A method for use in two-components electrostatic image developers is disclosed, in which secure separation of a carrier coating resinous materials from a core magnetic material is achieved without affecting the properties of the core materials through process steps benign to the environment in super- or sub-critical water compositions under the conditions of a temperature of 300.degree. C. or more and a pressure of 20 MPa. The core magnetic material is subsequently recycled for forming carrier. This method may also be useful for processing waste including magnetic materials with silicone resin coating.