JP2003093538A - Reduction method of hexavalent chrome by particle-size control of silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an effective method for reducing elution of hexavalent chrome at any period of time in the environment. SOLUTION: In this method for reducing elution of hexavalent chrome, a hexavalent chrome elution reducer containing silicon is added to the environment. The particle size of the silicon is controlled according to the targeted period of time.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for reducing the elution of hexavalent chromium in the environment at any time by adjusting the particle size of silicon.

[0002]

2. Description of the Related Art In recent years, industrial wastes, general wastes, sewage sludge, incineration have been actively promoted in various industrial fields for the treatment and recycling of industrial wastes due to social demands for environmental protection and purification. When processing waste such as ash,
Cement and cement-based solidifying materials are widely used. In recent years, a wide variety of recycled resources have been used as raw fuel for cement, and in some cases cement may contain components that were not previously contained.
As a result, a substance solidified with a hydraulic substance (hereinafter,
A small amount of hexavalent chromium may elute from the solidified body) depending on the environment and conditions of use.

As a method for reducing the elution amount of hexavalent chromium, for example, in JP-A-3-205331, addition of salts of ferrous iron, stannous tin, vanadium, cuprous, etc.
Further, JP-A-48-83114 proposes addition of a water-soluble ferrous salt. However, the heavy metals other than the ferrous salt are toxic, and elution of new heavy metals may pose a problem. Further, the ferrous salt is effective in reducing the elution of hexavalent chromium from the hydraulic composition in the initial stage, but since the effect disappears at an extremely early stage,
The effect of reducing the elution of hexavalent chromium in the long term cannot be expected.

Further, Japanese Patent No. 3047833 proposes a method of reducing hexavalent chromium, which was present in a certain amount in advance, to trivalent with silicon. However, in an environment where the concentration of hexavalent chromium changes over time, such as when solidifying industrial waste, sewage sludge, soil, etc. with a hydraulic composition, it is necessary to impart an elution reducing effect at an appropriate time, It is hard to say that this method alone exerts a sufficient effect.

[0005]

In view of such circumstances,
An object of the present invention is to provide a method for effectively reducing the elution amount of hexavalent chromium at any time in the environment. Furthermore, it aims at providing the method which has a hexavalent chromium reduction effect more than before by combining with a conventionally well-known material.

[0006]

[Means for Solving the Problems] As a result of intensive investigations by the present inventors to reduce the elution amount of hexavalent chromium from the environment,
It has been found that the amount of hexavalent chromium eluted from the environment at a target time can be effectively reduced by adding silicon having a controlled particle size to the environment.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The present invention is a method of adding a hexavalent chromium elution reducing material containing silicon to the environment, and by adjusting the particle size of the silicon, to reduce the elution of hexavalent chromium from the environment in an arbitrary period. There are features. It is convenient to use the average particle size as the particle size. The average particle size of silicon for effectively reducing hexavalent chromium varies depending on the other composition of the hexavalent chromium elution reducing material, the type of environment, etc.
If it is desired to exert a particular effect within about 7 days from the start of use, it is preferable to use silicon having an average particle size of 5 μm or less. In addition, when it is desired to exert the effect continuously for a long period from the start of use, the average particle size is 5 μm to 10 μm.
It is preferable to use 0 μm silicon. Further, the content of silicon in the hexavalent chromium elution-reducing material depends on the average particle size and the time when the effect is desired to be expressed, but is 0.05 to 20 with respect to 100 parts by weight of the hexavalent chromium elution-reducing material.
Part by weight is preferable, and 0.5 to 5 parts by weight is more preferable.
Although a waste containing silicon can be used as will be described later, in this case as well, the addition ratio in the same range is preferable in terms of the actual amount of silicon.

The present invention is characterized in that a hexavalent chromium elution reducing material containing silicon is added to the environment, but the method of addition is not particularly limited. For example, when the environment is soil A conventional method such as mechanically mixing the soil and the hexavalent chromium elution reducing material can be used. If the environment is originally alkaline, only the hexavalent chromium elution reducing material containing silicon may be added to the environment, but if the environment is neutral or acidic,
It is preferable to use a basic substance (cement, lime, etc.), an alkali metal salt and / or an alkaline earth metal salt together with the hexavalent chromium elution reducing material.

