A process is described in which a modified fly ash slurry at a ph 10- 13, formed in the reaction of s-containing combustion gases with limestone or dolomite and by coprecipitation with pulverized coal fly ash, can be converted into reusable carbonates by carbonization to a ph approximately 7.0 By the use of co2-containing gases (plant stack gases) on a slurry to which an anionic emulsifier has been added; the modified fly ash contains generally alkaline earth sulfates or sulfites 2-20, fly ash 25-65 pct, and unreacted alkaline earth oxides the rest. The carbonates formed are separated from the slurry by flotation, dried, and reinjected into the furnace; the flotation reject is dewatered and is converted in a reverberatory furnace into a molten mass, with a viscosity of up to 10 p, from which a fibrous mineral wool, high in si, is produced by air- blowing. The mineral wool produced is less corrosive to steel under humid conditions than other insulating materials; the so2 and so3 gases produced in the reverberatory furnace can be recovered for reprocessing to h2so4.
U.S. Pat. 3,642,445; Feb. 15, 1972; Chem Abstr. 76:89,733F