TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The mixture of gypsum and biomass is reacted with a carbon-dioxide absorber (D), and biomass is gasified absorbing one portion of carbon dioxide generated from the biomass by the carbon-dioxide absorber. During cooling, carbon dioxide is added and calcium sulfide is converted into calcium carbonate. The mixture containing calcium carbonate and hydrogen sulfide is guided to a dust collector (14), and separated into solid calcium carbonate and gaseous hydrogen sulfide.Preferred Conditions: The reaction is carried out at less than 1 MPa and 700-800degreesC. After removing the carbonate, carbon dioxide is re-used. Biomass is supplied such that the ratio of the number-of-moles (C) of carbon in biomass with respect to the number-of-moles (CaSO4) of gypsum is 4 or more. Steam is supplied such that the ratio of the number-of-moles (H2O) of water vapor with respect to the number-of-moles (C) of carbon in biomass during reaction is 2 or more.Preferred Absorber: The carbon-dioxide absorber is oxide or hydroxide of calcium, magnesium, strontium, barium and/or iron.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The mixture of gypsum and biomass is reacted with a carbon-dioxide absorber (D), and biomass is gasified absorbing one portion of carbon dioxide generated from the biomass by the carbon-dioxide absorber. During cooling, carbon dioxide is added and calcium sulfide is converted into calcium carbonate. The mixture containing calcium carbonate and hydrogen sulfide is guided to a dust collector (14), and separated into solid calcium carbonate and gaseous hydrogen sulfide.Preferred Conditions: The reaction is carried out at less than 1 MPa and 700-800degreesC. After removing the carbonate, carbon dioxide is re-used. Biomass is supplied such that the ratio of the number-of-moles (C) of carbon in biomass with respect to the number-of-moles (CaSO4) of gypsum is 4 or more. Steam is supplied such that the ratio of the number-of-moles (H2O) of water vapor with respect to the number-of-moles (C) of carbon in biomass during reaction is 2 or more.Preferred Absorber: The carbon-dioxide absorber is oxide or hydroxide of calcium, magnesium, strontium, barium and/or iron.