JP4960600B2 - Waste gypsum treatment method - Google Patents

Description

  The present invention relates to a novel method for treating waste gypsum. More specifically, the present invention relates to a method for treating waste gypsum that can recover 2-water type gypsum having good operability, high purity, and large average particle size from waste gypsum obtained from waste gypsum board or the like.

  The amount of waste gypsum board, the main factor of waste gypsum, is about 1.5 million tons per year. Of this, about 500,000 tons are scraps of new interior construction work at the time of production and houses. It is carried out. However, the remaining 1 million tons are discharged by land renovation and demolition work of buildings such as houses. The amount of waste gypsum board generated tends to increase year by year, and there is a need for an effective treatment method for waste gypsum from the point of lack of landfill and environmental burden.

  Up to now, many proposals have been made for methods for treating waste gypsum obtained from waste gypsum board and the like. For example, a method of separating base paper from waste gypsum board and reusing the obtained gypsum has been proposed (see Patent Document 1 and Patent Document 2).

  However, in the methods described in Patent Document 1 and Patent Document 2, organic substances such as surfactants remain in the recovered gypsum, and the reuse is limited to soil improvers and the like. . Patent Document 1 also discloses a method of incinerating waste gypsum with paper attached and reusing it as anhydrous gypsum. However, there is a problem that SOx is generated by incineration, There is room for improvement in that a separate water treatment step is required to obtain the same two-water type gypsum as the flue gas desulfurization gypsum used.

  Furthermore, the methods described in Patent Documents 1 and 2 are premised on a pulverization process in a dry state, and it is necessary to take measures against dust in all steps until the gypsum is recovered. Furthermore, waste gypsum generated from a demolition site such as a building site may be wet, and it has been difficult to handle the waste gypsum by the above method.

  A method of effectively using waste gypsum as an additive for cement has also been proposed. For example, a waste gypsum board is heated to 600 to 1200 ° C., and organic components such as papers and other surfactants are removed by incineration to obtain a cement additive (see Patent Document 3), heat treatment. There has been proposed a method of adding recovered gypsum obtained by removing paper from waste gypsum board to cement as at least a part of the gypsum component (see Patent Document 4).

  However, the gypsum of the method described in Patent Document 3 becomes an anhydrous gypsum by heat treatment. Therefore, as described above, a separate water treatment step is required in order to obtain a two-water type gypsum having the same crystal form as the flue gas desulfurization gypsum used as an additive for general cement. Furthermore, when anhydrous gypsum is used as an additive for cement, there is room for improvement in that the rate of hydration becomes very slow. Further, the recovered gypsum of the method described in Patent Document 4 is a two-water type gypsum. However, since the recovered gypsum is easily pulverized, when it is crushed together with other components such as cement clinker and gypsum, a crusher By delaying the charging time to be put in, adjustment such as preventing over-pulverization may be necessary, and there is room for improvement.

  Furthermore, a method for reusing the waste gypsum by wet processing has been proposed. For example, a method has been proposed in which α-type hemihydrate gypsum is produced by subjecting gypsum board waste material that has not been crushed to wet heat treatment under pressure, and this is reused as a raw material such as gypsum board (see Patent Document 5). ). This method can easily separate paper and gypsum even with wet gypsum board waste.

  However, in the method described in Patent Document 5, since waste gypsum is not pulverized, organic components such as surfactants contained in waste gypsum should be sufficiently reduced when processing large shapes. There was room for improvement. In addition, since waste gypsum is not crushed and treated, handling is difficult when waste gypsum is treated in large quantities continuously. Furthermore, hemihydrate gypsum obtained by the above method has a small average particle size, and when it is reused as a gypsum board raw material, it is difficult to use the entire amount, and it remains a partial substitute for the current raw material.

JP-A-10-286553 JP 2000-254531 Japanese Patent Laid-Open No. 10-36149 JP 2003-192403 A JP 2004-307321 A

  As described above, in the conventional method for treating waste gypsum, it is possible to recover or reuse dihydrate gypsum having a high purity and a particle size comparable to that of flue gas desulfurization gypsum used for general purposes. It was difficult.

  Accordingly, the object of the present invention is to improve the operability from waste gypsum such as a waste gypsum boat, and also to have a high purity and a large average particle size, and can be used as it is for the use of gypsum that has been conventionally used. An object of the present invention is to provide a method for treating waste gypsum that collects water-type gypsum.

  As a result of intensive studies to achieve the above object, the inventors of the present invention wet pulverized waste gypsum in a slurry state, and then mixed an alkali salt of oxycarboxylic acid having 4 to 6 carbon atoms and heated under pressure. The hemihydrate gypsum obtained by the treatment was further converted into 2-hydrate gypsum, thereby finding that the above object was achieved, and the present invention was completed.

