JP2000140792A - Treatment of fly ash containing heavy metals - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fly ash treatment method separating and recovering heavy metals in fly ash from salts and capable of corresponding to the tightening of drainage regulation in a method for treating fly ash containing salts based on chlorine and sodium generated from an incinerator and heavy metals based on zinc, copper and lead. SOLUTION: A first process for slurrying fly ash with water and a mineral acid, a second process for neutralizing the obtained slurry to adjust the pH thereof to perform solid-liquid separation, a third process for repulping the formed precipitate to leach the same by a mineral acid to obtain a lead product and a fourth process for neutralizing the obtained filtrate to recover copper, zinc or the like as hydroxides are provided and a ferric salt and an aluminum salt are added to a filtrate from the second process and the pH of this filtrate is adjusted not only to recover copper and zinc contained in the filtrate in a very small amt. in an iron/aluminum salt precipitate but also to obtain clarified filtered water. This clarified filtered water is passed through an activated carbon or chelating agent column if necessary to remove mercury or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating heavy metal-containing fly ash generated from an incinerator, a melting furnace, a cement kiln for treating sludge, or the like in an incinerator for municipal garbage or an industrial waste incineration plant.

[0002]

2. Description of the Related Art Garbage ("municipal waste" or "general waste") discharged from general business establishments and households is collected at municipal waste incineration facilities and industrial waste incineration plants and incinerated. Have been. At that time, incineration ash and fly ash generated from the incinerator are subjected to chemical treatment, intermediate treatment such as melting furnace, cement kiln treatment and the like, and are deposited at the final disposal site.

[0003] However, in the intermediate treatment in the melting furnace and the cement kiln, heavy metals such as lead, zinc, and cadmium having a high vapor pressure volatilize in the furnace and enter the exhaust gas, and the heavy metals entering the exhaust gas enter the exhaust gas treatment facility. There was a problem that it condensed and became fly ash again. During this second fly ash, in addition to salts such as chlorine, sodium, and calcium, lead, copper,
Heavy metals such as zinc and cadmium are contained in large amounts, and stable treatment methods for these metals have been demanded. For such fly ash, JP-A-7-109533 discloses that fly ash is suspended in water in a tank, and the pH of the suspension is adjusted to an appropriate value in an alkaline region by adding an acid or an alkali. Discloses a method of precipitating heavy metals in fly ash as hydroxide and recovering the precipitate.

[0004] The applicant of the present invention has also previously filed a method for coping with the wet processing method (Japanese Patent Application Laid-Open No. 8-11772).
No. 4 and JP-A-8-141439. JP 8
In Japanese Patent No. 117724, fly ash is slurried with water,
pH adjustment, the first step of solid-liquid separation, the second step of repulping the precipitate from the first step, leaching and dissolving with sulfuric acid, and then performing solid-liquid separation to obtain a lead product, A neutralizing agent or further sodium bisulfide is added to the acidic filtrate from the second step, a product containing zinc and copper is separated by filtration, and a third step of using the filtered water as a wastewater is disclosed. Kaihei 8-
Japanese Patent No. 141539 discloses a first step in which fly ash is neutralized with water and a neutralizing agent to perform solid-liquid separation, and the precipitate from the first step is repulped, leached and dissolved with sulfuric acid, and then subjected to solid-liquid separation. A second step of obtaining a lead product by filtration, a third step of adding a neutralizing agent to the filtrate from the second step to filter out a product containing zinc and copper, and filtering the filtered water of the third step by the second step. Repeat as a one-step neutralization solution,
A method is disclosed in which a sulphating agent is added to the filtrate from the first step for drainage treatment.

[0005] By such a wet treatment method, heavy metals contained in fly ash can be separated in a stable form and effectively used as a recovery resource for heavy metals, and the wastewater from this wet treatment method can be used to prevent water pollution. Detoxification has become possible in accordance with Article 3, Paragraph 1 of the Act.

