JP2007246306A - Reducing gypsum composition, method for producing the same, cement-based solidifying material, and solidifying method - Google Patents

Reducing gypsum composition, method for producing the same, cement-based solidifying material, and solidifying method Download PDF

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JP2007246306A
JP2007246306A JP2006068852A JP2006068852A JP2007246306A JP 2007246306 A JP2007246306 A JP 2007246306A JP 2006068852 A JP2006068852 A JP 2006068852A JP 2006068852 A JP2006068852 A JP 2006068852A JP 2007246306 A JP2007246306 A JP 2007246306A
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gypsum
cement
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calcium sulfite
gypsum composition
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JP4775045B2 (en
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Yukio Tasaka
行雄 田坂
Osamu Yoneda
修 米田
Mototaka Egawa
本隆 江川
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Ube Corp
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00025—Aspects relating to the protection of the health, e.g. materials containing special additives to afford skin protection

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Curing Cements, Concrete, And Artificial Stone (AREA)
  • Soil Conditioners And Soil-Stabilizing Materials (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reducible gypsum composition and a method of manufacturing the same by which the effect of suppressing the elusion of 6-valent chromium is uniformalized, the degradation of solidification strength is prevented and elusion suppressing cost is reduced and further, the cost of gypsum for solidification material is reduced and a solidification material manufacturing step is simplified. <P>SOLUTION: The reducible gypsum composition contains calcium sulfite hemihydrate and gypsum dihydrate. The method of manufacturing the reducible gypsum composition containing calcium sulfite hemihydrate and gypsum dihydrate is carried out by mechanically dehydrating slurry containing calcium sulfite hemihydrate in a flue gas desulfurization step and slurry containing gypsum dihydrate obtained by oxidizing the slurry containing calcium sulfite hemihydrate all together or separately, adding 0.25-1.0 mol calcium oxide based treating material per 1 mol free water of the dehydrated material and drying to be powdered. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、還元性せっこう組成物およびその製造方法に関し、特に、セメントに含有される六価クロムの溶出抑制、あるいは六価クロム汚染土壌からの六価クロムの溶出抑制を可能にする還元性せっこう組成物およびその製造方法に関する。本発明はまた、この還元性せっこう組成物をセメントに添加したセメント系固化材、さらにはこのセメント固化材で処理して六価クロムの溶出を抑制する固化処理方法に関する。   The present invention relates to a reductive gypsum composition and a method for producing the same, and in particular, reducibility that enables suppression of elution of hexavalent chromium contained in cement or suppression of elution of hexavalent chromium from hexavalent chromium-contaminated soil. The present invention relates to a gypsum composition and a method for producing the same. The present invention also relates to a cement-based solidified material obtained by adding this reducing gypsum composition to cement, and further to a solidified treatment method that suppresses elution of hexavalent chromium by treating with this cement solidified material.

セメントの主原料であるセメントクリンカーは、各種の原料をロータリーキルンにより高温焼成することで製造されている。しかしながら、このような高温条件で製造されたクリンカー中には、原料に不可避的に含まれるクロムが有害な六価クロムの形態で存在する場合がある。   A cement clinker, which is a main raw material of cement, is manufactured by firing various raw materials at a high temperature using a rotary kiln. However, in the clinker manufactured under such high temperature conditions, chromium inevitably contained in the raw material may exist in the form of harmful hexavalent chromium.

このようなセメントクリンカーを原料とするセメントをセメント系固化材として使用した場合、固化対象土によっては、固化処理土から、土壌環境基準値を上回る六価クロムが溶出する場合がある。   When a cement using such a cement clinker as a raw material is used as a cement-based solidifying material, hexavalent chromium exceeding the soil environment standard value may be eluted from the solidified soil depending on the solidification target soil.

一方、２００３年２月の土壌汚染対策法の施行に伴い、重金属汚染土壌の固化・不溶化処理技術への期待が高まっている。六価クロム汚染土は発見頻度の高い汚染物質の一つであり、その固化・不溶化技術が求められている。   On the other hand, with the enforcement of the Soil Contamination Countermeasures Law in February 2003, expectations for solidification / insolubilization treatment technology for heavy metal contaminated soil are increasing. Hexavalent chromium contaminated soil is one of the most frequently found pollutants, and its solidification / insolubilization technology is required.

このようなセメントに起因する固化処理土からの六価クロムの溶出防止方法または六価クロム汚染土壌の固化・不溶化などに関して、各種の還元剤の添加が知られている。例えば、特許文献１には、還元剤として、硫酸第一鉄、亜硫酸塩、チオ硫酸塩、硫黄、硫化物、高炉スラグ等が例示されている。さらには短・長期的な還元作用の持続性を確保するため、これらの還元剤を組合せて使用することも開示されている。   Addition of various reducing agents is known for the method for preventing elution of hexavalent chromium from the solidified soil caused by cement or the solidification / insolubilization of hexavalent chromium-contaminated soil. For example, Patent Document 1 exemplifies ferrous sulfate, sulfite, thiosulfate, sulfur, sulfide, blast furnace slag, and the like as a reducing agent. Furthermore, it is also disclosed that these reducing agents are used in combination in order to secure the short-term and long-term reduction action.

しかし、高炉スラグなどを除いて、これらの還元剤をセメントに５質量％以下程度の少量添加する場合、混合装置によっては、均一混合が困難であり不溶化効果のバラツキの一因となることがある。また、これらの還元剤を添加するためには、セメントとの混合のために、専用のタンク、計量器、輸送機器等の設備が必要になる。一方、高炉スラグなどは還元効果が小さく、多量添加が必要であり、このためセメント系固化材の強度発現性の低下に問題があった。また、高炉スラグを除いて、これらの還元剤は一般に高価であり、不溶化処理コストにも課題があった。   However, when these reducing agents are added in a small amount of about 5% by mass or less to cement, except for blast furnace slag, etc., uniform mixing may be difficult depending on the mixing device and may contribute to variations in the insolubilization effect. . Moreover, in order to add these reducing agents, facilities, such as a tank for exclusive use, a measuring device, and a transport apparatus, are needed for mixing with cement. On the other hand, blast furnace slag, etc. has a small reducing effect and needs to be added in a large amount. Therefore, there has been a problem in reducing the strength development of the cement-based solidified material. In addition, except for blast furnace slag, these reducing agents are generally expensive, and there is a problem in insolubilization costs.

