JPH04330991A - Treatment of heavy metal containing waste water and treating agent therefor - Google Patents

Abstract

PURPOSE:To remove heavy metals from a heavy metal-containing waste water. CONSTITUTION:Mercaptobenzothiazol or its water soluble salt and polyethylene imine are added into the heavy metal-containing waste water and the heavy metals contained in the waste water is treated. In this way, a flock containing the heavy metals is formed and is settled and separated easily to remove from the waste water.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method and agent for treating wastewater containing heavy metals. More specifically, the present invention relates to a method for efficiently removing heavy metals from heavy metal-containing wastewater containing cadmium, copper, lead, mercury, etc. by a simple coagulation-sedimentation method, and a drug for the same.

0002

[Prior Art] Conventionally, as one of the methods for treating various wastewater containing heavy metals, a method has been known in which a dithiocarbamate compound or a mercaptobenzothiazole compound is added to form an insoluble heavy metal salt (especially Kaisho 5
2-136279). However, the insoluble heavy metal salt flocs are small and light and do not easily settle. Therefore, in the invention disclosed in the above publication, it was necessary to further add a cationic foaming agent and perform solid-liquid separation by flotation separation, which resulted in the problem of lack of versatility.
. In particular, plating factories discharge wastewater containing various heavy metals, and copper plating factories of chemical companies in particular discharge wastewater that has a high pH and contains large amounts of ammine complex salts. When the above method is applied to such wastewater, there is a problem in that insoluble flocs are difficult to form and the method cannot be put to practical use. Another common treatment method for various types of wastewater containing heavy metals is to generate poorly soluble hydroxides and sulfides at an appropriate pH, and then perform flocculation treatment using an inorganic flocculant followed by a polymer flocculant. In this method, flocs are separated from the treated water using a clarifier. As an example of the above method, in JP-A-60-187394, compounds containing sulfur such as sodium sulfide and sodium dimethyldithiocarbamate are added to the copper plating wastewater of a chemical company, the pH is adjusted to 7, and then A method is disclosed in which solid-liquid separation is performed after adding aluminum chloride, bentonite, and a polymer flocculant. In this method, the optimum pH range when hydroxides and sulfides of heavy metals are formed is different from the optimum pH range when adding an inorganic flocculant, and the optimum pH range when adding an inorganic flocculant is generally a low value. It has drawbacks such as insufficient aggregation effect and difficulty in sufficient separation using a clarifier. Furthermore, Japanese Patent Publication No. 64-3549 discloses a method in which a compound having at least one dithio group or a salt thereof and at least one selected from sodium sulfide, sodium polysulfide, and sodium hydrogen sulfide are added together to polyethyleneimine. is disclosed. The method described in Japanese Patent Publication No. 64-3549 is preferable because heavy metals can be treated by the coagulation-sedimentation method, but various soda sulfides are contained in the wastewater and the pH decreases.
There is a risk of hydrogen sulfide being generated, which is undesirable from a pollution standpoint. In addition, in "Water Treatment Technology" Vol. 32, No. 3, pp. 1-10, published by the Japan Water Treatment Technology Study Group on March 15, 1991, wastewater containing heavy metals is precipitated as hydroxide. rear,
A method is disclosed in which flocs are formed by adding an inorganic flocculant and a polymeric flocculant, followed by ultrafiltration. The above-mentioned invention described in water treatment technology has the disadvantage that the treatment equipment is large-scale and the operation is complicated because it uses an ultrafiltration method, and it is not effective for wastewater containing Cd(II). It has enough drawbacks.

0003

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to efficiently treat heavy metal-containing wastewater by a simple coagulation-sedimentation method. One of our efforts was to efficiently treat wastewater discharged from chemical copper plating plants, which has a high pH and contains a large amount of ammine complex salts, by an easy coagulation-sedimentation method, which was previously thought to be difficult to treat. It is intended to serve one purpose.

