JP5599061B2 - Neutral solidifying material additive, neutral solidifying material and method for suppressing elution of heavy metals - Google Patents

Description

  The present invention relates to an additive for a neutral solidifying material that can solidify soil or the like containing heavy metals and suppress elution of heavy metals, a neutral solidifying material, and a method for inhibiting elution of heavy metals.

In recent years, there have been many reports that soils such as sites of factories, offices, and waste disposal sites are contaminated with heavy metals such as lead and arsenic, fluorine, and the like.
When soil is contaminated with heavy metals, the contaminated area of heavy metals diffuses into the groundwater, and eventually the heavy metals are accumulated in the human body and grain via the contaminated groundwater, resulting in a health hazard. sell.
In addition, if the concentration of heavy metals in the soil exceeds the environmental standard value, the site cannot be used as it is, which is also a problem from the viewpoint of effective use of the land.

  To deal with these problems, cement-based, lime-based, gypsum-based and magnesia-based solidified materials are used as a means to solidify heavy metals in contaminated soil and prevent heavy metals from leaching from the soil. It has been.

  However, since the slurry of cement-based and lime-based solidified material exhibits a high alkalinity of about pH 12, amphoteric metals such as lead that are easily dissolved under alkaline conditions from improved soil obtained by solidifying contaminated soil using the solidified material. Has a problem of elution. Moreover, when reclaiming improved soil or reusing it as embankment, etc., the pH of the liquid that exudes from the improved soil or embankment due to rainfall, etc. is pH 5.8 to 8.6 (Article 4 of the Water Supply Law) To meet water quality standard tolerances based on

In addition, since the gypsum-based solidified material is almost neutral but has a low solidification strength, its use is limited to fields where strength is not required.
Further, the magnesia-based solidified material is less alkaline than the cement-based or lime-based solidified material, but the pH of the liquid exuded from the improved soil or the like to which the magnesia-based solidified material is added is about 10, It is difficult to satisfy the pH of the drainage standard. Further, although its solidification strength is higher than that of the gypsum solidified material, it is still not sufficient.

Accordingly, various neutral solidification materials have been proposed for the purpose of reducing alkalinity and improving solidification strength in magnesia-based solidification materials.
For example, Patent Document 1 proposes a solidified material for hydrous soil consisting of 15 to 40 parts by weight of magnesium oxide, 4 to 10 parts by weight of aluminum sulfate and / or iron sulfate, and the balance of gypsum. The solidification material is a mixture of an acid salt (aluminum sulfate or iron sulfate) in an amount smaller than that of magnesium oxide in order to suppress the decrease in solidification strength while reducing the alkalinity of magnesium oxide. However, since the acid salt is a salt of strong acid and weak base and is weakly acidic, the addition of an acid salt in an amount smaller than that of strongly alkaline magnesium oxide does not reduce the alkalinity sufficiently, and also shows strength development. Since it contains 50% by weight or more of low-gypsum gypsum, its solidification strength is insufficient.

Patent Document 2 proposes a soil solidifying agent containing magnesium oxide and a solidifying agent such as aluminum sulfate. Further, Patent Document 3 proposes a soil neutral solidification material in which 10 to 100 parts by weight of an acidic solidification aid is mixed with 100 parts by weight of magnesium oxide.
However, since the solidifying materials of Patent Documents 2 and 3 both contain only 50% by mass or less of an acidic salt (acidic agent), like the solidified material described in Patent Document 1, the reduction in alkalinity is sufficient. Absent.

JP 2000-109829 A JP 2000-239660 A JP 2002-206090 A

Therefore, the present invention is a solution in which the pH of the liquid exuded from the solidified product satisfies pH 5.8 to 8.6 of the drainage standard, has a high solidification strength, and can suppress elution of heavy metals below the environmental standard value. An object of the present invention is to provide a method for suppressing elution of an additive for a neutral solidifying material, a neutral solidifying material, and heavy metals.
In addition, the said heavy metal which the neutral solidification material of this invention makes the object of elution suppression is cadmium, lead, hexavalent chromium, arsenic, total mercury, alkyl mercury, selenium, fluorine, boron, and cyan | 2nd type identification Toxic substances and nickel, molybdenum, antimony, nitrate nitrogen, nitrite nitrogen, etc. that require attention as items to be monitored.

