JP2014014793A - Method for producing inorganic particle, and inorganic particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily and stably producing inorganic particles with high whiteness at a low energy cost, and to provide the inorganic particles with high whiteness.SOLUTION: In a method for producing inorganic particles, papermaking sludge including waste newspaper deinked sludge as a main component is used as a raw material, and a dehydration process, a combustion process, and a calcination process are included. In the combustion process, a burnt material is obtained by supplying an oxygen-containing gas and discharging an exhaust gas with oxygen concentration of 5 to 10 vol%, and in the calcination process, a calcined product is obtained in such a way that a decomposition rate of calcium carbonate included in the papermaking sludge to calcium oxide is less than 50 mass%.

Description

  The present invention relates to a simple and stable production method of inorganic particles having high whiteness at a low energy cost, and to inorganic particles having high whiteness obtained by the production method.

  Conventionally, paper sludge generated in a paper mill is regarded as industrial waste and has been considered as a target for landfill and incineration. However, paper sludge contains a lot of inorganic components that can be reused as a papermaking raw material if it can be recovered. At present, the effective use and reuse of these, especially the production of inorganic particles from paper sludge, is attracting much attention. .

  As a method for producing such inorganic particles, for example, a method in which carbonization treatment is performed prior to the combustion treatment of papermaking sludge (Japanese Patent Nos. 4153411, 3563707, 2002-308619, and 2010-194486). No. 3), a device for use in combustion processing, a method for specifying in detail the combustion temperature, combustion time, etc. (see Japanese Patent No. 3831719, Japanese Patent Laid-Open No. 11-310732, and Japanese Patent Laid-Open No. 2008-207173) have been developed. Has been. However, these methods are complicated and it is difficult to stabilize the quality.

  Moreover, the origin (source) of the papermaking sludge used as a raw material varies, and it is difficult to stabilize the quality of the inorganic particles. For this reason, a technique in which the main raw material of papermaking sludge is limited to deinking sludge has also been developed (see JP 2008-127704 A). However, although this method can stabilize the quality, the manufacturing method becomes complicated.

  Furthermore, paying attention to the problems of hardening of the obtained inorganic particles, lowering of whiteness, thickening when solidified, and problems of solidification, the pulverization method is specified in detail, and a method of blowing carbon dioxide (special No. 2002-356629), a method for specifying in detail how to blow carbon dioxide (see JP 2009-292666A), and the like have also been developed. However, these methods are excellent in improving the problem of thickening and solidifying when slurried, but the manufacturing method is complicated.

  On the other hand, as a method for solving these problems, a method for producing inorganic particles has been developed that uses waste newspaper deinking sludge as a raw material, and preferably uses means for thermally decomposing calcium carbonate contained therein by 80 mass% or more. (See JP 2012-097368). However, the means for thermally decomposing calcium carbonate of 80% by mass or more requires a large amount of heat energy. Black foreign substances are generated by the formation of hot-melt hard substances accompanying high-temperature treatment or carbon black of organic substances contained in inorganic particles. Therefore, reduction of hard substances and black foreign matters is demanded. In particular, in order to use inorganic particles as a papermaking material such as a filler or a pigment, the inorganic particles are required to have flexible properties and higher whiteness.

  Therefore, although these conventional production methods have certain technical effects, they are not always satisfactory from the viewpoint of easily and stably producing inorganic particles having high whiteness at low energy costs.

Japanese Patent No. 4153411 Japanese Patent No. 3563707 JP 2002-308619 A JP 2010-194486 A Japanese Patent No. 3831719 JP-A-11-310732 JP 2008-207173 A JP 2008-127704 A JP 2002-356629 A JP 2009-292666 A JP 2012-097368 A

  The present invention has been made in view of these disadvantages, and an object of the present invention is to provide a simple and stable production method of inorganic particles having high whiteness at low energy costs and inorganic particles having high whiteness.

  As a result of intensive studies to solve the above-mentioned problems, the inventor uses papermaking sludge mainly composed of newspaper wastepaper deinking sludge as a raw material, and performs a combustion process and a firing process in a relatively mild atmosphere. Thus, it has been found that inorganic particles having high whiteness can be easily and stably produced at a low energy cost, and the present invention has been completed.

As a result, the invention made to solve the above problems is
Using a papermaking sludge mainly composed of newspaper waste paper deinking sludge as a raw material, a method for producing inorganic particles including a dehydration step, a combustion step and a firing step,
In the combustion step, a combustion product is obtained by supplying an oxygen-containing gas and discharging an exhaust gas having an oxygen concentration of 5% by volume to 10% by volume, and in the firing step, oxidation of calcium carbonate contained in the papermaking sludge A method for producing inorganic particles characterized in that a fired product is obtained so that the decomposition rate into calcium is less than 50% by mass.

  According to the manufacturing method, since the papermaking sludge mainly containing newspaper waste paper deinking sludge having a high calcium carbonate content and a low kaolin content is used as a raw material, a cementitious material derived from calcium carbonate and kaolin ( The generation of foreign matter) can be reduced, and the resulting inorganic particles can be hardened and whiteness can be suppressed.

  In addition, newspaper waste ink deinking sludge is high in calories due to the relatively low ash content of the newspaper used as a raw material and contains fat and oil components derived from newspaper ink, etc., and easily burns at a relatively low combustion temperature. . For this reason, the manufacturing method uses papermaking sludge mainly composed of waste newspaper deinking sludge as a starting material, so that a large amount of heat energy is not required for combustion, and self-combustion and exhaust gas with a predetermined oxygen concentration are emitted. The combustion process can be performed at a relatively mild temperature, and the decomposition rate of calcium carbonate into calcium oxide can be suppressed to less than 50% by mass. Furthermore, it is possible to reduce the generation of hard substances and the containment of unburned matter and black foreign substances in inorganic particles due to combustion at high temperatures.

  Also in the combustion process, decomposition of calcium carbonate into calcium oxide occurs, the carbon dioxide concentration in the exhaust gas increases, and the oxygen concentration decreases. However, by exhausting the exhaust gas having an oxygen concentration of 5% by volume or more and 10% by volume or less to the outside of the combustion furnace, the excessive decomposition in this step is suppressed, and the above-described relatively mild conditions are maintained. Combustion can be performed. Further, the exhaust gas can be preferably reused in the drying process and the carbon dioxide blowing process, and the manufacturing cost can be reduced. The oxygen concentration referred to here is a value obtained by measuring the oxygen concentration of a measurement sample sampled from each measurement area with an automatic oxygen concentration measurement apparatus (manufactured by Horiba, Ltd., product name ENDA-5250).

