JP4595048B2 - Aqueous solution for pickling, method for producing the same and resource recovery method - Google Patents

Description

  The present invention relates to an aqueous solution for pickling mainly for metals such as titanium and a method for producing the same, and a resource recovery method associated with the production of an aqueous solution for pickling.

  Titanium and stainless steel plates are manufactured by hot rolling or cold rolling, but the rolling increases the hardness and makes it difficult to process, so a process of heating to high temperature and softening (called annealing) is performed. . In hot rolling and annealing, the surface of these metals reacts with oxygen in the air to form an oxide layer (called oxide scale). Called wash). The pickling treatment may be performed not only for removing the oxide scale but also for the purpose of adjusting the surface roughness and gloss.

  For pickling titanium and austenitic stainless steel, an aqueous solution containing nitric acid and hydrofluoric acid (called nitric hydrofluoric acid) is most often used, and the surface is dissolved by immersing the material to be treated. Then, the oxide scale is removed (descaled). The titanium alloy is an alloy containing metals such as aluminum, vanadium, tin, and palladium in addition to titanium, but most of the composition is titanium, so that it can be pickled with nitric hydrofluoric acid.

  When pickling titanium with nitric hydrofluoric acid, the concentration ratio (weight ratio) of nitric acid and hydrofluoric acid is usually adjusted to 10: 1 or more in order to prevent the phenomenon that hydrogen is absorbed into titanium and becomes brittle. In this case, however, titanium is dissolved as a tetravalent fluoride. On the other hand, if absorption of hydrogen is not a problem, pickling may be performed with an aqueous solution of hydrofluoric acid not containing nitric acid. In this case, titanium is dissolved as a trivalent fluoride.

  As mentioned above, nitric acid or hydrofluoric acid is consumed by pickling titanium, titanium alloy, or stainless steel with nitric hydrofluoric acid or hydrofluoric acid, so pickling as the pickling amount increases. Ability is reduced. Therefore, an operation of adding new acid to recover the pickling ability or discarding part or all of the pickling solution as waste acid is performed. However, since the waste acid contains unreacted acid (called free acid) and metal fluoride such as titanium, it cannot be discharged into general sewage as it is. Therefore, conventionally, alkali such as calcium hydroxide is added to neutralize the free acid, and at the same time, the metal fluoride is converted to metal hydroxide and calcium fluoride precipitate, and then landfilled at the final disposal site. Has been done.

  However, in recent years, as the need for pollution prevention and resource saving increases, the effective use of waste acid has been actively researched, and its practical application is gradually progressing. The inventors of the present invention also neutralized the waste acid once used for the pickling of titanium with ammonia to recover titanium as a precipitate of hydroxide, and at the same time, the solution was subjected to electrodialysis or ion exchange to treat nitric acid or A method for regenerating hydrofluoric acid was disclosed in Japanese Patent Application Laid-Open No. 2003-236564. However, according to this method, since the free acid contained in the waste acid is neutralized by ammonia, there is a problem that valuable acid and ammonia are wasted.

  On the other hand, in the silicon wafer manufacturing process of the semiconductor manufacturing industry, nitric acid and hydrogen fluoride are used to remove the work-affected layer on the surface when a wafer is sliced from a single crystal of silicon (silicon silicon) and mechanically polished. Chemical etching is performed using a mixed acid of acid and acetic acid. Conventionally, since the free acid contained in the mixed acid waste liquid is neutralized with an alkali and then discarded, a large amount of cost is required for the landfill treatment of the neutralized sludge and the wastewater treatment.

  Therefore, in recent years, effective use of this waste liquid has been studied from the viewpoint of pollution prevention and resource saving. For example, JP-A-9-302483 discloses a method for recovering nitric acid by a distillation method. JP-A-2005-324164 discloses a method for separating and recovering acetic acid, nitric acid and hydrofluoric acid by an extraction method using an organic solvent.

However, in order to carry out the former method, a special distillation apparatus having excellent corrosion resistance and heat resistance is required, and an increase in processing cost due to a large equipment cost is inevitable. In addition, since the organic solvent is mixed in the acid recovered by the latter method, there is a concern about an adverse effect when the acid is reused for pickling or etching. Furthermore, none of the publications discloses a technique for recovering and using silicon or fluorine from silicon fluoride contained in the waste liquid.
JP 2003-236564 A JP-A-9-302483 JP 2005-324164 A

  Therefore, the first problem to be solved by the present invention is to effectively use the free acid remaining in the aqueous solution used for the pickling of titanium and titanium alloy or the mixed acid waste solution used for the etching of silicon metal. It is to produce an aqueous solution that can be used again for pickling of titanium or the like. A second problem is to recover titanium or silicon dissolved by pickling or etching as a resource.

  In order to use the free acid in the aqueous solution used for the pickling of titanium and titanium alloy or the mixed acid waste solution used for etching silicon metal, the solution is used with an alkali such as ammonia. It is necessary to precipitate titanium and silicon while keeping the acidity without being softened. As a result of various studies on the means, the present inventors have come up with a method for precipitating titanium or silicon in an aqueous solution as hexafluorotitanate or hexafluorosilicate, and the necessary conditions and the like have been investigated in detail by experiments. .

As a result, the titanium dissolved when pickled with nitric hydrofluoric acid is usually partially or mostly contained as hexafluorotitanic acid (H ₂ TiF ₆ ). It was found that it can be precipitated as a hardly soluble hexafluorotitanate by adding the ions. Similarly, silicon dissolved using a mixed acid of nitric acid, hydrofluoric acid and acetic acid is partly or mostly hexafluorosilicic acid (H ₂ SiF ₆ ). It has also been found that by adding ions, it can be precipitated as sparingly soluble hexafluorosilicate.

For example, when potassium is used as the alkali metal, titanium is precipitated as potassium hexafluorotitanate (K ₂ TiF ₆ ), and silicon is precipitated as potassium hexafluorosilicate (K ₂ SiF ₆ ). In order to add potassium ions, an electrolyte such as potassium fluoride (KF) may be used, and the precipitation reaction in this case is presumed to be according to the following formula (1) or (2). Moreover, since hydrogen fluoride (HF) is produced by this precipitation reaction, the pickling ability of titanium is enhanced. If potassium nitrate (KNO ₃ ) is used instead of potassium fluoride, the precipitation reaction of potassium hexafluorotitanate becomes the following formula (3) or (4), and nitric acid (also useful for pickling titanium) ( HNO ₃ ) is produced.
H ₂ TiF ₆ + 2KF → K ₂ TiF ₆ + 2HF (1) Formula H ₂ SiF ₆ + 2KF → K ₂ SiF ₆ + 2HF (2) Formula H ₂ TiF ₆ +2 KNO ₃ → K ₂ TiF ₆ + 2HNO ₃ (3) Formula H ₂ SiF ₆ + 2KNO ₃ → K ₂ SiF ₆ + 2HNO ₃ (4) Formula

Hexafluorotitanic acid (H ₂ TiF ₆ ) or hexafluorosilicic acid (H ₂ SiF ₆ ) reacting in the above formulas (1) to (4) is a mixed acid mainly composed of nitric acid and hydrofluoric acid. Alternatively, it is a compound produced when metal silicon is dissolved, and the molar ratio of fluorine (F) to titanium (Ti) or silicon (Si) in the compound is 6: 1. However, when almost no unreacted hydrofluoric acid is dissolved by dissolution, a compound having this ratio of less than 6: 1 is formed and precipitated as potassium hexafluorotitanate or potassium hexafluorosilicate. The amount of silicon is reduced. Therefore, in such a case, if hydrogen fluoride (HF) or fluoride (KF, etc.) is added so that the molar ratio of fluorine and titanium or silicon contained in the aqueous solution is 6: 1 or more. The amount of titanium or silicon deposited as potassium hexafluorotitanate or potassium hexafluorosilicate can be increased.

  After separating the hardly soluble hexafluorotitanate or hexafluorosilicate precipitated as described above by an appropriate method, nitric acid, hydrofluoric acid or water is added to the obtained aqueous solution as necessary. Can be reused for pickling of metals such as titanium. Note that it is not always necessary to separate the precipitated hexafluorotitanate or hexafluorosilicate for use in pickling titanium or the like, and pickling can be performed while coexisting.

  On the other hand, when the pickling of titanium is performed with an aqueous solution of hydrofluoric acid not containing nitric acid, titanium is dissolved as a trivalent fluoride as described above. In the form of hexafluorotitanate. For example, nitric acid or oxygen can be used as an oxidizing agent for that purpose.

  By the way, in the reactions of the above-mentioned formulas (1) and (3), two molecules of potassium fluoride or potassium nitrate react with one molecule of hexafluorotitanic acid, but in fact, a considerably excessive amount of potassium fluoride. In addition, precipitation of potassium hexafluorotitanate hardly occurs unless potassium nitrate (that is, potassium ion) is added. Therefore, a large amount of potassium ions is contained in the aqueous pickling solution after separating potassium hexafluorotitanate.

  When titanium or a titanium alloy is pickled using this pickling aqueous solution, hexafluorotitanic acid generated by dissolving titanium reacts with potassium ions to precipitate potassium hexafluorotitanate. When titanium or titanium alloy strips are pickled continuously, a portion of the precipitated potassium hexafluorotitanate is carried out of the pickling tank along with the strips. It is inevitable that the price will drop. On the other hand, if it is assumed that stainless steel is pickled using the aqueous solution for pickling and discarded after pickling, a large amount of potassium contained in the waste liquid is wasted.

