JP2012131704A - Method for recycling gypsum from gypsum board scrap material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recycling gypsum from gypsum board scrap materials, which can recover gypsum having a high purity and high quality, and a large average particle diameter and usable in applications of gypsum conventionally used, well operatively from gypsum board scrap materials.SOLUTION: The method for regenerating gypsum in gypsum board scrap materials includes dissolving and reprecipitating gypsum obtained from gypsum board scrap materials in an aqueous medium in which seed gypsum is present, wherein the step of dissolving and reprecipitating gypsum is carried out in a continuous process; and in the step of dissolving and reprecipitating gypsum, a step of crushing seed gypsum in the aqueous medium is carried out, or a step of supplying seed gypsum of a small particle diameter from outside the system is carried out.

Description

  The present invention relates to a method for reclaiming gypsum from gypsum board waste. More specifically, the present invention relates to a method for regenerating gypsum having good operability, high purity, good quality, and a large average particle size from waste gypsum obtained from gypsum board waste.

The amount of waste gypsum board waste, the main source of waste gypsum, is about 1.5 million tons per year, of which about 500,000 tons are scraps of new interior construction during production and houses. We are recycling. However, the remaining 1 million tons are discharged by renovation and demolition work of buildings such as houses, and are disposed of without being recycled. Here, when landfilled gypsum comes into contact with rainwater, hydrogen sulfide may be generated. Therefore, landfilling of gypsum must be performed in a management-type landfill, and disposal cost is a problem. Furthermore, the amount of gypsum board waste generated tends to increase year by year, and an effective treatment method for waste gypsum is required in view of the shortage of landfill and the environmental burden.
Up to now, many proposals have been made on a method for treating waste gypsum obtained from gypsum board waste and the like. For example, a method of separating base paper from gypsum board waste and reusing the obtained gypsum has been proposed (see Patent Literature 1 and Patent Literature 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, the problem of SO _x being generated by incineration, There was room for improvement in that a separate water treatment step was required to make the same two-water type gypsum as the flue gas desulfurization gypsum used in large quantities. Further, 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 collected. 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.

On the other hand, a method has been proposed in which waste gypsum is wet-treated and reused. For example, a method has been proposed in which α-type hemihydrate gypsum is produced by heat-treating gypsum board waste material that has not been crushed under pressure and wet conditions, and reused as a raw material for gypsum board (patent) Reference 3). This method can easily separate the base paper board and gypsum even with wet gypsum board waste. However, in the method described in Patent Document 3, since the waste gypsum is not pulverized, when processing a large shape, the content of organic components such as surfactants contained in the waste gypsum is sufficiently increased. There was room for improvement because it could not be reduced. Further, since waste gypsum is not pulverized, handling is difficult when waste gypsum is continuously processed in large quantities. Furthermore, the hemihydrate gypsum obtained by the above method has a very small average particle size of crystals and is a porous body. Therefore, when this is reused as a gypsum board raw material, it is necessary to increase the proportion of water used in the slurry as compared to the slurry using virgin gypsum in order to ensure the fluidity of the gypsum slurry in the manufacturing process. There is. As a result, the gypsum board manufactured using 100% of the recycled gypsum by the above method has a serious problem that its strength is insufficient. Therefore, it is difficult to make all of the gypsum board raw material into recycled gypsum, and at present, it is only a partial replacement for virgin materials.
Japanese Patent Laid-Open No. 10-286553 JP 2000-254531 A JP 2004-307321 A

  The object of the present invention is to recover gypsum from gypsum boat waste material that has good operability, high purity, good quality, large average particle size, and can be used as it is for gypsum used in the past. An object of the present invention is to provide a method for regenerating gypsum from gypsum board waste.

According to the present invention, the above objects and advantages of the present invention are:
A method for regenerating gypsum in gypsum board waste, wherein gypsum obtained from gypsum board waste is dissolved and reprecipitated in an aqueous medium in which seed gypsum is present,
The step of dissolving and reprecipitating the gypsum is performed in a continuous process, and the step of dissolving and reprecipitating the gypsum,
Achieved by a method of reclaiming gypsum in waste gypsum board characterized by performing a step of pulverizing seed gypsum in the aqueous medium or a step of supplying seed gypsum having a small particle size from outside the system Is done.

According to the method of the present invention, reclaimed gypsum having good operability, high purity, good quality, and a large average particle size can be recovered from gypsum boat waste.
In the method of the present invention, the gypsum having a large average particle diameter finally obtained 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 treatment facility accompanying an increase in the amount of waste gypsum obtained from gypsum board waste. 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.
The regenerated gypsum obtained by the method of the present invention can be suitably used as it is for conventional uses such as gypsum board raw materials or cement setting regulators.

