JPH1015551A - Treatment of waste water containing heavy metal ions - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove heavy metal ions from waste water with high treatment efficiency by using a small-sized treatment apparatus by adding a hardly solublizing precipitator to waste water containing heavy metal ions and filtering this waste water by a filter having fractionation of a specific dimension. SOLUTION: When waste water containing heavy metal ions such as arsenic or zinc discharged from a refinery is treated, raw water being waste water is introduced into a direction tank 1 and, after a hardly solublizing precipitator is added, the waste water is sent to a filter tank 3 to be filtered ander suction by using a hollow yarn membrane filter 4. At this time, an air diffusion pipe 5 is provided under the hollow yarn membrane filter 4 and air is diffused from the air diffusion pipe to wash the hollow yarn membrane filter 4. The hollow yarn membrane filter 4 has fractionation of 0.03-0.5μm. As the hardly solublizing precipitator, a mixture selected from hydrochloric acid, sulfuric acid or sodium hydroxide can be used. When Cu<2+> or Zn<2+> is removed from waste water, a coprecipitation agent is pref. added to waste water before the addition of the hardly solublizing precipitator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a treatment method for removing heavy metal ions from wastewater containing heavy metal ions.

[0002]

2. Description of the Related Art Wastewater containing heavy metal ions such as arsenic, cadmium, chromium, and zinc is generated in metal mines, glass factories, pharmaceutical factories, plating factories, and smelters. Before discharging such wastewater containing heavy metal ions into a river or the like, a process for removing heavy metal ions from the wastewater is performed in advance.

[0003] As a method for removing these heavy metal ions from wastewater, usually, after adding a hardly soluble precipitant to make the heavy metal ions into fine particles in the wastewater, an inorganic flocculant is added, and the generated floc is separated by heavy separation. A method of removing heavy metal ions from wastewater by passing wastewater through an ion-exchange resin tank or a method of removing heavy metal ions by filtering wastewater through a reverse osmosis membrane. .

[0004]

SUMMARY OF THE INVENTION In the case of a method in which a hardly soluble precipitant is added to waste water to form heavy metal ions into fine particles, which are then removed by heavy separation and sand filtration, the fractionation accuracy of the final sand filtration is low. Since the particle size is as large as 25 to 50 μm, the processing apparatus is enlarged in order to increase the particle diameter of the fine particles to 25 μm or more. Further, in order to increase the particle size of the fine particles, it is necessary to stir the wastewater for a long time in the presence of the sparingly soluble precipitant, so that the treatment efficiency of the wastewater is low.

When heavy metal ions are removed from wastewater using an ion-exchange resin, ionized heavy metals can be removed by the ion-exchange resin, but heavy metal components in fine particles contained in the wastewater cannot be sufficiently removed. There was an inconvenience of mixing in treated water.

In the method of removing heavy metal ions using a reverse osmosis membrane, fine metal ions contained in wastewater adhere to the surface of the reverse osmosis membrane in a short period of time. In order to recover the water content, a complicated regeneration operation of the reverse osmosis membrane was required, and it was difficult to stably perform the filtration treatment for a long period of time.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of such inconveniences, and is intended to remove heavy metal ions from wastewater with high treatment efficiency using a small-sized treatment apparatus. It was made as a result of studying wastewater treatment methods.

That is, the method of treating wastewater containing heavy metal ions according to the present invention comprises adding a hardly soluble precipitant to wastewater containing heavy metal ions, and then filtering the wastewater with a filter having a fraction of 0.03 to 0.5 μm. It is characterized by doing.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for treating wastewater containing heavy metal ions according to the present invention, heavy metal ions contained in the wastewater are first made into fine particles by adding a sparingly soluble precipitant to the wastewater. The sparingly soluble precipitant used in the present invention has a pH of wastewater.
Is changed to form fine metal ions in the form of a hardly soluble hydroxide or salt in the form of fine particles in waste water to precipitate out, and the fine particles thus generated are separated by the above-mentioned filter. This makes it possible to obtain treated water from which heavy metal ions have been removed from wastewater.

