JP2009262109A - Treating agent of chromium and arsenic, and treatment method using the same - Google Patents

Abstract

[Problem] To treat chromium and / or arsenic in wastewater, it is necessary to add a large amount of chemicals, and a large amount of processing waste is generated, so that efficient treatment cannot be performed.
In a chromium and / or arsenic treatment agent obtained by mixing a soluble aluminum compound and a soluble magnesium compound, chromium and / or arsenic can be efficiently added with a small amount of chemical addition without adding an oxidizing agent or a reducing agent. Can be processed. In particular, when aluminate and / or its salt is used, chromium and / or arsenic contained in the wastewater can be highly insolubilized by maintaining a small amount of chemicals and maintaining the wastewater at pH 8 or higher and 12.5 or lower. In addition, sludge produced can be significantly reduced.
[Selection] Figure 1

Description

  The present invention relates to a treatment agent and treatment method for chromium and / or arsenic, and not only highly adsorbs and removes chromium and / or arsenic in wastewater and groundwater, but also enables treatment with a very small amount of treatment agent. The present invention relates to a chromium and / or arsenic treatment agent capable of extremely reducing the sludge capacity after treatment and a treatment method using the same.

  Wastewater containing chromium and / or arsenic is discharged from various factories and facilities such as a plating factory, a semiconductor factory, a glass factory, and a thermal power plant. Regarding the discharge of chromium and arsenic, the uniform water drainage standard is set to 0.5 mg / liter for hexavalent chromium and 0.1 mg / liter for arsenic according to the Water Pollution Control Law. However, since a sufficient removal technique has not been established, development of an efficient treatment method is desired.

  For example, a method for treating chromium by reducing hexavalent chromium to trivalent chromium with divalent iron is known. (For example, patent document 1) Moreover, the arsenic processing method by oxidizing arsenous acid to pentavalent arsenic with hydrogen peroxide is known. However, since these methods use a reducing agent and an oxidizing agent, there is a problem that the chemical cost is high, and the treatment process is complicated because it includes a reducing step and an oxidizing step.

  Further, regarding the adsorption of chromium and arsenic by hydrotalcite, a method for improving the adsorption performance by reducing the crystal size by a special treatment method or not containing carbonate ions is disclosed. However, even with such a method, there is a problem that a large excess of hydrotalcite needs to be added to remove chromium and arsenic, and a large amount of sludge is generated.

Japanese Patent Laid-Open No. 7-80478 Japanese Patent Laid-Open No. 11-314094 Japanese Patent No. 4036237

  An object of the present invention is to remove a conventional chromium or arsenic-containing water without using an oxidizing agent or a reducing agent, and to remove them with a small amount of chemicals, and a sludge using the same. The present invention provides a processing method that can significantly reduce the amount of generation.

  The present invention adds a treatment agent formed by mixing a soluble aluminum compound and a soluble magnesium compound in wastewater containing chromium and / or arsenic, and particularly uses aluminate and / or a salt thereof as the soluble aluminum compound. Chromium and / or arsenic is removed by maintaining the pH of the waste water at 8 or more and 12.5 or less.

  The present invention is described in detail below.

  The chromium and / or arsenic treatment method of the present invention is to add a soluble aluminum compound and a soluble magnesium compound to waste water containing chromium and / or arsenic.

  The soluble aluminum compound used in the present invention is not particularly limited as long as it is soluble, but includes soluble (particularly water-soluble) aluminum compounds such as aluminum sulfate, aluminum nitrate, aluminum chloride, polyaluminum chloride, and sodium aluminate, One or two or more of these may be used. Of these, aluminate and / or a salt thereof are preferable, and a sodium salt is particularly preferable as the salt.

  When using aluminate and / or its salt, not only does it not contain anionic species such as sulfuric acid, chlorine, nitric acid as with other soluble aluminum, but also the influence of interfering anions contained in the waste water. In particular, high chromium and / or arsenic removal ability is exhibited.

  The soluble magnesium compound used in the present invention is not particularly limited as long as it is soluble, but examples thereof include soluble magnesium compounds such as magnesium sulfate, magnesium nitrate, magnesium chloride, magnesium carbonate, and one or more of these are used. May be. Among these, highly soluble magnesium chloride is particularly preferable.

  These soluble aluminum compounds and soluble magnesium compounds can be used by dissolving each solid in water, but mixing and using as an aqueous solution dissolved in water from the beginning can remove chromium and / or arsenic. Preferred in performance and operation.

