JP2005255496A - Method of manufacturing ceramic product using sewage sludge incineration ash and resultant ceramic product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a ceramic product using sewage sludge incineration ash in which the big change of the condition of firing of a formed body obtained by forming a body containing the sewage sludge incineration ash is not necessary even when the chemical composition of the the sewage sludge incineration ash is changed. <P>SOLUTION: The method of manufacturing the ceramic product using the sewage sludge incineration ash includes (i) a step for preparing the body containing a powdery mixture comprising the sewage sludge incineration ash, clay powder and ceramic powder (where ≥98 mass% of the clay powder is occupied by a particle having ≤50 μm particle diameter and the ratio of the particle diameter (d<SB>90</SB>) of the particle occupying 90% of the clay powder to the particle diameter (d<SB>50</SB>) of the particle occupying 50% of the clay powder is ≥3), (ii) a step for forming the resultant body and (iii) a step for firing the resultant formed boy. The resultant ceramic product has small water absorption, denseness and high mechanical strength. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention provides a method for producing a ceramic product using sewage sludge incineration ash, particularly sewage sludge incineration ash having a high content of Fe ₂ O ₃ and / or P ₂ O ₅ as one of the main raw materials, and is obtained by this method. The present invention relates to a ceramic product having high mechanical strength and low water absorption.

  So-called sewage sludge composed of domestic wastewater discharged from ordinary households, industrial wastewater, and rainwater containing earth and sand flowing into the sewage pipes, agglomerates solid components by adding a flocculant, and then dehydrates and burns Processed into sewage sludge incineration ash. It is desirable to reuse this sewage sludge incineration ash without disposal from the viewpoint of effective use of resources. To date, the sewage sludge incineration ash has been processed into ceramic products such as bricks, permeable blocks, and ceramic pipes. Consideration is being made.

In particular, ceramic pipes (ceramic pipes) made from sewage sludge incinerated ash as a raw material and having a low water absorption rate are expected to replace vinyl chloride pipes and fume pipes because of their excellent corrosion resistance and mechanical strength. Kai 2000-247730 (Patent Document 1) discloses a method for producing a ceramic pipe having a small water absorption rate, which is obtained by forming a mixed raw material made of natural clay, chamotte crushed ceramic pipe, and sewage sludge incinerated ash into a tubular shape and firing it. There is _disclosed, SiO 2: 50-70 _{wt%, Al} 2 O 3: _{15~25 wt%,} Na 2 O: _{0.5~2 wt%,} K 2 O: _1~3 wt%, CaO: A mixed raw material containing 1 to 3 wt%, MgO: 0.5 to 2 wt%, Fe ₂ O ₃ : 4 to 8 wt%, and P ₂ O ₅ : 2 to 8 wt% is used. JP 2003-026468 A (Patent Document 2) discloses a mixed powder for forming a ceramic comprising a sewage sludge incineration ash for producing ceramic products, a powdery clay material, and a ceramic powder material. The mechanical strength of the ceramic product obtained by increasing the utilization rate of sewage sludge incineration ash by making 85 wt% or more of the total particles constituting the particle size 50 μm or less and 0.1 wt% or less 250 μm or more. A method for enhancing the above is disclosed. In the examples in this publication, SiO ₂ : 52.4 wt%, Al ₂ O ₃ : 14.2 wt%, Na ₂ O: 0.9 wt%, K ₂ O: 1.6 wt%, CaO: 5.5 wt%, _{MgO: 1.5wt%, TiO 2:} 0.6wt%: Fe 2 O 3: 6.5wt%, P 2 O 5: sewage sludge ash containing 11.7wt% is used.

The sewage sludge incineration ash is Na ₂ O, K ₂ O, CaO, MgO, Fe ₂ O ₃ , P ₂ O in addition to SiO ₂ and Al ₂ O ₃ as main components, as can be seen from the above examples. _It contains a relatively large amount of so-called flux components such as ₅ , but the content of these components in the sewage sludge incineration ash is the source of sewage sludge (recovery location), weather (rainfall), coagulant used, etc. It varies greatly depending on. For example, when rainy weather continues, earth and sand flows into sewage along with rainwater, and thus the amount of SiO ₂ in the sewage sludge incineration ash increases. Further, when the sewage sludge contains a large amount of sewage such as manure from ordinary households, the amount of P ₂ O ₅ in the sewage sludge incineration ash increases. In addition, when industrial wastewater containing a lot of iron is mixed into sewage, or when iron-based flocculants such as ferric chloride solution and polyferric sulfate solution are used, it is processed into sewage sludge incineration ash When iron is added, the amount of Fe ₂ O ₃ in the sewage sludge incineration ash is significantly increased.

