JP2009214083A - Soil solidifying agent and solidifying method of soil - Google Patents

Abstract

A soil solidifying agent and a soil solidifying method capable of not only solidifying muddy soil but also reliably reducing the amount of fluorine eluted from the solidified soil to 0.8 mg / L of soil environmental standards. I will provide a.
A soil solidifying agent containing hemihydrate gypsum and calcium hydrogen phosphate dihydrate was used.
[Selection figure] None

Description

  The present invention relates to a soil solidifying agent and a soil solidifying method, and more specifically, dredged soil from rivers, ponds, lakes, etc., soil discharged from civil engineering work sites, construction work sites, etc., and the like, which has a relatively high water content. The present invention relates to a solidifying agent and a solidifying method for solidifying muddy soil.

  Conventionally, various examples using hemihydrate gypsum or gypsum are known as the soil solidifying agent as described above. Examples thereof include those containing hemihydrate gypsum and blast furnace slag (see, for example, Patent Document 1), those containing hemihydrate gypsum, paper sludge ash, fine powder of blast furnace slag, lime, etc. (see, for example, Patent Document 2), What contains at least one selected from gypsum, lime, and coal combustion ash (see, for example, Patent Document 3), hemihydrate gypsum, magnesia-based caking aid, inorganic water-absorbing hardening accelerator, inorganic hardening aid, etc. What is contained (for example, refer to Patent Document 4).

However, although there are few problems with the solidification of the soil using such a conventional soil solidifying agent, fluorine is eluted from the solidified soil due to the fluorine contained in the hemihydrate gypsum used and the soil to be solidified. There is a problem of doing. With conventional soil solidifying agents, it is difficult to reliably reduce the amount of fluorine eluted from the soil solidified using the same to 0.8 mg / L or less of the soil environment standard.
JP-A-9-263758 JP 2002-88362 A JP 2002-346595 A JP 2005-13973 A

  The problem to be solved by the present invention is to use a soil solidifying agent capable of reliably reducing the amount of fluorine eluted from the soil solidified by using the soil to 0.8 mg / L or less of the soil environment standard. It is a place that provides a method for solidifying soil.

  This invention which solves the said subject concerns on the soil solidification agent characterized by including hemihydrate gypsum and calcium hydrogenphosphate dihydrate. The present invention also relates to a method for solidifying soil, characterized in that an organic polymer flocculant is mixed with soil and subsequently the soil solidifying agent according to the present invention is mixed.

The soil solidifying agent according to the present invention (hereinafter simply referred to as the solidifying agent of the present invention) is composed of hemihydrate gypsum (CaSO ₄ · 1 / 2H ₂ O) and calcium hydrogen phosphate dihydrate (CaHPO ₄ · 2H ₂ O). It contains. Hemihydrate gypsum is various types of gypsum, such as gypsum obtained as a by-product when producing phosphoric acid from a phosphate ore by a wet phosphoric acid method, gypsum obtained as a by-product when performing flue gas desulfurization by a lime method, It can be obtained by heat treatment at about 160 ° C. It can also be obtained by pulverizing gypsum board waste materials (hereinafter simply referred to as waste gypsum) produced using these gypsums and heat-treating them in the same manner. When the one derived from waste gypsum is used as the hemihydrate gypsum, waste gypsum that is troublesome to dispose of can be used effectively.

The drug used with such hemihydrate gypsum is calcium hydrogen phosphate dihydrate. It is conceivable to use other calcium phosphate compounds such as tricalcium phosphate (Ca ₃ (PO ₄ ) ₂ ) instead of calcium hydrogen phosphate dihydrate, but the effect, ie, the amount of fluorine elution is reduced. The effect is significantly inferior compared to calcium hydrogen phosphate dihydrate.

  In the solidifying agent of the present invention, the content ratio of hemihydrate gypsum and calcium hydrogen phosphate dihydrate is not particularly limited, but calcium hydrogen phosphate dihydrate is usually 2 to 100 parts by mass of hemihydrate gypsum. Although it shall contain in the ratio of 10 mass parts, it shall contain in the ratio of 3-8 mass parts. When the content ratio of calcium hydrogen phosphate dihydrate is less than 3 parts by mass per 100 parts by weight of hemihydrate gypsum, the effect tends to be slightly reduced. Conversely, the content ratio of calcium hydrogen phosphate dihydrate is Even if it exceeds 8 parts by mass, the effect does not change so much, and it becomes uneconomical.

  The solidifying agent of the present invention may be composed of hemihydrate gypsum and calcium hydrogen phosphate dihydrate as described above, but may further contain an organic polymer flocculant. Examples of the organic polymer flocculant include various types such as polyacrylamide, sodium polyacrylate, polyacrylate, polymethacrylate, and the like, but polyacrylamide is preferable. Moreover, it is preferable that the content rate of this organic polymer flocculent shall be 0.1-1 mass part per 100 mass parts of hemihydrate gypsum.

