JP2005262050A - Ashes treatment method and its facility - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ashes treatment method remaining iron and aluminum in the ash and capable of selectively and inexpensively extracting useful metals such as lead, zinc, cadmium and copper, and its facility. <P>SOLUTION: The ashes are dissolved in an aqueous solution containing ammonium ions and chlorine ions under an acidic condition to extract a metal in the ashes. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ash treatment method and equipment, and more particularly to an ash treatment method and equipment for extracting and treating metals such as lead contained in ash.

  Most of the municipal waste (general waste) (about 70%, about 100,000 tons / day) is incinerated. As a result, about 9% of incinerated ash and about 1% of incinerated waste are incinerated. Fly ash is generated. These ash names contain metals such as lead, cadmium, zinc, and copper at high concentrations (about 1,000 to 10,000 ppm). May cause.

  In particular, incinerated fly ash contains a highly volatile metal such as lead, cadmium, and zinc in a high concentration, and since the particle size is small and the specific surface area is large, the metal is easily eluted. For this reason, intermediate treatment methods such as (1) melt solidification method, (2) cement solidification method, (3) chemical treatment method, and (4) extraction method using a solvent such as an acid have become obligatory.

  ・ The melting and solidification method is a method in which incinerated ash and incinerated fly ash are slagged at a temperature higher than the melting point, and this is cooled and solidified to confine and stabilize the metal in the slag. Then, since it shifts to molten fly ash, a metal having a higher concentration than ordinary incinerated fly ash is contained, and it becomes necessary to reprocess the molten fly ash separately.

  ・ The cement solidification method is a method in which incinerated fly ash is kneaded with cement and water, and the metal is contained inside, but the volume increases due to the addition of cement, and it contains a lot of lead that is easily eluted under alkaline conditions. There is a problem that it is not suitable for the treatment of fly ash.

  ・ The chemical treatment method is intended to stabilize fly ash by mixing incinerated fly ash with a chelating agent and water and reacting the metal in the fly ash with the chelating agent to produce an insoluble metal chelate compound. However, since an expensive chelating agent is used, the processing cost is increased. Moreover, the effect is small for those containing a large amount of metal such as molten fly ash and containing a large amount of salt.

The acid extraction method is a method in which ash is suspended in an acidic solution, extracted as metal ions, and then recovered and stabilized as a solid precipitate having low solubility by various methods. It can be said that there is no problem of the method, and it is easy to recover and recycle valuable metals in ash (for example, Patent Document 1).
Japanese Patent Laid-Open No. 9-316557

  However, the acid extraction method of the above prior art is neutralized by blowing an alkaline agent such as slaked lime in order to treat the harmful acid gas of hydrogen chloride and sulfurous acid gas generated in the process of waste incineration and melting process. Therefore, the unreacted alkaline agent remains in high concentration in the incinerated ash and the molten fly ash, and most of the acid added for extraction is neutralized with the residual alkaline agent and consumed.

  In addition, the ash contains a large amount of iron and aluminum that have low toxicity and are difficult to recover even if extracted in the liquid phase, and these also elute together with valuable metals and consume acid. Furthermore, when recovering the eluted metal from the solution, a neutralization step is required, which requires a large amount of an alkaline agent, and requires a high processing cost such as the addition of an acid again. Yes.

  Therefore, in view of the circumstances of the prior art, the problem to be solved by the present invention is to leave iron or aluminum in the ash and selectively extract useful metals such as lead, zinc, cadmium, and copper selectively and inexpensively. It is to provide a possible ash treatment method and equipment.

  The above object can be achieved by the invention described in the claims. That is, the characteristic configuration of the ash treatment method according to the present invention is that the ash is dissolved in an aqueous solution containing ammonium ions and chlorine ions under an acidic condition, and the metal in the ash is extracted.

  According to this configuration, the elution of iron and aluminum in ash can be minimized, and useful metals such as lead can be selectively extracted efficiently, and an expensive drug (sodium thiosulfate, etc.) Since a large amount of alkaline agent is not used, a treatment method with a low treatment cost can be carried out. In this specification, “ash” includes incineration ash and incineration fly ash generated in the process of incineration of municipal waste and industrial waste, as well as molten fly ash generated when these are melted. Use as a concept.