[0006]

However, in the invention disclosed in Japanese Patent Application Laid-Open No. 7-109533, a large amount of salts such as chlorine and calcium enter the recovered heavy metal deposits. Dislikes left a problem in terms of recycling heavy metals. further,
JP-A-8-117124 and JP-A-8-14153
In the invention of No. 9 as well, in recent years, regulations have been further strengthened in some regions due to concerns about environmental pollution, and regulations have been imposed on top of stricter standard values exceeding the wastewater standards of the above-mentioned countries, and it may not be possible to respond. It is becoming. For example, according to local ordinances (addition standard value of I city), cadmium 0.01 mg / l (national wastewater standard value 0.1 mg / l, the same applies hereinafter), fluorine 10 mg / l (1
5 mg / l), 0.0005 mg / l of mercury (0.005
mg / l) and COD 10 mg / l (120 mg / l) are strictly regulated.

In view of such circumstances, the present invention removes salts such as chlorine and calcium in fly ash, separates and collects useful heavy metals in a reusable and stable state in a smelting process, and removes wastewater. The aim is to provide a fly ash treatment method that can respond to strict regional drainage regulations.

[0008]

In order to achieve the above object, the present invention firstly provides a method for treating fly ash containing at least one of zinc, copper and lead and chlorine. Adding a mineral acid to the slurry to form a slurry and adjusting the pH to 5 or less; adding a neutralizing agent to the slurry in the first step to adjust the pH to 8 to 12; And a second step of solid-liquid separation into a salt-containing filtrate; a fly ash containing at least one of zinc, copper, and lead, and chlorine; The processing method of the above, a mineral acid is added to the fly ash to form a slurry,
a first step of adjusting the pH to 5 or less, and adding a neutralizing agent to the slurry in the first step to adjust the pH to 8 to 12, and performing solid-liquid separation into a heavy metal-containing precipitate and a salt-containing filtrate. In the second step, a mineral acid is added to the heavy metal-containing precipitate obtained in the second step, repulped, the pH is adjusted to 4 or less, and solid-liquid separation is performed to obtain a lead residue mainly containing lead. Third step, a neutralizing agent is added to the filtrate obtained in the third step, the pH is adjusted to 8 or more, and solid-liquid separation is performed to obtain a copper / zinc residue containing copper and zinc as main components. A method for treating fly ash containing heavy metals, characterized by comprising four steps; thirdly, by adding a ferric salt to the filtrate obtained in the second step to adjust the pH to 6 to 11, 3. A fly ash containing a heavy metal according to the first or second aspect, comprising a ferric salt coprecipitation step of performing solid-liquid separation to obtain clean filtered water. Treatment method: Fourth, ferric iron and aluminum salt are added to the filtrate obtained in the second step to adjust the pH to 6 to 11, and solid-liquid separation is performed to obtain clean filtered water. A method for treating fly ash containing a heavy metal according to the first or second aspect, which comprises a salt / aluminum salt co-precipitation step; fifthly, a ferrite is added to the filtrate obtained in the second step. A ferric salt coprecipitation step of adding a salt to adjust the pH to 6 to 11 to perform solid-liquid separation, and adding an aluminum salt to the filtrate obtained in the ferric salt coprecipitation step to adjust the pH to 6 to 11. 11
6. The method for treating fly ash containing heavy metals according to the first or the second aspect, wherein the method comprises a step of coprecipitating an aluminum salt to obtain solid filtrate by performing solid-liquid separation to obtain clean filtered water;
The filtered water obtained from the ferric salt co-precipitation step, the aluminum salt co-precipitation step or the ferric salt / aluminum salt co-precipitation step is subjected to an adsorption treatment of heavy metals and COD components with an adsorbent to obtain clean water. The third to fifth features are obtained.
A method for treating fly ash containing a heavy metal according to any one of the above;
Seventhly, the filtrate obtained from the fourth step is circulated to the first step as water for slurrying fly ash to the first step. A method for treating ash is provided.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the treatment process diagram of FIG. 1 in the case of a method for treating fly ash from an incinerator for industrial waste. First, fly ash is mixed with water to form a slurry, and while stirring this slurry, a mineral acid such as hydrochloric acid or sulfuric acid is added to adjust the pH to 5 or less, preferably pH
The salt such as chlorine, sodium and calcium is adjusted to 4 or less and transferred to the liquid (first step). In addition, since the pH of the slurry varies depending on the composition of fly ash,
The amount of mineral acid added is adjusted according to the fly ash. Therefore, if the pH of the slurry is already at the optimum pH, no mineral acid needs to be added.