  As a result of intensive studies to solve the above problems, the present inventor has found that a specific amount of an acid sulfate and a specific amount of calcium carbonate-containing additive for a neutral solidifying material and a specific amount of light-burned magnesia or The present inventors have found that a neutral solidified material containing light-burned magnesia partial hydrate can achieve the object of the present invention, and completed the present invention.

That is, the present invention provides the following [1] to [3].
[1] An additive for a neutral solidifying material containing 3 to 42 parts by mass of calcium carbonate-containing material in terms of calcium carbonate with respect to 100 parts by mass of acidic sulfate.
[2] A neutral solidified material containing the additive for a neutral solidified material according to [1] and light-burned magnesia or light-burned magnesia partial hydrate, according to [1] The neutral solidification material which contains 7-98 mass parts of said light-burning magnesia or light-burning magnesia partial hydrate in conversion of magnesium oxide with respect to 100 mass parts of acidic sulfates.
[3] A method for suppressing elution of heavy metals, wherein 1 to 40 parts by mass of the neutral solidifying material according to [2] is added to and mixed with 100 parts by mass of the processing object.

  According to the neutral solidifying material and the like of the present invention, the pH of the liquid exuded from the solidified product satisfies the drainage standard pH 5.8 to 8.6, the solidification strength is high, and the elution of heavy metals is below the environmental standard value. Can be suppressed.

  The present invention relates to an additive for a neutral solidifying material, a neutral solidifying material containing the additive, and a method for suppressing elution of heavy metals using the neutral solidifying material.

The additive for the neutral solidifying material will be described below.
The additive for a neutral solidifying material of the present invention contains a calcium carbonate-containing material in an amount of 3 to 42 parts by mass in terms of calcium carbonate with respect to 100 parts by mass of the acidic sulfate.

The acidic sulfate is a salt of sulfuric acid and a weak base, and is an acidic salt when made into an aqueous solution. Accordingly, the acidic sulfate does not include hemihydrate or dihydrate gypsum having a pH of about 7 and anhydrous gypsum having a pH of about 11.
Examples of the acidic sulfate include one or more selected from aluminum sulfate, ferrous sulfate, and the like and hydrates thereof. The acidic sulfate can reduce the pH of the magnesia-based solidified material exhibiting alkalinity to a neutral range.

  The calcium carbonate-containing material preferably contains 80% by mass or more of calcium carbonate, more preferably 85% by mass or more, and still more preferably 90% by mass or more. Examples of the calcium carbonate-containing material include industrial calcium carbonate powder, reagent calcium carbonate powder, limestone powder, ground shells of calcium carbonate, coral grounds, and the like. Among them, limestone powder is preferable because of its low cost.

Blaine specific surface area of the calcium carbonate-containing material is preferably ^{3000~7000cm 2 / g, 4000~6800cm 2 /} g is more preferable. When the value is less than 3000 cm ² / g, the production of dihydrate gypsum is not sufficient due to low reactivity with acidic sulfate described later, and when the value exceeds 7000 cm ² / g, it takes time and effort to grind. The grinding cost is increased.

  The additive for the neutral solidifying material reacts with sulfate ions derived from acidic sulfates and calcium ions derived from calcium carbonate-containing materials in water or in a wet state to form dihydrate gypsum. In addition to its original effect of increasing the initial strength of the solidified product, the dihydrate gypsum binds water into the compound (dihydrate gypsum) as crystal water in the formation process of the dihydrate gypsum. The water content of the object is reduced. As a result, the solidification material containing the additive of the present invention has a further increased solidification strength as compared with the solidification material containing gypsum in the form of dihydrate gypsum.

  As described above, the additive for a neutral solidifying material of the present invention contains 3 to 42 parts by mass of calcium carbonate-containing material in terms of calcium carbonate with respect to 100 parts by mass of acidic sulfate, and 5 to 40 masses. Those containing parts are preferred, and those containing 10 to 30 parts by mass are more preferred. When the content is less than 3 parts by mass, the effect of increasing the solidification strength is low, and when the content exceeds 42 parts by mass, the acidic sulfate is excessively consumed by the reaction with calcium carbonate, and the effect of reducing the pH of the solidification material is obtained. descend.