  As a result, iron and aluminum remained in the ash, and useful metals such as lead, zinc, cadmium and copper could be extracted selectively and inexpensively.

  The pH of the aqueous solution is preferably adjusted to 3 or more and less than 7 under sulfuric acid acidity.

  According to this configuration, useful metals can be selectively extracted more efficiently. When the pH of the aqueous solution is less than 3, it is not preferable because aluminum and calcium are easily eluted, and when the pH exceeds 7, the elution of iron and aluminum can be suppressed, but the extraction rate of zinc and lead is preferably decreased. Absent.

  The ammonium ion concentration is preferably 0.2M or more, and the chlorine ion concentration is preferably 3M or more.

  According to this configuration, useful metals can be selectively extracted more efficiently. If the concentration of ammonium ions is less than 0.2M and the concentration of chloride ions is less than 3M, it is difficult to selectively extract useful metals efficiently.

  It is preferable to perform a stabilization treatment by the sulfide precipitation method on the extract solution dissolved and extracted from the ash.

  According to this configuration, useful metals can be reliably recovered from the extract at a high recovery rate, and the recovered metals (sulfides) can be used as raw materials for various uses, such as non-ferrous smelting. For example, when sodium hydrosulfide is used as the sulfiding agent, 100% of lead, cadmium, copper and zinc in the extract can be recovered.

  It is preferable that after the stabilization treatment, a solid-liquid separation treatment is further performed, and the separated liquid is supplied to the dissolution tank and reused.

According to this configuration, since the separated liquid is reused as a solvent in the dissolution tank, the amount used for dissolution is minimized, which is effective in reducing processing costs and saving resources.
The characteristic configuration of the ash treatment facility according to the present invention is to have a dissolution tank for dissolving ash in an aqueous solution containing ammonium ions and chlorine ions under acidic conditions and extracting the metal in the ash. is there.

  According to this configuration, it is possible to provide an ash treatment facility capable of selectively and inexpensively extracting useful metals such as lead, zinc, cadmium, and copper with iron and aluminum remaining as much as possible in the ash.

  The dissolution tank preferably includes a precipitation tank that performs a stabilization treatment by adding a sulfiding agent to the extract solution dissolved and extracted from the ash.

  According to this structure, the useful metal in ash can be collect | recovered as a sulfide, and it can utilize for various uses.

  It is preferable that a solid-liquid separation device that performs solid-liquid separation is provided for an object to be processed which is processed by either or both of the dissolution tank and the precipitation tank.

  According to this configuration, the useful metal can be recovered as a sulfide as a solid, and the liquid can be reused, so that an efficient system can be configured.

  It is preferable that the liquid component separated by the solid-liquid separator is supplied to the dissolution tank so that it can be reused.

  According to this configuration, it is possible to minimize the amount of chemicals used for dissolving metals, reduce processing costs, and provide equipment that saves resources.

  Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic configuration of an ash treatment apparatus according to the present embodiment. This ash treatment apparatus separates the solid portion and the liquid portion of the dissolved ash from the dissolution tank 1 for extracting the metal component in the ash by mixing the ash, which is the object to be processed, with the dissolved extract in the previous stage. The first-stage solid-liquid separation device 2 is provided. In the subsequent stage, a settling tank 3 is arranged to stabilize the dissolved and extracted metals, and a flocculant is added to the extracted filtrate as necessary, and the solid-liquid separation device 4 in the subsequent stage is added. So that it is separated into solid and liquid. Hereinafter, in this embodiment, fly ash will be described as an example of ash.

  Fly ash is introduced into the previous dissolution tank 1, and a dissolved extract composed of an aqueous solution containing ammonium ions and chlorine ions is added thereto, mixed and stirred, and the metals in the fly ash are extracted. The aqueous solution containing ammonium ions and chlorine ions is not particularly limited as long as it contains ammonium ions and chlorine ions. For example, by dissolving a salt containing these ions in water, etc. Includes everything that can be obtained. In this case, the salt may contain both ions in one salt such as ammonium chloride, and an ammonium salt such as ammonium sulfate, ammonium nitrate, or ammonium carbonate is used as the ammonium source, and sodium chloride, chloride is used as the chloride ion source. A salt containing a chlorine ion such as calcium may be used.