0004

[Means for solving the problem] The inventors of this invention
From the above viewpoint, we conducted intensive research on the coagulation-precipitation method using mercaptothiazole compounds. As a result, by using it together with polyethyleneimine, which is an organic flocculant, heavy metals can be efficiently precipitated and removed without any complicated treatment, and even more surprisingly, dithiocarbamic acids and insoluble salts can be removed by precipitation. Even for wastewater that contains ammine complex salts of heavy metals, which are difficult to treat because they do not form, it is possible to easily remove heavy metals by the coagulation-sedimentation method by using a mercaptobenzothiazole compound and polyethyleneimine in combination. I found it. Thus, according to the present invention, heavy metal-containing flocs are formed by adding mercaptobenzothiazole or a water-soluble salt thereof and polyethyleneimine to the heavy metal-containing wastewater, and the flocs are removed by precipitation. A processing method is provided. Examples of mercaptobenzothiazole or its water-soluble salt used in this invention include mercaptobenzothiazole and its alkali metal (lithium, sodium, potassium, etc.) salts, magnesium salts, ammonium or amine salts. The polyethyleneimine used in this invention is water-soluble, and polyethyleneimine having a molecular weight (Mw) of 300 to 750,000 is suitable. Among them, molecular weight 5000
It is particularly preferable to use 0 or more in terms of the size of the formed flocs, improved sedimentation properties, and the effect of removing heavy metals. When adding mercaptobenzothiazole or its water-soluble salt and polyethyleneimine to heavy metal-containing wastewater, it is preferable to mix the two and add them as a one-component preparation, but it is preferable to add the former first, and then, The latter may be added, and even if the order of addition is reversed, the effect of removing heavy metals is almost the same. In this case, the mixing ratio of mercaptobenzothiazole or its water-soluble salt and polyethyleneimine is 20:1 to 1:5 (preferably 10:1 to 1).
It is suitable to add them together at a blending ratio of :1). And, relative to the total amount of heavy metal ions present in wastewater,
Mercaptobenzothiazole or its water-soluble salt is 0.1
It is preferable to add the amount in an amount of 5 to 5 times the mole, preferably 0.2 to 3 times the mole. Mixing ratios other than the above are not preferred because the other active ingredient is wasted and the amount added increases. Further, if the amount added is less than the above range, the effect of removing heavy metals will not be sufficient, which is not preferable, and even if the amount added is larger than the above range, the effect of removing heavy metals will not change, which is not economical. The treatment method of this invention can be applied to various types of wastewater that contain heavy metals and cannot be directly discharged outside the system, especially industrial wastewater. , arsenic, etc. However, if the pH of the heavy metal-containing wastewater to be treated is 6.
If it is less than that, it becomes difficult to form flocs that can be precipitated, which is not preferable. It is particularly preferable that the pH of the wastewater is 9 or higher in terms of the effect of removing heavy metals. Therefore, for wastewater with a pH of less than 6, add alkali (sodium hydroxide, potassium hydroxide, etc.) to raise the pH to 6 or more, preferably pH 6.
It is suitable to carry out after adjusting the liquid property to about H9-12. Note that since plating wastewater and the like usually have a pH of 9 or higher, such pH adjustment is not particularly necessary and can be carried out directly. Such treatment rapidly forms flocs containing heavy metals in the wastewater, which settle out over time. Therefore, after the flocs are formed, the wastewater treatment is completed by removing the flocs by a known precipitation removal method. Through such treatment, various heavy metals can be removed, and the particularly difficult process of removing heavy metals from plating wastewater can be carried out simply and efficiently.

[0005]

EXAMPLES The present invention will be explained by the following examples and comparative examples. Example 1 (Test method) 500 ml of heavy metal-containing wastewater with the following properties discharged from a copper plating factory of a certain chemical company was placed in a beaker.
A sample was taken, a predetermined amount of the test drug was added, and the sample was heated for a predetermined period of 120 r.
After stirring at pm, the mixture was allowed to stand for 5 minutes. At this time, the diameter of the formed flocs was observed with the naked eye. Then 100m of supernatant
1 was collected, and its appearance was observed, and the ss concentration and heavy metal ion concentration in the liquid were measured by atomic absorption spectrometry. The results are also shown in Table 1.