  In addition, in the manufacturing method, by setting the oxygen concentration of the exhaust gas within the above range, the oxidation (combustion) of the organic components contained in the paper sludge is advanced while suppressing carbonization, and the calcium oxide of calcium carbonate in the firing step. The combustion product is fired so that the decomposition rate into less than 50% by mass. Thereby, the said manufacturing method can suppress decomposition | disassembly of excess calcium carbonate, and can reduce the burden of a carbon dioxide blowing process. Moreover, the said manufacturing method can also reduce problems, such as thickening and solidification of the slurry at the time of the slurrying process considered as a problem conventionally. As a result, the production method can easily and stably produce inorganic particles having high whiteness at low energy costs.

  In the combustion step, the combustion temperature is preferably lower than 600 ° C. The volatilization rate of each organic component in papermaking sludge is not the same, and multiple components are contained, so some components may ignite when they reach the ignition temperature, and the fire is accompanied by the exhaust gas. As a result, partial ignition and combustion occurs at the location where the sparks are ignited, and only the surface portion becomes high temperature. As a result, for example, the internal components remain without being decomposed, and there is a problem that the product finally obtained has low whiteness. Further pursuing this cause, in the combustion process of papermaking sludge, typically three exothermic peaks are observed within a temperature range of about 200 ° C. or higher and lower than 500 ° C. (sometimes there are four cases). Then, the decomposition of calcium carbonate occurs from about 600 ° C., and the exothermic characteristics show a rapid decline tendency due to the endothermic reaction. By setting the temperature of the oxygen-containing gas within the above range, the temperature conditions during the combustion process are more moderate. can do.

  In the combustion step, it is preferable that the dehydrated product after the dehydration step is burned while being moved in a direction opposite to the flow direction of the oxygen-containing gas. By moving the dried product in the combustion furnace in the above-described direction, the dried product can be burned more uniformly and continuously. In addition, foreign matter adhering to the combustion product can be removed into the exhaust gas by wind.

  In the combustion process, it is preferable to use a rotary kiln furnace as the combustion furnace. By using a rotary kiln furnace as the combustion furnace, the dry matter can be burned more uniformly and continuously in this case as well.

  In the firing step, the firing temperature is preferably 680 ° C. or higher and 750 ° C. or lower. Decomposition of calcium carbonate in the firing step can be further suppressed.

  In the firing step, it is preferable to use a rotary kiln furnace as the firing furnace. The combustion product can be fired more uniformly and continuously.

Another invention made to solve the above problems is as follows:
Inorganic particles obtained by the above production method,
The inorganic particles have a calcium compound content of 70% by mass or more in terms of calcium oxide. The inorganic particles have high whiteness.

  According to the present invention, inorganic particles having high whiteness can be easily and stably produced at a low energy cost. Accordingly, papermaking sludge that has been conventionally treated as industrial waste can be suitably reused.

FIG. 1 shows a process chart of a manufacturing method according to the present invention.

  Hereinafter, the manufacturing method of the inorganic particle which concerns on this invention, and the inorganic particle obtained by the said manufacturing method are explained in full detail.

<Method for producing inorganic particles>
The method for producing inorganic particles of the present invention includes at least a dehydration step, a combustion step, and a firing step. Other steps other than the combustion step and the firing step are not particularly limited, and can be performed according to a known method. Hereinafter, the raw material to be used, each process, and a product are demonstrated.

<Paper sludge (newspaper deinking sludge)>
In the present invention, a papermaking sludge mainly composed of used newspaper deinking sludge is used as a raw material. “Paper sludge” refers to sludge separated from pulp fibers in a paper manufacturing process such as deinking. “Newspaper deinking sludge” refers to sludge separated from pulp fibers during the deinking process in the manufacturing process of newspaper deinking pulp (NDIP). Other sludge such as magazine deinking pulp (MDIP) Is preferably not contained as much as possible.

  “Paper sludge mainly composed of waste newspaper deinking sludge” means that the content of waste paper deinking sludge (based on solid content) in the paper sludge is 50% by mass or more, preferably 70% by mass or more, more preferably It means 90% by mass or more. The raw materials other than the used newspaper deinking sludge in the papermaking sludge are not particularly limited, and examples thereof include other papermaking sludges other than the newspaper deinking sludge. Specifically, sludge generated in other processes such as factory effluent and papermaking raw material preparation process, and other deinking sludges such as magazine deinking sludge can be mentioned.

  The raw material (waste paper) of magazine deinking sludge is mainly coated paper and contains a lot of calcium carbonate and kaolin. For this reason, when magazine deinking sludge is used as a raw material, a cement-like substance is easily generated as a foreign substance. Therefore, it is preferable to refrain from using magazine deinking sludge as a raw material for papermaking sludge and to use magazine deinking sludge as a main component. Further, as long as the desired effect is not affected, a small amount of chemicals such as a flocculant may be included in order to improve the dewaterability and granulation property of used newspaper deinking sludge.

  In recent years, since the papermaking used in the production of newsprint has become neutral papermaking, the content of calcium carbonate in the wastepaper deinking sludge is relatively high and the kaolin content tends to be relatively low. The ratio of calcium carbonate exceeds 70% by mass, and the proportion of kaolin is changed to less than 30% by mass. For this reason, if the main raw material of papermaking sludge is newspaper wastepaper deinking sludge, the amount of cementitious substances generated from calcium carbonate and kaolin derived from calcium carbonate is reduced, the resulting inorganic particles are hardened, and the whiteness is low. It is easy to improve the problem of thickening and the problem of thickening and solidifying when slurryed. Therefore, the calcium content ratio (based on solid content mass) in terms of oxide in papermaking sludge is usually 60% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more. On the other hand, the amount of kaolin in the paper sludge (based on solid content) is usually less than 40% by mass, preferably less than 30% by mass, more preferably less than 20% by mass, thereby suppressing the formation of hard metakaolin. Can do.

