TWI452010B - Method and apparatus for preparing purified phosphoric acid from phosphoric acid aqueous solution containing plural metal ions - Google Patents

Description

Method and device for preparing refined phosphoric acid from aqueous solution of phosphoric acid containing most metal ions

A mixed aqueous solution of nitric acid-acetic acid-phosphoric acid (hereinafter referred to as a mixed acid aqueous solution) used in a metal etching step or the like contains a large amount of metal as a concentration exceeding the use limit of etching (usually about 500 to 1000 ppm by weight). While the waste liquid of the ion is discharged, the present invention relates to a method and an apparatus for producing purified phosphoric acid by removing metal ions from such a mixed acid solution containing a large amount of metal ions (hereinafter referred to as a mixed acid aqueous solution waste liquid). In particular, it is about by melt crystallization. The residual phosphoric acid aqueous solution obtained by the solvent extraction method and the like (now, these are directly discarded) is suitable for containing a high concentration of metal ions (from 500 ppm on a weight basis to dissolve as a metal ion in an aqueous phosphoric acid solution). Method and apparatus for treating an aqueous phosphoric acid solution with a concentration of the upper limit.

In the manufacture of a semiconductor manufacturing plant or a liquid crystal display, a metal etching step of Al or the like uses a mixture of phosphoric acid, nitric acid, acetic acid, and water as a fresh liquid of an aqueous mixed acid solution, and the total metal concentration thereof is 100 ppb or less. However, the aqueous mixed acid solution dissolves the metal as it is used, increases the concentration of the metal ions, and changes the composition due to evaporation of the volatile substances (nitric acid, acetic acid, water) or adhesion to the material to be etched, and the etching ability is lowered. Therefore, in the past, a part or all of the fresh liquid was replaced, and the metal ion concentration was suppressed to be low (about 500 to 1000 ppm or less on a weight basis), and the composition change was suppressed to maintain the etching ability. However, in the past, the mixed acid aqueous solution waste liquid containing a large amount of metal ions discharged in the metal etching step was discarded because the etching ability was lowered as the metal ion concentration was increased. Therefore, it is required to have a treatment apparatus for recovering metal ions from the discharged mixed acid aqueous solution waste liquid and recovering the mixed acid aqueous solution at a high yield after self-use.

At the most advanced stage of the purification of the mixed acid aqueous solution discharged from the Al metal etching apparatus, volatile substances (most of nitric acid, acetic acid, and water) are evaporated and separated by evaporation or distillation. Phosphoric acid and metal ions are non-volatile substances, so it is difficult to separate by evaporation or distillation. The concentration of phosphoric acid (hereinafter referred to as concentrated phosphoric acid) at this stage is about 90% by mass, and water is about 10% by mass.

As a general method for separating metal ions present in a solution, there are an ion exchange resin method, a diffusion dialysis method, a membrane electrodialysis method, an electrodialysis method, and an adsorption method using activated carbon. However, even if it is applied to a mixed acid aqueous solution or a concentrated phosphoric acid, the high concentration of phosphoric acid is highly corrosive and contains both anion and a cation as a metal ion, and the following problems occur, so that metal ions cannot be completed. Fully separated.

In the ion exchange resin method, it is difficult to ion exchange metal ions dissolved in a high concentration of acid. It has also been understood that the regeneration efficiency of the resin is low. By diffusion dialysis, the resulting phosphoric acid needs to be diluted and a large amount of dialysis residue occurs. By membrane electrodialysis method, the mixed aqueous solution of nitric acid effluent NO _x production due to oxidation becomes a problem. According to the electrodialysis method, since the ionic radii of the phosphate ion and the molybdate ion are similar and the moving speed is equal, it is difficult to separate. By the adsorption method of activated carbon, the mixed acid aqueous solution waste liquid is colored by activated carbon.

On the other hand, as one of the concentrated phosphoric acid purification methods, there is a metal extractant method (Patent Document 1). However, although Mo is reduced, the reduction of Al cannot be achieved. Further, in the metal of the concentrated phosphoric acid, a cation (Al ³⁺ or the like) and an anion (a form in which a metal such as MoO ₄ ^{2- is} oxidized) are dissolved, and in order to reduce both ions, it is necessary to use an extraction column and a reverse extraction column. Two groups of cations and anions are used, and it is expected that the equipment cost will be greatly increased, and the operating cost will also increase, making the advantages of phosphoric acid reuse difficult to be effectively utilized.

Although other methods for purifying concentrated phosphoric acid disclose a crystallization method (Patent Documents 2 to 3), they are all batch processing methods, and there are problems in that the temperature must be carefully controlled so that the processing time becomes long.

