JP2008169424A - Method for treating substance containing heavy metals including zinc - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method by which a high grade zinc compound having low moisture content can be efficiently separated and recovered from a substance containing heavy metals including zinc. <P>SOLUTION: The method for treating the substance containing heavy metals including zinc comprises the following steps: (A) an acid leaching step where acid leaching is applied to the substance containing heavy metals including zinc to obtain a zinc-containing acidic aqueous solution; (B) a first alkali leaching step where the temperature of the acidic aqueous solution is held at ≥30°C and also the pH value of the acidic aqueous solution is adjusted to ≥12.0 to obtain alkaline slurry containing zinc-containing precipitates; (C) a second alkali leaching step where the temperature of the alkaline slurry is successively held at ≥30°C and also the alkaline slurry is formed into alkaline slurry of pH 9.0 to 11.5 to further precipitate zinc; and (D) a zinc recovery step where the alkaline slurry obtained in the step (C) is subjected to solid-liquid separation to obtain a solid content containing zinc. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a treatment method for separating and removing zinc from a substance containing heavy metals including zinc such as fly ash generated in a garbage incinerator or the like and recovering it as a high-grade zinc compound.

Incineration products such as fly ash generated in garbage incineration facilities and dust generated in the cement manufacturing process contain harmful heavy metals such as zinc and lead in addition to water-soluble components such as sodium, potassium and chlorine. ing. Therefore, if these wastes are disposed of in landfills or reused as raw materials for cement, harmful heavy metals may leach out and cause environmental pollution. A detoxifying process is in progress.
Here, as a method for removing zinc contained in the waste, in the method in which the waste is acid leached and solid-liquid separated, and zinc is recovered from the filtrate, a sulfide source is introduced into the acid leached filtrate, There has been proposed a waste treatment method characterized in that zinc is converted into zinc sulfide and precipitated, and the filtrate is adjusted to be alkaline and the remaining zinc in the solution is converted into zinc hydroxide to be precipitated ( Patent Document 1).
Further, a zinc recovery method for recovering zinc as zinc hydroxide from zinc-containing gas generated when zinc-containing molten fly ash or waste is treated in a heat treatment furnace, wherein (a) the molten fly ash or A step of obtaining a zinc-containing solution by acid treatment of the zinc-containing gas, (b) a step of adding an alkaline agent to the zinc-containing solution to obtain a precipitate of insoluble zinc hydroxide, and (c) the precipitate. There has been proposed a zinc recovery method characterized by including a step of removing chlorine in the precipitate by washing with water (Patent Document 2).
Japanese Patent Laid-Open No. 2002-126693 JP 2005-213527 A

According to the methods of Patent Documents 1 and 2, zinc in waste can be separated and recovered as a hydroxide. However, since chloride ions and sulfide ions are also leached simultaneously in the filtrate containing zinc obtained by acid leaching, chlorine compounds such as Zn ₅ (OH) ₈ Cl ₂ .H ₂ O and , there is a problem that _Zn 4 _SO 4 _(OH) sulfates such as 6 · 5H ₂ O is also precipitated. The recovered solid content usually contains 5% by mass or more of Cl (chlorine content) and 10% by mass or more of SO ₄ (sulfuric acid content). Therefore, in order to remove these chlorine content and sulfuric acid content, it is necessary to further perform treatment such as alkali cleaning, and there is a problem that the process becomes complicated.
Moreover, the obtained precipitate of zinc hydroxide has a problem that the solid-liquid separation property (filterability) is poor, the filtration time is long, and the filtration equipment is enlarged. In addition, the solid content obtained by solid-liquid separation of the precipitate has a high moisture content and is in the form of a gel. Therefore, there is a problem that the transportation load when transporting to a Yamamoto reduction factory is large.
Therefore, the present invention is a treatment method for separating and recovering zinc from a substance containing heavy metals including zinc, and is capable of efficiently producing a high-grade zinc compound having a low water content and a simple process. It is an object to provide a method that can be recovered.