  In the production of newspaper deinked pulp, in order to continuously obtain newspaper deinked pulp of stable quality, there is a tendency for newspapers of selected quality to be used as raw materials. Tend to be stable. Therefore, the quality of inorganic particles can be stabilized by using waste newspaper deinking sludge as the main raw material.

  Furthermore, waste paper deinking sludge has a relatively low ash content in the newspaper used as a raw material, and because the newspaper ink contains an oil and fat component, etc., it generates a calorific value sufficient for self-combustion, usually 1600 cal / g or more. Have. Therefore, fuel such as heavy oil used for burning papermaking sludge can be reduced by promoting self-combustion.

<Dehydration process>
In the dehydration step, the papermaking sludge can be dehydrated to obtain a dehydrated product. By performing this process, excess water in the papermaking sludge can be removed, and the combustion process can be performed efficiently.

  The moisture content in the dehydrated product is not particularly limited, and is usually 30% by mass to 60% by mass, preferably 30% by mass to 50% by mass, and more preferably 35% by mass to 45% by mass. When the upper limit of moisture is higher than 60% by mass, the load in the combustion process may increase. On the other hand, when the lower limit of moisture is lower than 30% by mass, there is a problem that the outflow of inorganic particles to the waste liquid is increased, the yield of the obtained inorganic particles is decreased, and the wastewater treatment load is increased.

  The equipment used in the dehydration step is not particularly limited, and examples thereof include a known filter, a centrifuge, a dehydrator and a press such as a centrifugal dehydrator, a rotary screen, a screw press and a filter press. .

  The dehydration process may be performed in one stage or in multiple stages. If the dehydration process is performed in multiple stages, rapid dehydration may be avoided and the outflow of inorganic particles may be suppressed. Furthermore, the hardening of the dehydrated product due to rapid dehydration can be suppressed, and the flammability and stable self-combustibility of the papermaking sludge can be obtained.

<Crushing process>
The production method of the present invention can optionally include a crushing step of crushing the dehydrated product after the dehydration step. By performing this step, the dehydrate can be more evenly crushed into small particle sizes, and the combustion step can be performed more efficiently by keeping the particle size constant. In addition, the water content in the dehydrated product before and after the crushing process becomes substantially the same by crushing to a small particle size equally and keeping the particle size constant.

  The average particle size of the dehydrated product after crushing is not particularly limited, and is usually 2.5 mm or more and 12.5 mm or less, preferably 2.5 mm or more and 7.0 mm or less, more preferably 2.5 mm or more and 4.0 mm or less. . If the upper limit of the average particle diameter is higher than 12.5 mm, heating in the following steps may not be performed uniformly. On the other hand, if the lower limit of the average particle diameter is lower than 2.5 mm, heating in the following steps may be excessive. Here, the “average particle size” of the dehydrated product after crushing is obtained by sieving with sieves with different eye holes, measuring the mass of each sieved sample (hydrated material), and the total value of these measured values is It is the size of the eye opening of the sieve at a stage corresponding to 50% by mass of the whole, and is a value measured using a metal plate sieve based on JIS Z 8801-2: 2000.

  It does not specifically limit as a crushing method, A well-known method can be mentioned. For example, a crusher having a cylinder through which a dehydrated product (hydrated material) passes and a net member that rotates within the cylinder can be used. Moreover, as a crushing method, it can crush by rotating the said net | network material and making the hydrated substance currently passing through the cylinder collide with the surface of a net | network material.

<Combustion process>
The dehydrated product or the dehydrated product after being crushed or dried is sent to a combustion process, which is then burned. The dehydrated product containing moisture is dried and burned in the combustion process. An independent drying process may be provided as a pre-process of the combustion process.

  In the combustion process, an oxygen-containing gas is supplied into the combustion furnace, and exhaust gas having an oxygen concentration of 5% by volume or more and 10% by volume or less is discharged outside the combustion furnace to obtain a combustion product. In the present invention, since papermaking sludge mainly composed of waste newspaper deinking sludge is used as a starting material, this process can be performed under a milder temperature condition and atmosphere than the conventional method due to its synergistic effect. As a result, high-quality inorganic particles having high whiteness and few hard substances can be produced.

  Specifically, in this step, by supplying an oxygen-containing gas into the combustion furnace, the dry matter derived from the papermaking sludge in the combustion furnace is burned, and as a result, a desired combustion product (combustion ash) is obtained. be able to. It does not specifically limit as oxygen-containing gas, For example, high temperature air is mentioned. Further, the oxygen concentration in the oxygen-containing gas tends to be consumed and lowered by the burner as the combustion means, but the oxygen concentration in the exhaust gas is 5% by volume to 10% by volume, preferably 6% by volume to 9%. By performing the combustion treatment so as to be equal to or less than the volume%, the combustion treatment can be achieved while suppressing the decomposition of calcium carbonate.

  If the upper limit of the oxygen concentration in the exhaust gas is higher than 10% by volume, excessive oxygen supply causes excessive combustion, which causes the problem of generating hard substances and promoting decomposition of calcium carbonate. Moreover, the raw material in the furnace is discharged out of the system together with the gas, and the production efficiency may be reduced. Excessive combustion of waste newspaper deinking sludge occurs, and the formation of hard substances and black foreign matter is likely to occur. On the other hand, if the upper limit of the oxygen concentration in the exhaust gas is lower than 5% by volume, the combustion becomes insufficient and the organic matter is carbonized and oxidation does not proceed. Moreover, the concentration of carbon monoxide increases due to incomplete combustion, and the exhaust gas may not be used in the carbon dioxide blowing process.

  The temperature of the oxygen-containing gas is preferably 600 ° C. or lower, more preferably 400 ° C. or higher and 500 ° C. or lower. When the upper limit of temperature is higher than 600 ° C., calcium carbonate may be excessively decomposed. On the other hand, when the lower limit of the temperature is lower than 400 ° C., self-combustion may be impaired and combustion may be insufficient depending on the properties of the papermaking sludge. Note that the temperature of the oxygen-containing gas refers to a temperature measured using a thermocouple at the oxygen-containing gas inlet in the combustion furnace.

