JP6195238B2 - How to recycle gypsum in gypsum board waste as dihydrate gypsum - Google Patents
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- 229910052602 gypsum Inorganic materials 0.000 title claims description 110
- 239000010440 gypsum Substances 0.000 title claims description 110
- 150000004683 dihydrates Chemical class 0.000 title claims description 46
- 239000002699 waste material Substances 0.000 title claims description 28
- 238000000034 method Methods 0.000 claims description 20
- 239000002245 particle Substances 0.000 claims description 19
- 239000000725 suspension Substances 0.000 claims description 11
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 8
- 239000012736 aqueous medium Substances 0.000 claims description 7
- 239000000203 mixture Substances 0.000 claims description 5
- 238000011069 regeneration method Methods 0.000 claims description 5
- 230000001376 precipitating effect Effects 0.000 claims description 2
- 239000003795 chemical substances by application Substances 0.000 claims 1
- 238000006703 hydration reaction Methods 0.000 description 22
- ZOMBKNNSYQHRCA-UHFFFAOYSA-J calcium sulfate hemihydrate Chemical compound O.[Ca+2].[Ca+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O ZOMBKNNSYQHRCA-UHFFFAOYSA-J 0.000 description 18
- 230000036571 hydration Effects 0.000 description 14
- 238000003756 stirring Methods 0.000 description 12
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 6
- 239000002585 base Substances 0.000 description 6
- 239000013078 crystal Substances 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- 239000000123 paper Substances 0.000 description 6
- 230000001172 regenerating effect Effects 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 5
- -1 alkali metal salt Chemical class 0.000 description 3
- 238000001914 filtration Methods 0.000 description 3
- 238000001878 scanning electron micrograph Methods 0.000 description 3
- 238000005245 sintering Methods 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000010298 pulverizing process Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 229910052783 alkali metal Inorganic materials 0.000 description 1
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 1
- 229910052921 ammonium sulfate Inorganic materials 0.000 description 1
- 235000011130 ammonium sulphate Nutrition 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 description 1
- 125000004432 carbon atom Chemical group C* 0.000 description 1
- 238000006477 desulfuration reaction Methods 0.000 description 1
- 230000023556 desulfurization Effects 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000003337 fertilizer Substances 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 239000003546 flue gas Substances 0.000 description 1
- 239000008187 granular material Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000011087 paperboard Substances 0.000 description 1
- 239000011505 plaster Substances 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000009418 renovation Methods 0.000 description 1
- 238000007873 sieving Methods 0.000 description 1
- 229910001415 sodium ion Inorganic materials 0.000 description 1
- 239000004094 surface-active agent Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
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- Processing Of Solid Wastes (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Description
本発明は、石膏ボード廃材から石膏を再生する方法に関し、更に詳細には、石膏ボード廃材中の石膏を二水石膏として再生する方法に関する。 The present invention relates to a method for regenerating gypsum from gypsum board waste, and more particularly to a method for regenerating gypsum in gypsum board waste as dihydrate gypsum.
石膏ボードは、石膏を板状にし、特殊な板紙で包んだ建築材料である。石膏ボード中で石膏は、二水石膏として存在しており、この結晶水により石膏ボードは優れた耐火性を有する。 Gypsum board is a building material that is made of plaster and wrapped with special paperboard. Gypsum is present in the gypsum board as dihydrate gypsum, and the gypsum board has excellent fire resistance due to this crystal water.
石膏ボード廃材の発生量は、年間約１５０万ｔあるといわれ、そのうち１００万ｔは再利用されずに埋立処分されている。埋立処分にも費用を要し、再利用が望まれる。石膏ボード廃材の再利用手段としては、石膏ボード廃材から原紙を分離し、得られた石膏をそのまま利用する方法（特許文献１）、石膏ボード廃材の粉砕物に炭素数４〜６のオキシカルボン酸アルカリ金属塩、硫酸アルカリ、硫酸アンモニウム等を添加することにより、二水石膏として再生する方法（特許文献２、３）、石膏ボード廃材の粉砕物に、水性媒体中で種晶石膏を添加し、５０〜８０℃で０．２〜６時間攪拌して二水石膏として再生する方法（特許文献４）等が報告されている。 The amount of gypsum board waste generated is said to be about 1.5 million tons per year, of which 1 million tons are landfilled without being reused. Landfill disposal is expensive, and reuse is desired. As a means for reusing gypsum board waste, a method of separating base paper from gypsum board waste and using the obtained gypsum as it is (Patent Document 1), oxycarboxylic acid having 4 to 6 carbon atoms in pulverized gypsum board waste A method of regenerating as dihydrate gypsum by adding an alkali metal salt, alkali sulfate, ammonium sulfate or the like (Patent Documents 2 and 3), adding seed crystal gypsum in an aqueous medium to pulverized gypsum board waste, A method of regenerating as dihydrate gypsum by stirring at -80 ° C for 0.2-6 hours has been reported (Patent Document 4).
