JP2001096280A - Waste water treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste water treatment method for removing a fluorine compound and a valuable metallic compound from the waste water containing the both, cleaning the waste water and also recovering valuable metal. SOLUTION: Alkali hydroxide is added to the waste water incorporating the fluorine compound and the metallic compound to form easily soluble alkali fluoride and hard soluble metallic hydroxide, etc., then the fluorine compound and the metallic compound are separated. A calcium compound is added to the waste water containing the fluorine compound to form hard soluble calcium fluoride and by removing this, metal and fluorine are removed from the waste water and the waste water is cleaned and also calcium fluoride less in heavy metals can be recovered. The sludge containing hard soluble metal is washed with alkali and then with water, thus a valuable metal compound not incorporating impurities such as fluorine is recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment method for treating wastewater containing at least fluorine and metal to separate the metal and fluorine, and more particularly to a method for removing fluorine and metal from wastewater almost completely. The present invention relates to a wastewater treatment method for purifying wastewater and recovering valuable metals contained in wastewater.

[0002]

2. Description of the Related Art In recent years, with the development of electronics, demands for semiconductor cleaning, printed circuit board cleaning, and the like have increased, and a large amount of fluorine-containing wastewater has been generated as cleaning wastewater. In addition, wastewater containing fluorine is discharged in the ceramics manufacturing industry. Examples of various cleaning fluorine compounds contained in the wastewater include boron trifluoride (BF ₃ ) for ion implantation, etching resist removal and chemical vapor deposition (C
Carbon tetrafluoride (CF ₄ ) for DV), methane trifluoride (CHF ₃ ) for etching resist removal,
Ethane trifluoride (C ₂ F ₃ Cl ₃ ) for cleaning tools, tools, wafers and chips, hydrogen fluoride (HF) for etching resist removal and cleaning tools, tools, wafers and chips, etching Ammonium fluoride (NH ₄ F) or the like is used for resist removal and wafer and chip cleaning. In addition, as the industrial structure becomes more diversified and more complex, the types of wastewater have become diversified, and wastewater containing both fluorine and metal has been generated. It is necessary to discharge these wastewaters in accordance with the wastewater standards, and it is essential to recover and reuse fluorine and valuable metals for cost reduction.

[0003]

Among the conventional industrial wastewaters, the treatment of wastewater containing these fluorine compounds and metal compounds has not been studied so far, and the wastewater is made harmless and can be discharged. In addition, if significant yields of fluorine and valuable metals, which have their own value, can be recovered, a wastewater treatment method excellent in terms of both environmental protection and cost reduction can be obtained. A common method of treating wastewater containing fluorine is to add calcium ions to wastewater containing a metal compound and a fluorine compound so that the fluorine ions in the fluorine compound are hardly soluble calcium fluoride, and heavy metals are hydroxides. Alternatively, it is precipitated as a carbonate. However, in order to recover valuable metals from the precipitate obtained by the method, fluorine contained in the sludge becomes a bottleneck, and almost all of the waste is disposed of. The present invention is intended to eliminate these drawbacks and realize a satisfactory level of recovery, by separating them from wastewater containing at least a fluorine compound and a metal compound, or recovering the fluorine compound and the metal compound separately. It is an object of the present invention to provide a wastewater treatment method capable of purifying wastewater and reusing expensive fluorine and valuable metals.

[0004]

According to the present invention, a wastewater containing at least a fluorine compound and a metal compound is added with an alkali metal hydroxide and / or a carbonate to adjust the pH of the wastewater to 8 to 10.
12 to form a hardly soluble alkali fluoride and a hardly soluble metal hydroxide and / or metal carbonate, and remove the hardly soluble valuable metal hydroxide and / or carbonate from the wastewater. A method for treating wastewater, and subsequently, a calcium compound is added to the wastewater to maintain the pH of the wastewater at 4 to 12 to generate insoluble calcium fluoride, and the fluoride is removed from the wastewater. A method of treating wastewater, and, in place of producing the hardly soluble fluoride, maintaining the pH of the wastewater at 9 to 12 after separating generated metal sludge from wastewater containing easily soluble alkali fluoride. A method of recovering metals in wastewater as valuable metals by performing alkali washing while further washing with water, and the hardly soluble fluorine compound after removing the valuable metal hydroxides and / or carbonates from wastewater. Raw And a method which is characterized in that the recovery of valuable metals.