  As a result of intensive studies to solve the above problems, the present inventor has determined that the liquid temperature is 30 ° C. or higher with respect to the liquid component containing zinc obtained by acid leaching a substance containing heavy metals including zinc. Holding and alkali leaching in a two-stage pH range of pH 12.0 or higher and 9.0 or higher and 11.5 or lower, the moisture content is low, and each of chlorine and sulfur is contained The present inventors have found that a high-quality zinc compound having an extremely low rate can be obtained, thereby completing the present invention.

That is, the present invention provides the following [1] to [3].
[1] (A) Acid leaching step of obtaining an acidic slurry by mixing a substance containing heavy metals containing zinc and an acid solution to obtain an acidic slurry, and then solid-liquid separating the acidic slurry to obtain an acidic aqueous solution containing zinc When,
(B) While maintaining the temperature of the acidic aqueous solution containing zinc obtained in the above step (A) at 30 ° C. or higher, an alkalinizing agent is added to the acidic aqueous solution to adjust the pH to 12.0 or higher. A first alkaline leaching step to obtain an alkaline slurry containing the containing precipitate;
(C) While maintaining the temperature of the alkaline slurry obtained in the step (B) above 30 ° C., an acid is added to the alkaline slurry to obtain an alkaline slurry having a pH of 9.0 or more and 11.5 or less, A second alkaline leaching step to further precipitate zinc;
(D) A zinc recovery step for solid-liquid separation of the alkaline slurry obtained in the step (C) to obtain a solid content containing zinc;
A method for treating a substance containing heavy metals containing zinc, characterized by comprising:
[2] The method for treating a substance containing a heavy metal containing zinc according to the above [1], wherein the substance containing a heavy metal containing zinc is dust.
[3] The solid content containing zinc has a water content of 50% by mass or less, a chlorine content after drying of 1.0% by mass or less, and a sulfur content of 1.0% by mass or less. The processing method of the substance containing the heavy metals containing zinc as described in said [1] or [2].

According to the method for treating a substance containing zinc-containing heavy metals of the present invention, the temperature of the acidic aqueous solution containing zinc is maintained at 30 ° C. or higher, the pH is in the region of 12.0 or higher, and 9.0 or higher and 11 Only by performing two-step alkaline leaching in the order of 5 or less in this order, a zinc-containing precipitate having excellent solid-liquid separation (filterability) can be obtained (steps (B) and (C)). Solid-liquid separation can be efficiently performed in a short time without requiring a large filtration facility. And finally (after solid-liquid separation), a zinc compound with a low water content (solid content containing zinc) is obtained (step (D)), so the load of transportation to the Yamamoto reduction destination is reduced. Can be planned.
Further, according to the treatment method of the present invention, a high-quality zinc compound having a very low content of chlorine and sulfur can be obtained. For this reason, processes such as alkali cleaning for the purpose of removing chlorine and sulfur are not required, and the number of processes can be reduced.
Furthermore, since the leaching time in the first and second alkali leaching steps is relatively short, the zinc compound can be obtained in a short time as the entire method of the present invention, which is efficient.