Further, a technique of continuous crystallization is known as a general purification method (Non-Patent Document 1). However, when this method is used to concentrate phosphoric acid, since the purified purity of the crystal of semi-crystalline water of phosphoric acid is related to the concentration of metal ions in the mother liquor, the yield is at most about 80% by mass, and it is expected to be further improved from the viewpoint of effective use of resources. Yield.

On the other hand, the coprecipitation method according to the present invention is described on the 74th page of Non-Patent Document 2 as follows.

"The so-called co-precipitation is a phenomenon in which a soluble substance is precipitated together when a precipitate precipitates. The phenomenon of coprecipitation is caused by the formation of mixed crystals, and is caused by ion adsorption during the formation of precipitates. In the former case, The impurities actually enter the crystal lattice of the precipitate. In the latter case, the adsorbed ions are attracted to the precipitate during the condensate process."

However, in Non-Patent Document 2, only the general coprecipitation phenomenon is described, and the metal ion coprecipitation in the concentrated phosphoric acid of the present invention is not described at all.

Patent Document 1: Japanese Patent Patent No. 2005-142444

Patent Document 2: Japanese Patent Special Wish 2004-255388

Patent Document 3: Japanese Patent No. 3382561

Non-Patent Document 1: "Additional Crystallization", pages 73 to 82, added on December 25, 2015, issued by the Chemical Industry Corporation

Non-Patent Document 2: "Quantitative Analytical Chemistry" (Revised 17th Edition), p. 74, original work of R.A. Dai, Jr. A.L. Anderwood, 1992, issued by Peifeng Museum

To this end, in this context, the proposed invention provides an object and apparatus for separating and removing metal ions from a phosphoric acid aqueous solution containing a plurality of metal ions to obtain purified phosphoric acid, and further aims to provide an application by application. A system for recovering purified phosphoric acid recovered by discharging a waste liquid of a mixed acid aqueous solution containing a high concentration of phosphoric acid discharged in a metal etching step.

The above problems can be solved by the methods of the following 1) to 8) of the present invention.

1) A method for producing refined phosphoric acid from an aqueous solution of phosphoric acid containing a plurality of metal ions, which comprises the steps of: [1] precipitating crystals of inorganic salts from a phosphoric acid aqueous solution containing a plurality of metal ions to precipitate a metal ion; Analysis. Coprecipitation step, the crystallization. The coprecipitation step consists of the following steps: (a) a step of mixing an aqueous solution of an inorganic salt in an aqueous phosphoric acid solution containing a plurality of metal ions; (b) precipitating crystals of the inorganic salt by further mixing with an organic weak solvent which is soluble in phosphoric acid and does not dissolve the inorganic salt, and at the same time a step of coprecipitation of the metal ion; (c) a solid-liquid separation step of filtering the crystal of the inorganic salt containing the metal ion; and [2] evaporating the organic weak solvent in the filtrate obtained by the filtering by evaporation Obtaining an evaporation step of the purified phosphoric acid, wherein the amount of the metal ions dissolved in the phosphoric acid/organic weak solvent mixture in the step [1] (b) is less than the metal in the aqueous phosphoric acid solution used in the step [1] (a) The amount of ions.

2) The method for producing a purified phosphoric acid according to the above 1), wherein the purified phosphoric acid obtained by the method described in 1) is further prepared by repeating the steps of [1] and [2] several times. Higher concentration of refined phosphoric acid.

(3) The method for producing a purified phosphoric acid according to the above, wherein the phosphoric acid aqueous solution containing a plurality of metal ions contains metal ions up to 500 ppm by weight to an upper limit concentration of metal ions soluble in the aqueous phosphoric acid solution. .

(4) A method of producing a purified phosphoric acid according to any one of the above 1 to 3, wherein the crystal of the inorganic salt containing the metal ion obtained in the step [1] is dissolved in water, followed by cooling to cause the inorganic salt Crystallization, separation of the coprecipitated metal from the inorganic salt, followed by filtration to recover the inorganic salt, and then self-return The inorganic salt is prepared to prepare an aqueous solution of an inorganic salt, and is reused in the step [1] (a) as described in 1).

5) A method for producing a purified phosphoric acid according to any one of the methods 1) to 3), characterized by comprising at least an inorganic salt dissolving tank for dissolving an inorganic salt to prepare an aqueous solution of an inorganic salt; The aqueous solution of the ionic phosphoric acid is mixed with the organic weak solvent and the aqueous solution of the inorganic salt to crystallize the inorganic salt and simultaneously crystallize the metal ion coprecipitate. a coprecipitation tank; a filtration device that performs solid-liquid separation by filtering the obtained crystal of the inorganic salt containing the metal ion; and an organic solvent evaporation device having a heating means for evaporating the organic weak solvent and water from the filtrate.