When the amount of Fe ₂ O ₃ or P ₂ O ₅ in the sewage sludge incineration ash increases, these are flux components, so that the molded body is deformed when the molded body formed using the sewage sludge incineration ash is fired. In addition, since air bubbles are easily generated in the molded body during firing, the water absorption of the obtained ceramic product increases and the mechanical strength decreases. Therefore, when producing ceramic products with uniform quality and low water absorption, the firing temperature of the compact is set in advance according to the chemical composition variation of the sewage sludge incineration ash, and then the sewage sludge incineration ash to be used is used. Each time the chemical composition is examined, and the firing conditions are appropriately adjusted according to the difference from the standard chemical composition incinerated ash. For example, if the P ₂ O ₅ content is different by 1%, the maximum temperature during firing is adjusted to about 10 to 20 ° C. Moreover, Unexamined-Japanese-Patent No. 2003-026467 (patent document 3) stocks what was obtained in the sewage sludge incineration ash produced within the predetermined period for the predetermined period of one month or more one by one. After the period has elapsed, a method in which the sewage sludge incinerated ash stocked during the period is divided into almost the same chemical composition from each other and used as a raw material for the production of ceramic products. It discloses and proposes to obtain a ceramic product of uniform quality without significantly changing the firing temperature by using sewage sludge incineration ash with a uniform chemical composition.

JP 2000-247730 A JP 2003-026468 A JP 2003-026467 A

  However, it is extremely complicated to analyze the chemical composition of the sewage sludge incineration ash used every time when trying to manufacture a large amount of ceramic products at low cost, and also to reduce the production efficiency of ceramic products. Connected. Furthermore, according to the method of Japanese Patent Application Laid-Open No. 2003-026467, it is possible to produce a ceramic product having a uniform quality using sewage sludge incineration ash having a uniform chemical composition, but over a long period of, for example, 2 to 4 months. In addition to requiring a large space for stocking sewage sludge incineration ash, it is necessary to stop the production of ceramic products during the period of stocking sewage sludge incineration ash.

Accordingly, an object of the present invention is to produce a ceramic product using sewage sludge incineration ash, even if the chemical composition of the sewage sludge incineration ash changes, in particular, the amount of Fe ₂ O ₃ and / or P _{2 as} a flux component. Even if the amount of O ₅ is greatly increased, a method for producing a ceramic product that does not require a significant change in the firing conditions of the molded body obtained by molding the clay containing sewage sludge incineration ash, and therefore also sewage sludge incineration ash It is to provide a method for producing a ceramic product that does not require uniform chemical composition of sewage sludge incineration ash by stocking for a certain period of time.

  As a result of repeated studies to achieve the above object, the inventors have prepared clay in a process for preparing a clay containing a mixed powder composed of sewage sludge incineration ash, clay powder and ceramic powder to produce a ceramic product. If a powder consisting essentially of fine particles with a particle size of 50 μm or less and having a relatively wide particle size distribution is used as the powder, even if the chemical composition of the sewage sludge incineration ash changes significantly, It was discovered that a ceramic product having a low water absorption rate and a high mechanical strength can be obtained without significantly changing the firing temperature of the molded body obtained by molding the kneaded clay.

That is, the present invention is a method for producing a ceramic product using sewage sludge incineration ash,
i) a step of preparing a clay containing mixed powder composed of sewage sludge incineration ash, clay powder and ceramic powder (however, 98% by mass or more of the entire clay powder is occupied by particles having a particle size of 50 μm or less, And the ratio of 90% particle size d ₉₀ to 50% particle size d ₅₀ in the clay powder is 3 or more).
ii) forming the obtained clay, and
iii) a step of firing the obtained molded body,
The manufacturing method characterized by including.