  By exhausting the exhaust gas having an oxygen concentration in the above range to the outside of the combustion furnace, it is possible to reuse the exhaust gas, preferably for the drying process or the carbon dioxide blowing process, and as a result, the manufacturing cost can be reduced. . Moreover, the decomposition | disassembly of the excessive calcium carbonate which was a problem conventionally can be suppressed, As a result, the burden of a carbon dioxide blowing process can be reduced. Furthermore, it is possible to suppress the thickening and solidification of the solution when it is slurried due to the generation of calcium oxide.

  The temperature of the exhaust gas is preferably 800 ° C. or lower, more preferably 640 ° C. or higher and 780 ° C. or lower, and even more preferably 680 ° C. or higher and 740 ° C. or lower. By setting the temperature of the exhaust gas within the above range, the combustion temperature during the combustion process becomes milder, and as a result, decomposition of calcium carbonate can be suppressed to a lower level. If the upper limit of the temperature is higher than 800 ° C, calcium carbonate may be excessively decomposed. On the other hand, if the lower limit of the temperature is lower than 640 ° C., combustion may be insufficient. The temperature of the exhaust gas refers to a temperature measured using a thermocouple at the exhaust gas outlet in the combustion furnace.

  When the internal heat kiln is adopted, the inner wall is stored by continuous operation, the raw material is likely to reach a temperature of 300 ° C. or higher, and even if the supply of heat by the burner is stopped, the papermaking sludge can be burned, which is even lower It can be manufactured at an energy cost.

  In addition, the dried product may be combusted so that the decomposition rate of calcium carbonate contained in the paper sludge to 30% by mass or less, preferably 26% by mass or less. By setting the decomposition rate within the above range, generation of hard substances due to combustion can be suppressed, and organic components can be burned gently.

  In the combustion process, it is preferable to burn while moving the dehydrated product, crushed product, dried product and the like after the dehydration step. In this case, combustion can be performed more uniformly and continuously by moving them so as to knead, and inorganic particles with higher whiteness can be obtained. Here, “moving” is not particularly limited, and means moving inside the combustion furnace by, for example, transfer. For example, the dehydrate is continuously transferred from the outside of the combustion furnace to the inside of the combustion furnace and from the inside of the combustion furnace to the outside of the combustion furnace by a moving means such as a lifter. Moreover, it does not specifically limit as a moving means, For example, well-known means like a lifter, a feeder, a screw feeder, and a conveyor can be mentioned.

  In the combustion process, it is preferable to burn the dehydrated product after the dehydration process while moving it in the direction opposite to the flow direction of the oxygen-containing gas. By moving these in the combustion furnace in the above-mentioned direction, these combustion can be performed more uniformly and continuously, and as a result, inorganic particles with higher whiteness can be produced. . Further, floating foreign substances such as black foreign substances are taken into the exhaust gas by wind force and removed together with the exhaust gas to the outside of the combustion furnace. As a result, the whiteness of the inorganic particles can be increased.

  The equipment used in the combustion process is not particularly limited. For example, a stalker furnace, a fluidized bed furnace, a cyclone furnace, a rotary kiln furnace, a cylindrical heat treatment furnace, a screw kiln furnace, a tower kiln furnace, a negative pressure combustion furnace, or a carbonization furnace. And a known kiln, and a rotary kiln furnace is preferable as the combustion furnace. In this case, the dried product can be burned more uniformly and continuously. In addition, it is possible to easily move the dried product as described above.

  Moreover, it does not specifically limit as a rotary kiln furnace, For example, well-known rotary kiln furnaces, such as a vertical rotary kiln furnace and a horizontal rotary kiln furnace, can be mentioned, A horizontal rotary kiln furnace is preferable. In this case, the crushed product and the dried product after the crushing process can be burned more uniformly and continuously.

  Similarly, for example, both an internal combustion type rotary kiln furnace and an external combustion type rotary kiln furnace can be mentioned, but an internal combustion type rotary kiln furnace is preferable. In this case, the oxygen consumption of the combustion furnace can be easily adjusted, and the self-combustion of the dry matter derived from the papermaking sludge can be directly adjusted. Further, the organic components contained in the papermaking sludge can be burned more gently. Furthermore, there is no need to control the combustion in detail, and the thermal efficiency is excellent. On the other hand, the oxygen-containing gas can be supplied and the exhaust gas discharged efficiently. Such equipment may comprise a member such as a heating jacket.

  Moreover, a combustion process can be performed on moderate temperature conditions by using the above raw materials. Specifically, the combustion temperature during the combustion process is usually lower than 600 ° C., preferably 300 ° C. or higher and 500 ° C. or lower.

  In particular, in the preferred combustion process according to the present invention, the first to third combustion treatments are used within the combustion temperature range, and the predetermined high calorific value components (acrylic organic matter and cellulose) are made in the first heat treatment. Heat treatment is removed from the sludge, thereby suppressing overcombustion and suppressing the formation of hard substances. Further, the regenerated particles obtained by pyrolyzing and gasifying acrylic organic substances and cellulose contained in the papermaking sludge in the first heat treatment and pyrolyzing and gasifying the styrenic organic substances remaining in the papermaking sludge in the second heat treatment. Therefore, it is possible to obtain regenerated particles uniformly and stably. In the third heat treatment, organic substances including residual carbon contained in the papermaking sludge are efficiently removed by heat treatment, and generation of hard substances caused by overcombustion is suppressed. Since the ignition temperature of the pyrolysis gas of cellulose is lower than the pyrolysis temperature of styrene, it is preferable that the cellulose is pyrolyzed and removed in the first heat treatment, and the styrene is pyrolyzed in the second heat treatment.

  If the upper limit of the combustion temperature is 600 ° C. or higher, excessive combustion occurs, and the production of calcium oxide due to excessive thermal decomposition of calcium carbonate is promoted, and an excessive amount of fuel is required, which may increase the manufacturing cost. It is also sufficient if the paper sludge has enough heat to start self-combustion. In addition, the generation of hard sintered material called gehlenite becomes obvious, and the papermaking equipment may be worn. On the other hand, if the lower limit of the combustion temperature is lower than 300 ° C., combustion may be insufficient. The combustion temperature and firing temperature in the present invention refer to the temperature obtained by measuring the outline of the combustion furnace with a known non-contact radiation thermometer in the external heating type rotary kiln furnace, and the internal heating type rotational kiln. In a kiln furnace, it means the temperature inside an internal combustion kiln furnace obtained by using a thermocouple. In addition, the combustion temperature of the internal heat kiln furnace may be adjusted by supplying heated air together with the supply gas into the combustion furnace. In the external heat kiln furnace, the combustion temperature should be adjusted by adjusting the temperature generated by the external heating equipment. Can do.