The waste gypsum used for the method of the present invention is dihydrate gypsum obtained from gypsum board waste material. Specifically, the waste gypsum is obtained from the gypsum board production process and the scraps generated in the construction site enforcement process, gypsum board waste made of residual material, and gypsum board waste generated as renovation and demolition work. It is done.
The waste gypsum used in the method of the present invention is preferably one that has been crushed to an appropriate particle size and from which the board base paper has been removed. The step of crushing the gypsum board waste and the step of separating the board base paper may be performed prior to the method of the present invention, and even if it is a separate process from the method of the present invention, it is a continuous process with the method of the present invention. Also good.
The crushing step and the board base paper separating step can be performed by known methods, respectively. For example, the board base paper separation step can be performed by a method described in Patent Document 1 (Japanese Patent Laid-Open No. 10-286553), Patent Document 2 (Japanese Patent Laid-Open No. 2000-245331), or the like.
The particle size of the waste gypsum used for the method of the present invention is not particularly limited, but is preferably 0.5 to 50 mm as an average particle size from the viewpoint of ease of mechanical transport, More preferably, it is 1-20 mm. The average particle size of the waste gypsum can be measured by sieving.

In the method of the present invention, the waste gypsum as described above is pulverized. In the present invention, it is preferable to control the pulverization step so that the total accumulated pore volume of gypsum after the pulverization step becomes a specific value. In the gypsum regeneration method in which the waste gypsum is dissolved and reprecipitated in an aqueous medium in which seed crystal gypsum exists, the inventors of the present application changed the pore property of the original gypsum to the pore property of the regenerated gypsum. I found out that it affected. Furthermore, it has been found that by controlling the total accumulated pore volume after pulverization within a certain range, a high-quality recycled gypsum can be stably produced. The method of the present invention can exert its advantageous effect more effectively, particularly when at least the step of dissolving and reprecipitating the gypsum is carried out in a continuous process. In the case where a portion is used as a seed crystal for circulation, the advantageous effects can be exhibited to the maximum.
It is preferable to adjust the amount of water in the waste gypsum by performing a heat treatment before the pulverization step. In particular, when the gypsum board waste material used in the method of the present invention is waste material from the dismantling site, some of it contains rainwater, so it is desirable to perform heat treatment before the pulverization step to remove it. . The heating temperature is preferably 100 to 200 ° C., more preferably 110 to 160 ° C., and the heating time is preferably 2 to 60 minutes, more preferably 5 to 30 minutes. Heating can be performed by an appropriate apparatus, and for example, a hot air dryer, a conductive electric heat dryer, or the like can be used.

In the pulverization step, it is preferable to control the total accumulated pore volume of the gypsum after pulverization to 1 mL / g or less, preferably 0.5 to 1 mL / g. This total cumulative pore volume is the cumulative pore volume measured with a mercury porosimeter for pores having a pore diameter in the range of 1 nm to 1 mm. As long as the total cumulative pore volume is in the above range, the particle size after pulverization is not limited. However, if the total cumulative pore volume requirement is satisfied, the volume average particle size is, for example, 0.5 to 30 μm, Is 1 to 20 μm. In the regeneration of gypsum board waste material known in the past, there are many cases that focus only on the average particle size after pulverization. However, gypsum board is originally made of a porous structure with a void in order to reduce the weight and function as a heat insulating material. The present inventors have found that even if the average particle size after pulverization is within the above range, the total cumulative pore volume is not necessarily within the above range, and a more effective process control factor. As a result, the total cumulative pore volume has been adopted. The inventors consider the reason why the correlation between the average particle diameter and the total cumulative pore volume does not match as follows. That is, it is speculated that through the pulverization step, the pores at the time of the board shape gradually decrease, but on the other hand, part of the reaggregation is caused by the progress of pulverization.
This pulverization step can be performed using an appropriate apparatus, and for example, an apparatus such as a pin mill, a ball mill, or a bead mill can be used.

In the present invention, it is preferable to monitor the total accumulated pore volume after pulverization and adjust the pulverization conditions so that these values do not deviate from the above range.
The gypsum obtained as described above, preferably having a specific total cumulative pore volume, can then be re-precipitated by dissolving it in an aqueous medium containing seed crystal gypsum to obtain regenerated gypsum. it can. As the aqueous medium, water is preferable.
Here, the desired regenerated gypsum can be obtained by adjusting the type of seed crystals and the temperature of the aqueous medium. In order to maintain an appropriate precipitation rate of gypsum, the pH is preferably in the range of 4-8.
For example, when regenerating dihydrate gypsum, dihydrate gypsum is present as a seed crystal, preferably in an aqueous medium of 90 ° C. or less, more preferably 50 to 80 ° C., preferably 0.2 to 6 hours, More preferably, it can be by a method of stirring for 0.5 to 2 hours.