[0010] Such poorly soluble precipitants include hydrochloric acid,
One or a mixture of two or more selected from sulfuric acid, carbon dioxide, sodium hydroxide, sodium carbonate, calcium oxide, calcium hydroxide, magnesium hydroxide, dolomite and the like can be used. By controlling the amount of the hardly soluble precipitant to be added to the wastewater, the pH of the wastewater is adjusted to an optimum pH range for atomizing heavy metal ions.

[0011] p of wastewater controlled by adding a hardly soluble precipitant
The H value varies depending on the type of heavy metal ions contained in the wastewater to be treated. For example, the pH of the wastewater is 6.0 or more when Cu ²⁺ is removed from the wastewater, and 6.5 when Zn ²⁺ is used.
To 3.5, Cd ²⁺ to 8.0 or more, Cr ³⁺ to 5.5 to 12.0, Fe ²⁺ to 8.0 or more, Fe ³⁺ Is 2.5 or more, and in the case of As ⁵⁺ , 2.
It is preferable to add a sparingly soluble precipitant to the wastewater so that the concentration becomes 5 to 7.5, and in the case of Al ³⁺ , it becomes 4.0 to 9.5.

In the treatment method of the present invention, Cu is removed from wastewater.
²⁺, Zn²⁺, Cd²⁺, Fe²⁺, Fe ³⁺, As⁵⁺, Al³⁺
When removing, etc., add the hardly soluble precipitating agent described above.
It is advisable to add a coprecipitant to the wastewater before
No. Coprecipitant dissolves in water and releases metal ions
Of heavy metal ions in wastewater by poorly soluble precipitant
Is a drug that promotes
Produces metallic iron, iron oxide, ferric chloride, aluminum salts, etc.
Can be used.

Further, in the case of removing the Cr ⁶⁺ included in waste water, calcium sulfite under acidic sulfate, a reducing agent such as ferric sulfate was added to the waste water, the Cr ^6+, the hardly soluble precipitating agent It is preferable to add a sparingly soluble precipitating agent after reduction to the form of Cr ³⁺ that is easy to precipitate.

When the heavy metal ion to be removed is present as cyanide in the wastewater, a sparingly soluble precipitant is added to the wastewater after the oxidative decomposition reaction. The oxidative decomposition reaction is to finally decompose cyan in wastewater into carbon dioxide and nitrogen, and is performed by adding an oxidizing agent such as sodium hypochlorite to the wastewater. By performing an oxidative decomposition reaction by adding an oxidizing agent, heavy metals present in the form of cyanide can be ionized in the wastewater, and then the heavy metal ions are precipitated in the wastewater by the addition of a hardly soluble precipitant. It becomes possible.

In the treatment method of the present invention, an inorganic flocculant may be added after the heavy metal ions in the wastewater are made finer by adding a hardly soluble precipitate. The inorganic coagulant is
It is a chemical that flocculates fine particles precipitated in wastewater by neutralizing electrostatic force and forms flocs.It is aluminum sulfate, sodium aluminate, basic aluminum oxide, ferrous sulfate, ferric sulfate, and chloride. Ferric iron, chlorinated copper or the like can be used.

The amount of the inorganic flocculant to be added is appropriately set in consideration of the concentration of the metal ions contained in the wastewater, the amount of the hardly soluble precipitant added in the preceding stage, and the like. Addition of an insoluble precipitant causes the heavy metal ion fine particles precipitated by addition of an inorganic coagulant to flocculate and enlarge, thereby preventing ultra-fine particles from passing through the filtration filter and entering the treated water. And the filtration resistance of the filtration filter can be reduced, and the wastewater can be treated with a high throughput.

In the method for treating wastewater of the present invention, after adding a hardly soluble precipitant to wastewater to form heavy metal ions into fine particles,
In order to remove these fine particles from the wastewater, a fraction of 0.0
Use a 3-0.5 μm filtration filter. By using a filtration filter having such a fraction, a large amount of insoluble precipitating agent and coagulant for increasing the particle diameter of the fine particles to 25 μm or more, which is necessary for conventional sand filtration, etc., into wastewater. There is no need to add the wastewater, and the wastewater can be treated with a small device, and the wastewater does not need to be stirred for a long time to enlarge the metal ion fine particles. It is possible to do.