しかしながら、特許文献１記載の方法で得られた石膏には界面活性剤等が含まれており、再利用は困難であった。また、特許文献２及び３の方法で得られた二水石膏中にも添加した成分に由来するナトリウムイオンやクエン酸イオンが二水石膏表面に吸着しており、再利用する際の硬化反応に悪影響を及ぼすという欠点があった。さらに、特許文献４の方法においては、種晶石膏が必要であることの他に、本発明者の追試では半水石膏と二水石膏の混合物しか得られず、さらに得られた混合物の粒子径が小さいため、再利用時の焼結反応で高純度の半水石膏が得られないという問題があった。 However, the gypsum obtained by the method described in Patent Document 1 contains a surfactant and the like, and is difficult to reuse. In addition, sodium ions and citrate ions derived from the components added also in the dihydrate gypsum obtained by the methods of Patent Documents 2 and 3 are adsorbed on the surface of the dihydrate gypsum and are used for the curing reaction when reused. There was a drawback of having an adverse effect. Furthermore, in the method of Patent Document 4, in addition to the need for seed crystal gypsum, in the follow-up test of the present inventor, only a mixture of hemihydrate gypsum and dihydrate gypsum can be obtained, and the particle size of the obtained mixture is Therefore, there is a problem that high-purity hemihydrate gypsum cannot be obtained by a sintering reaction at the time of reuse.
従って、本発明は、石膏ボード廃材中の石膏から、何ら添加剤を使用することなく、石膏ボードへの再利用が可能な粒子径が大きく、かつ高純度の二水石膏を再生する方法を提供することにある。 Therefore, the present invention provides a method for regenerating a high-purity dihydrate gypsum from gypsum in waste gypsum board that has a large particle size and can be reused in gypsum board without using any additives. There is to do.
そこで本発明者は、石膏ボード廃材から高純度で大粒子径の二水石膏を再生すべく種々検討したところ、石膏ボード廃材を加熱処理して半水石膏とし、これを水懸濁液とし、７０〜８５℃という高温で７〜２４時間という長時間かけて析出させることにより、二水石膏だけが選択的に析出し、かつその粒子が大形化することを見出し、本発明を完成した。 Therefore, the present inventor made various studies to regenerate the high-purity and large-particle-diameter dihydrate gypsum from the gypsum board waste material. By precipitating over a long time of 7 to 24 hours at a high temperature of 70 to 85 ° C., it was found that only dihydrate gypsum was selectively precipitated and the particles were enlarged, thereby completing the present invention.
すなわち、本発明は、次の〔１〕〜〔５〕の発明を提供するものである。 That is, the present invention provides the following inventions [1] to [5].
〔１〕石膏ボード廃材を加熱処理して石膏ボード廃材中の二水石膏を半水石膏とし、当該半水石膏を水性媒体中に懸濁した後、７０〜８５℃で７〜２４時間攪拌し、短径４０μｍ以上でアスペクト比１〜３の二水石膏を析出させることを特徴とする、石膏ボード廃材中の石膏を二水石膏として再生する方法。
〔２〕得られる二水石膏が、短径４０〜８０μｍ、長径８０〜１２０μｍ、アスペクト比１〜３の二水石膏である〔１〕記載の再生方法。
〔３〕攪拌時間が、７〜２０時間である〔１〕又は〔２〕記載の再生方法。
〔４〕半水石膏の水性媒体懸濁液中の濃度が、１５〜３５質量％である〔１〕〜〔３〕のいずれかに記載の再生方法。
〔５〕石膏ボード廃材の加熱処理が、１５０〜２５０℃で、３０分〜５時間である〔１〕〜〔４〕のいずれかに記載の再生方法。
[1] Gypsum board waste is heat-treated to make dihydrate gypsum in gypsum board waste into half-water gypsum, which is suspended in an aqueous medium and then stirred at 70 to 85 ° C. for 7 to 24 hours. A method for regenerating gypsum in gypsum board waste as dihydrate gypsum, characterized in that dihydrate gypsum having a minor axis of 40 μm or more and an aspect ratio of 1 to 3 is precipitated.
