + NH ₄ OH (10)

In general, NH_FourHF_TwoStripping liquid mainly composed of
Concentration and composition of F concentration a corresponding to total HF concentration
All NH_FourExpress as F concentration (ba) corresponding to F concentration
Can be. The reason is NH_FourHF_TwoComposition is NH_FourF
This is because it can be expressed by + HF. Therefore, FIG. 3 and FIG.
HF of 4 = 0 kg / m^ThreeThe stripper is NH_FourHF _Two
A = b−a, that is, 2a−b =
It becomes 0. HF of FIGS. 3 and 4 = 10 or 20 kg
/ M^ThreeThe stripper is NH_FourHF_TwoAnd free (excess)
When configured with HF, a> b−a, that is, 2a−b>
It becomes 0. Stripper is NH_FourHF_TwoAnd free (excess) NH
_FourWhen it is composed of F, a <b−a, that is, 2a−b <
It becomes 0. Therefore, using the above a and b, free H
F or free NH_FourF concentration and NH corresponding to F_FourH
F_TwoThe concentration is expressed as follows. Free HF or free NH_FourF concentration corresponding to F: 2a-b (kg / m^Three) (11) When 2a-b> 0 F concentration corresponding to free HF When 2a-b <0 Free NH_FourF concentration equivalent to F NH_FourHF_TwoConcentration: When 2a-b> 0 3 (ba) (kg / m^Three) (12) When 2a-b <0: 3a (kg / m^Three) (13)

Based on the result of the neutralization titration analysis of the stripping solution discharged from the crystallizer as described above, the concentration / composition of the stripping solution in the crystallizer is adjusted. The stripping solution discharged from the crystallizer is stored in the crystallizer in a state where the NH ₄ HF ₂ concentration is substantially increased by the absorption of the decomposition gas of the reaction of the formula (7) or (8) in the crystal decomposition step. Supplied. The stripping solution supplied to the crystallizer consumes NH ₄ HF ₂ by the iron stripping reaction of the formulas (3) to (5) in the mixing zone, and HF increases in balance. Therefore, ammonia is supplied to the crystal growth zone or cooling zone 17 of the crystallizer in order to substantially increase the NH ₄ HF ₂ concentration of the stripping solution discharged from the crystallizer and make the NH ₄ F excessive in balance. To do.

According to the invention, the mixing zone 1 of the crystallizer
NH of the stripping solution supplied to 3_FourHF _TwoNH concentration_FourHF
_TwoIs higher than the lower limit of crystallization and NH
_FourBy making F excessive, iron fluoride complex (NH_Four)_Three
FeF₆The temperature gradient of the solubility curve of
Liquid temperature and crystal growth zone during two-phase mixing of solvent and stripper
The temperature of the stripping solution in the cooling or cooling zone
Prevents unwanted crystal precipitation, adhesion, deposition and solidification
In addition, the residual Fe concentration of the organic solvent can be lowered.
You.

As a result of the inventors' studying the effects of the concentration, composition and temperature of the stripping solution, as shown in Examples and Comparative Examples, the concentration of the stripping solution discharged from the crystallizer was NH.
₄ HF ₂ is ^{150~400kg / m 3, (2a-} b) values ^{0~-20 (kg / m 3} ), and liquid temperature during the 2-phase mixture of stripping liquid and the organic solvent supplied to the apparatus 30-50
It was found that the temperature of the stripping solution in the crystal growth zone or the cooling zone is preferably 15 to 30 ° C. 2a-b =
(NH ₄ ) ₃ F for the NH ₄ HF ₂ concentration of the stripping solution of 0
The temperature gradient of the solubility curve of eF ₆ is shown in FIG. Further, FIG. 7 shows a suitable range of the concentration and composition of the stripping solution discharged.

NH ₄ H in the stripping solution discharged from the crystallizer
If the F ₂ concentration is less than 150 kg / m ³ , it is not possible to sufficiently prevent the (NH ₄ ) ₃ FeF ₆ crystals from adhering, depositing and solidifying in the crystallizer. Also, if it exceeds 400 kg / m ³ , NH ₄ HF _{2 can be} supplied by pipes or pumps other than the main body of the crystallizer.
Precipitation of crystals occurs, which is not preferable.

When the (2a-b) value is positive as in the prior art, that is, when HF is excessive, the residual Fe concentration of the organic solvent after iron stripping exceeds 2 kg / m ³ , so that the next iron extraction rate is 90%. %, Which is not preferable. Also (2
Setting the a-b) value to less than -20 (kg / m ³ ) means
A large amount of ammonia must be supplied to the crystal growth zone or the cooling zone of the crystallizer, which is not preferable because the running cost becomes high.

Further, if the liquid temperature at the time of two-phase mixing of the organic solvent and the stripping liquid is less than 30 ° C., crystal adhesion, deposition and solidification occur in the mixing zone, which is not preferable. Above 50 ° C,
It is not preferable because the deterioration of the extractant of the organic solvent due to the hydrolysis reaction becomes remarkable.

If the temperature of the stripping solution in the crystal growth zone or the cooling zone is lower than 15 ° C., the temperature gradient of the stripping solution in the crystallizer becomes large, and the adhesion, deposition and solidification of crystals occur around the downcomer. Not preferable. On the other hand, if it exceeds 30 ° C, the solubility of NH ₄ HF _{2 in} the stripping solution becomes sufficiently small,
Crystal precipitation is insufficient, which is not preferable.