In the present specification, the term “particle diameter” means the Stokes diameter, and “50% particle diameter d ₅₀ ” means that up to 50 mass% of the whole powder has a particle diameter not more than the value of d ₅₀ . “90% particle size d ₉₀ ” means that up to 90% by mass of the whole powder has a particle size equal to or less than the value of d ₉₀ . Therefore, the particle size distribution of the powder becomes wider as the value of the ratio _d 90 _{/ d 50} for 50% _{d 50} value of 90% particle diameter _{d 90} increases. In the present invention, the value of d ₉₀ / d ₅₀ is generally 3 or more. When such a clay powder having a wide particle size distribution, preferably a powder in which 15% by mass or more of the entire clay powder is occupied by particles having a particle size of 10 μm or more is used, the chemical composition of the sewage sludge incineration ash changes. However, even if the amount of Fe ₂ O ₃ and / or P ₂ O _{5 as the} flux component is significantly increased, the firing temperature of the molded body obtained by molding the clay containing sewage sludge incineration ash is greatly increased. A ceramic product having a low water absorption rate and a high mechanical strength can be obtained without changing to. In the present invention, a ceramic product having a low water absorption and a high mechanical strength even when the molded body is fired at a lower temperature (1030 to 1080 ° C.) than the temperature in the prior art (generally 1100 ° C. or higher). Even if the maximum temperature during firing is changed by about 30 to 50 ° C., ceramic products having substantially the same water absorption and mechanical strength values can be obtained.

The reason why the above good results can be obtained is considered as follows. That is, it is considered that clay particles having various particle diameters are closely packed between particles of sewage sludge incineration ash containing particles having various particle diameters, so that a compact molded body is formed. Further, due to the reaction of each component in the clay, for example, the reaction between the iron component and C, S, etc., gas such as CO ₂ and SO _x can be generated in the molded body. It is considered that the clay particles closely packed in between provide a passage (slit) for these gases to be detached from the molded body during firing. As a result, a dense sintered body can be obtained even when fired at a relatively low temperature, and a dense sintered body can be obtained even when sewage sludge incinerated ash containing a large amount of iron components causing a reaction with C, S, etc. is used. It is considered to be obtained.

Therefore, in the production method of the present invention, when using sewage sludge incinerated ash with a large amount of flux components that has conventionally been forced to change the calcination temperature, the content of Fe ₂ O _{3 is} particularly 25% by mass of the entire incinerated ash. It is suitable when the above and / or sewage sludge incineration ash whose content of P ₂ O ₅ is 15% by mass or more of the entire incineration ash is used. In the present invention, a mixed powder having a chemical composition that is not used in the above-described prior art documents, specifically, SiO ₂ : 49 to 54 mass%, Al ₂ O ₃ : 18 to 24 mass% with respect to the entire mixed powder. , _Fe 2 _O 3: 10~16 _wt%, TiO 2: _0.5~0.75 wt%, CaO: 1 to 3 wt%, MgO: 1 to 2.5 _wt%, Na 2 O: _1~1 It is also possible to use a mixed powder having a chemical composition of 0.5 mass%, K ₂ O: 1 to 2.5 mass%, and P ₂ O ₅ : 4 to 7 mass%.

In the method for producing a ceramic product of the present invention, it is desirable that the clay powder has a high Al ₂ O ₃ content such as kaolin (a clay composed of one or more of kaolinite, nacrite, dickite, halloysite, hydrous halloysite, etc.). . The Al ₂ O ₃ content is preferably 25% by mass or more based on the entire clay powder. When such a clay is used, a dense ceramic product having a high mechanical strength and a low water absorption rate can be obtained even when using sewage sludge incineration ash having a high Fe ₂ O ₃ content.

  Further, 98% by mass or more of the entire ceramic powder contained in the mixed powder is preferably occupied by fine particles having a particle size of 50 μm or less, and 98% by mass or more of the entire sewage sludge incineration ash is occupied by particles having a particle size of 200 μm or less. It is preferred that The use of each of these powders increases the homogeneity of the resulting ceramic product, leading to an improvement in the strength of the ceramic product and a decrease in water absorption. In addition, a ceramic product having a low water absorption can be obtained even at a relatively low firing temperature. Therefore, it can contribute to energy saving.

  Furthermore, it is desirable that particles having a particle size of 300 μm or more are removed from the mixed powder by classification treatment. If coarse particles remain, the surface of the obtained ceramic product is not flat, and the strength of the ceramic product is reduced and the water absorption rate is increased.

  In the method for producing a ceramic product of the present invention, the sewage sludge incineration ash is 20 to 40% by mass with respect to the entire mixed powder, the ceramic powder is 30 to 40% by mass with respect to the entire mixed powder, and the clay powder is mixed. It is preferable that it is 30-40 mass% with respect to the whole powder. When a mixed powder in which the respective components are mixed within this range is used, a dense ceramic product having a high mechanical strength and a low water absorption rate can be obtained.