特許文献２には、亜硫酸カルシウムとゼオライトとを併用することにより、六価クロムの溶出を抑制する方法が開示されている。しかし、工業薬品としての亜硫酸カルシウムは高価であり、固化成分として不活性なゼオライトの添加はやはり固化強度の低下に繋がる。   Patent Document 2 discloses a method for suppressing elution of hexavalent chromium by using calcium sulfite and zeolite in combination. However, calcium sulfite as an industrial chemical is expensive, and addition of an inactive zeolite as a solidifying component also leads to a decrease in solidification strength.

一方、従来、セメント系固化材として、軟弱地盤あるいは高含水泥状物を効率的に固化するため、エトリンガイトの多量生成を目的として各種セメントにせっこうを添加したものが使用されている。使用されるせっこうは固化材の製造方法によって異なるが、パン型、スクリュースネッキ型、パドル型ミキサーなどの汎用的な粉体混合装置を用いて製造する場合、乾燥粉体として流通しており、粉体としての取扱い性（混合性）が良好で、固化特性に優れるII型無水せっこうが主に用いられている。そしてこれらの添加・混合設備は汎用的に配備されている。   On the other hand, as a cement-based solidifying material, a material obtained by adding gypsum to various cements has been used for the purpose of producing a large amount of ettringite in order to efficiently solidify soft ground or highly hydrous mud. The gypsum used varies depending on the method of manufacturing the solidified material, but when manufactured using a general-purpose powder mixing device such as a pan type, screw snake type or paddle type mixer, it is distributed as a dry powder. Type II anhydrous gypsum, which has good handling properties (mixability) as a powder and excellent solidification characteristics, is mainly used. These addition / mixing facilities are provided for general use.

しかし、このII型無水せっこうは供給源が限られており、固化材を構成する主原料としては価格が高い。一方、比較的安価なせっこう源として排脱せっこうがあるが、通常５〜１０質量％前後の付着水分を含み、粉体流動性が悪く、上記の汎用的な混合設備では均一混合が困難である。この排脱せっこうの副生過程では、六価クロムの溶出抑制に効果の高い亜硫酸カルシウムが生成するが、通常、酸化処理されて二水せっこうとして副生している。また、排脱せっこうの副生過程で生成した亜硫酸カルシウムは熱風加熱乾燥時に酸化し易く取扱いが容易ではない。   However, this type II anhydrous gypsum has a limited supply source and is expensive as a main raw material constituting the solidified material. On the other hand, there is exhaust gypsum as a relatively inexpensive source of gypsum, but it usually contains 5 to 10% by mass of adhering moisture, and powder flowability is poor, and uniform mixing is difficult with the above-mentioned general-purpose mixing equipment. It is. In the by-product process of the excretion gypsum, calcium sulfite that is highly effective in suppressing elution of hexavalent chromium is produced, but it is usually oxidized and by-produced as dihydrate gypsum. In addition, calcium sulfite produced in the by-product process of gypsum is easily oxidized during hot air heating and drying and is not easy to handle.

特開２０００−８６３２２号公報JP 2000-86322 A 特開２００５−１１２７０６号公報JP-A-2005-112706

本発明は、従来の六価クロム溶出抑制対策材の問題点を解決すること、すなわち、セメントに含有される六価クロムの、または六価クロム汚染土壌からの六価クロムの溶出抑制効果の均一化、固化強度の低下防止、溶出抑制コストの低減を可能にし、かつ、固化材用せっこうコストの低減、固化材製造工程の簡略化を可能にする還元性せっこう組成物およびその製造方法を提供することを目的とする。   The present invention solves the problem of the conventional hexavalent chromium elution control material, that is, the uniform elution suppression effect of hexavalent chromium contained in cement or from hexavalent chromium contaminated soil. A reducing gypsum composition and a method for producing the same, which can reduce the cost of solidification material and simplify the production process of the solidification material. The purpose is to provide.

本発明者らは、これら従来技術の問題点を解決すべく鋭意検討した結果、排煙脱硫工程から副生する酸化処理前の亜硫酸カルシウム半水和物および二水せっこうを含む混合物の脱水物を、酸化カルシウム系処理材を用いて脱水物中の水分を消石灰（水酸化カルシウム）等に変換させるとともに、反応熱により乾燥させることにより乾燥粉末化した（以下、「乾粉化」という）。   As a result of intensive studies to solve the problems of the prior art, the present inventors have obtained a dehydration product of a mixture containing calcium sulfite hemihydrate and dihydrate gypsum before oxidation treatment by-produced from the flue gas desulfurization process. Was converted into hydrated lime (calcium hydroxide) or the like using a calcium oxide-based treatment material, and dried by reaction heat to form a dry powder (hereinafter referred to as “dry powder”).

その結果、乾粉化した還元性せっこう組成物は、良好な六価クロム溶出抑制性能を有し、さらに、固化材用せっこうとして、従来のII型無水せっこうと同等の固化作用を示すこと等を見出して、本発明を完成するに至った。   As a result, the dry powdered reducing gypsum composition has good hexavalent chromium elution suppression performance, and also exhibits a solidifying action equivalent to that of conventional type II anhydrous gypsum as a gypsum for solidifying material. As a result, the present invention has been completed.

すなわち、本発明は、亜硫酸カルシウム半水和物および二水せっこうを含有する還元性せっこう組成物である。   That is, the present invention is a reducing gypsum composition containing calcium sulfite hemihydrate and dihydrate gypsum.

本発明はまた、還元性せっこう組成物の全質量を基準に、亜硫酸カルシウム半水和物を５〜２０質量％、二水せっこうを６０〜９０質量％、および水酸化カルシウムを５〜２０質量％含む、上記の還元性せっこう組成物である。   The present invention also provides 5-20% by weight calcium sulfite hemihydrate, 60-90% by weight dihydrate gypsum, and 5-20% calcium hydroxide, based on the total weight of the reducing gypsum composition. It is said reducing gypsum composition containing a mass%.