Hereinafter, the present invention will be described in detail. In the present invention, wastewater containing at least a fluorine compound (which may be contained as a fluorine ion) and a metal compound (which may be contained as a metal ion) is targeted.
Such wastewater includes wastewater such as metal surface treatment wastewater and stainless steel plate manufacturing wastewater. As the fluorine compound, a compound of a fluorine ion (F ⁻ ) and a metal ion or an ammonium ion is a typical compound. In addition, a compound that reacts with an alkali metal ion to form a readily soluble fluorine compound is included. It is desirable that the easily soluble compound reacts with the calcium compound to form a hardly soluble compound,
In the form of removing fluorine ions from wastewater, the formation of the hardly soluble compound is essential.

The metal compound is a compound containing an arbitrary metal ion which reacts with an alkali metal hydroxide or carbonate to form a hardly soluble compound. Particularly, in the case of valuable metals such as iron, nickel and chromium, by removing and recovering them from wastewater, the effects of environmental conservation and cost reduction are produced. In the present invention, the wastewater is neutralized by adding an alkali metal hydroxide and / or a carbonate such as sodium hydroxide or sodium carbonate which does not generate a hardly soluble fluorine compound by reacting with fluorine ions. By the addition of the alkali metal salt, the fluorine compound contained in the waste water is converted into a readily soluble fluorine compound such as sodium fluoride, and the metal compound is converted into a hardly soluble metal hydroxide or metal carbonate.

The alkali metal hydroxide or carbonate may be added as a solution or as a solid, but the pH of the waste water after the addition is 8 to 12, preferably 10 to 11, which is weakly alkaline. To The higher the pH, that is, the higher the alkalinity, the less fluorine is adsorbed on the metal sludge, and the separation of the fluorine compound and the metal compound is performed efficiently. The upper limit is required to be about 12 in order to effectively perform the separation. On the other hand, the lower limit of the pH is determined in consideration of the permissible mixing ratio of fluorine ions to the poorly soluble metal sludge by adsorption. The lower the pH, the lower the amount of alkali to be added, which is advantageous in terms of cost.However, the amount of alkali required to convert metal ions to hydroxides and carbonates to make them less soluble tends to be insufficient. Further, there is a possibility that fluorine ions in the wastewater are adsorbed by the generated metal sludge and the fluorine and the metal cannot be sufficiently separated. Therefore p
As described above, the lower limit of H needs to be 8, and thereby fluorine and valuable metals can be economically separated. When the lower limit of the pH is set to 10, a poorly soluble metal compound is surely generated, and the incorporation of fluorine ions in wastewater into metal sludge can be minimized.

Since the generated fluorine compound is easily soluble and the metal compound is hardly soluble, the two can be easily separated easily by filtration or the like. Fluorine ions and alkali metal ions are present in the waste water after separation of the fluorine compound and the metal compound by the addition of the alkali. When a calcium compound, for example, calcium chloride, is added to the wastewater, calcium ions and fluorine ions react to form calcium fluoride with few impurities and precipitate. When this precipitate is separated by filtration or the like, only low-concentration alkali metal ions such as sodium ions and low-concentration chlorine ions are present in the wastewater. This is substantially low-concentration saline, and the wastewater is effectively discharged. As well as being purified, calcium fluoride with few impurities can be recovered.