In step ii) in the method for producing a ceramic product of the present invention, it is desirable to perform molding while deaeration. By doing in this way, the gas generated by the reaction of each component in the clay during the preparation of the clay, for example, CO ₂ and SO _x generated by the reaction between the iron component and C, S, etc. are formed from the molded body. Since it is desorbed, a dense molded body can be obtained, and thus a homogeneous and dense ceramic product can be obtained after firing of the molded body. Further, as described above, in step iii), a ceramic product having a low water absorption and a high mechanical strength can be obtained even when the molded body is fired at 1030 to 1080 ° C., which is lower than the firing temperature in the prior art. It can contribute to energy saving.

  The invention also relates to a ceramic product obtained by the manufacturing method described above. The ceramic product of the present invention is a ceramic product which has a water absorption rate of preferably 2.5% or less, is chemically stable and has high mechanical strength.

According to the method for producing a ceramic product of the present invention, even if the chemical composition of the sewage sludge incineration ash is changed, especially the amount of Fe ₂ O ₃ and / or P ₂ O _{5 as the} flux component is greatly increased, A ceramic product having a low water absorption rate and a high mechanical strength can be obtained without significantly changing the firing temperature of the molded body obtained by molding the clay containing sewage sludge incinerated ash. The ceramic product obtained by the production method of the present invention has a small water absorption rate, is dense, is chemically stable, and has a high mechanical strength.

The method for producing a ceramic product of the present invention comprises: i) a step of preparing a clay containing a mixed powder composed of sewage sludge incinerated ash, clay powder and ceramic powder (provided that 98% by mass or more of the entire clay powder has a particle size of 98% by mass or more). And the ratio of 90% particle size d ₉₀ to 50% particle size d ₅₀ in the clay powder is 3 or more)), ii) a step of molding the obtained clay; And iii) a step of firing the obtained molded body.

First, the step i) will be described. In the production method of the present invention, various sewage sludge incineration ash can be used without particular chemical composition limitations. Typical sewage sludge incineration ash is composed of lime feldspar, phosphate compound, quartz and the like, and in addition to SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , TiO ₂ , Na ₂ O, CaO, K _2. O, MgO, P ₂ O _{5 and the} like are contained. In the present invention, various sewage sludge incineration ash can be used regardless of their chemical composition, and other sewage sludge incineration ash, including those containing other minor components such as Cd, Pb, Cr, As, Hg, Se, etc. can do. When the production method of the present invention uses sewage sludge incinerated ash having a large amount of flux components such as Fe ₂ O ₃ and P ₂ O ₅ , particularly 25% by mass or more of Fe ₂ O ₃ and / or or it is suitable when using sewage sludge ash containing P ₂ O ₅ more than 15% by weight with respect to the total ash. In the case of using such sewage sludge incineration ash with a large amount of flux components, it has been necessary to change the firing conditions significantly in the past. However, according to the present invention, the firing conditions are hardly changed.

  In the method for producing a ceramic product of the present invention, the particle size of the sewage sludge incineration ash does not significantly affect the mechanical strength of the obtained ceramic product when coarse particles are present. Therefore, the particle size is preferably 300 μm or less. More preferably, 98% by mass or more of the entire sewage sludge incineration ash is 200 μm or less, and particularly preferably 100 μm or less. When the obtained sewage sludge incineration ash contains coarse particles, it is preferable to adjust the particle size by sieving and pulverizing with a pulverizer such as a ball mill or a hammer mill.

In the present invention, the ceramic powder can be used without particular limitation as long as it is a powder obtained by pulverizing a ceramic fired body having excellent fire resistance. For example, a crushed material obtained by pulverizing a ceramic material such as ceramic or porcelain, cement, glass, brick, or the like can be used. The ceramic powder is preferably a ceramic powder that can provide a slit for releasing a gas (for example, CO ₂ , SOx, etc.) that can be generated in the molded body during firing in step iii) to be described later. A ceramic tube or tile powdery chamotte fired in a temperature range (preferably 1100 ° C. or higher) higher than the firing temperature of the ceramic molded body implemented in the production method of the present invention is particularly suitable. Since such a powdered chamotte remains in the form of particles even in the fired body formed by the production method of the present invention, the gas generated in the molded body is released to the outside by these remaining particles. Can be secured.

