JP4952928B2 - Incineration ash stabilization method - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method for stabilizing incineration ash, and more specifically, to a method for stabilizing heavy incineration ash using light energy, and a method for stabilizing incineration ash related to a stabilization technology by reducing salt concentration. About.

  Currently, a total amount of incineration residues, etc., totaling over 8 million tons per year is discharged throughout Japan (Non-patent Document 1). The effective use of incinerated ash has not progressed due to legal restrictions, and is mainly landfill disposal. However, landfill sites are limited, and effective use of incinerated ash is considered essential in the future. Incinerated ash contains heavy metals and has a high salinity. Therefore, stabilization and reduction of the salinity are indispensable issues for effective use.

  At present, techniques for stabilizing heavy metals in incineration ash include, for example, a chemical stabilization method (Non-Patent Document 2), a carbon dioxide gas stabilization method (Non-Patent Document 3), and a water washing stabilization method. (Non-Patent Document 4).

  On the other hand, in Europe and the United States, the so-called weathering method in which incinerated ash is temporarily placed in a stock yard for about three months and then stabilized by using weather such as rain and wind and carbon dioxide in the atmosphere has become the mainstream. However, this weathering method cannot stabilize incineration ash completely. In addition, this weathering method has a problem that it requires treatment of leachate by rainwater or the like.

In the carbonation method and the weathering method, the elution amount of Pb, which is an amphoteric metal among heavy metals contained in incineration ash, decreases with time. That is, in the carbonic acid method and the weathering method, according to the characteristics of Pb, the amount of elution of Pb is suppressed when it is neutral, and is eluted when it is acidic and alkaline. As shown in FIG. 1, it can be seen that the amount of Pb elution increases as the pH increases or decreases (salification or acidification of the soil).
Therefore, this decrease in Pb elution is considered to be stabilized by neutralization of pH in the carbonic acid method, and PbCl ₂ , CrCl ₂ due to neutralization of pH and binding to Cl ^{− in the} weathering method. , BCl ₃ is produced (Non-patent Document 5), and is considered to be stabilized. In this way, the weathering method and the carbonic acid method can be said to be effective stabilization techniques, but incineration ash shows a high buffer capacity, and there is a concern that the neutralized incineration ash may subsequently become alkalinized. Suppression of elution associated with changes alone is unstable as a stabilization technique. Furthermore, the weathering method requires treatment of leachate.

  Moreover, since leachate from incineration ash contains heavy metals and salt, leachate cannot be drained as it is. In order to drain such leachate, it is necessary to remove or reduce heavy metals and salt. Examples of methods for removing and reducing heavy metals and salt in leachate include precipitation and adsorption treatment methods (Patent Document 1), water spraying methods (Patent Document 2), and neutralization treatment methods (Patent Document 3). it can.

  In addition, a method of treating incineration ash with ultraviolet rays is also known. For example, a method of treating refractory clean substances contained in fly ash with ultraviolet rays to oxidatively decompose them (Patent Documents 4 and 5), incineration ash A method of treating the contaminated water containing ozone with ultraviolet rays (Patent Document 6) and a method of decomposing organochlorine compounds in waste liquid with ultraviolet rays (Patent Document 7) can be used.

  As described above, the energy of light is considered to affect the stabilization of incinerated ash, and it has been found that the wavelength of ultraviolet rays is effective for photocatalysis among all light. Titanium oxide often used in photocatalysts requires a band gap energy of 3.2 eV for exciting electrons, and the energy converted from the wavelength of ultraviolet rays is applied to this band gap energy. Since incinerated ash contains heavy metals that require the same band gap energy as titanium oxide, it is considered that photocatalytic reaction using ultraviolet rays also occurs in incinerated ash. From these influences, we focus on ultraviolet rays and infrared rays contained in sunlight, and examine the effectiveness of stabilization technology for heavy metals using the wave energy of light.

  In addition to the incineration ash treatment method by ultraviolet irradiation, a method for treating incineration ash with infrared rays is also known. For example, a method for treating incineration ash with infrared rays to decompose harmful substances such as dioxins (Patent Documents 8 and 9). ) Etc. have been proposed. However, there is no report that the salt concentration of incineration ash can be reduced by infrared irradiation.