  When calorimetric analysis (TG / DTA) of papermaking sludge, there are three main components that burn at 200 ° C. or higher and lower than 300 ° C., 300 ° C. or higher and lower than 400 ° C., 400 ° C. or higher and lower than 500 ° C. In particular, the ratio of components that burn at 300 ° C. or higher and lower than 400 ° C. is large. From this, if the component of 300 ° C. or more and less than 400 ° C. is combusted, in particular, self-combustion, the temperature after the combustion rises to a temperature necessary for combusting the component combusted at 400 ° C. or more and less than 500 ° C. There is no need to use fuel to increase the burner temperature (combustion temperature). On the other hand, when the burner temperature is less than 300 ° C., the combustion of components that burn at 300 ° C. or more and less than 400 ° C. may be insufficient.

  The raw material input amount and combustion time are adjusted so that the unburned rate in the combustion product obtained in the combustion process is preferably 4% by mass to 12% by mass, more preferably 6% by mass to 9% by mass. May be. When the upper limit of the unburned rate is higher than 12% by mass, combustion may be insufficient and the whiteness of the inorganic particles may be reduced. On the other hand, if the lower limit of the unburned rate is lower than 4% by mass, the thermal decomposition of calcium carbonate becomes excessive, causing a fuel increase or solidification in the slurrying process, which may reduce the whiteness.

  The burning time in this step is not particularly limited, and is usually 5 minutes to 10 hours, preferably 1 hour to 8 hours. If the upper limit of the combustion time is longer than 10 hours, thermal decomposition of calcium carbonate may be excessive. On the other hand, if the lower limit of the combustion time is shorter than 5 minutes, combustion may be insufficient.

  The filling rate of the crushed material and the dried material after the crushing process in the facility in the combustion process is not particularly limited, and is usually 5% by volume or more and 70% by volume or less, preferably 10% by volume or more and 60% by volume or less. If the upper limit of the filling rate is higher than 70% by volume, combustion may not be performed uniformly. On the other hand, when the lower limit of the filling rate is lower than 5% by volume, the manufacturing cost may increase.

<Baking process>
In the firing step, the decomposition rate of calcium carbonate contained in the paper sludge into calcium oxide is less than 50% by mass, preferably 20% by mass to 45% by mass, more preferably 20% by mass to 30% by mass. Thus, the burned product after the burning step can be burned to obtain a burned product. By providing the firing step, the combustion product can be sufficiently fired, and as a result, inorganic particles with higher whiteness can be produced. When the upper limit of the decomposition rate is 50% by mass or more, inorganic particles having high whiteness cannot be easily and stably produced at a low energy cost. On the other hand, if the lower limit of the decomposition rate is lower than 20% by mass, firing may be insufficient.

  The equipment used in the firing process is not particularly limited, and publicly known equipment can be used as in the case of the drying process and the combustion process. The drying process, the combustion process, and the firing process may be performed using the same equipment or different equipment. If these steps are performed with the same equipment, the manufacturing cost may be reduced. Other process conditions in the firing process can be used by appropriately changing the process conditions of the combustion process as described above.

  Here, as the firing furnace, a rotary kiln furnace is preferable as in the combustion process. The combustion product obtained in the combustion process is controlled so that the decomposition rate of calcium carbonate to calcium oxide is less than 50% by adjusting the rotational speed of the rotary kiln, the temperature of the oxygen-containing gas to be supplied, the oxygen concentration, etc. However, firing can be performed more easily.

  The firing furnace may be an internal combustion type or an external combustion type as in the case of the combustion furnace, but the internal combustion type is preferable because the combustion product can be heated more uniformly and stably. . In this case, the heating method is not particularly limited and may be a known method, for example, supplying an oxygen-containing gas into the firing furnace and exhausting the exhaust gas out of the firing furnace. In this case, it is preferable to burn while moving in the direction opposite to the flow direction of the oxygen-containing gas, as in the combustion step. Firing can be performed more easily while controlling the decomposition rate of calcium carbonate into calcium oxide to be less than 50% by mass.

  The firing temperature is preferably 680 ° C. or higher and 750 ° C. or lower, more preferably 690 ° C. or higher and 730 ° C. or lower, and even more preferably 700 ° C. or higher and 730 ° C. or lower. When the upper limit of the firing temperature is higher than 750 ° C., the decomposition rate of calcium carbonate increases, and as a result, the slurry obtained in the slurrying step may thicken. On the other hand, if the lower limit of the firing temperature is lower than 680 ° C., firing may be insufficient and desired whiteness may not be obtained. Moreover, although decomposition of calcium carbonate occurs when the firing temperature is within the above range, the decomposition rate can be kept lower than 50% by mass, and as a result, thickening and solidification in the slurrying step can be suppressed. Tend.

  As an example of the firing step, as means for obtaining a fired product such that the decomposition rate of calcium carbonate into calcium oxide is less than 50% by mass, supply of an oxygen-containing gas and oxygen concentration of 5% by volume to 10% by volume are performed. Inorganic particles with higher whiteness can also be produced by using a series of facilities including a combustion step for exhaust gas discharge and a subsequent firing step.

  The firing time in the firing step is usually from 5 minutes to 10 hours, preferably from 1 hour to 8 hours. If the upper limit of the firing time is longer than 10 hours, thermal decomposition of calcium carbonate may be excessive. On the other hand, if the lower limit of the firing time is shorter than 5 minutes, firing may be insufficient. Further, exhaust gas may be generated in the firing process, but the exhaust gas obtained in this process may be reused in the drying process or the carbon dioxide blowing process.

<Slurry process>
In the slurrying step, the combustion product can be dispersed in water to obtain a slurry. By performing this step, calcium oxide contained in the combustion product is dispersed in water to obtain a calcium hydroxide solution, and the carbon dioxide blowing step can be performed more efficiently. The calcined product obtained through the combustion process and the calcining process as described above has a low decomposition rate of calcium carbonate and a small amount of foreign matter, thereby eliminating the problems of thickening and solidifying the slurry, which has been a problem in the past. And an emulsion slurry is obtained.