  In such a ceramic powder, 98% by mass or more of the entire ceramic powder is preferably occupied by fine particles having a particle size of 50 μm or less, preferably 30 μm or less. When such a fine ceramic powder is used, the ceramic powder is finely dispersed in the clay, and when the clay is formed into a predetermined shape, the fine ceramic powder is filled between the sewage sludge incineration ash particles. For this reason, the density of the molded body is increased, so that the homogeneity of the ceramic product obtained after firing is increased, the mechanical strength of the ceramic product is improved, and the water absorption is decreased. Further, even if a firing temperature lower than the firing temperature of the molded body in the prior art (generally 1100 ° C. or higher) is adopted, a ceramic product having a low water absorption rate can be obtained, which can contribute to energy saving. When the obtained ceramic powder is composed of relatively coarse particles, the particle size is adjusted using a pulverizer such as a ball mill or a hammer mill in addition to sieving.

Clay powder is an aggregate of particles mainly composed of hydrous silicate generated by weathering or metamorphism of rocks or minerals. In the method for producing a ceramic product of the present invention, the kind of clay powder is not particularly limited, and general kaolin, bentonite, kibushi clay, gillome clay and the like can be used, but Al ₂ O ₃ like kaolin. A high content is desirable. It is preferable to use clay powder in which Al ₂ O ₃ is 25% by mass or more, preferably 30% by mass or more of the whole. When such clay powder is used, even when using sewage sludge incinerated ash having a large amount of flux components such as Fe ₂ O ₃ and P ₂ O _5, a ceramic product having a high mechanical strength and a high density is produced. I know that.

The main feature of the method for producing a ceramic product of the present invention is that, as clay powder, 98% by mass or more of the entire clay powder is occupied by particles having a particle size of 50 μm or less, and 50% of 90% particle size d ₉₀ ratio of 3 or more to the diameter d _50, is to preferably 4 or more, particularly preferably using a powder is 5 or more. In other words, clay powder having a wide particle size distribution composed of fine particles is used (see FIG. 1). It is preferable that 15% by mass or more of the clay powder has a particle size of 10 μm or more. When such a clay powder is used, the clay powder is finely dispersed in the clay, and when the clay is formed into a predetermined shape, the clay powder becomes dense between the sewage sludge incineration ash particles having a wide particle size distribution. Since it is filled, the compactness of the compact is increased, and the clay particles closely packed between the sewage sludge incineration ash particles are generated by the reaction of each component in the clay (for example, iron component). CO ₂ , SO _x, etc. generated by the reaction of C with S, etc.) provide a passage (slit) for detachment from the compact during firing, so that the homogeneity of the ceramic product obtained after firing is improved. This is considered to increase the mechanical strength of the ceramic product and decrease the water absorption rate. In addition, even if the chemical composition of the sewage sludge incineration ash changes, the amount of Fe ₂ O ₃ and / or P ₂ O ₅ that is a flux component increases significantly, for example, the content of Fe ₂ O ₃ is increased. Sewage sludge incineration such that it is 25% by mass or more, especially 40% by mass or more of the entire incinerated ash, and / or the content of P ₂ O ₅ is 15% by mass or more, particularly 20% by mass or more of the entire incinerated ash Even when ash is used, a ceramic product having a low water absorption rate and a high mechanical strength can be obtained without significantly changing the firing temperature of the compact. When the obtained clay powder is composed of relatively coarse particles, the particle size is adjusted using a pulverizer such as a ball mill or a hammer mill in addition to sieving.

  When preparing the clay containing the mixed powder composed of the sewage sludge incinerated ash, clay powder and ceramic powder, it is preferable to remove particles having a particle size of 300 μm or more by classification treatment. If coarse particles remain, the surface of the obtained ceramic product is not flat, and the mechanical strength of the ceramic product is decreased and the water absorption rate is increased. The classification process is generally performed using a sieve. The classification treatment may be performed for each of the sewage sludge incinerated ash, clay powder, and ceramic powder, or may be performed after mixing at least two of the sewage sludge incinerated ash, clay powder, and ceramic powder. Further, classification may be performed after each powder or mixed powder is dispersed in a medium such as water.