Hereinafter, the processing method of the substance containing the heavy metals containing zinc of this invention is demonstrated in detail, referring drawings. FIG. 1 is a flowchart showing an example of an embodiment of a processing method of the present invention.
[(A) Acid leaching step]
This step is a step of obtaining an acidic slurry by mixing a substance containing heavy metals containing zinc and an acid solution to obtain an acidic slurry, and then solid-liquid separating the acidic slurry to obtain an acidic aqueous solution containing zinc.
Here, examples of the substance containing heavy metals including zinc include soot dust and incineration ash remaining as an incineration residue on the bottom of the incinerator and the like. As dust, for example, fly ash (incineration fly ash) generated from incinerators, fly ash (melted fly ash) generated from melting furnaces such as incineration ash, and powder collected by extraction from cement manufacturing processes And powder collected on a bag filter obtained at the time of manufacturing eco-cement.
In the present invention, as a substance containing heavy metals including zinc, waste such as soot is washed with water to remove water-soluble components such as sodium, potassium, and chlorine, and then obtained by solid-liquid separation. It is also possible to use a zinc-containing solid content. However, in the present invention, a high-grade zinc compound having a very low content of chlorine and sulfur can be obtained even if dust or the like that is not subjected to a washing treatment or the like is used as it is.
Here, as a specific method of acid leaching in this step, for example, there is a method in which water is added to a substance containing heavy metals including zinc to form a slurry, and then an acid is added to the slurry to form an acidic slurry. Can be mentioned.
The pH of the acidic slurry obtained in this step is usually 1.0 to 5.0, preferably 1.5 to 4.0. By setting the pH of the acidic slurry within the above range, zinc can be eluted into the solution while containing a heavy metal such as lead in the solid content. As the acid for adjusting the pH, sulfuric acid is preferably used.
The solid-liquid ratio of the acidic slurry (mass of solid content in 1 liter of solution) is preferably 100.
˜600 g / liter, more preferably 150 to 400 g / liter. When the solid-liquid ratio is less than 100 g / liter, the processing efficiency decreases, for example, the time required for solid-liquid separation of the slurry increases. If the solid-liquid ratio exceeds 600 g / liter, zinc may not be sufficiently eluted.
The slurry is usually stirred for a predetermined time (for example, about 15 to 60 minutes).
The slurry after stirring is separated into a solid content and a liquid content (acid solution) containing zinc using solid-liquid separation means such as a filter press.
In addition, although the substance containing heavy metals containing zinc, such as soot dust, normally contains lead etc., in the acid leaching of this process, heavy metals such as lead remain in the solid content. Lead or the like in the solid content can be recovered by appropriately performing treatment such as alkali leaching.

[(B) First alkali leaching step]
In this step, the temperature of the acidic aqueous solution containing zinc obtained in the step (A) is maintained at 30 ° C. or higher, and an alkaline agent is added to the acidic aqueous solution to adjust the pH to 12.0 or higher. This is a step of obtaining an alkaline slurry containing a zinc-containing precipitate (mainly a zinc compound containing a hydroxide).
The above temperature (specifically, the temperature of the acidic aqueous solution containing zinc and the temperature of the alkaline slurry obtained by adding an alkalizing agent to the acidic aqueous solution) is 30 ° C. or higher, preferably 33 ° C. or higher throughout this step. Retained. If the temperature is lower than 30 ° C., the moisture content of the solids containing zinc finally obtained is not preferable. When the acidic aqueous solution containing zinc has a temperature of 30 ° C. or higher in advance, the alkalizing agent may be added as it is.
The upper limit of the temperature is not particularly limited, but can be set to, for example, 50 ° C. (or 45 ° C. or the like) from the viewpoint of saving heat energy for heating.
The pH of the alkaline slurry obtained in this step is 12.0 or more, preferably 12.5 or more. When the pH of the alkaline slurry is less than 12.0, Zn ₅ (OH) ₈ Cl ₂ .H ₂ O and Zn ₄ SO ₄ (OH) ₆ .5H ₂ O are generated, and finally contain zinc. This is not preferable because the content of chlorine and sulfur in the solid content is increased and the quality is lowered.
Preferable examples of the alkalizing agent for adjusting the pH include sodium hydroxide and potassium hydroxide. As the use mode of the alkalizing agent, an aqueous solution such as the above-mentioned sodium hydroxide is preferable. In this case, the concentration of the alkalizing agent is preferably 20% by mass or less.
Although the leaving time of the obtained alkaline slurry is not specifically limited, Preferably it is 10 to 90 minutes, More preferably, it is 20 to 40 minutes. In the alkali leaching in this step, zinc can be sufficiently precipitated in the relatively short standing time as described above, and the property of the precipitate in the slurry can be improved in solid-liquid separation.