  The solvent for the slurry is not particularly limited, and water can be usually used. In addition, as long as the desired inorganic particles can be obtained, water may contain a small amount of a water-soluble organic solvent such as alcohol, and other components such as an electrolyte and a dispersant.

  The concentration of the fired product in the slurry is usually 2% by mass or more and 25% by mass or less, preferably 3% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 15% by mass or less. When the upper limit of the concentration is higher than 25% by mass, the viscosity of the slurry increases, and as a result, the carbonation reaction may not be performed sufficiently. On the other hand, if the lower limit of the concentration is lower than 2% by mass, the process efficiency may decrease due to a decrease in carbonation efficiency, a decrease in dehydration efficiency after carbonation, or the like.

<Crushing process>
The production method of the present invention may optionally be microparticulated through a pulverization step of pulverizing the fired product in the slurry after the slurrying step. The average particle size of the pulverized product is usually 0.5 μm or more and 10 μm or less, preferably 1 μm or more and 8 μm or less, more preferably 1 μm or more and 4 μm or less. If the upper limit of the average particle diameter is higher than 10 μm, there may be a problem that the paper surface is flattened as a foreign matter or as a foreign substance when used as a papermaking filler or pigment. On the other hand, if the lower limit of the average particle size is lower than 0.5 μm, the particles agglomerate and show a broad particle size distribution, or flow out in the papermaking system and yield decreases, and excessive energy is required for grinding. Can cause problems. The average particle diameter here is a volume average particle diameter (D50) measured using a particle size distribution diameter of a laser diffraction method (manufactured by Shimadzu Corporation, product name SA-LD-2200).

  It does not specifically limit as a grinding | pulverization method, For example, stirring a slurry with a serie mixer etc. is mentioned. Moreover, you may add a dispersing agent.

  The viscosity of the slurry is usually 100 mPa · s or more and 1100 mPa · s or less, preferably 250 mPa · s or more and 1050 mPa · s or less under the conditions of an atmospheric temperature of 20 ° C. and a rotor rotation speed of 60 rpm. If the upper limit of the viscosity is higher than 1100 mPa · s, transfer with a pump may be difficult. On the other hand, if the lower limit of the viscosity is lower than 100 mPa · s, the concentration is low, leading to a decrease in production efficiency.

<CO2 blowing process>
In the carbon dioxide blowing process, carbon dioxide is blown into the slurry, calcium carbonate is obtained from calcium oxide and calcium hydroxide derived from it (carbonation treatment), and the content of calcium carbonate in the inorganic particles is increased. High-quality inorganic particles with high degree can be obtained. Moreover, even when the coarse particles in the slurry contain a small amount of metakaolin or hydrous magnesium silicate, calcium carbonate obtained from calcium oxide or calcium hydroxide derived from it can adhere to and coat the surface. Also from the viewpoint, high-quality inorganic particles with high whiteness can be obtained.

  It does not specifically limit as a carbon dioxide blowing method, A well-known method can be mentioned. For example, carbon dioxide-containing gas is guided to the diffuser in the reaction vessel through the transport pipeline, and fine bubbles are generated from each of the diffuser groups in the slurry accommodated in the reaction vessel. Further, the slurry may be stirred with a stirring blade provided on the diffuser group.

  Carbon dioxide used in the carbon dioxide blowing step is not particularly limited, and examples thereof include commercially available carbon dioxide gas and mixed gas containing carbon dioxide. In this step, it is preferable to use the exhaust gas from the combustion step. The concentration of carbon dioxide in the exhaust gas is usually 5% by volume or more and 20% by volume or less, preferably 8% by volume or more and 20% by volume or less, more preferably 10% by volume or more and 20% by volume or less for the purpose of promoting the carbonation reaction. It is as follows. There is a tendency that a gas whose upper limit of concentration is higher than 20% by volume cannot be obtained as the capability of the combustion process. In order to obtain a carbon dioxide concentration of 20% or more, it is necessary to make a capital investment for separately installing equipment, and a desired combustion product may not be obtained in the combustion process. On the other hand, if the lower limit of the concentration is lower than 5% by volume, calcium carbonate may not be sufficiently precipitated in the carbon dioxide blowing step, and it takes a long time to complete the reaction, and the particle size cannot be controlled within the desired range. There is. In the present invention, since the exhaust gas obtained in the incineration process contains a large amount of carbon dioxide, the exhaust gas obtained in the combustion process can be reused in the drying process and the carbon dioxide blowing process. Also, dry ice can be used in combination as solid carbon dioxide.

  Completion of the carbonation reaction can also be confirmed by a decrease in the pH of the slurry solution. Specifically, assuming that the pH of the slurry at the end of the carbonation reaction after the blowing of carbon dioxide is the post-reaction pH, the post-reaction pH is usually 6.8 or more and 7.8 or less, preferably 6.9 or more. 7.7 or less.

  On the other hand, if the pH at the time when the pH fluctuation value per hour is 0.5 or less after the carbonation reaction is finished is the product pH, the product pH is usually from 9.3 to 10. 3 or less, preferably 9.4 or more and 10.2 or less.

  The viscosity of the slurry is usually 10 mPa · s or more and 200 mPa · s or less, preferably 10 mPa · s or more and 100 mPa · s or less, under the conditions of an atmospheric temperature of 20 ° C. and a rotor rotation speed of 60 rpm. If the upper limit of the viscosity is higher than 200 mPa · s, it may be difficult to transfer with a pump, and it may be difficult to pass through a screen, resulting in clogging. On the other hand, when the lower limit of the viscosity is lower than 10 mPa · s, the concentration is low, leading to a decrease in production efficiency.

  Next, the obtained inorganic particles are recovered, and desired inorganic particles are selectively recovered while removing highly soluble foreign matters in the solution. The recovery is not particularly limited, and can be usually performed by combining known methods. For example, the recovery can be performed by dehydrating the slurry in the same manner as the dehydration step. In addition, after collection, the inorganic particles may be redispersed or pulverized.

