JP4329865B1 - Method for producing inorganic particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recycle papermaking sludge in large quantities as a papermaking material, a coating pigment or a papermaking filler, and has good dispersibility without any scale troubles when used as a papermaking filler and coating pigment. It is providing the manufacturing method of the inorganic particle which has.
A method for producing inorganic particles using papermaking sludge as a raw material, a heat treatment step of heat-treating the papermaking sludge, a heat-treated fired product suspension step of mixing the heat-treated fired product with water, and the fired product suspension A carbonation step in which carbon dioxide or a carbon dioxide-containing gas is brought into contact with the liquid, and the fired product suspension has a liquid temperature of 70 ° C. or less, and is in contact with the carbon dioxide or carbon dioxide-containing gas in the carbonation step The time until is 9 hours or less.
[Selection] Figure 1

Description

  The present invention relates to reuse of papermaking sludge, and relates to a method for producing inorganic particles having suitability as a coating pigment or papermaking filler.

  In recent years, it has been forced to reduce industrial waste from activities associated with production from the viewpoint of environmental conservation. Even in the paper industry, the treatment of paper sludge has become a problem. Papermaking sludge is a solid raw material that is mixed with wastewater without being used in fibers such as pulp, which is a papermaking material, organic matter mainly composed of starch and synthetic adhesive, and inorganic matter mainly composed of white pigment, Consists of lignin washed out in the pulping process, fine fibers, or waste paper-derived filler, printing ink adhering thereto, and excess sludge resulting from the biological wastewater treatment process. The main sources of paper sludge other than excess sludge generated in the biological wastewater treatment process are (1) those that flowed out through the papermaking wire during papermaking, and (2) contamination contamination removal and deinking in the wastepaper treatment process. Waste generated during the treatment and washing process, and (3) generated during the washing process in the pulping process. Waste water containing these solids is solidified by a solid content separation device using precipitation or flotation. The fraction is separated and recovered, and then subjected to biological treatment such as activated sludge treatment if necessary, and then discharged. The solid content separated and recovered by such treatment and the excess sludge generated by the final biological treatment of waste water become papermaking sludge.

  Furthermore, in recent years, with the increase in the used paper utilization rate, papermaking sludge derived from the used paper deinking process has been increasing. Among them, used newspapers and high-quality used papers contain less inorganic matter (inorganic pigments) in the used paper, so the amount of papermaking sludge generated is relatively small and the usage rate for recycled paper is high. There are many inorganic substances contained, and as a result, the amount of papermaking sludge generated increases. This contributes to the low utilization rate of used magazine paper compared to used newspaper and high-quality used paper. In the future, in order to further promote the use of waste paper, it will be necessary to improve the utilization rate of used magazine paper. However, if the utilization rate increases, a new problem arises in that the amount of papermaking sludge increases.

  In the past, paper sludge generated from paper mills was often landfilled as industrial waste, but recently, organic substances in sludge are burned in incinerators such as fluidized bed furnaces and stoker furnaces. At the same time, the volume of papermaking sludge is reduced. However, since papermaking sludge contains inorganic substances, there is a problem that a large amount of residue (incinerated ash) remains after combustion. At present, some of the incineration ash is mixed with cement, used as an antioxidant for iron making, and a soil conditioner, but most of it is landfilled as industrial waste. In the future, as waste paper is reused, the amount of papermaking sludge becomes extremely large, and waste disposal becomes increasingly difficult. In addition, processing costs that are rising year by year are expected to press the profits of the pulp and paper industry. For this reason, in the paper industry that recycles used paper, the problem of papermaking sludge is extremely serious and its effective use is strongly demanded as part of its countermeasures. For this reason, if paper sludge incineration ash (inorganic matter) can be reused as papermaking fillers and coating pigments as papermaking materials, not only industrial waste will be reduced, but also the utilization rate of wastepaper will be improved. It can be linked and environmental problems can be solved. However, these incineration ash has a problem that it cannot be used as it is as a papermaking material because of its low whiteness and high hardness.

  In order to solve the above-described problems, many paper sludge firing and combustion conditions have been studied. For example, as a method of performing carbonization treatment before the paper sludge combustion treatment, a method of carbonizing the paper sludge at about 350 to 700 ° C. and then combustion treatment at 650 to 800 ° C. (Patent Document 1), the paper sludge is subjected to low oxygen conditions. A method in which carbonization is performed at a temperature below 600 ° C. (preferably under anaerobic conditions) and then combustion treatment is performed at 600 to 800 ° C. (Patent Document 2). After pulverizing, the method of combusting organic components at 650-700 ° C (Patent Document 3), carbonizing paper sludge at 400-700 ° C in an oxygen-poor atmosphere, and then performing two-stage combustion treatment at 650 ° C or higher A method (Patent Document 4) and the like have been proposed.

  On the other hand, as a method for performing combustion treatment under specific conditions without carbonizing the papermaking sludge, the deinking sludge in the papermaking sludge is subjected to a primary combustion process of 700 ° C. or less and a combustion time of 10 seconds or less using a cyclone furnace. (Patent Document 5), and a method in which incinerated ash obtained by incinerating papermaking sludge at 800 ° C is burned again at 500 to 1100 ° C (Patent Document 6). ) Etc. have been proposed.

  In addition, all of the above methods involve dry oxidation (so-called combustion) of paper sludge. As a method of combining dry oxidation and wet oxidation into sludge incinerated ash, the paper sludge is wet oxidized at 200 to 800 ° C. Then, a method (Patent Document 7) is proposed in which a dry oxidation treatment is performed at 800 to 1100 ° C., or a wet oxidation treatment is performed after the dry oxidation treatment.

  However, since these methods are heat-treated at 550 ° C. or more to improve whiteness, decomposition of calcium carbonate in the papermaking sludge cannot be avoided, and when the fired product is mixed with water and slurried. Free calcium ions will be present in If these calcined products are used as they are as fillers for papermaking, the effects of the internal sizing agent are hindered by the influence of free calcium ions, or calcium sulfate is generated by reaction with sulfate bands in the papermaking process, causing scale trouble. Or a decrease in filler yield, which may affect operability and productivity. In addition, when used as a coating pigment, due to the influence of free calcium ions, problems such as an increase in the viscosity of the coating liquid and poor dispersion occur, and a high concentration coating liquid cannot be prepared, resulting in poor drying. Invitation may affect operability and productivity.

As a method of suppressing the influence of free calcium ions, a method of returning to calcium carbonate by blowing carbon dioxide into a suspension in which the fired product and water are suspended (carbonation) (Patent Documents 8, 9, 10, and 11) 12) has been proposed. However, it has been found that, when carbon dioxide is blown into the fired product suspension and the pH is lowered, it cannot be dispersed at a high concentration when used as a coating pigment.
JP 2005-161239 A Japanese Patent No. 3563707 JP 2001-262002 A JP 2004-262701 A Japanese Patent No. 3831719 JP-A-11-310732 Japanese Patent Laid-Open No. 2001-026727 JP-A-10-29818 Japanese National Patent Publication No. 10-505055 JP 2002-356629 A JP 2004-176208 A JP 2007-209887 A

  The present invention can recycle papermaking sludge in large quantities as a papermaking material coating pigment or papermaking filler, and when used as a papermaking filler or coating pigment, there is no scale trouble and good dispersibility. It is providing the manufacturing method of the inorganic particle which has this.

The present invention is a paper sludge to a manufacturing method of the inorganic particles as a raw material, suspended a heat treatment step of heat-treating the formulation paper sludge, obtained Ru baked product baked product suspension fired product was heat-treated by mixing with water a turbid liquefaction process comprises the carbonation step of contacting carbon dioxide or carbon dioxide-containing gas into該焼Narubutsu suspension該焼liquid temperature of Narubutsu suspension is at 70 ° C. or less, the carbonation step dioxide Alternatively, the time until contact with the carbon dioxide-containing gas is 9 hours or less , and a carbonation step is performed while measuring the conductivity of the baked product suspension, and the conductivity is once lowered to less than 1.0 ms / cm. After that, the reaction is terminated when it becomes a range of 1.0 to 2.0 ms / cm .
Prior Symbol carbonation step, the top has a reaction vessel bottom conical cylindrical, with a cylindrical semi-batch reaction vessel at a number of holes in the cone, carbon dioxide or carbon dioxide containing from the hole It is preferable that fine bubbles of the gas are generated by blowing the gas and the bubbles are brought into contact with the fired product suspension .
In the carbonation step, it is preferable to carry out the carbonation reaction for 2 hours or more while stirring the fired product suspension at a peripheral speed of 2.0 m / s or more.
The heat treatment includes a primary combustion step in which flammable organic components in the sludge are burned and removed in an excess air atmosphere at a sludge temperature of 650 ° C. or less, and flame retardant organic components in the sludge are burned and removed at a sludge temperature of 700 to 850 ° C. The secondary combustion process is preferably performed through at least two stages of combustion processes .

  According to the present invention, papermaking sludge, most of which is disposed of as industrial waste, is heat-treated and subjected to a suspension process and a carbonation process of the optimized heat-treated fired product, thereby making papermaking having good dispersibility. It is possible to manufacture coating pigments and paper-making fillers, which can be reused in large quantities.

  The method for producing inorganic particles using the papermaking sludge of the present invention as a raw material includes a heat treatment step for heat treating the paper sludge, a fired product suspension step for suspending a fired product obtained by mixing the heat-treated fired product with water, and a fired product. It is recovered as white inorganic particles through a carbonation step in which carbon dioxide or a carbon dioxide-containing gas is brought into contact with the suspension.