Then, the pH is adjusted to 8 to 12 by adding an alkali neutralizing agent such as sodium hydroxide or sodium carbonate, followed by solid-liquid separation to remove a heavy metal-containing precipitate, chlorine and sodium. And a filtrate containing salts such as calcium and the like (second step). As described above, after the salts in the fly ash are sufficiently dissolved by the acid in the first step, the acid solution is neutralized in the second step, whereby the content of salts such as chlorine in the neutralized precipitate is determined. Can be significantly reduced. Further, by washing the neutralized precipitate from the second step with water in a pulp or filter press (forward washing, backwashing), salts such as chlorine, sodium and calcium can be further separated from the neutralized precipitate. .

Next, water is added to the neutralized precipitate obtained in the second step, repulped, and a mineral acid such as hydrochloric acid or sulfuric acid is added to adjust the pH to 4 or less, preferably to 3 or less, to adjust zinc,
Dissolve heavy metals mainly composed of copper and cadmium, lead products containing heavy metals mainly composed of hardly soluble lead, zinc,
It is solid-liquid separated into an aqueous solution containing heavy metals mainly composed of copper and cadmium (third step).

An alkali neutralizing agent is added to the filtrate obtained in the solid-liquid separation in the third step, and the pH is adjusted to 8 or more, preferably
By adjusting to about 11, a hydroxide of a heavy metal mainly composed of zinc, copper and cadmium is generated, and solid-liquid separation is performed to obtain a copper / zinc product and filtered water (fourth step). . By repeatedly using the filtered water from the fourth step as water for slurrying fly ash in the first step, it is possible to improve the economical efficiency of fly ash treatment as well as the recovery of heavy metals.

In the treatment of the filtrate in the second step,
When the presence of fluorine is not a problem, the filtrate contains
Add only ferric salt such as ferric chloride and adjust the pH to 6-1.
1, preferably by adjusting the pH to about 8 to 11 and performing solid-liquid separation to obtain traces of iron salt precipitates containing trace metals such as heavy metals such as copper and zinc, and filtered water, and the filtered water is drained as clean water. You.

Further, a ferric salt such as ferric chloride and an aluminum salt such as aluminum chloride are added to the filtrate obtained in the second step to adjust the pH to 6 to 11, preferably about 6 to 8. The residual heavy metal is co-precipitated by adjustment, and the contained fluorine is precipitated as aluminum fluoride. By solid-liquid separation of this solution, it can be separated into iron / aluminum salt deposits containing trace metals such as copper and zinc together with salts such as aluminum and calcium and filtered water, and the filtered water is drained as clean water. Is done.

Further, as shown in FIG. 2, a ferric salt such as ferric chloride is added to the filtrate in the second step to adjust the pH to 6-1.
1, preferably adjusted to a pH of about 8-11, coprecipitating the remaining heavy metals, solid-liquid separation to obtain iron salt precipitates,
An aluminum salt such as aluminum chloride is added to the obtained filtrate, the pH is adjusted to about 6 to 11, preferably about 6 to 8, and the remaining fluorine is precipitated as aluminum fluoride, and the solution is subjected to solid-liquid separation. It is possible to obtain iron salt and aluminum salt deposits containing trace amounts of heavy metals such as copper and zinc, and the filtered water is drained as clean water.