When regenerating type II anhydrous gypsum, type II anhydrous gypsum is present as a seed crystal, preferably in an aqueous medium at 110 ° C. or higher, more preferably 140 to 200 ° C., preferably 0.2 to 6 hours, More preferably, it can be by a method of stirring for 0.5 to 2 hours.
When regenerating α-hemihydrate gypsum, α-hemihydrate gypsum is present as a seed crystal, preferably in an aqueous medium at 90 to 130 ° C, more preferably 95 to 120 ° C, preferably 0.2 to The stirring can be performed for 6 hours, more preferably 0.5 to 2 hours. Here, since the stable production conditions of α-hemihydrate gypsum and type II anhydrous gypsum partially overlap, when regenerating α-hemihydrate gypsum, the existing ratio of type II anhydrous gypsum in the aqueous medium is It is preferable to control so that it becomes 5 mass% or less of the total gypsum mass. This control is performed by, for example, sampling an aqueous medium in which seed crystal gypsum is present in a timely manner to determine the abundance of type II anhydrous gypsum in the seed crystal gypsum, and showing an upward trend to the extent that this value is likely to exceed the above value. At least a part of the seed crystal gypsum in the aqueous medium and adding a corresponding amount of α-anhydride gypsum. When regenerating α-hemihydrate gypsum, an aqueous medium for dissolving and reprecipitating gypsum after pulverization treatment is sodium sulfate, potassium sulfate or ammonium sulfate in order to avoid duplication of stable production conditions with type II anhydrous gypsum. It is preferable to contain. Here, the concentration of sodium sulfate, potassium sulfate or ammonium sulfate is 1 to 10% by mass, more preferably 2 to 5% by mass. Furthermore, in this case, the temperature of the aqueous medium is preferably set to a relatively low temperature condition within the above temperature range.

The initial particle size of the seed crystal gypsum in the aqueous medium in which gypsum having a specific total cumulative pore volume is dissolved and reprecipitated is preferably 10 to 60 μm, and more preferably 20 to 40 μm. The abundance ratio of the seed crystals is preferably 100 to 400 g / L, more preferably 200 to 300 g / L.
The entire regenerated gypsum obtained as described above may be recovered as a product, or a part thereof may be recycled as a seed crystal. When a part of the regenerated gypsum is recycled as a seed crystal, it is preferably pulverized once and adjusted to an appropriate particle size to obtain a seed crystal.
The regenerated gypsum obtained as described above can be separated from water by a known filtration method. Specifically, a filtration device such as a rotary screen, drum filter, disc filter, Nutsche filter, filter press, screw press, tube press, etc .; a method of separating water from a centrifugal separator such as a screw decanter, screen decanter, etc. can do. The collected filtrate can be recycled and reused in the aqueous medium in the dissolution and reprecipitation process of hemihydrate gypsum.

The gypsum thus regenerated is a gypsum with a small total cumulative pore volume. That is, the total cumulative pore volume of the gypsum regenerated by the method of the present invention is 0.5 mL / g or less, preferably 0.3 to 0.4 mL / g, and further a fine pore diameter of 0.1 to 5 μm. The cumulative pore volume of the pores is 0.001 to 0.1 mL / g, preferably 0.005 to 0.05 mL / g. Moreover, the volume average particle diameter is 20-80 micrometers, for example, More preferably, it is 40-60 micrometers.
The heating step and the pulverizing step may be performed in a batch manner, or may be a continuous process. Furthermore, each may be an independent process, or may be a process in which both processes are connected in series. Further, these steps may be steps independent of the gypsum dissolution and reprecipitation steps, or may be continuous steps.

  The dissolution and reprecipitation steps of gypsum may be performed in a batch manner or a continuous process, but the advantages of the present invention are particularly exerted when performed in a continuous process. At least the pulverization step and the dissolution and reprecipitation step of gypsum are continuous processes, these are connected in series, and a process including a step of circulating a part of the obtained regenerated gypsum as seed gypsum has the advantage of the present invention. It is particularly preferable in that it can be maximized. In the present invention, since the dissolution and reprecipitation of gypsum occurs stably in the presence of seed crystal gypsum, the particle size of gypsum increases with time in the reaction tank (dissolution / reprecipitation tank). Although the seed crystal surface area in the reaction vessel decreases with the increase in the particle size of the gypsum, in the present invention, the gypsum in the reaction vessel is crushed or the seed crystal gypsum having a small particle size is supplied from outside the system. By responding, it is possible to stably produce gypsum of the same quality.

