JP4524493B2 - Fly ash treatment method - Google Patents

Description

  The present invention relates to a method for treating fly ash, and in particular, ash further includes molten fly ash generated when general garbage is melted in a gasification melting furnace, incineration ash generated when incinerating general garbage, and incineration fly ash. The present invention relates to a method for treating molten fly ash generated when melted in a melting furnace.

  Conventionally, as a method for treating fly ash from a high-temperature treatment furnace such as an incinerator or melting furnace, leaching is carried out while adjusting the pH to 3 or less by adding water containing mineral acid to the fly ash from the high-temperature treatment furnace, followed by filtration. To obtain a residue that can be used as a lead refining raw material and a filtrate containing a large amount of zinc, and by adding an alkali agent to the filtrate and adjusting the pH to 3 to 5, a silicon-based crystallization product is produced. A step of obtaining a purified filtrate by filtration and separation, and adding an alkali agent to the filtrate to precipitate heavy metal hydroxides mainly composed of zinc and copper, and further adding a sulfiding agent to the hydroxides The remaining heavy metal components that did not become precipitates are precipitated as sulfides, and these starches are separated by filtration to obtain a zinc-based material that can be used as a zinc smelting raw material and a filtrate that is substantially free of heavy metals. Including heavy metals from high-temperature processing furnaces Wet processing method fly ash have been proposed (e.g., refer to Patent Document 1).

JP-A-8-309313 (paragraph numbers 0008-0009)

  However, in the method of Patent Document 1, the slurry mainly composed of silicon obtained by leaching molten fly ash at pH 1 to 2 and then neutralizing to pH 3 to 5 has very high filterability due to gelation of silicon. Unfortunately, there is a problem that an industrially huge filter is required. In addition, since silicon contains a liquid when it gels, there is also a problem that much of the heavy metal leached into the liquid is distributed to the gel. Furthermore, since the gelled silicon residue has a high moisture content, it is difficult to process it.

  Thus, since there is a problem in industrially using the method of Patent Document 1, the molten fly ash, which is a specially managed general waste, is currently disposed of in a final disposal site after being subjected to an elution prevention treatment with a chelating agent or the like. Abandoned. However, since the remaining space of the existing final disposal site is tight and it is difficult to construct a new final disposal site, a process for reducing the volume of molten fly ash in a safe and stable state is desired.

  Therefore, in view of such a conventional problem, the present invention can be used industrially easily and inexpensively, and at the same time, it is possible to reduce the volume and recycle the molten fly ash in a safe and stable state. An object is to provide a method for treating fly ash.

  As a result of diligent research to solve the above-mentioned problems, the inventors of the present invention have obtained a water washing residue from which most of chlorides such as sodium and potassium have been removed by solid-liquid separation after washing heavy ash containing heavy metals. Then, water containing a mineral acid such as sulfuric acid is added to adjust the pH to 3 to 4, and the reaction temperature is 60 ° C. or higher, preferably 80 ° C. or higher for 2 hours or longer, preferably 3 hours or longer to perform leaching to obtain a silicon gel. By adding an alkaline agent such as lime to the obtained leachate and neutralizing it to pH 7 or higher, it can be used industrially easily and inexpensively, and the molten fly ash is safe and stable. The present inventors have found that it is possible to provide a fly ash treatment method capable of reducing the volume and recycling of the state, and have completed the present invention.

  That is, the method for treating molten fly ash according to the present invention includes a water washing step of washing fly ash containing heavy metals, and a water washing residue obtained by solid-liquid separation after the water washing step, by adding water containing a mineral acid. The pH was adjusted to 3 to 4, and the reaction temperature was 60 ° C. or higher, preferably 80 ° C. or higher for 2 hours or longer, preferably 3 hours or longer for leaching, and solid-liquid separation was performed after the leaching step. And a neutralization step of adding an alkaline agent to the leachate to neutralize to pH 7 or higher. In this fly ash treatment method, when fly ash contains zinc, it is preferable to recover the residue obtained by solid-liquid separation after the neutralization step as a residue concentrated in zinc. In addition, in order to prevent elution of Hg, Cd, Pb, Cr, As and the like from the residue obtained by solid-liquid separation after the leaching step and to dispose of the residue, the residue obtained by solid-liquid separation after the leaching step A neutralizing agent may be added to and kneaded. Furthermore, a liquid obtained by solid-liquid separation after the neutralization step may be used in the water washing step.