  When the solidifying agent of the present invention is mixed with muddy soil having a relatively high moisture content as described above, generally mud soil having a moisture content (moisture) of 40 to 70% by mass, such mud is mixed. In addition to solidifying the soil, the amount of fluorine eluted from the solidified soil is reliably reduced to 0.8 mg / L or less of the soil environment standard. This is because when the solidifying agent of the present invention is mixed with the muddy soil having a relatively high water content as described above, the particle surface of calcium hydrogen phosphate dihydrate in the solidifying agent has a size of several tens of nm. Activated in the form of a structure in which a large number of fine crystals are deposited, and the activated particle surface effectively insolubilizes the fluorine contained in hemihydrate gypsum in the solidifying agent and the soil to be solidified as fluorapatite. This is probably because of this. The characteristic effects of such calcium hydrogen phosphate dihydrate cannot be obtained with other calcium phosphate compounds such as tricalcium phosphate.

  The solidifying agent of the present invention can be directly mixed with the muddy soil having a relatively high water content as described above, but the organic polymer flocculant as described above is mixed in advance with such soil. A method of subsequently mixing the solidifying agent of the present invention is preferred. For example, while conveying mud soil using a screw conveyor, an organic polymer flocculant is added and mixed on the upstream side, and the solidifying agent of the present invention is added and mixed on the midstream side. .

  According to the present invention, not only can muddy soil be solidified, but also the amount of fluorine eluted from the solidified soil can be reliably reduced to 0.8 mg / L of the soil environment standard.

Test Category 1 (Preparation of solidifying agent)
Example 1 {Preparation of solidifying agent (P-1)}
The waste gypsum was pulverized and heat-treated at 140 to 160 ° C. for about 10 minutes to obtain a half-water gypsum. A solidifying agent (P-1) was prepared by mixing 2 parts by mass of calcium hydrogen phosphate per 100 parts by mass of the hemihydrate gypsum.

Examples 2 to 6 and Comparative Example 1 {Preparation of solidifying agents (P-2) to (P-6) and (R-1)}
In the same manner as the solidifying agent (P-1) of Example 1, the solidifying agents (P-2) to (P-6) of Examples 2 to 6 and the solidifying agent (R-1) of Comparative Example 1 were prepared. . The solidifying agent (P-6) of Example 6 was further mixed with a polyacrylamide organic polymer flocculant, and the solidifying agent of Comparative Example 1 was only hemihydrate gypsum. The contents of the solidifying agent prepared in each of the above examples are summarized in Table 1.

In Table 1,
DCPD: Calcium hydrogen phosphate dihydrate * 1: Polyacrylamide organic polymer flocculant

Test category 2 (solidification of soil)
Example 7
Dumping of excavated civil engineering construction site (water content 60 wt%, specific gravity 1.6, good muddy soil almost odorless less silt, hereinafter referred to as the original mud) 1 m ³ per pre polyacrylamide organic high The molecular flocculant was mixed at a rate of 0.15 kg, and then the solidifying agent (P-1) prepared in Test Category 1 was mixed at a rate of 100 kg to solidify the raw mud. Mixing is carried out using a screw conveyor. While feeding the raw mud into the screw conveyor, a polyacrylamide organic polymer flocculant is introduced upstream, and immediately thereafter a solidifying agent (P-1). Was introduced. The mixing time by the screw conveyor after charging the solidifying agent (P-1) was about 25 seconds.

Examples 8 to 24 and Comparative Examples 2 to 4
In the same manner as in Example 7, the raw soil was solidified under the conditions of each example described in Table 2.

Test Category 3 (Evaluation of solidified soil)
About the soil solidified in each example of Test Category 2, the fluorine elution amount, the corn index and the pH were obtained by the following methods after 10 days, 28 days and 90 days, and the results are summarized in Tables 2 and 3. .
Fluorine elution volume: 500 ml of pure water was added to 50 g of solidified soil, shaken at 200 times per minute for 6 hours, allowed to stand for 10 minutes, and then the supernatant was filtered through a 0.45 nm membrane filter to obtain an eluate. It was. The fluorine concentration in the eluate was measured with an ion selective electrode (lower limit of quantification was 0.02 mg / L). In each of the following examples, the elution amount of fluorine was measured by the same method.
Corn index: According to JIS-A1228, the solidified soil was compacted and the cone index was measured.
pH: According to the Geotechnical Society Standard (JGS0211-2000), the pH of the solidified soil suspension was measured.

In Tables 2 and 3,
Mixing ratio: the mixing amount on the day of the original mud 1 m ³ per solidifying agent: those original mud immediately after mixing the solidifying agent in the original mud: Hara mud before mixing the solidifying agent itself hemihydrate gypsum: using solidification agents Hemihydrate gypsum

  As is clear from the contents and results of each example for each comparative example in Tables 1 to 3, according to the solidifying agent of the present invention, not only does the solid mud solidify, but also the amount of fluorine eluted from the solidified soil. It turns out that it reduces reliably to 0.8 mg / L of soil environmental standard.

Claims (5)

  A soil-solidifying agent comprising hemihydrate gypsum and calcium hydrogen phosphate dihydrate.   The soil solidifying agent according to claim 1, comprising calcium hydrogen phosphate dihydrate at a ratio of 3 to 8 parts by mass per 100 parts by mass of hemihydrate gypsum.   The soil solidifying agent according to claim 1 or 2, further comprising an organic polymer flocculant.   The soil solidifying agent according to claim 3, comprising an organic polymer flocculant in a proportion of 0.1 to 1 part by mass per 100 parts by mass of hemihydrate gypsum.   A method for solidifying soil, comprising mixing an organic polymer flocculant with soil and subsequently mixing the soil solidifying agent according to any one of claims 1 to 4.