| 摘要 |
PURPOSE:To manufacture gypsum of good quality from waste water containing a sulfuric radical, by reacting waste water containing a sulfuric radical with a Ca compound to form gypsum, cyclically using a fine part of the formed gypsum as a seed crystal for gypsum, and separating gypsum of large particle size. CONSTITUTION:Industrial waste water 11 containing a sulfuric radical in an amount of 1.0-10.0% in terms of SO4 is introduced as slurry 12 containing a Ca compound such as CaO, Ca(OH)2 or CaCO3 in an amount of 10-30% in terms of CaO into a reaction tank 1, in a manner such that the amount of the Ca compound is stoichiometrically approximately equivalent to SO4 for the formation of CaSO4. The slurry is agitatively reacted at 40-80 deg.C with 6-7 as a reactive pH, to form fine gypsum. The formed gypsum is grown up by circulating it through a residence tank 2 and a maturing tank 3, and sent to a liquid cyclone 4 to classify it according to particle size. Seed crystal slurry in an amount of 1: 0.5-1:0.4 to the formed gypsum slurry is supplied through a liquid cyclone 6 to the reaction tank 1 for the growth of the gypsum crystal. On the other hand, coarse gypsum slurry 8 is concentrated in a liquid cyclone 9 and then recovered as a gypsum product by a separator 10.
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