  The ammonium ion concentration in the dissolved extract varies depending on the metal content in the fly ash, etc., but in the case of molten fly ash, it is preferably 0.2M or more, more preferably 0.4M or more. Similarly, although the chloride ion concentration also varies depending on the metal content in the fly ash, it is preferably 3M or more, more preferably 4M or more. By setting it as this density | concentration, the metal in fly ash can be efficiently dissolved and extracted.

  In addition, in order to avoid the metal ions extracted in the dissolution tank 1 from solidifying in the form of hydroxide or the like, an acid such as sulfuric acid is added so that the pH value after extraction is in the acidic range. Adjust the pH. Therefore, the pH is adjusted to less than 7, preferably adjusted to pH = 3 or more and less than 7, more preferably pH = 5 to less than 7.

  Also about the temperature of the melt | dissolution extract in the dissolution tank 1, although it changes with metal contents etc. in ash, it is preferable that it is 15-75 degreeC, and it is more preferable that it is 25-35 degreeC. This is because, in such a temperature range, various metals can be efficiently dissolved and extracted. For example, as shown in FIG. 2, the temperature is preferably 25 ° C. or higher for ash containing a large amount of zinc.

  In the dissolution tank 1, the dissolved extract may be added to the fly ash charged in advance and then stirred and mixed, or vice versa, in order to efficiently extract the metal in the fly ash. For example, when fly ash is molten fly ash, it is preferable that it is 1 to 50 weight% with respect to aqueous solution. In the case of molten fly ash, if it is less than 1% by weight, the amount of treatment is small and the efficiency is poor, and if it exceeds 50% by weight, extraction takes time and is not efficient. More preferably, it is 5 to 20% by weight. About 1 hour is usually sufficient for stirring in the dissolution tank 1. In FIG. 1, M denotes an electric motor that drives a stirrer.

  By the above method, useful metals such as lead, zinc, cadmium, and copper in fly ash are efficiently extracted. The mechanism is considered as follows.

Lead in the fly ash forms a chloride complex such as (PbCl ₄ ) ²⁻ or (PbCl ₃ ) ^{2 −} by chlorine ions in the molten extract and is eluted during extraction. On the other hand, zinc, cadmium, and copper react with ammonium ions to form Zn (NH ₃ ) _n ²⁺ , Cd (NH ₃ ) _n ²⁺ , Cu (NH ₃ ) _n ²⁺ , where n = 1 to Form an ammine complex such as 4) and elute into the extract. In this manner, it is understood that the method according to the present embodiment can selectively extract heavy metals in fly ash. However, in carrying out this embodiment, the reaction is not limited to the above mechanism.

  Next, stabilization of the metal in the extraction filtrate in the latter stage will be described. However, the stabilization treatment may be performed on an extracted filtrate that has been subjected to solid-liquid separation, or on an extract that is not subjected to solid-liquid separation.

  For the purpose of metal recovery in fly ash, the solid-liquid separated extract filtrate is fed to the precipitation tank 3, where the extract filtrate is added with a precipitating agent such as a sulfurizing agent by the sulfide precipitation method. Then, it is stirred and stabilized using the driving force of the electric motor M. On the other hand, the dissolved residue is remelted or disposed of in landfills.

  In particular, when the purpose is not to recover the metal in the fly ash but only to make the metals insoluble, the extract solution dissolved and extracted from the dissolution tank 1 is directly fed to the precipitation tank 3 together with the dissolution residue. Then, a sulfide precipitation treatment is performed to stabilize the extracted metal.

Here, the sulfide precipitation method refers to a method in which HS ^- is added to or generated in a solution and solidified and precipitated as a sulfide according to the following chemical formula 1. As the sulfiding agent for carrying out the sulfide precipitation, water flow soda, sodium sulfide, hydrogen sulfide gas and the like can be used.

[Chemical 1]
M (NH ₃ ) _n ²⁺ + HS ⁻ = MS + H ⁺ + nNH ₃
(PbCl ₄ ) ² + + HS ⁻ = PbS + H ⁺ + 4Cl ⁻
Here, M is a metal such as lead, zinc, cadmium, and copper, and n represents an integer.

  For the purpose of recovering the metal in the fly ash, the solid component separated by the solid-liquid separation device 4 is recovered as a metal recovery product and reduced to the mountain, while the liquid component is again returned to the dissolution tank 1 by the pump P. It is sent or discharged into sewers.