  Sludge is a raw material for inorganic particles according to the present invention. Raw material paper sludge is a combination of processes such as agglomeration, precipitation, concentration, and dewatering as a sludge recovery process for wastewater discharged from various processes in the paper mill such as pulping, paper manufacturing, and used paper recycling. Thus, the solids (various types of papermaking sludge) collected from each wastewater can be used alone or mixed and used as raw material sludge as appropriate. Of these, sludge from the used paper recycling process is subjected to agglomeration and dehydration treatment on the deinking waste liquid separated and discharged from the used paper pulp by pressurized flotation (flotation or flotation) and / or washing in the used paper deinking process. It is recommended to collect the solids in the deinking wastewater as deinking sludge. Also, when recovering sludge from waste paper raw materials with low whiteness, it is better to sufficiently perform deinking treatment and flotation treatment in the waste paper recycling process and remove ink particles including carbon black as much as possible. If necessary, a plurality of sludge pressurization and / or washing steps may be added. In addition, the deinking sludge collected from the wastepaper deinking process is separated into high-quality wastepaper, newspaper wastepaper, magazine (coated paper) wastepaper, etc. The deinked waste paper classified by waste paper type can be used alone or as a mixture and appropriately used as a raw material sludge.

The inorganic component (ash content) in the papermaking sludge is a main component in which kaolin (clay) and calcium carbonate derived from a papermaking filler or a coated paper pigment account for about 80 to 95% by weight of the whole inorganic component, A small amount of talc, titanium dioxide, etc. are mixed. The ratio of kaolin, which is the main component of the inorganic component, and calcium carbonate varies somewhat depending on the type of waste paper to be treated, but is generally in the range of 20/80 to 80/20 by weight ratio of kaolin / calcium carbonate. . Further, the calcium in the inorganic component (ash) (CaO equivalent), aluminum _(Al 2 _{O 3} basis) and silicon each content ratio (calcium / aluminum / silicon) of the (SiO ₂ equivalent), 13-73 / 12 -40 / 15-47.

  The ratio of the organic component and the inorganic component in the papermaking sludge varies somewhat depending on the type of waste paper to be treated and the degree of the deinking process. However, the weight ratio of the inorganic component / organic component is generally 30 / 70-80 / 20. Range.

  Apart from the sludge, RPF (Refused Paper & Plastic Fuel) mainly composed of low-grade waste paper that is difficult to reuse as papermaking material and plastic accompanying it can be used as a raw material.

  The method for heat-treating the papermaking sludge of the present invention is not particularly limited, but is preferably heat-treated at the following sludge temperature so as not to generate hard inorganic particles.

  In papermaking sludge, there are ink components such as carbon black, organic substances such as fibers and polymers, and inorganic particles such as calcium carbonate, kaolin, and talc. In order to improve the whiteness of the sludge fired product, it is necessary to remove carbon black which is a black ink component. To completely burn a single carbon black, at least an excess air (oxygen) atmosphere requires a combustion treatment time of at least 60 minutes at 600 ° C and 20 minutes at 850 ° C. Is good. However, if the temperature is too high, the inorganic particles in the sludge are sintered and changed, and the sludge fired product becomes hard, which tends to exhibit properties that are undesirable as a papermaking material.

  Hardening of the inorganic particles by the high temperature heat treatment is caused by a thermal alteration phenomenon of inorganic calcium carbonate and kaolin (clay) mainly contained in the following sludge. That is, calcium carbonate begins to be decarboxylated from around 525 ° C., and at least part of it begins to be decomposed into calcium oxide, and completely decomposes into calcium oxide at 900 ° C. Talc does not change its crystal structure up to 900 ° C. Titanium dioxide is stable even at 1000 ° C. and does not change at all. Kaolin is crystal water desorbed from around 400 ° C. and exists as amorphous metakaolin up to 500 to 850 ° C. This amorphous metakaolin is called calcined kaolin, and is an inorganic particle that is bulky, has good opacity, and is excellent in smoothness. When the temperature exceeds 900 ° C., γ-alumina and mullite are generated. Further, if amorphous metakaolin and calcium oxide decomposed from the above-mentioned calcium carbonate are present in a region slightly exceeding 850 ° C., gehlenite is generated by a chemical reaction. Appropriateness as a papermaking material is impaired by the production of hard sintered products such as gehlenite, γ-alumina, and mullite. In other words, when used as a paper filler or coating pigment prepared from a fired product mixed with such a hard sintered product, the manufacturing facilities such as paper making wire and coating blade are damaged. Will worsen the product quality.

  Therefore, it is preferable that the sludge temperature of the heat treatment step of the present invention does not exceed 850 ° C. at which a hard fired product is not generated. Further, if the maximum temperature is less than 600 ° C., it takes a very long processing time to improve the whiteness, which not only increases the energy cost but also increases the heat treatment apparatus, which is not preferable in practice. Accordingly, a preferable sludge temperature is preferably 600 ° C. or higher and 850 ° C. or lower, and more preferably 600 ° C. or higher and 800 ° C. or lower.

  Further, it is preferable that the sludge temperature during the heat treatment step is set to at least two stages so that all organic components contained in the papermaking sludge can be efficiently burned and removed, and inorganic particles suitable for the papermaking material can be obtained. . That is, the primary combustion process is set to combustion conditions with a sludge temperature of 650 ° C. or less in an excess air atmosphere, and the secondary combustion process is set to combustion conditions with a sludge temperature of 700 to 850 ° C. in an excess air atmosphere. The excess air atmosphere means an air atmosphere that does not cause incomplete combustion by giving a sufficient amount of oxygen to the combustion of organic components.

  First, in the primary combustion process, the combustion conditions are relatively low in an excess air atmosphere, so the easily combustible organic components in paper sludge are easily pyrolyzed and ignited starting from the functional group in the molecule, and carbonized. It disappears without burning. In the next secondary combustion step, high-temperature combustion conditions are obtained in an excess air atmosphere, so that the non-combustible organic components remaining without being burned in the primary combustion step are also surely burned and lost. In such a two-stage combustion process, it is reasonable to burn and remove easily combustible organic components without changing them into hard-to-burn carbides, and the entire organic components in paper sludge can be burned and removed efficiently in a short time. Yes. And since the obtained baked product does not contain unburned organic components such as soot and charcoal, it has a high whiteness and can be suitably used as a papermaking material.

  When the sludge temperature in the primary combustion process exceeds 650 ° C., as described above, the easily combustible organic component is carbonized and changed to a hardly combustible organic component, and the combustion efficiency is deteriorated. Further, if the combustion temperature in the primary combustion process is too low, even a readily combustible organic component is difficult to pyrolyze and ignite, and the combustion efficiency deteriorates. Therefore, the lower limit of the sludge temperature is preferably 250 ° C. Furthermore, the most suitable baking conditions of a primary combustion process are the range used as the sludge temperature of 350-630 degreeC.

  On the other hand, if the sludge temperature in the secondary combustion process is less than 700 ° C., it takes time to burn the non-combustible organic component, and the combustion efficiency deteriorates. On the contrary, when the sludge temperature becomes high temperature combustion exceeding 850 ° C., gehlenite is generated as described above, which is not preferable.

  In addition to performing the combustion process in the two stages consisting of the primary and secondary combustion processes described above, the combustion process as a transition section from the primary combustion process to the secondary combustion process is sandwiched, or the primary and secondary combustion processes. One or both of these can be further divided into a plurality of combustion steps having different combustion temperatures (sludge temperatures), so that there are three or more stages.

  The combustion treatment time in the primary combustion step is preferably at least 10 minutes and within 5 hours, and particularly preferably between 15 minutes and 2 hours. If it is less than 10 minutes, there is a risk that combustion and removal of the easily combustible organic components in the papermaking sludge may be insufficient, and if it exceeds 5 hours, heat energy is wasted. In any case, it is important to allow sufficient time for all flammable organic components to burn off. Further, the combustion treatment time in the secondary combustion process is preferably at least 10 minutes and within 5 hours, particularly preferably within 20 hours and within 2 hours. If it is less than 10 minutes, there is a risk that the combustion removal of the incombustible organic component in the paper sludge will be insufficient, and if it exceeds 5 hours, heat energy is wasted. And it is preferable to make the ratio of the combustion processing time of a primary combustion process and a secondary combustion process into the range of 1/10-10/1 in a primary combustion process / secondary combustion process.

  Although the heat treatment apparatus of the present invention is not particularly limited, FIG. 1 shows a configuration diagram of an example of the heat treatment apparatus suitably used. FIG. 1 is a configuration diagram of a heat treatment apparatus using an indirect heating type rotary kiln.

  There are no particular limitations on the firing furnace that is the main part of the heat treatment equipment. Box furnaces such as tunnel kilns, roller hearth kilns, pusher kilns, shuttle kilns, vertical cylindrical furnaces, rotary horizontal cylindrical furnaces, and screw-type horizontal furnaces A cylindrical furnace or the like can be used. As a method for supplying papermaking sludge, there are a batch method and a continuous method, but a continuous method capable of processing a large amount is preferable. It is preferable to use a rotary horizontal cylindrical furnace that has good heat transfer to the sludge and allows sludge in the heating furnace to come out to the surface more uniformly, or a screw type horizontal cylindrical furnace that can flow. A rotary kiln, which is a rotary horizontal cylindrical furnace that is as simple as possible from the viewpoint of maintenance of equipment and has a low driving energy, is preferable. As the shape of the rotary kiln firing chamber, a cylindrical shape, a hexagonal shape, or the like can be used. As rotary kilns, Takasago Industry Co., Ltd., externally heated continuous rotary kiln, Kurimoto Iron Works Co., Ltd., continuous externally heated rotary kiln IRK, Noritake Engineering Co., Ltd., indirectly heated continuous rotary kiln RKC-SG, Iwasa Machinery An externally heated rotary kiln manufactured by Co., Ltd. can be used.

  Therefore, a heat treatment apparatus using these firing furnaces that can be suitably used in the heat treatment apparatus used in the heat treatment step of the present invention is referred to as a cylindrical heat treatment apparatus because a horizontal or vertical cylinder is used.

  As shown in FIG. 1, the papermaking sludge S is put into a supply hopper 2 serving as a sludge supply port installed at one end in the cylinder axis direction of a continuous indirect heating type rotary kiln K1 which is an example of a cylindrical heat treatment apparatus. Then, it is supplied to the firing chamber 9 in the rotary kiln K1 through the screw feeder 10. As the sludge S passes through the firing chamber 9 of the rotary kiln K1, the organic components therein are burned. The burned papermaking sludge S is taken out of the furnace through a sludge discharge port 8 installed at the end opposite to the cylinder axis direction with respect to the sludge supply port, and sent to the next step.