[(C) Second alkali leaching step]
In this step, the temperature of the alkaline slurry obtained in the step (B) is continuously maintained at 30 ° C. or higher, and an acid is added to the alkaline slurry to obtain an alkaline slurry having a pH of 9.0 or higher and 11.5 or lower. And a step of further precipitating zinc.
The temperature (specifically, the temperature of the alkaline slurry) is maintained at 30 ° C. or higher, preferably 33 ° C. or higher throughout this step. If the temperature is lower than 30 ° C., the moisture content of the solids containing zinc finally obtained is not preferable.
The upper limit of the temperature is not particularly limited, but can be set to, for example, 50 ° C. (or 45 ° C. or the like) from the viewpoint of saving heat energy for heating.
The pH of the alkaline slurry obtained in this step is 9.0 or more and 11.5 or less, preferably 9.5 or more and 11.0 or less. By adjusting the pH of the alkaline slurry within the above range, zinc remaining in the solution can be precipitated as a hydroxide. If the pH of the alkaline slurry is less than 9.0, the solid-liquid separation of the zinc-containing precipitate is deteriorated, and it takes a long time for solid-liquid separation in the next step, or the solid content containing zinc finally obtained This is not preferable because the water content of is increased to, for example, about 80% by mass. On the other hand, when the pH of the alkaline slurry exceeds 11.5, a part of zinc is eluted in the solution, which is not preferable.
Examples of the acid added to adjust the pH include sulfuric acid and hydrochloric acid, and sulfuric acid is preferable. When sulfuric acid is used, the pH can be adjusted without increasing the chlorine concentration in the solution.
Although the leaving time of the obtained alkaline slurry is not specifically limited, Preferably it is 10 to 60 minutes, More preferably, it is 20 to 40 minutes. In the alkali leaching in this step, zinc can be sufficiently precipitated in the relatively short standing time as described above, and the property of the precipitate in the slurry can be improved in solid-liquid separation.

[(D) Zinc recovery step]
This step is a step of solid-liquid separation of the alkaline slurry obtained in the step (C) to obtain a solid content containing zinc.
Examples of the apparatus for solid-liquid separation of the alkaline slurry include a filter press, a belt filter, and a centrifugal filtration apparatus. A filter press is preferable from the viewpoint of reducing the water content of the solid content. Moreover, if a solid-liquid separator having a cake washing function is used, the chlorine content and sulfur content can be further reduced.

  Thus, according to the treatment method of the present invention described above, the water content of the solids containing zinc obtained after solid-liquid separation is reduced by performing two-step alkali leaching under a specific temperature condition, and , Each content of chlorine and sulfur can be reduced. Specifically, the water content of the solid content including zinc is preferably 50% by mass or less, more preferably 45% by mass or less, and still more preferably 40% by mass or less. Moreover, the chlorine content of the solid content (dried state) containing zinc is preferably 1.0% by mass or less, more preferably 0.7% by mass or less, and further preferably 0.5% by mass or less. The sulfur content of the solid content containing zinc (dry state) is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and further preferably 0.3% by mass or less.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[Example 1]
100 kg of water and 4 kg of sulfuric acid were added to 10 kg of molten fly ash containing zinc, and zinc was leached, followed by solid-liquid separation to obtain 110 kg of an acidic aqueous solution (pH: 2.7) containing zinc (acid leaching step). The chemical composition of this acidic aqueous solution is shown in Table 1.

  Next, the mixture was stirred while gradually adding a caustic soda aqueous solution (concentration: 20% by mass) to 50 kg of the acidic aqueous solution containing zinc (liquid temperature: 35 ° C.) to adjust the pH of the slurry to 12.5, and then left for 10 minutes. (First alkali leaching step). Thereafter, the mixture was stirred while gradually adding sulfuric acid (concentration: 98% by mass) to adjust the pH of the slurry to 11.0, and then allowed to stand for 10 minutes (second alkali leaching step). This slurry was subjected to solid-liquid separation with a filter press, and 2.7 kg of a solid content containing zinc was recovered (zinc recovery step). The water content of the solid content including the recovered zinc was 32% by mass. Moreover, this solid content had the component composition of Zn: 70 mass%, Cl: 0.3 mass%, S: 0.2 mass%, Ca: 0.8 mass% after drying.

