Stabilization of the hazardous materials by the Fe3O4-coating method was studied. In the ferrite-formation reaction in the aqueous solution, the adsorption of the metal ions and the oxidation of the adsorbed Fe(II) ions are repeated on the surface of the ferrite particles. This reaction was adopted to the coating of the hazardous materials with the Fe3O4(or ferrite). By repeating the two steps of l)the addition of the Fe(II) aqueous solution into the suspension of the hazardous materials, and 2)the oxidation by passing air through the reaction suspension, with the Fe3O4 layer, we could coat the surfaces of the hazardous materials, such as the heavy metal sludge from the neutralization-precipitation process, the CaF2 precipitates in the treatment of the waste waters containing fluoride ion along with hazardous metal ions, and the soils containing Cd(II) ion. These Fe3O4-coated hazardous materials are very stable and no heavy metal ions are leached under the normal environmental conditions. The ferrite sludges formed in the “Ferrite Process” were highly stabilized by the present method, and by the heat-treatment.