That is, according to the present invention, a slurry obtained by mixing 5 to 50 parts by mass of waste gypsum obtained from waste gypsum board with 100 parts by mass of water is subjected to a wet pulverization treatment, whereby 2-water gypsum contained in the waste gypsum. In a slurry containing a wet pulverization process in which the average particle size is pulverized to 20 μm or less, and a dihydrate gypsum obtained in the wet pulverization process, the number of carbon atoms is 4 to The concentration adjustment step of containing 6 oxycarboxylic acid alkali salt to be 0.2 to 50 mmol, and the slurry containing the oxycarboxylic acid alkali salt and dihydrate gypsum obtained in the concentration adjustment step under pressure, by heat treatment, wet heat treatment step of the 2 gypsum in the slurry to gypsum hemihydrate, generation step of the hemihydrate gypsum in the resulting slurry in the wet heat treatment step 2 gypsum It is comprised of a processing method of waste gypsum characterized by.

Since the present invention treats waste gypsum in a wet (slurry) state, it is possible to recover 2-water type gypsum having a large average particle size and high purity. In the treatment process of the present invention, the finally obtained dihydrate gypsum having a large average particle diameter can be fluidized as a slurry until it is washed and filtered. As a result, pumping is possible, and it is possible to easily cope with an increase in the size of a processing facility accompanying an increase in the amount of waste gypsum. Moreover, since it includes the process of processing in a wet state, it is not necessary to take measures against dust in all processes, and it is also possible to process wet waste gypsum.
In addition, in the production process, dihydric gypsum having a large particle size can be obtained from hemihydrate gypsum. In particular, when dihydric gypsum is mixed, the average particle size of the obtained dihydric gypsum is adjusted in a short time. be able to. As a result, the obtained dihydrate gypsum can be used as it is for conventional uses such as gypsum board raw materials or cement setting regulators.

  In the present invention, by treating waste gypsum in a wet (slurry) state, dihydrate gypsum with good operability and high purity can be obtained. The process includes mixing a water and waste gypsum, followed by a wet pulverization process for wet pulverization of 2-water gypsum, and a concentration in which a specific amount of an alkali oxycarboxylic acid salt is contained in the slurry obtained in the wet pulverization process. Obtained by an adjustment step, a wet heat treatment step in which the slurry containing dihydrate gypsum obtained in the concentration adjustment step is heated under pressure to form a slurry containing hemihydrate gypsum, and the wet heat treatment step And a production step for converting hemihydrate gypsum to dihydrate gypsum.

  The waste gypsum to be treated in the present invention is not particularly limited, and can be obtained from waste gypsum board or the like. Specifically, the waste gypsum is obtained from scrap gypsum board generated from gypsum board production process and construction site enforcement process, waste gypsum board consisting of residual material, waste gypsum board generated as construction waste material in renovation and demolition work It is.

  In the present invention, when the waste gypsum is obtained from waste gypsum board, the base paper may be attached, or the base paper may be removed from the waste gypsum board in advance. Good.

  In the case of using a paper obtained by removing the base paper from the waste gypsum board in advance, the method for removing the base paper from the waste gypsum board is not particularly limited, and the above-described known methods, for example, JP-A-10-286553 A method such as JP 2000-254531 can be employed. In the waste gypsum processing method of the present invention, even when the waste gypsum after removing the base paper is treated in a wet (slurry) state, the operability is good and high-purity dihydrate gypsum is obtained.

  The particle size of the waste gypsum to be treated in the present invention is not particularly limited, but in order to efficiently perform wet grinding described later, the average particle size is 0.1 to 50 mm, preferably 1 to 10 mm. It is preferable. Further, the method of making the waste gypsum into the particle size in the above range is not particularly limited, and the waste gypsum board can be pulverized by a known method to adjust the particle size. The waste gypsum from which the particles have been removed can be pulverized by a known method to adjust the particle size within the above range.

  First, in the present invention, 5 to 50 parts by mass of the waste gypsum is mixed with 100 parts by mass of water, and the resulting slurry is subjected to wet pulverization to pulverize 2-water gypsum contained in the waste gypsum. A wet pulverization process is performed.

  In the wet crushing process of the present invention, the method of wet crushing waste gypsum may be performed by crushing dihydrate gypsum contained in the slurry using a known crusher with a mixture of water and waste gypsum. Specifically, it can be processed using a fine pulverizer such as a high-speed rotary impact pulverizer, a ball mill, a medium agitating pulverizer, a jet pulverizer, or a wet high-speed rotary mill.