(6) The apparatus according to (5), further comprising an inorganic salt-purifying crystal in which crystals of an inorganic salt containing a metal ion filtered in the filtering device are dissolved in warm water, and then crystallizing the inorganic salt by cooling again A tank and a filtration device for separating crystals of the inorganic salt precipitated in the inorganic salt-refining crystallization tank.

7) A method for recycling an etching solution, comprising the steps of: using a mixed acid aqueous solution containing a plurality of metal ions generated in a metal etching step using an aqueous mixed acid solution composed of phosphoric acid, nitric acid, acetic acid, and water; The recovery step of recovering the waste liquid by evaporating most of the nitric acid, acetic acid and water from the waste acid aqueous solution waste liquid, and fractionating into a distillate containing nitric acid, acetic acid and water, and containing phosphoric acid and a step of evaporating concentrated phosphoric acid of a plurality of metal ions; and a step of purifying the purified phosphoric acid by coprecipitation separation of the metal ions in the concentrated phosphoric acid by the apparatus described in 5) or 6), by adding the aforementioned The distillate was adjusted to adjust the concentration of the solution, which was then used as a recovery mixed acid aqueous solution for the concentration adjustment step in the metal etching step.

8) The method for recycling an etching solution according to 7), further comprising the steps of: concentrating phosphoric acid obtained in the evaporation step, and crystallizing a semi-crystalline water of phosphoric acid in a melt crystallization apparatus, followed by a phosphoric acid half by a filtering device The crystal water crystal is subjected to solid-liquid separation, and then the obtained crystal of semi-crystalline water of phosphoric acid is transferred to the above-mentioned concentration adjustment step, and on the other hand, the concentrated filtrate of the metal ion is moved to the crystal formation described in 5) or 6). A precipitation step in the coprecipitation tank.

According to the present invention, there is provided a method and apparatus for easily removing a metal ion from a phosphoric acid aqueous solution containing a plurality of metal ions to obtain a purified phosphoric acid, and further providing a mixed acid aqueous solution containing a high concentration of phosphoric acid discharged by a metal etching step. The recovered purified phosphoric acid system can be reused.

Further, by combining the apparatus for obtaining purified phosphoric acid of the present invention on the metal etching apparatus line, it is possible to keep the metal ion concentration in the aqueous acid solution tank constant to a certain level or less, and it is possible to stably perform the etching step at the same time. The amount of replenishment of the fresh liquid of the mixed acid aqueous solution is reduced (it is 10 mass% or less in the past).

Best form for implementing the invention

The above invention will be described in detail below.

The inventors of the present invention conducted a deliberate study and found that a solution of a phosphoric acid aqueous solution containing a high concentration (500 ppm to the upper limit concentration of metal ions dissolved in an aqueous phosphoric acid solution) is particularly effective by utilizing crystals. Analysis. The method and apparatus for removing the metal ions by the coprecipitation phenomenon to obtain the purified phosphoric acid, and further, when applied to the concentrated phosphoric acid containing a large amount of metal ions in the metal etching step, the phosphoric acid can be recovered in a high yield and reused. Further, the purified phosphoric acid of the present invention is a phosphoric acid which separates and removes metal ions, and has a phosphoric acid concentration of about 90% by mass.

The method of the present invention consists of the following principles. A large amount of nitric acid, acetic acid, and water are distilled off from the waste liquid of an aqueous mixed acid solution containing a large amount of metal ions after etching, to obtain concentrated phosphoric acid, and an inorganic salt is added to the obtained concentrated phosphoric acid. At this time, since the inorganic salt has a property of being easily dissolved in ordinary water and difficult to be dissolved in an organic solvent or a thick phosphonium, one part of the inorganic salt is dissolved in a small amount of water in the concentrated phosphoric acid, and the other excess inorganic salts are not. Dissolved. An organic weak solvent is added thereto to crystallize the inorganic salt dissolved in the concentrated phosphoric acid, and the metal ions dissolved in the concentrated phosphoric acid are precipitated along with the crystallization of the inorganic salt. This is the so-called coprecipitation in the present invention. Subsequently, by causing crystallization. The suspension obtained by coprecipitation is filtered to crystallize from inorganic salts and The solid component composed of the metal ion dissolved in the concentrated phosphoric acid is subjected to solid-liquid separation with an organic weak solvent-phosphoric acid aqueous solution. Further, the obtained filtrate was subjected to distillation to fractionate the organic weak solvent and the phosphoric acid aqueous solution to obtain purified phosphoric acid. Figure 7 is a graph showing the coprecipitation mechanism of the present invention.