Further, a ferric salt such as ferric chloride is added to the filtrate in the second step, and heavy metals remaining together with the salts are coprecipitated by adjusting the pH, and then an aluminum salt such as aluminum chloride is added. The remaining fluorine is precipitated as aluminum fluoride by pH adjustment, and the solution is subjected to solid-liquid separation to obtain an iron / aluminum salt deposit containing a trace amount of heavy metal and filtered water. When there is a possibility that a trace amount of an equal heavy metal may be contained, as shown in FIG. 1, the residual heavy metal such as mercury is further removed by performing an adsorption treatment with an adsorbent such as activated carbon or a chelating agent, and the resultant is purified water and drained.

As described above, in the present invention, a heavy metal contained in fly ash is converted into a lead product mainly composed of lead and a copper / zinc product mainly composed of hydroxide copper, zinc and cadmium. It can be used as a raw material for smelting, and it collects iron salt or aluminum salt and uses it as a raw material for blast furnaces and cement kilns. It can be discharged.

[0018]

Example 1 Confirmation of Effect of Leaching Treatment on Acid Side [Test 1]

[Table 1]

500 g of the fly ash shown in Table 1 was weighed into a 10-liter beaker, repulped with 5 liters of pure water, and then added with 36% HCl to adjust the pH to 3 to 30.
Leached for a minute. Subsequently, 200 g / l NaOH solution was added to adjust the pH to 11, and after maintaining for 30 minutes,
Suction filtration (using C filter paper) was performed. Further, the total amount of the obtained product was repulped with 1.5 liters of pure water, and suction-filtered again.
A water wash product was obtained. The procedure is exactly the same, but the pH of the leaching is 4.5 or 6 or acid powder addition (pH = 8.9)
Was also performed, and a washed product, a washed product, and a washed product were obtained, respectively. Table 2 shows a comparison of the quality of the washed products.

[0020]

[Table 2] Once the acid was added and the leaching treatment was performed on the acidic side at pH 4 or less, the result of the removal of Ca and Cl was better.

[Test 2] of the washed product recovered in Test 1
2 liters of half or half of the washed product each
Measure into a car, repulp with 1.6 liters of pure water,
95% H _TwoSO_FourAnd adjust the pH to 3;
After leaching for 0 minutes, suction filtration (using C filter paper)
The product was collected. Table 3 shows the comparison of the quality of the obtained Pb products.
It was shown to.

[0022]

[Table 3] In the treatment method shown in Example 1, it was found that the presence or absence of the leaching step had a significant effect on the product quality in the Pb product recovery step shown in Test 2.

[0023]

Example 2 Confirmation of Effect of Coprecipitation Step [Test 1] (1) First Cycle of Circulation Step First, 7 liters of pure water was placed in a 10 liter beaker and stirred, and 700 g of fly ash having the composition shown in Table 4 was obtained. Into a slurry, and stirring for 10 minutes to obtain 36 as a mineral acid.
% Hydrochloric acid is added and adjusted to pH 4 to perform leaching treatment for 30 minutes (first step). Then, a 200 g / l caustic soda solution is added as an alkali neutralizer to adjust the pH to 11 and maintain it for 30 minutes. After that, the mixture was separated into a precipitate mainly composed of heavy metals and a filtrate mainly composed of salts by a filtration operation (second step).

Next, the obtained precipitate was transferred to a 6 liter beaker, and 3.1 liters of pure water was added to form a slurry.
After stirring and maintaining for minutes, a washed precipitate and a washed filtrate were obtained.
(Repulp process)

Subsequently, the whole amount of the obtained washed precipitate was transferred to a 10-liter beaker, repulped with 4.9 liters of pure water, 95% sulfuric acid was added as a mineral acid, the pH was adjusted to 3, and the contents other than lead were adjusted. The heavy metal was eluted to obtain a lead product mainly composed of lead (third step). 200 g in the separated filtrate
/ l caustic soda solution to adjust the pH to 11,
The precipitate of the hydroxide containing copper, zinc and cadmium as main components was separated from the filtrate after neutralization by filtration (fourth step).