Therefore, as a result of studying a method for recovering potassium ions contained in a large amount in the aqueous pickling solution after separating the potassium hexafluorotitanate, the present inventors added hexafluorosilicate ions to the aqueous solution. Then, a method for precipitating potassium as potassium hexafluorosilicate and separating and recovering it was found. That is, since potassium hexafluorosilicate precipitates even at a low potassium ion concentration such that potassium hexafluorotitanate hardly precipitates, most of potassium ions can be recovered. The precipitation reaction at this time is presumed to be according to the following equation (5).
2K ⁺ + SiF ₆ ²⁻ → K ₂ SiF ₆ (5) Formula

  In the above formula (5), hexafluorosilicate, potassium fluoride and potassium nitrate which react in the formulas (2) and (4) are dissociated into ions, and hexafluorosilicate ions and potassium ions are converted into ions. This is a reaction formula (ion reaction formula) when they are combined to form potassium hexafluorosilicate.

  The present inventor further used the waste liquid for pickling titanium and stainless steel as another means for effectively using the free acid remaining in the mixed acid waste liquid used for etching silicon metal. Later, the method of adding alkali metal ions was also examined. When titanium is pickled, hexafluorotitanic acid produced by the pickling of titanium and hexafluorosilicic acid contained before the pickling are contained in the aqueous solution. Precipitate as fluorosilicate.

  However, as described above, in order to precipitate most of the titanium in the aqueous solution as hexafluorotitanate, it is necessary to add a large excess of alkali metal ions, so the aqueous solution after separating the precipitated salt A high concentration of alkali metal ions remains inside. Therefore, in order to reduce the alkali metal ion concentration, it is necessary to add hexafluorosilicate ions to precipitate and separate as hexafluorosilicate.

  As described above, in the aqueous solution for pickling produced by using the reactions of the formulas (1) to (4), ions of alkali metals such as potassium are contained in addition to the main components hydrofluoric acid and nitric acid. , Hexafluorotitanate ions and hexafluorosilicate ions are included, and their concentrations vary depending on the production conditions.

Next, as a result of studying a method of recovering titanium and silicon as resources from precipitated and separated hexafluorotitanate and hexafluorosilicate, the present inventor added ammonia (NH ₃ ) to these salts. Can be converted into titanium hydroxide (Ti (OH) ₄ ) or silicic acid (SiO ₂ .nH ₂ O) precipitate, and this is separated and washed with water, and then heated and fired. Has been found to be able to change to titanium dioxide (TiO ₂ ) or silicon dioxide (SiO ₂ ). Ammonia may be added either as an aqueous solution or as a gas, but water needs to coexist. A series of reactions when potassium is used as the alkali metal is presumed to be according to the following formulas (6) to (9) (where n = 0.5 to 1.0).
K ₂ TiF ₆ + 4NH ₃ + 4H ₂ O → Ti (OH) ₄ + 2KF + 4NH ₄ F (6) Formula K ₂ SiF ₆ + 4NH ₃ + 4H ₂ O → SiO ₂ .nH ₂ O + 2KF + 4NH ₄ F
+ (2-n) H ₂ O (7) Formula Ti (OH) ₄ → TiO ₂ + 2H ₂ O (8) Formula SiO ₂ · nH ₂ O → SiO ₂ + nH ₂ O (9) Formula

As can be seen from the reactions of the above formulas (6) and (7), the aqueous solution after separation of titanium hydroxide or silicic acid contains potassium fluoride (KF) and ammonium fluoride (NH ₄ F). . Therefore, when an alkali metal hydroxide such as potassium hydroxide (KOH) is added to this, ammonium fluoride and potassium hydroxide react as shown in the following formula (10), and potassium fluoride and ammonia are reacted. (NH ₃ ) is produced. Further, when an alkaline earth metal hydroxide such as calcium hydroxide (Ca (OH) ₂ ) is added instead of potassium hydroxide, ammonium fluoride and hydroxide are expressed as shown in the following formula (11). Calcium reacts to produce calcium fluoride (CaF ₂ ) and ammonia.
NH ₄ F + KOH → KF + NH ₃ + H ₂ O (10) Formula 2NH ₄ F + Ca (OH) ₂ → CaF ₂ + 2NH ₃ + 2H ₂ O (11) Formula

  The ammonia produced by the reactions of the above formulas (10) and (11) can be separated and recovered by a method such as steam distillation and reused for the reactions of the above formulas (6) and (7). Further, most of the calcium fluoride produced by the reaction of the formula (11) is precipitated, so that it can be separated by a method such as filtration and reused for raw materials for producing hydrofluoric acid. After all, since the aqueous solution after separating titanium hydroxide, ammonia and calcium fluoride contains only potassium fluoride, it can be reused for the reaction of the formulas (1) and (2).

  Further, an aqueous solution of hydrofluoric acid and potassium hydroxide can be obtained by subjecting this aqueous solution to electrodialysis treatment or ion exchange treatment. A technique for obtaining an aqueous solution of an acid and an alkali from an aqueous solution of a salt such as potassium fluoride by electrodialysis or ion exchange is disclosed in, for example, the aforementioned Japanese Patent Application Laid-Open No. 2003-236564. Apply. By these treatments, one molecule of hydrogen fluoride (HF) and one molecule of potassium hydroxide (KOH) are generated from one molecule of potassium fluoride (KF). The obtained aqueous solution of hydrogen fluoride (that is, hydrofluoric acid) can be reused for pickling of titanium or the like, and potassium hydroxide can be reused for the reaction of the above formula (10).

  This invention is the invention completed based on the above examination, Comprising: It makes the summary the aqueous solution for pickling of postscript (1)-(9), its manufacturing method, and a resource recovery method.

(1) A volume of 1 dm ³ contains 10 to 600 g of nitric acid, 1 to 200 g of hydrofluoric acid and 0.02 to 200 g of alkali metal ions, and less than 50 g of hexafluorotitanate ions and 50 g of hexafluorosilicate ions. An aqueous solution for pickling characterized by containing one or both of less.

(2) The volume of 1 dm ³ contains 1 to 200 g of hydrofluoric acid, 0.02 to 200 g of alkali metal ions and less than 50 g of hexafluorotitanate ions, and further contains less than 50 g of hexafluorosilicate ions. Or an aqueous solution for pickling characterized by not containing hexafluorosilicate ions.

  (3) The aqueous pickling solution according to (1) above, which is produced by the method described in (5) or (6) below.

  (4) The pickling aqueous solution according to (2) above, which is produced by the method described in (7) or (8) below.

(5) A part or all of the following steps A, B and C are carried out using an aqueous solution containing nitric acid and hydrofluoric acid and further containing titanium and / or silicon fluoride as a raw material. A method for producing an aqueous solution for pickling:
(Step A) Step of adding hydrogen fluoride to the aqueous solution as necessary:
(Step B) A step of adding alkali metal ions to the aqueous solution: and (Step C) A step of separating a precipitate generated by performing the steps A and B.

(6) The method for producing an aqueous solution for pickling according to the above (5), which further comprises the steps D and E described later:
(Step D) Step of adding hexafluorosilicate ion to the aqueous solution from which the precipitate has been separated in Step C: and (Step E) Step of separating the precipitate generated in Step D.

(7) A method for producing an aqueous solution for pickling, wherein an aqueous solution containing hydrofluoric acid and a fluoride of titanium is used as a raw material, and part or all of the following steps F, G, H and I are performed:
(Step F) Step of adding hydrogen fluoride to the aqueous solution as necessary:
(Step G) Step of adding alkali metal ions to the aqueous solution:
(Step H) A step of oxidizing the trivalent titanium fluoride contained in the aqueous solution to convert it to a tetravalent titanium fluoride: and (Step I) performing steps F, G and H described above. Separating the precipitate generated by the step.

(8) The method for producing an aqueous solution for pickling according to the above (7), which further comprises the steps J and K described later:
(Step J) A step of adding hexafluorosilicate ions to the aqueous solution from which the precipitate has been separated in Step I above: and (Step K) a step of separating the precipitate produced in Step J above.

(9) A method for recovering resources accompanying the production of an aqueous solution for pickling, characterized in that a part or all of the following steps L, M, N, O, P and Q are performed
(Step L) Step C according to (5) above and / or Step E according to (6) above and / or Step I according to (7) above and / or (8 above) Step of adding ammonia to the precipitate separated by the step K described in
(Process M) The process of isolate | separating the deposit produced by the said process L:
(Step N) Steps of heating and baking after washing the precipitate separated in the step M:
(Step O) Step of separating ammonia after adding an alkali metal hydroxide and / or an alkaline earth metal hydroxide, if necessary, to the aqueous solution from which the precipitate has been separated in the above step M :
(Step P) Step of separating the precipitate produced in the step O: and (Step Q) Step of electrodialysis or ion exchange treatment of the step O or the aqueous solution obtained in the steps O and P .

  Using the aqueous solution for pickling of the present invention, the production method thereof, and the resource recovery method, an aqueous solution obtained by pickling titanium and a titanium alloy, or a mixed acid waste solution used for etching metal silicon, as a raw material. An aqueous solution for use in the production can be produced. Moreover, titanium dioxide, silicon dioxide, hydrofluoric acid, calcium fluoride, etc. can be recovered as resources by the manufacturing process and the addition process. Therefore, the industrial waste generation amount can be greatly reduced, and the environmental load can be reduced. Thus, a great industrial and social effect can be obtained.