In the present invention, an aqueous solution of a mixed acid solution containing a large amount of metal ions after use in etching is concentrated, and an inorganic salt is added to the obtained concentrated phosphoric acid. However, if the concentration of the phosphoric acid aqueous solution is insufficient in the above-mentioned treatment step, the water in the phosphoric acid is concentrated. When the content is increased, it is difficult to precipitate the inorganic salt contained in the water in the concentrated phosphoric acid even after the addition of the organic salt solution, and the inorganic salt is not precipitated and remains, so that the degree of purification of the phosphoric acid is deteriorated. Therefore, the aqueous phosphoric acid solution containing a large amount of metal ions to be treated is desirably concentrated to a concentration of about 90% by mass or more. When the concentration of phosphoric acid in the aqueous phosphoric acid solution to be treated is less than about 90% by mass, the proportion of water increases. Therefore, many of the organic salts dissolved in the water remain in the filtrate, and it is difficult to obtain the effects of the present invention.

Further, in the present invention, if the amount of metal ions dissolved in the phosphoric acid/organic weak solvent mixture in the coprecipitation step is larger than the amount of metal ions contained in the phosphoric acid aqueous solution (that is, concentrated phosphoric acid) before the mixing step, There is no refining effect, and it is difficult to obtain purified phosphoric acid having a high purity. Therefore, after the addition of the inorganic salt aqueous solution, it is also important that the inorganic salt is completely crystallized at the same time as the inorganic salt dissolved in the concentrated phosphoric acid, and the inorganic salt is not left in the phosphoric acid aqueous solution.

Further, when the concentration of the metal ions to be removed is lowered, the proportion of the cations constituting the inorganic salt among the cations contained in the filtrate after the solid-liquid separation When it is enlarged, the removed metal ions are simply exchanged with the cations of the inorganic salt, so that it is difficult to obtain the effects of the present invention. Therefore, it is necessary to make the metal ion concentration of the aqueous solution of phosphoric acid containing a large amount of metal ions higher than the solubility of the inorganic salt in the phosphoric acid/organic weak solvent mixture after the addition of the organic weak solvent. Specifically, the concentration of the metal ions in the phosphoric acid aqueous solution to be treated is preferably about 500 ppm or more based on the weight.

As an embodiment of the present invention, a method and apparatus for treating a mixed acid aqueous solution containing a plurality of metal ions discharged from a metal etching step will be described with reference to the drawings.

1 is a schematic view of a device for etching a metal, which is a portion which is etched by an etching liquid receiving groove, a mixed acid aqueous solution tank, a mixed acid aqueous solution waste liquid tank, a mixed acid aqueous solution refining device according to the present invention, and a piping for connecting the same. Composition. The process flow is as follows.

First, a fresh mixed acid aqueous solution is supplied to a mixed acid aqueous solution tank, and then a mixed acid aqueous solution is taken from the mixed acid aqueous solution tank, and the material to be etched is sprayed while being etched.

After the etching, the mixed acid aqueous solution passes through the etching solution to receive the solution, and the etched solution is returned to the mixed acid aqueous solution tank.

When the mixed acid aqueous solution tank is supplied with the mixed acid aqueous solution fresh liquid, the mixed acid aqueous solution overflowing from the mixed acid aqueous solution tank is transferred to the mixed acid aqueous solution waste liquid tank as the mixed acid aqueous solution waste liquid.

The mixed acid aqueous solution waste liquid collected in the mixed acid aqueous solution waste tank is supplied to the mixed acid aqueous solution refining device, and the metal ions dissolved in the mixed acid aqueous solution are crystallized by etching. Separation and purification by coprecipitation method, recycling and treatment The mixed acid aqueous solution is returned to the mixed acid aqueous solution tank. A part is discharged as waste liquid.

Fig. 2 is a schematic view showing an evaporation device of a part of a mixed acid aqueous solution refining device. The evaporation device may be a general evaporation device, but since the viscosity of phosphoric acid is high, it is preferably a thin film flow-down evaporation device. The operation of the device is as follows.

First, the mixed acid aqueous solution waste liquid supplied from the mixed acid aqueous solution waste tank of Fig. 1 is supplied to the liquid receiving tank through a reboiler.

Next, the system is maintained at 2000 to 7000 Pa, the liquid temperature is maintained at about 60 ° C to 90 ° C, and the mixed acid aqueous solution waste liquid is circulated between the liquid receiving tank and the reboiler by the pump, and steam is introduced into the waste pot. The mixed acid aqueous solution waste liquid is heated to make nitric acid. Acetic acid. The water is evaporated and distilled off.

Distilled nitric acid. Acetic acid. The water is condensed by a condenser having cooling water, and the distillate is stored and stored, and then reused as a raw material for adjusting the concentration of the etching liquid.

Distilled off nitric acid. Acetic acid. The concentrated phosphoric acid of water is transferred to the crystallization. A coprecipitation step or a melt crystallization step.

