JP2002292373A - Method for reducing heavy metal sludge and chemical used for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing heavy metal sludge generated when an alkali is added to heavy metal-containing water to remove heavy metals as their hydroxides. SOLUTION: The alkali is added to the water containing dissolved metals to precipitate the heavy metals as heavy metal hydroxides, and the sediment is recovered as the heavy metal sludge. At least a part of the heavy metal hydroxides is converted to their oxides in the presence of an oxidizing agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing heavy metal sludge generated when a heavy metal dissolved in water is removed as a hydroxide, and a chemical agent therefor.

[0002]

2. Description of the Related Art Conventionally, as a method for removing harmful metal ions contained in water, there is known a method in which an alkaline substance such as sodium hydroxide or calcium hydroxide is added to water and precipitated as a heavy metal hydroxide. Have been. The heavy metal sludge generated by such a method has a high water content and a large amount, and thus has a problem that a large amount of cost is required for disposal. Further, in recent years, the shortage of disposal sites has become a major problem, which has also caused a rise in disposal costs. For this reason, it has been desired to collect and reuse metal from sludge, but it has not been profitable and has hardly been realized. However, if the amount of generated sludge can be reduced, not only can transportation costs be reduced, but also sludge with a high metal content can be obtained, and the recovery of metal from sludge can be profitable.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a method for reducing heavy metal sludge generated when an alkali is added to treated water containing a heavy metal to remove the heavy metal as a hydroxide, and a chemical used for the method. Is to provide

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, a method for reducing heavy metal sludge and a chemical used therefor are provided. (1) An alkali is added to treated water containing a dissolved metal to precipitate the heavy metal as a heavy metal hydroxide, and when recovering the precipitate as heavy metal sludge, an oxidizing agent is present in the treated water to remove the heavy metal. A method for reducing heavy metal sludge, comprising converting at least a part of a heavy metal hydroxide to an oxide. (2) The method according to the above (1), wherein the oxidizing agent comprises sodium hypochlorite or hydrogen peroxide. (3) The above (1) wherein a carbonate ion generator is added to the water.
Or the method of (2). (4) The method according to any one of the above (1) to (3), wherein the carbonate ion generator comprises sodium carbonate. (5) The above (1) in which a coagulant is added to the water to be treated.
Any one of (4) to (4). (6) A drug used as an oxidizing agent in the method (1), comprising a mixture of (i) sodium hypochlorite and (ii) a water-soluble carbonate. (7) A drug used as an oxidizing agent in the method (1), comprising a mixture of (i) hydrogen peroxide and (ii) a water-soluble carbonate.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a process for adding an alkali to water to be treated in which a heavy metal is dissolved to precipitate the dissolved heavy metal contained therein as a water-insoluble hydroxide and recovering the precipitate as a heavy metal sludge. At this time, an oxidizing agent is added to the water to be treated, and the heavy metal hydroxide is converted into an oxide, thereby reducing heavy metal sludge.

The time of adding the oxidizing agent to the water to be treated is not particularly limited, and may be before, simultaneously with or after the addition of the alkali. Simultaneously or after addition of alkali.

As the alkali for converting heavy metals dissolved in the water to be treated into water-insoluble heavy metal hydroxides, conventionally known alkalis are used. Such materials include magnesium hydroxide, potassium hydroxide, sodium carbonate, ammonium hydroxide, and the like, in addition to sodium hydroxide and calcium hydroxide. In the present invention, it is particularly preferable to use sodium hydroxide or calcium hydroxide from the viewpoint of economy.

The amount of alkali to be added to the water to be treated may be such that the heavy metals dissolved in the water become insoluble hydroxides.
It is sufficient that the amount is controlled to 3, preferably in the range of 8 to 11.

The oxidizing agent used in the present invention may be any one having an oxidizing power capable of converting a heavy metal hydroxide into an oxide. Such substances include hypochlorous acid, chlorous acid, chloric acid, water-soluble salts thereof, such as oxyacids such as perchloric acid, hydrogen peroxide, and ozone. From the viewpoint, use of sodium hypochlorite or hydrogen peroxide is preferred.

In the present invention, the amount of the oxidizing agent added to the water to be treated is at least a part of the heavy metal hydroxide generated in the water,
Preferably 10% or more, more preferably 50 to 100%
Any amount can be used as long as it can be converted into an oxide.

When reacting an oxidizing agent with a heavy metal hydroxide in water according to the present invention, it is preferred that carbonate ions are present. By the presence of the carbonate ion, it is possible to obtain effects such as promoting generation of flocs as compared with the case of using only the oxidizing agent, and obtaining flocs having better sedimentation properties as compared with the case of using only the oxidizing agent.