The amount of calcium added at this time is such that the calcium concentration of the treatment liquid after addition is usually 0.5 to 10 g / l, preferably 2 to 3 g / l, and the pH is 4 to 12, preferably 6 to 9. To be added. If the pH is less than 4, the dissociation of hydrofluoric acid (HF → H ⁺ + F ⁻ , pKa = 3.2
) Is insufficient, so that fluorine is not easily ionized, and thus fluorine is not easily removed. The efficiency of the fluorine removal is not improved even if the pH is too high, and the upper limit of the pH is set to about 12 in order to save the amount of the neutralizing agent when the treatment liquid is discharged. On the other hand, a small amount of the fluorine compound remains in the metal sludge from which the fluorine compound has been removed by the alkali addition.

[0010] In order to recover the metal in the metal sludge as a metal, it is necessary to remove the residual fluorine compound. For this purpose, in the present invention, washing is performed by adding an alkaline compound to remove the remaining fluorine compound. This alkaline compound is added as a solution, and at the same time as the remaining fluorine compound is washed away, when the fluorine compound still exists as a hardly soluble compound or when it is adsorbed on metal sludge, it is converted into a readily soluble fluorine compound. Can be dissolved and removed. The alkaline compound is preferably a hydroxide or carbonate of an alkali metal, and for the purpose of removing a trace amount of a fluorine compound, instead of using a small amount of a high-concentration alkaline solution, use a large amount of a diluted alkaline solution. It is desirable. The p of the alkaline solution at this time
H is set to about 9 to 12, and preferably 11 to 12.

Since the fluorine solution is dissolved in the cleaning solution obtained by the alkali cleaning, the cleaning solution may be subjected to fluorine recovery in addition to the wastewater containing the readily soluble fluorine compound at the time of separating the metal sludge. Although metal sludge containing almost no fluorine compound is obtained by washing with this alkaline solution,
Since there is a possibility that the alkali used for the cleaning and a trace amount of the fluorine compound may remain, it is desirable to further wash the metal sludge after the alkali cleaning with water.

Next, the wastewater treatment and valuable metal recovery of the present invention will be described in detail with reference to the flowchart shown in FIG. FIG.
In the flow chart of the above, sodium hydroxide or sodium carbonate is added as an aqueous solution to industrial wastewater containing fluorine ions and valuable metal ions such as nickel ions and chromium ions (fluorine and metal-containing wastewater), and the mixture is thoroughly stirred and neutralized. The valuable metal hydroxide or carbonate precipitates, and the fluorine component in the waste water becomes sodium fluoride and dissolves in the waste water. The metal precipitate is separated from the wastewater containing sodium fluoride by filtration, and the separated metal sludge contains a trace amount of a fluorine component. To remove the fluorine component. The alkali washing filtrate obtained by the washing may be mixed with the sodium fluoride, or may be mixed by circulating in a wastewater containing a fluorine component.

[0013] The metal sludge subjected to the alkali cleaning contains the residual alkali and the fluorine component which has not been removed during the alkali cleaning, and is cleaned by using a large amount of water to remove these. By the washing, fluorine contained in the wastewater before the treatment is almost completely removed, and a water washing sludge containing only the metal contained in the wastewater as its hydroxide or the like is obtained. When other impurities are contained in the water washing sludge, only a substantially pure valuable metal is recovered by performing a removing step corresponding to each impurity. By adding a calcium compound such as calcium chloride to the neutralized filtrate after the neutralization solid-liquid separation mixed with the alkali washing filtrate, a precipitate of calcium fluoride containing no impurities such as heavy metals is generated. When this precipitate is removed from the wastewater by filtration or the like, usually, depending on the conditions, a defluorinated wastewater having a fluorine ion concentration of 10 mg / liter or less is obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the wastewater treatment method according to the present invention will be described, but the embodiment is not intended to limit the present invention.

Example 1 Processing of a test solution was performed according to the flowchart of FIG.
In 1 liter of pure water, metallic iron (22.5 g / l), chromium chloride (2.7 g / l in chromium conversion), nickel chloride (0.8 g / l in nickel conversion) and hydrofluoric acid (18.5 g / l in fluorine conversion) Liter, the weight ratio of fluorine to the total amount of metals is 71%) to prepare a test solution. The test solution was neutralized by adding a 6N aqueous solution of sodium hydroxide until the pH reached 12, and the resulting metal sludge (neutralized sludge) was filtered to separate it from waste water (neutralized filtrate).