  In the wet crushing process of the present invention, the ratio of mixing water and waste gypsum is 5 to 50 parts by mass of waste gypsum with respect to 100 parts by mass of water. When the proportion of waste gypsum is less than 5 parts by mass, the ratio of the amount of water to be heated to the amount of waste gypsum to be treated (2-water gypsum) is increased when performing wet heat treatment described later. When processing waste gypsum, the processing facilities become large, and more energy is required, which is not economical. On the other hand, when the proportion of the waste gypsum exceeds 50 parts by mass, the fluidity of the slurry is lowered, which makes it difficult to transport the pump as a fluid. Considering the economy and the fluidity of the slurry, the proportion of waste gypsum is preferably 10 to 30 parts by mass with respect to 100 parts by mass of water.

In the present invention, the particle size of 2 gypsum obtained when the wet grinding process waste gypsum by the method, average particle size shall be the 20μm or less. When the average particle size of the dihydric gypsum is 20 μm or less, the dihydric gypsum can be converted into a semi-hydrated gypsum in a short time in the wet heat treatment step described later. Furthermore, it is preferable that the average particle diameter of the dihydrate gypsum is 20 μm or less because water-soluble organic substances such as surfactants contained in the waste gypsum can be easily removed.

  Furthermore, when the waste gypsum to which a part or all of the base paper adheres is wet pulverized, the base paper and the dihydrate gypsum can be easily separated by setting the average particle diameter of the obtained dihydrate gypsum to 20 μm or less. In the present invention, since waste gypsum is pulverized in a wet (slurry) state, paper and gypsum components are easily separated. In addition, when the average particle size of dihydrate gypsum obtained by wet pulverization is 20 μm or less, paper is more difficult to pulverize than gypsum, and thus becomes larger than the dihydrate gypsum. Therefore, the slurry containing dihydrate gypsum having an average particle diameter of 20 μm or less and the slurry containing paper can be easily separated into the slurry containing dihydrate gypsum and the paper. In the study by the present inventors, when the average particle diameter of dihydric gypsum obtained by wet pulverization is 20 μm or less, the slurry containing dihydric gypsum and paper is passed through a filter of about 100 to 600 μm to obtain two water It was found that the slurry containing gypsum and paper could be separated. As a method of passing through this filter, a known method can be adopted, and a method of pressing with a screw or a drum or a method of passing with a centrifugal force can be adopted.

  The lower limit of the average particle diameter of the dihydrate gypsum is not particularly limited, but it is preferably 1 μm or more in consideration of industrial wet grinding.

  Next, in the present invention, 4 to 6 carbon oxycarboxylic acid alkali salt is added to 1 mol of dihydrate gypsum contained in the slurry in the slurry containing dihydrate gypsum obtained in the wet pulverization treatment step. Then, a concentration adjusting step is performed in which the alkali salt of oxycarboxylic acid is contained in an amount of 0.2 to 50 mmol. By performing this concentration adjustment step, the fluidity of the slurry containing hemihydrate gypsum can be improved in the wet heat treatment step described later.

  The concentration adjusting step of the present invention is a step of adding an alkali salt of oxycarboxylic acid having 4 to 6 carbon atoms to the slurry containing dihydrate gypsum obtained in the wet pulverization treatment step. When the alkali salt of oxycarboxylic acid is contained in the slurry containing the dihydrate gypsum and the alkali salt of oxycarboxylic acid is not contained, the oxycarboxylic acid is directly added to 1 mol of dihydrate gypsum. What is necessary is just to add 0.2-50 mmol of alkali salts. In addition, when separating the dihydrate gypsum obtained in the production step described later and water, and using the obtained water in the wet pulverization treatment step, the alkali oxycarboxylate is originally contained in the slurry containing the dihydrate gypsum. Contains salt. In this case, considering the amount of the alkali salt of oxycarboxylic acid originally contained, the alkali salt of oxycarboxylic acid is contained so that 0.2-50 mmol of the alkali salt of oxycarboxylic acid is contained per 1 mol of 2-hydrate gypsum. What is necessary is just to add salt.

  In the concentration adjusting step of the present invention, the alkali salt of oxycarboxylic acid having 4 to 6 carbon atoms is added to the slurry containing dihydrate gypsum obtained in the wet pulverization treatment step with respect to 1 mol of dihydrate gypsum contained in the slurry. , 0.2 to 50 mmol. By including the alkali oxycarboxylic acid salt within this range, even when the amount of waste gypsum is 5 parts by mass or more with respect to 100 parts by mass of water, the slurry containing hemihydrate gypsum described below maintains good fluidity. be able to.