  According to the present invention, there is provided a fly ash treatment method that can be used industrially easily and inexpensively, and that can achieve safe and stable volume reduction and recycling of molten fly ash. Can be provided.

  Hereinafter, embodiments of a fly ash treatment method according to the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1, first, molten fly ash containing heavy metal is washed with water and subjected to solid-liquid separation to remove a large amount of chlorides such as Na, K, and Cl, and the washing water is subjected to drainage treatment.

  Next, water containing a mineral acid such as sulfuric acid is added to the obtained water washing residue to adjust the pH to 3 to 4 and the reaction temperature to 60 ° C. or higher, preferably 80 ° C. or higher, preferably 2 hours or longer, preferably 3 hours or longer. React. By this leaching, it is possible to obtain a leaching residue having good filterability by suppressing the gelation of silicon, and to dissolve the heavy metal mainly composed of zinc contained in the molten fly ash into the leaching solution without dissolving the silicon in the leaching solution. Can be migrated. The reason for setting the reaction time to 2 hours or longer is to precipitate silicon once dissolved, and a higher reaction temperature is advantageous for silicon precipitation.

  The obtained leaching residue is stabilized by kneading an alkaline agent such as lime, and then made into a state suitable for being landfilled in a final disposal site and can be used as landfill disposal. Thus, the molten fly ash is washed with water and leached, so that the volume of the molten fly ash can be reduced and the load on the final disposal site can be reduced. Further, since the standard for landfill disposal can be satisfied, there is no need to use an expensive chelating agent. In addition, since a part of heavy metal remains in the leaching residue, the heavy metal can be recovered as fly ash again by performing a dry treatment using a melting furnace or the like.

  Next, the obtained leachate is neutralized with an alkaline agent such as lime to a pH of 7 or more to recover heavy metal hydroxides and oxides as precipitates. At this time, if silicon is dissolved in the leachate, it is gelled by neutralization to obtain a residue with extremely poor filterability. In the embodiment of the fly ash treatment method according to the present invention, silicon is contained in the leachate. Since it is not dissolved, a filterable residue that does not gel is obtained. Further, by neutralizing the leachate to pH 7 or higher, heavy metals mainly composed of zinc contained in fly ash can be recovered in a neutralized residue with high quality and used as a non-ferrous smelting raw material. In addition, if neutralization and filtration are performed in two stages, Zn and Cu and Cd and Mg can be separated and recovered to some extent. On the other hand, the neutralized solution is a solution from which heavy metals have been removed, and industrially, it is desirable to reuse it in the washing step in order to reduce the amount of drainage.

  Hereinafter, embodiments of the fly ash treatment method according to the present invention will be described in detail.

[Example 1]
Prepare molten fly ash 1, 2, and 3 of the grade shown in Table 1, each washed with water at a pulp concentration of 300 g / L, and water containing sulfuric acid was added to each washing residue obtained by filtration to obtain a pulp concentration of 100 g. / L, and adjusted to pH 3, pH 3.5, and pH 4, respectively, and reacted at 80 ° C. for 4 hours for leaching. FIG. 2 shows the rate of occurrence of each leaching residue obtained (rate of dry base residue relative to the amount of fly ash). From this figure, it can be seen that the volume of molten fly ash is reduced by washing and leaching. The filtration rate of the leach residue was as good as about 20 L / min / m ² at a filtration pressure of 6 kg / cm ² .