Further, in the present invention, two or more kinds of silicon having different particle sizes can be mixed and used. 2 with different grain sizes
By mixing at least one kind of silicon, it becomes possible to provide an effect even for a period which cannot be provided by one kind of silicon. For example, by mixing silicon with an average particle size of 1 μm or less and silicon with an average particle size of 1 μm or more,
Silicon less than μm exerts an elution reduction effect within 7 days before addition to the environment, and silicon of 1 μm or more exerts an effect over a period of about 7 days, resulting in an elution reduction effect over a wide period. Can be given. The type of particle size of silicon is not limited to two, and three or more types of silicon having an average particle size may be mixed.

The type of silicon used in the present invention is not particularly limited, and various types such as metallic silicon, polysilicon, ferrosilicon, and porous silicon can be used. Generally, these silicons have a purity of about 80%, but in the present invention, the purity is not particularly specified, and if the silicon content is 10% or more, the addition ratio is adjusted as necessary. It is fully available.

Further, in the present invention, it is possible to use silicon generated as a waste product or a by-product. In recent years when there is concern about environmental conservation and shortage of landfill sites,
From the viewpoint of effective use of resources, the use of waste and by-products is effective. There is no particular limitation on the purity or the content rate of silicon, and if the content rate of silicon is 10% or more, it can be sufficiently used by adjusting the addition rate. Examples of wastes or byproducts containing silicon include silicon wafer scrap products, waste silicon catalysts, and various other waste materials.

The hexavalent chromium elution reducing material used in the present invention is
Besides silicon, cement, fine inorganic powder, reducing agent,
It can contain at least one selected from alkali metal salts and alkaline earth metal salts. Examples of the cement that can be used in the method of the present invention include Portland cement, mixed cement, low heat cement, white cement, ecocement, alumina cement, jet cement and the like. Specifically, Portland cement is a normal, early strength, super early strength, moderate heat, low heat, sulfate resistant cement, and a mixed cement is blast furnace cement, fly ash cement, silica cement and the like. Eco-cement is a cement made from at least one kind of waste such as municipal waste incineration ash and sewage sludge incineration ash, and contains 10-40% by weight of one or more of calcium chloroaluminate, calcium fluoroaluminate and calcium aluminate. It is a cement containing gypsum and the like. In addition, jet cement is a cement containing calcium fluoroaluminate and having a rapid hardening property. By including these cements in the hexavalent chromium elution-reducing material, the hexavalent chromium elution-reducing material can be effectively used as a ground improvement material having solidifying performance such as soft ground.

Examples of the inorganic fine powder that can be used in the method of the present invention include blast furnace slag, fly ash, silica powder, limestone powder and silica fume. Of these, blast furnace slag is known to have the effect of reducing the elution of hexavalent chromium, and is used for the same purpose as in the present invention. However, the blast furnace slag exhibits the elution-reducing effect for a long period of about 7 days after the start of use, and does not show a large elution-reducing effect before that. Therefore, it is possible to reduce the elution amount of hexavalent chromium from the initial stage to a long period of time by using the blast furnace slag together with silicon having a particle size that exhibits an effect 7 days before the start of use.

The reducing agent in the present invention is not particularly limited, but a substance that exerts an effect of reducing the elution of hexavalent chromium in a cement-based material is practically preferable. Examples of the reducing agent include ferrous sulfate and sulfides such as calcium sulfide and sodium sulfide. Of these, it is known that especially ferrous sulfate has an excellent hexavalent chromium reducing effect on hydraulic compositions such as cement without impairing its performance. However, the ferrous sulfate showing the effect of reducing hexavalent chromium is limited to the very early stage, about one day before the start of use, and the effect disappears almost thereafter. Therefore, it is possible to reduce the elution amount of hexavalent chromium over a long period from the initial stage by using together a ferrous sulfate salt with a particle size that produces an effect one day after the start of use. In addition, the amount of hexavalent chromium eluted can be reduced over a long period of time by using together with ferrous sulfate, blast furnace slag, and silicon of a particle size that produces an effect during a period that could not be supplemented with these elution reducing materials alone. It is also possible.

In the method of the present invention, an alkali metal salt or an alkaline earth metal salt may be used in combination. Alkali metal salts and alkaline earth metal salts can be used to adjust the setting time when silicone and hydraulic materials such as cement are used together.
It is used for the purpose of adjusting the timing of imparting the effect of reducing hexavalent chromium. Examples of the alkali metal salt include sodium carbonate, and examples of the alkaline earth metal salt include gypsum such as gypsum dihydrate and gypsum hemihydrate and calcium hydroxide.