It is the figure which showed an example of the procedure of the manufacturing method of nitric acid and a hydrofluoric acid type pickling aqueous solution, and a resource recovery method. It is the figure which showed an example of the procedure of the manufacturing method of nitric acid and a hydrofluoric acid type pickling aqueous solution, and a resource recovery method. It is the figure which showed an example of the procedure of the manufacturing method of the aqueous solution for pickling of nitric acid, a hydrofluoric acid, and an acetic acid type, and a resource recovery method. It is the figure which showed an example of the procedure of the manufacturing method and resource recovery method of the hydrofluoric acid type pickling aqueous solution. It is sectional drawing which showed typically the structure of the apparatus used for a chemical reaction and distillation. It is sectional drawing which showed the structure of the electrodialysis apparatus typically. It is sectional drawing which showed the structure of the ion exchange column typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Treatment tank 2 Stirrer 3 Heater 4 Temperature sensor 5 pH sensor 6 Cooler 7 Cooling water 8 Distillate receiving tank 9 Distillate 10 Intake pipe 11 Discharge pipe 12 Gas infeed pipe 13 Gas exhaust pipe 14-1-3 Valve 15 Electrolytic cell 16 Anode 17 Cathode 18-1, 2 Cation exchange membrane 19 Anion exchange membrane 20 DC power supply 21 Conductor 22-25 Cell (small chamber)
26 Ion Exchange Resin Container 27-1, 2 Perforated Plate 28 Liquid Inlet Pipe 29 Liquid Discharge Pipe 30

The pickling aqueous solution according to the present invention is divided into a nitric hydrofluoric acid aqueous solution whose main components are nitric acid and hydrofluoric acid, and a hydrofluoric acid aqueous solution whose main components are hydrofluoric acid. Both contain 1 to 200 g / dm ³ of hydrofluoric acid as an essential component. Hydrofluoric acid has a function of activating the metal surface and eluting the metal as ions, but at a concentration of less than 1 g / dm ³ , the function is weak, so that it takes a long time for pickling the metal. If dm ³ is exceeded, the dissolution reaction of metals such as titanium becomes so intense that it becomes difficult to control.

In the case of the former aqueous solution of nitric hydrofluoric acid, 10 to 600 g / dm ³ of nitric acid is contained in addition to hydrofluoric acid. Nitric acid has a function of promoting a reaction in which a metal is eluted as an ion. However, at a concentration of less than 10 g / dm ³ , the function is weak, so that it takes a relatively long time for pickling the metal, and 600 g / dm ³ If the concentration exceeds 1, the effect is not only saturated, but a large amount of nitrogen oxide gas is generated, which is not preferable in the working environment.

The aqueous pickling solution according to the present invention contains 0.02 to 200 g / dm ³ of alkali metal ions. Alkali metal ions are added to precipitate and separate titanium or silicon in the raw material aqueous solution as sparingly soluble hexafluorotitanate or hexafluorosilicate, but the residual concentration is 0.02 g / dm ^3. Although it is technically possible to make it less than this, it causes an increase in manufacturing cost, which is not preferable economically. Further, if it remains at a concentration exceeding 200 g / dm ³ , the amount lost in the process of using or discarding the produced pickling aqueous solution becomes excessive, which is also not economically preferable.

  As the alkali metal, potassium, sodium and rubidium can be used, but potassium is most recommended from the viewpoint of the effect and cost of addition. Sodium has relatively high solubility of hexafluorotitanate and low solubility of fluoride, so that it is difficult to use alone, but it can be used in combination with potassium. On the other hand, rubidium has an excellent effect but is expensive, and its use is limited in terms of cost.

  In the production of an aqueous solution for pickling, fluoride is most recommended as an electrolyte used for adding alkali metal ions, and nitrate is also recommended in the case of a nitric hydrofluoric acid aqueous solution. However, other electrolytes (for example, chloride, sulfate, etc.) may be used as long as they do not adversely affect the pickling of the material to be treated.

  Table 1 shows examples of the pickling aqueous solution and the method for producing the same according to the present invention. No. in Table 1 The aqueous pickling solutions 1 to 8 all use potassium fluoride as an electrolyte for adding alkali metal ions to the raw material aqueous solution, and deposit titanium as potassium hexafluorotitanate and silicon as potassium hexafluorosilicate. -The example manufactured by separating is shown. Each example will be described in more detail below.

  No. in Table 1 Example 1 was prepared by using an aqueous solution obtained by pickling titanium using nitric hydrofluoric acid as a raw material, adding potassium fluoride thereto, and separating the precipitated potassium hexafluorotitanate. Is shown. At this time, the amount of hexafluorotitanate ions remaining in the pickling aqueous solution of the upper composition produced by adding potassium fluoride so that the molar ratio of potassium ions to titanium is about 6 to 10 or A small amount of potassium in remains.

In addition, the potassium ion remaining in the pickling aqueous solution of the lower composition produced by adding potassium fluoride so that the molar ratio is about 2 is small, but the hexafluorotitanate ion is A large amount remains. Incidentally, as used herein, multimers, the term minor and trace, respectively, schematic 10 g / dm ³ or more, which means that in a concentration of less than 1 to 10 g / dm ³ and 1 g / dm ^3.

  No. in Table 1 The aqueous solution for pickling of No. 2 is the above-mentioned No.2. An example is shown in which hexafluorosilicate ions are added to an aqueous pickling solution having an upper composition of 1, and the precipitated potassium hexafluorosilicate is separated. In this case, if the molar ratio of potassium ion to silicon is about 2, the potassium ion, hexafluorotitanate ion and hexafluorosilicate ion remaining in the produced pickling aqueous solution are all Can be in small or trace amounts.

  At this time, if excessive hexafluorosilicate ions are added so that the molar ratio of potassium ions to silicon is less than 2, it is possible to further reduce potassium ions in the pickling aqueous solution. Cannot be removed. This is presumed to be because not all potassium hexafluorosilicate produced by the reaction of the above formula (5) precipitates but dissociates into potassium ions and hexafluorosilicate ions after some of them are dissolved. .

  No. in Table 1 The aqueous solution for pickling of No. 3 uses as a raw material a waste liquid obtained by etching metal silicon (silicon wafer) using a mixed acid mainly composed of nitric acid, hydrofluoric acid and acetic acid, and potassium fluoride is added thereto. An example is shown in which silicon is precipitated and separated as potassium hexafluorosilicate. No. The aqueous solution for pickling No. 4 uses the above mixed acid waste solution to pickle stainless steel that does not contain titanium, and then potassium potassium fluoride is added thereto to precipitate silicon as potassium hexafluorosilicate. The example manufactured by isolate | separating is shown. In these examples, if potassium fluoride is added so that the molar ratio of potassium ions to silicon is about 2, small amounts or trace amounts of potassium ions and hexafluorosilicate ions remaining in the produced pickling aqueous solution are used. Can be.

  No. in Table 1 No. 5 aqueous solution for pickling After pickling titanium using the same mixed acid waste liquid as No. 3, potassium fluoride was added, and it was produced by separating and separating silicon as potassium hexafluorosilicate and titanium as potassium hexafluorotitanate. An example is shown. The aqueous solution for pickling having the upper composition is obtained by adding 6-10 times the number of moles of titanium and 3 times the number of moles of silicon to add potassium ions, and remains in the aqueous solution for pickling. Hexafluorotitanate ions and hexafluorosilicate ions are in small or trace amounts, but a large amount of potassium ions remain. The aqueous solution for pickling having the lower composition is one in which the number of moles of the above potassium ions is about three times the number of moles of silicon, and the potassium ions remaining in the pickling aqueous solution and hexafluorosilicic acid. Although the amount of ions is small, a large amount of hexafluorotitanate ions remain.

  No. in Table 1 No. 6 aqueous solution for pickling is the same as the above No. 1. 5 shows an example produced by adding hexafluorosilicate ions to an aqueous pickling solution having the upper composition of 5, and separating the precipitated potassium hexafluorosilicate. In this case, if the molar ratio of potassium ion to silicon is about 2, small amounts or trace amounts of potassium ion, hexafluorosilicate ion and hexafluorotitanate ion remaining in the produced pickling aqueous solution are used. Can be.

  No. in Table 1 The aqueous solution for pickling of No. 7 is made from an aqueous solution obtained by pickling titanium using hydrofluoric acid, and potassium fluoride and nitric acid (oxidant) are added thereto to separate the precipitated potassium hexafluorotitanate. The example manufactured by doing is shown. At this time, the amount of hexafluorotitanate ions remaining in the pickling aqueous solution of the upper composition produced by adding potassium fluoride so that the molar ratio of potassium ions to titanium is about 6 to 10 or A small amount of potassium in remains.

  In addition, the potassium ion remaining in the pickling aqueous solution of the lower composition produced by adding potassium fluoride so that the molar ratio is about 2 is small, but the hexafluorotitanate ion is A large amount remains. In the above example, nitric acid used as an oxidizing agent needs to be added in an amount sufficient to change the trivalent titanium fluoride contained in the raw material aqueous solution to the tetravalent titanium fluoride. .