As the compound capable of generating carbonate ions (carbonate ion generator), any compound capable of generating carbonate ions in water can be used. Such substances include water-soluble carbonates such as sodium carbonate and sodium hydrogen carbonate, and carbon dioxide. The amount added to the water to be treated is such that the carbonate ion concentration in the water to be treated is 0.00
0005-0.1 mol / L, preferably 0.00005
It is such a ratio that it becomes ０．０１0.01 mol / L.

The time of addition of the carbonate ion generator is not particularly limited, and may be before, during or after the addition of the oxidizing agent.
It is preferably immediately before or simultaneously with the addition of the oxidizing agent.

When the oxidizing agent is reacted with the heavy metal hydroxide in the water to be treated according to the present invention, the temperature may be room temperature, but it is more preferable to heat it to increase the reaction rate. The higher the heating temperature is, the more the reaction is promoted. However, it is required to perform the heating in consideration of the energy cost required for the reaction. For example, 30 to 70 ° C., preferably 3
Temperatures from 0 to 55C can be employed. The reaction at such an elevated temperature is carried out by heating the water to be treated.

One preferred embodiment of the drug of the present invention (drug A) comprises a mixture of (i) sodium hypochlorite and (ii) a water-soluble carbonate such as sodium carbonate. If necessary, (iii) sodium hydroxide can be added to this mixture. Another preferred embodiment of the drug according to the present invention (drug B) comprises a mixture of (i) hydrogen peroxide and (ii) a water-soluble carbonate such as sodium carbonate.

In the case of producing the drug A of the present invention preferably containing sodium hydroxide, first, the sodium hydroxide is dissolved in an aqueous solution of sodium hypochlorite having an effective chlorine concentration of 8 to 13%. And add carbonate to dissolve it. In this case, the ratio of sodium hydroxide is 0.01 to 1 mol, preferably 0.1 to 1 mol, per 1 mol of available chlorine of sodium hypochlorite. The ratio of the carbonate is 0.001 to 1 mol, preferably 0.01 to 0.5 mol, per 1 mol of available chlorine of sodium hypochlorite.

In the case of manufacturing the above-mentioned drug A, when manufacturing a product not containing sodium hydroxide, a carbonate is added to and dissolved in an aqueous solution of sodium hypochlorite having an effective chlorine concentration of 8 to 13%. In this case, the proportion of carbonate is calculated per mole of available chlorine of sodium hypochlorite,
It is 0.001-1 mol, preferably 0.01-0.5 mol.

In order to preferably produce the drug B of the present invention,
Sodium carbonate is added to and dissolved in a hydrogen peroxide solution having a concentration of 3 to 35%. In this case, the proportion of sodium carbonate is
The amount is 0.01 to 1 mol, preferably 0.05 to 1 mol, per 1 mol of hydrogen peroxide.

When the heavy metal sludge is reduced by the chemical A of the present invention, either a chemical containing sodium hydroxide or a chemical not containing sodium hydroxide may be used, but a chemical containing no sodium hydroxide is used. In this case, if the pH decreases after the addition of the chemical, the alkali may be added again. In order to reduce heavy metal sludge by the agent A of the present invention, an alkali is added to the water to be treated, the pH is adjusted to 7 to 13, preferably 8 to 12, more preferably 9 to 11, and the agent A is added. do it.

The amount of the chemical agent to be added is 0.002 to 1 equivalent, preferably 0.004 to 0.4 equivalent, more preferably 0.01 to 1 equivalent of the heavy metal hydroxide.
~ 0.2 equivalents.

In order to reduce heavy metal sludge by the agent B of the present invention, an alkali is added to the water to be treated, and the pH is reduced.
From 7 to 13, preferably 8 to 12, more preferably 9
It should be adjusted to ~ 11 and the medicine B may be added. The amount of the drug to be added is 0.01 to 10 equivalents, preferably 0.05 to 5 equivalents, and more preferably 0.05 to 4 equivalents per equivalent of the heavy metal hydroxide in terms of the number of equivalents of the oxidizing agent.

In the present invention, a coagulant is preferably used in combination. The flocculant in this case may be any one that is used for floc flocculation. Examples of such a flocculant include cationically modified polyacrylamide, dimethylaminoethyl polyacrylate, and dimethylaminoethyl polymethacrylate. Cationic organic flocculants such as esters, polyethyleneimine and chitosan; nonionic organic flocculants such as polyacrylamide; anionic organic flocculants such as polyacrylic acid, copolymers of acrylamide and acrylic acid and salts thereof Is included. Usually, the coagulant may be added to the water to be treated after the addition of the chemical.

The treated water containing flocs after the treatment of the present invention is subjected to a solid-liquid separation treatment. The solid-liquid separation method in this case includes a conventional method, for example, filtration separation, centrifugation, sedimentation separation and the like.

