Magnetic Roasting of Iron Ores in a Traveling Grate Roaster

The large quantities of iron-bearing materials, including taconite, semi-taconite," and other low-grade ferruginous materials occurring in Minnesota and elsewhere, constitute an important potential source of iron. Satisfactory grade and recovery of iron ore concentrate cannot ordinarily be obtained from these ferruginous materials by simple methods of beneficiation. Iron is distinctive in that the free metal and two of its oxides [magnetite (Fe,O,) and maghemite (gamma-Fe,O,) ] are strongly ferromagnetic. The successful magnetic separation of natural magnetite from taconite has already been established on a commercial scale. The iron in semi-taconite, how- ever, occurs largely as goethite (Fe,Os.H,O) and hematite (Fe90,) which do not respond to ordinary magnetic separation methods. Magnetic roasting converts these iron oxides to magnetite, which can, after liberation, be magnetically concentrated.