Flash Magnetization Roasting technology can be used to recover superfine low-magnetism iron residue/slag, especially those from zinc PLS purification and nickel laterite leaching, to standard iron ore. It treats weakly magnetic iron material like hematite, limonite, siderite and goethite. Minerals preheated by off gas waste heat are charged into the furnace and distributed uniformly in fluidized status for heat exchange and flash reaction.The roasting process encourages these minerals to have crystal transition for higher magnetism, thus making it possible to be concentrated to standard iron ore.