Patent ID: 7052660

Claim:
A wet-processing method for combustion ashes of petroleum fuels, which are collected by a dust collector disposed in an exhaust gas passage of a boiler using petroleum fuels and contain at least vanadium, comprising: a slurry preparation step of preparing a slurry of the combustion ashes, thereby dissolving vanadium contained in the combustion ashes in water; a metal oxidation step of feeding ammonia and an oxidative gas to the slurry for oxidizing vanadium in the presence of an aqueous ammonium sulfate solution, thereby preparing a slurry containing ammonium metavanadate; a solid/liquid separation step of removing solids from the slurry containing ammonium metavanadate and recovering an aqueous solution of ammonium sulfate; a double decomposition step for ammonium sulfate, of adding a metal compound capable of forming a water-soluble sulfate to the aqueous ammonium sulfate solution recovered from the solid/liquid separation step; and an ammonia recovery step of recovering ammonia from a reaction solution recovered from the double decomposition step, wherein the metal oxidation step is conducted while controlling an ammonium sulfate concentration of the aqueous solution to 20 to 45% by weight and a temperature of the aqueous solution to not more than 50° C., and the solid/liquid separation step is conducted using a filtration solid/liquid separator while controlling a temperature of the slurry to not more than 40° C.