  No. in Table 1 The aqueous pickling solution of No. 8 is the above-mentioned No. 7 shows an example produced by adding hexafluorosilicate ion to an aqueous solution for pickling having an upper composition of 7 to separate precipitated potassium hexafluorosilicate. In this case, if the molar ratio of potassium ions to silicon is about 2, small amounts or trace amounts of potassium ions, hexafluorotitanate ions and hexafluorosilicate ions remaining in the produced pickling aqueous solution are used. Can be.

When an aqueous solution for pickling is produced by the method of the present invention, it is difficult to completely eliminate hexafluorotitanate ions and hexafluorosilicate ions, and it is not necessary. The permissible concentration of hexafluorotitanate ions is difficult to limit strictly, but if it exceeds 50 g / dm ³ , the tendency of the pickling rate of titanium and titanium alloy to decrease is not preferable. Further, although it is difficult to strictly limit the allowable concentration of hexafluorosilicate ion, if it exceeds 50 g / dm ³ , the tendency of the pickling rate of stainless steel to decrease is not preferable.

The aqueous pickling solution according to the present invention contains hydrofluoric acid and nitric acid as main components and alkali metal ions as additive components, but other components do not adversely affect the pickling of titanium and titanium alloys. If so, it may be added. For example, less than 200 g / dm ³ of non-oxidizing acid such as hydrochloric acid or sulfuric acid may be added to a hydrofluoric acid-based or nitric hydrofluoric acid-based aqueous solution, and the generation of nitric oxide gas is suppressed in the nitric hydrofluoric acid-based aqueous solution. Therefore, urea, hydrogen peroxide or the like less than 100 g / dm ³ may be added.

In addition, when a mixed acid waste solution containing nitric acid, hydrofluoric acid and acetic acid as a main component after etching silicon metal is used as a raw material, a large amount of acetic acid is contained in the pickling aqueous solution produced by the method of the present invention. . Since acetic acid tends to reduce the pickling rate of titanium or stainless steel, the concentration is preferably less than 200 g / dm ³ .

  Next, among the representative examples of the pickling aqueous solution shown in Table 1 and the manufacturing method thereof (No. 2, No. 5, and No. 8 in Table 1), the manufacturing method and accompanying resources The example which illustrated the procedure of the collection | recovery method is shown in FIGS. FIG. 1 shows No. 1 in Table 1 above. In addition to producing a pickling aqueous solution from a waste solution obtained by pickling titanium using a fluorinated hydrofluoric acid aqueous solution, hexafluorotitanate and hexafluoro produced in the process An example of a procedure for recovering titanium dioxide, silicon dioxide, etc. from silicate as a resource is shown. Below, according to the procedure of a figure, the implementation content of the manufacturing method of an aqueous solution for pickling and a resource recovery method is demonstrated more concretely.

When the amount of titanium contained in the raw material nitric hydrofluoric acid aqueous solution is large and the amount of free hydrofluoric acid is small, hydrogen fluoride is added and potassium fluoride is added. In order to add hydrogen fluoride, it is usually sufficient to use hydrofluoric acid having a concentration of about 48 to 50%. In addition, it is easy to add potassium fluoride in an aqueous solution having a concentration of about 1 to 2 mol / dm ³ , but in order to reduce the concentration of the aqueous solution as much as possible, it can be added and dissolved with potassium fluoride chemicals. Also good.

The amount of hydrogen fluoride added should be such that the total amount of fluorine in the waste liquid and hydrogen fluoride and potassium fluoride to be added and the molar ratio of titanium (F / Ti molar ratio) is 6 or more. . The addition amount of potassium fluoride is such that the molar ratio of potassium to titanium (K / Ti molar ratio) is 6 or more and the concentration of potassium in the aqueous solution is 0.6 mol / dm ³ or more. Good. However, even if the addition amount does not satisfy these conditions, potassium hexafluorotitanate is produced (the production amount is relatively small).

  When producing and separating potassium hexafluorotitanate on an industrial scale, facilities and devices for efficiently collecting the precipitate of potassium hexafluorotitanate that settles in the lower part of the production treatment tank (for example, precipitation A chamber designed to accumulate and a pump or piping to send the precipitate from the chamber with the solution to the filtration device.

  When the precipitate of potassium hexafluorotitanate is separated by filtration, the precipitate on the filter paper or filter cloth is washed with water, transferred to a suitable container, and water and ammonia are added and mixed. The amount of water to be added does not need to be particularly strictly defined, but about 300 to 1000 times the weight of titanium contained in the precipitation is appropriate. Ammonia needs to be added so that the pH of the solution is 9 or more (more desirably 10 or more). Ammonia can be easily added as a 10 to 28% aqueous solution, but ammonia gas generated during the regeneration process according to the method of the present invention may be blown.

After adding and mixing ammonia, it is necessary to heat the solution to 60 to 100 ° C. and hold it for about 30 minutes to 2 hours. Then, after cooling to room temperature to around 50 ° C. and measuring the pH again, when the pH is less than 9, after adding ammonia so that it becomes 9 or more, the generated titanium hydroxide precipitate is filtered, etc. Separate by the method. The separated titanium hydroxide precipitate can be converted into titanium dioxide (TiO ₂ ) by thoroughly washing with water and then heating at 800 to 1000 ° C. for 1 to 5 hours using an electric furnace or the like.

In the above treatment, when the pH of the solution to which ammonia is added is less than 9 or the heating after the addition of ammonia is omitted, a large amount of fluorine is contained in the generated titanium hydroxide precipitate. -When titanium dioxide is obtained by firing, a part of titanium is volatilized as titanium tetrafluoride (TiF ₄ ), and the recovery rate decreases.

  As an apparatus for industrially performing a process of adding ammonia and water to a precipitate of potassium hexafluorotitanate to convert it to titanium hydroxide, an apparatus having a schematic cross section shown in FIG. 5 is recommended. . A mixture of potassium hexafluorotitanate precipitate and water is charged into the treatment tank 1 through the feed pipe 10, and then the solution is stirred with the stirrer 2. At the same time, the pH of the solution is measured using the pH sensor 5. While adding ammonia water from the feed pipe 10. Instead of ammonia water (or together with ammonia water), ammonia gas may be blown from the gas inlet pipe 12.

  When the pH of the solution becomes 9-10, the solution is heated using the heater 3 and held at 60-100 ° C. for 30 minutes to 2 hours. Thereafter, the pH is measured while cooling to room temperature to around 50 ° C., and when the pH is less than 9, after adding ammonia so that it becomes 9 or more, the generated titanium hydroxide precipitate is discharged together with the solution. The tube 11 is discharged out of the device and transferred to a filtration device or the like. The ammonia gas evaporated together with the water vapor from the liquid level is led from the gas discharge pipe 13 to the cooler 6 to become ammonia water, which is stored in the distillate receiving tank 8.

  The apparatus of FIG. 5 can also be used for the distillation of ammonia. That is, after the titanium hydroxide is separated, the solution is charged into the treatment tank 1 from the feed pipe 10, and the temperature of the solution becomes 80 to 100 ° C. using the heater 3 while stirring the solution with the stirrer 2. To heat. Further, air and water vapor at around 100 ° C. are sent from the gas charging pipe 12 to evaporate ammonia in the solution together with the water vapor, and this is led from the gas discharge pipe 13 to the cooler 6 to become ammonia water. Save to 8.

  After confirming that the ammonia in the solution has all evaporated and the pH of the solution is near neutral, a small amount of the solution in the treatment tank is collected and analyzed for the ammonium ion concentration. Is calculated. Next, an amount of potassium hydroxide (aqueous solution) necessary for changing all of the ammonium ions (that is, ammonium fluoride) into ammonia and potassium fluoride by the reaction of the above-described formula (10) is supplied from the feeding pipe 10. After the addition, the solution is heated so that the temperature of the solution becomes 80 to 100 ° C. using the heater 3 while stirring the solution with the stirrer 2. Further, air and water vapor at around 100 ° C. are sent from the gas charging pipe 12 to evaporate ammonia in the solution together with the water vapor, and this is led from the gas discharge pipe 13 to the cooler 6 to become ammonia water. Save to 8.

  As an apparatus for electrodialyzing a solution from which ammonia has been separated, for example, an apparatus having a schematic diagram (side view) shown in FIG. 6 is recommended. The electrolytic cell 15 of this apparatus is composed of four cells (chambers) 22 to 25 separated by two cation exchange membranes 18-1 and 18-2 and one anion exchange membrane 19, and the anode 16 and A DC voltage is supplied to the cathode 17 from the DC power supply 20 through the conducting wire 21.

Here, an aqueous solution of an acid such as sulfuric acid (H ₂ SO ₄ ) is placed in the cell 24 provided with the anode 16, and an aqueous solution of low-concentration potassium hydroxide (KOH) is placed in the cell 25 provided with the cathode 17. A cell 22 formed between the cation exchange membrane 18-2 and the anion exchange membrane 19 is filled with a solution after separating ammonia (that is, an aqueous solution of potassium fluoride). -1 and the anion exchange membrane 19 are filled with a low concentration hydrofluoric acid aqueous solution or pure water.