[2] The regeneration method according to [1], wherein the obtained dihydrate gypsum is dihydrate gypsum having a minor axis of 40 to 80 μm, a major axis of 80 to 120 μm, and an aspect ratio of 1 to 3.
[3] The regeneration method according to [1] or [2], wherein the stirring time is 7 to 20 hours.
[4] The regeneration method according to any one of [1] to [3], wherein the concentration of hemihydrate gypsum in the aqueous medium suspension is 15 to 35% by mass.
[5] The regeneration method according to any one of [1] to [4], wherein the heat treatment of the gypsum board waste material is performed at 150 to 250 ° C. for 30 minutes to 5 hours.
本発明方法によれば、石膏ボード廃材から短径４０μｍ以上でアスペクト比１〜３という大形かつ粒子状の二水石膏が高純度で得られる。このようにして得られる大粒径かつ高純度の二水石膏は、焼成工程で半水石膏への移行がスムーズであることから、石膏ボード原料として直接再利用することができる。また、その他肥料、地盤改良材等としても再利用可能である。 According to the method of the present invention, large and particulate dihydrate gypsum having a minor axis of 40 μm or more and an aspect ratio of 1 to 3 can be obtained with high purity from waste gypsum board. The large particle size and high purity dihydrate gypsum obtained in this manner can be directly reused as a gypsum board raw material because the transition to hemihydrate gypsum is smooth in the firing step. It can also be reused as other fertilizers and ground improvement materials.
本発明方法においては、まず、石膏ボード廃材を加熱処理して石膏ボード廃材中の二水石膏を半水石膏とする。
原料である石膏ボード廃材としては、石膏ボードの生産工程及び建築現場の施工工程で発生する端材、残材、改装、解体工事で発生する石膏ボード廃材が挙げられる。石膏ボード廃材は、通常その大きさが一定でなく、また原紙を有しているので、粉砕し、原紙を除去して使用するのが好ましい。
上記破砕及び原紙の除去は、いずれも公知の方法によって行うことができる。例えば原紙の分離工程は、特開平１０−２８６５５３号公報、特開２０００−２５４５３１号公報等に記載された方法で行うことができる。
粉砕後の石膏ボード廃材の粒径は、機械的に運搬する際の容易さから、平均粒径として０．１〜１０mmであることが好ましく、０．１〜５mmであることがより好ましい。この平均粒径は、ふるい分けにより測定することができる。
In the method of the present invention, first, the gypsum board waste material is heat-treated, and the dihydrate gypsum in the gypsum board waste material is used as the half-water gypsum.
Examples of the gypsum board waste material, which is a raw material, include scraps generated in the gypsum board production process and construction site construction process, remaining materials, renovation, and gypsum board waste generated in demolition work. Since the gypsum board waste is usually not uniform in size and has base paper, it is preferably used after pulverizing and removing the base paper.
Both the crushing and the removal of the base paper can be performed by known methods. For example, the separation process of the base paper can be performed by a method described in JP-A-10-286553, JP-A-2000-254531, and the like.
The particle size of the gypsum board waste after pulverization is preferably 0.1 to 10 mm, more preferably 0.1 to 5 mm as an average particle size, from the viewpoint of ease of mechanical transportation. This average particle size can be measured by sieving.
