JP5274739B2 - Method for reducing hexavalent chromium by adjusting the particle size 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

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

  In recent years, processing and recycling of industrial waste has been actively promoted in various industrial fields due to social demands for environmental protection and environmental purification. Waste such as industrial waste, general waste, sewage sludge, incineration ash, etc. In this treatment, cement and a solidified material mainly composed of cement are widely used. In recent years, a wide variety of recycled resources have been used as raw materials for cement, and there have been cases where components that have not been contained in cement have been contained. As a result, a trace amount of hexavalent chromium may be eluted from a substance solidified with a hydraulic substance (hereinafter referred to as a solidified substance) depending on the use environment and conditions.

  As a method for reducing the elution amount of hexavalent chromium, for example, in JP-A-3-205331, addition of salts such as ferrous iron, stannous, first vanadium, cuprous, etc. Japanese Patent No. 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 be a problem. Moreover, although ferrous salt is effective in reducing the elution of the initial hexavalent chromium from the hydraulic composition, the effect disappears at an extremely early stage. The elution reduction effect cannot be expected.

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

Problems to be solved by the invention

  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 the hexavalent chromium reduction effect more than before by combining with the material known conventionally.

Means for solving the problem

  As a result of intensive studies to reduce the elution amount of hexavalent chromium from the environment, the present inventors have added silicon having an adjusted particle size to the environment, so that hexavalent chromium from the environment at the target time can be reduced. It was found that the amount of elution can be effectively reduced.

DETAILED DESCRIPTION OF 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 and cement to a soil and solidifying it, and adjusting the particle size of the silicon by mixing two or more types of silicon having different particle sizes By doing so, there is a feature in reducing elution of hexavalent chromium from the solidified soil in an arbitrary period. As the particle size, it is convenient to use an average 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 and the type of soil, but it is particularly effective within 7 days from the start of use. If desired, it is preferable to use silicon having an average particle size of 5 μm or less. Further, when it is desired to exert the effect continuously over a long period from the start of use, it is preferable to use silicon having an average particle diameter of 5 μm to 100 μm. Further, the content of silicon in the hexavalent chromium elution reducing material depends on the average particle diameter, the time when the effect is desired to be manifested, etc., but 0.05 to 20 weights per 100 parts by weight of the hexavalent chromium elution reducing material. Part is preferable, and 0.5 to 5 parts by weight is more preferable. As will be described later, waste containing silicon can also be used, but in this case as well, an addition rate in the same range is preferable with a substantial amount of silicon.

  In the present invention, a hexavalent chromium elution reducing material containing silicon is added to the environment. However, the addition method is not particularly limited. For example, when the environment is soil, A conventional method such as mechanically mixing a valent chromium elution reducing material can be used. In addition, when the environment is originally alkaline, only a hexavalent chromium elution reducing material containing silicon may be added to the environment, but when the environment is neutral or acidic, basic substances (cement, lime, etc.) An alkali metal salt and / or an alkaline earth metal salt is preferably used in combination with the hexavalent chromium elution reducing material.

  In the present invention, two or more types of silicon having different particle sizes can be mixed and used. By mixing two or more kinds of silicon having different particle sizes, an effect can be imparted even for a period that cannot be imparted with one kind of silicon. For example, by mixing silicon with an average particle size of 1 μm or less and silicon of 1 μm or more, silicon of 1 μm or less exhibits an elution reduction effect in a period of 7 days before the addition to the environment, and silicon of 1 μm or more is 7 As a result of exerting an effect in a period after about a day, an elution reduction effect can be imparted over a wide period. The type of silicon particle size is not limited to two, and silicon having an average particle size of three or more types may be mixed.

  The type of silicon used in the present invention is not particularly limited, and various types of silicon such as metal silicon, polysilicon, ferrosilicon, and porous silicon can be used. These silicons generally have a purity of about 80%, but in the present invention, there is no particular restriction on the purity. If the silicon content is 10% or more, the addition rate is adjusted as necessary. Sufficient use is possible.

  In the present invention, silicon generated as a waste or by-product can be used. In recent years when there is concern about environmental conservation and the shortage of landfill sites, the use of waste and by-products is effective from the viewpoint of effective use of resources. The purity or content rate of silicon is not particularly specified, and if the silicon content rate is 10% or more, it can be sufficiently utilized by adjusting the addition rate. Examples of waste or by-products containing silicon include silicon wafer scrap products, waste silicon catalysts, and other various waste materials.

The hexavalent chromium elution reducing material used in the present invention may contain at least one selected from cement, inorganic fine powder, reducing material, alkali metal salt, and alkaline earth metal salt in addition to silicon.
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, eco cement, alumina cement, and jet cement. Specifically, Portland cement is usually early strength, very early strength, moderate heat, low heat, sulfate resistant cement, and mixed cement is blast furnace cement, fly ash cement, silica cement and the like. Ecocement is a cement made from one or more wastes such as municipal waste incineration ash and sewage sludge incineration ash, and 10 to 40% by weight of one or more of calcium chloroaluminate, calcium fluoroaluminate, and calcium aluminate. Cement containing plaster. Jet cement is a cement containing calcium fluoroaluminate and having fast curing. 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 solidification 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 stone powder, limestone powder, and silica fume. Of these, blast furnace slag is known to have an effect of reducing elution of hexavalent chromium, and is used for the same purpose as in the present invention. However, the blast furnace slag exhibits an elution reduction effect for a long period of time after about 7 days from the start of use, and does not show a large elution reduction effect before that. Therefore, it becomes possible to reduce the elution amount of hexavalent chromium from the initial stage over a long period of time by using silicon having a particle size that exhibits an effect 7 days before the start of use and blast furnace slag in combination.

