JP6126460B2 - Heavy metal adsorption layer materials, and adsorption layer construction methods using them - Google Patents

Description

  The present invention relates to a heavy metal adsorption layer base material used in the adsorption layer construction method, a heavy metal adsorption layer material including the base material and the heavy metal adsorption material, and an adsorption layer construction method. In addition, the heavy metal as used in the field of this invention is the concept containing a fluorine and boron other than a heavy metal.

Soil and rock crushing (shears) generated during slope excavation or tunnel excavation may contain a lot of naturally-occurring heavy metals. From such soils, heavy metals often tend to elute beyond environmental standards.
Conventionally, naturally-derived heavy metals were outside the scope of regulation under the Soil Contamination Countermeasures Law, but became subject to regulation due to the 2010 revision of the law. Therefore, in a construction where a large amount of heavy metal-containing soil or the like (object to be treated) is generated, the heavy metal treatment cost is increased, which contributes to an increase in the total construction cost.
By the way, as a heavy metal treatment (diffusion suppression) method, an insolubilization method and an adsorption layer method have been mainly used.
Among these, the insolubilization method is a method of suppressing elution of heavy metals by mixing heavy metal adsorbents such as natural minerals with soil containing heavy metals.
In addition, as shown in FIG. 1 below, the adsorption layer construction method embanks a soil containing heavy metal on a heavy metal adsorption layer constituted by laying a mixture of a heavy metal adsorbent and a base material such as sand, Further, the embankment is a method of covering the embankment with covering soil or asphalt pavement. The adsorption layer construction method can prevent heavy metal diffusion by the heavy metal adsorption layer below even if heavy metal in the embankment elutes in the water that has penetrated into the embankment due to rainfall, etc., and it is less expensive than the insolubilization method. It is.

Therefore, several methods for suppressing the diffusion of heavy metals in soil using the adsorption layer method have been proposed.
For example, Patent Document 1 proposes a method for treating pollutants contained in excavated residual soil using a pollutant adsorption mat. The adsorbing mat includes an adsorbing material layer including an adsorbent that adsorbs contaminants, a first sheet disposed above the adsorbing material layer, and a second sheet disposed below the adsorbing material layer. It is said that by sewing the first sheet, the adsorbing material layer, and the second sheet, non-uniform thickness can be suppressed over the whole, and a certain thickness or more can be maintained.
Patent Document 2 proposes a method for treating excavated residual soil using a pollutant adsorbing material. The adsorbing material is obtained by impregnating a water-retaining inorganic material with a slurry adsorbent that adsorbs contaminants.
Furthermore, Patent Document 3 proposes a method for insolubilizing heavy metal-contaminated soil in which a specially prepared insolubilizer is mixed with uncontaminated soil to form a soil, and a heavy metal-contaminated soil is formed as an embankment on the top. Has been. The insolubilizing agent is a complex of zirconium hydroxide and mineral particles produced by adding zirconium oxychloride, slaked lime, and water in the presence of mineral particles containing diatomaceous earth.

However, the pollutant adsorbing mat of Patent Document 1 requires labor for sewing and manufacturing, and the pollutant adsorbing material of Patent Document 2 requires labor for impregnating an inorganic material with a slurry adsorbent. Take it. In addition, the insolubilizer of Patent Document 3 uses a zirconium compound, which is a rare metal, in addition to the labor of manufacturing, so that the material cost is remarkably high.
Therefore, the method of the above literature cannot be said to be highly practical when used for treating a large amount of soil or the like.

JP 2013-059724 A JP 2012-254432 A JP 2012-110852 A

  Therefore, an object of the present invention is to provide a heavy metal adsorption layer base material having a high heavy metal adsorption removal effect and a low treatment cost even when used for treatment of a large amount of soil, etc., the base material and the heavy metal adsorbent It is providing the adsorption layer material using these, and the material for adsorption layers of the heavy metal containing these.