本発明はさらに、これらの還元性せっこう組成物を、セメント１００質量部に対して５〜２０質量部を含むセメント系固化材である。   Furthermore, this invention is a cement-type solidification material which contains 5-20 mass parts of these reducing gypsum compositions with respect to 100 mass parts of cement.

本発明はまた、亜硫酸カルシウム半水和物および二水せっこうを含有する還元性せっこう組成物の製造方法であって、排ガス脱硫工程での亜硫酸カルシウム半水和物を含むスラリーおよび該スラリーを酸化して得られる二水せっこうを含むスラリーを機械脱水した脱水物、またはそれぞれのスラリーを別々に機械脱水した脱水物を混合した脱水混合物に、付着水分１モル当たり０．２５〜１．０モルの酸化カルシウム系処理材を加えて乾粉化する、還元性せっこう組成物の製造方法である。   The present invention also provides a method for producing a reduced gypsum composition containing calcium sulfite hemihydrate and dihydrate gypsum, the slurry containing calcium sulfite hemihydrate in the exhaust gas desulfurization step, and the slurry. To a dehydrated product obtained by mechanically dehydrating a slurry containing dihydrate gypsum obtained by oxidation, or by mixing a dehydrated product obtained by mechanically dehydrating each slurry separately, 0.25 to 1.0 per mole of attached water This is a method for producing a reducing gypsum composition in which a molar calcium oxide-based treatment material is added to dry powder.

さらに本発明は、酸化カルシウム系処理材がセメント仮焼原料である、還元性せっこう組成物の製造方法である。   Furthermore, this invention is a manufacturing method of a reducing gypsum composition whose calcium oxide type processing material is a cement calcination raw material.

そして本発明は、還元性せっこう組成物を添加して調製されたセメント系固化材を使用する、六価クロムの溶出を抑制する固化処理方法である。   And this invention is the solidification processing method which suppresses the elution of hexavalent chromium using the cement-type solidification material prepared by adding a reducing gypsum composition.

本発明によれば、副生品として発生する亜硫酸カルシウム半水和物および二水せっこうの混合物を、亜硫酸カルシウムの還元性能を損ねることなく乾粉化することが可能であり、また、この乾粉は固化材用添加材としてのII型無水せっこうと同等の固化性能を併せ持つことから、セメントへの添加のための製造工程・設備を簡略化することができ、六価クロムの不溶化処理コストの大幅な削減が期待される。また、還元剤となる亜硫酸カルシウムおよび二水せっこうが均一に混合されており、これを通常の還元剤に比較して多くの量をセメントに混合することにより、不溶化効果のバラツキが少ない効果を奏する。   According to the present invention, it is possible to dry the mixture of calcium sulfite hemihydrate and dihydrate gypsum generated as by-products without impairing the reduction performance of calcium sulfite. Since it has the same solidification performance as Type II anhydrous gypsum as an additive for solidifying material, it can simplify the manufacturing process and equipment for addition to cement, and greatly increase the cost of insolubilizing hexavalent chromium. Reduction is expected. In addition, calcium sulfite and dihydrate gypsum, which are reducing agents, are mixed uniformly, and by mixing a larger amount of this with cement compared to ordinary reducing agents, there is little effect on insolubilizing effects. Play.

本発明における亜硫酸カルシウム半水和物および二水せっこうは各種排煙脱硫工程からの副生品、代表的には、消石灰もしくは炭酸カルシウム等を吸収剤とする火力発電所等の処理工程から発生するものを好適に使用することができる。通常の排煙脱硫工程では、吸収工程の初期に発生した亜硫酸カルシウム半水和物は、ｐＨ調整後、酸化器で空気酸化され二水せっこうとされたのち、遠心脱水され、付着水分として５質量％前後の湿潤状態で排出される。   Calcium sulfite hemihydrate and dihydrate gypsum in the present invention are by-products from various flue gas desulfurization processes, typically generated from treatment processes such as thermal power plants using slaked lime or calcium carbonate as an absorbent. What to do can be used conveniently. In a normal flue gas desulfurization process, calcium sulfite hemihydrate generated at the beginning of the absorption process is subjected to pH oxidation, air-oxidized in an oxidizer to dihydrate gypsum, centrifugal dehydration, and 5% as adhering moisture. It is discharged in a wet state of around mass%.

本発明では、この過程におけるｐＨ調整および酸化処理工程を調整し、亜硫酸カルシウムの酸化率（残存率）を調整するか、もしくは各工程のスラリーを混合調製することにより、所定の亜硫酸カルシウム半水和物および二水せっこうを含むスラリーを得ることができる。その割合は、乾粉化した還元性せっこう組成物中の亜硫酸カルシウム半水和物の割合が５〜２０質量％となるように、脱水後の付着水分と酸化カルシウム系処理材の添加量を勘案して調整する。   In the present invention, the pH adjustment and oxidation treatment steps in this process are adjusted, the oxidation rate (residual rate) of calcium sulfite is adjusted, or the slurry of each step is mixed and prepared, whereby predetermined calcium sulfite hemihydrate is obtained. And a slurry containing dihydrate gypsum. The ratio takes into account the adhering moisture after dehydration and the amount of calcium oxide-based treatment material added so that the ratio of calcium sulfite hemihydrate in the dry gypsum composition reduced to 5 to 20% by mass. And adjust.

亜硫酸カルシウム半水和物の量が５質量％より少ない場合、還元効果が小さく、セメントからの六価クロムの溶出を抑制することが困難となり、亜硫酸カルシウム半水和物の量が２０質量％より多いと、相対的に二水せっこう量が低下し、この還元性せっこう組成物を添加した固化材において十分な固化強度を得ることが困難になる。また、微結晶である亜硫酸カルシウム半水和物の量が増加することにより、混合物の脱水性が低下し、付着水分が増加するか、もしくは脱水時間が長くなるため、好ましくない。   When the amount of calcium sulfite hemihydrate is less than 5% by mass, the reduction effect is small and it becomes difficult to suppress the elution of hexavalent chromium from the cement, and the amount of calcium sulfite hemihydrate is less than 20% by mass. If the amount is too large, the amount of gypsum dihydrate relatively decreases, and it becomes difficult to obtain sufficient solidification strength in the solidified material to which the reducing gypsum composition is added. In addition, an increase in the amount of calcium sulfite hemihydrate, which is a microcrystal, is not preferable because the dehydrating property of the mixture is lowered and the attached water is increased or the dehydrating time is increased.