石膏ボード廃材の加熱処理は、石膏ボード廃材中の二水石膏を半水石膏に変換できる条件であればよく、１１０〜２５０℃に１０分〜１０時間加熱するのが好ましく、１５０〜２５０℃に３０分〜５時間加熱するのがより好ましく、１５０〜２５０℃に４０分〜４時間加熱するのがさらに好ましい。加熱装置としては、熱風乾燥機、伝導電熱乾燥機等を用いることができる。なお、ここで加熱した半水石膏はできるだけIII型無水石膏を含まないほうがよい。 The heat treatment of the gypsum board waste material may be performed under the condition that dihydrate gypsum in the gypsum board waste material can be converted into hemihydrate gypsum, and is preferably heated to 110 to 250 ° C. for 10 minutes to 10 hours, and to 150 to 250 ° C. Heating for 30 minutes to 5 hours is more preferable, and heating to 150 to 250 ° C. for 40 minutes to 4 hours is even more preferable. As the heating device, a hot air dryer, a conductive electric heat dryer or the like can be used. The heated hemihydrate gypsum should contain as little as possible type III anhydrous gypsum.
前記加熱処理により、石膏ボード廃材中の二水石膏が半水石膏に変換される。 By the heat treatment, dihydrate gypsum in the gypsum board waste material is converted to hemihydrate gypsum.
次に、得られた半水石膏を水性媒体中に懸濁する。用いられる水性媒体としては、水が好ましい。半水石膏の水性媒体懸濁液中の濃度は、１０〜３５質量％が好ましく、１５〜３５質量％がより好ましく、２０〜３５質量％がさらに好ましい。懸濁液中の半水石膏濃度がこの範囲にあると、攪拌性及び粒径の大きな二水石膏が得られる点で好ましい。なお、この懸濁は、室温、例えば１０〜３５℃の条件で行うことができる。 The resulting hemihydrate gypsum is then suspended in an aqueous medium. The aqueous medium used is preferably water. 10-35 mass% is preferable, as for the density | concentration in the aqueous medium suspension of hemihydrate gypsum, 15-35 mass% is more preferable, and 20-35 mass% is further more preferable. When the concentration of hemihydrate gypsum in the suspension is in this range, it is preferable in that dihydrate gypsum having a large stirring property and a large particle size can be obtained. In addition, this suspension can be performed on the conditions of room temperature, for example, 10-35 degreeC.
次に懸濁液を７０〜８５℃で７〜２４時間攪拌して、短径４０μｍ以上でアスペクト比１〜３の二水石膏を選択的に析出させる。反応温度が７０℃未満又は反応時間が７時間未満では、大粒径の二水石膏は得られるが、アスペクト比が大きくなる。例えば６０℃で攪拌した場合には、長時間攪拌すれば二水石膏は得られるが、その粒子はアスペクト比の大きい針状であり、大粒径のものが得られない。一方、７０℃を超える温度で攪拌しても攪拌時間が６時間程度では半水石膏と二水石膏の混合物となってしまう。
より好ましい攪拌条件（水和反応条件）は、７０〜８５℃で７〜２０時間であり、さらに好ましくは７０〜８５℃で７〜１５時間である。
また、攪拌速度は、特に限定されず、１００ｒ／ｍｉｎ以上が好ましく、１００〜４００ｒ／ｍｉｎがより好ましく、１００〜３００ｒ／ｍｉｎがさらに好ましい。
また、攪拌前に種晶を添加する必要はないが、得られる二水石膏の粒子径が小さくならず、アスペクト比が大きくならない範囲で添加してもよく、例えば、０〜１質量％濃度の排煙脱硫石膏を添加してもよい。
Next, the suspension is stirred at 70 to 85 ° C. for 7 to 24 hours to selectively precipitate dihydrate gypsum having a minor axis of 40 μm or more and an aspect ratio of 1 to 3. When the reaction temperature is less than 70 ° C. or the reaction time is less than 7 hours, a large particle size dihydrate gypsum can be obtained, but the aspect ratio becomes large. For example, in the case of stirring at 60 ° C., dihydrate gypsum can be obtained by stirring for a long time, but the particles are needle-shaped with a large aspect ratio, and those having a large particle size cannot be obtained. On the other hand, even if stirring is performed at a temperature exceeding 70 ° C., if the stirring time is about 6 hours, a mixture of hemihydrate gypsum and dihydrate gypsum is obtained.
More preferable stirring conditions (hydration reaction conditions) are 7 to 20 hours at 70 to 85 ° C, and more preferably 7 to 15 hours at 70 to 85 ° C.