Therefore, the present inventors have studied based on the following prediction.
(1) The heavy metal adsorption layer has the highest composition ratio, so the heavy metal adsorption performance by the matrix with the largest occupied volume is expected to be an important factor in the material design of the matrix. The adsorption performance of heavy metals was investigated. next,
(2) It was predicted that the amount of heavy metal adsorbed and removed increased as the time during which the heavy metal-containing water stayed in the heavy metal adsorption layer increased. And in order to find out an important factor in the material design of the heavy metal adsorption layer having a long residence time, the water permeability of the heavy metal adsorption layer, the addition amount of the heavy metal adsorbent, the coarse rate of the base material, the particle size distribution index of the base material, Various investigations were made from the viewpoint of the degree of compaction of the heavy metal adsorption layer. further,
(3) Based on each factor found by the above examination, a heavy metal adsorption layer was constructed, and a water permeability test simulating an actual environment was conducted, and it was confirmed that the heavy metal adsorption layer has a high elution suppression effect on heavy metals. .
The details of these examinations and the results will be described in the examples below.

From the above results, the adsorption layer for contributing materials such as heavy metals having the structure below, found to be able to solve the problems, and completed the present invention.
[1] The content ratio of SiO ₂ is 70 to 90 mass% , the content ratio of Al ₂ O ₃ is 5 to 15 mass% , the coarse particle ratio is 2.0 to 6.0, and the particle size distribution index is 1. heavy-metal-adsorbing layer that Do from shale is from 20 to 1.60 preform 1 m ³ per includes 10~200kg a light burned magnesia and / or light burned magnesia partially hydrate, adsorption layer material of heavy metals.
[2] the above heavy metal heavy metal adsorption layer formed by laying a material for adsorption layer according to [1], comprising the step of placing an object to be processed comprising a heavy metal adsorption layer method.
[3] The adsorption layer method according to [ 2 ], wherein the compaction degree of the heavy metal adsorption layer is 80% or more.
[4] The adsorption layer construction method according to [ 2 ] or [ 3 ], wherein the simple water permeability of the heavy metal adsorption layer is 1.0 × 10 ⁻³ m / s or less.

The heavy metal adsorption layer base material of the present invention has a high effect of heavy metal adsorption removal even with the base material alone, and the heavy metal adsorption layer material of the present invention has a higher heavy metal adsorption removal effect.
Moreover, the adsorption layer construction method of the present invention is suitable for processing an object to be processed containing heavy metals generated in a large amount, and the processing cost is low.

It is a figure which shows the outline of the adsorption layer construction method.

Below, the base material for the adsorption layer of the heavy metal of this invention, the material for the adsorption layer of heavy metal, and the adsorption layer construction method are demonstrated.
1. Base material for adsorption layer of heavy metal The base material is a shale having a SiO ₂ content of 70 to 90% by mass and an Al ₂ O ₃ content of 5 to 15% by mass. If the content ratio of SiO ₂ and Al ₂ O ₃ is within the above range, as shown in Tables 3 and 7 described later, the heavy metal adsorption removal effect is high. The content of SiO _{2 in} the shale is preferably 75 to 90% by mass, more preferably 75 to 85% by mass, and the content of Al ₂ O _{3 in} the shale is preferably 7 to 13% by mass. Preferably it is 9-12 mass%.
In the present invention, heavy metals to be adsorbed are cation species such as cadmium (Cd ²⁺ ), lead (Pb ²⁺ ), and nickel (Ni ²⁺ ), selenium (SeO ₄ ²⁻ , SeO ₃ ²⁻ ), fluorine. (F ⁻ ), hexavalent chromium (CrO ₄ ²⁻ , Cr ₂ O ₇ ²⁻ ), arsenic (AsO ₄ ³⁻ , AsO ₃ ³⁻ ), boron (B ₄ O ₇ ²⁻ ), molybdenum (MoO ₄ ^{2) -),} antimony (SbO ₃ ^-), cyanide (CN ^-), etc. anionic species, and include neutral species such as mercury and alkyl mercury.