Next, the neutral solidifying material of the present invention will be described.
The neutral solidification material of the present invention contains the additive for the neutral solidification material and light-burned magnesia or light-burned magnesia partial hydrate. It is a neutral solidified material containing 7 to 98 parts by mass of calcined magnesia or light calcined magnesia partial hydrate in terms of magnesium oxide.

  The light-burned magnesia can be obtained, for example, by firing a solid containing magnesium carbonate and / or magnesium hydroxide at 650 to 1300 ° C.

The content of magnesium carbonate and / or magnesium hydroxide in the solid is 80% by mass or more, preferably 85% by mass or more, and more preferably 90% by mass or more. When the content is less than 80% by mass, the magnesium oxide component contained in the light-burned magnesia is small, and the solidification strength and the elution suppressing effect of heavy metals tend to decrease.
Examples of the solid material include lump or powdery particles such as magnesite, dolomite, brucite, or magnesium hydroxide obtained by precipitating a magnesium component in seawater with an alkali such as slaked lime.

  The baking temperature of the solid is usually 650 to 1300 ° C, preferably 750 to 950 ° C, and more preferably 800 to 900 ° C. When the firing temperature is less than 650 ° C., light-burned magnesia is difficult to generate, and when the firing temperature exceeds 1300 ° C., the solidification strength and the effect of suppressing the elution of heavy metals may be reduced. The firing time of the solid is usually 30 minutes to 5 hours, although it depends on the amount of solids charged and the particle size.

  The light-burned magnesia partial hydrate to be used in place of the light-burned magnesia is obtained by pulverizing the light-burned magnesia and then adding water to the pulverized product and stirring or mixing the mixture, It can be obtained by keeping it in an atmosphere of 80% or more for 1 week or more.

  The light-burned magnesia partial hydrate preferably contains 65 to 96.5% by mass of magnesium oxide and 3.5 to 30% by mass of magnesium hydroxide, 70 to 95% by mass of magnesium oxide and magnesium hydroxide. Is more preferable, and what contains 75-90 mass% magnesium oxide and 7-17 mass% magnesium hydroxide is still more preferable. If the value is within a preferable range, the solidification strength and the elution suppressing effect of heavy metals can be further enhanced.

  The light-burned magnesia or light-burned magnesia partial hydrate may contain calcium oxide and / or calcium hydroxide in addition to the above components. The total content of calcium oxide and / or calcium hydroxide in light-burned magnesia or light-burned magnesia partial hydrate is preferably 3.0% by mass or less, more preferably 2.5% by mass or less in terms of oxide. Preferably, it is 2.0 mass% or less. When the content exceeds 3.0% by mass, the effect of suppressing the elution of heavy metals may be reduced when used for a processing object having a high degree of contamination by heavy metals.

  The light-burned magnesia or light-burned magnesia partial hydrate is preferably a component other than the above components (magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide) (for example, impurities such as silica and iron oxide). May be included at 4.0 mass% or less. When the content exceeds 4.0% by mass, the solidification strength and the elution suppression effect of heavy metals may be reduced when used for a processing object having a high degree of contamination with heavy metals.

Blaine specific surface area of the light burned magnesia or light burned magnesia partially hydrate is preferably 3000~15000cm ² / g, more preferably ^{4000~10000cm 2 / g, 4500~7000cm 2 /} g is particularly preferred. When the value is in the range of 3000 to 15000 cm ² / g, the elution suppressing effect of heavy metals increases.

As described above, the neutral solidified material of the present invention contains an additive for a neutral solidified material and light-burned magnesia or light-burned magnesia partial hydrate. On the other hand, usually it contains 7 to 98 parts by mass of light-burned magnesia or light-burned magnesia partial hydrate in terms of magnesium oxide, preferably 10 to 90 parts by weight, more preferably 20 to 80 parts by weight. -70 mass parts is still more preferable.
If the content is less than 7 parts by mass, the solidification strength and the elution suppressing effect of heavy metals are not sufficient, and if it exceeds 98 parts by mass, it may be difficult to adjust the pH of the solidified material to a neutral range. .

