To suppress the elution of heavy metals from heavy metal-containing wastes and to make inexpensive treatment by adding a solidifying material to the heavy metal-containing wastes and kneading, molding or granulating the mixture and coating the outer layers of resulted solid materials with a solidifying material.

The solidifying material is added to the heavy metal-containing wastes and the mixture is kneaded, molded or granulated. The outer layers of the resulted solid materials are coated with the solidifying material. The heavy metal-containing wastes are referred to be the flying ash discharged from an incineration furnace and the solidifying material to be added to the heavy metal-containing wastes and the solidifying material used for coating the outer layers are cement. Also, the outer layers of the solid materials formed by solidifying the heavy metal-containing wastes are coated with the solidifying material and the solid materials are formed as granular materials of ≤5 mm in grain size. The heavy metal-containing wastes is the flying ash discharged from the incineration furnace and the solidifying material to be added to the heavy metal-containing wastes and the solidifying material used for coating the outer layers are the cement.