  An exhaust fan 4 as an exhaust means is installed in the vicinity of the supply hopper 2. This exhaust fan forcibly exhausts the air in the rotary kiln K 1, and the air installed in the vicinity of the sludge discharge port 8 into the rotary kiln K 1. Air is sucked into the rotary kiln K1 from the supply port 3 as indicated by a broken line arrow A. In this way, the air flow indicated by the broken-line arrow A always occurs from the air supply port 3 toward the exhaust fan 4. This air flow becomes an unburned matter conveying air flow A described later. The air amount is controlled by controlling the exhaust amount of the exhaust fan 4. This amount of air is preferably controlled to be excessively sucked so that the inside of the furnace is in an excess (rich) oxygen atmosphere. Details of this will be described later.

  Heat for heating the inside of the rotary kiln K1 is mainly supplied from the indirect heating means 5. The inside of the baking chamber 9 is indirectly heated by this heat. Heat is also generated by burning combustible components in the sludge in the firing chamber 9 of the rotary kiln K1, but the heat supplied from the indirect heating means 5 is much larger than this heat. By controlling the indirect heating means 5, the temperature in the rotary kiln K1 is kept uniform. The indirect heating means 5 can be electrically heated, but heating with a combustion gas of kerosene or heavy oil or heating with a gas burner is economically preferable. Combustion exhaust gas discharged from existing incineration facilities can be used, and steam or the like can also be used. In the example shown in FIG. 1, the combustion exhaust gas is supplied as the indirect heating means 5 by the circulation blower 7.

  The organic components in the sludge are basically combusted in the firing chamber 9 of the rotary kiln K1, but a part of the unburned matter is put on the air flow A and taken out from the rotary kiln K1. Since the air flow forcedly exhausted through the exhaust fan 4 is hot air, it is preferable to use the hot air circulation fan 6 to be sent to a sludge dryer (not shown) and reused as heat energy.

  As described above, the heat treatment step of the present invention is performed by an indirect heating method capable of uniform temperature control in an excess air (oxygen) atmosphere. The indirect heating method is a method of heating the firing chamber (inside the furnace) 9, and the indirect heating type combustion furnace does not directly contact the combustion gas or hot air generated by the combustion gas and sludge. Is provided with a partition wall. As another heating method, there is a direct heating method in which a flame, combustion gas, or hot air is blown from one end of a cylinder. Since the direct heating type firing furnace is a method of heating from one end of the firing chamber (inside the furnace), the temperature differs greatly between the heating side and the opposite side, and the temperature of the entire firing chamber (inside the furnace) is accurately set. I can't control it. In contrast, the indirect heating method is not a method in which combustion gas or hot air is blown from one end of the cylinder as in the direct heating method, but a method in which the entire firing chamber (inside the furnace) is heated. Uniform temperature control is facilitated.

  In the heat treatment step of the present invention, the reason why the heat treatment apparatus is heat-treated in an excess air atmosphere, that is, in an oxygen-rich atmosphere is to efficiently burn organic substances contained in the papermaking sludge. The excess (rich) oxygen atmosphere here refers to supplying sufficient air (oxygen) necessary for combustion to the organic matter to be burned so that the residual oxygen concentration in the combustion exhaust gas is 5% or more. In this state, organic matter can be completely burned. It is also possible to adjust the sludge temperature according to the amount of air to be exhausted and the temperature of the air to be sucked.

  The amount of air sucked into the heat treatment apparatus is preferably equal to or greater than the theoretical oxygen amount necessary for burning organic components. However, since the combustion gas generated by burning the organic component is larger than the air amount corresponding to the theoretical oxygen amount, it is necessary to exhaust at least the generated combustion gas to make excess (rich) oxygenation. . Therefore, the amount of air to be sucked is controlled by adjusting the exhaust amount of the exhaust fan. The displacement is preferably 1.1 times or more of the theoretical air amount, more preferably 1.5 times or more, and even more preferably 2 times or more. However, if the amount of intake air is too large, the sludge temperature is lowered, which is not preferable in terms of energy cost. Further, the inhaled air may contain more carbon dioxide than usual. Note that when the oxygen amount in the heat treatment apparatus is less than the theoretical oxygen amount and becomes deficient, it becomes in an oxygen-poor state and the papermaking sludge is carbonized, so that unburned carbon remains in the sludge. In order to remove this unburned carbon, it is necessary to increase the heat treatment temperature or to treat for a long time. After all, it is difficult to obtain a desired sludge fired product. Therefore, it is absolutely necessary to avoid making the inside of the furnace poorly oxygenated.

  In the present invention, as shown in FIG. 1, the air supply port 3 is installed in the vicinity of the sludge discharge port 8, and the exhaust fan 4 that discharges the air flow A for conveying unburned matter is installed in the vicinity of the sludge supply port 2. In this case, the unburnt substance conveying air flow A can be generated in a direction opposite to the direction B in which the papermaking sludge S proceeds in the heat treatment apparatus.

  In this invention, the method of generating the unburned matter conveying air flow A in the direction opposite to the traveling direction B of the papermaking sludge S is called a countercurrent method. In this counterflow method, the unburned matter conveying air flow flows in the opposite direction to that sent to the sludge discharge port 8 side of the sludge fired product, so that the unburned product can be efficiently removed from the sludge fired product. The whiteness of the fired product can be improved, which is more preferable. In particular, unburned matter such as that generated during combustion in the first stage of the heat treatment process is difficult to be completely burned until later, and thus can be effectively removed by this counter-flowing unburned matter carrying air flow.

  Therefore, in order to increase the whiteness, the sludge temperature is set to a higher value, and 100% complete combustion is abandoned rather than 100% complete combustion of the unburned sludge. It is a feature of the present invention to obtain inorganic particles that have a high whiteness and do not contain a high-hardness composite by removing from the fired sludge. Here, the above-mentioned unburned substances are unburned organic substances, and most of them are unburned carbon particles, in other words, carbide particles. That is, it is a carbon black-like substance, and the carbon black is in the form of a fine powder having a size of 10 to 500 nm and a specific gravity of 1.8 to 1.9. In order to remove the unburned matter in the form of fine powder, the air in the furnace is exhausted by the exhaust fan 4 to generate an unburned matter transfer air flow A in the heat treatment apparatus and put it on the transfer air flow A. The unburned material is taken out. In this way, it is very preferable to forcibly exhaust the unburned-substance conveying air flow using an exhaust fan or the like. More preferably, air and / or oxygen is forcibly introduced in addition to such forced exhaust.

  The flow rate of the unburned product air flow by forced exhaust or the like is not particularly limited as long as it can remove the fine powdery unburned product, but when the flow rate is slow, the air flow flows to the supply hopper 2 side. Therefore, there is a concern that unburned matter cannot be removed well and is mixed in the sludge fired product, resulting in a decrease in whiteness. The flow rate of the unburned matter transporting air flow for transporting unburned matter containing carbon black having the above properties is preferably 0.4 m / min or more, more preferably 0.8 to 1.5 m / min or more, and particularly Preferably it is 1.5 m / min or more. However, if the flow rate of the air flow is too high, there is a greater possibility that the fired sludge will be mixed with the exhaust fan 4 side and the thermal efficiency will be reduced. The flow rate of the air flow was theoretically determined from the values of the exhaust fan, the air temperature, and the like, and the temperature in the heat treatment apparatus.

  Further, in the present invention, when the sludge combustion temperature in the heat treatment apparatus becomes high, by increasing the air inflow amount above a certain level, excess sludge combustion heat is discharged out of the heat treatment apparatus by the air flow. That is, the combustion temperature of the sludge S in the firing chamber 9 can be lowered by discharging the high-temperature combustion exhaust gas in the firing chamber 9 in the rotary kiln K1 to the outside of the rotary kiln K1 by the exhaust fan 4 on the sludge supply side. Therefore, in this heat treatment device, sludge combustion heat is discharged outside the heat treatment device by increasing the air inflow amount above a certain amount even when the temperature is high, contrary to general combustion control, that is, the rotary kiln's The temperature can be lowered by discharging heat from the main body cylinder part to the outside of the sludge supply side together with the air flow. That is, it is possible to perform control so as to avoid a rise above the set heat treatment temperature. Therefore, the unburned matter transport air flow A described above also serves as a sludge combustion heat exhaust air flow. Also in this point, the counterflow method has an exhaust port near the sludge supply port that discharges the airflow, so that the sludge combustion heat is heat treated without passing through the heat treatment device compared to the parallel flow method. Since it can discharge | emit out of an apparatus, control of sludge temperature can be made easy and it is more preferable.

  In addition, when the sludge combustion temperature is high, the combustion can be suppressed (carbonized) by controlling the air inflow amount, and the temperature can be controlled. However, in the present invention, heat treatment is performed for the purpose of firing the sludge with high whiteness. Since it is necessary to bring the inside of the apparatus into an oxygen-rich state and to sufficiently burn the sludge, it is not preferable to reduce the air inflow amount more than necessary. On the other hand, even when the sludge combustion temperature is low, a large amount of air can be introduced to increase the temperature. That is, in the present invention, the combustion temperature can be adjusted by the air inflow amount.

  Unburned matter collected and separated on the unburned matter conveying air stream A is collected and removed by a bag filter provided after the hot air circulation fan 6 or burned together with exhaust gas by an appropriate heating combustion device. It is good to let them.

  The hot air discharged from the heat treatment apparatus is preferably reused as a heat source such as a heat treatment apparatus or a drier by the heat circulation fan 6, so that the energy cost can be reduced.

