METHOD OF PREPARING COAL-COMBUSTION FLY ASH FOR UTILIZATION IN MANUFACTURE OF BUILDING MATERIALS Russian patent published in 1999 - IPC

FIELD: waste reclamation. SUBSTANCE: fly ash from coal combustion is treated with sulfuric acid concentrated to 50 to 300 g/l at ash weight to solution volume ratio 1:(4- 10) and temperature 18-90 C. To intensify leaching process, acid solution is supplemented by sodium chloride additive to chloride ion concentration 0.5 to 25.0 g/l. Process is carried out for 1 to 6 hr at 40-90 C. In heap leaching process, acid solution with temperature 18-40 C is passed through ash bed by gravity. In this process, sulfuric acid concentration is 50 to 200 g/l and ash weight to solution volume ratio is 1: (5-6). EFFECT: enhanced process efficiency. 5 cl, 2 tbl, 4 ex