The present invention is applied to water to be treated containing heavy metal ions. In this case, the heavy metals include copper, zinc, iron, nickel and the like. The concentration of heavy metal in the water to be treated is usually 0.01 to 100 g / L, especially 0.5 to 100 g / L.
２０20 g / L. Specific examples of the water to be treated include a copper etching waste liquid, a soft etching liquid, a hot dip galvanizing liquid, and washing water.

According to the present invention, since at least a part of the heavy metal hydroxide formed as a precipitate is converted into the heavy metal oxide, the finally obtained heavy metal sludge is reduced in both weight and volume. Can be done.

The heavy metal hydroxide, at least part of which is converted to an oxide, has a good dehydration property, and the heavy metal sludge separated from the water to be treated is easily dehydrated by dehydration treatment such as pressurization. Can be sludge. In the case of the present invention, dewatered sludge having a water content of 70% or less, particularly 60% or less, can be efficiently obtained.

[0027]

Next, the present invention will be described in more detail with reference to examples.

Reference Example 1 Aqueous sodium hypochlorite solution (for industrial use) (effective chlorine 12%)
To 1 liter of a solution prepared by dissolving 43 g of sodium hydroxide, 36 g of sodium carbonate was added and dissolved. This solution is referred to as drug I.

Reference Example 2 Aqueous sodium hypochlorite solution (for industrial use) (effective chlorine 12%)
To 1 liter, 36 g of sodium carbonate was added and dissolved. This solution is designated as drug II.

Reference Example 3 36 g of sodium carbonate was added to 1 liter of a hydrogen peroxide solution (concentration: 30%) diluted 5 times with water and dissolved. This solution is designated as drug III.

Example 1 A 70% dilution of a copper etching waste solution having a pH of -0.98, a copper ion concentration of 118 g / L and a chlorine concentration of 250 g / L was added to a calcium hydroxide suspension (0.4%). %) Was added to adjust the pH to about 10, and a precipitate was formed. 0.3 ml / L of Drug I was added to this slurry and stirred. 43 mg / L of an anionic polymer coagulant AP120C was added and stirred. When the sludge was subjected to solid-liquid separation and copper in the solid content was measured, the copper content was 73.1%.

Comparative Example 1 A suspension of calcium hydroxide (0.4%) was added to a 70-fold dilution of the waste liquid of Example 1 to adjust the pH to about 10, thereby producing a precipitate. To this slurry, 45 mg / L of an anionic polymer flocculant AP120C was added and stirred. This slurry had poor cohesiveness and dewaterability, and the discharged sludge had a copper content of 20.2%.

Example 2 To a 70-fold dilution of the waste liquid of Example 1, a suspension of calcium hydroxide (0.4%) was added to adjust the pH to about 10, thereby producing a precipitate. 0.3 mg of drug II was added to this slurry.
ml / L was added and stirred. Anionic polymer flocculant A
45 mg / L of P120C was added and stirred. When the sludge was subjected to solid-liquid separation and the copper content in the solid content was measured, the copper content was 74.9%.

Example 3 A 70-fold dilution of the waste liquid of Example 1 was added with a suspension of calcium hydroxide (0.4%) to adjust the pH to about 10, thereby producing a precipitate. Add 3m of medicine III to this slurry
1 / L was added and stirred. Anionic polymer coagulant AP
120C was added at 45 mg / L and stirred. When the sludge was subjected to solid-liquid separation and copper in the solid content was measured, the copper content was 65.3%.

Example 4 0.3 ml / L of Drug I was added to a 70-fold dilution of the waste liquid of Example 1 and stirred. To this, a calcium hydroxide suspension (0.4%) was added to adjust the pH to about 10, and a precipitate was formed. Anionic polymer flocculant AP1
20C was added at 45 mg / L and stirred. When the sludge was subjected to solid-liquid separation and copper in the solid content was measured, the copper content was 62.3%.

Example 5 Acid containing zinc and iron discharged in a hot-dip galvanizing process having a pH of -1.83, a zinc concentration of 242.5 g / L, an iron concentration of 48 g / L, and a chlorine concentration of 381 g / L. To a 25-fold dilution of the waste liquor, a calcium hydroxide suspension (4%) was added to adjust the pH to about 10, and a precipitate was formed. 5 ml / L of Drug I was added to this slurry and stirred. After adding 550 mg / L of the cationic polymer flocculant KP1200SV and stirring, the anionic polymer flocculant AP825 was added.
430 mg / L of C was added and stirred. This slurry was sent to a screw press, and the screw rotation speed was 0.3 rpm.
After dewatering, the sludge discharged has a water content of 3
The content of zinc, iron and chlorine in the solid content was 64.7%, 23.7% and 2.1%, respectively.

COMPARATIVE EXAMPLE 2 The waste liquid of Example 1 was diluted 25-fold, and a calcium hydroxide suspension (4%) was added to adjust the pH to about 10.
A precipitate formed. To this slurry, 550 mg / L of a cationic polymer flocculant KP1200SV was added, and the mixture was stirred.
g / L was added and stirred. This slurry was poor in cohesiveness and dewaterability, and the discharged sludge contained 33%, 7% and 16% of zinc, iron and chlorine, respectively.