  The time during which the sludge is heated to a constant temperature (heat treatment time) is not particularly limited, but there is a time during which the organic matter remaining in the firing chamber 9 is completely burned without being blown off by the air flow A for conveying the unburned air flow. Since it is necessary to hold, one hour or more is preferable. However, an unnecessarily long heat treatment time not only increases the energy cost but also increases the heat treatment apparatus. Therefore, the heat treatment time in the heat treatment step of the present invention is more preferably 1 to 5 hours.

  The furnace main body of the cylindrical heat treatment furnace used in the present invention is not limited to the horizontal cylindrical type as shown in FIG. 1, and a multi-partition structure or a multi-partition structure in which the interior is partitioned into a plurality of compartments by providing partitions and partition walls. A rotating drum having a multi-chamber structure can also be used. Examples of these rotary cylinders having a multi-divided structure or a multi-chamber multi-chamber structure are shown in FIGS. 2 to 4 are cross-sectional views (radial cross-sectional views) in a direction orthogonal to the longitudinal direction of the horizontally long rotating drum, and the vertical direction of the drawing coincides with the actual vertical direction. Yes.

  The rotating drum 1 shown in FIG. 2 (a) has a six-partitioned partition structure having a substantially hexagonal outer shell 11a. The partition 11b has a hexagonal section in the inside, and is divided into six compartments 12 having a regular triangular section. It is divided. FIG. 2 (b) shows the state of lamination and deposition of the papermaking sludge S in each compartment 12 when the rotating cylinder 1 to which the granulated material of the papermaking sludge S is rotated in the direction of the arrow d. Yes.

  The rotating cylinder 1 shown in FIG. 3A has a six-cylinder multi-cylinder structure in which six pipe parts 13 are bundled in a substantially annular shape by a donut plate-like pipe part fixing member 14. A central cavity portion 15 surrounded by the center portion 14 communicates in the axial direction through the center hole 14 a of the tube portion fixing member 14. FIG. 3 (b) shows the lamination and deposition state of the papermaking sludge S in each pipe section 13 when the rotating cylinder 1 supplied with the granulated material of the papermaking sludge S is rotated in the direction of the arrow d. Yes.

  The rotating drum 1 shown in FIG. 4A has a 12-partitioned partition structure, and the annular space between the inner cylinder part 16a and the outer cylinder part 16b forming a double pipe is radially divided by 12 partition walls 16c. Thus, twelve compartments 17 are formed, and the inside of the inner cylinder portion 16a forms a cavity portion 15. FIG. 4 (b) shows the state of lamination and deposition of the papermaking sludge S in each compartment 17 when the rotating cylinder 1 to which the granulated product of the papermaking sludge S is rotating in the direction of the arrow d. Yes.

  As illustrated in FIGS. 2 to 4, if the horizontally long rotating drum 1 has a multi-divided structure or a multi-cylinder multi-chamber structure, the supplied papermaking sludge S is distributed little by little to a plurality of compartments or torso parts. Therefore, as compared with a simple horizontal cylindrical rotary drum that forms a single furnace space as a whole, deposition of objects to be treated (paper sludge S, fired product) during the transfer process in the rotary drum 1 While the thickness is remarkably reduced, the stirring action of the object to be processed accompanying the rotation of the rotary drum 1 is strengthened, and the contact efficiency between air (oxygen) for burning organic components and the object to be processed is remarkably improved. As a result, the combustion efficiency of the organic component is dramatically increased, and high-quality fired products and inorganic particles can be obtained.

In addition, it is recommended that the number of divisions of the transfer path in such a multi-divided structure or a multi-cylinder multi-chamber structure is at least 6 or more in order to sufficiently exhibit the above-described effects. Further, the divided structure of the rotary drum is not limited to the structure illustrated in FIGS. 2 to 4, for example, a multi-partition partition such as an 18-part type, a 24-part type, or a 36-part type introduced in Japanese Patent Application No. 2006-252751 A multi-cylinder / multi-divided structure in which a partition or partition is provided for each tubular member of the multi-cylinder structure introduced in Japanese Patent Application No. 2006-279813, and the total number of divisions is 6 to 126. Various structures are possible, such as a rotating barrel structure. Further, in addition to the rotating drum and the structure in which the inside of the tubular member is divided into a plurality of compartments by a partition wall, a rotary stirring blade having a shape similar to the partition wall is provided in the rotating drum and the tubular member. By inserting in a non-fixed state, the inside of the rotary drum may be divided into a plurality of compartments, and the papermaking sludge S supplied into the rotary drum may be distributed to the plurality of compartments.

  In addition, by providing a lifter and a stirring member that can be driven to rotate in the kiln furnace, more sludge and oxygen are in uniform contact with each other, so that the organic matter is burned efficiently and the whiteness of the sludge burned product is improved. However, it is more preferable because the quality becomes uniform.

  By appropriately controlling the conditions such as heat treatment time, sludge temperature, air flow rate, flow rate, etc., the decomposition rate of the calcium carbonate component in the sludge is preferably more than 50%, more preferably 60% or more, and still more preferably Is preferably 70% or more. This is because in the present invention, the thermally decomposed calcium carbonate can be returned to calcium carbonate in the carbonation step described later, and therefore it is not necessary to suppress the decomposition of calcium carbonate in the heat treatment step. On the other hand, if the decomposition rate of calcium carbonate is less than 50%, the thermal decomposition of calcium carbonate that occurs from a temperature of about 525 ° C. lower than the combustion temperature while burning the organic components in the sludge at a sludge temperature of 600 ° C. or higher. Therefore, it becomes inefficient and is not suitable for efficiently obtaining a desired high whiteness sludge fired product.

  Since the calcium carbonate in the papermaking sludge is decomposed in the heat-treated calcined product, when it is used as it is as an aqueous suspension as a coating pigment or a papermaking filler, free calcium ions are eluted in the aqueous solution, and the slurry Since there are problems such as an increase in viscosity, poor dispersion, and reaction with other chemicals to cause scale trouble, it is necessary to suppress free calcium in the aqueous solution. In the present invention, in order to blow carbon dioxide or carbon dioxide-containing gas into the suspension, it is necessary to provide a baked product suspension process and a carbonation process in which the baked product and water are mixed.

  In order to suppress these free calcium, carbon dioxide or carbon dioxide-containing gas is blown into the calcined product suspension, and when performing carbonation to regenerate calcium carbonate, the calcined product is mixed with water followed by the calcined product suspension. It is important that the time until carbon dioxide or carbon dioxide-containing gas is blown in the carbonation step is 9 hours or less. Preferably it is 6 hours or less. Incidentally, when 9 hours are exceeded, free calcium is eluted only gradually, and therefore, when carbonation is carried out by blowing carbon dioxide or a carbon dioxide-containing gas, the carbonation reaction time becomes long. In addition, when the holding time is short, the elution of free calcium is small, so that the influence of free calcium may not be suppressed even if a carbonation reaction is performed. A more preferable time is 0.1 to 3 hours, and further preferably 0.25 to 2 hours.

  Moreover, the baked product suspension temperature at the time of performing a carbonation reaction needs to be 70 degrees C or less, Preferably it is 15-60 degreeC, More preferably, it is 25-50 degreeC. When the suspension temperature exceeds 70 ° C., it becomes difficult to elute free calcium, and even if the subsequent carbonation reaction is performed, the influence of free calcium cannot be suppressed, and the dispersibility of the slurry becomes poor. The suspension temperature is preferably lower, but if it is less than 15 ° C., a cooling device such as cooling the heat-treated calcined ash or water is required, which increases costs and increases productivity. Since it is inferior, it is not preferable. The suspension temperature referred to here is the temperature when the calcined product and water are mixed, and is the temperature up to the subsequent carbonation step, which is different from the reaction start temperature. In addition, when quick lime is digested with water, dehydration heat is generated, but in the suspension process of the present invention, there is almost no increase in temperature from the start to the end of the process, so the suspension temperature is set to 70 ° C. or less. be able to.

  Here, the solid content concentration of the baked product suspension can be adjusted to the range of 5 to 20% by mass to efficiently carry out the subsequent carbonation treatment, and the viscosity of the suspension is kept low, and the fluid stirring property is maintained. In addition, it is preferable for maintaining good liquid feeding properties. When the solid content concentration of the fired product suspension is less than 5% by mass, productivity is inferior, which is not preferable. On the other hand, when the content is higher than 20%, the viscosity of the baked product suspension becomes high, so that the stirring power is increased and the operability is inferior. The suspension may be stirred at a peripheral speed at which the fired product does not settle, and may be about 2.0 to 3.0 m / s.

In addition to the calcined sludge of the present invention, calcium oxide (CaO: quick lime) or calcium hydroxide [Ca (OH) ₂ : slaked lime] is separately added to the calcined product suspension as necessary. In this case, calcium oxide and calcium hydroxide can be mixed with calcium hydroxide [Ca (OH), which is a form after dehydration. ₂ : Slaked lime] can be added up to 100 parts by weight (sludge: calcium hydroxide = 50: 50) with respect to 100 parts by weight of the burned sludge. Although calcium hydroxide can be added in excess of 100 parts by weight, it is not preferable because the blending ratio of the sludge fired product in the slaked suspension is reduced and sludge use does not proceed.

In the present invention, by performing the carbonation step after the baked product suspension step, the calcium generated by the decomposition is regenerated and converted to calcium carbonate (CaCO ₃ ), and the increase in the viscosity of the inorganic particle slurry is suppressed. It is possible to suppress the occurrence of poor dispersion. Moreover, problems such as scale trouble caused by reaction with other chemicals can be eliminated. Regenerated calcium carbonate can be confirmed using X-ray diffraction, and depending on the decomposition rate of calcium carbonate by heat treatment, it is preferable that 80% or more is regenerated with respect to calcium carbonate before heat treatment, More preferably, it is 90% or more.