  When the alkali salt of oxycarboxylic acid is less than 0.2 mmol with respect to 1 mol of dihydrate gypsum contained in the slurry, the fluidity of the slurry containing hemihydrate gypsum obtained in the wet heat treatment step described later is obtained. This is not preferable because it decreases and makes it difficult to pump as a fluid. On the other hand, when it exceeds 50 mmol, it is not preferable because the rate of producing dihydrate gypsum from hemihydrate gypsum is delayed, and further, the effect of inclusion is not preferred any more, so this is not preferable. Considering the fluidity and the treatment efficiency of the slurry containing hemihydrate gypsum, the oxycarboxylic acid alkali salt having 4 to 6 carbon atoms is added to the slurry containing the dihydrate gypsum in an amount of 0.4 per mol of dihydrate gypsum. -20 mmol is preferable, and 1-10 mmol is more preferable.

  Moreover, when an oxycarboxylic acid alkali salt having 4 to 6 carbon atoms is specifically exemplified, alkali metal salts of succinic acid, tartaric acid, citric acid and gluconic acid are preferable. As an alkali metal, sodium and calcium are preferable. The alkali oxycarboxylic acid salt can be easily separated from dihydrate gypsum when the finally obtained dihydrate gypsum is separated from water.

  In the present invention, the reason why the fluidity of the slurry containing hemihydrate gypsum described later is improved by containing the alkali salt of oxycarboxylic acid is not clear, but is estimated as follows. That is, when dihydrate gypsum obtained by wet pulverizing waste gypsum is converted to hemihydrate gypsum by wet heat treatment described later, when the oxycarboxylic acid alkali salt is not present, the obtained hemihydrate gypsum is fine. Acicular crystals are formed. For this reason, it is considered that the crystals are entangled to lower the fluidity of the slurry containing hemihydrate gypsum. On the other hand, in the present invention, when dihydrate gypsum is converted into hemihydrate gypsum, the crystal form of hemihydrate gypsum can be made into a microplate by adding the alkali oxycarboxylic acid salt to the slurry. By taking such a crystal form, it is considered that the fluidity is improved.

  Next, in the present invention, the slurry containing the alkali salt of oxycarboxylic acid and dihydrate gypsum obtained in the concentration adjusting step is heat-treated under pressure, so that the dihydrate gypsum in the slurry is semi-watered. Wet wet heat treatment process to make gypsum.

  In the present invention, the wet heat treatment step is a heat treatment under pressure on the slurry containing the alkali salt of oxycarboxylic acid and dihydrate gypsum obtained in the concentration adjustment step. Specifically, using an apparatus equipped with an industrially available pressure vessel, for example, a device equipped with a pressure vessel such as an autoclave, the slurry is at a temperature of 110 to 150 ° C, preferably 130 to 140 ° C. Stir constantly. The pressure is increased from 0.2 to 0.4 MPa. In addition, the treatment time is not particularly limited, but if it is 1 to 2 hours, the entire amount of 2-hydrate gypsum in the slurry is converted to hemihydrate gypsum within the temperature range and the pressure range. Can do. When adjusting the particle diameter of the obtained dihydric gypsum by mixing dihydric gypsum into the slurry containing hemihydrate gypsum in the production process described later, the entire amount of dihydric gypsum is treated with half water in the wet heat treatment process. Although it is preferable to use gypsum, the object of the present invention can be sufficiently achieved if 90% by mass or more of dihydrate gypsum is converted to hemihydrate gypsum.

  Whether the total amount of dihydrate gypsum has become hemihydrate gypsum can be confirmed by thermogravimetric analysis or powder X-ray diffraction measurement results.

  In the present invention, it is important to perform a wet heat treatment step and convert dihydrate gypsum to hemihydrate gypsum. That is, dihydrate gypsum obtained from waste gypsum is once converted into hemihydrate gypsum, and by producing dihydrate gypsum in the production process described later, high purity dihydrate gypsum whose particle size is adjusted in a short time is obtained. Obtainable. Usually, dihydrate gypsum obtained by wet crushing waste gypsum has a small particle size. Since this slurry contains a large amount of fine dihydrogypsum particle size of 5 μm or less, it is difficult to filter and the operability is poor, and as a result, impurities may not be reduced. Moreover, even if the particle size is reduced, it is difficult to remove water-soluble organic substances such as surfactants only by washing. Here, as an advantage of performing the wet heat treatment, when changing to hemihydrate gypsum, the surfactant and the like in the dihydrate gypsum can be moved to the aqueous phase of the slurry, and finally obtained 2 water The purity of gypsum can be increased.

Next, this invention has the production | generation process which converts the hemihydrate gypsum obtained at the said wet heat processing process into dihydrate gypsum. 2 gypsum generated in this process is a most contained no particle size distribution of the following minute particle child 5 [mu] m. The hemihydrate gypsum obtained by the wet heat treatment has a particle size similar to that of dihydrate gypsum obtained by wet crushing waste gypsum. As a result, semi water gypsum also containing many less fine grain child 5 [mu] m, even if filtered washing the hemihydrate gypsum, it is difficult to reduce the impurities attached to the surface. Therefore, in this invention, it has the production | generation process which transform | converts the hemihydrate gypsum obtained at the said wet heat processing process into dihydrate gypsum again, It is characterized by the above-mentioned.