(Example 1)
Extraction of metal contained in ash from the ash collected by the bag filter from the incinerated ash discharged from the stoker-type waste incinerator and the molten fly ash generated when the incinerated fly ash is melted in the plasma melting furnace Went. When the main metals contained in 1 kg of the molten fly ash were analyzed by plasma emission spectrometry, lead: 27.8 g, zinc: 102.1 g, cadmium: 1.2 g, copper: 1.4 g, calcium: 69. It was 8 g, aluminum: 4.9 g, and iron: 3.3 g. For comparison, (A) pure water, (B) 5 M NaCl, (C) 5 M NaCl + 1 M (NH ₄ ) ₂ SO ₄ , (D) 5 M NaCl + 1 M (NH ₄ ) ₂ SO ₄ +0.2 MH ₂ SO for comparison. ₄ , (E) 0.2 MH ₂ SO ₄ , (F) 6 M NaCl + 0.2 MH ₂ SO ₄ were used.

  For extraction, 1 g of fly ash sample and 10 mL of each of the above extracts (A) to (F) were put into a conical flask with a glass stopper of 50 mL capacity, and the mixture was shaken and stirred at 25 ° C. in the atmosphere. I went. After 1 hour, the extract was filtered through a Millipore filter having a pore size of 0.2 μm, and the amount of metal in the filtrate was quantitatively measured by the plasma emission method to determine the elution amount of each metal. For the filtrate, the pH was measured.

  The extract (A) showed a high alkalinity of 12 or more due to the elution of alkaline components such as CaO in the fly ash, and almost no metal other than Ca was eluted. The extract (B) showed high alkalinity of 12 or more due to elution of alkali components such as CaO contained in the fly ash as in (A), and metals other than Ca were hardly eluted. The pH of the extract (C) was lowered to about 7 due to the acidity of ammonium sulfate, and most of lead, cadmium and copper were extracted, but the extraction of zinc was as low as about 50%. It can be seen that the pH of the extract (D) becomes 6.24 by adding sulfuric acid, and most of lead, zinc, cadmium and copper are extracted. The extract (E) became strongly acidic with a pH of 5.86 due to the addition of sulfuric acid, and most of zinc and cadmium were extracted, but the extraction rate of lead and copper was low. In particular, lead has a low extraction rate because it produces sulfate radicals and insoluble compounds. The extract (F) had a pH of 6.66, and the extraction rates of lead, cadmium, and zinc were high, but the extraction rate of copper was low.

  The results are summarized in Table 1.

表１より、灰類を酸性下において、アンモニウムイオンと塩素イオンを含む抽出液（Ｄ）により抽出することが最も好ましいと言える。
（実施例２）
実施例１と同じ溶融飛灰を用いて、溶融抽出温度に対する抽出率の影響を調べた。溶解抽出液には、上記（Ｄ）の抽出液を用い、１５〜７５℃の範囲で抽出した結果を図２に示す。カドミウム、銅については、全温度範囲で８０％以上の抽出率を示したが、鉛は１５〜３５℃で高い抽出率を示し、亜鉛は温度上昇に伴い抽出率が増加することがわかる。従って、飛灰中の性状により、好ましい温度範囲を設定して高い抽出率を確保することができる。
（実施例３）
実施例１と同じ溶融飛灰を用い、上記（Ｄ）の抽出液を用いて金属を抽出し、この抽出液から硫化物法により金属を回収した。硫化物としては、水硫化ナトリウムを用い、抽出液１０ｍＬに２Ｍの水硫化ナトリウムを添加して、抽出液中の水硫化ナトリウム濃度を０〜０．１Ｍとし、硫化物沈殿を生成させた後、孔径０．２μｍのミリポアフィルターでろ過し、ろ液中の金属をプラズマ発光法で定量分析し、各金属の残存濃度から回収率を求めた。その結果を図３に示す。