If the fraction of the filtration filter exceeds 0.5 μm, it is not appropriate because the removal of precipitated fine particles becomes insufficient. On the other hand, the fraction of the filtration filter was 0.0
When the thickness is less than 3 μm, the amount of water permeation is reduced and the energy cost is increased. The value of the fraction referred to in the present invention means a value at which the permeation inhibition rate of a polystyrene latex having a particle size of 90% or more is obtained.

In the method for treating wastewater of the present invention, the filtration of the wastewater containing fine particles by the filtration filter is performed by a suction method.
Any of the external pressure type may be used. When it is necessary to design the processing apparatus compactly, external pressure filtration that does not require a huge filtration tank is preferable. In the case where the wastewater treatment is performed for a long time, suction-type filtration in which clogging of the membrane surface with fine particles is small is preferable.

The filtration filter used in the present invention may be a filter provided with a hollow fiber membrane, a flat membrane, or a tubular membrane as a separation membrane if the fraction is 0.03 to 0.5 μm. Yes, but it is possible to filter heavy metal ion particles in wastewater with high volumetric efficiency.
It is preferable to use a hollow fiber membrane filter provided with a plurality of hollow fiber membranes as the separation membrane. When a hollow fiber membrane filter is used as a filtration filter, a hollow fiber membrane such as a cellulose-based, polyolefin-based, polyvinyl alcohol-based, or polysulfone-based hollow fiber membrane can be used as the hollow fiber membrane to be provided. When a polyolefin-based hollow fiber membrane having high elongation is used, the filtration life of the filter is long, and wastewater treatment can be performed stably for a long period of time.

The hollow fiber membrane is preferably a permanent hydrophilization membrane having a hydrophilic group on its surface, because filtration of wastewater can be performed at a high filtration flow rate. Examples of such a hollow fiber membrane include hollow fiber membranes in which the surface of the hollow fiber membrane is coated or graft-polymerized with a hydrophilic polymer such as polyvinyl alcohol or ethylene vinyl alcohol copolymer.

If the filter is configured so that it can be washed while being installed in the wastewater treatment apparatus, when the surface of the separation membrane included in the filter is blocked by fine particles and the filtration flow rate decreases, This is preferable because the fine particles that have blocked the surface of the separation membrane can be peeled off by washing to recover the filtration function. As a method of washing the filtration filter, for example, a compressor is connected to the secondary side of the filtration filter, and by performing reverse flow of the filtered treated water from the secondary side to the primary side of the filtration filter. Can be. Alternatively, an air diffuser may be provided below the filter, and the filter may be washed by bubbling air from the air diffuser, or a stirrer may be provided near the filter to remove wastewater in the tank. By stirring, the filtration filter may be washed. By arranging the filtration filter in this way, it is not necessary to perform complicated replacement work of the filtration filter, and the wastewater can be stably treated for a long period of time.

The treated water from which fine particles of heavy metal ions have been removed from the wastewater by the filtration filter is preferably subjected to an adsorption treatment. Examples of the adsorption treatment performed on the treated water include a method of passing the treated water through an adsorption treatment tank filled with activated carbon, ion exchange resin, or the like. By performing the adsorption treatment on the treated water, even a trace amount of heavy metal ions dissolved in the treated water can be removed.

The treated water obtained by the method for treating wastewater of the present invention is preferably neutralized and neutralized before being discharged.

[0025]

The present invention will be described below in more detail with reference to examples.

<Embodiment 1> FIG. 1 is a conceptual diagram showing a processing method of this embodiment.

