Physical and Image Analysis Sizing of Mine Run Taconite Ore

Abstract

The United States Bureau of Mines (USBM) has developed an image analysis system to determine the size distribution of mine-run taconite ore. The results can be used to evaluate fragmentation so that blasts can be designed for better productivity. ~he Coleraine Minerals Research Laboratory (CMRL) has been testing the system at Minntac with apparent success, but there was no method available for testing the accuracy of size distributions determined by image analysis. The Iron Ore Cooperative Research Committee approved and funded a project to screen mine-run ore and compare the results to sizing by image analysis. Three samples, about 2500 tons each, were sized on 6 and 12 inches in a contractor's vibrating grizzly plant at Minntac. Size analyses were extended to 65 mesh by sizing samples of minus-6 inch at the Coleraine laboratory. Between 30 and 60 plus- 12 inch pieces from each bulk sample were measured to provide thickness-width-length aspect ratios and to indicate large-fragment dimensions and weights that are encountered in mine-run ore. The average ratio of thickness to width to length was 1.00:2.20:3.21. Fragment volumes ranged from 4 to 80 cubic feet. Weights of these would be approximately 800 pounds and 16,000 pounds. After the size fractions had been weighed, they were recombined, each sample was loaded into rail cars, and they were dumped at number one primary crusher. The USBM and CMRL video-taped the ore as it was dumped and processed the tapes through a computer to produce an image analysis size distribution for each of the three samples. Because of a large discrepancy between the contractor's and the track scale weights, the size analysis of sample number one was not acceptable. The physical size analyses of samples two and three and their corresponding image analysis size distributions were nearly identical for fragment widths of at least 12 inches. Size. distributions of mine-run ore by the image analysis system have been proven reliable for evaluating the effective fragmentation of individual blasts for sizes down to 12 inches in width.