<Others>
Other process conditions such as temperature, pressure, time and equipment in each process are not particularly limited, and are appropriately set according to the raw materials used. Further, the number of steps in each step is not particularly limited, and may be performed in one step or in multiple steps. On the other hand, quantification and qualification of raw materials and products can be performed according to known methods such as NMR, IR, elemental analysis, and mass spectrum.

<Inorganic particles>
The inorganic particles according to the present invention use papermaking sludge mainly composed of newspaper waste ink deinking sludge as a raw material, and are manufactured through the manufacturing process as described above. Therefore, papermaking sludge in which various conventional components are mixed is used. Unlike the case of using as a raw material, the obtained inorganic particles have a small amount of foreign matter mixed therein. Specifically, according to the present invention, the calcium-based compound in the inorganic particles is preferably 70% by mass or more, more preferably 75% by mass or more in terms of calcium oxide. “Inorganic particles” mean particles recovered from the slurry after the carbon dioxide blowing step. The “calcium-based compound” may contain not only calcium carbonate but also a small amount of other components such as unreacted calcium oxide and calcium hydroxide as contamination.

  The whiteness of the inorganic particles is preferably 70% or more, more preferably 80% or more and 90% or less. This indicates that the whiteness of the inorganic particles is high. Therefore, inorganic particles can be suitably used in applications where a higher level of whiteness is required.

  The average particle diameter of the inorganic particles is preferably 1 μm to 12 μm, more preferably 1.5 μm to 10 μm, and even more preferably 2 μm to 6 μm. If the upper limit of the average particle diameter is higher than 12 μm, there may be a problem that the paper surface is flattened as a foreign matter or as a foreign substance when used as a papermaking filler or pigment. On the other hand, if the lower limit of the average particle diameter is lower than 1.0 μm, the particles may aggregate to occupy a broad particle size distribution, or may flow out in the papermaking system, resulting in a decrease in yield. The average particle diameter here is a volume average particle diameter (D50) measured using a particle size distribution diameter of a laser diffraction method (manufactured by Shimadzu Corporation, product name SA-LD-2200).

  The oil absorption of the inorganic particles is preferably 30 mL / 100 g or more and 100 mL / 100 g or less, more preferably 50 mL / 100 g or more and 100 mL / 100 g or less, and even more preferably 60 mL / 100 g or more and 100 mL / 100 g, according to JIS K 5101 method. It is as follows. This indicates that the inorganic particles have excellent oil absorption.

  The degree of wear of the inorganic particles is preferably 70 mg or more and 150 mg or less, more preferably 75 mg or more and 145 mg or less. This indicates that the inorganic particles have excellent wear properties.

  Therefore, the inorganic particles according to the present invention can be suitably used as a papermaking material such as a filler or a pigment. In addition, the inorganic particles according to the present invention contain calcium carbonate and an amorphous component derived from kaolin showing properties similar to those of calcined kaolin as a main component. For this reason, the inorganic particles are excellent in whiteness (opacity), smoothness, oil absorption, water repellency (drying), and the like, which are their characteristics.

  According to the present invention, inorganic particles having high whiteness can be easily and stably produced at a low energy cost as described above. Accordingly, papermaking sludge that has been conventionally treated as industrial waste can be suitably reused.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to these.

<Calcium content in paper sludge>
Calcium in terms of oxide obtained by elemental analysis of the residue obtained by ashing the sample in accordance with JIS P 8251 using an X-ray microanalyzer (manufactured by Horiba, Ltd., product name E-MAX · S-2150) It is a content ratio value.

<Moisture content>
This is a value obtained by the following formula, where the sample is left in a constant temperature dryer and the mass at which no change in mass is observed by holding at about 105 ° C. for 6 hours or longer is regarded as the mass after drying.
Moisture content (%) = (mass before drying−mass after drying) / mass before drying × 100

<Average particle size of crushed material>
Sieving was performed with sieves having different eye holes, and the mass of each sieve was measured. The average particle diameter is the size of the screen hole at the stage where the total value of the measured values corresponds to 50% by mass of the whole, and is measured using a metal plate sieve based on JIS Z8801-2: 2000. It is the value.

<Process temperature>
It is the value which measured the temperature in process equipment using a thermocouple etc.

<Decomposition rate of calcium carbonate>
The decomposition rate of calcium carbonate was measured using a measuring device (product name: TG / DTA6200, manufactured by SII Nano Technology), and the measurement conditions were as follows: (1) Temperature rising rate: 20 ° C./min (25 ° C. or higher and 1050 ° C. or lower) (2) Supply gas air (oxygen concentration about 5% by volume), (3) Value obtained at a supply gas flow rate of about 48 mL / min.

<Oxygen concentration>
It is the value which measured the oxygen concentration in an equipment main body using the automatic oxygen concentration measuring apparatus (Horiba Seisakusho make, product name ENDA-5250).

<Unburnt rate>
This is a value obtained by preheating the electric muffle furnace in advance to 600 ° C., putting the sample in a crucible and burning it completely in about 3 hours, and calculating the unburned amount from the weight change before and after combustion.

<Filling rate>
This is a value obtained by visually observing the inside of the facility and measuring the filling rate.

<Average particle diameter of pulverized product and inorganic particles>
It is the value which measured the volume average particle diameter (D50) using the particle size distribution diameter (Shimadzu Corporation make, product name SA-LD-2200) of a laser diffraction system.

<Viscosity>
It is a value measured using a B-type viscometer (product name TVM-10M, manufactured by Toki Sangyo Co., Ltd.) under the conditions of an atmospheric temperature of 20 ° C. and a rotor rotational speed of 60 rpm. The lower the viscosity (mPa · s), the better the dispersibility.

<Appearance of slurry>
The appearance of the slurry was visually observed to determine the presence or absence of thickening or solidification.

<CO2 concentration>
It is the value which measured the carbon dioxide concentration using the automatic carbon dioxide concentration measuring apparatus (Techjam company, brand name TESTO-535).

<PH>
The pH (post-reaction pH and product pH) is a value measured using an automatic pH measuring device (product name: PH450G, manufactured by Yokogawa Electric Corporation).

<Whiteness>
It is a value measured by using a color difference meter (manufactured by Tokyo Denshoku Co., Ltd., product name SP-80), grinding a powder sample with a mortar, and packing it in a glass cell.