Fig. 3 is a schematic explanatory view showing an example of a metal etching solution in which a device for obtaining purified phosphoric acid according to the present invention is combined with a metal etching apparatus line in a circulation system.

The etching apparatus and the evaporation apparatus are the same as those described in Figs. 1 and 2, respectively. Unless otherwise specified, the operating temperature and pressure are normal temperature and normal pressure.

As described above, the mixed acid aqueous solution discharged from the etching device is transferred to The evaporation device separates into concentrated phosphoric acid and distillate (nitric acid, acetic acid, water).

The distillate is transferred to an etchant concentration adjusting device for reuse.

The concentrated phosphoric acid is transferred to the crystallization. The coprecipitation tank is mixed with an aqueous solution of an inorganic salt previously mixed in an inorganic salt dissolution tank. The inorganic salt may, for example, be a phosphate such as sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate or magnesium phosphate; or a sulfate such as sodium sulfate or ammonium sulfate; or an acetate such as sodium acetate or ammonium acetate; It is phosphate and sulfate.

After thorough mixing, an organic weak solvent is added to precipitate crystals of the inorganic salt while coprecipitating the metal in the concentrated phosphoric acid. The amount of the organic weak solvent is from 2 to 10 times, more preferably from about 3 to 5 times, in terms of volume ratio. As for the organic weak solvent, it is necessary to use only an inorganic salt such as an alcohol or a ketone to be dissolved to less than 0.1% by mass. Specific examples thereof include isopropyl alcohol (hereinafter referred to as IPA), isobutanol, acetone, and methyl isobutyl ketone.

Crystallization. After the coprecipitation is completed, the slurry is transferred to a filtration device for solid-liquid separation. The filter device is preferably a pressure filter or a Nutche filter.

Further, the type of the inorganic salt or the organic weak solvent and the amount thereof to be added can be appropriately determined by the concentration of the metal ion in the concentrated phosphoric acid.

The filtrate (phosphoric acid, organic weak solvent, and water mixture) of the filtration device is transferred to an organic solvent evaporation device, and the organic weak solvent and water are distilled off. The organic weak solvent is dehydrated and refined by an organic solvent dehydration device, and then crystallized. Reuse in the coprecipitation tank.

The purified phosphoric acid obtained by distilling off the organic weak solvent is mixed with the distillate of the evaporation device in the etching solution concentration adjusting device to supplement the insufficient component To the same extent as the fresh aqueous solution of the mixed acid solution, it is recycled as an recycled mixed acid aqueous solution in an etching apparatus.

The method and device of the invention are suitable for processing by melt crystallization. The solvent extraction method or the like contains a high concentration (500 ppm by weight based on the weight of the phosphoric acid aqueous solution containing a relatively low concentration (less than 500 ppm by weight) of the metal ion aqueous solution, and is dissolved in the phosphoric acid aqueous solution by metal ions. The upper limit of the aqueous solution of metal ions.

The residue of the filtration device (inorganic salt containing the coprecipitated metal) is supplied with water (not shown) to be dissolved, and transferred to an inorganic salt purification crystallization vessel. The amount of water is about 1.5 times the amount of residue.

After a certain amount of water is distilled off in the inorganic salt-refining crystallization tank, the inside of the tank is cooled and the inorganic salt is crystallized for about 0.5 to 1 hour, and then transferred to a centrifugal filter device to be separated into purified inorganic salts and waste water.

The refined inorganic salt is reused in the inorganic salt dissolution tank.

In the foregoing crystallization. In the coprecipitation tank, since the solubility of the inorganic salt in the crystallization of the inorganic salt is extremely changed by the addition of the organic weak solvent, the crystal shape is coarse and has micropores, and the metal ions are coprecipitated in a state of being adsorbed in the coarse structure. However, the crystallization tank is refined with an inorganic salt, and since the liquid is concentrated and cooled, the entire crystal is kept in a uniform state, so that the generated crystal becomes strong and densely crystallized, and the mother liquid adsorbed on the crystal surface is centrifuged (G=1500 or more). ) Refined, crystals containing no metal ions can be taken out.

Fig. 5 is a schematic explanatory view showing another example of a metal etching solution recirculation system in which a purified phosphoric acid device of the present invention is combined on a metal etching apparatus line.

The difference from the system shown in Figure 3 is that the melt crystallization device is located in the crystallization. Before the coprecipitation tank, the other is substantially the same as in the case of FIG.

The concentrated phosphoric acid separated by the evaporation device is transferred to a molten crystallization apparatus, and cooled to about 10 ° C to crystallize the semi-crystalline water of the phosphoric acid, followed by solid-liquid separation by a filtration device (not shown).

The separated crystals of the semi-crystalline water of phosphoric acid are dissolved by heating, transferred to an etching solution concentration adjusting device, and the insufficient components are replenished, and then reused in the metal etching step.

