JP4264226B2 - Purification of wastewater, groundwater or soil leachate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying waste water, groundwater or soil leachate containing selenium and / or organochlorine compounds and heavy metals.
[0002]
[Prior art]
Contaminated soil may contain selenium and / or organochlorine compounds and heavy metals, and heavy metals in these soils may elute into groundwater or soil leachate and contaminate the surrounding environment. is there. Conventionally, techniques for removing heavy metals such as mercury, cadmium and lead include: (1) a method for removing carbonates and hydroxides, (2) a method for removing sodium sulfide as a mixture, and (3) a chelating agent. The method of making it adsorb | suck to is known.
[0003]
However, the method (1) requires a large amount of flocculant because the solubility of heavy metals is larger than that of sulfides. As a result, there is a problem that the amount of sludge generated is large and the optimum pH differs depending on the heavy metal to be treated, so that it cannot be treated in one step, and many steps of pH adjustment are required.
[0004]
The method (2) is difficult to handle due to the strong alkalinity of sodium sulfide used, and hydrogen sulfide is generated during use, which may cause corrosion of the device and secondary pollution such as bad odor. is there. Furthermore, in the method (3), the chelating agent is expensive and difficult to reuse, and not much heavy metal can be treated. As described above, the conventional heavy metal removal technique has problems such as high processing cost and difficulty in operation, and a technique for removing selenium and / or organochlorine compounds has not been known.
[0005]
[Problems to be solved by the invention]
The present invention solves the above-mentioned conventional problems and purifies drainage, groundwater or soil leachate that can easily purify groundwater or soil leachate containing selenium and / or organochlorine compounds and heavy metals at low cost. It was made to provide a method.
[0006]
[Means for Solving the Problems]
Invention of Claim 1 made | formed in order to solve said subject is the waste water containing selenium and a heavy metal, groundwater, or soil leachate to the iron sulfide powder of purity 30-80% containing Fe at least other than FeS. The hexavalent selenium is reduced by contact to be coprecipitated with the iron hydroxide colloid, heavy metals are precipitated as sulfides, and heavy metals that do not produce sulfides are precipitated as hydroxides to precipitate them from the water. It is characterized by removing. According to the invention of claim 2, wastewater, groundwater or soil leachate containing an organic chlorine compound and heavy metal is brought into contact with iron sulfide powder containing 30% to 80% purity containing at least Fe in addition to FeS. It is detoxified by dechlorination, and precipitates heavy metals as sulfides, and further removes heavy metals that do not generate sulfides as hydroxides, thereby removing them from the water. . Note that fluorine and boron can be removed by adding a calcium salt at a later stage. Moreover, groundwater can be purified by supporting iron sulfide containing Fe on a water permeable body and installing it in a groundwater vein. In any of the inventions, iron sulfide containing Fe and Fe ₃ O ₄ , Fe and Fe ₂ O ₃ , and Fe, Fe ₃ O ₄ and Fe ₂ O ₃ can be used. Further, the reaction can be carried out at a pH in the range of 5.5-8.
[0007]
According to the present invention, hexavalent selenium in waste water, ground water or soil leachate is reduced to tetravalent selenium or simple selenium by the reducing power of Fe and iron sulfide, and in the iron hydroxide colloid produced. Tetravalent selenium or simple selenium can be taken in and coprecipitated and separated from water. When dissolved oxygen is abundant, even if Fe ₂ O ₃ is not contained, there is no problem since iron hydroxide colloid is generated by dissolution of iron sulfide and Fe, but when dissolved oxygen is not included, Fe ₂ O ₃ It is preferable that iron is contained since iron hydroxide colloids are easily formed.
