JP5196332B2 - Heavy metal elution reducing material and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heavy metal elution reducing material that suppresses the elution of harmful heavy metals mainly from contaminated soil and the like, and its manufacturing method, and particularly to a heavy metal elution reducing material suitable for contaminated soil containing harmful chemical substances and its production. Regarding the method.

  In recent years, soil contamination at the site of factories and soil contamination due to illegal dumping of industrial waste, etc. have been pointed out as social problems, and various attempts have been made to prevent chemical substances from eluting from such contaminated soil. It has been.

  For example, it has been proposed that a heavy metal contained in the contaminated soil be subjected to an elution reduction treatment using magnesium oxide, light burned dolomite, cement, zeolite, iron salt, blast furnace slag, or the like. Among them, dolomite is a mineral that is produced in large quantities in Japan such as the Kuzuu region in Tochigi Prefecture, so it can be obtained relatively inexpensively. It is attracting attention (see Patent Document 1 below).

By the way, this light-burned dolomite is said to suppress elution of heavy metals by causing calcium ions and magnesium ions derived from CaCO ₃ and MgCO ₃ which are the main components of dolomite to cause a pozzolanic reaction or a gelling reaction. However, in the conventional light burned dolomite, when lightly burned dolomite is prepared by lightly burning the produced dolomite, the dissolution reduction effect of the light burned dolomite may vary greatly depending on the preparation conditions. There was a problem that it was difficult to set the preparation conditions.

  In addition, the use of conventional light burned dolomite alone is not sufficient to suppress elution of heavy metals and the like, and there is a problem that other elution reducing means must be used in combination to enhance the elution reduction effect. .

JP 2006-289306 A

In view of the above problems of such prior art, to provide an excellent elution reducing material elution suppression effect of heavy metals, and a manufacturing method excellent elution reducing material elution suppression effect of heavy metals The purpose is to provide.

  As a result of diligent research by the present inventors, when a magnesium carbonate-containing mineral such as dolomite is fired at a relatively low temperature (also referred to as “light calcining” in the present invention) to produce a composition containing calcium and magnesium, The inventors have found that an elution reducing material having an excellent elution suppression effect can be prepared by using a specific light baking condition, and have arrived at the present invention.

That is, the present invention contains a mineral in the form of particles having a CaCO ₃ content of 9 to 40% by weight in terms of CaO, a MgCO ₃ content of 10 to 38% by weight in terms of MgO, and a Blaine value of 2000 to 3000 cm ² / g. A light-burning product obtained by light-burning at a temperature of ˜1000 ° C. and terminating the light-burning when the weight reduction rate due to the light baking reaches 9-20%, Provided is a heavy metal elution reducing material characterized by containing a light-burning product having a surface area of 5 to 10 m ² / g and a peak radius of pore size distribution within a range of 10 to 20 nm.

In the present invention, a mineral containing 9 to 40% by weight of CaCO ₃ in terms of CaO and 10 to 38% by weight of MgCO ₃ in terms of MgO is pulverized into particles having a brain value of 2000 to 3000 cm ² / g, Lightly baked under conditions of 650 to 1000 ° C., and when the weight reduction rate due to the light baking reaches 9 to 20%, the light baking is terminated to obtain a lightly burned product, and the light burned product is used. to provide a method of manufacturing a heavy metal elution reducing material, characterized by preparing a heavy metal elution reducing material Te.

The heavy metal elution reducing material according to the present invention contains CaCO ₃ in an amount of 9 to 40% by weight in terms of CaO, MgCO ₃ in an amount of 10 to 38% by weight in terms of MgO, and has a Blaine value of 2000 to 3000 cm ² / g. Lightly burned product obtained by lightly burning minerals under conditions of 650 to 1000 ° C. and terminating the light burning when the weight reduction rate due to the light burning reaches 9 to 20%. A light burn product having a BET specific surface area of 5 to 10 m ² / g and a peak radius of the pore size distribution in the range of 10 to 20 nm. The product has a smaller pore size and a larger BET specific surface area compared to conventional light-burning products. By using an elution-reducing material containing such light-burning products, excellent elution suppression is achieved. The effect can be exhibited.

Moreover, the manufacturing method of the heavy metal elution reducing material according to the present invention has a Blaine value of 2000 to 3000 cm ^{2 of} a mineral containing 9 to 40% by weight of CaCO ₃ in terms of CaO and 10 to 38% by weight of MgCO ₃ in terms of MgO. / G is pulverized into particles and lightly baked under conditions of 650 to 1000 ° C., and when the weight reduction rate due to the light baking reaches 9 to 20%, It is possible to obtain a light-burning product having a small pore diameter and a large BET specific surface area as compared with the light-burning product. Therefore, the elution reducing material which can exhibit the outstanding elution inhibitory effect can be manufactured by preparing the elution reducing material using the light-burning product obtained through such a process.