Next, the method for suppressing elution of heavy metals according to the present invention will be described.
The heavy metal elution suppression method of the present invention includes the following (1) powder addition method and (2) slurry addition method.

(1) Powder addition method This method is a method of adding 1 to 40 parts by mass of a neutral solidifying material to 100 parts by mass of the object to be processed and mixing them. When the addition amount is less than 1 part by mass, it is difficult to uniformly mix the object to be treated and the neutral solidifying material, and the solidification strength is low, and the elution suppressing effect of heavy metals is not sufficient. When the added amount exceeds 40 parts by mass, the increase in solidification strength tends to be saturated, and the cost is rather increased.
Here, it is desirable that the object to be treated includes an amount of water necessary for mixing (kneading) with a neutral solidifying material, hydration of light-burned magnesia, and dissolution of acidic sulfate. The water content in the treatment object is preferably 0.2 to 2.0, preferably 0.3 to 1.5 in terms of the water content ratio (mass ratio of water in the treatment object to the solid content in the treatment object). More preferred is 0.4 to 1.0. If the water content is less than 0.2, it becomes difficult to mix the object to be treated and the neutral solidified material, and if it exceeds 2.0, the solidification strength is not sufficient. When the water content ratio is small, it is necessary to add water to the object to be treated in advance and prepare it within the range of the water content ratio.

(2) Slurry addition method This method includes the following methods (i) and (ii).
(I) An aqueous solution of acidic sulfate (A) and 100 parts by mass of the acidic sulfate, calcium carbonate-containing material, 3 to 42 parts by mass in terms of calcium carbonate, and light calcined magnesia or light calcined magnesia partial water A method of mixing a slurry (B) containing 7 to 98 parts by mass of a Japanese product in terms of magnesium oxide, and then adding and mixing the mixture of (A) and (B) to the object to be treated.
(Ii) An aqueous solution of acidic sulfate, with respect to 100 parts by mass of the acidic sulfate, 3 to 42 parts by mass of calcium carbonate-containing material in terms of calcium carbonate, and light-burned magnesia or light-burned magnesia partial hydrate, A method in which 7 to 98 parts by mass in terms of magnesium oxide is added as powder and mixed to prepare a slurry, and then the slurry is added to the object to be treated and mixed.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
1. Preparation of each component of solidified material, etc. (1) Light-burned magnesia pulverized product (M1) and light-burned magnesia partial hydrate (W1)
Magnesite containing 97% by mass of magnesium carbonate was fired at 850 ° C. for 30 minutes in an electric furnace (manufactured by Chugai Engineering Co., Ltd., model: KSL-2) to obtain light-burned magnesia. Next, the light-burned magnesia was pulverized to obtain a pulverized light-burned magnesia (M1) having a Blaine specific surface area of 6500 cm ² / g. Further, the pulverized product is left in a constant temperature and humidity chamber at a temperature of 20 ° C. and a relative humidity of 100% for 10 days to hydrate part of the light-burned magnesia, and light-burned magnesia partial water having a Blaine specific surface area of 6500 cm ² / g. A Japanese product (W1) was obtained.
The light-burned magnesia partial hydrate (W1) contained 88.0% by mass of magnesium oxide and 8.5% by mass of magnesium hydroxide.

(2) Acid Sulfate As the acid sulfate, anhydrous aluminum sulfate (reagent grade 1, manufactured by Kanto Chemical Co.) and ferrous sulfate monohydrate (reagent grade 1, manufactured by Kanto Chemical Co., Ltd.) were used.

(3) Calcium carbonate-containing material Granular limestone containing 92% by mass of calcium carbonate was pulverized to obtain a calcium carbonate-containing material having a Blaine specific surface area of 5500 cm ² / g.
(4) Dihydrate gypsum As the dihydrate gypsum, flue gas desulfurization dihydrate gypsum (manufactured by Chubu Electric Power Company Shonan Thermal Power Plant, Blaine specific surface area of 6000 cm ² / g) was used.