  The carbonation step is a step of blowing carbon dioxide gas or carbon dioxide-containing gas into the fired product suspension. The gas used for carbonation is industrially preferably a carbon dioxide-containing gas, for example, sludge calcined exhaust gas, limestone calcined exhaust gas, lime calcined exhaust gas, waste incineration exhaust gas, power generation boiler exhaust gas, or causticized carbon dioxide used in pulp manufacturing processes. An exhaust gas discharged from a calcium calcining kiln or the like can be used after dust removal by an appropriate means. In particular, the use of exhaust gas from a sludge firing facility is preferable because the amount of carbon dioxide released into the atmosphere can be suppressed and the manufacturing cost can be reduced. The carbon dioxide concentration of the carbon dioxide gas to be used is not particularly limited, but preferably 5 to 40% by volume, more preferably 7 to 35% by volume of carbon dioxide-containing gas is used. When the carbon dioxide gas concentration is low, the carbonation reaction can be performed rapidly by reducing the solid content concentration of the fired product suspension. For example, when the carbon dioxide gas concentration is 8%, the baked product suspension solid content is preferably about 8%.

  Carbon dioxide gas or carbon dioxide-containing gas is blown into the fired product suspension so as to be a rate of 0.5 to 15 L / min per 1 kg of the fired product as carbon dioxide gas. If the amount of carbon dioxide introduced is less than 0.5 L / min, the productivity is inferior, and an amount exceeding 15 L / min can be adopted, but it is commensurate with the power load necessary to increase the amount of use. The effect cannot be expected.

The reaction temperature in the carbonation step is 70 ° C. or less, preferably 15 to 60 ° C., and more preferably 25 to 50 ° C. In the carbonation reaction, free calcium in water and carbon dioxide react to generate calcium carbonate. However, when the reaction temperature exceeds 70 ° C., carbon dioxide is difficult to dissolve in water, the carbon dioxide gas used for the reaction is insufficient, the reaction time is prolonged, and the properties of the inorganic particles are also affected. May cause problems that cannot be dispersed at a high concentration. Also, if the reaction temperature is low, the amount of carbon dioxide gas used in the reaction increases. However, in order to reduce the reaction temperature to less than 15 ° C., it is necessary to cool the exhaust gas and the like. Absent. The temperature of carbon dioxide gas and exhaust gas used for the carbonation reaction is preferably 70 ° C. or lower and 50 ° C. or lower in advance.

  The suspension temperature and the carbonation temperature are preferably the same. This is because when the suspension temperature is higher than the carbonation temperature, the suspension needs to be cooled, and when the suspension temperature is lower, it is necessary to heat the suspension, which causes unnecessary energy costs.

Incidentally, carbonation reaction end point pH, but also can be determined in either of the conductivity, it determined by conductivity. This is because calcium carbonate regeneration of inorganic particles is difficult to determine the reaction end point at pH using hydroxide ions as an indicator, as in light calcium carbonate production, and the conductivity using metal ions as an indicator is easier to determine. . In addition, the conductivity is temporarily lowered to less than 1.0 ms / cm and again becomes 1.0 ms / cm or more, and the conductivity at the end of the reaction is 1.0 to 2.0 ms / cm.

  As a reaction tank of the carbonation step of the present invention, a semi-batch type reaction tank such as a cylindrical type or a cylindrical cone type that is conical only in the lower part is used, and carbon dioxide or carbon dioxide-containing gas is introduced from the lower part of the reaction tank. Blowing is preferred from the viewpoint of efficiency. In addition, by making many holes in the lower cone of the semi-batch reaction tank, carbon dioxide gas becomes fine bubbles, and these fine bubbles come into contact with the baked product suspension, so that they react efficiently and uniformly. This is preferable.

  In addition, in order to improve the contact between the calcined product and carbon dioxide or carbon dioxide-containing gas, the reaction vessel is equipped with a stirrer, and by performing carbonation while stirring, the carbon dioxide gas becomes fine, and the calcined product The contact with the suspension is improved, and the reaction is carried out uniformly and efficiently. The stirring peripheral speed of the stirrer is preferably 2.0 m / s or more, and more preferably 2.5 m / s or more. Here, the stirrer is not particularly limited as long as the peripheral speed is 2.0 m / s or more, and a uniaxial or biaxial tank agitator, a coreless mixer, a high-speed agitating disperser, or the like can be used. Furthermore, the shear force of the suspension can be increased by installing a baffle plate in the reaction vessel.

  The shape of the regenerated calcium carbonate component contained in the inorganic particles is not particularly limited. In addition, seed crystals can be added to obtain crystals having a desired shape during the carbonation step, and can be formed into rice grains, spindles, colloids, needles, cubes, plates, and the like.

  In addition, the inorganic particles after the carbonation treatment of the present invention are fine particles of primary calcium carbonate produced by the carbonation treatment to form secondary particles (aggregated particles), which are suitable for papermaking fillers. There may be a diameter. In such a case, this suspension can be used as it is by blending it with a papermaking raw material such as pulp as a papermaking filler.

  When using the inorganic particle slurry (slurry after carbonation) of the present invention as a coating pigment, a dehydration step of dehydrating the composition inorganic particle slurry after the carbonation step to obtain a dehydrated composition, and the dehydration step It is preferable to include a dispersion step in which moisture is added to the dehydrated composition obtained by the above to obtain a slurry-like dispersion composition, and a pulverization step to adjust the particle size to a desired value.

  The dehydration step can be performed by operations such as filtration, centrifugation, pressure dehydration, and pressing. As a suitable dehydrating apparatus, there is a press filtration apparatus called a filter press, and a dehydrated cake of a carbonized product can be obtained. The dispersion process may be any process as long as water is added to the dehydrated composition obtained by the dehydration process to form a slurry-like dispersion composition. It is preferable to add a dispersing agent in addition to moisture during the dispersion step because inorganic particles made from papermaking sludge can be dispersed well, improving the quality as a papermaking material and facilitating handling. As the dispersing agent, for example, a general dispersing agent used in the manufacture of a papermaking material such as a synthetic polymer dispersing agent such as sodium polyacrylate can be used.

  In the present invention, the pulverization step may be provided after the dispersion step. By carrying out the pulverization treatment, the particle diameter of the regenerated inorganic particles can be reduced, and the smoothness is improved, which is preferable. As a pulverizer used in the pulverization step, a wet pulverizer such as a sand mill, a bead mill, a wet ball mill, a vibration mill, a stirring tank mill, a flow tube mill, or a coball mill can be used. Moreover, you may grind | pulverize, blowing in a carbon dioxide.

  The size (particle diameter) of the inorganic particles of the present invention is preferably 0.1 to 20 μm, and particularly preferably 0.3 to 5 μm, as an average particle diameter by laser diffraction particle size distribution measurement. .

  This average particle size should be a balanced particle size in terms of operation and quality so as to obtain a quality excellent in opacity, whiteness, smoothness, and printability when finished as a paper product as a coating pigment. It ’s the one you ’ve chosen. Therefore, by setting the average particle size of the inorganic pigment within the range of the particle size, it can be handled in the same manner as a conventional coating pigment in operation, and the quality of the coated paper coated with inorganic particles Thus, it is possible to develop a quality substantially equivalent to that of a conventional coating pigment.

  Incidentally, when the inorganic particles become fine particles with an average particle size of less than 0.1 μm, it is effective for improving the opacity, whiteness, smoothness, etc., but on the other hand, the coating layer strength is expressed. Therefore, it is not preferable because a very large amount of adhesive is required. On the other hand, when the average particle diameter of the inorganic particles is larger than 20 μm, the smoothness and gloss of the coated paper product are lowered, and as a result, the printability is also lowered.

  It is preferable to provide a dispersion step and a pulverization step after the dehydration step in order to make the inorganic particles have the desired particle size, but when the average particle size of the regenerated pigment after the dispersion treatment falls within the range of the particle size described above Naturally, the dispersion of the inorganic particles after the dispersion treatment may be used as it is as a coating pigment without performing the pulverization step.

  Further, in the dispersion step, the inorganic particle dehydration composition is mixed with the calcium carbonate slurry, and is pulverized as a mixed slurry using a wet pulverizer, so that the quality is better than calcium carbonate and moreover than the calcium carbonate slurry. The grinding time can be shortened and a highly concentrated slurry can be prepared. The ratio between the inorganic particles and calcium carbonate can be adjusted according to the white paper quality of the coated paper and is not particularly limited.

  In addition, since it may add the process of dehydration-> drying-> granulation before using for the heat processing mentioned above, it explains in full detail below.

  Examples of a method for recovering raw material sludge from wastewater of various processes as a solid content include methods such as filtration, centrifugal separation, pressure dehydration, and pressing, and a papermaking sludge having a required water content is obtained by combining the various methods. As a suitable filtration device, there is a filtration device called a rotary screen, and as a dehydrating device, there is a pressurizing / squeezing dewatering device called a screw press. These filtration devices and squeezing devices can be used alone or in appropriate combination. Moreover, as a centrifugal dehydrator, there is a decanter type centrifugal dehydrator.

  Since the solid content concentration in the sludge varies depending on the capacity of the dehydrator, it is usually 5 to 60% by mass. However, a solid content concentration exceeding 60% by mass can be achieved with the current dehydrator or concentrator capacity. difficult.

  In the present invention, the solid content concentration of the paper sludge used in the heat treatment step is not particularly limited, but from the viewpoint of reducing the energy cost during the heat treatment step, and from the viewpoint of reducing the heat treatment apparatus, the solid content of the paper sludge. Since the concentration is preferably as high as possible, it should be 70% or more. However, although only the above-mentioned dehydration step varies depending on the capacity of the dehydrator, the solid content concentration is about 5 to 60% by mass, and therefore it is recommended to further increase the solid content concentration by drying treatment.

  In order to increase the solid content concentration of the papermaking sludge, it is preferable to provide a drying step for drying the papermaking sludge before the heat treatment step. The dryer used in the drying process is not particularly limited, and a direct heating rotary kiln, an indirect heating rotary kiln, an air flow dryer, a fluidized bed dryer, an oscillating fluid dryer, a rotary / aeration rotary dryer (cyclone), or the like is used. be able to. Moreover, as a heat source of these dryers, it is possible to reduce energy cost by using the exhaust heat of the baking process mentioned later.