As described above, according to the present invention, it is possible to provide an excellent elution reducing material elution suppression effect of heavy metals, also provides a method for producing superior elution reducing material elution suppression effect of heavy metals It becomes possible to do.

The graph which plotted the relationship between light baking time (min), a BET specific surface area (m < ² > / g), and a brain value (cm < ² > / g) about the elution reduction material of an Example and a comparative example. The graph which showed the pore size distribution measured about the elution reduction material of an Example and a comparative example. The graph which plotted the relationship between the light baking time (min) and the weight reduction rate (%) measured about the elution reduction material of the Example and the comparative example.

  Hereinafter, the elution reducing material and the manufacturing method thereof according to the present invention will be specifically described. First, the manufacturing method of the elution reducing material will be described.

  In the method for producing an elution reducing material according to the present invention, as described above, a mineral containing magnesium carbonate as a main component is lightly burned under a condition of 650 to 1000 ° C., and the weight reduction rate due to the light firing is 9 to 20%. At this point, the light-burning is terminated to obtain a light-burning product, and an elution reducing material is prepared using the light-burning product.

  As the mineral containing magnesium carbonate as a main component, a mineral containing 40% by weight or more of magnesium carbonate can be suitably used, and a mineral containing 45 or more of magnesium carbonate can be more suitably used. Specific examples of the mineral include dolomite and magnesite.

Dolomite is not particularly limited as long as it contains magnesium carbonate as a main component and contains calcium carbonate. In addition to naturally occurring dolomite (white dolomite), magnesium hydroxide slurry and lime milk Synthetic dolomite obtained by firing the mixture can also be used.
In addition, naturally produced dolomite generally has a molar ratio of double salt represented by CaO / MgO in the range of 0.70 to 1.63, CaCO ₃ is about 9 to 40% by weight in terms of CaO, MgCO ₃ Is about 10 to 38% by weight in terms of MgO.

These minerals are pulverized into particles before light burning.
The mineral is in the form of particles having a Blaine value in the range of 2000 to 3000 (cm ² / g) .

  As temperature conditions at the time of light baking, it is set as the range of 650-1000 degreeC, Preferably it is 700-900 degreeC, More preferably, you may be 750-850 degreeC. Moreover, in order to finish light baking when the weight reduction rate by this light baking becomes 9-20%, although light baking time changes also with temperature conditions, it is about 10 to 60 minutes normally. .

  Moreover, although the weight reduction rate by light baking shall be 9-20%, Preferably it is 10-17%, More preferably, you may be 16-17%. By setting the rate of weight reduction due to light firing within such a numerical range, a composition containing calcium and magnesium can be sufficiently produced by decarboxylation from magnesium carbonate or the like, and carbonation by the decarboxylation reaction. It is considered that a lightly burned product is obtained in a state where relatively small pores formed by transient gas escape are left, that is, in a state where the BET specific surface area is large.

  In addition, about other baking conditions, such as baking atmosphere, and the baking apparatus used for baking, a conventionally well-known baking condition and baking apparatus are employable.

Next, the elution reducing material according to the present invention is obtained by, for example, lightly burning a mineral containing magnesium carbonate as a main component by the above-described method, having a BET specific surface area of 5 to 10 m ² / g, and a pore diameter. It contains lightly burned products with a distribution peak radius in the numerical range of 10-20 nm.

BET specific surface area of the light burned product is a 5 to 10 m ² / g, preferably from 7~10m ² / g.

Further, the light burned product is not particularly limited as long as it is a light burned product having the BET specific surface area and the pore size distribution as described above, but the brane specific surface area of the light burned product is not particularly limited. , About 3000 to 5000 cm ² / g, preferably 4000 to 4500 cm ² / g.
When the firing is advanced more than necessary, the mineral is disintegrated and becomes fine due to excessive decarboxylation, and as a result, the BET specific surface area tends to be small and the peak radius of the pore diameter distribution tends to be large.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Preparation of Elution Reduction Materials (Examples and Comparative Examples) Seven samples were prepared from dolomite (Sumitomo Osaka Cement Co., Ltd., Karasawa Mining Co., Ltd., Brain value: 2500 cm ² / g) produced in Kuzuu, Tochigi Prefecture. Elution reduction materials were prepared by light baking in a furnace for 0 minutes (no light firing), 5 minutes, 10 minutes, 15 minutes, 30 minutes, 60 minutes, 120 minutes.