  When the Mg / Al molar ratio is less than 0.5, the amount of the soluble magnesium compound added decreases the precipitation of aluminum and deteriorates the processing efficiency. The upper limit of the Mg / Al molar ratio is not particularly limited as processing performance, but the amount of sludge generated increases as the amount of soluble magnesium compound added increases, so the purpose of removing chromium and / or arsenic can be achieved. However, the amount of waste increases. A preferred Mg / Al molar ratio is 0.5 or more, particularly in the range of 0.7 to 4. In the advanced treatment below the wastewater treatment standard, higher treatment performance is exhibited when the Mg / Al molar ratio is in the range of 0.7 to less than 3, particularly preferably in the range of 1 to less than 2.

  The amount of soluble aluminum compound and soluble magnesium compound added is 0.5 to 100 times the aluminum / Al / (Cr + As) molar ratio of chromium and / or arsenic to remove chromium and / or arsenic. it can. If the addition amount of the soluble aluminum compound is less than 0.5 in terms of Al / (Cr + As) molar ratio, a sufficient removal effect cannot be obtained, and if it is more than 100, the purpose of removing chromium and / or arsenic can be achieved. Sludge is generated, and the amount of waste increases. The particularly preferable amount of soluble aluminum added is in the range of 1 to 50, particularly 20 or less, and further 5 to 15 in terms of Al / (Cr + As) molar ratio.

  When aluminum and magnesium are dissolved in the treated water from the beginning, the amount of dissolved aluminum and magnesium can be reduced from the amount of the above-mentioned soluble aluminum compound and soluble magnesium compound.

  A method for adding the soluble aluminum compound and the soluble magnesium compound is not particularly limited, and a treatment agent prepared as a mixed solution or suspension previously mixed at a molar ratio in the above range may be added. It is particularly preferred that two separate agents, a compound containing agent and a soluble magnesium compound containing agent, are simultaneously added to the waste water so as to have a molar ratio in the above range and mixed on-site. Further, one soluble compound may be mixed with waste water in advance, and the other soluble compound may be added later so as to have a molar ratio in the above range. In any case, it is preferable to use a solvent, particularly one stabilized in an aqueous solution. When the two agents are mixed and precipitated and dried, the cause is not clear, but the removal performance is lowered.

  In this invention, when mixing a soluble aluminum compound and a soluble magnesium compound, it is not necessary to heat waste water, and it can process at room temperature. In addition, the processing of the present invention is not limited to a batch processing apparatus, and can be performed in a continuous processing apparatus.

  It is preferable that the soluble aluminum compound and the soluble magnesium compound are sufficiently diffused in the wastewater by an operation such as stirring and shaking after the wastewater is treated. If the diffusion is insufficient, the removal effect of the present invention may not be sufficiently obtained.

  In the treatment of the present invention, after adding a soluble aluminum compound and a soluble magnesium compound to the treated waste water, the pH of the waste water is maintained at 8 or more and 12.5 or less, or the pH of the waste water is maintained at 8 or more and 12.5 or less. It is preferable to add a soluble aluminum compound or a soluble magnesium compound because the removal performance is improved.

  The pH adjustment in the treatment of the present invention may be performed by adding an acid or an alkali as necessary. In the treatment of the present invention, the soluble magnesium compound and the soluble aluminum capture and deposit chromium and / or arsenic in the wastewater, but at a pH below 8, the precipitation of magnesium deteriorates, so a large amount of chemicals must be added. There are cases where efficient processing cannot be performed. On the other hand, if the pH exceeds 12.5, the precipitation of aluminum deteriorates, so a large amount of chemicals must be added, and efficient treatment may not be performed. The preferred pH is in the range of 9.5 to 11.5.

  For adjusting the pH of the wastewater, inorganic acids such as sulfuric acid, hydrochloric acid and nitric acid, or inorganic alkalis such as sodium hydroxide, potassium hydroxide and calcium hydroxide can be used effectively.

  Although the pH of the waste water may be controlled after adding the soluble aluminum compound and the soluble magnesium compound, it is particularly preferable to add the soluble aluminum compound and the soluble magnesium compound while maintaining the pH of the waste water within the above range.