The concentrated filtrate of the metal is transferred to the crystallization. The coprecipitation tank was treated in the same manner as in the case of Fig. 3 .

However, when the concentration of the metal ions contained in the purified phosphoric acid in which the organic weak solvent is distilled off by the organic solvent evaporation apparatus is not sufficiently satisfied, the molten crystallization apparatus (the path shown by the broken line in Fig. 5) can be returned. deal with.

Moreover, in FIG. 5, the molten crystallization apparatus is illustrated as being disposed in the crystallization. The design example before the coprecipitation tank, but due to the correlation between the amount of metal and the concentration of the mother metal in the crystal of semi-crystalline water discharged from the molten crystallization apparatus, the molten crystallization is carried out under the condition that the concentration of the concentrated metal ions of the phosphoric acid is extremely high. Device and crystallization. The order of the coprecipitation tanks is interchangeable.

Example

Hereinafter, the present invention will be more specifically described by showing examples, but the present invention is not limited to the examples.

Example 1

The treatment of the mixed acid aqueous solution waste liquid in the Al etching step was carried out using the recycling system shown in FIG. Further, the constituent unit is "kg", and "N.D." indicates a value below the detection lower limit.

The mixed acid aqueous solution waste liquid (about 100 kg) discharged from the etching step is composed as follows. The amount of metal ions other than Al and Mo is negligible.

Further, the distillate (about 27.8 kg) from the evaporation device was composed as follows.

Further, the concentrated phosphoric acid (about 72.2 kg) by the evaporation device was composed as follows.

Next, dissolve 7.4 kg of sodium dihydrogen phosphate in 10 kg of water and add Crystallization. In the coprecipitation tank, it is thoroughly mixed with the concentrated phosphoric acid. After thorough stirring, 260 kg of anhydrous IPA was added with stirring. The treatment liquid (about 349.6 kg) at this stage was composed as follows.

Further, since Na is an inorganic salt and is contained in an inorganic substance, the composition is described in terms of metal ions. The same applies to the filtrate, the residue, and the purified phosphoric acid described later.

Further, the composition of the filtrate (about 338.7 kg) which passed through the filtration device was as follows.

Further, the composition of the residue of the filtration device (about 10.9 kg) was as follows.

The amount of Al and Mo in the filtrate and the residue was compared, and Al and Mo were moved toward one of the residues (coprecipitation). It has been confirmed that Al and Mo in the concentrated phosphoric acid can be separated by this operation. However, since Na ions are added by the addition of the inorganic salt, it is necessary to remove as much as possible, and in order to increase the purity of the phosphoric acid, it is necessary to remove the inorganic substance dissolved in the concentrated phosphoric acid as much as possible.

Next, the filtrate was transferred to an organic solvent evaporation apparatus to separate the IPA from the water, and the IPA was recovered by a distillation apparatus for IPA recovery, not shown, and reused. Further, in order to completely distill off the IPA from the phosphoric acid, water was added to the phosphoric acid after the IPA distillation, and the solvent was removed by re-evaporation and azeotropy. Refined phosphoric acid is obtained from the bottom of the organic solvent evaporation device.

The resulting refined phosphoric acid (about 71.1 kg) was composed as follows.

The above purified phosphoric acid is subjected to one crystallization. When the operator is coprecipitated, but the composition is not satisfied, the same operation is performed again, and the removal of metal ions is better. Next, an example is shown.

Since the metal ion concentration of the first mother liquid is low, the amount of the inorganic salt (sodium dihydrogen phosphate) added is 1/5.

The obtained purified phosphoric acid (about 70.5 kg) has the following composition, and a purified phosphoric acid having a higher purity can be obtained.

The crystal composition of the purified inorganic salt (about 7.5 kg) which was transferred to the inorganic salt-refining crystallization tank and treated as described above was as follows, and it was not problematic to reuse it in the inorganic salt dissolution tank.

As described above, according to the system of the present invention, about 98% by mass of the phosphoric acid in the mixed acid aqueous solution waste liquid can be reused, and the amount of the fresh liquid of the mixed acid aqueous solution can be greatly reduced.

Example 2

The treatment of the mixed acid aqueous solution waste liquid in the Al etching step was carried out in the same manner as in the first embodiment.

The composition of the mixed acid aqueous solution waste liquid (about 100 kg) discharged from the etching step, the composition of the distillate from the evaporation device (about 27.8 kg), and the composition of the concentrated phosphoric acid (about 72.2 kg) by the evaporation device were the same as in Example 1.

Then, the same procedure as in Example 1 was carried out except that the inorganic salt was changed to 4.43 kg of sodium sulfate and dissolved in 18 kg of water. This stage The treatment liquid (about 354.6 kg) was composed as follows.

