JP2010221156A - Artificial water retention material and method for producing the material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an artificial water retention material and a method for producing the material, wherein an artificial water retention material is produced using the incineration ash of paper making sludge as a raw material, the elution amount of hexavalent chromium is low, and pH is within a neutral range. <P>SOLUTION: The artificial water retention material provided herein is produced by carbonating granules mainly comprising the incineration ash of paper making sludge with a pressure of 0.1 MPa or more, carbon dioxide concentration of 60 vol.% or more, and treatment time of 15 minutes or more. Also, the method for producing the artificial water retention material provided herein comprises granulating the raw material mainly comprising the incineration ash of paper making sludge and then carbonating the granules with a pressure of 0.1 MPa or more, carbon dioxide concentration of 60 vol.% or more, and treatment time of 15 minutes or more. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to an artificial water-retaining material with little elution of hexavalent chromium and a pH in a neutral range, and a method for producing the same.

Conventionally, artificial water retention materials have been produced by preparing and granulating raw materials and then curing and solidifying them, or firing them in a firing kiln such as a rotary kiln. In recent years, waste incineration ash such as paper sludge incineration ash has been used as a raw material for artificial water retention materials from the viewpoint of effective use of waste. However, waste incineration ash contains chromium, and when this is used as a raw material to produce an artificial water retention material, the chromium in the raw material is oxidized to hexavalent chromium. There is a possibility that hexavalent chromium in an amount exceeding the soil environment standard value may be eluted.
In addition, paper sludge incineration ash also contains calcium, and when an artificial water retention material is baked or cured and solidified, strong alkaline components such as free lime and calcium hydroxide are produced in the artificial water retention material, resulting in soil and rivers. There is a risk of deteriorating soil quality and water quality such as inhibiting plant growth.

By the way, as a method of reducing hexavalent chromium in a fired product such as cement, a hexavalent chromium produced by introducing a combustible substance into a firing kiln and making the raw material in the kiln a low-oxygen atmosphere to suppress or oxidize chromium. There are known methods for reducing For example, in the production of cement, when a clinker is produced by firing a raw material to about 1450 ° C. using a rotary kiln, from the position where the maximum temperature is reached in the kiln such as before the kiln burner, to the range on the outlet side of the clinker, A method has been disclosed in which a combustible substance is introduced to reduce the oxidation of chromium in a low oxygen atmosphere and hexavalent chromium in the raw material is reduced to trivalent chromium (Patent Document 1).
As a method for reducing the pH of the fired product, there is a method of increasing the firing temperature. However, since the sintering reaction tends to proceed at a high temperature, the water retention of the fired product is lowered and does not satisfy the water retention block standard value of 0.15 g / cm ³ or more of the Interlocking Block Pavement Technology Association. There is a fear.
On the other hand, in the production by granulation solidification, there is no possibility that hexavalent chromium is eluted from the solidified product, but the pH of the solidified product becomes high. However, there is a method for curing the solidified product for a long period of time as a method for lowering the pH of the solidified product, but this is not preferable from the viewpoint of industrial productivity.

Japanese Patent Application Laid-Open No. 11-1000024

However, even if processing by adding and mixing flammable substances in the production by firing, the hexavalent chromium remains temporarily generated due to high heat, and the reduction reaction proceeds stably thereafter, and the hexavalent chromium Can not be reduced. Therefore, a method for reducing hexavalent chromium more reliably is required. Moreover, even if the elution of hexavalent chromium is suppressed, the pH remains high, so a method for reducing this pH is also required.

An object of the present invention is to provide an artificial water retention material manufactured using paper sludge incineration ash as a raw material, an artificial water retention material having a small elution amount of hexavalent chromium, and a neutral pH, and a method for producing the same. And

As a result of intensive studies to solve the above problems, the present inventor has found that the artificial water retention material produced under specific carbonation treatment conditions has a low elution amount of hexavalent chromium and has a pH in a neutral range. Completed the invention.
That is, the present invention is an artificial product obtained by carbonizing a granulated material mainly composed of paper sludge incineration ash at a pressure of 0.1 MPa or more, a carbon dioxide concentration of 60 vol% or more, and a treatment time of 15 minutes or more. It is a water retention material and its manufacturing method.