When a DC voltage is applied between the anode 16 and the cathode 17 in this state, fluoride ions (F ⁻ ) generated by dissociation of potassium fluoride in the aqueous solution of the cell 22 move toward the anode by electric force. And enters the cell 23 through the anion exchange membrane 19. At the same time, hydrogen ions (H ⁺ ) generated by dissociation of sulfuric acid in the cell 24 move toward the cathode by an electric force, and enter the cell 23 through the cation exchange membrane 18-1. In this way, fluoride ions and hydrogen ions entering the cell 23 are combined to form hydrofluoric acid (HF), and its concentration increases as the electrodialysis proceeds. Can be reused for pickling such as titanium.

In addition, potassium ions (K ⁺ ) generated by dissociation of potassium fluoride in the aqueous solution of the cell 22 move toward the cathode by an electric force and enter the cell 25 through the cation exchange membrane 18-2. At this time, in the cell 25, hydroxide ions (OH ⁻ ) are generated on the cathode surface by the electrode reaction shown in the following formula (12) (at the same time, hydrogen gas is generated). Combines with ions to form potassium hydroxide (KOH).
2H ₂ O + 2e → 2OH ⁻ + H ₂ (12) In this way, the concentration of the potassium hydroxide aqueous solution in the cell 25 becomes higher as the electrodialysis progresses. Can be reused for.

On the other hand, in the cell 24, hydrogen ions (H ⁺ ) are generated on the surface of the anode 16 by the electrode reaction shown in the following formula (13) (at the same time, oxygen gas is generated), and the hydrogen ions entering the cell 23 are replenished. Therefore, the concentration of sulfuric acid hardly changes.
2H ₂ O → 4H ⁺ + O ₂ + 4e (13)

Next, as an apparatus for ion-exchange treatment of a solution from which ammonia has been separated, for example, an apparatus having a schematic diagram (cross-sectional view) shown in FIG. The solution injected from the liquid inlet tube 28 at the upper part of the apparatus flows out of the liquid discharge pipe 29 at the lower part of the apparatus through the porous plate 27-1, the ion exchange resin 30 and the porous plate 27-2. As the ion exchange resin, either a cation exchange resin or an anion exchange resin may be used. In the case of an anion exchange resin, a functional group whose functional group has been converted to OH ⁻ type in advance is used.

Fluoride ions (F ⁻ ) generated by dissociation of potassium fluoride in the ammonia-separated solution are replaced with hydroxide ions (OH ⁻ ) captured by the functional groups of the anion exchange resin, and the following (14 As shown in the formula, potassium hydroxide (KOH) is produced and can be reused for the ammonia distillation treatment. In the formula (14), R ⁺ represents a positively charged anion exchange resin substrate.
^{KF + R + OH - → KOH} + R + F - (14) the formula

Next, when water (H ₂ O) is injected from the liquid inlet tube 28 at the upper part of the apparatus, fluoride ions (F ⁻ ) captured by the functional group of the anion exchange resin are expressed by the following formula (15). Thus, hydrofluoric acid (HF) flows out and can be reused for pickling such as titanium. The anion exchange resin returns to the OH ⁻ type again.
H ₂ O + R ⁺ F ⁻ → HF + R ⁺ OH ⁻ (15) Formula

  On the other hand, the solution after separating the potassium hexafluorotitanate was No. 1 in Table 1 above. 1 in the case of excessive addition of potassium fluoride so that the molar ratio of potassium ion to titanium is 6 to 10 as in the example of composition 1. The pickling aqueous solution contains a large amount of potassium ions (potassium fluoride). When this aqueous solution is used for pickling of titanium or a titanium alloy, titanium dissolved by the pickling immediately precipitates as potassium hexafluorotitanate. Therefore, in industrial pickling operations, measures and facilities relating to the recovery of precipitated potassium hexafluorotitanate are required.

Therefore, in order to reduce the potassium ions contained in a large amount, hexafluorosilicate is added to precipitate potassium hexafluorosilicate in the method for producing the pickling aqueous solution shown in FIG. Since hexafluorosilicate is a strong acid, most of it is dissociated into hydrogen ions (H ⁺ ) and hexafluorosilicate ions (SiF ₆ ²⁻ ) in the aqueous solution as shown in the following formula (16). Silicate ions are combined with potassium ions by the reaction of the above-described formula (5) to form potassium hexafluorosilicate.
H ₂ SiF ₆ → 2H ⁺ + SiF ₆ ²⁻ (16) Formula

Further, instead of hexafluorosilicate, a readily soluble salt such as ammonium hexafluorosilicate ((NH ₄ ) ₂ SiF ₆ ) may be added. In this case, the dissolved salt is dissociated as shown in the following formula (17) to generate hexafluorosilicate ions.
(NH ₄ ) ₂ SiF ₆ → 2NH ₄ ⁺ + SiF ₆ ²⁻ (17) Formula

In addition, the hexafluorosilicic acid to be added does not necessarily have to be a high-purity chemical. For example, waste liquid obtained by dissolving glass with hydrofluoric acid or metal silicon dissolved with a mixed acid containing hydrofluoric acid and nitric acid. Waste liquid (for example, silicon wafer etching waste liquid) may be added.
In these waste liquids, hexafluoro produced by the dissolution of silicon dioxide (SiO ₂ ) and metal silicon (Si), which are the main components of glass, by the reactions of the following formulas (18) and (19): Contains silicic acid.
SiO ₂ + 6HF → H ₂ SiF ₆ + 2H ₂ O (18) Formula Si + 6HF + 2HNO ₃ → H ₂ SiF ₆ + 2HNO ₂ + 2H ₂ O (19)

On the other hand, not the method of directly adding hexafluorosilicate ions themselves as described above, but glass or metal silicon is immersed in the solution after separating the potassium hexafluorotitanate, and the above (18 ) Or (19), or an indirect addition method in which hexafluorosilicic acid is generated by the reaction of the formula (19), or a direct method and an indirect method may be used in combination.

  The amount of hexafluorosilicic acid added may be such that the molar ratio of potassium in the solution to silicon of the added hexafluorosilicic acid (K / Si molar ratio) is about 2, but it is not necessarily limited to this. There is no. When the K / Si molar ratio exceeds 2, a relatively large amount of potassium remains in the solution and a relatively small amount of hexafluorosilicate ions. On the other hand, when the K / Si molar ratio is less than 2, the amount of potassium remaining in the solution is relatively small, and the amount of hexafluorosilicate ions is relatively large.

  After the produced precipitate of potassium hexafluorosilicate is separated by a method such as filtration, the solution can be reused as an aqueous solution for pickling. On the other hand, the processing conditions for obtaining silicon dioxide and hydrofluoric acid from the separated potassium hexafluorosilicate are the same as in the case of the above-mentioned potassium hexafluorotitanate, and thus the description thereof is omitted. Although FIG. 1 shows a procedure for separately treating the separated potassium hexafluorotitanate and potassium hexafluorosilicate, it is also possible to treat them together, in which case titanium dioxide and titanium dioxide are treated together. A mixture of silicon, hydrofluoric acid and the like are obtained as resources.

  2 is the same as FIG. In addition to producing a pickling aqueous solution from a waste solution obtained by pickling titanium using a fluorinated hydrofluoric acid aqueous solution, hexafluorotitanate and hexafluoro produced in the process An example of a procedure for recovering titanium dioxide, silicon dioxide, etc. from silicate as a resource is shown. The process up to separation of the titanium hydroxide precipitate is the same as in FIG. Since the excessively added ammonia is contained in the solution from which the titanium hydroxide is separated, the solution is charged into the treatment tank of the apparatus of FIG. 5 and the temperature becomes 80 to 100 ° C. as in the case of FIG. After heating in this manner, air and water vapor at around 100 ° C. are sent in to evaporate the ammonia in the solution together with the water vapor and collect it as ammonia water.

  After confirming that all the ammonia in the solution had evaporated and the pH of the solution was near neutral, the amount of ammonium ions in the solution was analyzed, and all the ammonium fluoride was removed by the reaction of the formula (11) described above. After adding the amount of calcium hydroxide (solution mixed with water) necessary for changing to ammonia and calcium fluoride from the inlet tube 10, the temperature of the solution using the heater 3 while stirring the solution with the agitator 2. Is heated to 80-100 ° C. Further, air and water vapor at around 100 ° C. are sent from the gas charging pipe 12 to evaporate ammonia in the solution together with the water vapor, and this is led from the gas discharge pipe 13 to the cooler 6 to become ammonia water. Save to 8. Since the solution after separation of ammonia contains calcium fluoride precipitate, it is discharged from the discharge pipe 11 together with the solution to the outside of the apparatus and transferred to a filtration apparatus or the like.

  Since the solution from which calcium fluoride precipitate is separated contains only potassium fluoride, it is heated and concentrated if necessary, and then potassium hexafluorotitanate is produced by the reaction of the above formula (1) or (2). Can be reused for. Further, as in the case of FIG. 1, hydrofluoric acid and potassium hydroxide can be obtained by electrodialysis or ion exchange.

  FIG. 3 shows No. 1 in Table 1 above. 5 is an aqueous solution for pickling using a waste solution of mixed acid (nitric acid + hydrofluoric acid + acetic acid) used for etching silicon metal as a raw material aqueous solution. And it is the figure which showed an example of the procedure which collect | recovers titanium dioxide, a silicon dioxide, etc. as a resource from the hexafluoro titanate and hexafluorosilicate which are produced | generated in the process.