[0008]
Further, by using the reducing power of iron sulfide itself and the reducing power of Fe contained, the organic chlorine compound can be dechlorinated and rendered harmless. In addition, heavy metals such as mercury, cadmium, copper, and lead, which have a high solubility product due to the nature of iron sulfide itself, can be separated from the water by being deposited on the surface of iron sulfide. Furthermore, even in the case of a heavy metal that does not generate sulfides such as hexavalent chromium, it can be reduced and precipitated as a hydroxide of trivalent chromium. Of course, trivalent chromium can also be precipitated as a hydroxide, and manganese can also be precipitated as a hydroxide. This is because iron hydroxide generated on the surface of iron sulfide or iron sulfide serves as a nucleus to accelerate precipitation or precipitation of chromium or manganese hydroxide.
[0009]
Fe ₃ O ₄ is generally called black rust and acts as an antioxidant. That is, it plays the role of an antioxidant that prevents internal oxidation when iron sulfide having reducing power is stored for a long period of time. Further, since it has magnetism and sticks to the magnet, it is desirable that iron sulfide is included because it can be easily recovered by magnetic force when used in powder form. What is used in the present method is inexpensive and safe iron sulfide containing Fe and optionally Fe ₃ O ₄ or Fe ₂ O ₃ , so that the purification cost is low. In addition, the reaction is possible in the neutral range, and hydrogen sulfide is not generated, and the operation is easy.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention are shown below.
FIG. 1 shows a first embodiment of the present invention, which is a method for purifying drainage, ground water taken from the ground or soil leachate. Waste water, groundwater or soil leachate containing selenium and / or organochlorine compounds and heavy metals is once stored in the storage tank 1 and sent to the reaction tank 2. The reaction vessel 2 is provided with a stirring device 3.
[0011]
Although the iron sulfide particles 4 are introduced into the reaction vessel 2, it is not high-purity iron sulfide but low-purity iron sulfide containing Fe and possibly Fe ₃ O ₄ and Fe ₂ O _3. . It is sufficient that the purity of iron sulfide is about 30%, and a very high purity is not preferable because Fe and Fe ₃ O ₄ and Fe ₂ O ₃ are relatively decreased in some cases. The purity of preferable iron sulfide is about 30 to 80%. The iron sulfide particles 4 are preferably set to 110 μm or less in order to secure a surface area. Although it is difficult to identify the crystalline phase of the iron sulfide surface in the form of particles, it is difficult to identify the crystalline phase of the iron sulfide used in this method. Furthermore, it is desirable to identify the non-oxidized fracture surface by X-ray diffraction after crushing to a certain size in consideration of the effect of surface oxidation.
[0012]
When ground water or soil leachate containing selenium and / or organochlorine compound and heavy metal is put into the reactor 2 and stirred with iron sulfide particles 4 containing Fe and possibly Fe ₃ O ₄ and Fe ₂ O ₃ , Most of the heavy metals become sulfides and precipitate on the surfaces of the iron sulfide particles 4. That is, of the heavy metal sulfides and iron sulfide (FeS), the one with the smaller solubility product in water is precipitated, but mercury, copper, lead, cadmium, tin, cobalt, nickel, zinc, arsenic, antimony, bismuth. Since sulfides such as these have a smaller solubility product than iron sulfide, they precipitate on the surface of the iron sulfide particles 4 and are separated from the water. Moreover, since iron sulfide and iron hydroxide formed on the surface serve as a nucleus to promote precipitation, hexavalent chromium that does not produce sulfide is reduced by the reducing power of iron sulfide and iron, and then trivalent chromium hydroxide. And manganese is also separated from water as hydroxide.
[0013]
In addition, by setting the pH of the reaction tank 2 to a neutral range of 5 to 8, it is possible to remove heavy metals without generating hydrogen sulfide, and the reaction proceeds sequentially while switching to various pH as in the conventional method. There is no need to let them. Further, the reaction of the present invention can proceed in the air without any trouble and no hydrogen sulfide is generated, so that it is not necessary to perform special atmosphere control.