In the artificial water retention material according to the present invention, the elution amount of hexavalent chromium from the artificial water retention material is less than the soil environmental standard value (0.05 mg / L), and there is little possibility of causing environmental pollution. In addition, the pH of the artificial water retaining material is less than the standard value (pH 8.7) of the ordinance that establishes the standard of water quality related to the restriction of the removal of sewage from a specific business site, and there is little possibility of causing environmental pollution, and plant growth Can be used as a water retention material for greening. Furthermore, the artificial water-retaining material produced by using raw materials mainly composed of papermaking sludge incineration ash, which is a waste, is inexpensive, and can simultaneously promote the volume reduction of waste and its effective use.

Hereinafter, the present invention will be specifically described together with test examples.
The raw material used in the present invention is paper sludge incinerated ash (also referred to as paper sludge incinerated ash or paper sludge ash) as the main raw material, natural ore, industrial waste, as long as it does not impair the strength and water retention amount of the resulting artificial water retention material, You may mix the general waste and the 1 type, or 2 or more types of raw material chosen from construction generation | occurence | production soil. Industrial waste mixed with paper sludge incineration ash includes, for example, raw concrete sludge, sewage sludge, purified water sludge, construction sludge, iron sludge, and other sludge, construction waste, concrete waste, boring waste, coal ash and Examples include incineration ash such as incineration fly ash, foundry sand, rock wool, waste glass, blast furnace secondary ash, and the like. Moreover, as a general waste mixed with papermaking sludge incineration ash, sewage sludge dry powder, municipal waste incineration ash, a shell, etc. are mentioned, for example. Examples of construction generated soil mixed with papermaking sludge incineration ash include soil and residual soil generated from construction sites and construction sites, and waste soil. The strength of the artificial water retentive material is at least 100 N with a crushing load that is not crushed by humans, and the water retentivity is a water retentive block standard value of 0.15 g / cm ³ or more of the Interlocking Block Pavement Technology Association. It is preferable that the amount of raw materials other than papermaking sludge incineration ash is 20% by mass or less of the total raw materials.

The particle diameter of the raw material is preferably a median diameter of 400 μm or less, and more preferably 250 μm or less. If the particle size of the raw material is larger than 400 μm, granulation becomes difficult, or even if granulation is possible, the crushing load of the granulated product or product (cured product) will be 100 N or less, and it can be easily stepped on about the weight of a person. Since it is crushed, it is not preferable.

As a means for obtaining a raw material having the above particle diameter, the raw material to be used may be selected at the time of acceptance, or classification such as sieving may be performed. A plurality of raw materials having different particle diameters may be mixed. Further, if necessary, pulverization may be performed with a ball mill or the like. The pulverization may be performed before or after mixing the raw materials, or may be performed only by pulverizing only one of the raw materials used.

The raw material preferably contains 1% by mass or more of free lime (CaO) and / or calcium hydroxide in total, more preferably 2% by mass or more. If the total content of free lime or calcium hydroxide in the raw material is less than 1% by mass, the amount of carbonation reaction during the carbonation treatment is reduced, and the strength of the obtained cured product may be insufficient. is there.

As a means for obtaining a raw material containing the above-mentioned free lime and / or calcium hydroxide, the raw material to be used may be selected at the time of reception, or free lime or calcium hydroxide may be mixed.

The powder raw material is granulated by adding water or a binder as necessary. Generally, the addition amount (weight) of water is preferably 30% to 50% as an external ratio with respect to the raw material. If the addition amount is less than 30%, the water retention is decreased and the neutralization becomes insufficient, which is not preferable. If the addition amount exceeds 50%, it becomes a paste and difficult to granulate, and the granulated product In addition, the strength of the product cannot be sufficiently obtained, which is not preferable. For granulation, a pan pelletizer, an extruder, a mixer or the like can be used.

With the carbonation treatment in the present invention, a granulated product containing calcium silicate and calcium hydroxide exhibiting alkalinity is contacted and reacted with carbon dioxide (hereinafter also referred to as “carbonation”) to produce calcium carbonate, The process which hardens and neutralizes a granulated material. Examples of such carbonation treatment include a method using carbon dioxide in a gas or supercritical state.

The temperature of the carbonation treatment is not particularly limited, but is preferably 20 to 50 ° C. When the treatment temperature is less than 20 ° C., the reaction amount of carbonation decreases, so that the pH is less likely to be less than 8.7, and the strength of the cured product tends to decrease. Since the amount of carbon dioxide dissolved in water decreases and the amount of carbonation reaction decreases, the pH is unlikely to be less than 8.7.

The pressure for the carbonation treatment is preferably 0.1 MPa or more, and more preferably 0.2 MPa or more. If the carbonation pressure is less than 0.1 MPa, the amount of carbonation reaction decreases, so that the pH is less likely to be less than 8.7, and the strength of the cured product tends to decrease.