[0023]

The present invention will be specifically described below with reference to examples and comparative examples. (NH ₄ ) ₃ F as shown in FIG.
The nitric hydrofluoric acid waste liquid recovery treatment facility having a crystallizer with an eF ₆ crystal production capacity of 130 tons / month was operated. 30v / v
Fe ³⁺ ions in an organic solvent having a composition of% D2EHPA + 70 v / v% n-paraffin from 16.3 to 19.8 kg / m
Those containing ³ extracts were fed to the mixing zone 13 at a rate of 2.2 m ³ / hour. As a stripping solution, a NH ₄ HF ₂ concentration as shown in Table 1 and a (2a-b) value as shown in Table 1 was used at a rate of 4.5 m ³ / hr (organic phase / aqueous phase flow ratio 0.4
It was fed to the mixing zone 13 in 9). At that time, the liquid temperature during the two-phase mixing was maintained at 40 to 45 ° C, and the temperature of the stripping liquid in the cooling zone was maintained at 25 to 28 ° C. Table 1 below shows the state of precipitation of crystals other than the mixing zone, the downcomer and the apparatus main body and the residual Fe concentration of the organic solvent after the iron was peeled off together with Comparative Examples. From Table 1 it is clear that good results are obtained when operating within the scope of the invention.

[0024]

[Table 1]

[0025]

As described in detail above, according to the present invention, it is possible to prevent undesired precipitation, adhesion, deposition and solidification of crystals which may occur inside and outside the crystallizer, and also to prevent iron extraction. The residual Fe concentration of the organic solvent can be lowered. Therefore, the frequency of cleaning the interior by stopping the crystallizer can be reduced to ⅙ or less of the conventional frequency, and the number of man-hours required for the worker can be significantly reduced. As a result, the running cost for the recovery treatment of the nitric-hydrofluoric acid waste liquid is significantly reduced, the processing capacity is improved, and a stable recovery process can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a process flow of a general method for recovering and treating waste liquid of nitric hydrofluoric acid.

FIG. 2 is a diagram showing an example of a crystallizer used in an iron stripping step.

[Fig. 3] Iron fluoride complex (NH_Four)_ThreeFeF₆Each of
NH_FourHF_TwoConcentration 75kg / m ^ThreeFor fluoride-based stripper
It is a graph of solubility against.

FIG. 4 is a graph showing the solubility of iron fluoride complex (NH ₄ ) ₃ FeF _{6 in} a fluoride-based stripping solution having an NH ₄ HF ₂ concentration of 150 kg / m ³ .

FIG. 5 is a graph showing an example of a neutralization titration curve of a stripping solution discharged from a crystallizer.

FIG. 6 is a graph showing the temperature gradient of the solubility curve of (NH ₄ ) ₃ FeF ₆ with respect to the NH ₄ HF ₂ concentration of the stripping solution of 2a-b = 0.

FIG. 7 is a diagram showing a preferable range (hatched line) of the concentration and composition of the stripping solution to be discharged.

[Explanation of symbols]

A ₀ Waste acid A Recovered acid C Hydrochloric acid solution D Iron stripping solution E Ammonia water G Decomposition gas H Iron oxide I Metallic iron S Organic solvent X Iron complex crystal 1 Iron extraction 2 Iron stripping (crystallization) 3 Solvent conversion 4 Ammonia recovery 5 Solid-Liquid Separation 6 Crystal Drying 7 Crystal Decomposition 10 Crystallizer Main Body 11 Solvent Temperature Controller 12 Stripping Liquid Heater 13 Mixing Zone 14 Solvent Standing Area 15 Solvent Discharge Port 16 Downcomer 17 Crystal Growth or Stripping Liquid Cooling Zone 18 Stripping Liquid Heat exchanger 19 Stripping liquid forced circulation zone 20 Crystal separation zone 21 Stripping liquid discharge port 22 Crystal discharge pipe

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01D 9/02 625 B01D 9/02 625D 625E C23G 1/36 C23G 1/36

Claims (1)

[Claims] 1. After removing Fe ³⁺ ions in the waste liquid of nitric-hydrofluoric acid used for pickling stainless steel by solvent extraction,
In a crystallizer having a mixing zone, a standing zone, a crystal separation zone, and a crystal growth zone or a cooling zone sequentially from the top, an organic solvent containing Fe ³⁺ ions is contacted with a fluoride stripper in the mixing zone. When the apparatus for precipitating iron complex crystals is operated, the neutralization titration analysis of the stripping solution discharged from the apparatus is performed to determine the F concentration a (kg / m ³ ) and the total F corresponding to the total HF concentration.
^- determine the concentration of F b (kg / m ³⁾ corresponding to the concentration, NH ₄ concentration and composition of the stripping solution discharged from the front Stories device
HF ₂ is adjusted to 150 to 400 kg / m ³ , the (2a-b) value is set to 0 to -20 (kg / m ³ ), and the concentration of the stripping solution and the amount of ammonia supplied to the apparatus are adjusted, and The temperature of the stripping solution in the crystal growth zone or the cooling zone is kept at 15 to 30 ° C. and the temperature of the stripping solution at the time of two-phase mixing of the organic solvent supplied to the apparatus and the stripping solution is maintained at 30 to 50 ° C. And a method for operating the crystallizer.