[0006]

[Table 1] In Table 1, No. Examples 2 to 4 are examples of the present invention, in which mercaptobenzothiazole sodium salt (abbreviated as MBT-Na) was added as a test agent, and after stirring at 120 rpm for 15 minutes, polyethyleneimine (PEI) with an average molecular weight of 500,000 was added. ) and 120 rpm.
These are the results when stirring was performed for 1 minute at m. No. 1 and 5 are comparative examples, in which 120 r after adding the test drug.
These are the results obtained after stirring at pm for 15 minutes. Also, no
．． 6 to 11 are Examples of the present invention, in which mercaptobenzothiazole sodium salt (MBT-
These are the results obtained when a one-component formulation (aqueous solution) of polyethyleneimine (abbreviated as PEI) with an average molecular weight of 500,000 was added and stirred at 120 rpm for 15 minutes. (Properties of wastewater) pH: 9.5 Cu++: 2
68 mg/l (present in the form of ammine complex salt)

0007
] Example 2 500 ml of heavy metal-containing wastewater discharged from a certain plating factory with the following properties was collected in a beaker, and used as a test chemical.
Mercaptobenzothiazole sodium salt (MBT-N
A predetermined amount of a one-component formulation (aqueous solution) of polyethyleneimine (abbreviated as PEI) having an average molecular weight of 100,000 was added, stirred at 120 rpm for 15 minutes, and then left to stand for 5 minutes. At this time, the diameter of the formed flocs was observed with the naked eye. After that, 100 ml of supernatant liquid was collected,
The appearance of the liquid was observed and the concentration of heavy metal ions in the liquid was measured using atomic absorption spectrometry. The results are also shown in Table 2. (Properties of wastewater) pH: 9.0Pb++: 1
5mg/l Cd++: 19mg/l (test results)

[0008]

[Table 2]

Example 3 500 ml of heavy metal-containing cleaning wastewater discharged from a certain electrical equipment factory and having the following properties was collected in a beaker, and calcium hydroxide was added to adjust the pH of the wastewater to 10. Thereafter, as a test drug, mercaptobenzothiazole sodium salt (abbreviated as MBT-Na) and an average molecular weight of 30
0000 polyethyleneimine (abbreviated as PEI)
Add a predetermined amount of a one-component formulation (aqueous solution) and leave it for 15 minutes.
After stirring at 20 rpm, the mixture was allowed to stand for 5 minutes. At this time,
The diameter of the formed flocs was observed with the naked eye. After that, 100 ml of supernatant liquid was collected, its appearance was observed, and ss
The concentration of heavy metal ions in the liquid was measured by concentration and atomic absorption spectrometry. The results are shown in Table 3. (Properties of wastewater) pH: 1.5Pb++: 3
00mg/l (test results)

0010

[Table 3]

Example 4 (Test method) 500 ml of heavy metal-containing wastewater discharged from a certain plating factory and having the following properties was collected in a beaker, and mercaptobenzothiazole sodium salt (abbreviated as MBT-Na) and mercaptobenzothiazole sodium salt (abbreviated as MBT-Na) were used as test chemicals. Average molecular weight 500000
A predetermined amount of a one-component formulation (aqueous solution) with polyethyleneimine (abbreviated as PEI) was added, and the mixture was heated at 120 rpm for 15 minutes.
After stirring at m, the mixture was allowed to stand for 5 minutes. At this time, the diameter of the formed flocs was observed with the naked eye. Then 100m of supernatant
1 was collected, and its appearance was observed, and the ss concentration and heavy metal ion concentration in the liquid were measured by atomic absorption spectrometry. The results are shown in Table 4. (Properties of wastewater) pH: 10Ni++: 30
0 mg/l (present in the form of ammine complex salt) (test results)

0012

[Table 4]

[0013]

According to the present invention, heavy metals in various heavy metal-containing wastewaters can be efficiently removed by a simple coagulation-sedimentation method. In particular, wastewater discharged from copper plating plants of chemical companies that has a high pH and contains a large amount of ammine complex salts, which has been difficult to treat in the past, has been treated to reduce heavy metal ions to below the emission standards without adjusting the pH. can do.

Claims (4)

[Claims] 1. A method for treating heavy metal-containing wastewater, which comprises adding mercaptobenzothiazole or a water-soluble salt thereof and polyethyleneimine to heavy metal-containing wastewater to form a heavy metal-containing floc, and removing the floc by precipitation. 2. The treatment method according to claim 1, wherein the pH of the heavy metal-containing wastewater is 6 or more. 3. The treatment method according to claim 1, wherein the heavy metal-containing wastewater is wastewater discharged from a plating factory. 4. A treatment agent for heavy metal-containing wastewater, which contains mercaptobenzothiazole or a water-soluble salt thereof and polyethyleneimine as active ingredients.