JP3595826B2 - Heavy metal sludge reduction method and chemicals used for it - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for reducing heavy metal sludge generated when removing heavy metals dissolved in water as hydroxide, and an agent therefor.
[0002]
[Prior art]
Conventionally, as a method of removing harmful metal ions contained in water, a method of adding an alkaline substance such as sodium hydroxide or calcium hydroxide to water and precipitating it as a heavy metal hydroxide has been known. The heavy metal sludge generated in 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 recover 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 having a high metal content can be obtained, and the recovery of metal from sludge can be profitable.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to provide 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 an agent used for the method. .
[0004]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, completed the present invention.
That is, according to the present invention, there is provided a method for reducing heavy metal sludge and a chemical used therefor as described below.
(1) An oxidizing agent and carbonate ions are present in the water to be treated when an alkali is added to the water to be treated containing the dissolved metal to precipitate the heavy metal as a heavy metal hydroxide and the precipitate is recovered as heavy metal sludge. And converting at least a part of the heavy metal hydroxide into an oxide.
(2) The method according to the above (1), wherein the oxidizing agent comprises sodium hypochlorite or hydrogen peroxide.
(3) The method according to (1) or (2) above, wherein a carbonate ion generator is added to the water to cause carbonate ions .
(4) The method according to the above (3) , wherein the carbonate ion generator comprises sodium carbonate.
(5) The method according to any one of (1) to (4), wherein a coagulant is added to the water to be treated.
(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 provides a method for adding an alkali to water to be treated in which heavy metals are dissolved to precipitate the dissolved heavy metal contained therein as a water-insoluble hydroxide, and recovering the precipitate as heavy metal sludge. The present invention is characterized in that heavy metal sludge is reduced by causing a heavy metal hydroxide to be converted into an oxide by causing an oxidizing agent and a carbonate ion to be present .
[0006]
The time when the oxidizing agent is added to the water to be treated is not particularly limited, and may be before the addition of the alkali, at the same time as the addition of the alkali or after the addition of the alkali. After the addition of
[0007]
As the alkali for converting the heavy metal dissolved in the water to be treated into a water-insoluble heavy metal hydroxide, a conventionally known alkali is 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.
[0008]
The amount of the alkali to be added to the water to be treated may be any amount as long as the heavy metal dissolved in the water becomes an insoluble hydroxide. Generally, the pH of the water to be treated is 6-13, preferably 8-11. Any amount may be used as long as the amount is controlled within the range.
[0009]
The oxidizing agent used in the present invention only needs to have an oxidizing power capable of converting heavy metal hydroxide to an oxide. Such substances include hypochlorous acid, chlorous acid, chloric acid, oxyacids such as perchloric acid and their water-soluble salts, hydrogen peroxide, ozone, etc. From the viewpoint, use of sodium hypochlorite or hydrogen peroxide is preferred.
[0010]
In the present invention, the amount of the oxidizing agent added to the water to be treated is a proportion that can convert at least a part, preferably 10% or more, and more preferably 50 to 100% of the heavy metal hydroxide generated in the water to an oxide. Should be fine.
[0011]
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 promotion of generation of flocs as compared with the case of using only the oxidizing agent, and obtaining flocs having better sedimentation properties than the case of using only the oxidizing agent.
[0012]
As the compound that generates carbonate ions (carbonate ion generator), any compound that generates 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 0.000005 to 0.1 mol / L, preferably 0.00005 to 0.01 mol / L.
[0013]
The point of addition of the carbonate ion generator is not particularly limited, and may be before, during or after the addition of the oxidizing agent, but is preferably immediately before or simultaneously with the addition of the oxidizing agent.
[0014]
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, a temperature of 30 to 70C, preferably 30 to 55C can be employed. The reaction at such an elevated temperature is carried out by heating the water to be treated.
[0015]
One preferred embodiment of the drug of the present invention (drug A) consists of 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.
[0016]
In the case of preferably producing the drug A of the present invention, when producing a drug containing sodium hydroxide, first, sodium hydroxide is dissolved in an aqueous solution of sodium hypochlorite having an effective chlorine concentration of 8 to 13%. Add carbonate and dissolve. 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.
[0017]
In the case of manufacturing the 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 the carbonate is 0.001 to 1 mol, preferably 0.01 to 0.5 mol, per 1 mol of available chlorine of sodium hypochlorite.
[0018]
In order to preferably produce the drug B of the present invention, sodium carbonate is added to and dissolved in a 3 to 35% aqueous hydrogen peroxide solution. In this case, the ratio of sodium carbonate is 0.01 to 1 mol, preferably 0.05 to 1 mol, per 1 mol of hydrogen peroxide.
[0019]
When the heavy metal sludge is reduced by the agent A of the present invention, either a drug containing sodium hydroxide or a drug not containing sodium hydroxide may be used. If the pH decreases after the addition, 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.
[0020]
The amount of the drug to be added is 0.002 to 1 equivalent, preferably 0.004 to 0.4 equivalent, and more preferably 0.01 to 0.2 equivalent per equivalent of heavy metal hydroxide in terms of the number of equivalents of the oxidizing agent. It is.
[0021]
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, the pH is adjusted to 7 to 13, preferably 8 to 12, and more preferably 9 to 11, and the agent B is added. do it. The amount of the drug to be added is 0.01 to 10 equivalents, preferably 0.05 to 5 equivalents, 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.
[0022]
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 coagulants such as esters, polyethyleneimine and chitosan; nonionic organic coagulants such as polyacrylamide; anionic organic coagulants such as polyacrylic acid, copolymers of acrylamide and acrylic acid, and salts thereof Is included. The coagulant may be usually added to the water to be treated after adding the chemical.