  Since the manufacturing method and the resource recovery method of the pickling aqueous solution are the same as those in FIG. 1, detailed explanation is omitted, but in the case of FIG. 3, both hexafluorotitanic acid and hexafluorosilicic acid are contained in the raw material aqueous solution. As it is contained, both potassium hexafluorotitanate and potassium hexafluorosilicate can be precipitated by adding potassium fluoride.

  As described in Table 1 above, at this time, most of the titanium and silicates can be obtained by adding potassium fluoride having a mole number of 6 to 10 times the mole number of titanium and 3 times the mole number of silicon. Elementary silicon precipitates as potassium hexafluorotitanate and potassium hexafluorosilicate, and the amount of hexafluorotitanate and hexafluorosilicate ions remaining in the pickling aqueous solution is small or trace, but a large amount of potassium ion remains. To do. If it is necessary to recover this potassium ion, hexafluorosilicate may be added and precipitated and separated as potassium hexafluorosilicate as in FIGS.

  4 shows No. 1 in Table 1 above. 8 is used to produce a pickling aqueous solution from a waste solution obtained by pickling titanium using a hydrofluoric acid aqueous solution, and to produce potassium hexafluorotitanate and hexa It is the figure which showed an example of the procedure which collect | recovers titanium dioxide, silicon dioxide, etc. as a resource from potassium fluorosilicate. The only difference from FIG. 1 is that nitric acid is added as an oxidizing agent, and the others are exactly the same. In the case where oxygen is used as the oxidant, air may be blown into the aqueous solution or the aqueous solution may be sprayed into the air. In this case, almost no drug cost is required, but a relatively long time is required because the oxidation rate is slow.

An aqueous solution obtained by dissolving 9.67 g of industrial pure titanium (JIS 1 type: Ti content 99.5%) in nitric hydrofluoric acid pickling solution 1 dm ³ containing nitric acid 200 g / dm ³ and hydrofluoric acid 30 g / dm ³ Was used as a sample solution, and 50 cm ³ was collected from each sample solution and transferred to 12 plastic containers. Among them, 0.0202, 0.0505 or 0.1009 mol of potassium fluoride or rubidium fluoride was dissolved in the sample solution in 11 containers, and nothing was added to the remaining one. After standing for 30 minutes, it was filtered using filter paper, and the filtrate was diluted to 60 cm ³ with water. A smaller amount was collected to analyze the concentration of potassium or rubidium, and 50 cm ³ was collected and transferred to a plastic container.

After adding 0.0038 to 0.0423 mol of hexafluorosilicic acid to the solution of 8 containers and mixing, and adding 10 cm ³ of water to the solution of the remaining 4 containers and leaving it for 30 minutes, It filtered using the filter paper. The filtrate was diluted to 70cm ³ of water, was collected lesser amounts, potassium or rubidium, hexafluoro titanic acid ion, hexafluoro silicic acid ions, while analyzing the concentration of hydrofluoric acid and nitric acid, 50 cm ³ The sample was collected, transferred to a plastic container, and subjected to a pickling test for titanium.

  The potassium, rubidium and hexafluorotitanate ions were analyzed by ICP emission spectroscopic analysis, and the hexafluorosilicate ion was analyzed by molybdenum blue absorptiometry. The concentration of hydrofluoric acid was determined by analyzing the fluorine concentration of potassium fluoride or rubidium fluoride, hexafluorotitanate ion and hexafluorosilicate from the total fluorine concentration analysis obtained by lanthanum / alizarin complexone spectrophotometry. It calculated | required by converting from the value which deducted the fluorine concentration analysis value of an acid ion. The concentration of nitric acid was determined by conversion from the analysis value of nitrate ion by absorptiometry.

  In addition, the pickling test for titanium was conducted after immersing an industrial pure titanium (JIS type 1) test piece having a thickness of 0.5 mm, a width of 30 mm, and a length of 30 mm in an aqueous solution for pickling heated to 30 ° C. for 5 minutes. The sample was taken out, washed with water and dried, and the difference in the weight of the test piece before and after immersion was adjusted to decrease in dissolution by pickling. Table 2 shows test conditions such as the addition amount of the alkali metal-containing compound, the analysis result of the aqueous solution subjected to the pickling test, and the dissolution loss by titanium pickling test.

  Test No. in Table 2 Examples 1 to 11 are examples of the pickling aqueous solution produced by the method of the present invention and the dissolution loss of titanium thereby. Compared to 12 comparative examples, the hydrofluoric acid concentration in the aqueous solution was high, and the dissolution loss was also large. This is presumably because in the examples of the present invention, the added potassium fluoride or rubidium fluoride reacted with hexafluorotitanic acid or hexafluorosilicic acid to generate hydrofluoric acid.

Test No. 1 in Table 2 of Example 1 6-8 and test no. A 50 cm ³ pickling aqueous solution produced under the same conditions as in No. 12 was placed in a plastic container and heated to 50 ° C., and a stainless steel test piece (steel type: SUS304) having a thickness of 1 mm, a width of 50 mm, and a length of 50 mm was added thereto. It was immersed, taken out after 10 minutes, washed with water and dried. The weight of the test piece before and after the immersion was measured, and the difference was taken as the dissolution loss by pickling. Table 3 shows the production conditions of the pickling aqueous solution and the dissolution loss by pickling.

Test No. in Table 3 1-3 are examples of weight loss of stainless steel by the pickling aqueous solution produced by the method of the present invention. Compared with the comparative example of 4, the dissolution weight loss was much larger.
This is presumed to be because the added potassium fluoride reacted with hexafluorotitanic acid or hexafluorosilicic acid to produce hydrofluoric acid in the inventive examples.

Various alkali metal compounds (electrolytes) were added and dissolved in 1 dm ³ of each of the two raw material aqueous solutions A or B having the compositions shown in Table 4, and the resulting hexafluorosilicate precipitate was filtered and separated. Water was added to the filtrate to adjust the liquid volume to 1.5 or 2 dm ³ to prepare pickling aqueous solutions a to f and h to j. For comparison, the raw material solution A and B1dm ³ to prepare an aqueous solution g and k for pickling diluted 1.5 or 2 dm ³ of water.

  Analytical samples are collected from these pickling aqueous solutions, and hexafluorosilicate ions are quantified by ICP emission spectrophotometry with alkali metal, aluminum chloride added and molybdenum blue absorptiometry (for example, see 9.2 of JISR1616). analyzed. The concentrations of nitric acid, hydrofluoric acid, and acetic acid in the pickling aqueous solution shown in Table 4 are theoretically estimated values, but nitric acid and hydrofluoric acid are the same as those in Example 1 described above. Similar analysis values were obtained by the same analysis method.

Next, 100 cm ³ of each of these 11 kinds of pickling aqueous solutions was placed in a plastic container and heated in a water bath adjusted to 50 ° C. A stainless steel test piece (steel type: SUS304) having a thickness of 1 mm, a width of 50 mm, and a length of 50 mm was immersed in this for 10 minutes, then taken out, washed with water, and dried. This operation was repeated three times, and the weight of the test piece before and after immersion was measured each time, and the difference was taken as the dissolution loss by pickling. Table 5 shows the measurement results of dissolution loss.

  Symbols a to g are pickling aqueous solutions manufactured using the raw material aqueous solution A, but compared with a comparative example (symbol g) in which no alkali metal-containing compound is added, an alkali metal-containing compound is added and hexafluorosilicic acid is added. The dissolution loss by the pickling aqueous solution of the present invention example (symbols a to f) in which the salt was precipitated and separated was large, especially when potassium fluoride was added as the alkali metal-containing compound (symbol d). . This is presumably because hydrofluoric acid was produced by the addition of potassium fluoride. Similarly, with respect to the pickling aqueous solution (symbol h to k) produced using the raw material aqueous solution B, the dissolution loss when the alkali metal-containing compound was added was larger than when the alkali metal-containing compound was not added.

  Water was added to the three types of aqueous solutions A, B, and C whose compositions are shown in Table 6, and diluted so that the liquid amount became 4 times (concentration was 1/4). However, the aqueous solution A simulates a mixed acid waste solution used for etching a silicon wafer and contains nitric acid, hydrofluoric acid, acetic acid, and hexafluorosilicic acid. On the other hand, B does not contain acetic acid, and C does not contain acetic acid and hexafluorosilicic acid.

100 cm ³ of each of these dilutions was placed in a plastic container and heated in a water bath adjusted to 30 ° C. or 50 ° C. To this, an industrial pure titanium test piece (material: JIS type 1) having a thickness of 0.5 mm, a width of 30 mm, and a length of 30 mm, or a stainless steel test piece (steel type: SUS304) having a thickness of 1 mm, a width of 50 mm, and a length of 50 mm. After dipping for 5 minutes or 10 minutes, the sample was taken out, washed with water and dried, and the weight difference between the test pieces before and after the immersion was measured to determine the loss of dissolution by pickling.

  Next, 8 g of potassium fluoride (crystal) was added and dissolved in each of these pickled aqueous solutions, and the resulting precipitate was filtered and separated. To the obtained aqueous solution, an industrial pure titanium test piece (material: JIS type 1) having a thickness of 0.5 mm, a width of 30 mm, and a length of 30 mm, or a stainless steel test piece having a thickness of 1 mm, a width of 50 mm, and a length of 50 mm (steel type: SUS304) was immersed for 5 minutes or 10 minutes, then taken out, washed with water and dried, and the weight difference between the test pieces before and after immersion was measured to determine the weight loss by pickling. Table 7 summarizes the test conditions and the measurement results of dissolution loss.

