Size Distributions of Taconite Ore by Image Analysis of Video Tapes of Muckpiles

Abstract

A computer-based digital imaging system has been developed by the United States Bureau of Mines (USBM), with the assistance of NORAMCO Engineering Corporation of Hibbing and the Coleraine Minerals Research Laboratory (CMRL), to determine size distributions of mine-run taconite ore. One such system, operating at a primary crusher at United States Steel's Minntac mine, produces size distributions of mine-run ore that are accurate for fragment widths of 12 inches and more. The CMRL proposed a project to develop a method of sizing mine-run ore in muckpiles by image analysis. These size analyses could provide rapid evaluations of blast fragmentation so that later blasts could be designed for more effective breakage. It was assumed that video tapes of muckpiles processed through an I.A. computer program could provide these rapid analyses. The Iron Ore Cooperative Research Committee approved and funded this project. After the CMRL camcorder was calibrated so that I.A. size distribution computer output could be converted from pixels to inches, several muckpiles at Minntac and at Eveleth Taconite were video taped at lens-to-subject distances of 24 to 116 feet. Video tape size distributions from one Minntac muckpile were compared to the size distributions established for that blast at the primary crusher. The size distributions from the muckpile were much coarser than those from the crusher which indicated that fragment resolution at the long distances was too insensitive to provide accurate sizing. The same Minntac blast was then video-taped by the CMRL by walking over the muckpile so that the lens-to-subject distance was 7.5 feet. Size distributions from this video tape were quite close to the average size distribution established by 120 trains at the primary crusher. This indicated that video tapes could be representative of muckpile surfaces and that the I.A. resolution is adequate at the shorter distance. Additional experimental blast areas will be video-taped by the CMRL by walking over muckpiles to generate size analyses to compare to sizing of the same blasts at the primary crusher. If these sets of size analyses are very similar and both muckpile and crusher data show the same size variations between experimental areas, the sizing method could be recommended for use at all Minnesota taconite mining operations.