[Example 2]
In the second alkali leaching step, the experiment was performed in the same manner as in Example 1 except that the pH of the slurry was adjusted to 9.5. The mass of the solid containing the recovered zinc was 3.0 kg, and the water content of the solid was 37% by mass. Moreover, this solid content had the component composition of Zn: 68 mass%, Cl: 0.5 mass%, S: 0.1 mass%, Ca: 0.9 mass% after drying.
[Comparative Example 1]
After gradually adding a caustic soda aqueous solution (concentration: 20% by mass) to 50 kg of acidic aqueous solution containing zinc used in Example 1 (liquid temperature: 20 ° C.) and adjusting the pH of the slurry to 10.5, Left for 10 minutes. This slurry was subjected to solid-liquid separation with a filter press, and 16.7 kg of a solid content containing zinc was recovered. The water content of the solid content including the recovered zinc is 82% by mass, and the solid content is, after drying, Zn: 43% by mass, Cl: 6.2% by mass, S: 7.1% by mass, Ca: It had a component composition of 0.8% by mass.

[Comparative Example 2]
In the first alkali leaching step, the experiment was performed in the same manner as in Example 1 except that the liquid temperature was 25 ° C. The mass of the solid containing the recovered zinc was 9.4 kg, and the water content of the solid was 75% by mass. Moreover, this solid content had the component composition of Zn: 51 mass%, Cl: 3.5 mass%, S: 5.5 mass%, Ca: 0.9 mass% after drying.
[Comparative Example 3]
The experiment was performed in the same manner as in Example 1 except that the pH of the slurry was adjusted to 11.5 in the first alkaline leaching step. The mass of the solid content including the recovered zinc was 13.2 kg, and the water content of the solid content was 81% by mass. Moreover, this solid content had the component composition of Zn: 51 mass%, Cl: 2.8 mass%, S: 5.5 mass%, Ca: 1.1 mass% after drying.

[Comparative Example 4]
The experiment was performed in the same manner as in Example 1 except that the pH of the slurry was adjusted to 8.5 in the second alkali leaching step. The mass of the solid containing the recovered zinc was 9.0 kg, and the water content of the solid was 73% by mass. Moreover, this solid content had the component composition of Zn: 53 mass%, Cl: 3.5 mass%, S: 6.7 mass%, Ca: 0.6 mass% after drying.
[Comparative Example 5]
The experiment was performed in the same manner as in Example 1 except that the pH of the slurry was adjusted to 12.0 in the second alkali leaching step. The mass of the solid containing the recovered zinc was 3.8 kg, and the water content of the solid was 51% by mass. Moreover, this solid content had the component composition of Zn: 65 mass%, Cl: 0.5 mass%, S: 0.5 mass%, Ca: 0.8 mass% after drying. In addition, 200 mg / liter of zinc remained in the filtrate after solid-liquid separation.

It is a flowchart which shows an example of embodiment of the processing method of the substance containing the heavy metals containing zinc of this invention.

Claims (3)

(A) An acid leaching step of obtaining an acidic aqueous solution containing zinc by solid-liquid separation of the acidic slurry after mixing a substance containing heavy metals containing zinc and an acid solution to obtain an acidic slurry;
(B) While maintaining the temperature of the acidic aqueous solution containing zinc obtained in the above step (A) at 30 ° C. or higher, an alkalinizing agent is added to the acidic aqueous solution to adjust the pH to 12.0 or higher. A first alkaline leaching step to obtain an alkaline slurry containing the containing precipitate;
(C) While maintaining the temperature of the alkaline slurry obtained in the step (B) above 30 ° C., an acid is added to the alkaline slurry to obtain an alkaline slurry having a pH of 9.0 or more and 11.5 or less, A second alkaline leaching step to further precipitate zinc;
(D) A zinc recovery step for solid-liquid separation of the alkaline slurry obtained in the step (C) to obtain a solid content containing zinc;
A method for treating a substance containing heavy metals containing zinc, characterized by comprising:   The method for treating a substance containing heavy metals containing zinc according to claim 1, wherein the substance containing heavy metals containing zinc is dust. The solid content containing zinc has a water content of 50% by mass or less, a chlorine content after drying of 1.0% by mass or less, and a sulfur content of 1.0% by mass or less. Item 3. A method for treating a substance containing heavy metals containing zinc according to item 1 or 2.

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