Unlike the present invention, any of the prior arts for treating incineration ash, waste water, and the like as described above is different from this invention, and incineration ash is irradiated with ultraviolet rays or infrared rays for the purpose of removing or reducing heavy metals and salt. It is not a wastewater treatment.
Ministry of the Environment website http://www.env.go.jp/recycle/waste_tech/ippan/h16/index.html Yamamoto et al .: Proceedings of the 11th Annual Meeting of Japan Society of Waste Management, pp. 892-894, 2000 Kiyono et al .: Proceedings of the 10th Annual Conference of Japan Society of Waste Management, pp. 497-499, 1999 Ueda et al .: Proceedings of the 15th Annual Meeting of the Waste Society, pp. 1078-1080, 2004 Nakahara et al .: Proceedings of the 11th Annual Conference of Japan Society for Waste Management, pp. 895-897, 2000 JP 2002-282875 A JP 2003-334507 A JP-A-11-156370 JP 2003-190908 A JP 2003-183514 A JP 2003-136078 A JP 2002-282875 A JP 11-314073 A JP 2005-58979 A

  As a result of examining the effectiveness of the stabilization technology of heavy metals using the wave energy of light, the present inventors have determined that the concentration of heavy metals present in the incineration ash by irradiating the ultraviolet incineration ash for a certain period of light energy. It was found that the incineration ash can be stabilized by reducing the salt concentration of the incineration ash by irradiating infrared rays for a certain period of time, and the incineration ash can be stabilized.

  Then, this invention aims at providing the incineration ash stabilization method which irradiates an incineration ash with ultraviolet rays for a fixed period, and stabilizes incineration ash by the fall of the heavy metals which exist in incineration ash.

  Another object of the present invention is to provide a method for stabilizing incineration ash comprising stabilizing incineration ash by irradiating incineration ash with infrared rays for a certain period of time, thereby reducing the salt concentration in the incineration ash. That is.

  In order to achieve the above object, the present invention provides incineration ash comprising stabilizing incineration ash by reducing the concentration of heavy metals present in the incineration ash by irradiating the incineration ash with ultraviolet light for a certain period of time. Provide a stabilization method.

  In a more preferred embodiment of the present invention, incineration ash stabilization comprising stabilizing heavy metals, particularly lead (Pb), chromium and cadmium, present in the incineration ash by irradiating the incineration ash with ultraviolet light for a certain period of time. A method is provided.

  Moreover, this invention provides the incineration ash stabilization method which lowers | hangs the salt concentration in incineration ash by irradiating infrared rays for a fixed period, and stabilizes incineration ash.

The ultraviolet irradiation method of the present invention has the effect of reducing the amount of lead elution, regardless of pH, without the generation of by-products associated with curing. The present invention also shows that not only lead but also other heavy metals such as chromium and cadmium can be stabilized.
Moreover, the infrared irradiation method which is another aspect of this invention also has the effect of reducing the salt concentration of incineration ash.

  In the ultraviolet irradiation method according to the present invention, the amount of elution of Pb, which is an amphoteric metal, decreases with the passage of time, as in the carbonation method and the weathering method. The amount of Pb elution decreased in the UV irradiation method in which the pH and salinity did not decrease. Some effects, such as photocatalysis, occur due to light energy, and because the ionization energy of Pb is small, binding to hydroxy radicals is reduced. It is thought that it was promoted. However, it was found that the amount of elution was reduced regardless of pH by the UV irradiation method without the generation of by-products accompanying curing.

  As shown in FIG. 2, it can be seen that when ultraviolet light is irradiated, elution of Pb is suppressed even at pH 12. As shown in the figure, Pb is eluted on the acidic side, but the incineration ash contains a lot of alkali, and the incineration ash has a high buffer capacity, so the pH becomes acidic. Is hard to think. Therefore, it can be said that ultraviolet rays have an effect of stabilizing the incineration ash because the elution suppression effect is recognized on the alkali side. It was recognized that not only Pb but also other heavy metals such as chromium and cadmium had the same stabilizing effect.

  The ultraviolet light that can be used in the present invention has a wavelength of about 352 nm (UVA) and an energy of about 3.52 eV. Infrared rays may have a wavelength of 600 to 780 nm and an energy of about 1.59 to 2.07 eV. In any case, ultraviolet light is not particularly limited as long as its wavelength and energy are sufficient to suppress elution of heavy metals in the incineration ash. There is no particular limitation as long as the salt concentration in the medium can be reduced.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples, and the following examples are not intended to limit the present invention. .

The amount of elution of heavy metals at the time of sampling was examined as follows.
(Ultraviolet and infrared irradiation equipment)
FIG. 1 is a schematic diagram showing the ultraviolet / infrared irradiation device used in the first embodiment. The ultraviolet ray used in this apparatus had a wavelength of 352 nm (UVA), the infrared ray had a wavelength of 600 to 780 nm, and the energy was 3.52 eV for ultraviolet rays and 1.59 to 2.07 eV for infrared rays. Incineration ash used the general waste generated from the A city incineration facility. In this example. Curing with ultraviolet rays and infrared rays was performed in 56 days, with ultraviolet rays and infrared rays being irradiated in two patterns with irradiation distances of 2 cm and 10 cm from one direction of the incinerated ash in a sealed darkroom.
In any curing, after elapse of a predetermined time, a predetermined amount of sampling was performed from the apparatus, and after pretreatment, the elution amount of heavy metals was measured using an ICP emission spectrometer. As the dissolution test method, the Environmental Notification No. 46 method was used. The results are shown in Table 1.