The temperature of the drying process should be 600 ° C or less in order to prevent paper sludge from burning and carbonization in equipment that uses hot air, such as an air dryer or rotary / aeration rotary dryer. Is preferable, and it is especially preferable to set it as 250 degrees C or less. If the hot air temperature is too high, the papermaking sludge will ignite, and if the drying conditions at that time are not appropriate, there is a concern that the readily combustible organic component will carbonize and change to incombustibility. Further, in the drying step, it is preferable to break the papermaking sludge finely in order to improve the drying efficiency, and it is preferable to forcibly break the papermaking sludge with a stirrer or a mechanical roll and dry it.

  The papermaking sludge used in the heat treatment step of the present invention is not particularly limited as long as it has a size and shape that can contact oxygen when the sludge is laminated in the heat treatment apparatus. However, if the papermaking sludge is made fine and uniform in size, the sludge is laminated like a close packing, and oxygen does not enter into the lamination, so the burning of organic matter, especially carbon, becomes insufficient and the whiteness improves There is a possibility not to. Further, if the papermaking sludge is too large, carbon cannot be burned completely, and unburned carbon may remain in the center of the papermaking sludge block. From the above, it is preferable to use the papermaking sludge used in the present invention having a length or diameter of 2 mm or more and 30 mm or less. As the shape, a columnar shape, a spherical shape, an ellipse, a triangle, other polygonal shapes, or those having irregularities can be used.

  In order to form the papermaking sludge in the desired size and shape, it is possible to perform granulation. The method of granulating sludge is a method using a compression molding machine such as a briquette machine or a roller compactor, a method using a semi-dry granulator such as a disk pelleter, a rolling granulation method, a stirring granulation method, an extrusion molding. There are laws.

  The paper using the inorganic particles obtained in the present invention as a filler can impart opacity and bulkiness, as long as it is a paper internally containing the inorganic particles of the present invention as in the case of conventional fillers. There is no limitation. In addition, paper types include recording paper such as wrapping paper, paper containers, inkjet paper, and PPC paper, newsprint paper, high-quality paper, medium-quality paper, various coating base papers, wallpaper, fiberboard, photographic base paper, impregnation Examples include base paper and flame retardant paper.

  Further, the inorganic particles obtained in the present invention, when used as a pigment, have excellent properties such as smoothness, coverage, opacity, and ink setting properties, and can be used in the same manner as conventional pigments. It is preferable to contain it in the coating layer provided on the base paper, since the effect of improving smoothness, covering property, opacity, and ink setting property can be expressed more. Examples of the coated paper include printing paper, publishing paper, book paper, white board paper, kraft paper, inkjet paper, and thermal paper.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In addition, unless otherwise indicated, the part and% in an example show a mass part and the mass%, respectively. The measurement method and evaluation for each item are as follows.

[Measurement of average particle size of inorganic particles by laser diffraction scattering method]
Using Nikkiso Co., Ltd. Microtrac HRAX-100, the particle size distribution of the inorganic particles was measured, and the particle size at a point corresponding to a cumulative mass of 50% was determined.

[Method for measuring pH of slurry]
Using a Lacom Tester pH meter (pHScanWPBN type: manufactured by ASONE), the pH electrode was directly immersed in various dispersions to measure the pH of the pigment dispersion. In addition, about the pH meter used for pH measurement, after performing pH calibration using NIST reference | standard calibration liquid (pH 6.86 and two types of pH 9.18), pH measurement was performed.

[Measurement of whiteness of sludge burned product and inorganic particles]
About 10 g of the sample (dried product) was ground until coarse particles disappeared in a mortar, and then powdered using a powder sample molding machine (Rigaku Denki Kogyo Co., Ltd .: Cat9302 / 30) at a pressure of 100 kN for 30 seconds. A body sample was molded. The whiteness of the molded sample was measured according to JIS P8148 (2001) using a spectral whiteness colorimeter (manufactured by Suga Test Instruments Co., Ltd .: SC-10WP type).

[Calcium carbonate decomposition rate after combustion treatment]
As evaluations other than the items listed in Table 1, for each example, the decomposition rate of calcium carbonate after heat treatment was determined by the following steps (1) to (6). The amount of residual calcium carbonate in the medium was determined and evaluated.

(1) Preparation of calibration curve of calcite calcium carbonate Zinc oxide (made by Kishida Chemical Co., Ltd .: reagent grade) is used as an internal standard substance for calcium carbonate having a crystal structure of calcite (Okutama Kogyo Co., Ltd .: Tamapearl 222H). They were mixed so that the weight ratio was 1: 5, 1: 1, 5: 1. Next, each mixture was sufficiently ground using a mortar and then measured using an X-ray diffractometer (manufactured by Max Science: MO3XHF) under conditions of 40 kV, 20 mA, and a diffraction angle measurement range of 5 to 50 degrees. Then, based on the X-ray diffraction 100% peak areas of calcium calcite and zinc oxide, a calibration curve for calcium calcite was prepared.

(2) Preparation of calibration curve of aragonite calcium carbonate Aragonite calcium carbonate was prepared in the same manner as the calibration curve of calcite calcium carbonate, except that calcium carbonate having an aragonite crystal structure (Okutama Kogyo Co., Ltd .: Tama Pearl 123) was used. A calibration curve was created.

(3) Quantification of calcium carbonate in papermaking sludge before combustion treatment Weighed zinc oxide (reagent grade above) was added and mixed to the weighed absolute dry papermaking sludge. Next, the mixture was sufficiently ground using a mortar, and then measured using an X-ray diffractometer (MO3XHF, supra) at 40 kV, 20 mA, a diffraction angle measurement range of 5 to 50 degrees, Obtain 100% peak area of X-ray diffraction of calcium calcite carbonate and aragonite calcium carbonate with respect to zinc oxide, and calculate the amount of calcium carbonate (g) contained in 1 g of papermaking sludge based on the calibration curve of each calcium carbonate described above. did.

(4) Measurement of ash content of papermaking sludge Weighed absolute dry papermaking sludge in a muffle furnace at 350 ° C. for 30 minutes, and weighed the obtained sludge fired product. Measured as ash content (%).
Ash content (%) = (weight of sludge burned product / weight of paper drying sludge) × 100

(5) Quantitative determination of calcium carbonate in the burned sludge The weighed sludge burned product was added and mixed with a weighed zinc oxide (reagent special grade mentioned above). Next, the mixture was sufficiently ground using a mortar, and then measured using an X-ray diffractometer (MO3XHF, supra) at 40 kV, 20 mA, a diffraction angle measurement range of 5 to 50 degrees, Obtain 100% peak area of X-ray diffraction of calcium calcite carbonate and aragonite calcium carbonate with respect to zinc oxide, and based on the calibration curve of each calcium carbonate described above, the amount of calcium carbonate (g) contained in 1 g of the sludge fired product Calculated.

(6) Decomposition rate of calcium carbonate after combustion treatment The amount of calcium carbonate (g) in 1 g of the sludge fired product is A, the amount of calcium carbonate (g) in 1 g of papermaking sludge is B, and the ash content (%) is C. The decomposition rate of calcium carbonate after the combustion treatment was calculated by the following equation.
Calcium carbonate decomposition rate (%) = 100− [A × (C / 100)] ÷ B × 100

Example 1
[Sludge]
Paper sludge consisting of solids and surplus sludges such as activated sludges obtained by separating wastewater from paper mills with paper and paperboard machines and coating machines, as well as paper mills with deinking pulping equipment, using a wastewater treatment clarifier The raw material was dehydrated to a solid content of about 50% using a dehydrator. This papermaking sludge had an inorganic content of 65% and its composition was 55% calcium carbonate, 40% kaolin and 5% talc.

[Drying and granulating process]
The dehydrated papermaking sludge was dried to a solid content of about 75% using a rotary dryer, and then granulated and formed into pellets having a diameter of about 12 mm and a length of about 15 mm using a disk pelleter.

[Combustion process]
The combustion treatment was performed using an externally heated rotary kiln furnace (externally heated rotary kiln made by Takasago Industries, heating part: diameter of rotating drum 300 mm, length 2400 mm). Raw material papermaking sludge granules were fed at a rate of 10 kg / h. The sludge temperature is 750 ° C., the heated part is retained for 2.5 hours (kiln inclination: 1%, rotation speed: 1.0 rpm), and the combustion exhaust gas is discharged from the fired product discharge side at 20 Nm ³ / h, The same amount of outside air as the exhaust gas discharged from the exhaust port due to the decompression action was sucked from the air supply port, and the entire inside of the rotating drum was always maintained in an excess air atmosphere to obtain a fired product.

  As a result of examining the composition of the fired product obtained by this combustion treatment by X-ray diffraction, the hard high-temperature sintered product (Gerenite) was not included, and the calcium carbonate contained in the papermaking sludge before the combustion treatment was 55% was decomposed. Moreover, in the components other than calcium carbonate, all of kaolin was changed to an amorphous substance, but talc was not changed at all. Part of unburned material was found in the fired product. The whiteness of the fired product was 72%.

[Suspension / Carbonation process]
Next, the fired product obtained by the combustion treatment is mixed with warm water of 65 ° C. using a suspension tank (dissolving tank), and stirred for 8 hours while maintaining the temperature of the suspension tank at 65 ° C. Thus, a fired product suspension having a solid concentration of about 8% was prepared. Then, 10 kg of the baked product suspension was charged into a cylindrical carbonation reaction tank equipped with a stirrer, and the suspension was stirred at a peripheral speed of 2.5 m / s while maintaining the temperature of the carbonation reaction tank at 65 ° C. However, 10% by volume of carbon dioxide-containing gas was blown at 20 liters / minute, and the reaction was terminated after 30 minutes from when the conductivity started to increase.