Moreover, the stirring speed is not particularly limited, and is preferably 100 r / min or more, more preferably 100 to 400 r / min, and still more preferably 100 to 300 r / min.
Moreover, it is not necessary to add a seed crystal before stirring, but it may be added in a range where the particle size of the resulting dihydrate gypsum is not reduced and the aspect ratio is not increased. Flue gas desulfurization gypsum may be added.
本発明方法により得られる二水石膏は、短径４０μｍ以上でアスペクト比１〜３という粒状であり、石膏ボードに再利用する際の焼結反応が効率的に進行する。二水石膏のより好ましい形状は、短径４０〜８０μｍ、長径８０〜１２０μｍ、アスペクト比１〜３のものである。また、本発明方法により得られる二水石膏は高純度であり、純度９０％以上であり、より好ましくは９５％以上である。 The dihydrate gypsum obtained by the method of the present invention is a granule having a minor axis of 40 μm or more and an aspect ratio of 1 to 3, and the sintering reaction proceeds efficiently when reused in a gypsum board. More preferable shapes of the dihydrate gypsum are those having a minor axis of 40 to 80 μm, a major axis of 80 to 120 μm, and an aspect ratio of 1 to 3. Further, the dihydrate gypsum obtained by the method of the present invention has a high purity and is 90% or more in purity, more preferably 95% or more.
析出した二水石膏は、粒径が大きく、かつアスペクト比が小さいのでろ過性が極めて良好であり、通常のろ過手段、遠心分離手段により容易に採取することができる。具体的には、ロータリースクリーン、ドラムフィルター、ディスクフィルター、ヌッチェフィルター、フィルタープレス、スクリュウプレス、チューブプレス等のろ過装置；スクリュウデカンター、スクリーンデカンター等の遠心分離機等により、水と分離する方法を採用することができる。 The precipitated dihydrate gypsum has a large particle size and a small aspect ratio, and therefore has very good filterability, and can be easily collected by ordinary filtration means and centrifugal separation means. Specifically, a filtration device such as a rotary screen, drum filter, disk filter, Nutsche filter, filter press, screw press, tube press, etc .; a method of separating from water using a centrifugal separator such as a screw decanter or screen decanter can do.
得られた二水石膏は、例えばメタノール等により洗浄して乾燥を促進させることもできる。 The obtained dihydrate gypsum can be washed with, for example, methanol to accelerate drying.
本発明方法により得られる二水石膏は、高純度でかつ粒子径が大きいため、石膏ボードとして利用する際の焼結反応が効率的に進行する。従って、石膏ボードへの再利用が促進できる。 Since the dihydrate gypsum obtained by the method of the present invention has a high purity and a large particle diameter, the sintering reaction when used as a gypsum board efficiently proceeds. Therefore, the reuse to the gypsum board can be promoted.
次に実施例を挙げて、本発明を更に詳細に説明するが、本発明は何らこれに限定されるものではない。 EXAMPLES Next, although an Example is given and this invention is demonstrated still in detail, this invention is not limited to this at all.
実施例１
（１）操作条件
石膏ボード廃材（原紙除去、粉砕済、粒径０．１〜１mm）を２２０℃に６０分間加熱し、半水石膏を得た。室温下、得られた半水石膏に純水を添加し、１１〜３３質量％の半水石膏懸濁液を得た。半水石膏懸濁液を、攪拌速度２００ｒ／ｍｉｎ、４０〜７３℃で１８０分〜４８０分攪拌（水和反応）した。析出した石膏をろ取し、メタノールで洗浄した。
Example 1
(1) Operating conditions Gypsum board waste (base paper removed, ground, particle size 0.1 to 1 mm) was heated to 220 ° C. for 60 minutes to obtain hemihydrate gypsum. Pure water was added to the obtained hemihydrate gypsum at room temperature to obtain a 11-33% by mass hemihydrate gypsum suspension. The hemihydrate gypsum suspension was stirred (hydration reaction) at a stirring speed of 200 r / min at 40 to 73 ° C. for 180 to 480 minutes. The precipitated gypsum was collected by filtration and washed with methanol.