The hexavalent chromium elution reducing material used in the present invention may contain various fine aggregates and coarse aggregates as required in addition to the above materials. Further, for the purpose of improving fluidity and durability, and for other purposes, the AE is used within a range that does not impair the effects of the present invention.
Agents, water-reducing agents, high-performance water-reducing agents, high-performance AE water-reducing agents, defoaming agents, shrinkage-reducing agents and the like may be added.

[0017]

EXAMPLES Examples of the present invention will be shown below. The present invention is not limited to the examples below.

Example 1 [Materials used] Cement: Prototype ordinary Portland cement Silicon: Commercial reagent (purity 4N) Average particle size 33 μm Calcium hydroxide: Commercial special grade reagent Sample soil: Kanto loam, water content 170% [solidification Blending of Treated Soil] Silicon was obtained by crushing the above reagents so that the average particle size was 9 μm and 1 μm. To 100 parts by weight of the sample soil, 15 parts by weight of a hexavalent chromium elution reducing material (of which 0.3 to 0.75 parts by weight of silicon and the rest is cement) was added to prepare a solidified treated soil. . In addition, as a sample for comparison, a solidified treated soil containing no silicon was prepared. Age of these solidified soils 1
The elution amount of hexavalent chromium on the 7th, 28th, 91st days was measured in accordance with Notification No. 46. That is, the mixture was shaken at a ratio of sample: water = 1: 10 for 6 hours, and the chromium content in the filtrate after filtration was measured by ICP to obtain the hexavalent chromium elution amount. The results are shown in Table 1.

[0019]

[Table 1]

In the case of the hexavalent chromium elution-reducing material in which 0.3 parts by weight of silicon having an average particle diameter of 9 μm is added, the elution amount of hexavalent chromium is reduced from the age of one day, as compared with the case where no silicon is added. However, it was continuously reduced over a long period of time, especially after 7 days of age. Further, in the case of the hexavalent chromium elution-reducing material to which 0.3 part by weight of silicon having an average particle diameter of 1 μm was added, the elution amount of hexavalent chromium was reduced particularly during the period of 1 to 28 days of age. Further, in the case of the hexavalent chromium elution-reducing material which was used by mixing silicon having an average particle diameter of 1 μm and 9 μm, the elution amount was reduced over the entire period after the age of 1 day.

Example 2: Using the sample soil and materials shown in Example 1, 1 part of cement was used per 100 parts by weight of the sample soil.
0.5 parts by weight, blast furnace slag 4.5 parts by weight and 0.52
A hexavalent chromium elution reducing material consisting of 5 parts by weight of silicon powder (average particle size 0.5 μm, 3.38 parts by weight to 100 parts by weight of hexavalent chromium elution reducing material) was mixed to prepare a solidified treated soil. . Further, as a comparative sample, solidified treated soil having a composition in which only 15 parts by weight of cement was mixed with 100 parts by weight of sample soil and a composition in which 10.5 parts by weight of cement and 4.5 parts by weight of blast furnace slag were mixed were prepared. The elution amount of hexavalent chromium at each age from the solidified soil was measured in the same manner as in Example 1 according to Notification No. 46. The results are shown in Table 2.

[0022]

[Table 2]

When the blast furnace slag was mixed, the elution-reducing effect was not observed at 1 day of age and gradually increased after 7 days of age, as compared with the case of cement alone. On the other hand, in the case of the hexavalent chromium elution-reducing material added with 0.525 parts by weight of silicon having an average particle diameter of 1 μm, the elution-reducing effect is given to the period before the age of 7 days which could not be compensated by the blast furnace slag alone. It was possible to reduce the elution amount of hexavalent chromium over the entire period.

[0024]

As described above, according to the method of the present invention, the elution amount of hexavalent chromium from the environment can be effectively reduced at any time.

Continued front page    F-term (reference) 2E191 BA02 BB01 BD11                 4G066 AA22B BA20 CA45 DA07

Claims (4)

[Claims] 1. A method for reducing the elution of hexavalent chromium by adding a hexavalent chromium elution reducing material containing silicon to the environment, wherein the particle size of the silicon is adjusted according to the intended time. Hexavalent chromium elution reduction method. 2. The hexavalent chromium elution reducing method according to claim 1, wherein the adjustment of the particle size of silicon is an adjusting method of mixing two or more kinds of silicon having different particle sizes. 3. The method for reducing hexavalent chromium elution according to claim 1, wherein the silicon contained in the hexavalent chromium elution reducing material is derived from waste or by-products. 4. The hexavalent chromium elution reducing material contains at least one selected from cement, inorganic fine powder, reducing material, alkali metal salt and alkaline earth metal salt. 6. The method for reducing the elution of hexavalent chromium according to any one of the above.