  Moreover, in the production | generation process of this invention, the particle size of the obtained 2 water gypsum can be adjusted in a short time by mixing the appropriate particle size and quantity of dihydrate gypsum with the slurry containing hemihydrate gypsum. it can.

  In this invention, the method of producing | generating 2 water gypsum from the hemihydrate gypsum obtained by the said wet heat processing should just stir the slurry containing the said hemihydrate gypsum at 50 to 80 degreeC for about 0.5 to 6 hours. Good. The dihydrate gypsum produced in this step has a particle size distribution containing almost no fine particle size of 5 μm or less. Further, by mixing dihydrate gypsum with the slurry containing hemihydrate gypsum obtained by the wet heat treatment, it is possible to produce dihydrate gypsum with a particle size adjusted in a shorter time. Specifically, a slurry containing the hemihydrate gypsum as it is, a method of adding and mixing commercially available dihydrate gypsum such as flue gas desulfurization gypsum to the slurry containing the hemihydrate gypsum, and the dihydrate gypsum obtained in the production step as it is The method of mixing with is mentioned. Among these, the measure of mixing dihydrate gypsum obtained in the production step is economical and preferable. As a countermeasure for mixing the dihydrate gypsum obtained in the production process, after separating the obtained dihydrate gypsum and water, it is possible to add and mix only the 2-water gypsum, or without separating from water A slurry of 2-hydrate gypsum can be added and mixed. Furthermore, in order to further simplify the process, a part of the slurry containing dihydrate gypsum obtained in the production process is left as it is in the production process, and a slurry containing hemihydrate gypsum obtained in the wet heat treatment process is added. It is also possible to adopt a mixing method.

  Specific conditions for mixing the slurry containing hemihydrate gypsum obtained by the wet heat treatment and dihydrate gypsum are as follows. The slurry in the production step is set to a temperature of 50 to 80 ° C. and mixed with dihydrate gypsum. It is preferable to stir for 0.5 to 2 hours. The amount of dihydrate gypsum to be mixed is suitably 5 to 120 parts by mass with respect to 100 parts by mass of hemihydrate gypsum to be treated.

  In the production process of the present invention, when dihydrate gypsum is used, the particle size of dihydrate gypsum mixed with the slurry containing hemihydrate gypsum is not particularly limited, but the average particle size is 10 to 80 μm. Those are preferred. By mixing dihydrate gypsum having an average particle size in the above range within the above range, the final particle size of dihydrate gypsum becomes a large particle size of 40 μm or more in a short time. When mixing relatively small dihydrate gypsum with an average particle diameter within the above range, it is preferable to mix a relatively small amount within the above range. In addition, when mixing relatively large dihydric gypsum with an average particle size within the above range, it is preferable to mix a relatively large amount within the above range. By appropriately adjusting the mixing amount corresponding to the average particle size of the dihydrate gypsum to be mixed, it is possible to easily obtain dihydrate gypsum having an average particle size of 40 μm or more. Considering the treatment efficiency, it is more preferable to mix 20 to 80 parts by mass of dihydrate gypsum having an average particle diameter of 40 to 60 μm with respect to 100 parts by mass of the hemihydrate gypsum to be treated. When the average particle diameter of the finally obtained dihydrate gypsum is 40 μm or more, it becomes easy to separate water and dihydrate gypsum by operations such as filtration. As a result, dihydrate gypsum with high purity can be obtained.

  In the present invention, the dihydrate gypsum obtained in the production step can be separated from water by a known filtration method. Specifically, a method of separating water from a rotary screen, a drum filter, a disk filter, a Nutsche filter, a filter press, a screw press, a tube press, and a centrifugal separator such as a screw decanter or a screen decanter can be employed.

  In the present invention, the water (filtrate) separated from the dihydrate gypsum obtained in the production step can be reused again as water used in the wet pulverization treatment step. The amount of waste water can be reduced by reusing and circulating the water (filtrate). Moreover, even if some surfactant and an alkali salt of oxycarboxylic acid having 4 to 6 carbon atoms are contained in water, as described above, the dihydrate gypsum obtained by the method of the present invention adjusts the particle size. Therefore, it can be easily separated from the surfactant and the like by filtration. It should be noted that water (filtrate) that is used in circulation can be used without any problem even if a water-soluble organic substance such as a surfactant is contained in the water (filtrate) in a total organic carbon amount of about 5000 ppm. it can. Even when this amount is exceeded, it can be diluted with water and used in the wet grinding process. The concentration of the alkali salt of oxycarboxylic acid having 4 to 6 carbon atoms in the water (filtrate) to be circulated can be quantified by measuring with an ion chromatograph.