The above-mentioned sewage sludge incineration ash, clay powder, and ceramic powder are sufficiently kneaded with water to prepare a clay. Binders and other additives may be added to the clay as necessary. At this time, sewage sludge incineration ash is 20-40 mass% with respect to the whole mixed powder, ceramic powder is 30-40 mass% with respect to the whole mixed powder, and clay powder is 30- with respect to the whole mixed powder. It is preferably 40% by mass. When a mixed powder in which the respective components are mixed within this range is used, a dense ceramic product having a high mechanical strength and a low water absorption rate can be obtained. When the chemical composition of the mixed powder is, for example, 30% by mass of sewage sludge incineration ash, 35% by mass of clay powder, and 35% by mass of ceramic powder with respect to the entire mixed powder, SiO _{2 with} respect to the entire mixed powder. : 49 to 64 _{wt%, Al} 2 O 3: 18 to 24 _{wt%, Fe} 2 O 3: 4 to 16 _wt%, TiO 2: 0.5 to 0.75 mass%, CaO: 1 to 3 mass%, MgO: 1 to 2.5 _wt%, Na 2 O: _{1~1.5 wt%,} K 2 O: 1~2.5 _{wt%, P} 2 O 5: the 2-7 wt%. Also, when using sewage sludge incineration ash in which the content of Fe ₂ O ₃ is 25% by mass or more of the entire incineration ash and the content of P ₂ O ₅ is 15% by mass or more of the entire incineration ash It is, _SiO 2 on the entire mixed powder: 49 to 54 _{wt%, Al} 2 O 3: _{18~24 wt%, Fe} 2 O 3: _{10~16 wt%,} TiO 2: 0.5 to 0.75 mass %, CaO: 1 to 3 mass%, MgO: 1 to 2.5 mass%, Na ₂ O: 1 to 1.5 mass%, K ₂ O: 1 to 2.5 mass%, P ₂ O ₅ : 4 -7% by mass.

  Mixing in preparing the kneaded clay can be performed by using various conventional mixers such as a kneader, a ribbon mixer, and a roller mixer. The moisture content of the clay is generally 15 to 25% by mass, preferably 17 to 23% by mass, based on the entire clay. If the moisture content of the clay is too lower than 15% by mass, the clay may become too hard and extrusion molding may be difficult. If the moisture content of the clay is too high, the ceramic molded body. Since shape retention at the time of molding is reduced, it is not preferable. There is no particular limitation on the kneading time, and it may be a time for preparing a homogeneous clay, but it is generally in the range of 10 minutes to 2 hours.

Next, step ii) in the method for producing a ceramic product of the present invention will be described. There is no particular limitation on the method of forming the ceramic product in the forming step of step ii), and a known method is selected according to the ceramic product to be manufactured. Various methods commonly used in the manufacture of ceramic products, for example, general casting A molded body having a desired shape can be obtained by molding, extrusion molding, press molding (uniaxial press method, CIP molding method, etc.). For example, when producing a ceramic pipe, extrusion molding is suitable. A ceramic pipe having a constant cross-sectional shape can be formed by extruding a molded body from the die while supplying clay to an extruder having a die having a certain size and shape. It is desirable to perform the molding while deaeration. By degassing, the gas generated by the reaction of each component contained in the clay during the preparation of the clay or during the molding process, for example, CO ₂ and SO _x generated by the reaction of the iron component with C, S, etc. Is detached from the molded body, so that a dense molded body can be obtained. Therefore, a homogeneous and dense ceramic product can be obtained after firing of the molded body. Molding while degassing can be performed by a conventional vacuum extrusion molding machine.

  It is desirable to dry the obtained molded body before the firing treatment. In particular, it is preferable to carry out the drying treatment until the residual water content becomes 2% or lower. There is no particular limitation on the drying method. In addition to natural drying, the molded body can be put in a constant temperature dryer and dried. By the drying treatment, the expansion of water vapor during firing can be suppressed, and thus a dense ceramic product can be obtained.

  Next, the dried product is preferably fired at a maximum temperature of 1000 to 1200 ° C., preferably 1030 to 1080 ° C. in step iii) in the method for producing a ceramic product of the present invention. When the maximum temperature is lower than 1000 ° C., the resulting ceramic product has insufficient mechanical strength and also has a high water absorption rate. In the present invention, a ceramic product having a low water absorption and a high mechanical strength can be obtained even when firing is performed at a lower temperature (1030 to 1080 ° C.) than the temperature in the prior art (generally 1100 ° C. or higher). Furthermore, even if the maximum temperature during firing is changed by about 30 to 50 ° C., ceramic products having substantially the same water absorption rate and mechanical strength can be obtained. In the present invention, since it is not necessary to significantly change the firing temperature depending on the content ratio of the sewage sludge incineration ash in the mixed powder and the chemical composition of the sewage sludge incineration ash, it is particularly advantageous when manufacturing ceramic products continuously in large quantities. . The time for maintaining the maximum temperature depends on the type of ceramic product to be manufactured, but is generally 10 minutes or more and 20 hours or less.