The neutralized sludge contains iron, chromium,
When elemental analysis of nickel and fluorine was performed, the results shown in Table 1 were obtained, and the weight ratio of fluorine to the total amount of metals was:
5.6%, a significant decrease from 71% of the test solution. Also, when the metal content and the fluorine content of the neutralized filtrate were measured,
All metals were below the detection limit (<1 mg / L) and the fluorine content was 14.3 g / L. Next, the neutralized sludge was suspended in 0.3 liter of an aqueous solution of sodium hydroxide having a pH of 12, and filtered to obtain an alkali-washing sludge and an alkali-washing filtrate. Elemental analysis of the metals and fluorine contained in this alkali cleaning sludge gave the results shown in Table 1. The weight ratio of fluorine to the total metal was 0.28%, which was significantly reduced from 0.98% of the neutralized sludge. did.

When the contents of each metal and the fluorine content of the alkaline washing filtrate were measured, all the metals were below the detection limit (<1
mg / L) and the fluorine content was 1.8 g / liter. Next, the alkali washing sludge was suspended in 0.3 liter of pure water and filtered to obtain a water washing sludge and a water washing filtrate. Elemental analysis of the metals and fluorine contained in the water-washed sludge yielded the results shown in Table 1. The weight ratio of fluorine to the total metal was 0.14%.
Alkaline cleaning sludge was halved from 0.28%. Further, when the amounts of each metal and the fluorine content of the water-washed filtrate were measured, all the metals were below the detection limit (<1 mg / L), and the fluorine content was 0.06 g / liter.

[0018]

[Table 1]

Examples 2 to 4 The test solution was treated under the same conditions as in Example 1 except that the pH 12 during neutralization and the pH 12 during alkali washing were changed to pH 11 and pH 11, respectively (Example 2). The results are shown in Table 1. Although the pH was lower than in Example 1 (because the alkalinity was weak), the residual amount of fluorine in the sludge was large, but a sufficient amount of fluorine was transferred to the wastewater (neutralized filtrate, alkali-washed filtrate and water-washed filtrate). You can see that it is doing.

The test solution was treated under the same conditions as in Example 1 except that the pH 12 during neutralization and the pH 12 during alkaline washing were respectively set to pH 10 and pH 11 (Example 3). The results are shown in Table 1. P compared to Example 1
Since H was low, the amount of fluorine remaining in the sludge was large as compared with Example 1. However, it can be seen that a sufficient amount of fluorine was transferred to the wastewater also in this example. The test solution was treated under the same conditions as in Example 1 except that pH 12 during neutralization and pH 12 during alkali washing were set to pH 9 and pH 11, respectively (Example 4). The results are shown in Table 1. Since the pH was lower than in Example 1, the residual amount of fluorine in the sludge was larger than in Example 1, but it can be seen that a sufficient amount of fluorine was transferred to the wastewater.

[0021]

[Table 2]

Examples 5 to 8 The test solution was treated under the same conditions as in Example 1 except that the pH 12 during neutralization and the pH 12 during alkaline washing were respectively set to pH 8.5 and pH 11 (Example 5). . The results are shown in Table 2. Compared with Example 1 and Examples 2 to 4, the residual amount of fluorine in the sludge was large because the pH at the time of neutralization was particularly low, but the final amount of fluorine in the water-washed sludge was 0.59%. 0.14% of Example 1, 0.23 of Example 4
%, But a sufficient decrease in the fluorine content was observed as compared with the prior art. In Example 1, pH 12 during neutralization and pH 12 during alkaline washing were respectively p
The test solution was treated under the same conditions except that H10 and pH 10 were used (Example 6). The results are shown in Table 2. 0.14% of Example 1 due to lower pH as compared to Example 1
The amount of fluorine remaining in the sludge was as large as 0.22% as compared with (the fluorine content in the water-washed sludge).
(0.21%) and Example 4 (0.23%) showed almost the same value.