The particle size of the shale is not particularly limited, but is preferably 50 mm or less, more preferably 40 mm or less, still more preferably 30 mm or less, and particularly preferably 20 mm or less. When the particle size exceeds 50 mm, it becomes difficult to uniformly mix with the heavy metal adsorbent.
The coarse grain ratio of the shale is preferably 2.0 to 6.0. If the coarse grain ratio is within the above range, as shown in Table 9, the simple water permeability coefficient is small, the time during which heavy metal-containing water is in contact with the base material is prolonged, and the effect of removing heavy metal by adsorption is improved. The coarse grain ratio of the shale is more preferably 2.5 to 5.5, still more preferably 3.0 to 5.5, and particularly preferably 3.5 to 5.0.
Moreover, the particle size distribution index of the shale is preferably 1.20 to 1.60. If the particle size distribution index is within the above range, as shown in Tables 2 and 7, the heavy metal adsorption removal effect is improved. The particle size distribution index is more preferably 1.25 to 1.55, still more preferably 1.30 to 1.50, and particularly preferably 1.35 to 1.45.
The particle size distribution index is a parameter relating to the characteristics of the particle size distribution obtained by using the Rosin-Rammler equation represented by the following equation (1).
R (d) = 100exp (−k · d ⁿ ) (1)
However, in the formula, R (d) is a residual ratio (%) of the base material, d is a particle size of the base material, k is a particle size characteristic coefficient, and n is a particle size distribution index.
The base material for the heavy metal adsorption layer of the present invention may contain rock species other than shale as part of the base material as long as the effect of removing heavy metal by adsorption is not impaired.

2. Material for adsorbing layer of heavy metal The material for adsorbing layer is a mixture of heavy metal adsorbent containing light burned magnesia and / or light burned magnesia partial hydrate as essential components, and the base material, per 1 m ^{3 of the} base material It is a material containing 10 to 200 kg of heavy metal adsorbent. When the content of the heavy metal adsorbent is less than 10 kg, the improvement of the heavy metal adsorption / removal effect is small, and when it exceeds 200 kg, the material cost increases. Further, the content of the heavy metal adsorbent is preferably 20 to 160 kg, more preferably 30 to 120 kg per 1 m ^{3 of the} base material.

(1) Light-burned magnesia etc. Next, light-burned magnesia and / or light-burned magnesia partial hydrate, which are essential components of the heavy metal adsorbent, will be described.
The light-burned magnesia can be obtained, for example, by baking a solid containing magnesium carbonate and / or magnesium hydroxide at 650 to 1300 ° C. The light-burned magnesia referred to in the present invention includes both the fired product obtained by firing and the pulverized product of the fired product.
The content of magnesium carbonate and / or magnesium hydroxide in the solid is preferably 80% by mass or more, more preferably 85% by mass or more, and further preferably 90% by mass or more. When the content is less than 80% by mass, the magnesium oxide component in the light-burned magnesia is small, and the heavy metal adsorption / removal effect tends to decrease.
Examples of the solid material include magnesite, dolomite, brucite, or a lump or powdery material such as magnesium hydroxide obtained by precipitating a magnesium component in seawater with an alkali such as slaked lime.

The firing temperature of the solid is 650 to 1300 ° C. If the temperature is less than 650 ° C., light-burned magnesia is difficult to generate, and if it exceeds 1300 ° C., the effect of removing heavy metals may be reduced. The firing temperature is preferably 750 to 950 ° C, more preferably 800 to 900 ° C.
Moreover, although the baking time of the said solid substance is based also on the preparation amount, particle size, etc. of a solid substance, it is 30 minutes-5 hours normally.

  The light-burned magnesia partial hydrate is added to light-burned magnesia (pulverized product) with stirring and mixed, or the pulverized product is mixed in an atmosphere having a relative humidity of 80% or more for one week or longer. It is obtained by holding.