Further, the relationship between the amount of Na and the amount of inorganic substances is the same as in the examples.

Further, the composition of the filtrate (about 346.5 kg) which passed through the filtration device was as follows.

Further, the composition of the residue of the filtration device (about 8.1 kg) was as follows.

The amount of Al and Mo in the filtrate and the residue was compared, and Al and Mo were moved toward one of the residues (coprecipitation). It has been confirmed that Al and Mo in the concentrated phosphoric acid can be separated by this operation. However, by adding an inorganic salt, since Na ions are added with SO ₄ ^2- ions, it is necessary to remove them as much as possible, and in order to increase the purity of phosphoric acid, it is necessary to remove the inorganic substances dissolved in the concentrated phosphoric acid as much as possible.

Next, the filtrate was supplied to an organic solvent evaporation apparatus, and as a result of the same operation as in Example 1, the obtained purified phosphoric acid (about 71.1 kg) was composed as follows. The SO ₄ ^2- ion ion remained in a state of forming a sodium sulfate salt with a little residual Na (0.006 kg) which was not removed.

Example 3

The treatment of the mixed acid aqueous solution waste liquid in the Al etching step was carried out in the same manner as in Example 1 using the recirculation system shown in FIG. Figure 4 is a graph showing the inflow and outflow of matter per basic processing unit.

In this embodiment, in order to maintain the metal ion concentration (the total amount of Al, Mo, and Na) of the mixed acid aqueous solution tank at 500 ppm or less based on the weight, the treatment amount of the mixed acid aqueous solution waste liquid is 100 kg/h, and the recycled mixed acid aqueous solution is used. The upper limit of the amount of metal to be etched is 90%/h, and the metal ion concentration of the recycled mixed acid aqueous solution is 30 ppm or less by weight and 10 kg/h of the mixed acid aqueous solution (for replenishment), as shown in the following formula. It becomes 0.0473kg/h.

100kg/h×0.0005-100kg/h×0.9×0.00003=0.0473kg/h

Example 4

The treatment of the mixed acid aqueous solution waste liquid in the Al etching step was carried out using the recycling system shown in FIG. The composition of the mixed acid aqueous solution waste liquid (about 100 kg) discharged from the etching step, the distillate from the evaporation device (about 27.8 kg), and the composition of concentrated phosphoric acid (about 72.2 kg) by the evaporation device were the same as in Example 1.

Next, the concentrated phosphoric acid was transferred to a molten crystallization apparatus, and cooled to about 10 ° C to crystallize and crystallize the semi-crystalline water of phosphoric acid. Next, the semi-crystalline water of the phosphoric acid is crystallized and separated by a filtration device, and then dissolved by heating and transferred to an etching solution concentration adjusting device to replenish the insufficient component in the metal etching process. The composition of the obtained crystal of semi-crystalline water of phosphoric acid is as follows.

Further, the filtrate composition is as follows.

The above filtrate is transferred to crystallization. The coprecipitation tank was subjected to the same treatment as in Example 1, and the obtained purified phosphoric acid (13.8 kg) was composed as follows. .

The purified phosphoric acid is returned to the melt crystallization step, and the same treatment as above is carried out again to obtain a purified phosphoric acid having the following composition.

It has been clarified that if the above-described melt crystallization is repeated, a purified phosphoric acid having a high purity can be obtained.

Example 5

The treatment of the mixed acid aqueous solution waste liquid in the Al etching step was carried out in the same manner as in Example 1 using the recirculation system shown in Fig. 5 . Fig. 6 is a graph showing the inflow and outflow of substances per basic processing unit.

In this embodiment, in order to maintain the metal ion concentration (the total amount of Al, Mo, and Na) of the mixed acid aqueous solution tank at 500 ppm or less based on the weight, the treatment amount of the mixed acid aqueous solution waste liquid is 100 kg/h, and the recycled mixed acid aqueous solution is used. The concentration of metal ions of 98kg/h, recycled mixed acid aqueous solution is suppressed When the weight is based on 30 ppm or less and the mixed acid aqueous solution fresh liquid (for replenishment) is supplemented by 2 kg/h, the upper limit of the amount of metal to be etched is 0.04706 kg/h as shown in the following formula.

100kg/h×0.0005-100kg/h×0.98×0.00003=0.04706kg/h

Figure 1 shows an overview of the apparatus for the metal etching step.

Figure 2 is a schematic view showing an evaporation device of a part of a mixed acid aqueous solution refining device.

Fig. 3 is a schematic explanatory view showing an example of a metal etching solution recirculation system.

Fig. 4 is a graph showing the inflow and outflow of substances per basic treatment unit in Example 3.