(2) After the second cycle of the circulation step First, in a 10-liter beaker, 1.8 liters of the washing filtrate obtained in the repulp step and 4.2 parts of the neutralized filtrate obtained in the fourth step are placed. Add a liter and stir,
600 g of fly ash having the composition shown in Table 4 was put into a slurry,
Hereinafter, in the same manner as shown in the second step, a precipitate mainly composed of heavy metals and a desalted filtrate mainly composed of salts were separated (second step of this test). Table 5 shows the obtained desalted filtrate.

Next, the obtained precipitate was transferred to a 5-liter beaker, and 1.8 liters of pure water was added to form a slurry, and the mixture was stirred and maintained for 30 minutes to obtain a washed precipitate and a washed filtrate.

Subsequently, the entire amount of the obtained washed precipitate was transferred to a 10-liter beaker, and repulped with 4.0 liters of pure water. A lead product mainly containing lead was obtained in exactly the same manner as described in the third step below. Was. Table 4 shows the quality of the obtained lead products. Further, a hydroxide precipitate (copper-zinc precipitate) was obtained from the separated filtrate in exactly the same manner as shown in the fourth step below. Table 4 shows the obtained hydroxide precipitates (copper-zinc products).
Shown in

[0029]

[Table 4]

Test 2 One liter of the desalted filtrate obtained in the second step of this test was placed in a 2 liter beaker, and 200 mg / l of ferric chloride was added as a ferric salt to adjust the pH. After adjusting and maintaining 8.5 and reacting for 30 minutes, it was separated into an iron precipitate and a final filtrate by suction filtration (using C filter paper). Table 5 shows the quality of the desalted filtrate and the final filtrate.

[0031]

[Table 5]

[Test 3] One liter of the desalted filtrate obtained in the second step of this test was placed in a 2 liter beaker, and 200 mg / l of ferric chloride was added as a ferric salt to adjust the pH. The mixture was adjusted and maintained at 8.5 and reacted for 30 minutes. Then, 200 mg / l of aluminum chloride was added as aluminum salt to adjust the pH to 7.
After maintaining and reacting for 30 minutes, the mixture was separated into an iron / aluminum salt precipitate and a final filtrate by suction filtration (using C filter paper). Table 6
The grades of the desalted filtrate and the final filtrate are shown in FIG.

[0033]

[Table 6]

[Test 4] One liter of the desalted filtrate obtained in the second step of this test was placed in a 2 liter beaker, and 200 mg / l of ferric chloride was added as a ferric salt to adjust the pH. After adjusting and maintaining at 10 and reacting for 30 minutes,
The solution was separated into an iron precipitate and a filtrate by suction filtration (using C filter paper). To the obtained filtrate, 50 mg / l of aluminum chloride as an aluminum salt was added as an aluminum salt to adjust and maintain the pH at 7, and reacted for 30 minutes. Then, the aluminum salt precipitate was collected by suction filtration (using C filter paper). And the final filtrate. Table 7 shows the quality of the desalted filtrate and the final filtrate.

[0035]

[Table 7]

[Test 5] The final filtrate of Test 3 was applied to a mini column filled with coconut shell activated carbon for wastewater treatment by SV.
The liquid was passed under the condition of a ratio of 5 to obtain a final drainage. Table 8
Shows the quality of the final wastewater.