[Example 2]
Prepare molten fly ash 1 of the grade shown in Table 1, wash with water at a pulp concentration of 300 g / L, add water containing sulfuric acid to the water washing residue obtained by filtration, and adjust to a pulp concentration of 100 g / L, The pH was adjusted to pH 3, pH 3.5 and pH 4, respectively, and leaching was performed by reacting at 80 ° C. FIG. 3 and FIG. 4 show the relationship between the concentration of silicon and zinc in each leachate and the reaction time. From these figures, it can be seen that, at pH 3 and pH 3.5, silicon is once dissolved in the liquid, but the precipitation is completed as time passes, and a residue having good filterability is obtained. Further, the final concentration of zinc was constant regardless of pH. From these silicon precipitation behavior and zinc leaching behavior, it was found that the reaction time is preferably 2 hours or longer.

[Example 3]
Prepare molten fly ash of the grade shown in Table 2, wash with water at a pulp concentration of 300 g / L, add water containing sulfuric acid to the water washing residue obtained by filtration, adjust to a pulp concentration of 100 g / L, pH 4, Leaching was performed by reacting at 60 ° C. and 80 ° C., respectively. FIG. 5 shows the relationship between the concentration of silicon in the leachate and the reaction time at reaction temperatures of 60 ° C. and 80 ° C. As can be seen from this figure, silicon precipitates at 60 ° C. and a residue with good filterability is obtained, so the reaction temperature is preferably 60 ° C. or higher.

[Example 4]
Prepare molten fly ash 2 of the grade shown in Table 1, wash with water at a pulp concentration of 300 g / L, add water containing sulfuric acid to the water washing residue obtained by filtration, and adjust to a pulp concentration of 100 g / L and pH 4. After leaching by reacting at 80 ° C., the obtained leachate was neutralized to pH 8 with quick lime. Table 3 shows the contents of Ca, S and Zn in the obtained neutralization residue. As can be seen from Table 3, a residue obtained by concentrating zinc can be obtained by this neutralization, and this residue can be used as a raw material for zinc smelting.

[Example 5]
Prepare molten fly ash 1, 2, and 3 of the grade shown in Table 1, each washed with water at a pulp concentration of 300 g / L, and water containing sulfuric acid was added to each washing residue obtained by filtration to obtain a pulp concentration of 100 g. / L, adjusted to pH 4, and reacted at 80 ° C. to perform leaching, and then added quick lime to the obtained leaching residue at various ratios and kneaded, and an elution test from the kneaded product was performed. The results of this dissolution test are shown in Tables 4-6. From these tables, it can be seen that it is preferable that all the kneaded materials satisfy the landfill standard and the powder pH of the kneaded material is about 10.

It is process drawing of embodiment of the processing method of the fly ash by this invention. It is a graph which shows the generation | occurrence | production rate (the generation rate of the residue of a dry base with respect to the quantity of fly ash) of the leaching residue of Example 1. It is a graph which shows the relationship between the density | concentration of the silicon in the leachate of Example 2, and reaction time. It is a graph which shows the relationship between the density | concentration of zinc in the leaching solution of Example 2, and reaction time. It is a graph which shows the relationship between the density | concentration of the silicon in the leaching solution of Example 3, and reaction time.

Claims (5)

Water washing step for washing molten fly ash containing heavy metal, and water washing residue obtained by solid-liquid separation after this water washing step, adjusted to pH 3-4 by adding water containing mineral acid, reaction temperature 60 ° C. or higher A leaching step for leaching by reacting for 2 hours or more, and a neutralization step for neutralizing the leaching solution obtained by solid-liquid separation after the leaching step by adding an alkali agent to pH 7 or more. A method for treating fly ash. The method for treating fly ash according to claim 1, wherein the reaction temperature is 80 ° C. or higher. The flying fly according to claim 1 or 2, wherein the molten fly ash contains zinc, and a residue obtained by solid-liquid separation after the neutralization step is recovered as a residue in which zinc is concentrated. Ash processing method. The fly ash treatment method according to any one of claims 1 to 3, wherein a neutralizer is added to the residue obtained by solid-liquid separation after the leaching step and kneaded. The method for treating fly ash according to any one of claims 1 to 4, wherein a liquid obtained by solid-liquid separation after the neutralization step is used in the water washing step.

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