From Table 1, it can be said that ash is most preferably extracted with an extract (D) containing ammonium ions and chlorine ions under acidic conditions.
(Example 2)
Using the same molten fly ash as in Example 1, the influence of the extraction rate on the melt extraction temperature was examined. FIG. 2 shows the results of extraction in the range of 15 to 75 ° C. using the extract of (D) above as the dissolved extract. Cadmium and copper showed an extraction rate of 80% or more in the entire temperature range, but lead showed a high extraction rate at 15 to 35 ° C., and zinc showed that the extraction rate increased with increasing temperature. Therefore, a high extraction rate can be ensured by setting a preferable temperature range depending on the properties in the fly ash.
(Example 3)
Using the same molten fly ash as in Example 1, the metal was extracted using the extract of (D) above, and the metal was recovered from this extract by the sulfide method. As the sulfide, sodium hydrosulfide was used, 2M sodium hydrosulfide was added to 10 mL of the extract, the sodium hydrosulfide concentration in the extract was adjusted to 0 to 0.1 M, and a sulfide precipitate was generated. The solution was filtered through a Millipore filter having a pore size of 0.2 μm, and the metal in the filtrate was quantitatively analyzed by the plasma emission method, and the recovery rate was determined from the residual concentration of each metal. The result is shown in FIG.

From FIG. 3, copper was 100% recovered by adding sodium hydrosulfide concentration of 0.0025M, almost all of lead and cadmium were recovered by adding 0.025M, and all of zinc was recovered by adding 0.075M. I understand.
Example 4
Using the same molten fly ash as in Example 1, H ₂ SO ₄ was added to 5M NaCl to adjust the pH to 6.1 to 6.7, and the concentration of (NH ₄ ) ₂ SO ₄ was changed to obtain an extraction rate. I investigated. The results are shown in Table 2.

表２より、（ＮＨ₄）₂ＳＯ₄の濃度は０．２Ｍ 以上において、Ｐｂ，Ｚｎ，Ｃｄ，Ｃｕのいずれに対しても高い抽出率を確保できることが分かる。

From Table 2, the concentration of (NH ₄ ) ₂ SO ₄ is 0.2M. From the above, it can be seen that a high extraction rate can be secured for any of Pb, Zn, Cd, and Cu.

[Another embodiment]
(1) In the above embodiment, an example in which the object to be treated stabilized by the settling tank is recovered as it is, but a plurality of settling tanks are arranged in series and processed by the upstream settling tank to be subjected to solid-liquid separation. The collected liquid may be further fed to the downstream sedimentation layer to increase the recovery rate.
(2) The specifications and types of the dissolution tank and the precipitation tank are not particularly limited, and various types can be used.

1 is a schematic overall configuration diagram of an ash treatment apparatus according to an embodiment of the present invention. Graph showing the effect of extraction rate on melt extraction temperature in fly ash Graph showing the relationship between sulfide concentration and metal recovery by the sulfide method

Explanation of symbols

1 Dissolution tank 2, 4 Solid-liquid separator 3 Precipitation tank

Claims (9)

An ash treatment method in which ash is dissolved in an aqueous solution containing ammonium ions and chlorine ions under acidic conditions, and a metal in the ash is extracted. The ash treatment method according to claim 1, wherein the pH of the aqueous solution is adjusted to 3 or more and less than 7 under sulfuric acid acidity. The ash treatment method according to claim 1 or 2, wherein the ammonium ion concentration is 0.2M or more and the chlorine ion concentration is 3M or more. The ash treatment method according to any one of claims 1 to 3, wherein the extraction solution dissolved and extracted from the ash is subjected to a stabilization treatment by a sulfide precipitation method. 5. The ash treatment method according to claim 4, wherein after the stabilization treatment, a solid-liquid separation treatment is further performed, and the separated liquid is supplied to the dissolution tank and reused. An ash treatment facility having a dissolution tank that dissolves ash in an aqueous solution containing ammonium ions and chlorine ions and extracts the metal in the ash under acidic conditions. The ash treatment facility according to claim 6, further comprising a precipitation tank that performs a stabilization process by adding a sulfurizing agent to the extract solution dissolved and extracted from the ash in the dissolution tank. The ash treatment facility according to claim 6 or 7, wherein a solid-liquid separation device that performs solid-liquid separation on an object to be processed that has been processed by one or both of the dissolution tank and the precipitation tank is provided. The ash treatment facility according to claim 8, wherein the liquid component separated by the solid-liquid separator is supplied to the dissolution tank so as to be reusable.

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