Abstract: Aqueous slurry which includes solid foreign matter and paper dust is pressed by means of a screw press, provided with a mesh having openings not less than 1.5 mm and not greater than 3 mm, to separate the aqueous slurry into the solid foreign matter and the paper dust, and liquid component passing through the mesh. Then, the liquid component is sieved by means of a sieve having openings not greater than 1 mm to separate from the liquid component the solid foreign matter and the paper dust.

Abstract: 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° C. or higher.

Abstract: 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° C. or higher.

Abstract: 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° C. is not less than 40 wt % of the amount of the surfactant before heating.

Abstract: A method for removing metal pieces contained in gypsum board wastes from the gypsum board wastes by means of a drum magnetic separator, wherein the method comprises the step of dropping cut pieces obtained by cutting the gypsum board wastes at fixed intervals “D” on the drum magnetic separator at a drop height “h”; and the drop height “h” is 0.8 to 3 times the interval “D”.

Abstract: 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° C. is not less than 40 wt % of the amount of the surfactant before heating.

Abstract: A method of manufacturing hemihydrate gypsum powders for the production of a gypsum molded product from gypsum board waste, comprising at least the following two steps in a random order: a compression step for compressing gypsum obtained from gypsum board waste; and a baking step for converting dihydrate gypsum obtained from gypsum board waste to hemihydrate gypsum.

Abstract: A method for removing metal pieces contained in gypsum board wastes from the gypsum board wastes by means of a drum magnetic separator, wherein the method comprises the step of dropping cut pieces obtained by cutting the gypsum board wastes at fixed intervals “D” on the drum magnetic separator at a drop height “h”; and the drop height “h” is 0.8 to 3 times the interval “D”.

Abstract: 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.

Abstract: A cement setting accelerator comprising calcium hydroxide particles having an average particle diameter of 3 ?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.

Abstract: 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.

Abstract: A cement setting accelerator comprising calcium hydroxide particles having an average particle diameter of 3 ?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.