[Dehydration / Dispersion / Crushing process]
Next, the suspension of the carbonation-treated product obtained by the carbonation treatment is dehydrated with a filter press, and the cake-like carbonation-treated product having a solid content concentration of about 50% is obtained with a coreless mixer. By dispersing in water, an inorganic particle slurry having a solid content concentration of about 47% was prepared. In addition, in this water to disperse, a polyacrylic acid type dispersing agent (trade name: Aron T-50, manufactured by Toa Gosei Co., Ltd.) is added as a dispersing agent to 1.5 parts by mass relative to 100 parts by mass of the solid content of the carbonized product. Part by mass was added. The pH of this dispersion slurry was 9.5. Finally, the above inorganic particles were wet pulverized to an average particle diameter of 1.5 μm using a sand grinder to obtain fine inorganic particles suitable for a coating pigment. The pH of this inorganic particle slurry was 10.2.

Example 2
Inorganic particles were obtained in the same manner as in Example 1 except that the combustion process and the suspension / carbonation process were changed as follows.

[Combustion process]
The combustion treatment was performed using an externally heated rotary kiln furnace (externally heated rotary kiln made by Takasago Industries, heating part: diameter of rotating drum 300 mm, length 2400 mm).
Raw material papermaking sludge granules were fed at a rate of 10 kg / h. The sludge temperature is kept at 860 ° C. for 2.5 hours in the heated part (kiln inclination: 1%, rotation speed: 1.0 rpm), and combustion exhaust gas is discharged from the sludge supply side at 20 Nm ³ / h. The same amount of outside air as the exhaust gas discharged from the exhaust port due to the pressure reducing action accompanying this was sucked from the air supply port, and the entire inside of the rotary drum was always maintained in an excess air atmosphere to obtain a fired product.

  As a result of examining the composition of the fired product obtained by the combustion treatment by X-ray diffraction, 100% of the calcium carbonate contained in the papermaking sludge before the combustion treatment was decomposed, and all the kaolin was converted to an amorphous substance. Although talc was not changed at all, a hard high-temperature sintered product (Gerlenite) was slightly observed. In the fired product, no unburned product was found to be mixed. The whiteness of the fired product was 78%.

[Suspension / Carbonation process]
The fired product obtained by the combustion treatment is mixed with 65 ° C. warm water using a suspension tank (dissolving tank), and stirred for 8 hours while maintaining the temperature of the suspension tank at 65 ° C. A fired product suspension having a solid concentration of about 8% was prepared. Then, 10 kg of the baked product suspension was charged into a cylindrical carbonation reaction tank equipped with a coreless mixer, and the suspension was stirred at a peripheral speed of 10 m / s while maintaining the temperature of the carbonation reaction tank at 65 ° C. However, 10% by volume of carbon dioxide-containing gas was blown at 20 liters / minute, and the reaction was terminated after 30 minutes from when the conductivity started to increase.

Example 3
Inorganic particles were obtained in the same manner as in Example 1 except that the combustion process and the suspension / carbonation process were changed as follows.

[Combustion process]
The combustion treatment was performed using an external heating type rotary kiln furnace (external heating type rotary kiln made by Takasago Industries, heating part: diameter of rotating drum 300 mm, length 2400 mm, with lifter).
The raw papermaking sludge granulated product is supplied at a rate of 25 kg / h, the sludge temperature is 600 ° C., and the heated portion is held for 0.5 hours (kiln inclination: 2%, rotation speed: 2.6 rpm), and combustion exhaust gas is discharged. Exhaust from the sludge supply side at 50 Nm ³ / h, and the same amount of external air as the exhaust gas exhausted from the exhaust port is sucked in from the exhaust port due to the decompression action, and the entire inside of the rotary cylinder is always maintained in an excess air atmosphere. The primary combustion product was prepared. The prepared primary combustion product is supplied again to the rotary kiln furnace, and the temperature of the primary treatment combustion product is kept at 800 ° C. for 1.5 hours (kiln inclination: 1%, rotation speed: 1.8 rpm) in the heated part, and combustion The exhaust gas was discharged at 20 Nm ³ / h to obtain a fired product.

  As a result of examining the composition of the fired product obtained by this combustion treatment by X-ray diffraction, the hard high-temperature sintered product (Gerenite) was not included, and the calcium carbonate contained in the papermaking sludge before the combustion treatment was 75% was decomposed. Moreover, in the components other than calcium carbonate, all of kaolin was changed to an amorphous substance, but talc was not changed at all. Part of unburned material was found in the fired product. The whiteness of the fired product was 82%.

[Suspension / Carbonation process]
The fired product obtained by the combustion treatment is mixed with warm water of 65 ° C. using a suspension tank (septic tank), and stirred for 5 hours while maintaining the temperature of the suspension tank at 65 ° C. A fired product suspension having a solid concentration of about 8% was prepared. Then, 10 kg of the baked product suspension was charged into a cylindrical semi-batch carbonation reaction tank equipped with a stirrer, and the suspension was kept at a peripheral speed of 3.0 m / h while maintaining the temperature of the carbonation reaction tank at 65 ° C. With stirring, 10% by volume of carbon dioxide-containing gas was blown at a rate of 20 liters / minute, and the reaction was terminated after 30 minutes from when the conductivity started to rise.

Example 4
Inorganic particles were obtained in the same manner as in Example 1 except that the combustion process and the suspension / carbonation process were changed as follows.

[Combustion process]
The combustion treatment was carried out using an externally heated rotary kiln furnace (externally heated rotary kiln made by Takasago Industries, heating part: diameter of rotary cylinder 300 mm, length 2400 mm, 6 divisions in the furnace). The raw papermaking sludge granulated product is supplied at a rate of 60 kg / h, the sludge temperature is 600 ° C., and the heated portion is held for 0.5 hours (kiln inclination: 2%, rotation speed: 3.0 rpm) to generate combustion exhaust gas. Exhaust from the sludge supply side at 120 Nm ³ / h, and the same amount of outside air as the exhaust gas discharged from the exhaust port due to the accompanying decompression action is sucked from the air supply port, so that the entire inside of the rotary cylinder is always kept in an excess air atmosphere. Maintained and prepared a primary combustion product. The prepared primary combustion product is again supplied to the rotary kiln furnace, and the temperature of the primary treatment combustion product is kept at 800 ° C. for 1 hour (kiln inclination: 2%, rotation speed: 2.0 rpm) in the heated part, The product was discharged at 30 Nm ³ / h to obtain a fired product.

  As a result of examining the composition of the fired product obtained by this combustion treatment by X-ray diffraction, the hard high-temperature sintered product (Gerenite) was not included, and the calcium carbonate contained in the papermaking sludge before the combustion treatment was 85% was decomposed. Further, in the components other than calcium carbonate, all of kaolin was changed to an amorphous substance, but talc was not changed at all. The whiteness of the fired product was 84%.

[Suspension / Carbonation process]
The fired product obtained by the above combustion treatment is mixed with 45 ° C. warm water using a suspension tank (dissolving tank) and stirred for 5 hours while maintaining the temperature of the suspension tank at 45 ° C. A fired product suspension having a solid content concentration of about 8% was prepared. Then, 10 kg of this calcined product suspension was charged into a cylindrical semi-batch type carbonation reaction tank equipped with a stirrer, and while maintaining the temperature of this carbonation reaction tank at 45 ° C., the suspension was discharged at a peripheral speed of 3.0 m / While stirring at s, 10% by volume of carbon dioxide-containing gas was blown at a rate of 20 liters / minute, and the reaction was terminated after 30 minutes when the conductivity started to increase.

Example 5
Inorganic particles were obtained in the same manner as in Example 4 except that the suspension / carbonation step was changed as follows.

[Suspension / Carbonation process]
The fired product obtained by the combustion treatment of Example 4 was mixed with 45 ° C. warm water using a suspension tank (dissolving tank) and stirred for 1 hour while maintaining the temperature of the suspension tank at 45 ° C. Thus, a fired product suspension having a solid content concentration of about 8% was prepared. Then, 10 kg of this calcined product suspension was charged into a cylindrical semi-batch type carbonation reaction tank equipped with a stirrer, and while maintaining the temperature of this carbonation reaction tank at 45 ° C., the suspension was discharged at a peripheral speed of 3.0 m / While stirring at s, 10% by volume of carbon dioxide-containing gas was blown at a rate of 20 liters / minute, and the reaction was terminated after 30 minutes when the conductivity started to increase.

Example 6
Inorganic particles were obtained in the same manner as in Example 4 except that the suspension / carbonation step was changed as follows.

[Suspension / Carbonation process]
The fired product obtained by the combustion treatment of Example 4 was mixed with 45 ° C. warm water using a suspension tank (dissolving tank) and stirred for 1 hour while maintaining the temperature of the suspension tank at 45 ° C. Thus, a fired product suspension having a solid content concentration of about 8% was prepared. Then, 10 kg of the baked product suspension was charged into a cylindrical semi-batch carbonation reaction tank equipped with a stirrer, and the suspension was kept at a peripheral speed of 3.0 m / h while maintaining the temperature of the carbonation reaction tank at 65 ° C. While stirring at s, 10% by volume of carbon dioxide-containing gas was blown at a rate of 20 liters / minute, and the reaction was terminated after 30 minutes when the conductivity started to increase.

Example 7
Inorganic particles were obtained in the same manner as in Example 4 except that the suspension / carbonation step was changed as follows.

[Suspension / Carbonation process]
The fired product obtained by the combustion treatment of Example 4 was mixed with 45 ° C. warm water using a suspension tank (dissolving tank) and stirred for 1 hour while maintaining the temperature of the suspension tank at 45 ° C. Thus, a fired product suspension having a solid content concentration of about 8% was prepared. Then, 10 kg of this calcined product suspension was charged into a cylindrical semi-batch carbonation reaction tank equipped with a stirrer, and while maintaining the temperature of this carbonation reaction tank at 70 ° C., the suspension was discharged at a peripheral speed of 3.0 m / While stirring at s, 10% by volume of carbon dioxide-containing gas was blown at a rate of 20 liters / minute, and the reaction was terminated after 30 minutes when the conductivity started to increase.

Example 8
Inorganic particles were obtained in the same manner as in Example 5 except that the carbonation reaction tank in the carbonation step was changed to a cylindrical semi-batch reaction tank without a stirrer.