Hereinafter, the method of the present invention will be described more specifically with reference to the drawings.
Below, the case where it is set as the continuous process performed in order of a heating process, a grinding | pulverization process, the melt | dissolution of a gypsum, and a reprecipitation process is demonstrated as one aspect | mode of the method of this invention. Moreover, the crushing of the gypsum board waste material and the separation process of the board base paper as the pretreatment and the filtration process of the produced recycled gypsum were also shown at the same time.

FIG. 1 is an explanatory schematic view showing an example of an apparatus for suitably carrying out one embodiment of the method of the present invention.
The recovered gypsum board waste 1 is first primarily crushed to a size of about 100 to 300 mm by a biaxial crusher 2, and then the dihydrate gypsum is about 0.5 to 2 mm by a biaxial impact crusher 3. Secondary crushing. Thereafter, the crushed pieces are sent to the trommel 4 and separated into waste board base paper 5 and waste gypsum.

The waste gypsum is then put into the calcining furnace 6 and heat treated. The obtained gypsum is once stored in the silo 7 and then quantitatively fed to the ball mill 8. Here, the gypsum after pulverization is sampled from the outlet of the ball mill 8 in a timely manner, the total cumulative pore volume of the gypsum is analyzed by a mercury porosimeter, and the pulverization conditions of the ball mill 8 are appropriately adjusted. Is controlled to be within the above range.
The gypsum after pulverization is sent to the crystallization reaction tank 9. The gypsum after pulverization is once dissolved in the crystallization reaction tank 9, and depending on the type of seed crystal present in the aqueous medium in the reaction tank, the temperature condition of the reaction tank, and the type of the aqueous medium, dihydrate gypsum, type II Reprecipitate as anhydrous gypsum or α-hemihydrate gypsum.
Part of the recycled gypsum slurry 13 exiting from the reaction tank is optionally returned to the reaction tank 9 and recycled as seed crystals, and most of the remainder is sent to the drum filter 10. In the drum filter 10, the aqueous medium and the regenerated gypsum are separated to obtain regenerated gypsum 11. On the other hand, the separated filtrate 12 is returned to the crystallization reaction tank 9 and recycled as an aqueous medium.

  Hereinafter, the effect of the method of the present invention will be verified by examples.

Example 1
Dihydrate gypsum of about 0.2 to 5 mm obtained from gypsum board waste was heated at 140 ° C. for 60 minutes in a hot air dryer. This gypsum was hemihydrate gypsum with a total cumulative pore volume of 1.8 mL / g.
This was pulverized by a ball mill, the volume average particle diameter was 8 μm, and the total cumulative pore volume was 0.9 mL / g.
On the other hand, the volume average particle diameter is 30 μm, the total cumulative pore volume is 0.5 mL / g, and the cumulative pore volume of pores having a pore diameter of 0.1 to 5 μm is 20% by mass of 0.08 mL / g dihydrate gypsum. The water slurry was prepared in a continuous reaction tank having a capacity of 6 L while being maintained at 50 ° C. with stirring.
To this reactor, the ground hemihydrate gypsum produced above was supplied at a feed rate of 0.4 kg / h and water at a feed rate of 1.6 kg / h, and a 2.0 kg / h slurry was taken out from the reactor outlet. .
When the gypsum at the outlet of the reaction vessel was analyzed 4 hours after the start of the supply, the volume average particle size was 35 μm, the total cumulative pore volume was 0.5 ml / g, and the cumulative pore volume was 0.06 ml / g with a pore size of 0.1 to 5 μm. The dihydrate gypsum. Further analysis after 4 hours revealed that the dihydrate gypsum had a volume average particle size of 42 μm, a total cumulative pore volume of 0.4 ml / g, and a pore size of 0.1 to 5 μm and a cumulative pore volume of 0.05 ml / g. It was. At this point, a homogenizer was introduced into the slurry in the reaction vessel, and operation was continued until the volume average particle size of the gypsum at the exit of the reaction vessel reached 40 μm. Thereafter, the same analysis was performed after 2 hours. As a result, dihydrate gypsum having a volume average particle diameter of 41 μm, a total cumulative pore volume of 0.4 ml / g, and a cumulative pore volume of 0.05 ml / g having a pore diameter of 0.1 to 5 μm. Met. As described above, the control of the particle size can be easily performed by appropriately crushing the gypsum in the reaction tank around the target particle size, and stably produce dihydrate gypsum of the above quality. It was confirmed that it was possible.