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. When the value is within the above range, the heavy metal adsorption removal effect is higher. The light-burned magnesia partial hydrate is more preferably 70 to 95% by mass of magnesium oxide and 5 to 20% by mass of magnesium hydroxide, more preferably 75 to 90% by mass of magnesium oxide and hydroxylated. It contains 7 to 17% by mass of magnesium.
Moreover, the Blaine specific surface area of the light-burned magnesia or light-burned magnesia partial hydrate is preferably 3000 to 7000 cm ² / g. When the value is within the above range, the heavy metal adsorption removal effect is higher. In addition, the said Blaine specific surface area becomes like this. More preferably, it is 4000-6800 cm < ² > / g.

(2) Calcium carbonate powder The heavy metal adsorbent is composed of, as an optional component, calcium carbonate powder, light-burned magnesia and / or light-burned magnesia part, in addition to the essential components of light-burned magnesia and / or light-burned magnesia partial hydrate. It can contain 0.1-50 mass parts with respect to 100 mass parts of hydrates. If this content is 0.1-50 mass parts, the adsorption removal effect of a heavy metal will improve.
The Blaine specific surface area of the calcium carbonate powder is preferably 3000 to 7000 cm ² / g. If the value is less than 3000 cm ² / g, it is difficult to improve the effect of removing heavy metals, and if it exceeds 7000 cm ² / g, it takes time to grind and increases the cost of grinding. The Blaine specific surface area is more preferably 4000 to 6000 cm ² / g.

(3) Manufacturing method of heavy metal adsorbing layer material Examples of the manufacturing method include a method of mixing a heavy metal adsorbent and a base material in a dry state, and a slurry obtained by adding water to the heavy metal adsorbent and then slurrying the slurry. And a method of mixing the base material. The mass ratio of the water / heavy metal adsorbent in the slurry is preferably 0.5 to 1.5, more preferably 0.00 in order to mix uniformly although it depends on the particle size of the heavy metal adsorbent and the base material. 8 to 1.2.

3. Adsorption layer construction method The adsorption layer construction method comprises a step of placing an object to be treated containing heavy metal on the heavy metal adsorption layer base material or the heavy metal adsorption layer formed by laying the heavy metal adsorption layer material. It is a construction method including.
The compaction degree of the heavy metal adsorption layer is preferably 80% or more. If the degree of compaction is 80% or more, as shown in Tables 10 and 13, the simple water permeability is small and the time for heavy metal-containing water to stay in the heavy metal adsorption layer is increased, and the heavy metal adsorption removal effect is improved. . The degree of compaction is more preferably 85% or more, still more preferably 90%, and particularly preferably 95% or more. The degree of compaction (Dc, unit is%) can be calculated using the following equation (2).
Compaction degree (Dc) = 100 × Dry density of compacted soil observed in the field (ρ _d ) / Maximum dry density obtained from the compaction test (ρ _max ) (2)
In addition, the tamping test in the formula (2) means JIS A 1210 “Soil compaction test method by tamping”.
Moreover, if this is expressed with the simple hydraulic conductivity of the said heavy metal adsorption layer, this simple hydraulic conductivity becomes like this. Preferably it is 1.0 * 10 < ^-3 > m / s or less. When the simple water permeability is 1.0 × 10 ⁻³ m / s or less, the time for heavy metal-containing water to stay in the heavy metal adsorption layer is long, and the heavy metal adsorption removal effect is high. The simple hydraulic conductivity is more preferably 5.0 × 10 ⁻⁴ m / s or less, further preferably 1.0 × 10 ⁻⁴ m / s or less, and particularly preferably 5.0 × 10 ⁻⁵ m / s or less. It is. The lower limit of the simple water permeability coefficient is not particularly limited, but is preferably 1.0 × 10 ⁻⁷ m / s. If it is less than 1.0 × 10 ⁻⁷ m / s, the permeated water may leak from the embankment side without passing through the heavy metal adsorption layer. The simple hydraulic conductivity (m / s) can be calculated using the following formula (3) based on Darcy's law.
Simplified hydraulic conductivity = (Thickness of heavy metal adsorption layer x amount of water passing through) / (Cross sectional area x Passing time x Water level difference) (3)
The adsorption layer construction method of the present invention having the above-described configuration is suitable for processing an object to be processed containing a large amount of heavy metal, and the processing cost is low.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.
1. Main materials used
(1) Base material As the base material, limestone, shale A, and shale B1 to B3 having the characteristics shown in Tables 1 to 4 were used. The shale B1 to B3 are pulverized products of shale B, and have a coarse particle ratio (FM) shown in Table 2 and a particle size distribution index (n) obtained by using the Rosin-Rammler equation.
Table 5 shows the elution amount of heavy metals in the limestone, shale A, and shale B into water.

