Abstract: The `ferrite process' is an excellent method for treating waste water containing iron and arsenic, but cannot be directly applied to mine drainage where silicon and aluminum ions are present, because they strongly inhibit ferrite formation. As a result of the development of related technologies such as the elimination of silicon, the concentration of iron, and the oxidation of ferrous ions using iron-oxidation bacteria, a new ferrite formation process has been developed and applied to the mine drainage of the Matsuo Mine. The paper discusses the application of the ferrite sludge to magnetic marking materials, magnetic fluid for metal separation and recovery, and the semiactive magnetic damper is described. The related technologies which will be expected to play an important role in solving the environmental problems are also described. These technologies will change the ferrite sludge to beneficial materials, which can be used for carbon dioxide decomposing catalysts, reuse of dry batteries, fish gathering blocks, and cement tracer for ground improvement