Although the temperature increasing / decreasing rate at the time of firing also depends on the type of ceramic product to be manufactured, the temperature rising time until reaching the maximum temperature from the normal temperature and the temperature decreasing time until reaching the normal temperature from the maximum temperature are generally at least 1 It is preferable to set the time so that it takes 4 hours or more, preferably 4 hours or more. If the rate of temperature increase is too fast, gas (CO ₂ , SO _x, etc.) generated in the molded body may remain in the ceramic product without coming out to the outside. On the other hand, if the temperature raising / lowering speed is too high, excessive thermal strain is applied to the molded body, which may promote deformation and crack generation of the ceramic product.

  According to the above-mentioned method for producing a ceramic product, the water absorption is not more than about 4%, preferably not more than 2.5%, particularly preferably not more than 1%, and is chemically stable and mechanical strength. Large ceramic products such as ceramic pipes, roof tiles, wall panels, and manhole inner wall surface repair panels can be suitably manufactured. In particular, the ceramic pipe obtained by molding into an annular shape can be suitably used as a pipe for underground burial or the like that replaces a PVC pipe or a fume pipe. In addition, as described above, sewage sludge incinerated ash containing heavy metals can be used in the present invention, but since the heavy metals are released to the outside during firing, the obtained ceramic product is safe and contains almost no heavy metals. Is.

  EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the forms shown in the following examples.

  In the following examples, the chemical composition was measured by fluorescent X-ray analysis according to JIS K 0119. However, the loss on ignition was measured according to JIS M 88537. The particle size distribution was measured by a laser diffraction method in accordance with JIS R 1629. The water absorption was determined by measuring the weight increase after the dried test piece was immersed in water. The bending strength was measured by a three-point bending test. The test speed in the test is 1 mm / min, the radius of the pressing metal is 5 mm, the radius of the supporting metal is 5 mm, and the distance between the fulcrums is 50 mm.

(1) Sewage sludge incineration ash Table 1 shows the chemical composition and particle size (after classification treatment) of the sewage sludge incineration ash used. The sewage sludge incinerated ash with a large amount of flux components was used with an Fe ₂ O ₃ content of 28.77 to 43.5 mass% and a P ₂ O ₅ content of 15.9 to 20.07 mass%.

(2) Ceramic powder Table 2 shows the chemical composition and particle size (after classification treatment) of the ceramic powder (chamotte) used.

(3) Clay powder Table 3 shows the chemical composition of the clay powder used. Moreover, the measurement result of a particle size distribution is shown in FIG. 1 and FIG.

(4) Preparation of test piece and measurement of water absorption rate and bending strength Examples 1 to 15 and Comparative Examples 1 to 9
The combination of sewage sludge incinerated ash, ceramic powder, and clay powder shown in Table 4 below is a small soil mixer SS-S-338 in an amount corresponding to 30% by mass, 35% by mass, and 35% by mass with respect to the entire mixed powder, respectively. (Shinohara Seisakusho Co., Ltd.) and kneaded for 10 minutes. Thereafter, the water was added so that the water content of the clay was 21% by mass with respect to the entire clay, and kneading was further performed for 10 minutes. Next, the obtained clay was put into a vacuum extrusion molding machine PZVM8d (manufactured by Hendley) and molded into a columnar shape having a diameter of 15 mm and a length of 100 mm. The obtained molded body is placed in a constant temperature dryer SSN-155S (manufactured by Isuzu Seisakusho) and held at 45 ° C for 12 hours, further at 90 ° C for 2 hours, further at 110 ° C for 2 hours, and further at 150 ° C for 12 hours. The molded body was sufficiently dried. Next, the dried molded body was fired at the maximum temperature shown in Table 4 below. In firing, the temperature was raised to 1000 ° C. at 28 ° C./min, held at 1000 ° C. for 10 minutes, further raised to the maximum temperature at 10 ° C./min, and further held at the maximum temperature for 10 minutes.