  The soluble aluminum compound and the soluble magnesium compound may be added at one time, but it is particularly preferable to add them continuously or intermittently over time. The addition time is not particularly limited, but is preferably about 5 minutes to 1 hour. When the time is shorter than 5 minutes, the processing performance may be deteriorated. When the processing time is longer than 1 hour, the processing performance does not change, but the amount of waste water that can be processed per unit time is reduced, which is not efficient. By adding the soluble aluminum compound and the soluble magnesium compound over time while maintaining the pH of the wastewater within the above range, it is presumed that the generation of insolubilized products generated at a specific pH is promoted.

  When carbonic acid is dissolved in the wastewater to be treated, a calcium compound may be added.

  In the treatment method of the present invention, the removal performance can be further improved by further adding an acid after adding and treating soluble aluminum and soluble magnesium in the wastewater by the above-described method.

  The pH after the acid addition is preferably in the range of 5 to 12, particularly preferably 7 or more. When the final pH becomes acidic, chromium and / or arsenic may elute.

  The insolubilized material obtained by the treatment of the method of the present invention is discarded after solid-liquid separation. For solid-liquid separation, for example, general solid-liquid separation methods such as sedimentation separation, flotation separation, pressing, and filtration are usefully applied. At this time, if the amount of the soluble aluminum compound and the soluble magnesium compound added is extremely small, the insolubilized product may not be sufficiently aggregated and solid-liquid separation may be difficult. In this case, it is preferable to perform solid-liquid separation after adding a flocculant, for example, a general inorganic flocculant such as sulfate band, polyaluminum chloride, ferric chloride, polytetsu, etc. to form a floc having good coagulation. A preferred inorganic flocculant is ferric chloride.

  However, since the pH of the wastewater after the addition of the inorganic flocculant affects the treatment performance, it is necessary to pay attention to the pH of the wastewater until solid-liquid separation. The pH of the wastewater to be maintained is preferably 5 or more and 12.5 or less. When the pH of the waste water is less than 5 or exceeds 12.5, the captured chromium and / or arsenic is eluted, and the processing performance may be greatly deteriorated. A more preferable pH of the waste water is in the range of 6 to 11. If a polymer flocculant such as acrylic polymer, sodium alginate, or chitosan is used in combination with the inorganic flocculant, solid-liquid separation can be further facilitated.

  The treatment method of the present invention can be used in combination or in combination with other treatment methods. For example, the treatment method of the present invention is performed after the primary treatment by the reduction treatment method of hexavalent chromium with divalent iron or metallic iron, or the arsenous acid is subjected to the primary treatment by the oxidation treatment method of hypochlorite or the like. By performing the treatment method, or treating with an adsorbent such as a chelate resin or a rare earth after the primary treatment by the treatment method of the present invention, highly removed high-quality treated water can be obtained.

  The treatment method of the present invention can also be performed in combination with or in combination with other harmful substance treatment methods. For example, chromium and / or arsenic and other harmful substances can be treated simultaneously with fluorine, phosphoric acid treatment with calcium, zirconium and rare earth treatment agents, or heavy metal treatment with chelating agents such as dithiocarbamate. It is possible to obtain a high-quality wastewater from which substances have been removed to a high degree.

  The treatment agent of the present invention is a mixture of a soluble aluminum compound and a soluble magnesium compound. A liquid in which a soluble aluminum compound and a soluble magnesium compound are dissolved in water is preferable because it is easy to handle in operation, but may be used by dissolving a solid.

  The Mg / Al molar ratio of the soluble aluminum compound and soluble magnesium compound in the treatment agent of the present invention is a composition that is 0.5 or more, preferably 0.7 or more and 4 or less, more preferably 0.7 or more and less than 3, particularly preferably. Is preferably contained in a composition of 1 or more and less than 2.

  It is particularly preferable that the treatment agent is one agent containing a soluble aluminum compound and a soluble magnesium compound, because it is easy to handle in terms of operation, but the soluble aluminum compound-containing agent and the soluble magnesium compound-containing agent are separately mixed and used in waste water. You may be comprised with 2 agents. In the case of being composed of two agents, the ratio at which the Mg / Al molar ratio between the soluble aluminum compound and the soluble magnesium compound is 0.5 or more when used, preferably 0.7 or more and 4 or less, particularly preferably 0.7 It is preferable to use two agents at a ratio of 3 or less.