(Reference Example 1: Weathering device)
For comparison, curing was performed by a weathering method in which incineration ash was left outdoors. FIG. 2 is a simulated weathering device used for curing in Europe. In the weathering method, the apparatus was left outdoors for 56 days, and the amount of elution of heavy metals was measured. In this curing as well, a predetermined amount of sampling was performed from each device after a predetermined time, and after pretreatment, the amount of elution of heavy metals was measured using an ICP emission analyzer. As the dissolution test method, the Environmental Notification No. 46 method was used as described above.

(Reference Example 2: Carbonation curing device)
FIG. 3 simulates a carbonic acid curing device used for stabilization by carbonation. Curing was performed by a carbonic acid method that allowed carbon dioxide to permeate for a certain period of time.
This carbonation method was carried out at a curing period of 24 hours by passing carbon dioxide through the curing box shown in the figure at a rate of 20 ml / min for the first 4 minutes and then 4 ml / min. In any curing, a predetermined amount of sampling was performed from each device after a predetermined time, and after pretreatment, the amount of elution of heavy metals was measured using an ICP emission spectrometer. Similarly, the Environmental Notification No. 46 method was used as the dissolution test method.

  Table 1 also shows the leaching amount of heavy metals eluted in the leachate during curing by the weathering method, in addition to the content and elution amount at the time of collection.

The water content ratio, salinity concentration, and pH were analyzed according to the difference in stabilization technology between the ultraviolet / infrared method according to the present invention and the conventional weathering method and carbonic acid method.
Tables 2 to 6 show the results of the water content ratio, salinity concentration, and pH measured during sample sampling in each curing method.
Among these, with respect to pH, in the ultraviolet / infrared method, there is no change around pH 12, and the alkali remains high. On the other hand, the weathering method and the carbonic acid method are gradually decreased and neutralized as the number of days increases. In addition, regarding the salt concentration, it can be seen that the infrared irradiation method has a slight tendency to decrease. In contrast, the weathering method decreased due to rainfall, but the carbonic acid method and the ultraviolet irradiation method showed almost no reduction effect.

Elution amount of heavy metals, such as chromium (Cr), boron (B) and lead (Pb), which are determined by soil environment standards, by the ultraviolet / infrared irradiation method, weathering method and carbonation method of this invention Examined. The result is shown in FIG. Fig. 4 (a) shows the elution amount of chromium (Cr), Fig. 4 (b) shows the elution amount of boron (B), and Fig. 4 (c) shows the elution amount of lead (Pb). Cd is not shown for any stabilization technique because the elution amount was below the lower limit of quantification.
As a result, as shown in FIG. 4, it was found that the amount of elution of Pb, which is an amphoteric metal, decreased with time even in the carbonization method and the weathering method, including the ultraviolet ray method. This decrease in the amount of dissolved Pb is considered to be stabilized by neutralization of pH in the carbonic acid method, and PbCl ₂ , CrCl ₂ and BCl ₃ are generated by neutralization of pH and binding to Cl ^{− in} the weathering method. It is thought that it stabilizes.
From these results, the UV irradiation method did not show a decrease in pH or salinity, but the Pb elution amount decreased because of some effects such as photocatalysis due to light energy, and the ionization of Pb. This is probably because the bond with the hydroxy radical was promoted because of the low energy.

Effect on pH dependence test Incinerated ash was cured at pH 4, pH 7 and pH 12 for 56 days by each curing method, and a pH dependence test was conducted. The results are shown in FIGS. 5 to 7 for the pH dependence test results of each curing.
As a result, focusing on Pb, which is an amphoteric metal, it was found that, in the weathering method and the carbonic acid method, the elution amount was suppressed according to the characteristics of Pb, and the elution was acidic and alkaline. In other words, the suppression of Pb elution by weathering and carbonation is considered to be due to neutralization of pH. Therefore, as shown in the figure, it was found that the elution amount of Pb increases with the increase or decrease of pH (that is, soil alkalinization or acidification). Incineration ash shows a high buffering capacity, and even if the incineration ash is once neutralized, there is a concern that the incineration ash may become alkalinized later. Therefore, it can be said that instability alone is unstable as a stabilization technique only by suppressing elution associated with a change in pH. However, it was found that the Pb elution was suppressed even at pH 12 by the ultraviolet method. Although Pb is eluted on the acidic side, the incineration ash contains a large amount of alkali, and it is unlikely that it will become acidic due to the high buffering capacity of the incineration ash. Therefore, it can be said that ultraviolet rays have an effect of stabilizing incineration ash. The same can be seen for Pb as well as other heavy metals.