[0014]
However, since selenium cannot be removed by the above-described method, in the present invention, selenium is separated from water by a method in which it is incorporated into iron hydroxide colloid and coprecipitated. As described above, the iron sulfide particles 4 used in the present invention contain Fe and optionally Fe ₃ O ₄ and Fe ₂ O ₃ , and first, hexavalent in water by the reducing power of Fe and iron sulfide. Is reduced to tetravalent selenium or simple selenium. On the other hand, Fe ₂ O ₃ is eluted by stirring and becomes iron hydroxide Fe (OH) ₃ to form a colloid. The reduced tetravalent selenium or simple selenium co-precipitates with this colloid and is separated from the water.
[0015]
In the case of abundant dissolved oxygen, there is no problem because iron hydroxide colloid is generated by dissolution of iron sulfide and Fe even if Fe ₂ O ₃ is not contained, but in the case of water that does not contain dissolved oxygen It is desirable that Fe ₂ O ₃ is contained because iron hydroxide colloids are easily formed on the iron sulfide surface. Moreover, since iron sulfide and iron hydroxide formed on the surface serve as a nucleus to promote precipitation, hexavalent chromium that does not generate sulfide is reduced by the reducing power of iron sulfide and iron, and then the hydroxylation of trivalent chromium is performed. It precipitates as a product, and manganese is also separated from water as a hydroxide.
[0016]
Thus, according to the method of the present invention, selenium can be separated from water together with heavy metals such as mercury, copper, lead, cadmium, tin, cobalt, nickel, zinc, arsenic, antimony, bismuth, chromium and manganese. It becomes. Even when organic chlorine compounds such as trichlorethylene and tetrachloroethylene are contained in water, they can be decomposed by the reducing power of Fe and iron sulfide. Further, by adding a calcium salt at a later stage, fluorine and boron can be aggregated and precipitated as calcium fluoride or calcium boride and removed.
[0017]
FIG. 2 is a diagram showing a second embodiment of the present invention. In this embodiment, iron sulfide particles 5 containing Fe and possibly Fe ₃ O ₄ and Fe ₂ O ₃ are supported on the water permeable body 6 and installed in the underground water channel 7. As the water permeable body 6, a filter can be used, for example. The groundwater flowing through the groundwater vein 7 comes into contact with Fe and possibly iron sulfide containing Fe ₃ O ₄ and Fe ₂ O ₃ when passing through the permeable body 6, and the heavy metal is the same as in the first embodiment. It can be precipitated as sulfides or hydroxides, and selenium can be separated from the water by trapping in iron hydroxide colloids. Furthermore, when organic chlorine compounds such as trichlorethylene and tetrachloroethylene are contained in water, these can be decomposed by the reducing power of Fe and iron sulfide. If the “permeation wall method” is used in this way, the groundwater can be purified without requiring any power or facilities.
[0018]
【Example】
Examples of the present invention are shown below.
(Example 1) Test groundwater containing mercury 1 ppm, lead 10 ppm, copper 1 ppm, cadmium 1 ppm, arsenic 2.5 ppm, hexavalent selenium 5 ppm, tetravalent selenium 5 ppm, hexavalent chromium 1 ppm, trivalent chromium 1 ppm, manganese 5 ppm. Created. 1 L of this groundwater for test was placed in a beaker together with 5 g of iron sulfide powder and stirred at room temperature with a 200 rpm stirrer for 3 hours. The iron sulfide powder has a composition of 9% Fe, 15% Fe ₃ O ₄ , 13% Fe ₂ O ₃ and 63% FeS, and its particle size is 106 μm. The pH in the beaker is neutral from 6.4 to 7.1.
[0019]
After stirring for 3 hours, each component in the groundwater for testing was analyzed. As a result, mercury was 0.005 ppm or less, and lead, copper, cadmium, arsenic, hexavalent chromium, trivalent chromium, and manganese were all 0.05 ppm or less. It was greatly reduced and all heavy metals were separated. In addition, tetravalent selenium and hexavalent selenium each decreased to 0.05 ppm or less, and it was confirmed that they were separated from water. When the surface of the iron sulfide powder was observed with a microscope, deposits were observed on the surface, and it was confirmed that heavy metals and selenium in water were captured on the surface of the iron sulfide powder.