（２）水和温度６０℃で１８０分（３時間）水和反応させ、得られた石膏の走査型電子顕微鏡（ＳＥＭ）写真を撮影した。結果を図１に示す。懸濁液濃度１１質量％、２０質量％、２８質量％及び３３質量％のいずれにおいても、得られた結晶は針状でありアスペクト比の大きいものであった。この結晶のろ過性は低かった。この結果、特許文献４の攪拌条件では、アスペクト比が小さく、大粒径の二水石膏は得られないことが判明した。 (2) A hydration reaction was performed at a hydration temperature of 60 ° C. for 180 minutes (3 hours), and a scanning electron microscope (SEM) photograph of the resulting gypsum was taken. The results are shown in FIG. At any of the suspension concentrations of 11% by mass, 20% by mass, 28% by mass and 33% by mass, the obtained crystals were acicular and had a large aspect ratio. The filterability of this crystal was low. As a result, it has been found that, under the stirring conditions of Patent Document 4, a dihydrate gypsum having a small aspect ratio and a large particle size cannot be obtained.
（３）懸濁濃度２８質量％、水和温度を７３℃とし、水和時間を１８０分〜４８０分に変化させ、得られた石膏のＸ線回折スペクトルを測定した。
その結果、図２に示すように、水和温度７３℃の場合、水和時間６時間までは半水石膏又は半水石膏と二水石膏の混合物が生成するが、水和時間が７時間以上になると高純度の二水石膏が得られることが判明した。
(3) The suspension concentration was 28% by mass, the hydration temperature was 73 ° C., the hydration time was changed from 180 minutes to 480 minutes, and the X-ray diffraction spectrum of the obtained gypsum was measured.
As a result, as shown in FIG. 2, when the hydration temperature is 73 ° C., hemihydrate gypsum or a mixture of hemihydrate gypsum and dihydrate gypsum is produced up to a hydration time of 6 hours, but the hydration time is 7 hours or more. It was found that high purity dihydrate gypsum was obtained.
また、得られた石膏のＳＥＭ写真を図３に示す。図３より、水和時間７時間以上の場合に、アスペクト比が小さく大粒径の二水石膏が生成していることがわかる。 Moreover, the SEM photograph of the obtained gypsum is shown in FIG. FIG. 3 shows that dihydrate gypsum having a small aspect ratio and a large particle size is formed when the hydration time is 7 hours or more.
（４）懸濁液濃度２８質量％で、水和温度を４０〜７３℃に変化させ、水和時間を６〜８時間に変化させた場合に得られる石膏のＳＥＭ写真を図４に示す。
また、水和反応終了時間（二水石膏生成時間）及び石膏の溶解度に及ぼす水和温度の影響を図５に示す。
また、得られた二水石膏の平均長径及び平均短径に及ぼす過飽和度の影響を図６に示す。
図４より、水和温度７０℃以上、かつ水和時間７時間以上の場合に短径４０μｍ以上アスペクト比１〜３の大粒径の二水石膏が選択的に生成することが判明した。また、図５及び図６より、過飽和度〔（半水石膏の溶解量−二水石膏の溶解量）／二水石膏の溶解量〕が０．７６以下の時にアスペクト比の小さな二水石膏が選択的に生成することがわかる。
(4) FIG. 4 shows an SEM photograph of gypsum obtained when the suspension concentration is 28% by mass, the hydration temperature is changed to 40 to 73 ° C., and the hydration time is changed to 6 to 8 hours.
Moreover, the influence of the hydration temperature on the hydration reaction completion time (dihydrate gypsum formation time) and the solubility of gypsum is shown in FIG.
Moreover, the influence of the degree of supersaturation on the average major axis and the average minor axis of the obtained dihydrate gypsum is shown in FIG.
From FIG. 4, it was found that dihydric gypsum having a large particle size with a minor axis of 40 μm or more and an aspect ratio of 1 to 3 was selectively produced when the hydration temperature was 70 ° C. or more and the hydration time was 7 hours or more. Further, from FIGS. 5 and 6, when the degree of supersaturation [(dissolved amount of hemihydrate gypsum−dissolved amount of dihydrate gypsum) / dissolved amount of dihydrate gypsum] is 0.76 or less, dihydrate gypsum having a small aspect ratio is obtained. It turns out that it produces | generates selectively.
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