(2) Preparation of heavy metal adsorbent (light calcined magnesia) Magnesite containing 97% by mass of magnesium carbonate was calcined in an electric furnace (manufactured by Chugai Engineering Co., Ltd., model: KSL-2) at 850 ° C. for 30 minutes. I got magnesia. Next, the light-burned magnesia was pulverized to prepare a pulverized product of light-burned magnesia having a Blaine specific surface area of 6500 cm ² / g.

2. Adsorption test of heavy metal with base material alone Using limestone, shale A, and shale B2 shown in Table 2 with a coarse particle ratio of about 4 and the same particle size distribution, the base material alone Heavy metal adsorption performance was tested.
Specifically, each of the above-mentioned base materials and the simulated waste liquid having the concentration shown in Table 6 prepared using the reagent shown in Table 6 in a polyethylene container, the base material / simulated waste liquid = 1/100 (mass ratio). The container was shaken at 20 ° C. and 200 rpm for 4 hours.
After shaking, the simulated waste liquid is filtered using a 0.45 μm membrane filter, and the concentration of As (III) in the filtrate, which is often the main control item in actual management, is determined according to JIS K 0102: 2088 “IPC”. Measured according to “mass spectrometry”. Then, the amount of As (III) adsorbed on the base material was determined from the difference between the measured concentration and the concentration at the start of the test. The results are shown in Table 7.
As shown in Table 7, all shale adsorbs As (III) 2 to 5 times more than limestone, and has high adsorption performance. In particular, the lower the As (III) concentration, the more the difference in the adsorption performance becomes.

2. Water permeability test of heavy metal adsorption layer (examination test of each factor)
(1) Examination from the viewpoint of the amount of heavy metal adsorbent added After adjusting the water content ratio of limestone, shale A, and shale B2 shown in Table 2 to 9%, the limestone, shale A, and shale B2, respectively, As a material, 35 kg, 70 kg, and 105 kg of the heavy metal adsorbent are added per 1 m ^{3 of} each base material, mixed with a Henschel mixer, and used for adsorbing layers of three types of heavy metals with different amounts of heavy metal adsorbent added. Materials were prepared.
Further, the base material alone and the heavy metal adsorbing layer material are packed in an acrylic resin column having an inner diameter of 50 mm and a height of 220 mm, respectively, and compacted as shown in the formula (2) using a 1.5 kg rammer. The heavy metal adsorbing layer was formed by compacting to a degree of about 90%.
Next, the simulated waste liquid was passed through the column, the amount of passing water and the passing time were measured, and a simple water permeability coefficient was calculated using the equation (3). The results are shown in Table 8.
As shown in Table 8, the simple hydraulic conductivity decreases as the amount of heavy metal adsorbent added increases.

(2) Examination from the viewpoint of the coarse grain ratio of the base material As described above, the coarse grain ratio of the base material is preferably in the range of 2.0 to 6.0, and 1 in terms of the grain size distribution index. .20 to 1.60 is preferred. Then, in order to investigate in detail the relationship between the coarse grain ratio of the base material and the water permeability, the following examination was performed.
Specifically, after adjusting the water content ratio of shale B1 to B3 shown in Table 2 to 9%, each shale B1 to B3 is used as a base material, and the heavy metal adsorbent is 70 kg per 1 m ^{3 of} each base material. Added and mixed with a Henschel mixer, three types of heavy metal adsorbent layer materials with different amounts of heavy metal adsorbent added were prepared.
The water permeability test of the heavy metal adsorption layer formed using the heavy metal adsorption layer material was carried out in the same manner as in “(1) Examination from the viewpoint of the addition amount of heavy metal adsorbent”, and the simple permeability coefficient was obtained. The results are shown in Table 9.
In general, the lower the coarse grain ratio of the base material, that is, the wider the particle size distribution, the smaller the simple hydraulic conductivity as a whole, and the simple hydraulic conductivity shown in Table 9 is a value that can secure a sufficient residence time.