  About the obtained test piece (sintered body), the water absorption rate and the bending strength were measured. The results obtained are summarized in Table 4 below. In this experiment, the bending strength of 60 MPa is 41.4 kN / m (standard value is 36 kN / m) when converted to the external pressure strength of a ceramic pipe with a nominal diameter of 150 mmφ, and the external pressure strength of a ceramic pipe with a nominal diameter of 200 mmφ. This corresponds to 47.4 kN / m (standard value is 43 kN / m). Therefore, in Table 4 below, when the value of the bending strength is 60 MPa or more, it is determined that a ceramic pipe that satisfies the standard value is formed.

  From Table 4, in Comparative Examples 1 to 9 using clay powder B, the values of water absorption and bending strength vary greatly depending on the type of sewage sludge incineration ash and the firing temperature, but Example 1 using clay powder A ~ 15, the water absorption and bending strength values do not change much even when the sewage sludge incineration ash type (chemical composition, etc.) and the firing temperature change, and the water absorption value is small and the bending strength value is small. It can be seen that a large specimen is obtained. That is, by using a powder having a wide particle size distribution width such as clay powder A, even if the composition of the sewage sludge incineration ash changes greatly, the mechanical strength is high and the water absorption is not changed without significantly changing the firing temperature. It is possible to obtain a dense ceramic product with a low rate.

  Furthermore, a heavy metal elution test was conducted for Comparative Example 1 by the method defined in Environmental Notification No. 13. Sewage sludge incineration ash A has Cd of 0.010 mg / l, Pb of less than 0.02 mg / l, Cr (VI) of less than 0.04 mg / l, As of 2.1 mg / l, and Hg of 0.0005 mg / l. 1 and less than 0.01 mg / l, but the test piece after firing had Cd less than 0.001 mg / l, Pb less than 0.005 mg / l, and Cr (VI) 0.005 mg / l. Less than l, As is 0.004 mg / l, Hg is less than 0.00005 mg / l, Se is less than 0.001 mg / l, environmental standard value is Cd 0.3 mg / l or less, Pb 0.3 mg / l Compared with values of 1 or less, Cr (VI) 1.5 mg / l or less, As 0.3 mg / l or less, Hg 0.005 mg / l or less, Se 0.3 mg / l or less, it contains very little heavy metal. It was.

It is a figure which shows the particle size distribution of the clay powder A used in the Example of this invention. It is a figure which shows the particle size distribution of the clay powder B used in the comparative example of this invention.

Claims (12)

A method for producing a ceramic product using sewage sludge incineration ash,
i) a step of preparing a clay containing mixed powder composed of sewage sludge incinerated ash, clay powder and ceramic powder (however, 98% by mass or more of the entire clay powder is occupied by particles having a particle size of 50 μm or less, And the ratio of 90% particle size d ₉₀ to 50% particle size d ₅₀ in the clay powder is 3 or more).
ii) forming the obtained clay, and
iii) a step of firing the obtained molded body,
The manufacturing method characterized by including.   The manufacturing method according to claim 1, wherein 15% by mass or more of the entire clay powder is occupied by particles having a particle size of 10 µm or more. The manufacturing method according to claim 1, wherein the clay powder contains 25% by mass or more of Al ₂ O ₃ with respect to the whole powder.   The manufacturing method according to claim 1, wherein 98% by mass or more of the entire ceramic powder is occupied by particles having a particle size of 50 μm or less.   The manufacturing method according to claim 1, wherein 98% by mass or more of the entire sewage sludge incineration ash is occupied by particles having a particle size of 200 μm or less.   The manufacturing method according to claim 1, wherein the mixed powder is a powder from which particles having a particle size of 300 μm or more have been removed by classification treatment. The sewage sludge incineration ash contains 25% by mass or more of Fe ₂ O ₃ and / or 15% by mass or more of P ₂ O ₅ with respect to the entire incineration ash. The manufacturing method as described in.   Sewage sludge incineration ash is 20 to 40% by mass with respect to the entire mixed powder, ceramic powder is 30 to 40% by mass with respect to the entire mixed powder, and clay powder is 30 to 40% by mass with respect to the entire mixed powder. The production method according to claim 1, wherein:   The manufacturing method according to claim 1, wherein in step ii), molding is performed while deaeration.   The manufacturing method according to any one of claims 1 to 9, wherein in the step iii), the molded body is fired at a maximum temperature of 1030 to 1080 ° C.   The ceramic product obtained by the manufacturing method in any one of Claims 1-10. The ceramic product according to claim 11, wherein the product has a water absorption of 2.5% or less.

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