JP4434156B2 - Treatment method of fluorine-contaminated soil - Google Patents

Description

  The present invention relates to a method for treating fluorine-contaminated soil. More specifically, the amount of fluorine eluted from fluorine-contaminated soil can be reduced to 0.8 mg / L or less of the soil environment standard with a simple operation economically and reliably. It relates to the processing method.

  Conventionally, as a treatment method for reducing the amount of fluorine eluted from fluorine-contaminated soil, an example using an aluminum salt and an iron salt (see, for example, Patent Document 1), an example using a calcium compound and an aluminum compound are used. (For example, refer to Patent Document 2), an example using a rare earth element-containing material selected from rare earth element compounds and rare earth ores (for example, refer to Patent Document 3), an example using a steelmaking slag powder and a collection material containing alkanolamine (for example, Patent Document 4), examples using calcium compounds and phosphate compounds (see, for example, Patent Document 5) are known.

However, the conventional treatment method such as Patent Document 1 has a problem that it is actually difficult to reduce the amount of fluorine eluted from fluorine-contaminated soil to 0.8 mg / L or less of the soil environment standard. Moreover, in the conventional processing methods like patent document 2 and 5, although the elution amount of the fluorine from fluorine-contaminated soil can be reduced to 0.8 mg / L or less of soil environmental standard, as a treatment agent for that purpose Since it is necessary to use two or more compounds in combination, there is a problem that actual use is very bothersome and the degree of reduction is greatly affected by the combination. Furthermore, the conventional processing method such as Patent Document 3 has a problem that it is expensive because it uses rare earth resources. The conventional treatment method as disclosed in Patent Document 4 uses an organic material called alkanolamine, and thus has a problem of causing secondary environmental pollution.
JP 2002-326081 A JP 2003-236521 A JP 2004-305935 A JP-A-2005-74280 JP 2005-305387 A

  The problem to be solved by the present invention is to reduce the amount of fluorine eluted from fluorine-contaminated soil economically and reliably by simple work without causing secondary environmental pollution. It exists in the process which provides the processing method which can be reduced below.

The present invention that solves the above-mentioned problems activates the particle surface by suspending powdery particles of fluorine-contaminated soil and calcium hydrogen phosphate dihydrate (CaHPO ₄ .2H ₂ O) in water. A treatment agent is mixed with a specific ratio so as to have a specific moisture, and is cured for at least one day to insolubilize fluorine in the fluorine-contaminated soil.

  First, the treating agent (hereinafter simply referred to as the treating agent of the present invention) used in the method for treating fluorine-contaminated soil according to the present invention will be described. The treatment agent of the present invention is obtained by activating the particle surface of calcium hydrogen phosphate dihydrate. When calcium hydrogen phosphate dihydrate is mixed with fluorine-contaminated soil in the form of powder or in the form of water suspension, fluorine in the fluorine-contaminated soil is insolubilized as fluorapatite. As is well known, fluorapatite itself is the main component of natural phosphate ore, and other organic substances and heavy metals may not be used. According to such calcium hydrogen phosphate dihydrate, Without causing environmental pollution, the elution amount of fluorine from fluorine-contaminated soil can be reduced economically and reliably by simple work.

The effect of calcium hydrogen phosphate dihydrate, which insolubilizes fluorine in fluorine-contaminated soil as fluorapatite, is characteristic. For example, calcium phosphate (Ca ₃ (PO ₄ ) ₂ ) has an effect of correspondingly insolubilizing fluorine in fluorine-contaminated soil, but the degree is significantly inferior to calcium hydrogen phosphate dihydrate. The characteristic action and effect of such calcium hydrogen phosphate dihydrate is further increased by suspending powder particles of calcium hydrogen phosphate dihydrate in water and activating the particle surface. When powder particles of calcium hydrogen phosphate dihydrate are suspended in water and left under stirring or shaking conditions for several hours to several tens of hours, the particles recovered from the suspension have a size of several tens on the surface. It has a structure in which a large number of fine crystals of about nm are uniformly deposited. Such particles have activated surfaces, and more effectively insolubilize fluorine in fluorine-contaminated soil as will be described in detail later. Therefore, as the treatment agent of the present invention, as described above, a powdered particle of calcium hydrogen phosphate dihydrate is suspended in water and the particle surface recovered from the suspension is activated. .