(3) Examination from the viewpoint of the degree of compaction of the heavy metal adsorption layer After adjusting the water content ratio of the shale A shown in Table 2 to 9%, the shale A is used as a base material, and per 1 m ^{3 of the} base material, 70 kg of heavy metal adsorbent was added and mixed with a Henschel mixer to prepare a heavy metal adsorption layer material.
Next, the heavy metal adsorption layer material was packed in the column and compacted in the same manner as described above so as to obtain the compaction degree shown in Table 10, thereby forming a heavy metal adsorption layer. The water permeability test of the heavy metal adsorption layer was carried out in the same manner as in “(1) Examination from the viewpoint of the amount of heavy metal adsorbent added” to obtain a simple water permeability coefficient. The results are shown in Table 10.
From Table 10, it can be seen that the higher the degree of compaction, the smaller the simple hydraulic conductivity.

3. Heavy metal adsorption test of heavy metal adsorption layer Based on the standard adsorption layer construction adsorption layer and embankment design conditions shown in Table 11, the heavy metal adsorption layer was formed under the conditions shown in Table 12 scaled down. A heavy metal adsorption test was performed using a column.
Specifically, the heavy metal adsorbing layer material for forming the heavy metal adsorbing layer was prepared by mixing 70 kg of the heavy metal adsorbing material per 1 m ^{3 of the} base material using shale A shown in Table 2 as a base material. The simple hydraulic conductivity of the heavy metal adsorption layer and the residence time of the simulated waste liquid in the heavy metal adsorption layer were adjusted by the degree of compaction. Incidentally, the compaction level 1 in Table 12 has a simple hydraulic conductivity of 6.4 × 10 ⁻⁴ m / s, the residence time is 140 seconds, and the compaction level 2 has a simple hydraulic conductivity of 2.5 ×. 10 ⁻⁵ m / s, residence time was 20000 seconds. The precipitation in Table 11 was based on the annual precipitation in Sapporo.

As the simulated waste liquid, an aqueous solution having an As (III) concentration of 0.1 mg / L (exactly 0.094 mg / L) shown in Table 6 was used. As (III) concentration was measured every time the amount of simulated waste liquid passing through the column reached 434 mL, a part of the water passing at that time was sampled and filtered through a 0.45 μm membrane filter. The concentration of As (III) in the liquid was measured according to JIS K 0102: 2008 “IPC mass spectrometry”. The results are shown in Table 13. The numerical values in Table 13 are As (III) concentrations, and the unit is mg / L.
As shown in Table 13, the As (III) concentration decreases to about 1/4 of the initial concentration in the heavy metal adsorption layer with a compaction level of 1, and 1 / of the initial concentration in the heavy metal adsorption layer with a compaction level of 2. It decreased to about 100.

Claims (4)

The content ratio of SiO ₂ is 70 to 90 mass% , the content ratio of Al ₂ O ₃ is 5 to 15 mass% , the coarse particle ratio is 2.0 to 6.0, and the particle size distribution index is 1.20 to 1. that Do shale 60 heavy metal adsorption layer preform 1 m ³ per includes 10~200kg a light burned magnesia and / or light burned magnesia partially hydrate, adsorption layer material of heavy metals. On the heavy metal heavy metal adsorption layer formed by laying a material for the adsorption layer of claim 1, comprising the step of placing an object to be processed comprising a heavy metal adsorption layer method. The adsorption layer construction method according to claim 2 , wherein the compaction degree of the heavy metal adsorption layer is 80% or more. The adsorption layer construction method according to claim 2 or 3 , wherein a simple water permeability coefficient of the heavy metal adsorption layer is 1.0 x ^10-3 m / s or less.

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