Measurement of physical properties of elution reducing material For each of the above powders, the BET specific surface area (m ² / g) was measured using a BET specific surface area measuring device (manufactured by Nippon Bell Co., Ltd., high-precision gas adsorption device “BELSORP-mini”). In addition, the brain value (cm ² / g) was measured using a brain measuring device (manufactured by Maruhishi Kagaku Kikai Seisakusho, “Blaine Air Permeability Fineness Measuring Device”), and further, after light firing relative to the weight before light firing. The weight (ie, weight loss rate (%)) was measured. The results are shown in Table 1 below.

Further, based on the above measurement results, a graph plotting the relationship between the light baking time (min), the BET specific surface area (m ² / g), and the brain value (cm ² / g) for the elution reducing materials of Examples and Comparative Examples. Is shown in FIG.

  Further, for the elution reducing materials of the above Examples and Comparative Examples, the pore diameter distribution was measured using a BET specific surface area measuring device (manufactured by Nippon Bell Co., Ltd., high-precision gas adsorption device “BELSORP-mini”). The results are shown in FIG. Moreover, the graph which plotted the relationship between the baking time (minutes) measured about the elution reduction material of the Example and the comparative example and weight reduction rate (%) is shown in FIG.

Evaluation of Elution Reduction Materials Each of the elution reduction materials in Examples and Comparative Examples was added at a rate of 1 g to 100 ml of standard solutions of 5 mg / l and 100 mg / l of arsenic and lead, respectively, and stirred and mixed for 4 hours, followed by filtration. The heavy metal concentration in the filtrate was measured using an ICP analyzer (manufactured by Varian Technologies Japan Limited, device name “VARIAN ICP emission spectroscopic analyzer 730-ES”). From the measurement results, the adsorption removal rate was determined using the following calculation formula.

Adsorption removal rate [%] = (initial concentration-concentration in filtrate) ÷ initial concentration x 100

Moreover, the pH of the filtrate was also measured with a pH meter (manufactured by Horiba Ltd.). These results are shown in Tables 2 and 3 below.

  From Tables 2 and 3, and FIG. 3, Example 1 in which dolomite was lightly burned for 15 minutes and the weight reduction rate was 9.8%, and dolomite was lightly burned for 30 minutes and the weight reduction rate was 16.5%. The elution reducing material of Example 2, which has a BET specific surface area larger than that of the comparative elution reducing material, and the pH of the filtrate is suppressed to about 11 or less. It can be seen that can also exhibit an excellent adsorption action.

  On the other hand, in the elution reducing materials of Comparative Examples 1 to 3 in which the weight reduction rate is less than 9% by light firing for less than 15 minutes, a sufficient elution reduction action for arsenic has not been demonstrated, conversely In the elution reducing materials of Comparative Examples 4 and 5 in which the weight reduction rate after light burning exceeds 30% for more than 30 minutes, although the brane value increases with the light baking time, the adsorption removal action for arsenic and lead is changed. It is observed that it is decreasing. Moreover, in these comparative examples, the pH of the filtrate greatly exceeds 11, and heavy metals and the like are re-eluted by exposing the contaminated soil to such alkalis. Stability may be impaired. This seems to be because quick lime is generated by being heated excessively and is likely to have a high pH.

Claims (5)

A mineral containing CaCO _{3 in an amount of 9} to 40% by weight in terms of CaO, MgCO ₃ in an amount of 10 to 38% by weight in terms of MgO, and having a Blaine value of 2000 to 3000 cm ² / g, under conditions of 650 to 1000 ° C. And a light-burning product obtained by terminating the light-burning when the weight reduction rate due to the light-burning reaches 9 to 20%, and a BET specific surface area of 5 to 10 m ^2. A heavy metal elution reducing material comprising a light-burning product having a pore radius distribution within a range of 10 to 20 nm. The heavy metal elution reducing material according to claim 1, wherein the mineral is dolomite produced in Kuzuu, Tochigi Prefecture. A mineral containing 9 to 40% by weight of CaCO ₃ in terms of CaO and 10 to 38% by weight of MgCO ₃ in terms of MgO is pulverized into particles having a brane value of 2000 to 3000 cm ² / g, and a condition of 650 to 1000 ° C. Lightly baked at the bottom, and when the rate of weight reduction due to the light calcination becomes 9 to 20%, the light calcination is terminated to obtain a light baked product, and a heavy metal elution reducing material is obtained using the light baked product. A method for producing a heavy metal elution reducing material, characterized by comprising: The method for producing a heavy metal elution reducing material according to claim 3, wherein a weight reduction rate due to the light firing is 10 to 17%. The method for producing a heavy metal elution reducing material according to claim 3 or 4, wherein the light baking time is 10 minutes or more and 60 minutes or less.

Images