  When aluminum and / or magnesium is dissolved in the wastewater to be treated from the beginning, the amount of aluminum and magnesium dissolved in the wastewater is taken into consideration so that the molar ratio is within the above range. It is preferable to adjust the amount of the soluble aluminum compound and the soluble magnesium compound.

  The chromium and / or arsenic-containing wastewater treatment agent of the present invention may contain a soluble calcium compound, a pH adjuster, a flocculant and the like in addition to the soluble aluminum compound and the soluble magnesium compound.

  The soluble calcium compound is not particularly limited, but calcium chloride having high solubility is desirable.

  The pH adjuster is not particularly limited, and examples thereof include inorganic acids such as sulfuric acid, hydrochloric acid and nitric acid, and inorganic alkalis such as sodium hydroxide, potassium hydroxide and calcium hydroxide.

  Examples of the flocculant include general inorganic flocculants such as ferric chloride and polytetsu, and general polymer flocculants such as acrylic polymers, sodium alginate, and chitosan.

  The treatment agent comprising a mixture of a soluble aluminum compound and a soluble magnesium compound has a high adsorption performance for chromium and / or arsenic, and particularly uses aluminate and / or a salt thereof as the soluble aluminum, so that the pH of the waste water is 8 to 12.5. By maintaining and adding over time, it can be removed to a high degree by using a smaller amount of the drug than before without adding an oxidizing agent or a reducing agent during the adsorption treatment. Since this can be achieved by adding a small amount of an aqueous solution of a soluble compound to the wastewater, the operability is excellent, the amount of generated sludge is extremely small, and the amount of processing waste can be reduced.

  EXAMPLES Next, although an Example demonstrates this invention further more concretely, this invention is not limited at all by these Examples.

  All processing operations were performed at room temperature.

(Preparation of treatment agent A)
Two solutions: 11.7 g of 70% sodium aluminate dissolved in water to a total amount of 100 g, and 30.5 g of magnesium chloride hexahydrate dissolved in water to a total amount of 100 g Treatment agent A was prepared.

(Preparation of treatment agent B)
Treatment agent B was prepared by dissolving 24.1 g of aluminum chloride hexahydrate and 30.5 g of magnesium chloride hexahydrate in water to a total amount of 100 g.

Example 1
An arsenic treatment test was conducted using 1 liter of a solution containing 10 mg / liter of pentavalent arsenic prepared by dissolving 41.6 mg / liter of disodium hydrogen arsenate heptahydrate as a model waste water.

  While maintaining the pH of the model wastewater at 10 with 1N sodium hydroxide solution, 1.3 g of each of the two liquids of treatment agent A was added at a constant rate over 5 minutes using a syringe pump with stirring. . The amounts of Al and Mg added were 10 and 15 moles, respectively, compared to arsenic in the model waste water. After stirring for 10 minutes after the addition, 0.1 g of 40% ferric chloride solution was added, stirred for 5 minutes while maintaining the pH of the wastewater at a predetermined value, and then allowed to stand for 30 minutes. The arsenic in the filtrate was quantitatively analyzed by ICP. The relationship between the pH of the waste water and the remaining amount of arsenic is shown in FIG.

Example 2
Chromium treatment using 1 liter of a solution containing 10 mg / liter of hexavalent chromium as a model effluent by dissolving 10 g of a 1000 mg / liter standard solution for atomic absorption prepared by dissolving potassium dichromate to 1 liter A test was conducted.

  While maintaining the pH of the model waste water at 10 using a 1N sodium hydroxide solution, 1.9 g of each of the two liquids of treatment agent A was added over 8 minutes at a constant rate using a syringe pump with stirring. . After stirring for 5 minutes after the addition, 0.1 g of 40% ferric chloride solution was added, stirred for 5 minutes while maintaining the pH of the wastewater at a predetermined value, and allowed to stand for 30 minutes. The chromium in the filtrate was quantitatively analyzed by ICP. The relationship between the pH of the waste water and the residual amount of chromium is shown in FIG.

Example 3
Chromium treatment using 1 liter of a solution containing 10 mg / liter of hexavalent chromium as a model effluent by dissolving 10 g of a 1000 mg / liter standard solution for atomic absorption prepared by dissolving potassium dichromate to 1 liter A test was conducted.

