JP5171350B2 - Solid waste treatment method - Google Patents

Description

  The present invention relates to a method for treating waste such as coal ash, incinerated ash, or contaminated soil mainly containing harmful components such as selenium and boron, and more particularly to a treatment method for solidifying these harmful components to prevent their elution.

  In order to prevent the elution of wastes such as coal ash, incineration ash, or contaminated soil containing harmful components such as fluorine, boron, selenium and chromium, to prevent elution of these harmful components, There is known a method of treatment by solidification by chemical or chemical solidification by a chelating agent (see Patent Documents 1 and 2 below).

  However, since these known treatment methods are limited in the types of harmful components to be treated, they still remain inadequate to reliably prevent elution, and there are problems in cost. Therefore, Patent Document 3 below discloses an invention in which this point is improved.

  This method mixes cement and lime with waste containing boron, fluorine, selenium, and even chromium, and hydrothermally treats the crystalline calcium silicate that is produced to supplement the harmful components and dissolve them. It is an invention characterized by reducing the above. This method can be carried out at a lower cost than high-temperature melting or chemical solidification with a chelating agent, and can give a processed product with high strength, which is also suitable for recycling applications.

  The invention of Patent Document 3 is one of a series of technological development results by the present inventor and has been confirmed to be useful for the economical and industrial treatment of this kind of waste. Some of the waste that is discharged after conversion is still with room to be resolved.

That is, the treatment method of the present invention may not be sufficient for waste containing high concentrations of selenium and boron or waste containing selenium and boron in a form that easily dissolves in water. It is. In other words, it has been found that even if such waste is subjected to the hydrothermal treatment described above, the selenium and boron elution amounts may not be reliably reduced to the extent that the environmental standards announced by the Environment Agency are satisfied. . This is because the concentration of selenium and boron contained in the waste is too high and the containment process cannot be achieved.
JP 2003-206172 A JP 2002-320952 A JP 2007-268513 A

The basic object of the present invention is to effectively treat boron, fluorine, selenium, chromium, and the like contained in waste, but further, the amount of selenium and boron is required by environmental standards. The problem to be solved is to reliably and sufficiently reduce it to the extent.

  In order to solve the above problems, the present invention is characterized by the following processing method.

(1) In a waste treatment method in which cement and / or lime or both are added to and mixed with waste containing selenium and boron, and the mixture is hydrothermally treated, the obtained hydrothermal solidified product is sufficiently dried in advance. The weight ratio of the hydrothermal solidified product with respect to the aqueous solution of lime is 0.1 to 5 by charging into the aqueous solution of lime or by directly spraying the aqueous solution of lime with respect to the obtained hydrothermal solidified product. Thus, the solidification processing method of the waste characterized by immersing the hydrothermal solidified material in the aqueous solution of lime, and curing at normal temperature over 1 day to 2 weeks.

(2) solid formulated treatment of waste according to the selenium and cement or lime waste containing boron or above, wherein the admixing and both the gypsum (1).

(3) solidifying treatment of waste according to any one of the cement or lime for waste or the 5 to 60 percent by weight the amount of both (1) or (2).

( 4 ) The waste solidification method according to any one of (1) to ( 3 ), wherein hydrothermal treatment is performed at a temperature of 130 to 300 ° C. and a pressure equal to or higher than a saturated water vapor pressure at this temperature.

( 5 ) Solid waste according to any one of the above (1) to ( 4 ), wherein quick lime or slaked lime is used as lime, and the lime concentration in the aqueous solution is in the range of 0.5 to 5% in terms of CaO. Chemical treatment method.

  As described above, the present invention encapsulates harmful components contained in waste by immersing the hydrothermal solidified product of waste mixed with cement, lime, and gypsum in an aqueous solution of lime and curing it. Although it is a method for suppressing elution to the outside, it has an epoch-making effect in that elution of selenium and boron in harmful components can be surely prevented to below the environmental standard value.

  The waste to be treated by the present invention contains harmful substances such as boron, selenium, fluorine or chromium, such as coal ash, incinerated ash, sludge, sludge, slag, or contaminated soil. It contains both harmful selenium and boron. Selenium and boron as harmful substances should be removed to the extent that they meet the environmental standards described later, but compared to other harmful components, they are more resistant to containment to the extent that they do not elute to the outside world. This is because the present invention particularly addresses this problem.

  In the present invention, cement or lime or both are first added to and mixed with waste that essentially contains selenium and boron. As the cement, for example, blast furnace cement, Portland cement, fly ash cement, and quicklime or slaked lime can be used as the lime content. Further, gypsum may be additionally added to and mixed with these calcium compounds. Examples of the gypsum include dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum.

  The amount of the cement, lime, etc. added to the waste is preferably in the range of 5 to 60% by weight. When gypsum is further added, the range of 3 to 30% with respect to the waste is good.

  Mixing of waste and these additives can be carried out using a suitable mixer, but since so-called hydrothermal treatment is performed in the next step, the waste and these additives are mixed with a predetermined amount of water. It is recommended to feed the three together and mix them well.

  This hydrothermal treatment is performed at a temperature of 130 to 300 ° C. and a pressure equal to or higher than the saturated water vapor pressure at this temperature.

  By subjecting the mixture of waste and additive to hydrothermal treatment, SiO2 contained in these materials to be treated reacts with a calcium compound such as CaO to produce crystalline calcium such as tobermorite, that is, calcium silicate. And this calcium silicate takes in selenium, boron, and other harmful components, and suppresses the elution.

  However, in this case, when the concentration of selenium and boron as harmful components contained in the waste is particularly high, or when the waste to be treated is particularly soluble in water, the above hydrothermal treatment There may be a case where a sufficient elution suppression effect cannot be reliably expected only by the effect of taking in harmful components.