Comparing the pickling loss of the first pickling machine (before adding potassium fluoride) and the second picking (after adding potassium fluoride), the pickling weight loss by the pickling aqueous solution C was less than the first. . This is presumed to be because free hydrofluoric acid was reduced by the first pickling. On the other hand, for the pickling aqueous solutions A and B, the second pickling weight loss increased. This is presumably because the addition of potassium fluoride produced more hydrofluoric acid than the amount consumed in the first pickling due to the reactions of the above-mentioned formulas (1) and (2).

An aqueous solution prepared by dissolving 15.21 g of industrial pure titanium (JIS type 1: Ti content 99.5%) in hydrofluoric acid-based pickling solution 1 dm ³ containing hydrofluoric acid 50 g / dm ³ was used as a sample solution. From this, 50 cm ³ was collected and transferred to 11 plastic containers. Among them, 0.0318, 0.0794 or 0.1588 mol of potassium fluoride was added to the sample solution in 10 containers and dissolved, and nothing was added to the remaining one. While measuring the oxidation-reduction potential using a commercially available ORP meter, an aqueous nitric acid solution having a concentration of about 300 g / dm ³ was added dropwise to change all trivalent titanium to tetravalent. After standing for 30 minutes, it was filtered using filter paper, and the filtrate was diluted to 60 cm ³ with water. A small amount was collected to analyze the potassium concentration, and 50 cm ³ was collected and transferred to a plastic container.

After adding 0.0060 to 0.0665 mol of hexafluorosilicic acid to the solution of 7 containers, and mixing the solution of the remaining 4 containers with 10 cm ³ of water, and leaving it for 30 minutes, It filtered using the filter paper. Dilute the filtrate to 70 cm ³ with water and collect a small amount of this to analyze the concentration of potassium, hexafluorotitanate ion, hexafluorosilicate ion and hydrofluoric acid, and collect 50 cm ³ to obtain plastic. The product was transferred to a container and subjected to a pickling test for titanium.

  The concentrations of potassium, hexafluorotitanate ion, hexafluorosilicate ion and hydrofluoric acid were analyzed by the same method as in Example 1 described above. In addition, the pickling test for titanium was conducted after immersing an industrial pure titanium (JIS type 1) test piece having a thickness of 0.5 mm, a width of 30 mm, and a length of 30 mm in an aqueous solution for pickling heated to 30 ° C. for 5 minutes. The sample was taken out, washed with water and dried, and the difference in the weight of the test piece before and after immersion was adjusted to decrease in dissolution by pickling. Table 8 shows the test conditions such as the addition amount of the alkali metal-containing compound, the analysis result of the aqueous solution subjected to the pickling test, and the dissolution loss by titanium pickling test.

  Test No. in Table 8 Examples 1 to 10 are examples of the pickling aqueous solution produced by the method of the present invention and the dissolution loss of titanium thereby. Compared with 11 comparative examples, the hydrofluoric acid concentration in the aqueous solution was high, and the dissolution loss was also large. This is presumed to be because the added potassium fluoride reacted with hexafluorotitanic acid or hexafluorosilicic acid to produce hydrofluoric acid in the inventive examples.

No. 1 in Table 2 of Example 1 For tests 6 to 10, the first filtered and separated precipitate (potassium hexafluorotitanate) was rinsed with water and transferred to a plastic container. After adding water to adjust the liquid volume to about 250 cm ³ , the concentration Was adjusted to pH 8.2 to 10.1 by adding about 15% ammonia water. The solution in four containers was heated to 95 to 98 ° C., and the solution in one container was allowed to stand at room temperature for 1 or 2 hours, and then the pH was adjusted to 8.5 to 10.1 with aqueous ammonia. The mixture was filtered using filter paper, and the precipitate (titanium hydroxide) on the filter paper was thoroughly washed with water, transferred to a platinum crucible together with the filter paper, and heated and fired at 1000 ° C. for 2 hours using an electric furnace. After cooling in the dryer, the weight of the fired product (titanium dioxide) was measured. Table 9 shows the test conditions and measurement results. The TiO ₂ recovery rate in the table indicates the percentage of the measured TiO ₂ value relative to the weight (0.8025 g) when all of the titanium in the collected sample solution 50 cm ³ becomes TiO ₂ .

Test No. No. 3 has an alkali metal (K) addition amount of 0.1009 mol, an alkali metal (K) / Ti molar ratio of 10.0, and an initial and final pH of 9 or more (10.1), 90 ° C. or more (95 C.) for 1 hour, the TiO ₂ recovery was 98% or more. In contrast, test no. 1 and 2 had low alkali metal (K) addition amounts of 0.0202 and 0.0505 mol and low K / Ti molar ratios of 2.0 and 5.0, so the TiO ₂ recovery was 32.2 and It was as low as 85.6%. In addition, Test No. 4 had an initial and final pH of less than 9, so the TiO ₂ recovery was as low as 66.1%. No. 5 was not heated after the addition of ammonia, so the TiO ₂ recovery was as low as 38.8%.

No. 1 in Table 2 of Example 1 Tests 8-10 and No. For two sets of tests under the same conditions as in No. 10, the second filtered and separated precipitate (potassium hexafluorosilicate) was rinsed with water, transferred to a plastic container, and water was added to a volume of about 500 cm ³ . After the adjustment, the pH was adjusted to 6.8 to 10.1 by adding ammonia water having a concentration of about 15%. The solution in four containers was heated to 97 to 98 ° C., and the solution in one container was allowed to stand at room temperature for 2 hours, and then the pH was adjusted to 6.5 to 10.1 with aqueous ammonia. The mixture was filtered using filter paper, and the precipitate (silicic acid) on the filter paper was thoroughly washed with water, then transferred to a platinum crucible together with the filter paper, and heated and fired at 1000 ° C. for 2 hours using an electric furnace. After cooling in the dryer, the weight of the fired product (silicon dioxide) was measured. Table 10 shows the test conditions and measurement results. Note that the SiO ₂ recovery in the table shows the percentage of SiO ₂ measurements for the weight of the case where the added silicon in the hexafluorosilicic acid ions all become SiO _2.

Test No. No. 3 is a test in which the alkali metal (K) / Si molar ratio is 3.0 and the initial and final pH are 9 or more (10.0 and 10.1) and heated to 98 ° C. for 2 hours. ₂ Recovery was 95.0%. In contrast, test no. Since 1 and 2 had low K / Si molar ratios of 1.6 and 2.0, the SiO ₂ recovery was as low as 77.1 and 90.9%. In addition, Test No. 4 is less than 9 for both initial and final pH. Since No. 5 was not heated after addition of ammonia, no SiO ₂ powder was obtained.

Using 1 dm ^{3 of} diluent A shown in Table 6 of Example 4 above, pure industrial titanium (JIS type 1: titanium content 99.5%) or stainless steel (SUS304: silicon content 0.47) %) Was pickled to dissolve 5.03 g or 3.11 g, respectively. Each 20 cm ³ is accurately weighed from the pickled aqueous solution (sample solution A1 or A2), transferred to 12 plastic containers, and alkali metal nitrate (KNO ₃ , NaNO ₃ or 2 mol / dm ³ concentration). RbNO ₃ ) aqueous solution was added in 5, 10 or 15 cm ³ (0.01, 0.2 or 0.03 mol as alkali metal), water was added to adjust the liquid volume to 40 cm ³ , mixed and left for 30 minutes . After filtration using filter paper, the precipitate (hexafluorosilicate and hexafluorotitanate) on the filter paper was washed away with water and transferred to a plastic container.

Water was added to adjust the liquid volume to about 100 cm ³ , and then aqueous ammonia having a concentration of about 15% was added to adjust the pH to 6.8 to 10.3. The solution in 10 containers was heated to 90-96 ° C., the solution in 2 containers was left at room temperature (25 ° C.) for 1.5 or 2 hours, and then the pH was adjusted to 6.6-10. Adjusted to 1. The mixture was filtered using filter paper, and the precipitate on the filter paper was thoroughly washed with water, and then transferred together with the filter paper into a platinum crucible.

After heating and firing at 1000 ° C. for 2 hours using an electric furnace, the mixture was allowed to cool, 2 g of sodium carbonate was added to the fired product (silicon dioxide and titanium dioxide), and again heated at 1000 ° C. for 20 minutes to melt. After standing to cool, the melt was dissolved in water and hydrochloric acid to obtain an aqueous solution, and silicon was quantitatively analyzed by molybdenum blue spectrophotometry and titanium was quantitatively analyzed by ICP emission spectrophotometry. Test conditions and analysis results are shown in Table 11. In the table, the molar ratio (M / Si or M / Ti) means the molar ratio of alkali metal to silicon or titanium represented by M, and the SiO ₂ recovery rate and TiO ₂ recovery rate were collected. The percentages of the respective analysis values with respect to the weight when silicon or titanium in 20 cm ^{3 of the} aqueous solution are all SiO ₂ or TiO ₂ are shown.