  In the method for treating fluorine-contaminated soil according to the present invention (hereinafter simply referred to as the processing method of the present invention), the fluorine-contaminated soil and the treating agent of the present invention as described above are mixed, cured for a required period, and the fluorine-contaminated soil. The fluorine inside is insolubilized as fluorapatite. The curing period required to reduce the amount of fluorine eluted from the fluorine-contaminated soil to 0.8 mg / L or less of the soil environmental standard is determined by the mixing ratio of the treatment agent of the present invention to the fluorine-contaminated soil, the moisture at the time of mixing, etc. Is also affected, but more than a day. Curing may be performed while gently mixing a mixture of fluorine-contaminated soil and the treatment agent of the present invention, but such a mixture may be simply left, and no special treatment such as heating is required.

  The mixing ratio of the treatment agent of the present invention with respect to fluorine-contaminated soil is less than 0.8 mg / L of soil environmental standard, with the fluorine elution amount from the fluorine-contaminated soil being more reliably and in a shorter period of time while taking into consideration the economy. In order to reduce, the treatment agent of the present invention is adjusted to a ratio of 5 to 20 parts by mass per 100 parts by mass of the dry matter of fluorine-contaminated soil.

  In addition, the moisture content of the mixture of the fluorine-contaminated soil and the treatment agent of the present invention is the same as in the case described above. In order to reduce it to 0.8 mg / L or less, the water content of the mixture is adjusted to 5 to 20% by mass. Such water adjustment includes a method of adding a required amount of water to fluorine-contaminated soil, a method of using the treatment agent of the present invention as a water suspension of a required concentration, a method of adding a required amount of water to a mixture, two or more of these. It can carry out by the method of using together. Thus, when the water content of the mixture is adjusted, the curing of the mixture is preferably carried out so as to suppress the evaporation of such water as much as possible.

  As is clear from the above, the present invention described above has a simple and easy operation economically and reliably to reduce the amount of fluorine eluted from the fluorine-contaminated soil without causing secondary environmental pollution. There is an effect that it can be reduced to 8 mg / L or less.

  FIG. 1 is a photomicrograph of the surface of a powdered particle of calcium hydrogen phosphate dihydrate observed with an electrolytic emission scanning electron microscope, and FIG. 2 is the same calcium hydrogen phosphate dihydrate as FIG. In the micrograph when the surface of the particle | grains collect | recovered after suspending the powder-like particle | grains of a thing in 200 mass times pure water and shaking for 24 hours at 200 times / min in a plastic container similarly to FIG. is there. FIG. 2 shows the treatment agent of the present invention. The surface of the particle in FIG. 1 is relatively smooth, whereas the surface of the particle in FIG. It has a structure in which complex fine irregularities are deposited on the surface. As will be described later in detail, the surface of the particle in FIG. 2 is activated, and insoluble in the fluorine-contaminated soil more efficiently than the particle in FIG.

Test category 1
Fluorine-contaminated soil collected from a gypsum factory was placed in a plastic container, and pure water was added to make the moisture 10% by mass. To this, powdery particles of calcium hydrogen phosphate dihydrate (hereinafter simply referred to as DCPD) were added and mixed at a ratio of 1 to 10 parts by mass per 100 parts by mass of dry matter of fluorine-contaminated soil, and the mixture Was allowed to stand for 5 days. The cured treated soil was subjected to the following fluorine elution test, and the fluorine elution amount (mg / L) was measured. A mixture was prepared in the same manner, but the mixture was subjected to a fluorine elution test as it was without curing, and the amount of fluorine elution (mg / L) was measured. The results are summarized in FIG.

  Fluorine elution test: 10 mass times pure water was added to the treated soil and shaken at 100 times per minute for 24 hours. After standing for 10 minutes, the supernatant was filtered through a 0.45 μm membrane filter, and the filtrate was obtained as an eluent. The fluorine concentration in this eluate was measured with an ion-selective electrode, and the amount of fluorine eluted (mg / L) was determined.

  The horizontal axis of FIG. 3 shows the mass part of the added DCPD per 100 mass parts of the dried material of fluorine-contaminated soil. In FIG. 3, the solid line 11 connecting the white circles indicates the result when the curing is performed for 5 days, and the broken line 21 connecting the black circles indicates the result when the curing is not performed. As is apparent from the results of FIG. 3, when DCPD is used as a treating agent, the amount of fluorine eluted can be reduced by simply mixing with fluorine-contaminated soil. It can be seen that in order to reduce to L or less, curing for about 5 days is necessary.