所定の割合に調整した亜硫酸カルシウム半水和物および二水せっこうの混合スラリーは、遠心脱水機などの機械脱水により付着水分を３〜１０質量％程度にする。なお、所定割合の亜硫酸カルシウム半水和物および二水せっこうの混合物を得る方法としては、それぞれのスラリーを別々に機械脱水処理し、その後、両者を所定割合に混合することもできる。その際、亜硫酸カルシウム半水和物は、上述のように脱水性が悪いため、フィルタープレスなどを用いることが好ましい。脱水物の付着水分が１０質量％以上になると、乾粉化のための酸化カルシウム系処理材の添加量が増加し、固化の有効成分である二水せっこう含有量の減少に伴う固化強度の低下等好ましくない現象の発現に繋がり、さらにはトータルコストの増加に繋がる。一方、脱水物の付着水分が３質量％以下になると、保管中の脱水物が一部乾燥するなどして、亜硫酸カルシウム半水和物が酸化して還元性能が損なわれる恐れがある。   The mixed slurry of calcium sulfite hemihydrate and dihydrate gypsum adjusted to a predetermined ratio brings the adhering moisture to about 3 to 10% by mass by mechanical dehydration such as a centrifugal dehydrator. As a method for obtaining a mixture of calcium sulfite hemihydrate and dihydrate gypsum in a predetermined ratio, each slurry can be separately mechanically dehydrated, and then both can be mixed in a predetermined ratio. At that time, since calcium sulfite hemihydrate has poor dehydration property as described above, it is preferable to use a filter press or the like. When the moisture content of the dehydrated product is 10% by mass or more, the amount of calcium oxide-based treatment material added to dry powder increases, and the solidification strength decreases as the content of dihydrate gypsum, which is an active ingredient for solidification, decreases. This leads to the appearance of undesirable phenomena and the like, and further increases the total cost. On the other hand, when the moisture content of the dehydrated product is 3% by mass or less, the dehydrated product being stored may partially dry, and the calcium sulfite hemihydrate may be oxidized to impair the reduction performance.

酸化カルシウム系処理材としては、生石灰およびセメント製造工程において、サスペンションプレヒーター部分からキルン窯尻投入部までの工程から抜出したセメント仮焼原料の１種または２種を使用することができる。生石灰は通常の工業製品を使用することができるが、その粒度は５mm以下のものが好ましく、１mm以下であるものがより好ましい。   As a calcium oxide type processing material, 1 type or 2 types of the cement calcining raw materials extracted from the process from a suspension preheater part to a kiln kiln bottom input part in a quicklime and cement manufacturing process can be used. As the quicklime, a normal industrial product can be used, but the particle size is preferably 5 mm or less, more preferably 1 mm or less.

一方、セメント仮焼原料は、遊離酸化カルシウムを３０質量％以上含有するものが好ましい。なお、酸化カルシウム系処理材としてセメント仮焼原料を使用した場合には、仮焼粘土鉱物の共存により、せっこう付着水分の酸化カルシウムの単位質量当たりの脱水化率が生石灰を使用した場合よりも高くなる特徴がある。   On the other hand, the cement calcined raw material preferably contains 30% by mass or more of free calcium oxide. In addition, when the cement calcined raw material is used as the calcium oxide-based treatment material, the dehydration rate per unit mass of calcium oxide of the gypsum adhering moisture is higher than that when quick lime is used due to the coexistence of the calcined clay mineral. There is a feature that increases.

乾粉化は、脱水した亜硫酸カルシウム半水和物および二水せっこうの混合物に含まれる付着水分１モルあたり０．２５〜１モルの酸化カルシウム、もしくは含有される酸化カルシウム量が当該割合となるように、生石灰やセメント仮焼原料を加えて混合して行う。これにより、還元性せっこう組成物の付着水分を１．５質量％以下に低減でき、パウダーテスターにより測定された見掛け比重、安息角、スパチュラ角等を指数化して得られるＣａｒｒの粉体流動性指数が２０以上の還元性せっこう組成物を得ることができる。   Dry powdering is performed so that the amount of calcium oxide contained in the mixture of dehydrated calcium sulfite hemihydrate and dihydrate gypsum is 0.25 to 1 mol of calcium oxide per mol, or the amount of calcium oxide contained In addition, quick lime and cement calcined raw materials are added and mixed. As a result, the moisture content of the reduced gypsum composition can be reduced to 1.5% by mass or less, and the powder fluidity of Carr obtained by indexing the apparent specific gravity, repose angle, spatula angle, etc. measured by a powder tester. A reducing gypsum composition having an index of 20 or more can be obtained.

還元性せっこう組成物中の二水せっこう量は、亜硫酸カルシウム半水和物および二水せっこうの混合物の付着水分、生石灰系処理剤の種類及び添加量によって変化するが、せっこう本来の機能を発現させるためには、還元性せっこう組成物の全質量を基準に、６０〜９０質量％の範囲で含有させるのが好ましく、６５〜９０質量％の範囲で含有させるのがより好ましく、７０〜９０質量％の範囲で含有させるのが特に好ましい。   The amount of dihydrate gypsum in the reductive gypsum composition varies depending on the moisture content of the mixture of calcium sulfite hemihydrate and dihydrate gypsum, the type and amount of quicklime treatment agent, In order to express the function, it is preferably contained in the range of 60 to 90% by mass, more preferably in the range of 65 to 90% by mass, based on the total mass of the reducing gypsum composition, It is especially preferable to make it contain in 70-90 mass%.

また、脱水物の乾粉化のために添加した酸化カルシウム系処理材の水和の結果として生成する消石灰（水酸化カルシウム）は、亜硫酸カルシウム半水和物の乾粉化時の酸化を抑制するとともに、せっこうとしての機能発現に重要な役割を担うものである。このため、亜硫酸カルシウム半水和物および二水せっこうの混合物の付着水分量、酸化カルシウム系処理材の種類、添加量を調整して、水酸化カルシウム量は、還元性せっこう組成物の全質量を基準に、５〜２０質量％の範囲にあることが好ましい。   In addition, slaked lime (calcium hydroxide) generated as a result of hydration of the calcium oxide-based treatment material added to dry powder of dehydrated product suppresses oxidation during dry powdering of calcium sulfite hemihydrate, It plays an important role in the development of gypsum function. For this reason, the amount of calcium hydroxide is adjusted to the total amount of the reducing gypsum composition by adjusting the amount of adhering moisture, the type of calcium oxide-based treatment material, and the amount added in the mixture of calcium sulfite hemihydrate and dihydrate gypsum. It is preferably in the range of 5 to 20% by mass based on the mass.