  As described above, according to the present invention, dihydrate gypsum in waste gypsum having a small particle size and limited use can be efficiently converted into dihydrate gypsum having a large particle size. Therefore, the finally obtained dihydrate gypsum can be used as it is as a current gypsum board raw material or a cement setting regulator.

  EXAMPLES Hereinafter, examples will be shown to describe the present invention more specifically, but the present invention is not limited to these examples.

1. Confirmation of average particle diameter The volume average particle diameter of the gypsum was confirmed by a laser diffraction scattering type particle size distribution meter. The commercially available flue gas desulfurization gypsum for cement setting regulator was 50 μm.

2. Evaluation of water-soluble organic substance content The water-soluble organic substance content in gypsum was evaluated by measuring the total organic carbon content in an aqueous solution in which gypsum was dissolved. The total amount of organic carbon in the waste gypsum used in Examples described later was 2200 ppm based on the gypsum mass.

3. Firing test Each gypsum was fired in an electric furnace to produce hemihydrate gypsum. The average particle size of the hemihydrate gypsum produced from the flue gas desulfurization gypsum for a commercial cement setting regulator was 51 μm. Moreover, when the waste gypsum used for the Example mentioned later was baked, it became hemihydrate gypsum with an average particle diameter of 10 micrometers.

4). Grinding test Each plaster was ground for 30 minutes with a planetary ball mill, and the average particle size after grinding was confirmed. The average particle diameter of the commercially available flue gas desulfurization gypsum for pulverizing cement setting agent pulverized under these conditions was 5 μm. Moreover, when the waste gypsum used in the examples described later was crushed under these conditions, it became gypsum having an average particle size of 0.5 μm.

Example 1
After roughly pulverizing the waste gypsum and roughly removing the paper, 10 parts by mass of waste gypsum was mixed with 100 parts by mass of water to prepare a slurry. The slurry was wet crushed with a planetary ball mill and then passed through 300 μm and 150 μm meshes to remove the remaining paper fibers. At this time, the average particle diameter of the dihydrate gypsum in the slurry was 18 μm. Next, 1.6 mmol of sodium citrate was added to 1 mol of dihydrate gypsum contained in this slurry, and this slurry was heated at 135 ° C. and 0.3 MPa for 1.5 hours while stirring in an autoclave. At this time, it was confirmed that all the gypsum in the slurry was hemihydrate gypsum. This hemihydrate gypsum slurry was stirred at 80 ° C. for 4 hours. Then, when performing solid-liquid separation by filtration, washing was performed with the same amount of water as the obtained cake mass. The obtained gypsum was dihydrate gypsum having an average particle size of 42 μm. On the other hand, the total amount of organic carbon contained in the dihydrate gypsum was 30 ppm.

  Moreover, when the firing test was performed by the above method, the average particle diameter of the hemihydrate gypsum produced from the above-mentioned 2 hydrogypsum was 41 μm, which was almost the same as that of commercially available flue gas desulfurization gypsum, and normally used flue gas desulfurization gypsum. It was shown that a board with an appropriate strength can be formed even if it is used as it is, for example, as a raw material for gypsum board.

  Further, when the pulverization test was performed by the above method, the average particle diameter of the gypsum was 4 μm, which was the same level as that of commercially available flue gas desulfurization gypsum, and the same use as that of normally used flue gas desulfurization gypsum, for example, cement condensation It was shown that it can be used as it is for a regulator.

Example 2
After roughly pulverizing the waste gypsum and roughly removing the paper, 25 parts by mass of waste gypsum was mixed with 100 parts by mass of water to prepare a slurry. The slurry was wet crushed with a planetary ball mill and then passed through 300 μm and 150 μm meshes to remove the remaining paper fibers. At this time, the average particle diameter of the dihydrate gypsum in the slurry was 18 μm. Next, 1.6 mmol of sodium citrate was added to 1 mol of dihydrate gypsum contained in this slurry, and this slurry was heated at 135 ° C. and 0.3 MPa for 1.5 hours while stirring in an autoclave. At this time, it was confirmed that all the gypsum in the slurry was hemihydrate gypsum. This hemihydrate gypsum slurry and 100 parts by mass of hemihydrate gypsum in the slurry are mixed with a slurry containing 70 parts by mass of a flue gas desulfurization gypsum having an average particle size of 50 μm and stirred at 65 ° C. for 1.5 hours. Stirring was performed. Then, when performing solid-liquid separation by filtration, washing was performed with the same amount of water as the obtained cake mass. The obtained gypsum was dihydrate gypsum having an average particle size of 54 μm. On the other hand, the total amount of organic carbon contained in the dihydrate gypsum was 12 ppm.