  Since the amount of general waste incineration ash varies depending on when it is generated, the concentration of Pb contained in the incineration ash is considered to differ depending on the timing of collection. Therefore, the influence of the amount of Pb elution by UV curing was examined on the incinerated ash collected in FY2017 and the incinerated ash collected in FY18. As a result, as can be seen from FIG. 8 and Tables 2 and 3, the amount of Pb elution decreased in both 2005 and 2006 despite the fact that the pH maintained high alkalinity due to the buffer capacity of incineration ash. It shows a trend. Since the amount of Pb elution at the start of curing and the amount of Pb at the end of curing decreased in the same way with almost no difference between the two years, the light energy from the experimental results does not depend on the timing of incineration ash generation or collection, This is considered to be effective for stabilizing heavy metals.

  In this example, the influence of the Pb elution amount on the irradiation distance of ultraviolet rays was examined. Experiments were conducted with 2 patterns of UV irradiation distance of 2 cm and 10 cm, and the amount of elution of Pb was measured. As shown in Figs. I found out that Although the time to suppress Pb elution was different, the decrease trend was similar, and it was found that the irradiation distance was not related in the photocatalytic reaction. In addition, since the ultraviolet rays used are 3.52 eV and close to the band gap energy of ZnO, it is considered that some influence by light energy such as photocatalytic reaction occurred.

In this example, the influence on the Pb elution amount due to the difference in irradiation conditions was examined. The experiment was conducted by changing the conditions of the irradiation light with two wavelengths (energy) of ultraviolet rays and infrared rays. The result is shown in FIG.
Irradiation conditions consisted of four experimental patterns: 56 days of total curing, continuous irradiation of ultraviolet rays and infrared rays for 56 days, 28 days of curing from ultraviolet to infrared, and vice versa. The experiment was conducted. As can be seen from FIG. 11, the Pb elution suppression effect appears from the day of irradiation with ultraviolet rays.
On the other hand, incineration ash irradiated with infrared rays has not been able to suppress Pb elution, and after irradiating with ultraviolet rays for 28 days, the effect of suppressing Pb elution has stopped at that point. From this, it was found that although some influences of light energy are caused by ultraviolet rays, the infrared rays do not have the same influence as ultraviolet rays, and the elution suppression effect is obtained only with the incinerated ash irradiated with ultraviolet rays.

According to this invention, in each curing, the total chromium (T-Cr) and boron (B), many of which shows an elution amount below the soil environmental standard value, lead (Pb) is the soil environmental standard value It became clear that it was greatly exceeded. In the stabilization method by the ultraviolet irradiation method using light energy, (1) it does not depend on the difference in the collection time and irradiation distance of the incinerated ash. (2) It is not suppression of elution by neutralization of pH. (3) The irradiation condition is stabilized only by ultraviolet rays. From the above, it is considered that the irradiation with ultraviolet rays does not require a secondary operation, and the amount of Pb elution can be reduced to promote stabilization.
On the other hand, the weathering method and the carbonation method are effective stabilization technologies, but there is concern about elution when the pH of the soil changes due to the buffer capacity of the incinerated ash, and the weathering method requires treatment of leachate. It becomes. Thus, it was found that the amount of elution increased and decreased with the change of the situation. However, it has been found that the ultraviolet irradiation method according to the present invention does not generate by-products or the like accompanying curing, and particularly reduces the elution amount of Pb regardless of pH. Furthermore, the effect of reducing the salt concentration in incineration ash by infrared irradiation was also found.

Schematic which shows an ultraviolet-ray and infrared irradiation apparatus (Example 1). Schematic which shows a weathering apparatus (reference example 1). Schematic which shows a carbonic acid curing apparatus (reference example 2). (A) Elution amount of total chromium (T-Cr), (b) Elution amount of boron (B) 6 and (c) Elution amount of lead (Pb). The graph which shows an ultraviolet irradiation 56 day pH dependence test result. The graph which shows a weathering 56 day pH dependence test result. The graph which shows a carbonation pH dependence test result. The graph which shows the influence by the difference in collection time. The graph which shows the influence by the difference in irradiation distance. The graph which shows the influence (expansion after 28th) by the difference in irradiation distance. The graph which shows the influence by the difference in irradiation conditions.

Claims (1)

By certain period irradiated with ultraviolet rays ash containing lead, to cause a photocatalytic action of the ultraviolet heavy metals that are equally band gap energy and titanium oxide present in said incinerated ash, the lead and hydroxyl radicals The incineration ash stabilization method characterized by stabilizing the lead in incineration ash by accelerating | stimulating a coupling | bonding and reducing the said lead elution amount .