水酸化カルシウム量が５質量％より少ないと、亜硫酸カルシウム半水和物および二水せっこうの混合物と酸化カルシウムとの水和反応および攪拌混合との相乗効果によってもたらされる、六価クロム溶出抑制効果が低下するか、あるいは固化強度が低下する。一方、水酸化カルシウム量が２０質量％より多いと、相対的に二水せっこう量が少なくなり、せっこうに起因する本来の機能が損なわれることになる。   When the amount of calcium hydroxide is less than 5% by mass, the hexavalent chromium elution suppression effect brought about by the hydration reaction of calcium sulfite hemihydrate and dihydrate gypsum mixture with calcium oxide and stirring and mixing. Or solidification strength decreases. On the other hand, when the amount of calcium hydroxide is more than 20% by mass, the amount of dihydrate gypsum becomes relatively small, and the original function due to gypsum is impaired.

なお、還元性せっこう組成物には、原材料である亜硫酸カルシウム半水和物、二水せっこう、および酸化カルシウム系処理材に含まれることがある炭酸カルシウム、シリカ、アルミナ、アルカリ等、あるいは、これらの化合物が不可避成分として混入されることがある。   The reducing gypsum composition includes calcium sulfite hemihydrate, dihydrate gypsum as raw materials, and calcium carbonate, silica, alumina, alkali, etc. that may be contained in the calcium oxide-based treatment material, or These compounds may be mixed as an inevitable component.

亜硫酸カルシウム半水和物および二水せっこうの混合物と酸化カルシウム系処理材との攪拌・混合には、通常のパドル、リボン、パン、ナウタ、傾胴型等の各種ミキサーを使用することができる。この攪拌・混合時には、亜硫酸カルシウム半水和物および二水せっこうの混合物中の付着水分と酸化カルシウム系処理材との水和反応の発熱により、二水せっこう中の結晶水の脱水による半水せっこう化あるいは無水せっこう化を起す場合がある。この結晶水の脱水が過度に起こると、固化材スラリーなどにおいて、化学混和剤（分散剤等）との相互作用も含めて流動性が大きく変化するため、還元性せっこう組成物に含まれる半水せっこうの含有量は、１５質量％以下が好ましく、１０質量％以下に抑制するのがより好ましい。   For mixing and mixing the calcium sulfite hemihydrate and dihydrate gypsum mixture with the calcium oxide-based treatment material, various types of mixers such as ordinary paddles, ribbons, breads, nauta, and tilted barrel types can be used. . During this stirring and mixing, the heat generated by the hydration reaction between the adsorbed water in the calcium sulfite hemihydrate and dihydrate gypsum mixture and the calcium oxide-based treatment material causes the half of the crystal water in the dihydrate gypsum to be dehydrated. Water gypsumification or anhydrous gypsumization may occur. If this dehydration of crystal water occurs excessively, the fluidity of the solidifying material slurry and the like, including the interaction with the chemical admixture (dispersant, etc.), changes greatly, so that it is included in the reducing gypsum composition. The content of water gypsum is preferably 15% by mass or less, and more preferably 10% by mass or less.

せっこうの半水化は、付着水分が１０質量％以下の亜硫酸カルシウム半水和物および二水せっこうの混合物を使用し、ミキサーへの亜硫酸カルシウム半水和物および二水せっこうの混合物あるいは酸化カルシウム系処理材の投入順序、添加速度、混合時間等を調整するか、必要に応じて冷却機能（ジャケット等）を付与することによって、乾粉化工程におけるせっこう温度を６０℃以下、好ましくは５０℃以下にすることで、抑制することができる。また、得られる還元性せっこう組成物の付着水分を０．０５〜１．５質量％に留めるのがより好ましい。なお、本発明の還元性せっこう組成物は、亜硫酸カルシウム半水和物および二水せっこうを含む混合物の脱水物から水分を、酸化カルシウム系処理材を用いて消石灰（水酸化カルシウム）等に変換させ、併せて反応熱により乾粉化したものであり、一般的には、０．５〜１０００μmの範囲の粒子からなる粉状体または顆粒状体が好適に用いられる。なお、顆粒状体の場合、乾粉化の条件により、１０００μm以上のものも生成するが、このような粗大な顆粒状体のものは、更に分級や粉砕して使用目的に合わせることもできる。   Gypsum hemihydrate uses a mixture of calcium sulfite hemihydrate and dihydrate gypsum with an adhering moisture content of 10% by weight or less, and a mixture of calcium sulfite hemihydrate and dihydrate gypsum to the mixer or The gypsum temperature in the dry-powdering step is adjusted to 60 ° C. or less by adjusting the order of addition of the calcium oxide-based treatment material, the addition rate, the mixing time, etc., or by providing a cooling function (jacket etc.) if necessary. It can suppress by setting it as 50 degrees C or less. Moreover, it is more preferable to keep the adhering moisture of the obtained reducing gypsum composition to 0.05 to 1.5% by mass. In addition, the reducing gypsum composition of the present invention uses water from the dehydrated mixture of calcium sulfite hemihydrate and dihydrate gypsum to slaked lime (calcium hydroxide) using a calcium oxide-based treatment material. These are converted into powders by reaction heat, and generally, a powdery body or a granular body composed of particles in the range of 0.5 to 1000 μm is preferably used. In addition, in the case of a granular body, a thing of 1000 micrometers or more is produced | generated according to the conditions of dry-powdering, However, The thing of such a coarse granular body can be further classified and grind | pulverized and it can match | combine with the intended purpose.

参考として、還元性せっこう組成物の製造フローの一例を図１に示した。   For reference, an example of the production flow of the reducing gypsum composition is shown in FIG.