  While maintaining the pH of the model waste water at 10 using a 1N sodium hydroxide solution, the two solutions of treatment agent A are simultaneously stirred at a constant rate of 2.5 g of solution per 10 minutes using a syringe pump. Added. After stirring for 5 minutes, 0.1 g of 40% ferric chloride solution was added, stirred for 5 minutes while maintaining the pH of the waste water at 9, and allowed to stand for 30 minutes. The supernatant was filtered through 5A filter paper. The chromium in the filtrate was quantitatively analyzed by ICP. The relationship between the molar ratio of aluminum to the amount of chromium in the waste water and the residual amount of chromium is shown in FIG.

Example 4
Chromium treatment using 1 liter of a solution containing 10 mg / liter of hexavalent chromium as a model effluent by dissolving 10 g of a 1000 mg / liter standard solution for atomic absorption prepared by dissolving potassium dichromate to 1 liter A test was conducted.

  While maintaining the pH of the model waste water at 10 using a 1N sodium hydroxide solution, 1.9 g of treatment agent B was added at a constant rate over 8 minutes using a syringe pump with stirring. After stirring for 5 minutes after the addition, 0.1 g of 40% ferric chloride solution was added, stirred for 5 minutes while maintaining the pH of the wastewater at a predetermined value, and allowed to stand for 30 minutes. The chromium in the filtrate was quantitatively analyzed by ICP. The relationship between the pH of the waste water and the remaining amount of chromium is shown in FIG.

Comparative Example 1
1 liter of a solution containing 10 mg / liter of pentavalent arsenic prepared by dissolving 41.6 mg / liter of disodium hydrogen arsenate heptahydrate was used as a model wastewater, and only iron chloride was added without treating agent A. An arsenic treatment test was conducted.

  While maintaining the pH of the model wastewater at 8 using a 1N sodium hydroxide solution and a 1N hydrochloric acid solution, 0.1 g of 40% ferric chloride solution was added with stirring and stirred for 10 minutes, and then 30 The mixture was allowed to stand for 5 minutes, and the supernatant was filtered through 5A filter paper. Arsenic in the filtrate was quantitatively analyzed by ICP. Arsenic remained at 1.4 mg / liter in the waste water after treatment, and pentavalent arsenic could not be sufficiently treated with iron chloride alone.

Comparative Example 2
A treatment agent using 1 liter of a solution containing 10 mg / liter of hexavalent chromium as a model effluent by dissolving 10 g of a 1000 mg / liter standard solution for atomic absorption prepared by dissolving potassium dichromate to 1 liter A chromium treatment test was performed only with iron chloride without adding A and B.

  While maintaining the pH of the model waste water at 8 using a 1N sodium hydroxide solution and a 1N hydrochloric acid solution, 0.2 g of a 40% ferric chloride solution was added with stirring and the mixture was stirred for 10 minutes and then 30 The mixture was allowed to stand for 5 minutes, and the supernatant was filtered through 5A filter paper, and the chromium in the filtrate was quantitatively analyzed by ICP. Chromium in the waste water after treatment remained at 10 mg / liter, and chromium could not be treated at all with iron chloride alone.

4 is a graph showing the remaining amount of arsenic after arsenic treatment in Example 1. It is a graph which shows the chromium residual amount after the chromium process of Example 2. FIG. It is a graph which shows the chromium residual amount after the chromium process of Example 3. FIG. It is a graph which shows the chromium residual amount after the chromium process of Example 4.

Claims (10)

A method for treating water containing chromium and / or arsenic, wherein a soluble aluminum compound and a soluble magnesium compound are added to water containing chromium and / or arsenic. The treatment method according to claim 1, wherein the soluble aluminum compound is aluminate and / or a salt thereof. The treatment method according to any one of claims 1 to 2, wherein the soluble aluminum compound and the soluble magnesium compound are added while maintaining the pH of the waste water at 8 or more and 12.5 or less. The processing method according to any one of claims 1 to 3, wherein a molar ratio Mg / Al of magnesium and aluminum is 0.5 or more. The treatment method according to any one of claims 1 to 4, further comprising adding a calcium compound. 6. The processing method according to claim 1, wherein an acid is further added after the addition of the soluble aluminum compound and the soluble magnesium compound. The treatment method according to claim 6, wherein the pH after addition of the acid is in the range of 5 to 12. A chromium and / or arsenic treating agent used by mixing a soluble magnesium-containing solution and a solution containing aluminate and / or a salt thereof. Furthermore, the processing agent of Claim 8 which mixes and uses soluble calcium. Furthermore, the processing agent of Claim 9 which mixes and uses an acid.

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