Among the recovery tests using the sample solution A1 (aqueous solution obtained by pickling industrial pure titanium), the test No. 3 and 4, the alkali metal (M) addition amount is 0.03 mol, the M / Si molar ratio is 7.20, and the M / Ti molar ratio is 14.35. In each of the tests, the SiO ₂ recovery rate was 95% or more and the TiO ₂ recovery rate was 97% or more. In contrast, test no. In Nos. 1 and 2, the alkali metal (M) addition amount was as small as 0.01 and 0.02 mol. The SiO ₂ recovery of No. ₂ was 95% or more. The SiO ₂ recovery rate of No. 1 was as low as 90.5%, and the TiO ₂ recovery rates were as low as 11.1 and 90.2%. In addition, Test No. Since 5 was 6.8 and 6.6, both initial and final pH were less than 9, silicon and titanium oxide powders were not obtained (analysis omitted). Furthermore, test no. Since No. 6 was not heated after the addition of ammonia, silicon and titanium oxide powders were not obtained.

Among the recovery tests using the sample solution A2 (aqueous solution obtained by pickling stainless steel), the test No. 8 and 12 are tests in which the amount of alkali metal (M) added was 0.02 mol, the M / Si molar ratio was 4.79, both the initial and final pH were 9 or more, and the sample was heated to 95 ° C. or more for 1.5 hours. However, the recovery rate of SiO ₂ was 95% or more. In contrast, test no. No. 7 had an alkali metal (M) addition amount as small as 0.01 and an M / Si molar ratio as low as 2.40, so the SiO ₂ recovery rate was as low as 92.5%. In addition, Test No. Since 9 was 7.0 and 6.7 with both initial and final pH less than 9, no silicon oxide powder was obtained. Furthermore, test no. Since No. 10 was not heated after the addition of ammonia, no silicon oxide powder was obtained. In addition, Test No. No. 11 SiO ₂ recovery was Test No. The reason why it was a little lower than 8 and 12 is presumed to be that Na was used as the alkali metal, so that the amount of hexafluorosilicate produced was small.

In the test of Example 7, among the solutions after filtration and separation of the silicic acid precipitate generated by adding aqueous ammonia, test No. The solution of No. ³ (liquid amount of about 650 cm ³ ) was transferred to a glass container, and air and water vapor at around 100 ° C. were blown in for about 1 hour while heating to the vicinity of the boiling point with a heater. The solution was cooled to room temperature, and the pH of the solution was measured (measured value: 7.2). After being diluted accurately to 1000 cm ³ with water, the ammonium ion concentration was measured by the Nessler method. From this, 200 cm ³ was fractionated, and after adding 0.667 g of calcium hydroxide mixed with 50 cm ³ of water, air and water vapor near 100 ° C. were blown in for about 1 hour while heating to the vicinity of the boiling point with a heater. . The amount of calcium hydroxide added was calculated as the amount of calcium hydroxide that reacted without excess or deficiency with the amount of ammonium ions (that is, ammonium fluoride) measured by the Nessler method by the reaction of the above-mentioned equation (11). Is.

  Next, after cooling a solution to room temperature, pH was measured (measurement value: 8.0), and it filtered using the filter paper. The calcium fluoride precipitate on the filter paper was washed with water, transferred to a porcelain crucible with the filter paper, and heated and fired at 800 ° C. for 2 hours using an electric furnace. After cooling in the dryer, the weight of the fired product (calcium fluoride) was measured and found to be 0.6886 g. This amount is the theoretical value (0 when 200/1000 of the added hexafluorosilicic acid precipitates 100% as potassium hexafluorosilicate and 4/6 of the fluorine is 100% recovered as calcium fluoride. About 98% of .7027 g).

The filtrate after filtering and separating the calcium fluoride precipitate is put into the cell 22 of the apparatus having the same structure as that shown in FIG. 6. The cell 23 has pure water, and the cell 24 has a concentration of 100 g / dm ³ sulfuric acid. Then, after putting potassium hydroxide having a concentration of 50 g / dm ³ into the cell 25, a DC voltage of 3.2 V was applied between the anode 16 (titanium plate coated with iridium oxide) and the cathode 17 (nickel plate). Held for hours. In addition, in the electrodialysis apparatus used in the present Example, the Tokuyama Neocepta CM-1 was used as the cation exchange membranes 18-1 and 18-2, and the same AM-1 was used as the anion exchange membrane. .

  After the above electrodialysis treatment, the hydrofluoric acid in the aqueous solution in the cell 23 was quantitatively analyzed by acetylacetone iron complex fading spectrophotometry. As a result, it was confirmed that 0.1765 g of hydrofluoric acid was produced. This is because 200/1000 of the added hexafluorosilicic acid precipitates 100% as potassium hexafluorosilicate, and the potassium therein becomes potassium fluoride, which is converted to hydrofluoric acid by electrodialysis and 100% is recovered. About 98% of the theoretical value (0.1801 g).

The pickling aqueous solution, the production method thereof, and the resource recovery method of the present invention can be used to significantly reduce the pickling cost of metals such as titanium. It is also highly likely to be used for industrial waste reduction and resource saving.

Claims (9)

In a volume of 1 dm ³ , it contains 10 to 600 g of nitric acid, 1 to 200 g of hydrofluoric acid and 0.02 to 200 g of alkali metal ions, and one of less than 50 g of hexafluorotitanate ions and less than 50 g of hexafluorosilicate ions. Alternatively, an aqueous solution for pickling characterized by containing both. Containing 1 to 200 g of hydrofluoric acid, 0.02 to 200 g of alkali metal ions and less than 50 g of hexafluorotitanate ions in a volume of 1 dm ³ , and further containing less than 50 g of hexafluorosilicate ions, or An aqueous solution for pickling characterized by not containing hexafluorosilicate ions. Production of an aqueous solution for pickling characterized by performing the following steps A, B and C using an aqueous solution containing nitric acid and hydrofluoric acid and further containing titanium and / or silicon fluoride as a raw material Method:
[Step A] Step of adding hydrogen fluoride to the aqueous solution as necessary:
[Step B] A step of adding alkali metal ions to the aqueous solution: and [Step C] a step of separating the precipitate generated in the step B and step A performed as necessary . The method for producing an aqueous solution for pickling according to claim 3, further comprising performing steps D and E described later:
[Step D] Step of adding hexafluorosilicate ion to the aqueous solution from which the precipitate has been separated in the above step C: and
[Step E] A step of separating the precipitate produced in the above step D. A method for producing an aqueous solution for pickling, characterized in that an aqueous solution containing hydrofluoric acid and a fluoride of titanium is used as a raw material, and the following steps F, G, H and I are performed :
[Step F] A step of adding hydrogen fluoride to the aqueous solution as necessary:
[Step G] Step of adding alkali metal ions to the aqueous solution:
[Step H] Steps of oxidizing the trivalent titanium fluoride contained in the aqueous solution to convert it into a tetravalent titanium fluoride: and [Step I] Steps G and H described above and, if necessary, The process of isolate | separating the deposit produced by the process F to perform . The method for producing an aqueous solution for pickling according to claim 5, further comprising performing steps J and K described later:
[Step J] Step of adding hexafluorosilicate ion to the aqueous solution from which the precipitate has been separated in Step I above:
[Step K] A step of separating the precipitate produced in the step J. The aqueous solution for pickling according to claim 1, which is produced by the method according to claim 3 or 4. The aqueous solution for pickling according to claim 2, which is produced by the method according to claim 5 or 6. A method for recovering resources associated with the production of an aqueous solution for pickling, which comprises performing some or all of the following steps L, M, N, O, P and Q:
[Step L] A step of adding ammonia to the precipitate separated by the steps a, b, c and / or d described later :
[Step a] Steps e, f and g described below are carried out using an aqueous solution containing nitric acid and hydrofluoric acid and further containing titanium and / or silicon fluoride as raw materials:
(Step e) Step of adding hydrogen fluoride to the aqueous solution as necessary:
(Step f) Step of adding alkali metal ions to the aqueous solution: and
(Step g) A step of separating the precipitate generated in the step f and the step e performed as necessary.
[Step b] Steps h and i described later are performed after step a.
(Step h) Step of adding hexafluorosilicate ion to the aqueous solution from which the precipitate has been separated by the above step g: and
(Process i) The process of isolate | separating the deposit produced by said process h.
[Step c] A step characterized in that the following steps j, k, m and n are carried out using an aqueous solution containing hydrofluoric acid and a fluoride of titanium as raw materials:
(Step j) Step of adding hydrogen fluoride to the aqueous solution as necessary:
(Step k) Step of adding alkali metal ions to the aqueous solution:
(Step m) A step of oxidizing the trivalent titanium fluoride contained in the aqueous solution to convert it into a tetravalent titanium fluoride: and
(Step n) A step of separating the precipitate generated in the steps k and m and the step j performed as necessary.
[Step d] Step p and q described later are performed after step c.
(Step p) Step of adding hexafluorosilicate ion to the aqueous solution from which the precipitate has been separated by the above step n: and
(Process q) The process of isolate | separating the deposit produced by the said process p.
[Step M] A step of separating the precipitate generated in the above step L:
[Step N] Step of washing and precipitating the precipitate separated in Step M, followed by heating and baking:
[Step O] Step of separating ammonia after adding an alkali metal hydroxide and / or an alkaline earth metal hydroxide, if necessary, to the aqueous solution from which the precipitate has been separated in the above step M :
[Step P] A step of separating the precipitate generated in the above step O:
[Step Q] A step of subjecting the aqueous solution obtained by the step O or the steps O and P to an electrodialysis treatment or an ion exchange treatment.

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