Comparative Example 1
Inorganic particles were obtained in the same manner as in Example 1 except that the suspension / carbonation step and the dehydration / dispersion / pulverization step were changed as follows.

[Suspension / Carbonation process]
The fired product obtained by the combustion treatment of Example 1 was mixed with 75 ° C. warm water using a suspension tank (dissolving tank) and stirred for 8 hours while maintaining the temperature of the suspension tank at 75 ° C. Thus, a fired product suspension having a solid content concentration of about 8% was prepared. Then, 10 kg of the baked product suspension was charged into a cylindrical semi-batch carbonation reaction tank equipped with a stirrer, and the suspension was kept at a peripheral speed of 3.0 m / h while maintaining the temperature of the carbonation reaction tank at 65 ° C. While stirring at s, 10% by volume of carbon dioxide-containing gas was blown at a rate of 20 liters / minute, and the reaction was terminated after 30 minutes when the conductivity started to increase.

[Dehydration / Dispersion / Crushing process]
Next, the suspension of the carbonation-treated product obtained by the carbonation treatment is dehydrated with a filter press, and the cake-like carbonation-treated product having a solid content concentration of about 40% is obtained with a coreless mixer. By dispersing in water, an inorganic particle slurry having a solid concentration of 39% was prepared. In addition, in this water to disperse, a polyacrylic acid type dispersing agent (trade name: Aron T-50, manufactured by Toa Gosei Co., Ltd.) is added as a dispersing agent to 1.5 parts by mass relative to 100 parts by mass of the solid content of the carbonized product. Part by mass was added. The pH of this dispersion slurry was 10.3. Finally, the above inorganic particle slurry was wet pulverized to an average particle size of 1.5 μm using a sand grinder. The pH of this inorganic pigment slurry was 11.0.

Comparative Example 2
Inorganic particles were obtained in the same manner as in Example 4 except that the suspension / carbonation step and the dehydration / dispersion / pulverization step were changed as follows.

[Suspension / Carbonation process]
The fired product obtained by the combustion treatment of Example 4 was mixed with hot water at 65 ° C. using a suspension tank (dissolving tank), and the suspension tank temperature was maintained at 65 ° C. while maintaining 12.5 The mixture was stirred for a time to prepare a fired product suspension having a solid content concentration of about 8%. Then, 10 kg of this calcined product suspension was charged into a cylindrical semi-batch type carbonation reaction tank equipped with a stirrer, and while maintaining the temperature of the carbonation reaction tank at 30 ° C., the suspension was discharged at a peripheral speed of 3.0 m / While stirring at s, 10% by volume of carbon dioxide-containing gas was blown at a rate of 20 liters / minute, and the reaction was terminated after 30 minutes when the conductivity started to increase.

[Dehydration / Dispersion / Crushing process]
Next, the suspension of the carbonation-treated product obtained by the carbonation treatment is dehydrated with a filter press, and the cake-like carbonation-treated product having a solid content concentration of about 42% is obtained with a coreless mixer. By dispersing in water, an inorganic particle slurry with a solid content concentration of 40% was prepared. In addition, in this water to disperse, a polyacrylic acid type dispersing agent (trade name: Aron T-50, manufactured by Toa Gosei Co., Ltd.) is added as a dispersing agent to 1.5 parts by mass relative to 100 parts by mass of the solid content of the carbonized product. Part by mass was added. The pH of this dispersion slurry was 10.2. Finally, the above inorganic particle slurry was wet pulverized to an average particle size of 1.5 μm using a sand grinder. The pH of this inorganic pigment slurry was 11.0.

Comparative Example 3
Inorganic particles were obtained in the same manner as in Example 4 except that the suspension / carbonation step was changed.

[Suspension / Carbonation process]
The fired product obtained by the combustion treatment of Example 4 was mixed with 75 ° C. warm water using a suspension tank (septic tank), and the suspension tank temperature was maintained at 75 ° C. while maintaining the temperature of 12.5. The mixture was stirred for a time to prepare a fired product suspension having a solid content concentration of about 8%. Then, 10 kg of the baked product suspension was charged into a cylindrical semi-batch carbonation reaction tank equipped with a stirrer, and the suspension was kept at a peripheral speed of 3.0 m / h while maintaining the temperature of the carbonation reaction tank at 75 ° C. While stirring at s, 10% by volume of carbon dioxide-containing gas was blown at a rate of 20 liters / minute, and the reaction was terminated after 30 minutes when the conductivity started to increase.

[Dehydration / Dispersion / Crushing process]
Next, the carbonized suspension obtained by the carbonation treatment is dehydrated with a filter press, and the cake-like carbonized product having a solid concentration of about 38% is obtained with a coales mixer. To prepare an inorganic particle slurry having a solid concentration of 35%. In addition, in this water to disperse, a polyacrylic acid type dispersing agent (trade name: Aron T-50, manufactured by Toa Gosei Co., Ltd.) as a dispersing agent is 1.5% with respect to 100% by mass of the solid content of the carbonized product. Mass% was added. The pH of this dispersion slurry was 10.4. Finally, the above inorganic particles were wet pulverized to an average particle size of 1.5 μm using a sand grinder. The pH of this regenerated pigment slurry was 11.2.

Reference example 1
Without using papermaking sludge, the suspension / carbonation step and the dehydration / dispersion / pulverization step were performed using quick lime as described below to obtain inorganic particles.

[Suspension / Carbonation process]
Quick lime (manufactured by Yabashi Kogyo Co., Ltd.) was mixed with 75 ° C. warm water using a suspension tank (soda tank) and stirred for 12.5 hours while maintaining the temperature of the suspension tank at 75 ° C. A sanitizing solution having a partial concentration of about 12% was prepared. Then, 10 kg of this decontamination solution was charged into a cylindrical carbonation reaction tank, and while maintaining the temperature of this carbonation reaction tank at 75 ° C., 20 vol% carbon dioxide-containing gas was added to the suspension at 20 liters / minute. The carbonation was carried out by stirring until pH 7.0 while blowing.

[Dehydration / Dispersion / Crushing process]
Next, the calcium carbonate slurry obtained by the carbonation treatment is dehydrated with a filter press, and the obtained solid calcium carbonate is dispersed in water with a Coreless mixer by dispersing cake-like calcium carbonate having a solid content concentration of about 70%. A calcium carbonate slurry having a partial concentration of 69% was prepared. In addition, in this water to disperse, a polyacrylic acid type dispersant (trade name: Aron T-50, manufactured by Toa Gosei Co., Ltd.) is used as a dispersant in an amount of 1.0 with respect to 100 parts by mass of the solid content of the carbonized product. Part by mass was added. Finally, the above calcium carbonate was wet pulverized to an average particle size of 1.5 μm using a sand grinder. The pH of this calcium carbonate slurry was 9.0.

  As shown in the results of Table 1, in the inventive examples 1 to 8, the dispersion concentration is much higher than that of the comparative example, and scale trouble occurs when reused as papermaking materials such as coating pigments and papermaking fillers. It was possible to efficiently produce inorganic particles having good dispersibility and the like.

The model longitudinal cross-sectional side view which shows an example of the heat processing apparatus used for this invention. The longitudinal front view which shows an example of the rotary drum of the 6 division partition structure of the heat processing apparatus. The longitudinal cross-sectional front view which shows an example of the rotating drum of the 6 cylinder type multicylinder structure of the heat processing apparatus. The longitudinal cross-sectional front view which shows an example of the rotary drum of the 12 division partition structure of the heat processing apparatus.

Explanation of symbols

K1 .... Indirect heating type rotary kiln 1 ... Rotary drum 2 ... Supply hopper (sludge supply port)
3 .... Air supply port 4 ... Exhaust fan 5 ... Indirect heating means 6 ... Hot air circulation fan 7 ... ..Circulating blower 8 ... Sludge discharge port 9 ... Baking chamber 10 ... Screw feeder 11a ... Outer shell 11b ... Bulk 12 ··· Division chamber 13 ··· Pipe portion 14 ··· Tube portion fixing member 14a ··· Center hole 15 · · · Hollow portion 16a · · · Inner tube portion 16b ... outer cylinder part 16c ... partition 17 ... division chamber d ... rotation direction S of the rotary drum ... papermaking sludge A ...・ ・ Air flow B ・ ・ ・ ・ ・ ・ Paper sludge traveling direction

Claims (4)

The paper sludge to a manufacturing method of the inorganic particles as a raw material, a heat treatment step of heat-treating the formulation paper sludge, fired product and baked product suspension step Ru obtain a calcined product suspension was mixed with water and heat-treated comprises a carbonation step of contacting carbon dioxide or carbon dioxide-containing gas into該焼Narubutsu suspension, the liquid temperature of該焼Narubutsu suspension is not less 70 ° C. or less, carbon dioxide or carbon dioxide-containing carbonation step The time until contact with the gas is 9 hours or less , and the carbonation step is performed while measuring the conductivity of the baked product suspension. After the conductivity once decreases to less than 1.0 ms / cm, 1 A method for producing inorganic particles, characterized in that the reaction is terminated when it is in the range of 0.0 to 2.0 ms / cm . In the carbonation step, a cylindrical semi-batch type reaction vessel having a reaction vessel with a cylinder at the top and a cone at the bottom and a number of holes in the cone is used. 2. The method for producing inorganic particles according to claim 1, wherein fine bubbles of the gas are generated by blowing and the bubbles are brought into contact with the fired product suspension . 3. The method for producing inorganic particles according to claim 1, wherein in the carbonation step, a carbonation reaction is performed for 2 hours or more while stirring the baked product suspension at a peripheral speed of 2.0 m / s or more. . The heat treatment includes a primary combustion step in which flammable organic components in the sludge are burned and removed under an excess air atmosphere at a sludge temperature of 650 ° C. or less, and flame retardant organic components in the sludge are burned and removed at a sludge temperature of 700 to 850 ° C. The manufacturing method of the inorganic particle of any one of Claim 1 to 3 performed by passing through the combustion process of at least 2 steps | paragraphs with the secondary combustion process to do.

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