これらの方法によって得られた還元性せっこうを、セメント１００質量部に対して５〜２０質量部添加して、六価クロム溶出抑制型セメント系固化材を製造する。その添加量は、セメント中の六価クロム含有量、固化対象とする土質の性状、六価クロム汚染土壌の汚染状況によって異なるため、還元性せっこう組成物の所要量を調整する。   The reducing gypsum obtained by these methods is added in an amount of 5 to 20 parts by mass with respect to 100 parts by mass of cement to produce a hexavalent chromium elution suppression type cement-based solidified material. The amount of addition varies depending on the hexavalent chromium content in the cement, the properties of the soil to be solidified, and the contamination status of the hexavalent chromium-contaminated soil, so the required amount of the reducing gypsum composition is adjusted.

還元性せっこう組成物が５質量部以下では、必要な六価クロム溶出抑制性能が得られないおそれがあるほか、十分な固化強度が得られない。一方、２０質量部以上添加しても、それ以上の効果が望めないか、あるいは固化強度が低下するか、処理土が過度に膨張する恐れがある。   If the reducing gypsum composition is 5 parts by mass or less, the necessary hexavalent chromium elution suppression performance may not be obtained, and sufficient solidification strength cannot be obtained. On the other hand, even if added in an amount of 20 parts by mass or more, no further effect can be expected, the solidification strength is lowered, or the treated soil may be excessively expanded.

還元性せっこう組成物を添加するセメントとしては、JIS R 5210:2003「ポルトランドセメント」に規定されている各種ポルトランドセメントや混合セメントを挙げることができる。この他、混合材として、生石灰、消石灰、高炉スラグや石炭灰（フライアッシュ）を併用しても良い。還元性せっこう組成物のセメントへの添加・混合は、通常、無水せっこうと同じ混合工程で行うことができるが、その他、粉砕、分級、輸送などの所定の混合効果が見込める工程での添加も可能である。   Examples of the cement to which the reducing gypsum composition is added include various Portland cements and mixed cements defined in JIS R 5210: 2003 “Portland cement”. In addition, quick lime, slaked lime, blast furnace slag, or coal ash (fly ash) may be used in combination. Addition and mixing of reductive gypsum composition to cement can usually be performed in the same mixing process as anhydrous gypsum, but addition in processes where a predetermined mixing effect such as crushing, classification and transportation can be expected. Is also possible.

このように調製したセメント系固化材は、粉体あるいはスラリーの状態で軟弱土などに添加・攪拌して土壌を改良する。固化材添加量は、改良目標強度や対象となる土質性状によって異なるが、通常、５０〜４００kg/m3の範囲から選択する。本発明の固化材がスラリー施工される場合においても、スラリー中で還元性せっこうが浮上あるいは沈降分離することなく、均質な固化処理土が得られる。本発明は、このような工程を経て、六価クロムの溶出量が抑制された固化処理方法を含むものである。 The cement-based solidified material thus prepared is added and stirred to soft soil or the like in the form of powder or slurry to improve the soil. The amount of the solidifying material added varies depending on the improved target strength and the target soil properties, but is usually selected from the range of 50 to 400 kg / m 3 . Even when the solidifying material of the present invention is applied in a slurry, a homogeneous solidified soil can be obtained without reducing gypsum floating or settling in the slurry. The present invention includes a solidification method in which the elution amount of hexavalent chromium is suppressed through such steps.

以下に、本発明を、実施例を用いて詳細に説明するが、本発明はこれらの実施例に限定されるものではない。   Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to these examples.

〔実験１〕
火力発電所の排煙脱硫工程のｐＨ調整槽前のスラリーと酸化塔を出た酸化後のスラリーとの混合物を想定して、還元性せっこう組成物を調製した。すなわち、通常の処理工程を経て副生された湿潤排脱二水せっこう（付着水分５．２％）に亜硫酸カルシウム半水和物（試薬一級：和光純薬（株）製）を、湿潤排脱二水せっこうと亜硫酸カルシウム半水和物とのドライベースでの合計量を１００質量％とした場合に、亜硫酸カルシウム半水和物の割合が１５質量％なるように添加し、実施例１の還元性せっこう組成物を得た。これに、上水を加えて付着水分８０％の混合スラリーを調製した。次に、このスラリーを減圧濾過して脱水し、付着水分８．０質量％の脱水ケーキを得た。 [Experiment 1]
A reducing gypsum composition was prepared assuming a mixture of the slurry before the pH adjustment tank in the flue gas desulfurization process of the thermal power plant and the slurry after oxidation exiting the oxidation tower. In other words, calcium sulfite hemihydrate (reagent grade: manufactured by Wako Pure Chemical Industries, Ltd.) is wet-excluded into wet-exhaust dihydrate gypsum (adhesion moisture 5.2%) by-produced through normal processing steps. When the total amount of dehydrated gypsum and calcium sulfite hemihydrate on a dry basis was 100% by mass, it was added so that the proportion of calcium sulfite hemihydrate was 15% by mass. A reduced gypsum composition was obtained. To this was added clean water to prepare a mixed slurry with 80% adhesion water. Next, this slurry was filtered under reduced pressure and dehydrated to obtain a dehydrated cake having an attached water content of 8.0% by mass.

ついで、ホバートミキサー（容量５Ｌ）を用い、この亜硫酸カルシウム半水和物および二水せっこうの混合物に、生石灰（０〜１mm品：宇部マテリアルズ（株）製）を付着水分１モルあたり０．２４〜０．５２モルとなるように添加し（生石灰中の酸化カルシウムは１００％として計算）、２０分間低速で混合・攪拌し、実施例１Ａ、１Ｂ、１Ｃの還元性せっこう組成物を調製した。   Then, using a Hobart mixer (capacity 5 L), quick lime (0 to 1 mm product: manufactured by Ube Materials Co., Ltd.) was added to the mixture of calcium sulfite hemihydrate and dihydrate gypsum at a moisture content of 0. Add to 24-0.52 mol (calculated as 100% calcium oxide in quicklime), mix and stir at low speed for 20 minutes to prepare reducing gypsum compositions of Examples 1A, 1B, 1C did.