Example 6 A 25-fold dilution of the waste liquid of Example 1 was adjusted to a pH of about 10 by adding a calcium hydroxide suspension (4%).
A precipitate formed. 5 ml / L of Drug II was added to this slurry and stirred. Cationic polymer flocculant KP1200
After adding 550 mg / L of SV and stirring, 430 mg / L of anionic polymer coagulant AP825C was added and stirred. When this slurry was sent to a screw press and dewatered at a screw rotation speed of 0.3 rpm, the discharged sludge had a water content of 38.5%, and the content of zinc, iron and chlorine in the solid content was 62%, respectively. 0.4%, 2
4.8% and 2.5%.

Example 7 A 25-fold dilution of the waste solution of Example 1 was mixed with 5 parts of Drug I.
ml / L was added and stirred. A calcium hydroxide suspension (4%) was added thereto to adjust the pH to about 10, and a precipitate was formed. 5 KP1200SV cationic polymer flocculant
After adding 50 mg / L and stirring, 430 mg / L of anionic polymer coagulant AP825C was added and stirred. When this slurry was sent to a screw press and dewatered at a screw rotation speed of 0.3 rpm, the discharged sludge had a water content of 39.4%, and the content of zinc, iron and chlorine in the solid content was 61%, respectively. 0.3%, 24.6% and 2.6%.

Example 8 pH 3.4, zinc concentration 11 g / L, iron concentration 1.9 g
The calcium hydroxide suspension (2%) was added to the washing water containing zinc and iron discharged in the hot-dip galvanizing process of 1 / L to adjust the pH to 10 to generate a precipitate. 5 ml / L of Drug I was added to this slurry and stirred. After adding 520 mg / L of a cationic polymer flocculant KP1200SV and stirring, 25 mL of an anionic polymer flocculant AP825C was added.
0 mg / L was added and stirred. When this slurry was sent to a screw press and dewatered at a screw rotation speed of 0.3 rpm, the discharged sludge had a water content of 38%, and the content of zinc, iron and chlorine in the solid content was 61.5%, respectively. %, 24.0% and 2.8%.

[0041]

According to the present invention, the dissolved heavy metal in the water to be treated is precipitated as a water-insoluble hydroxide, and when the precipitate is recovered as heavy metal sludge, the heavy metal sludge can be efficiently reduced. , Its industrial significance is enormous.

 ──────────────────────────────────────────────────続 き Continued on the front page (71) Applicant 000005979 Mitsubishi Corporation 2-6-3 Marunouchi, Chiyoda-ku, Tokyo (72) Inventor Kenji Tatsumi 16-3 Onogawa Tsukuba, Ibaraki Pref. Ministry of Economy, Trade and Industry (72) Inventor Shinji Wada 16-3 Onogawa, Tsukuba-shi, Ibaraki Pref. Ministry of Economy, Trade and Industry Ministry of Economy, Trade and Industry AIST (72) Inventor Yasuhiro Yukawa Sengen 2, Tsukuba-shi, Ibaraki −1-6 Mitsubishi Corporation Project Development Department Environmental Resources Laboratory F-term (reference) 4D015 BA19 BA21 BA23 BB12 CA17 DA39 DA40 DB03 DB07 DB08 DB10 DB12 DB15 DB19 DB32 DC06 DC07 DC08 EA15 EA16 EA23 EA33 EA35 EA39 4D038 AA08 AB66 AB67 AB68 AB69 AB81 BB01 BB13 BB16 BB17 BB18 4D050 AA13 AB55 AB56 AB57 AB58 BB02 BB06 BB07 BB09 CA01 CA13 CA15 CA16 CA20

Claims (7)

[Claims] 1. An alkali is added to water to be treated containing a dissolved heavy metal to precipitate the heavy metal as a heavy metal hydroxide, and an oxidizing agent is present in the water to be treated when the precipitate is recovered as heavy metal sludge. Converting at least a part of the heavy metal hydroxide into an oxide by using the method. 2. The method of claim 1 wherein said oxidizing agent comprises sodium hypochlorite or hydrogen peroxide. 3. The method according to claim 1, wherein a carbonate ion generator is added to the water. 4. The method according to claim 1, wherein said carbonate ion generator comprises sodium carbonate. 5. The method according to claim 1, wherein a coagulant is added to the water to be treated. 6. The method according to claim 1, which comprises using (i) sodium hypochlorite and (i)
i) A drug characterized by comprising a mixture with a water-soluble carbonate. 7. The method according to claim 1, wherein the method comprises a mixture of (i) hydrogen peroxide and (ii) a water-soluble carbonate.