Comparative Example 1
The dihydrate gypsum of about 0.2 to 5 mm obtained from the gypsum board waste material was heated at 140 ° C. for 60 minutes in a hot air dryer, and then passed through a sieve having an opening of 2 mm. The total cumulative pore volume of hemihydrate gypsum after passing through the sieve was 1.8 mL / g.
On the other hand, the volume average particle diameter is 30 μm, the total cumulative pore volume is 0.5 mL / g, and the cumulative pore volume of pores having a pore diameter of 0.1 to 5 μm is 20% by mass of 0.08 mL / g dihydrate gypsum. The water slurry was prepared in a continuous reaction tank having a capacity of 6 L while being maintained at 50 ° C. with stirring.
Into this reaction tank, the hemihydrate gypsum after passing through the sieve manufactured above was supplied at a feed rate of 0.4 kg / h and water at a feed rate of 1.6 kg / h, and 2.0 kg / h of slurry was taken out from the reaction tank outlet. It was.
When gypsum at the outlet of the reaction vessel was analyzed 4 hours after the start of the supply, the volume average particle size was 29 μm, the total cumulative pore volume was 0.53 mL / g, and the cumulative pore volume was 0.12 mL / g with a pore size of 0.1 to 5 μm. The dihydrate gypsum. Further analysis after 4 hours revealed that the dihydrate gypsum had a volume average particle diameter of 27 μm, a total cumulative pore volume of 0.61 mL / g, and a cumulative pore volume of 0.18 mL / g with a pore diameter of 0.1 to 5 μm. It was.

The explanatory schematic diagram showing an example of the device for carrying out the method of the present invention.

1: Waste gypsum board 2: 2-axis crusher 3: 2-axis impact crusher 4: Trommel 5: Waste board base paper 6: Calcining furnace 7: Silo 8: Pin mill 9: Crystallization reactor 10: Drum filter 11: Regeneration Gypsum 12: Filtrate 13: Regenerated gypsum slurry

Claims (11)

A method for regenerating gypsum in gypsum board waste, wherein gypsum obtained from gypsum board waste is dissolved and reprecipitated in an aqueous medium in which seed gypsum is present,
The step of dissolving and reprecipitating the gypsum is performed in a continuous process, and the step of dissolving and reprecipitating the gypsum,
A method for reclaiming gypsum in gypsum board waste, characterized by performing a step of pulverizing seed crystal gypsum in the aqueous medium or a step of supplying seed crystal gypsum having a small particle diameter from outside the system.   The method of Claim 1 including the process of performing the process which heats gypsum before the process of melt | dissolving and reprecipitating the said gypsum.   The method of Claim 1 including the process of circulating a part of re-deposited reproduction | regeneration gypsum as seed crystal gypsum. In the process of circulating a part of the re-deposited regenerated gypsum as seed crystal gypsum,
The method according to claim 3, wherein a part of the re-deposited regenerated gypsum is pulverized and then circulated as seed crystal gypsum.   The regenerated gypsum is dihydrate gypsum, and the dissolution and reprecipitation are performed in an aqueous medium at a temperature of 90 ° C or lower where dihydrate gypsum is present as seed crystal gypsum. The method described in 1.   The regenerated gypsum is type II anhydrous gypsum, and the dissolution and reprecipitation are performed in an aqueous medium at a temperature of 110 ° C or higher where type II anhydrous gypsum is present as seed crystal gypsum. The method according to one item.   The regenerated gypsum is α-hemihydrate gypsum, and the dissolution and reprecipitation is performed in an aqueous medium at a temperature of 90 to 130 ° C where α-hemihydrate gypsum is present as seed crystal gypsum. The method as described in any one of.   Furthermore, the method of Claim 7 which controls so that the abundance ratio of the type II anhydrous gypsum in the aqueous medium in which the said dissolution and reprecipitation are performed will be 5 mass% or less of the total gypsum mass.   The method according to claim 7 or 8, wherein the aqueous medium in which the dissolution and reprecipitation takes place contains sodium sulfate, potassium sulfate or ammonium sulfate.   The method as described in any one of Claims 1-9 whose total cumulative pore volume of the reproduction | regeneration gypsum obtained is 0.5 mL / g or less.   The method according to claim 10, wherein a cumulative pore volume of pores having a pore diameter of 0.1 to 5 μm in the obtained regenerated gypsum is 0.001 to 0.1 mL / g.

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