  Further, when the firing test was performed by the above method, the average particle size of the hemihydrate gypsum produced from the above-mentioned 2-hydrate gypsum was 55 μm, which was almost the same as that of commercially available flue gas desulfurization gypsum. It was shown that a board with an appropriate strength can be formed even if it is used as it is, for example, as a raw material for gypsum board.

  Further, when the pulverization test was performed by the above method, the average particle size of the gypsum was 6 μm, which was the same level as that of commercially available flue gas desulfurization gypsum, and the same use as that of normally used flue gas desulfurization gypsum, for example, cement condensation It was shown that it can be used as it is for a regulator.

Example 3
After roughly pulverizing the waste gypsum and roughly removing the paper, 25 parts by mass of waste gypsum was mixed with 100 parts by mass of the filtrate generated in Example 1 to prepare a slurry. Thereafter, wet pulverization was performed in the same manner as in Example 1. At this time, the average particle diameter of the dihydrate gypsum in the slurry was 18 μm. Next, the amount of sodium citrate in the filtrate was quantified by ion chromatography, and the sodium citrate was adjusted to 1.6 mmol with respect to 1 mol of dihydrate gypsum contained in this slurry. The slurry was wet crushed with a planetary ball mill and then passed through 300 μm and 150 μm meshes to remove the remaining paper fibers. The slurry was heated at 135 ° C. and 0.3 MPa for 1.5 hours while stirring in an autoclave. At this time, it was confirmed that all the gypsum in the slurry was hemihydrate gypsum. Then, the slurry containing 80 parts by mass of 2-hydrate gypsum obtained in Example 2 is mixed with the hemihydrate gypsum slurry and 100 parts by mass of hemihydrate gypsum in the slurry, and stirred at 65 ° C. for 1 hour. went. Then, when performing solid-liquid separation by filtration, washing was performed with the same amount of water as the obtained cake mass. The obtained gypsum was dihydrate gypsum having an average particle diameter of 62 μm. On the other hand, the total amount of organic carbon contained in the dihydrate gypsum was 15 ppm.
Further, when a firing test was performed by the above method, the average particle size of the hemihydrate gypsum produced from the above-mentioned 2-hydrate gypsum was 56 μm, which was almost the same as that of commercially available flue gas desulfurization gypsum. It was shown that a board with an appropriate strength can be formed even if it is used as it is, for example, as a raw material for gypsum board.

  Further, when the pulverization test was performed by the above method, the average particle size of the gypsum was 6 μm, which was the same level as that of commercially available flue gas desulfurization gypsum, and the same use as that of normally used flue gas desulfurization gypsum, for example, cement condensation It was shown that it can be used as it is for a regulator.

Example 4
The operation of Example 2 was repeated, and 25 parts by mass of waste gypsum from which paper was roughly removed was mixed with 100 parts by mass of the liquid-soluble organic substance concentration in the liquid phase that was concentrated to 5000 ppm in terms of total organic carbon. It was created. Thereafter, wet pulverization was performed in the same manner as in Example 1. At this time, the average particle diameter of the dihydrate gypsum in the slurry was 18 μm. Next, the amount of sodium citrate in the filtrate was quantified by ion chromatography, and the sodium citrate was adjusted to 1.6 mmol with respect to 1 mol of dihydrate gypsum contained in this slurry. The slurry was wet crushed with a planetary ball mill and then passed through 300 μm and 150 μm meshes to remove the remaining paper fibers. The slurry was heated at 135 ° C. and 0.3 MPa for 1.5 hours while stirring in an autoclave. At this time, it was confirmed that all the gypsum in the slurry was hemihydrate gypsum. Then, the slurry containing 80 parts by mass of 2-hydrate gypsum having an average particle size of 55 μm, which was prepared by repeating the operation of Example 2, was added to 100 parts by mass of the hemihydrate gypsum slurry and the half water gypsum in the slurry, Stirring was carried out at 65 ° C. for 1 hour. Then, when performing solid-liquid separation by filtration, washing was performed with the same amount of water as the obtained cake mass. The obtained gypsum was 2-water gypsum having an average particle size of 55 μm. On the other hand, the total amount of organic carbon contained in the dihydrate gypsum was 20 ppm.

  Further, when the firing test was performed by the above method, the average particle size of the hemihydrate gypsum produced from the above-mentioned 2-hydrate gypsum was 55 μm, which was almost the same as that of commercially available flue gas desulfurization gypsum. It was shown that a board with an appropriate strength can be formed even if it is used as it is, for example, as a raw material for gypsum board.

  Further, when the pulverization test was performed by the above method, the average particle size of the gypsum was 5 μm, which was almost the same as that of commercially available flue gas desulfurization gypsum, and the same use as that of normally used flue gas desulfurization gypsum, for example, cement condensation It was shown that it can be used as it is for a regulator.