[0020]
In addition, when the experiment was performed under the same conditions while changing the particle size of the iron sulfide powder to 212 to 355 μm, lead 4.6 ppm, copper 0.4 ppm, hexavalent selenium 1.8 ppm and the like were measured. Thus, it turns out that the one where the particle size of iron sulfide powder is fine is preferable. However, if it is too fine, it becomes difficult to separate from water.
[0021]
(Example 2) 10 mL of test waste water containing 10 mg / L of trichlorethylene and 1 mg / L of Hg was prepared and placed in a vial. After 100 mg of iron sulfide was added and sealed, the mixture was stirred at room temperature for 3 hours at 200 rpm. When each component was analyzed, trichlorethylene was not detected, and Hg was 0.005 mg / L or less. In addition, about 90% of the amount of trichlorethylene added by decomposition of trichlorethylene was detected.
[0022]
【The invention's effect】
As described above, according to the method for purifying groundwater or soil leachate containing selenium and heavy metals of the present invention, by using Fe and optionally Fe ₃ O ₄ , Fe ₂ O ₃ containing iron sulfide, Selenium and heavy metals can be separated and removed from the water. This Fe and, in some cases, Fe ₃ O ₄ and Fe ₂ O ₃ containing iron sulfide can be obtained at low cost, and the reaction proceeds simultaneously in the neutral region without setting special reaction conditions. Therefore, drainage, ground water and soil leachate can be purified easily and inexpensively. Moreover, since there is no generation of hydrogen sulfide, there is no possibility of causing corrosion of the apparatus or secondary pollution such as bad odor.
[0023]
Further, fluorine or boron can be removed by adding a calcium salt at a later stage as in claim 2, and sulfur containing Fe and optionally Fe ₃ O ₄ and Fe ₂ O ₃ as in claim 3. If iron is supported on a permeable body and installed in a groundwater vein, it becomes possible to purify the groundwater without requiring any special equipment or power.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a first embodiment.
FIG. 2 is a cross-sectional view showing a second embodiment.
[Explanation of symbols]
1 recovery tank, 2 reaction tank, 3 stirrer, 4 iron sulfide particles, 5 iron sulfide particles, 6 permeable body, 7 underground water vein

Claims (8)

Wastewater containing selenium and heavy metals, groundwater or soil leachate is brought into contact with iron sulfide powder with a purity of 30-80% containing at least Fe in addition to FeS to reduce hexavalent selenium, and colloidal iron hydroxide A method for purifying drainage water, groundwater or soil leachate, characterized by coprecipitation, precipitation of heavy metals as sulfides, and removal of heavy metals that do not produce sulfides from the water by precipitation as hydroxides . Wastewater containing organic chlorine compounds and heavy metals, groundwater or soil leachate is brought into contact with iron sulfide powder with a purity of 30 to 80% containing at least Fe in addition to FeS to detoxify the organic chlorine compounds. In addition, a method for purifying drainage water, groundwater or soil leachate is characterized in that heavy metals are precipitated as sulfides, and heavy metals that do not generate sulfides are precipitated as hydroxides, thereby removing them from the water.   The method for purifying wastewater, groundwater or soil leachate according to claim 1 or 2, wherein a calcium salt is added at a later stage.   The method for purifying wastewater, groundwater or soil leachate according to claim 1 or 2, wherein iron sulfide containing Fe is supported on a water-permeable body and installed in a groundwater vein. Method for purifying waste water, ground water or soil leachate according to any one of claims 1 to 4, characterized by using iron sulfide containing Fe and Fe ₃ O _4. Method for purifying waste water, ground water or soil leachate according to any one of claims 1 to 4, characterized by using iron sulfide containing Fe and Fe ₂ O _3. The method for purifying waste water, ground water or soil leachate according to any one of claims 1 to 4, wherein iron sulfide containing Fe, Fe ₃ O ₄ and Fe ₂ O ₃ is used.   The method for purifying waste water, ground water or soil leachate according to any one of claims 1 to 7, wherein the pH is between 5.5 and 8.

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