At the MacIntyre Development of the Titanium Division of National Lead Company a magnetite-ilmenite ore together with gabbro-anorthosite waste is mined front an open pit by shovels and trucks. The ore from the pits is trucked to ore stockpiles for blending ahead of the crusher and to free the mine from crusher delivery schedules.
The ore is reclaimed from stockpile by an electric shovel and trucked to the crusher; all ore has been blasted or drop-ball fractured to feed the 48 x 60 inch jaw crusher. The jaw feed is controlled by a chain feeder over a stationary grizzly with 6-8 inch opening to bypass most of the fines.
Fine magnetic cobbing of minus one-half inch material was recognized as desirable very early in the operation. Maximum waste removal was not attainable, however, with i the conventional radial magnetic pulley. As mentioned earlier, the liberation of ilmenite and magnetite starts at 10 mesh so that the practical range for dry fine cobbing is minus one-half plus 10 mesh.
Many types of magnetic separator equipment have been investigated over the years. Full success in fine cobbing however was not achieved until a laboratory wet permanent magnetic drum separator for magnetite was disassembled and the alternating polarity drum was tried as a cobbing pulley. This gave indications of success in that the winnowing action of the alternating poles liberated non-magnetics that all of the radial type magnets had entrained in the concentrate. This separator could accept unscreened feed and do a good job of rejecting the non-magnetics.