PURPOSE: To precipitate and recover the heavy metal in molten fly ash as the hydroxide or sulfide by introducing a fly ash contg. heavy metals discharged from a melting furnace into water to form suspension, controlling the pH of the suspension and further adding a hydrosulfide.
CONSTITUTION: The molten fly ash discharged from a refining furnace for the heavy metals such as Pb, Zn, Cd and Cu contains such heavy metals and pollutes the environment. Accordingly, the molten fly ash is charged into a dissolution tank 1, agitated by an agitator 5 and sufficiently mixed with water to form a suspension 6, which is transferred to a first reaction tank 2, acid or alkali is added to control the suspension 9 to pH 10-10.5, and the suspension is sufficiently agitated by an agitator 8 to precipitate the heavy metals as the hydroxides. The soln. is sent to a reaction tank 3 and agitated by an agitator 10, and an aq. soln. of NaHS as the water-soluble sulfide is added, the pH is monitored by a pH meter 11 and kept at 10-10.5, and the unreacted heavy metals in a suspension 12 are precipitated as the additive. The liq. is transferred to a precipitation tank 4, and the mixed precipitate 13 of the heavy metals is separated from a supernatant 14 and recovered.
NAKAI SHIRO
SHIBANOKI SATORU