The test solution was treated under the same conditions as in Example 6 except that the reagent used for neutralization was changed from sodium hydroxide to sodium carbonate (Example 7). The results are shown in Table 2. As compared with Example 6, although the fluorine content in the sludge at each stage fluctuates, the fluorine content in the water-washed sludge is finally 0.15%, which is lower than 0.22% of Example 6, and The ratio of fluorine to total metal in the sludge was lower than in Example 6. The test solution was treated under the same conditions as in Example 7 except that the pH 10 during neutralization and the pH 10 during alkali washing were respectively set to pH 9 and pH 9 (Example 8). The results are shown in Table 2. Since the pH was lower than that of Example 7, the fluorine content in the sludge was large as a whole, and the ratio of fluorine to the total metal amount was the same as or higher than that of Example 7.

Example 9 Neutralized filtrate of Example 1 (fluorine content 14.3 g / l)
Was used as a test solution, and calcium chloride and sodium hydroxide were added thereto to adjust the calcium concentration of the test solution to 1 g / liter and the pH to 12, and the calcium content of the obtained calcium chloride precipitate and The fluorine content, the calcium content and the fluorine content in the defluorinated wastewater were measured. Table 3 shows the results. The total weight of fluorine and calcium in the resulting calcium fluoride sludge is 43.5% by weight, and the remainder is considered to be water.
On the other hand, the amount of fluorine ions remaining in the defluorinated wastewater was 9.8 mg /
18.5 g / liter of test liquid before starting treatment
Decreased to 0.05%.

Examples 10 to 14 The neutralized filtrate of Example 1 was used as a test solution, and calcium chloride and hydrochloric acid were added to the test solution to adjust the calcium concentration of the test solution to 1 g.
/ Liter, pH is adjusted to 8 (Example 1
0), the calcium content and the fluorine content of the obtained precipitate of calcium chloride, and the calcium content and the fluorine content in the defluorinated wastewater were measured. Table 3 shows the results. In this example, the fluorine in the defluorinated wastewater was 9.4.
It could be removed up to mg / liter. The measurement was performed under the same conditions as in Example 10 except that the pH was set to 6 (Example 11). Table 3 shows the results. Also in this example, fluorine in the fluorine wastewater could be removed up to 9.4 mg / liter.

The measurement was carried out under the same conditions as in Example 10 except that the amount of calcium added was changed to 5.2 g (Example 12).
Table 3 shows the results. In this example, the amount of fluorine ions was further reduced, to about 0.02%. The measurement was performed under the same conditions as in Example 10 except that the amount of added calcium was changed to 5.6 g (Example 13). Table 3 shows the results.
In this embodiment, the amount of fluorine ions is further reduced to about 0.01%
Down to. The measurement was performed under the same conditions as in Example 10 except that the pH was set to 4 (Example 14). Table 3 shows the results. In this example, the amount of fluorine ions was reduced to about 0.05%.

Comparative Example 1 The measurement was carried out under the same conditions as in Example 10 except that the pH was set to 3. However, no calcium chloride precipitate was formed, and the fluorine content in the defluorinated wastewater was 14.3 g of the neutralized filtrate. 13.6 g / liter, which is almost equal to 1 / liter.

[0028]

[Table 3]

[0029]

According to the present invention, an alkali metal hydroxide and / or a waste water containing at least a fluorine compound and a metal compound are contained.
Alternatively, a carbonate is added so that the pH of the waste water becomes 8 to 12 to form a sparingly soluble alkali fluoride and a sparingly soluble metal hydroxide and / or a carbonate. A method for treating wastewater, comprising removing matter and / or carbonate from wastewater (claim 1). By this treatment method, a soluble fluorine compound and a hardly soluble metal compound are generated by a simple method of adding an alkali metal compound while maintaining the wastewater at a predetermined pH, and the fluorine compound and the metal compound in the wastewater are separated. Thus, the metal compounds can be substantially removed from the wastewater to be converted to wastewater containing less impurities.