Example 5
After roughly pulverizing the waste gypsum and roughly removing the paper, 25 parts by mass of waste gypsum was mixed with 100 parts by mass of water to prepare a slurry. The slurry was wet crushed with a planetary ball mill and then passed through 300 μm and 150 μm meshes to remove the remaining paper fibers. At this time, the average particle diameter of the dihydrate gypsum contained in the slurry was 18 μm. Next, 10 mmol of sodium gluconate was added to 1 mol of dihydrate gypsum contained in this slurry, and this slurry was heated at 135 ° C. and 0.3 MPa for 1.5 hours while stirring in an autoclave. At this time, it was confirmed that all the gypsum in the slurry was hemihydrate gypsum. To this hemihydrate gypsum slurry and 100 parts by mass of hemihydrate gypsum in the slurry, a slurry containing 100 parts by mass of the flue gas desulfurization gypsum was mixed and stirred at 65 ° C. for 1.5 hours. Then, when performing solid-liquid separation by filtration, washing was performed with the same amount of water as the obtained cake mass. The obtained gypsum was dihydrate gypsum having an average particle size of 53 μm. On the other hand, the total amount of organic carbon contained in the dihydrate gypsum was 12 ppm.

  Further, when a firing test was performed by the above method, the average particle size of the hemihydrate gypsum produced from the above-mentioned 2-hydrate gypsum was 53 μm, which was almost the same as that of commercially available flue gas desulfurization gypsum. It was shown that a board with an appropriate strength can be formed even if it is used as it is, for example, as a raw material for gypsum board.

  Further, when the pulverization test was performed by the above method, the average particle size of the gypsum was 5 μm, which was almost the same as that of commercially available flue gas desulfurization gypsum, and the same use as that of normally used flue gas desulfurization gypsum, for example, cement condensation It was shown that it can be used as it is for a regulator.

Comparative Example 1
By the same operation as in Example 1, a waste gypsum slurry was prepared, wet pulverized, and paper fibers were removed. The slurry was filtered and washed with water 10 times the mass of the cake. The total amount of organic carbon in the obtained 2-hydrate gypsum was 1200 ppm.

Comparative Example 2
Hemihydrate gypsum was prepared in the same manner as in Example 1 under the condition where sodium citrate was not added. The produced hemihydrate gypsum became a cake-like lump and could not be handled as a slurry.

Comparative Example 3
The waste gypsum was coarsely pulverized, and the paper was roughly removed. Then, the waste gypsum having a particle diameter of 10 to 30 mm was selected by a sieve. 100 parts by mass of water was mixed with 25 parts by mass of the waste gypsum, and the mixture was heated at 135 ° C. and 0.3 MPa for 1.5 hours while stirring in an autoclave. The produced hemihydrate gypsum was equivalent to the particle size of the original waste gypsum. This hemihydrate gypsum was washed with the same mass of 95 ° C. water and dried at 100 ° C. to obtain hemihydrate gypsum. The total amount of organic carbon contained in this hemihydrate gypsum was 960 ppm.

It is an example of the flowchart of the processing method of the waste gypsum concerning this invention.

Claims (4)

A slurry obtained by mixing 5 to 50 parts by mass of waste gypsum obtained from waste gypsum board with respect to 100 parts by mass of water is subjected to wet pulverization treatment, so that the average particle diameter of 2 gypsum contained in the waste gypsum is 20 μm. The slurry containing the wet pulverization treatment step to be pulverized below and the dihydric gypsum obtained in the wet pulverization treatment step, the alkali oxycarboxylate having 4 to 6 carbon atoms with respect to 1 mol of dihydric gypsum contained in the slurry. By subjecting the slurry containing salt to 0.2 to 50 mmol and adjusting the slurry containing the oxycarboxylic acid alkali salt and dihydrate gypsum obtained in the concentration adjustment step under pressure, A wet heat treatment step for converting dihydrate gypsum in the slurry to half water gypsum, and a generation step for converting the hemihydrate gypsum in the slurry obtained in the wet heat treatment step to dihydrate gypsum. Treatment method of waste gypsum characterized by. 2. The method for treating waste gypsum according to claim 1, wherein after the dihydrate gypsum obtained in the generation step and water are separated, the obtained water is used in the wet pulverization treatment step . 3. The waste gypsum according to claim 1 , wherein in the production step, dihydrate gypsum having an average particle diameter of 10 to 80 μm is mixed with the slurry containing hemihydrate gypsum, so that the half water gypsum is converted to dihydrate gypsum. Processing method. In the said production | generation process, the dihydric gypsum obtained by the production | generation process is mixed with the slurry containing a hemihydrate gypsum, A hemihydrate gypsum is made into a 2-water gypsum. The processing method of the waste gypsum as described.

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