Tokuyama Corporation

Shingo Hiranaka

Genji Taga

Hiroyoshi Kato

Makoto Kataoka

Kentaro Matsuo

Wasted gypsum boards are crushed and calcined to gypsum granular solid, and the gypsum granular solid is mixed with water to form gypsum slurry. Gypsum particles are deposited from the gypsum slurry in a crystallization tank. Heated steam is blown into the gypsum slurry at a height from surface of the gypsum slurry and down to upper ⅕ of the gypsum slurry to heat the gypsum slurry and to eliminate foam on the gypsum slurry.

Crystallization method of gypsum

Wasted gypsum boards are crushed and heated to convert semi-hydrated gypsum and/or anhydrous type III gypsum, and the obtained semi-hydrated gypsum and/or anhydrous type III gypsum is mixed with gypsum slurry. The gypsum slurry is solid/liquid separated by a filtration device into gypsum particles and filtrate which has passed through the filter cloth of the filtration device. The filtrate is returned into the gypsum slurry. The solid/liquid separation is performed such that the concentration of the suspended solid in the filtrate that has passed through the filter cloth and consists of gypsum granules and inorganic impurities derived from wasted gypsum boards is made 1000 to 8000 mass ppm. The clogging of the filter cloth is reduced.

Method for reclaiming gypsum from wasted gypsum boards

Gypsum derived from waste gypsum boards is calcined and converted into gypsum granules including hemihydrate and/or anhydrous type III gypsum. The calcined gypsum granules are dropped into water to prepare a gypsum slurry. Then, dihydrate gypsum particles are crystalized in the slurry. The temperature of the gypsum granules just before being dropped into the water is 90&#xb0; C. or higher.

Recycling method of dihydrate gypsum from waste gypsum boards

Surfactant-coated hemihydrate gypsum which is coated with 0.01 to 1 part by weight of a surfactant based on 100 parts by weight of hemihydrate gypsum, wherein the residual rate of the surfactant when the surfactant-coated hemihydrate gypsum is heated up to 300&#xb0; C. is not less than 40 wt % of the amount of the surfactant before heating.

Surfactant-coated hemihydrate gypsum and production method thereof

A method for removing metal pieces contained in gypsum board wastes from the gypsum board wastes by means of a drum magnetic separator, wherein

Method for removing metal pieces from gypsum board wastes

A stripping liquid of the present invention is used for separating the paper from a plaster/paper laminate such as waste plasterboard, and comprises an aqueous solution of an alkali metal salt or an ammonium salt of carboxylic acid. The stripping liquid is fed onto the surface (paper surface) of the plaster/paper laminate so as to infiltrate into the bonding surface between the plaster and the paper, so that the carboxylate is made present on the bonding surface. Upon stripping off the paper in the presence of the carboxylate, it is allowed to entirely separate the paper from the plaster. Upon mixing the stripping liquid and a nonionic surfactant or a water-soluble organic solvent together, further, the stripping liquid can be quickly and reliably infiltrated into the bonding surface between the plaster and the paper.

Stripping liquid for use in separating paper from plaster/paper laminate

A cement setting accelerator comprising calcium hydroxide particles having an average particle diameter of 3 &#x3bc;m or less, and a cement composition comprising 100 parts by weight of a cement and 0.05 to 10 parts by weight of the above setting accelerator. A wet ground product of calcium hydroxide or a fine precipitate formed by a reaction between a calcium salt and an alkali hydroxide can be used as the above calcium hydroxide particles. This setting accelerator shows a high setting accelerating effect and does not exert a bad influence upon the quality, especially durability of a hardened product of the cement composition.

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Shunan, Japan

Shingo Hiranaka