得られた還元性せっこう組成物の計算上の化学組成およびＣａｒｒの流動性指数（下記参照）の測定結果を表１に示す。付着水分はJIS R9101-1995「セッコウの分析方法」に準拠して測定した。また粉体流動性指数は、ホソカワミクロン（株）製パウダーテスターＰＴ−Ｅ型により測定した。比較として、通常の亜硫酸せっこうを含まない排脱せっこう付着水分５質量％品（比較例１Ａ）およびII型無水せっこう（比較例１Ｂ）のデータを併記した。   Table 1 shows the calculated chemical composition of the obtained reduced gypsum composition and the measurement results of the Carr's fluidity index (see below). Adhering moisture was measured in accordance with JIS R9101-1995 “Analytical method of gypsum”. The powder fluidity index was measured with a powder tester PT-E type manufactured by Hosokawa Micron Corporation. As a comparison, the data of 5 mass% of dehydrated gypsum adhering water (Comparative Example 1A) and type II anhydrous gypsum (Comparative Example 1B) not containing normal sulfite gypsum are also shown.

Ｃａｒｒの流動性指数：(1)安息角、(2)圧縮度、(3)スパチュラ角、(4)凝集度および(5)均一度などの結果を総合して求める（下記非特許文献を参照のこと）。
横山藤平，浦山清，粉体工学研究会誌，6,264(1969).
横山藤平，粉砕，14,102(1965). Carr's fluidity index: (1) Angle of repose, (2) Compressibility, (3) Spatula angle, (4) Agglomeration and (5) Uniformity, etc. )
Yokoyama Tohei, Urayama Kiyoshi, Journal of Powder Engineering, 6,264 (1969).
Yokoyama Tohei, Grinding, 14,102 (1965).

表１に示すように、生石灰を添加することで還元性せっこうの流動性を、比較例１Ｂに示す現状のII型無水せっこうと同等以上に改善することが可能となる。   As shown in Table 1, the flowability of reducing gypsum can be improved to be equal to or higher than the current type II anhydrous gypsum shown in Comparative Example 1B by adding quick lime.

〔実験２〕
〔実験１〕で得られた還元性せっこう組成物のうち、生石灰／付着水のモル比＝０．４で乾粉化した還元性せっこう組成物（実施例１Ｂ）を、普通セメント（宇部三菱セメント（株）製）１００質量部に８〜１２質量部添加、混合して、実施例２Ａ、２Ｂ、２Ｃの六価クロム溶出抑制型セメント系固化材を調製した。この固化材を関東ローム（埼玉県上福岡産、含水比１０８．６質量％、細粒分８８．９質量％）に３００kg/m3添加し、ホバートミキサー（容量５Ｌ）を用い低速で２分間練混した後、掻き落と操作を行い、さらに２分間低速で混合した。この場合、固化材はスラリー（水／固化材比６０質量％）で添加した。 [Experiment 2]
Among the reducing gypsum composition obtained in [Experiment 1], the reducing gypsum composition (Example 1B) dry-ground at a quick lime / adhesion water molar ratio = 0.4 was treated with ordinary cement (Mitsubishi Ube). 8 to 12 parts by mass was added to 100 parts by mass of Cement Co., Ltd. and mixed to prepare the hexavalent chromium elution suppression type cement-based solidified materials of Examples 2A, 2B, and 2C. 300 kg / m 3 of this solidified material is added to Kanto Loam (from Kamifukuoka, Saitama Prefecture, water content 108.6% by mass, fine particle content 88.9% by mass) using a Hobart mixer (capacity 5L) for 2 minutes at low speed. After kneading, scraping and manipulation were performed, and the mixture was further mixed at low speed for 2 minutes. In this case, the solidifying material was added as a slurry (water / solidifying material ratio 60 mass%).

この固化処理土をJGS 0821-2000「安定処理土の締固めをしない供試体の作成方法」に準拠して、直径５×高さ１０cmの円筒形供試体を作製し、２０℃で所定材齢まで密封養生した。７日間養生した円柱供試体をJIS A 1216:1998「土の一軸圧縮試験方法」に準拠し、一軸圧縮強さを測定した。一軸圧縮試験後の供試体を２mm以下に解砕して、下記の六価クロム溶出試験を行った。この結果を、表２に示す。   In accordance with JGS 0821-2000 “How to make specimens without compaction of stabilized soil”, cylindrical specimens with a diameter of 5 × height of 10 cm were prepared from this solidified soil, and a specified age at 20 ° C. Sealed and cured until. The cylindrical specimens cured for 7 days were measured for uniaxial compressive strength according to JIS A 1216: 1998 “Soil uniaxial compression test method”. The specimen after the uniaxial compression test was crushed to 2 mm or less, and the following hexavalent chromium elution test was performed. The results are shown in Table 2.

なお、比較として、通常の処理工程を経て副生された湿潤排脱二水せっこう（付着水分５．２％）を５０℃で付着水分１％に乾燥した二水せっこう乾燥物、II型無水せっこう単体を、各々普通セメントに添加した固化材（比較例２Ａ、２Ｂ）についても同じ試験を行った。   As a comparison, a dried dihydrate gypsum dry product obtained by drying wet dehydrated gypsum gypsum (adhered moisture 5.2%) produced as a by-product through normal processing steps at 50 ° C. to 1% adhered moisture, type II The same test was performed on solidified materials (comparative examples 2A and 2B) in which anhydrous gypsum alone was added to ordinary cement.

六価クロムの溶出試験は、環境省告示４６号（平成８年８月２３日）に則り、６時間振とう後のろ液を、ジフェニルカルバジド方法（吸光光度方法）を用いて溶出六価クロムを定量した。本吸光光度方法の測定限界は０．０１mg/Lであり、これ以下はＮＤと記載する。   The elution test for hexavalent chromium was conducted in accordance with the Ministry of the Environment Notification No. 46 (August 23, 1996), and the filtrate after shaking for 6 hours was eluted with the diphenylcarbazide method (absorption photometric method). Chromium was quantified. The measurement limit of this absorptiometric method is 0.01 mg / L, and below this is described as ND.