Test category 2
The treated soil cured for 5 days using DCPD was obtained in the same manner as in test category 1. Further, treated soil cured for 5 days was obtained in the same manner except that powdered particles of calcium phosphate were used instead of DCPD. For both treated soils, the amount of fluorine eluted (mg / L) was measured in the same manner as in Test Category 1. The results are summarized in FIG. The horizontal axis of FIG. 4 shows the mass part of the added powder particles of DCPD or calcium phosphate per 100 mass parts of the dried material of fluorine-contaminated soil. In FIG. 4, the solid line 12 connecting the white circles indicates the result when DCPD is used as the treatment agent, and the broken line 22 connecting the black circles indicates the result when calcium phosphate is used as the treatment agent. ing. As is apparent from the results of FIG. 4, the calcium phosphate powder particles cannot reduce the fluorine elution amount to 0.8 mg / L or less of the soil environmental standard even after curing for 5 days. For example, it can be seen that the amount of fluorine eluted can be reduced to 0.8 mg / L or less of the soil environment standard by curing for 5 days.

Test category 3 (Example)
Fluorine-contaminated soil collected from a gypsum factory was placed in a plastic container, and pure water was added to make the moisture 10% by mass. To this, DCPD is added and mixed at a ratio of 5 parts by weight, 10 parts by weight or 20 parts by weight per 100 parts by weight of the dried material of fluorine-contaminated soil, and the mixture is left to stand for 1 to 7 days and then cured. Soil was obtained. Separately, DCPD was suspended in 200 mass times pure water, placed in a plastic container, shaken at 200 times per minute for 24 hours, and then the surface activated particles from the suspension (hereinafter simply referred to as β-DCPD). It was collected. Then, treated soil cured for 1 to 7 days was obtained in the same manner as in the example using DCPD except that β-DCPD was used instead of DCPD (Example). For both treated soils, the amount of fluorine eluted (mg / L) was measured in the same manner as in Test Category 1.

  The results when DCPD is used are collectively shown in FIG. 5, and the results when β-DCPD is used are collectively shown in FIG. 5 and 6, solid lines 13 and 16 connecting the white circles indicate the results when DCPD or β-DCPD is added at a ratio of 5 parts by mass, and the solid line 14 connecting the white triangles. 17 and 17 show the results when DCPD or β-DCPD is added to a ratio of 10 parts by mass, and solid lines 15 and 18 connecting white square marks indicate the ratio of 20 parts by mass of DCPD or β-DCPD. The result when added so that As is apparent from the results of FIGS. 5 and 6, when β-DCPD in which the surface of DCPD particles is activated is used as the treatment agent, the curing period is much less than DCPD or much less. Thus, it can be seen that the fluorine elution amount can be reduced to 0.8 mg / L of the soil environment standard.

The electron micrograph which shows the particle | grain surface of DCPD used as a processing agent. The electron micrograph which shows the particle | grain surface of (beta) -DCPD used as a processing agent. The graph which illustrates the result of the fluorine elution amount (mg / L) with respect to the addition amount (mass part) of DCPD. The graph which illustrates the result of the fluorine elution amount (mg / L) with respect to the addition amount (mass part) of DCPD or calcium phosphate. The graph which illustrates the result of the amount of fluorine elution (mg / L) with respect to the addition amount (parts by mass) of DCPD and the number of days of curing (days). The graph which illustrates the result of the amount of fluorine elution (mg / L) with respect to the addition amount (parts by mass) of β-DCPD and the number of days of curing (days) in the treatment method of the present invention.

  11 to 18, 21 and 22 Solid line or broken line showing results of each example

Claims (1)

Fluorine-contaminated soil and a treatment agent obtained by suspending powder particles of calcium hydrogen phosphate dihydrate in water and activating the particle surface recovered from the suspension , 100 mass of dry matter of fluorine-contaminated soil The treatment agent per part is mixed so as to have a ratio of 5 to 20 parts by mass and the water content of the mixture becomes 5 to 20% by mass, and is cured for at least one day to insolubilize fluorine in the fluorine-contaminated soil. Fluorine-contaminated soil treatment method.

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