[0023]
The water to be treated including flocs after the treatment of the present invention is subjected to a solid-liquid separation treatment. As the solid-liquid separation method in this case, a conventional method, for example, filtration separation, centrifugation, sedimentation and the like can be mentioned.
[0024]
The present invention is applied to water to be treated containing heavy metal ions. In this case, 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, particularly 0.5 to 20 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.
[0025]
According to the present invention, since at least a part of the heavy metal hydroxide generated as a precipitate is converted into a heavy metal oxide, the finally obtained heavy metal sludge can be reduced in both weight and volume. it can.
[0026]
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 converted into a dewatered sludge by a dehydration treatment such as pressurization. be able to. 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]
【Example】
Next, the present invention will be described in more detail with reference to examples.
[0028]
Reference Example 1
36 g of sodium carbonate was added to 1 liter of sodium hypochlorite aqueous solution (industrial use) (effective chlorine 12%) in which 43 g of sodium hydroxide had been dissolved. This solution is referred to as drug I.
[0029]
Reference Example 2
36 g of sodium carbonate was added to 1 liter of aqueous sodium hypochlorite solution (for industrial use) (effective chlorine 12%) to dissolve it. This solution is designated as drug II.
[0030]
Reference Example 3
36 g of sodium carbonate was added to and dissolved in 1 liter of a hydrogen peroxide solution (concentration: 30%) diluted 5 times with water. This solution is referred to as drug III.
[0031]
Example 1
A calcium hydroxide suspension (0.4%) was added to a 70-fold diluted 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. The pH was adjusted to about 10 to produce a precipitate. 0.3 ml / L of Drug I was added to the 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%.
[0032]
Comparative Example 1
A 70-fold dilution of the waste liquid of Example 1 was added with a calcium hydroxide suspension (0.4%) to adjust the pH to about 10, thereby producing a precipitate. To this slurry, 45 mg / L of an anionic polymer coagulant AP120C was added and stirred. This slurry had poor cohesiveness and dewatering properties, and the discharged sludge had a copper content of 20.2%.
[0033]
Example 2
A 70-fold dilution of the waste liquid of Example 1 was added with a calcium hydroxide suspension (0.4%) to adjust the pH to about 10, thereby producing a precipitate. 0.3 ml / L of Drug II was added to this slurry and stirred. 45 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 74.9%.
[0034]
Example 3
A 70-fold dilution of the waste liquid of Example 1 was added with a calcium hydroxide suspension (0.4%) to adjust the pH to about 10, thereby producing a precipitate. 3 ml / L of Drug III was added to the slurry and stirred. 45 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 65.3%.
[0035]
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. 45 mg / L of an anionic polymer coagulant AP120C 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 62.3%.
[0036]
Example 5
Acid waste liquid containing zinc and iron discharged in the hot-dip galvanizing process with 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 is diluted 25 times. To the resulting mixture, 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 a cationic polymer flocculant KP1200SV and stirring, 430 mg / L of an anionic polymer flocculant 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 36.2%, and the content of zinc, iron and chlorine in the solid content was 64%, respectively. 0.7%, 23.7% and 2.1%.
[0037]
Comparative Example 2
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%) to produce a precipitate. After adding 550 mg / L of a cationic polymer flocculant KP1200SV to this slurry and stirring, 430 mg / L of an anionic polymer flocculant AP825C was added and stirred. This slurry had poor cohesiveness and dewaterability, and the discharged sludge contained 33%, 7% and 16% of zinc, iron and chlorine, respectively.
[0038]
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%) to produce a precipitate. 5 ml / L of Drug II was added to this slurry and stirred. After adding 550 mg / L of a cationic polymer flocculant KP1200SV and stirring, 430 mg / L of an anionic polymer flocculant 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%, 24.8% and 2.5%.
[0039]
Example 7
5 ml / L of Drug I was added to a 25-fold dilution of the waste liquid of Example 1 and stirred. To this, a calcium hydroxide suspension (4%) was added to adjust the pH to about 10, and a precipitate was formed. After adding 550 mg / L of a cationic polymer flocculant KP1200SV and stirring, 430 mg / L of an anionic polymer flocculant 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% each. 0.3%, 24.6% and 2.6%.
[0040]
Example 8
A calcium hydroxide suspension (2%) was added to washing water containing zinc and iron discharged in a hot-dip galvanizing process having a pH of 3.4, a zinc concentration of 11 g / L, and an iron concentration of 1.9 g / L. PH was adjusted to pH 10 to produce a precipitate. 5 ml / L of Drug I was added to this slurry and stirred. After adding 520 mg / L of cationic polymer flocculant KP1200SV and stirring, 250 mg / L of anionic polymer flocculant 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%, and the content of zinc, iron and chlorine in the solid content was 61.5%, respectively. %, 24.0% and 2.8%.
[0041]
【The invention's effect】
According to the present invention, the dissolved heavy metal in the water to be treated is precipitated as a water-insoluble hydroxide, and when this precipitate is recovered as heavy metal sludge, the heavy metal sludge can be efficiently reduced. Is enormous.

Claims (7)

Alkali is added to the water to be treated containing dissolved heavy metals to precipitate the heavy metals as heavy metal hydroxides.When the precipitates are collected as heavy metal sludge, the oxidizing agent and the carbonate ions are present in the water to be treated to remove the heavy metals. A method for reducing heavy metal sludge, comprising converting at least a part of a heavy metal hydroxide to an oxide. 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 to cause carbonate ions . The method of claim 3 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. 2. A drug used as an oxidizing agent in the method of claim 1, comprising a mixture of (i) sodium hypochlorite and (ii) a water-soluble carbonate. 2. A drug for use as an oxidizing agent in the method of claim 1, comprising a mixture of (i) hydrogen peroxide and (ii) a water-soluble carbonate.