<Oil absorption>
It was measured according to the kneading method of JIS K 5101. That is, 2 g of a sample dried at 105 ° C. or higher and 110 ° C. or lower for 2 hours was taken on a glass plate, and refined linseed oil (having an acid value of 4 or less) was dropped little by little from the burette to the center of the sample and kneaded with a spatula each time. . This dripping and kneading are repeated, and when the whole is first assembled into one rod shape, the end point is obtained, and the dripping amount of refined linseed oil at this point is obtained, and is a value calculated by the following formula.
Oil absorption = [linseed oil amount (mL) × 100] / sample (g)

<(Wire) wear degree>
It is a value measured with a plastic wire wear degree (manufactured by Nippon Filcon Co., Ltd., product name: wire wear tester, 3 hours), slurry concentration of 2% by weight.

<Calcium compound content>
The value calculated from the oxide-converted mass ratio of various elements contained in the combustion product using an elemental analyzer (X-ray microanalyzer (manufactured by Hitachi / Horiba, Ltd., product name E-MAX / S-3400N)) is there.

Example 1
(Paper sludge (raw material))
In the waste paper deinking process, a flocculant (product name: MX2101) is added to the foamy deinking flotation waste liquid that floats and separates from the used paper pulp by the floating sorting method (flotation method). The solid content in the waste liquid was agglomerated to obtain a papermaking sludge having a calcium content of 80% by mass in terms of calcium oxide as a raw material.

(Dehydration process)
Subsequently, the raw material was sequentially passed through a rotary screen (manufactured by Togoku Kogyo Co., Ltd.) and a screw press (manufactured by Hokurin Seisakusho Co., Ltd.) to recover a dehydrated product having a moisture content of 40% by mass.

(Crushing process)
Next, the dehydrated product was crushed using a crusher to obtain a crushed dehydrated product having an average particle size of 3.0 mm.

(Combustion process)
Next, the dried product after granulation was burned at a combustion temperature of 450 ° C., a combustion time of 4 hours, and a filling rate of 40% by volume using an internal combustion rotary kiln furnace (manufactured by Actley). In this combustion process, the dried product is supplied from the raw material charging port at a supply rate of 200 kg / hour using a hopper, and is fed into the raw material supply port of the rotary drum by a screw feeder as a raw material supply means, and moved in the rotary drum. And burned. At the time of combustion, the oxygen-containing gas is supplied into the combustion furnace while moving the dry matter in the combustion furnace in the direction opposite to the supply direction of the oxygen-containing gas and the discharge direction of the exhaust gas. A volume% exhaust gas was discharged out of the combustion furnace. The decomposition rate of calcium carbonate contained in the papermaking sludge into calcium oxide was 24% by mass, and the unburned rate in the combustion product was 7% by mass.

(Baking process)
Next, the combustion product was fired at a firing temperature of 720 ° C. and a firing time of 3 hours using a rotary kiln furnace (manufactured by Actley). After the firing step, the decomposition rate of calcium carbonate contained in the papermaking sludge into calcium oxide was 35% by mass.

(Slurry process)
Next, the combustion product was mixed with water, and then these were dispersed using a mixer (manufactured by Eirich Co.), and no thickening, solidification, or the like was confirmed for the appearance of the slurry having a concentration of 20% by mass.

(Crushing process)
Next, the combustion product slurry was pulverized using a bead mill type wet pulverizer (manufactured by Eirich) to obtain a combustion product having an average particle size of 2.5 μm. The slurry had a viscosity of 100 mPa · s.

(CO2 blowing process)
Next, exhaust gas containing carbon dioxide having a concentration of 15% by volume was introduced into the obtained slurry (post reaction pH 7.0, product pH 9.4), and the target inorganic substance having a calcium content of 79% by mass in terms of oxides was obtained. Particles were collected.

Example 2 to Example 16, Comparative Example 1 to Comparative Example 3 and Reference Example Example 2 to Example 16, Comparative Example 1 to Comparative Example 3 and Reference Example show the raw materials and process conditions as shown in Table 1 to Table 4. The procedure was the same as in Example 1 except that the change was made.

  The production steps of the production methods of Examples 2 to 16, Comparative Examples 1 to 3 and Reference Example are shown in Tables 1 to 4 together with the raw materials and products used.

  From Table 1 to Table 4, it can be seen that the inorganic particles obtained in Examples have higher whiteness than those of Comparative Examples and Reference Examples. It can also be seen that the examples are simple and stable production methods at a lower energy cost than the comparative examples. Therefore, according to the present invention, inorganic particles having high whiteness can be easily and stably produced at a low energy cost as described above.

  Therefore, according to the present invention, paper sludge that has been conventionally treated as industrial waste can be suitably reused. In particular, inorganic particles can be suitably used as a papermaking material such as a filler or a pigment.

S Papermaking sludge R Inorganic particles

Claims (7)

Using a papermaking sludge mainly composed of newspaper waste paper deinking sludge as a raw material, a method for producing inorganic particles including a dehydration step, a combustion step and a firing step,
In the combustion step, a combustion product is obtained by supplying an oxygen-containing gas and discharging an exhaust gas having an oxygen concentration of 5% by volume to 10% by volume, and in the firing step, oxidation of calcium carbonate contained in the papermaking sludge A method for producing inorganic particles, characterized in that a fired product is obtained so that the decomposition rate into calcium is less than 50% by mass.   The method for producing inorganic particles according to claim 1, wherein the combustion temperature is lower than 600 ° C. in the combustion step.   The method for producing inorganic particles according to claim 1 or 2, wherein in the combustion step, the dehydrated product after the dehydration step is burned while being moved in a direction opposite to the flow direction of the oxygen-containing gas.   The method for producing inorganic particles according to claim 1, wherein a rotary kiln furnace is used as the combustion furnace in the combustion step.   The method for producing inorganic particles according to any one of claims 1 to 4, wherein in the firing step, a firing temperature is 680 ° C or higher and 750 ° C or lower.   The method for producing inorganic particles according to any one of claims 1 to 5, wherein a rotary kiln furnace is used as the firing furnace in the firing step. An inorganic particle obtained by the production method according to any one of claims 1 to 6,
An inorganic particle having a calcium compound content of 70% by mass or more in terms of calcium oxide.

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