Raw water containing waste metal ions is introduced into a reaction tank, and Mg (OH) ₂ is added as a hardly soluble precipitating agent in a volume of 200 m.
After the addition at a rate of g / liter, the wastewater was sent to a filtration tank, and the hollow fiber membrane filter Stellapore L (trade name, manufactured by Mitsubishi Rayon Co., Ltd., fraction 0.1 μm, membrane area 4 m ² )
, And suction filtration was performed at an LV of 0.015 m ³ / m ² · hr to obtain treated water. An air diffuser was provided below the hollow fiber membrane filter, and air was diffused from the air diffuser at a flow rate of 60 Nl / min once every 10 minutes for 10 seconds to wash the hollow fiber membrane filter.

Table 1 shows the amounts of heavy metal ions and ss contained in the obtained treated water. The amount of heavy metal ions contained in the treated water was measured according to JIS K0102. The amount of ss contained in the treated water is shown in Showa 46
It was measured by the method shown in Appendix 8 of the Notification of the Environment Agency, No. 59, December 2012.

<Comparative Example 1> Wastewater to which a poorly solubilized precipitant was added in a reaction tank was filtered by gravity separation with a separation time of 4 hours and a sand filtration method (sand particle size: 0.35 mm, filter layer thickness: 180 mm). Except that, the same wastewater as in Example 1,
Filtration of the wastewater was performed under the insolubilized precipitant and the filtration conditions to obtain treated water. The amount of heavy metal ions contained in the obtained treated water, s
Table 1 shows the results of measuring the s content.

Example 2 NaOH was used as a hardly soluble precipitant.
And treated in the same manner as in Example 1 except that the wastewater was added at a rate of 130 mg / liter to obtain treated water. The amount of heavy metal ions contained in the obtained treated water, ss
The results of the measurement are shown in Table 1.

Example 3 Ca (O) was used as a hardly soluble precipitant.
H) ₂ and the same treatment as in Example 1 was performed, except that it was added to the wastewater at a rate of 225 mg / liter, to obtain treated water. Table 1 shows the results of measuring the amounts of heavy metal ions and ss contained in the obtained treated water.

[0032]

[Table 1]

[0033]

According to the method for treating wastewater containing heavy metal ions according to the present invention, after adding the hardly soluble precipitant to the wastewater containing heavy metal ions, the wastewater is filtered into a filter having a fraction of 0.03 to 0.5 μm. Wastewater, it is possible to treat the wastewater with a small device, and it is not necessary to stir the wastewater for a long time to enlarge the metal ion fine particles. It is possible to perform processing. In this case, when a hollow fiber membrane filter is used as a filtration filter, it is possible to treat wastewater containing heavy metal ions with high volumetric efficiency.

If the filtration filter has a washable structure, when the surface of the separation membrane is blocked by fine particles,
Since the filtration function can be restored, there is no need to replace the filtration filter, and the wastewater can be stably treated for a long period of time.

Further, if the treated water filtered by the filtration filter is further subjected to an adsorption treatment, it is possible to sufficiently remove even trace amounts of heavy metal ions dissolved in the treated water from the wastewater.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of a method for treating wastewater containing heavy metal ions according to the present invention.

[Description of Signs] 1 Reaction tank 2 Stirrer 3 Filtration tank 4 Filtration filter 5 Aeration tube

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C02F 1/62 ZAB C02F 1/62 ZAB (72) Inventor Kojo Jo 2-12 Nishijiya, Ota-ku, Tokyo No. 5 Inside Oxylo International Co., Ltd. (72) Inventor Hiroshi Tokuyama 2-12-5 Nishikojiya, Ota-ku, Tokyo Inside Oxylo International Co., Ltd.

Claims (3)

[Claims] 1. A method for treating wastewater containing heavy metal ions, comprising adding a hardly soluble precipitant to wastewater containing heavy metal ions and then filtering through a filtration filter having a fraction of 0.03 to 0.5 μm. Method. 2. The method for treating wastewater containing heavy metal ions according to claim 1, wherein a hollow fiber membrane filter is used as the filtration filter. 3. The method for treating wastewater containing heavy metal ions according to claim 1, wherein the treated water filtered by the filtration filter is subjected to an adsorption treatment.