2. PH and solidification strength of solidified soil and elution test of heavy metals [Preparation of specimen]
A solidified material was prepared according to the formulation shown in Table 1. Next, 20 parts by mass of the solidified material was added to 100 parts by mass of the viscous soil (water content ratio 0.5) containing lead, arsenic, and fluorine, and mixed using a Hobart mixer to prepare a mixture. For comparison, 0.5 parts by mass and 50 parts by mass of the solidified material of Formulation 2 in Table 1 were added to 100 parts by mass of the clay and mixed to prepare a mixture.
Using the mixture, a specimen was prepared according to JGS0821-2009 “Method for preparing specimen without compaction of stabilized soil”.

[PH measurement]
The prepared specimen was wet-cured in a thermostatic chamber at 20 ° C., and then the pH of the specimen one day old was measured in accordance with JGS0211-2009. By the way, the pH of the drainage standard is 5.8 to 8.6.

[Elution test of heavy metals]
The elution test for heavy metals from the specimen was conducted in accordance with Ministry of the Environment Notification No. 46 and JIS K 0120-2008 5.4 “ICP Mass Spectrometry” for lead, and for Ministry of the Environment Notification No. 46 and JIS K for arsenic. In accordance with 0120-2008 61.4 “ICP Mass Spectrometry”, fluorine was carried out in accordance with Ministry of the Environment Notification No. 46 and Annex 6 of the Environment Agency Notification No. 59 in December 1971, “Ion Chromatograph Method”. . Incidentally, the environmental standard value of heavy metals is 0.01 mg / L for lead and arsenic, and 0.8 mg / L for fluorine.

[Uniaxial compressive strength test]
The mixture was put in a mold having an inner diameter of 50 mm and a length of 100 mm, and hermetically cured at 20 ° C. for 3 days to prepare a specimen, and then the uniaxial compression strength of the specimen was measured by an automatic uniaxial compression test apparatus (win Measured using Soil 2007 (manufactured by Tesco).
The results are shown in Table 2.
In Comparative Example 7, dihydrate gypsum was used instead of the additive for the neutral solidifying material. In the reference example, only viscous soil was used.

As shown in Table 2, since the pH of the liquid exuded from the solidified product using the neutral solidifying material of the present invention (Examples 1 to 14) is 5.9 to 8.5, the drainage standard is used in all cases. Of 5.8 to 8.6.
In addition, the concentrations of lead, arsenic and fluorine in the leachate are all below the environmental standard value.

Furthermore, the uniaxial compressive strength of the solidified product was 270 to 298 kN / m ² in Examples 2, 5, 7 and 8 containing 120 parts by mass of sulfate and calcium carbonate in total, whereas dihydrate gypsum In Comparative Example 7 containing the same 120 parts by mass, 179 kN / m ² . Therefore, when the neutral solidified material containing the additive of the present invention is used, the uniaxial compressive strength of the solidified product is remarkably high compared to the case of using the solidified material containing dihydrate gypsum from the beginning.
Moreover, the pH of the liquid exuded from the solidified product is 7.4 (Example 8) to 7.8 (Example) when the neutral solidified material (Examples 2, 5, 7, and 8) is used. 2) and in the neutral range, it is 10.4 when using a solidifying material containing dihydrate gypsum from the beginning. Therefore, the neutralizing material additive of the present invention has a much higher pH reduction effect than dihydrate gypsum.

Claims (3)

  An additive for a neutral solidifying material, comprising 3 to 42 parts by mass of calcium carbonate-containing material in terms of calcium carbonate with respect to 100 parts by mass of acidic sulfate. A neutral solidified material comprising the additive for a neutral solidified material according to claim 1 and light-burned magnesia or light-burned magnesia partial hydrate, wherein 100 mass of acidic sulfate according to claim 1 7 to 98 parts by mass of the light calcined magnesia or the light calcined magnesia partial hydrate in terms of magnesium oxide is contained with respect to parts.   A method for suppressing elution of heavy metals, comprising adding 1 to 40 parts by mass of the neutral solidifying material according to claim 2 and mixing with respect to 100 parts by mass of the object to be treated.