  Although it does not specifically limit as a reducing material in this invention, The substance which expresses the hexavalent chromium elution reduction effect in a cement-type material is preferable practically. Examples of the reducing material include ferrous sulfate, sulfides such as calcium sulfide and sodium sulfide. Among these, it is known that ferrous sulfate, in particular, exhibits an excellent hexavalent chromium reducing effect on hydraulic compositions such as cement without impairing its performance. However, the ferrous sulfate salt shows the effect of reducing hexavalent chromium only in the very early days before about one day from the start of use, and the effect disappears almost thereafter. Therefore, the combined use of silicon having a particle size that exhibits an effect after one day from the start of use and ferrous sulfate can reduce the elution amount of hexavalent chromium from the beginning to the long term. In addition, the amount of hexavalent chromium eluted can be reduced over a long period of time by using together with silicon having a particle size that produces an effect during the period that cannot be supplemented with ferrous sulfate, blast furnace slag, and 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 are used for the purpose of adjusting the setting time and adjusting the time to give the effect of reducing hexavalent chromium when a hydraulic substance such as silicon and cement is used in combination. Examples of the alkali metal salt include sodium carbonate, and examples of the alkaline earth metal salt include gypsum such as dihydrate gypsum and hemihydrate gypsum, and calcium hydroxide.

  The hexavalent chromium elution reducing material used in the present invention may contain various fine aggregates and coarse aggregates as necessary in addition to the above materials. In addition, AE agent, water reducing agent, high performance water reducing agent, high performance AE water reducing agent, antifoaming agent, shrinkage reducing agent within the range that does not impair the effects of the present invention for the purpose of improving fluidity and durability. Etc. may be added.

  Examples of the present invention will be described below. In addition, this invention is not limited to a following example.

Example 1:
[Materials used]
Cement: Prototype normal Portland cement Silicon: Commercial reagent (purity 4N) Average particle size 33μm
Calcium hydroxide: Commercial grade reagent sample soil: Kanto loam, prepared to a moisture content of 170% [Composition of solidified soil]
The silicon used was the above reagent crushed so that the average particle size was 9 μm and 1 μm. A solidified soil was prepared by adding 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 made of cement) to 100 parts by weight of sample soil. . In addition, as a comparative sample, solidified soil without addition of silicon was prepared. The amount of elution of hexavalent chromium at the age of 1 day, 7 days, 28 days, and 91 days of these solidified soils was measured in accordance with Circular 46. That is, it 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 a hexavalent chromium elution amount. The results are shown in Table 1.

  Compared to the case where no silicon is added, in the case of a hexavalent chromium elution reducing material to which 0.3 parts by weight of silicon having an average particle size of 9 μm is added, the elution amount of hexavalent chromium is reduced from the age of 1 day. It decreased continuously over a long period from the age of 7 days. In addition, in the case of the hexavalent chromium elution reducing material to which 0.3 parts by weight of silicon having an average particle diameter of 1 μm was added, the hexavalent chromium elution amount was reduced particularly in the period from the 1st to 28th ages. Furthermore, in the case of a hexavalent chromium elution reducing material using a mixture of silicon having an average particle size of 1 μm and 9 μm, the elution amount was reduced over the entire period after the material age 1 day.

Example 2:
Using the sample soil and material shown in Example 1, 10.5 parts by weight of cement, 4.5 parts by weight of blast furnace slag, and 0.525 parts by weight of silicon powder (average particle size of 0. 100 parts by weight). A hexavalent chromium elution reducing material composed of 3.38 parts by weight with respect to 100 parts by weight of 5 μm hexavalent chromium elution reducing material was mixed to prepare a solidified soil. Further, as a comparative sample, a solidified soil having a mixture in which only 15 parts by weight of cement was mixed with 100 parts by weight of sample soil and a mixture in which 10.5 parts by weight of cement and 4.5 parts by weight of blast furnace slag were mixed was prepared. The elution amount of hexavalent chromium at each age from these solidified soils was measured in the same manner as in Example 1 according to Circular 46. The results are shown in Table 2.

  When blast furnace slag was mixed, as compared with the case of cement alone, the elution reduction effect was not recognized at the age of 1 day, and the effect was gradually recognized after the age of 7 days. On the other hand, in the case of a hexavalent chromium elution reducing material to which 0.525 parts by weight of silicon having an average particle diameter of 1 μm is added, an elution reducing effect is imparted to a period of 7 days before material age that cannot be compensated only with blast furnace slag. The amount of elution of hexavalent chromium could be reduced over the entire period.

Effects of the present invention

  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.

Claims (3)

A hexavalent chromium elution reducing method comprising adding a hexavalent chromium elution reducing material containing silicon and cement to a soil and solidifying the same, wherein the silicon has a different particle size depending on a target time. A hexavalent chromium elution reduction method characterized by adjusting by mixing more than one kind of silicon .
The hexavalent chromium elution reducing method according to claim 1 , wherein the silicon contained in the hexavalent chromium elution reducing material is derived from waste or by-products.
The hexavalent chromium elution reducing material according to claim 1 or 2 , wherein the hexavalent chromium elution reducing material contains at least one selected from an inorganic fine powder, a reducing material, an alkali metal salt, and an alkaline earth metal salt. Method.