Solid waste from the spray-dry process for flue gas desulfurization, cont. CaSO3-1/2H2O 59.3%, Ca(OH)(2) 12%, CaSO4-1/2H2O 11.1% CaCO3 10.4% and CaCl2 center dot 4H(2)O 2% was used as an addnl. sorbent in the wet technique of SO2 removal. The solid waste from an industrial process, limestone and water were used to prepare the absorption suspension. The flue gas (300-350 m(3)/h, SO2 concentration of 2800 mg/m(3)) was desulfurized in a pilot plant at 40 degrees C. The quality of gypsum produced in the process was also investigated. An increase in the waste concn. in the absorption slurry (up to 45 g/dm(3)) did not have any substantial effect on desulfurization efficiency and the gypsum quality.