The concentration of carbon dioxide in the carbonation treatment is preferably 60 vol% or more, and more preferably 70 vol% or more. If the carbon dioxide concentration in the carbonation treatment is less than 60 vol%, the amount of carbonation reaction is reduced, so that the pH is less likely to be less than 8.7, and the strength of the cured product tends to decrease.

The carbonation time is preferably 15 minutes or longer, and more preferably 30 minutes or longer. When the carbonation treatment time is less than 15 minutes, the amount of carbonation reaction decreases, so that the pH is less likely to be less than 8.7, and the strength of the cured product tends to decrease.

The manufactured artificial water retention material may be used as it is, or may be used as a water retention block material. Further, it may be pulverized and adjusted in particle size as necessary.

Test examples are shown below, but the present invention is not limited thereto.
1. As a raw material for producing the artificial water retaining material, paper sludge incinerated ash (median diameter 150 μm, free lime amount 4.0 mass%) was used alone.
Next, after adding 40% (by weight) of water to the raw material, it was granulated by a pan pelletizer to obtain a granulated product having a pellet diameter of 5 mm to 15 mm.
Furthermore, the obtained granulated material was carbonized at a temperature, a carbon dioxide concentration and a treatment time shown in Table 1 at a temperature of 50 ° C. to obtain an artificial water retention material.

2. Measurement of elution amount of hexavalent chromium, pH and crushing load The elution amount of hexavalent chromium of the artificial water retaining material is determined according to the method specified in Notification No. 46 of the Environment Agency. Hexavalent chromium is dissolved by diphenylcarbazide absorption photometry. The concentration of was measured.
Moreover, it was determined whether the pH of the artificial water retaining material was less than pH 8.7 based on the presence or absence of a color reaction with a phenolphthalein solution.
Moreover, the crushing load of the artificial fired water retaining material was measured based on the Japan Society of Civil Engineers standard "Testing method for high strength fly ash artificial bone crushing load (draft)".
Table 1 shows the measurement results of the elution amount of hexavalent chromium of the artificial water retaining material, the presence or absence of a color reaction by the phenolphthalein solution, and the crushing load.

1. About hexavalent chromium elution amount As is clear from Table 1, in all of the examples and comparative examples, the hexavalent chromium elution amount was less than 0.02 mg / L. Therefore, there is no possibility that hexavalent chromium is eluted from the artificial water retention material subjected to the carbonation treatment.

2. As shown in Table 1, the pressure of the carbonation treatment is not colored in Example 1 in which the pressure of the carbonation treatment is 0.1 MPa, and the crushing load is as high as 120 N. On the other hand, Comparative Example 1 in which the pressure of carbonation treatment was 0.07 MPa was colored and the crushing load was as low as 86 N, which was only strong enough to be crushed by a person. .
Therefore, from the viewpoint of pH and crushing load, the carbonation pressure is preferably 0.1 MPa or more.

3. As shown in Table 1, the carbon dioxide concentration in the carbonation treatment is not colored in Example 2 in which the carbon dioxide concentration in the carbonation treatment is 60 vol%, and the crushing load is as high as 135 N. In contrast, Comparative Example 2 in which the carbon dioxide concentration in the carbonation treatment was 50 vol% was colored, and the crushing load was 110 N, which was lower than that in Example 2.
Therefore, from the viewpoint of pH, the carbon dioxide concentration is preferably 60 vol% or more.

4). As shown in Table 1, the time for the carbonation treatment was colored in Example 3 in which the time for the carbonation treatment was 15 minutes, and the crushing load was as high as 118 N. On the other hand, Comparative Example 3 in which the carbonation time was 13 minutes was colored, and the crushing load was as low as 89 N, which was only strong enough to be crushed by a person.
Therefore, from the viewpoint of pH and crushing load, the carbonation treatment time is preferably 15 minutes or more.

Claims (2)

An artificial water retention material obtained by carbonizing a granulated product mainly composed of papermaking sludge incinerated ash at a pressure of 0.1 MPa or more, a carbon dioxide concentration of 60 vol% or more, and a treatment time of 15 minutes or more. Artificial water retention characterized by granulating a raw material mainly composed of paper sludge incineration ash, and then subjecting the granulated product to carbonation treatment at a pressure of 0.1 MPa or more, a carbon dioxide concentration of 60 vol% or more, and a treatment time of 15 minutes or more. A method of manufacturing the material.