A noxious metal(s) containing waste material is treated with an acid solution of a metal of group VIIa or VIII of the Periodical System, preferably iron or manganese. Subsequently, the metal of group VIIa or VIII dissolved in the acid is precipitated as a metal hydroxide and simultaneously the noxious metal(s) dissolved from said waste by said acid solution are incorporated in said precipitating metal hydroxide. The waste material together with precipitated metal hydroxide is subjected to an immobilization treatment. Manganese hydroxide is particularly suitable for removing cadmium. An acid solution of iron and preferably simultaneously manganese to be used for treating the waste is obtained by dissolving oxysludge caught during iron or steel manufacture. The method is particularly for treating dredged harbor sludge. The dredge sludge may be formed into granules after mixing with a preformed mixture of the amount of a binder and 50 to 90% of the total amount of fly ash and subsequently the granules are treated with the remaining amount of fly ash. Carbon black and/or a water repellent substance may be added to the remaining amount of fly ash.