表２に示すように、生石灰で乾粉化した還元性せっこう組成物を用いたセメント系固化材（実施例２Ａ、２Ｂ、２Ｃ）は、乾燥二水せっこう、II型無水せっこうを、各々普通セメントに添加した固化材（比較例２Ａ、２Ｂ）と比較して、六価クロムの溶出量ＮＤとすることが可能であり、固化強度についても、比較例２ＢのII型無水せっこうを添加した固化材を用いた場合と同等の固化強度を得ることができる。   As shown in Table 2, cement-based solidified materials (Examples 2A, 2B, and 2C) using a reductive gypsum composition dry-dried with quicklime are dried dihydrate gypsum and type II anhydrous gypsum, respectively. Compared with the solidified material added to ordinary cement (Comparative Examples 2A and 2B), it is possible to obtain the hexavalent chromium elution amount ND, and the solidified strength is added with the type II anhydrous gypsum of Comparative Example 2B. A solidification strength equivalent to that obtained when the solidified material is used can be obtained.

〔実験３〕
生石灰／付着水のモル比＝０．３となるようにセメント仮焼原料で乾粉化した実施例３の改質せっこう（粉体流動性指数２８）を用いて、六価クロム溶出抑制型セメント系固化材（実施例４Ａ、４Ｂ、４Ｃ）を調製した他は、〔実験２〕と同様の試験を行った。なお、セメント仮焼原料はＣａＯ含有量が４０質量％（残余成分は、ＳｉＯ２、Ａｌ２Ｏ３、Ｆｅ２Ｏ３等のセメントの構成成分よりなる）のものを使用した。得られた還元性せっこう組成物の計算上の化学組成および粉体流動性指数を表３に、固化試験結果を表４に示す。 [Experiment 3]
Using the modified gypsum (powder fluidity index 28) of Example 3 which was dry-pulverized with a cement calcining raw material so that the molar ratio of quicklime / adhered water = 0.3, hexavalent chromium elution suppression type cement A test similar to [Experiment 2] was conducted except that the solidified material (Examples 4A, 4B, 4C) was prepared. The cement calcined raw material used had a CaO content of 40% by mass (the remaining components are composed of cement constituents such as SiO 2 , Al 2 O 3 , Fe 2 O 3 ). Table 3 shows the calculated chemical composition and powder flowability index of the resulting reduced gypsum composition, and Table 4 shows the results of the solidification test.

表４に示すように、セメント仮焼原料で乾粉化した還元性せっこう組成物を含有する実施例４Ａ、４Ｂ、４Ｃの固化材は、乾燥二水せっこう、II型無水せっこうを添加した固化材（比較例２Ａ、２Ｂ）に比較して六価クロムの溶出量ＮＤとすることが可能である。また固化強度についても、生石灰で乾粉化した還元性せっこう組成物を含有する実施例２Ａ、２Ｂ、２Ｃの固化材に比較してやや低いものの、乾燥二水せっこう、II型無水せっこうを含有する固化材（比較例２Ａ、２Ｂ）と同等以上の固化強度を得ることができる。   As shown in Table 4, the solidified materials of Examples 4A, 4B, and 4C containing the reduced gypsum composition dried with cement calcined raw material were added dry dihydrate gypsum and type II anhydrous gypsum. Compared to the solidified material (Comparative Examples 2A and 2B), the hexavalent chromium elution amount ND can be obtained. Also, the solidification strength is slightly lower than the solidification materials of Examples 2A, 2B, and 2C containing the reduced gypsum composition dried with quick lime, but contains dry dihydrate gypsum and type II anhydrous gypsum. Solidification strength equal to or higher than that of the solidifying material (Comparative Examples 2A and 2B) to be obtained can be obtained.

還元性せっこう組成物の製造フローの一例を図１に示す図である。It is a figure which shows an example of the manufacture flow of a reducing gypsum composition in FIG.

Claims (6)

亜硫酸カルシウム半水和物および二水せっこうを含有する還元性せっこう組成物。   A reducing gypsum composition containing calcium sulfite hemihydrate and dihydrate gypsum. 還元性せっこう組成物の全質量を基準に、亜硫酸カルシウム半水和物を５〜２０質量％、二水せっこうを６０〜９０質量％、および水酸化カルシウムを５〜２０質量％含む、請求項１記載の還元性せっこう組成物。   5-20% by weight calcium sulfite hemihydrate, 60-90% by weight dihydrate gypsum, and 5-20% by weight calcium hydroxide, based on the total weight of the reducing gypsum composition Item 6. A reducing gypsum composition according to Item 1. 請求項１または２記載の還元性せっこう組成物を、セメント１００質量部に対して５〜２０質量部を含む、セメント系固化材。   A cement-based solidifying material comprising 5 to 20 parts by mass of the reducing gypsum composition according to claim 1 or 2 with respect to 100 parts by mass of cement. 亜硫酸カルシウム半水和物および二水せっこうを含有する還元性せっこう組成物の製造方法であって、
排ガス脱硫工程での亜硫酸カルシウム半水和物を含むスラリーおよび該スラリーを酸化して得られる二水せっこうを含むスラリーを機械脱水した脱水物、またはそれぞれのスラリーを別々に機械脱水した脱水物を混合した脱水混合物に、付着水分１モル当たり０．２５〜１．０モルの酸化カルシウム系処理材を加えて乾粉化する、ことを特徴とする還元性せっこう組成物の製造方法。 A method for producing a reducing gypsum composition containing calcium sulfite hemihydrate and dihydrate gypsum, comprising:
A slurry containing calcium sulfite hemihydrate in an exhaust gas desulfurization step and a dehydrate obtained by mechanically dehydrating a slurry containing dihydrate gypsum obtained by oxidizing the slurry, or a dehydrated product obtained by mechanically dehydrating each slurry separately. A method for producing a reducing gypsum composition, comprising adding 0.25 to 1.0 mol of a calcium oxide-based treatment material to 1 mol of adhering moisture to a mixed dehydrated mixture to dry the mixture. 酸化カルシウム系処理材がセメント仮焼原料である、請求項４記載の還元性せっこう組成物の製造方法。   The manufacturing method of the reducing gypsum composition of Claim 4 whose calcium oxide type processing material is a cement calcination raw material. 請求項３記載のセメント系固化材を使用する、六価クロムの溶出を抑制する固化処理方法。   The solidification processing method which suppresses the elution of hexavalent chromium using the cement-type solidification material of Claim 3.
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