After the separation of the fluorine compound and the metal compound, a calcium compound such as calcium chloride is added to the wastewater at pH.
Is added so as to be 4 to 12 to produce calcium fluoride (claim 2), which may be removed from the wastewater by filtration or the like. The calcium fluoride produced at this time is low in heavy metals and can be used as a flux for steel or a hydrofluoric acid raw material.

When the metal contained in the wastewater is a valuable metal and the main purpose is to recover the valuable metal rather than purifying the wastewater, the sludge of the hardly soluble metal compound described above contains a readily soluble alkali fluoride. PH 9-12 after separation from wastewater
It is sufficient to wash with alkali and then with water (Claim 3), whereby iron substantially free of fluorine compounds,
Valuable metals such as nickel and chromium can be recovered. Next, when both purification of wastewater and recovery of valuable metals are necessary, the latter is removed from the wastewater containing a readily soluble fluorinated compound and a poorly soluble metal compound by filtration or the like, and the two are separated. Is added to the wastewater containing water so as to have a calcium concentration of 0.5 g / liter or more and a pH of 4 to 12 to form sparingly soluble calcium fluoride. The sludge of the latter metal compound is alkali-washed at pH 9 to 12. Water washing may be performed (claim 4).

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a method for performing a wastewater treatment method according to the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22B 7/00 C22B 7/00 H 3/00 Q (72) Inventor Hironori Tateiwa 1333- Hara-shi, Ageo-shi, Saitama 2 Mitsui Kinzoku Mining Co., Ltd. F-term (Ref.) 4D038 AA08 AB41 AB65 AB66 AB67 AB81 AB82 BB13 BB17 BB18 4K001 AA08 AA10 AA19 BA21 CA02 CA08 DB23 EA06

Claims (4)

[Claims] 1. An alkali metal hydroxide and / or carbonate is added to a waste water containing at least a fluorine compound and a metal compound so that the pH of the waste water becomes 8 to 12, so that the alkali metal hydroxide and / or the carbonate can be easily dissolved. A method for treating wastewater, comprising forming a soluble metal hydroxide and / or metal carbonate and removing the hardly soluble metal hydroxide and / or carbonate from the wastewater. 2. An alkali metal hydroxide and / or carbonate is added to a waste water containing at least a fluorine compound and a metal compound so that the pH of the waste water becomes 8 to 12, so that the alkali metal hydroxide and / or the carbonate are easily dissolved. A soluble metal hydroxide and / or metal carbonate is formed, and the hardly soluble metal hydroxide and / or carbonate is removed from the wastewater. Is 4-12
A method for treating wastewater, comprising adding hardly soluble calcium fluoride by adding the fluorine compound to the wastewater and removing the fluorine compound from the wastewater. 3. An alkali metal hydroxide and / or carbonate is added to waste water containing at least a fluorine compound and a metal compound so that the pH of the waste water becomes 8 to 12, so that the alkali metal hydroxide and / or the carbonate can be easily dissolved. A soluble metal hydroxide and / or a metal carbonate is formed to form a metal sludge, and the metal sludge is separated from a wastewater containing a readily soluble alkali fluoride, washed with an alkali at pH 9 to 12, and further washed with water. A wastewater treatment method, wherein the metal in the wastewater is collected as valuable metal. 4. An alkali metal hydroxide and / or carbonate is added to waste water containing at least a fluorine compound and a metal compound so that the pH of the waste water becomes 8 to 12, so that the alkali metal hydroxide and / or the carbonate can be easily dissolved. A soluble metal hydroxide and / or metal carbonate is formed, and the hardly soluble metal hydroxide and / or carbonate is removed from the wastewater, and a calcium compound is added to the wastewater so that the pH becomes 4 to 12. To form hardly soluble calcium fluoride, remove the fluorine compound from the wastewater, separate the formed metal sludge from the wastewater containing the easily soluble alkali fluoride, wash with alkali at pH 9 to 12, and further wash with water. A wastewater treatment method comprising washing and collecting metals in wastewater as valuable metals.