Figure 5 shows a schematic illustration of another example of a metal etchant recirculation system.

Fig. 6 is a graph showing the inflow and outflow of substances per basic treatment unit in Example 5.

Figure 7 shows a schematic diagram of the coprecipitation mechanism carried out in the present invention.

Claims (8)

A method for producing refined phosphoric acid, comprising the steps of: [1] crystallizing inorganic salts from an aqueous solution of phosphoric acid containing a plurality of metal ions to cause crystallization of metal ions by coprecipitation. Coprecipitation step, the crystallization. The coprecipitation step consists of the following steps: (a) a step of mixing an aqueous solution of an inorganic salt in an aqueous solution of phosphoric acid containing a plurality of metal ions; (b) an organic weak solvent which is further soluble in phosphoric acid and which does not dissolve the inorganic salt. And a step of precipitating crystals of the inorganic salt while coprecipitating the metal ions; (c) a solid-liquid separation step of filtering the crystals of the inorganic salt containing the metal ions; and [2] organically absorbing the filtrate obtained by the filtration An evaporation step of obtaining a purified phosphoric acid by evaporation of a weak solvent and water, wherein the amount of metal ions dissolved in the phosphoric acid/organic weak solvent mixture in the step [1] (b) is less than the phosphoric acid used in the step [1] (a) The amount of metal ions in the aqueous solution. A method for producing a purified phosphoric acid according to the first aspect of the patent application, wherein in the refined phosphoric acid obtained by the method of claim 1, the steps of [1] and [2] are repeated by several operations. A higher concentration of refined phosphoric acid is produced. A method for producing purified phosphoric acid according to claim 1 or 2, wherein a phosphoric acid aqueous solution containing a plurality of metal ions is contained on a weight basis The metal ion is measured from 500 ppm to the upper limit concentration of the metal ions soluble in the aqueous phosphoric acid solution. A method for producing a purified phosphoric acid according to the first or second aspect of the invention, wherein the crystal of the inorganic salt containing the metal ion obtained in the step [1] is dissolved in water, and then the crystal of the inorganic salt is precipitated by cooling. The coprecipitated metal is separated from the inorganic salt, and then the inorganic salt is recovered by filtration, and then the inorganic salt aqueous solution is prepared from the recovered inorganic salt, and reused in the step [1] (a) in the first item of the patent application. The apparatus for producing a refined phosphoric acid according to any one of the above-mentioned items of the present invention, characterized in that it has at least an inorganic salt dissolving tank which dissolves an inorganic salt to prepare an aqueous solution of an inorganic salt; A metal ion aqueous phosphoric acid solution is mixed with an organic weak solvent and an aqueous solution of the inorganic salt to crystallize the inorganic salt and simultaneously crystallize the metal ion coprecipitate. a coprecipitation tank; a filtration device that performs solid-liquid separation by filtering the obtained crystal of the inorganic salt containing the metal ion; and an organic solvent evaporation device having a heating means for evaporating the organic weak solvent and water from the filtrate. The apparatus of claim 5, further comprising an inorganic salt-purifying crystal which dissolves crystals of the inorganic salt containing metal ions filtered in the filtration device in warm water, and then recrystallizes the inorganic salt by cooling again. A flotation device and a filtration device for separating crystals of inorganic salts precipitated in the inorganic salt purification crystallization vessel. A method for recycling an etchant, characterized by comprising the following steps Step: a recovery step of recovering a used mixed solution of a mixed acid solution containing a plurality of metal ions generated in a metal etching step of an aqueous mixed acid solution composed of phosphoric acid, nitric acid, acetic acid, and water, by using a self-mixing acid aqueous solution waste liquid Evaporating most of the nitric acid, acetic acid and water, fractionating into a distillate containing nitric acid, acetic acid and water, and an evaporation step of concentrated phosphoric acid containing phosphoric acid and most metal ions; by means of the device of claim 5 or 6 The coprecipitation separation of the metal ions in the concentrated phosphoric acid to obtain a purification step of the purified phosphoric acid, the solution concentration is adjusted by adding the distillate to the obtained purified phosphoric acid, and then used as a recovery mixed acid aqueous solution in the metal etching step again. The concentration adjustment step. The method for recycling an etching solution according to claim 7 , further comprising the steps of: concentrating the phosphoric acid obtained in the evaporation step, and crystallizing the semi-crystalline water of the phosphoric acid in the melt crystallization apparatus, and then using the filtering device to make the phosphoric acid half The crystal water crystal is subjected to solid-liquid separation, and then the obtained crystal of the semi-crystalline water of phosphoric acid is transferred to the concentration adjustment step, and on the other hand, the concentrated filtrate of the metal ion is moved to the crystallization of the fifth or sixth item of the patent application. . A precipitation step in the coprecipitation tank.