  In this invention, the elution effect of a selenium and a boron can be improved more by immersing the hydrothermal solidified material hydrothermally treated by the above-mentioned method in the aqueous solution of lime, and performing a curing treatment. As lime, quick lime or slaked lime can be used, and the lime concentration in the aqueous solution is preferably in the range of 0.5 to 5% in terms of CaO.

  In order to carry out this treatment, the hydrothermal solidified material that has been sufficiently dried may be charged into a container of lime aqueous solution, or the aqueous lime solution may be sprayed directly onto the hydrothermal solidified product. And the ratio of a hydrothermal solidified material and lime aqueous solution has the range of 0.1-5 by weight ratio, in order to fully exhibit the elution effect of a selenium and a boron, Preferably the range of 0.5-2 is good. If this weight ratio is less than 0.1, drying of the hydrothermal solidified product in the curing treatment process becomes insufficient, and further increases the treatment cost. If this weight ratio exceeds 2, sufficient elution is achieved. The effect may not be obtained.

The hydrothermal solidified product immersed in the lime aqueous solution is a crystal that grows at room temperature by immersing in the lime aqueous solution and the main curing treatment in addition to the crystals of tobermorite etc. generated by the hydrothermal treatment described above by curing at room temperature. And the elution effect is sufficiently strengthened, and as a result, the elution of selenium and boron is reliably prevented. The curing period is suitably from 1 day to 2 weeks, and if it is excessively long, the processing capacity of the facility may be reduced.
(Examples) Examples of the present invention and comparative examples are shown in Table 1 for coal ash wastes that essentially contain selenium and boron. Needless to say, harmful components other than selenium and boron are included. Since the elution effect is exhibited without fail, the numerical description for each component is omitted. Then, in place of the contents of boron and selenium contained in the waste of coal ash, the elution amounts are shown in the column of Comparative Example 1. In addition, this elution amount and the elution amount of each Example and Comparative Example are all values measured according to the attached table of Environmental Agency Notification No. 46 “Environmental Standards Concerning Soil Contamination”.

  Examples 1 to 4 and Comparative Examples 2 and 3 target the same coal ash waste according to the treatment method of the present invention. As shown in each column of Table 1, 10% blast furnace cement or 10% blast furnace cement 10% of dihydrate gypsum was charged into a mixer together with an appropriate amount of water and mixed well so as to be uniform.

  Next, this was transferred to an autoclave, and as shown in the treatment column of Table 1, only hydrothermal treatment or hydrothermal treatment and immersion curing treatment in lime aqueous solution were performed. The hydrothermal treatment at this time was 180 ° C. for 5 hours. In addition, the CaO concentration of the aqueous lime solution during the immersion treatment is 2%, and the ratio of the hydrothermal solidified product and the aqueous lime solution is divided into 0.5 and 1.0 as shown in each column of Table 1, respectively. It was.

  Table 1 shows the elution amounts of boron and selenium of each sample obtained by processing under the above conditions, and can be considered as follows.

  The untreated waste has a boron elution amount of 8.0 mg / L and a selenium elution amount of 0.16 mg / L, which greatly exceeds the environmental standard value (Comparative Example 1). The amount of elution of both elements is clearly reduced just by adding and hydrothermally treating (Comparative Example 2).

  On the other hand, Example 1 of the present invention is an example in which blast furnace cement and water are added to waste and subjected to hydrothermal treatment, and then the hydrothermal solidified product is immersed in a lime aqueous solution and cured at room temperature for 7 days indoors. The boron elution amount is halved to 4.0 mg / L, and the selenium elution amount is drastically reduced to 0.027 mg / L.

  In addition, Example 2 is an example in which the hydrothermal solidified product was immersed in a lime aqueous solution in a half amount and cured in the same manner. The boron elution amount was further reduced to 1.8 mg / L, and the selenium elution amount was also reduced. It has decreased to 0.021 mg / L.

  Examples 3 and 4 were examples in which blast furnace cement and dihydrate gypsum were added and subjected to similar hydrothermal treatment and curing, and the boron elution amount was further increased from 1.2 mg / L to 0.9 mg / L. The selenium elution amount is dramatically decreased from 0.011 mg / L to 0.006 mg / L.

  As is clear from the above examples or comparative examples, by carrying out the curing treatment of the hydrothermal solidified product in the lime aqueous solution according to the present invention, the boron and selenium elution suppression effect is remarkable, both of which are environmental standard values. Can be surely cleared.

Claims (5)

In a waste treatment method in which cement and / or lime or both are added to and mixed with waste containing selenium and boron, and the mixture is hydrothermally treated, the resulting hydrothermal solidified product is sufficiently dried in advance, and then an aqueous solution of lime. Or by directly spraying the lime aqueous solution to the obtained hydrothermal solidified product so that the weight ratio of the hydrothermal solidified product to the lime aqueous solution is 0.1-5. A method for solidifying waste , wherein the hydrothermal solidified material is immersed in an aqueous solution of lime and cured at room temperature for 1 day to 2 weeks.   The waste solidification method according to claim 1, wherein cement and / or lime or both and gypsum are added to and mixed with waste containing selenium and boron. The method for solidifying waste according to claim 1 or 2 , wherein the amount of cement and / or lime added to the waste is 5 to 60% by weight. The waste solidification method according to any one of claims 1 to 3 , wherein hydrothermal treatment is performed at a temperature of 130 to 300 ° C and a pressure equal to or higher than a saturated water vapor pressure at the temperature. The solidification of waste according to any one of claims 1 to 4 , wherein quick lime or slaked lime is used as the lime, and the lime concentration in the aqueous solution is in the range of 0.5 to 5% in terms of CaO. Processing method.