[0037]

[Table 8]

[0038]

According to the invention as set forth in claim 1, the salts in the fly ash are sufficiently dissolved by an acid and then neutralized, and the separation of heavy metals from soluble salts is greatly improved, and the recovered heavy metal products Has the effect of being a raw material for the smelting process. According to the second aspect of the present invention, in addition to the effect of the first aspect, an effect of improving the separability between lead products and other products such as copper and zinc is achieved. According to the invention described in claim 3, heavy metals can be sufficiently separated from the filtrate,
According to the invention of claims 4 and 5, heavy metals in the filtrate are separated, and if necessary, fluorine in the filtrate is separated and removed,
This has the effect of increasing the cleanliness of the final filtered water. According to the sixth aspect of the invention, in addition to the effects of the fourth or fifth aspect, an effect is provided in which trace heavy metals such as mercury in the filtered water can be separated and removed as necessary, thereby increasing the cleanliness of the final filtered water. . According to the seventh aspect of the invention, in addition to the effects of the second to sixth aspects, it is possible to increase the efficiency of heavy metal recovery and to increase the economical efficiency of the treatment.

[Brief description of the drawings]

FIG. 1 is a process chart showing a fly ash treatment method of the present invention.

FIG. 2 is a process chart showing a partially modified example of the processing method of FIG. 1;

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Toshimitsu Tokumitsu 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Masahisa Miyazaki 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Same as above F mining term in WA Mining Co., Ltd. (reference) 4D004 AA37 AB05 CA35 CA47 CC11 CC20 DA03 DA20

Claims (7)

[Claims] 1. A method for treating fly ash containing at least one of zinc, copper and lead and chlorine, wherein the fly ash is slurried by adding a mineral acid and the pH is adjusted to 5 or less. And adding a neutralizing agent to the slurry of the first step to obtain a pH.
And the second step of solid-liquid separation into a heavy metal-containing precipitate and a salt-containing filtrate. 2. A method for treating fly ash containing at least one of zinc, copper and lead and chlorine, wherein the fly ash is slurried by adding a mineral acid and the pH is adjusted to 5 or less. ,
A neutralizing agent is added to the slurry in the first step to adjust the pH to 8 to
12, a solid-liquid separation into a heavy metal-containing precipitate and a salt-containing filtrate, a mineral acid is added to the heavy metal-containing precipitate obtained in the second step, and the mixture is repulped to have a pH of 4 or less. In the third step of obtaining a lead residue containing lead as a main component, a neutralizing agent is added to the filtrate obtained in the third step,
A method for treating fly ash containing heavy metals, comprising: a fourth step of adjusting the pH to 8 or more and performing solid-liquid separation to obtain a copper / zinc residue containing copper and zinc as main components. 3. The ferric salt co-precipitation step of adding a ferric salt to the filtrate obtained in the second step to adjust the pH to 6 to 11 and performing solid-liquid separation to obtain clean filtered water. The method for treating fly ash containing a heavy metal according to claim 1 or 2, wherein: 4. A ferric salt obtained by adding a ferric salt and an aluminum salt to the filtrate obtained in the second step to adjust the pH to 6 to 11 and performing solid-liquid separation to obtain clean filtered water. 3. The method for treating fly ash containing a heavy metal according to claim 1, which comprises an aluminum salt coprecipitation step. 5. A ferric salt coprecipitation step in which a ferric salt is added to the filtrate obtained in the second step to adjust the pH to 6 to 11 and solid-liquid separation is carried out. An aluminum salt co-precipitation step comprising adding an aluminum salt to the filtrate obtained in the precipitation step to adjust the pH to 6 to 11, performing solid-liquid separation, and obtaining clean filtered water. 3. A method for treating fly ash containing heavy metals according to 2. 6. Filtration water obtained from the ferric salt co-precipitation step, aluminum salt co-precipitation step or ferric salt / aluminum salt co-precipitation step is subjected to an adsorption treatment of heavy metals and COD components with an adsorbent. The method for treating fly ash containing a heavy metal according to any one of claims 3 to 5, wherein clean water is obtained. 7. The heavy metal-containing fly according to claim 2, wherein the filtrate obtained from the fourth step is circulated to the first step as water for slurrying fly ash. Ash treatment method.