Microwave-assisted grinding

The use of rapid microwave heating to stress-fracture ore samples is discussed. Iron ores containing hematite, magnetite, and goethite were subjected to microwave energy in batch operations at 3 kW and heated to average maximum temperatures between 840 degrees C and 940 degrees C. Scanning electron microscope (SEM) photomicrographs verified fracturing along grain boundaries and throughout the gangue matrix. Standard Bond grindability tests showed that microwave heating reduced the work index of iron ores by 10 to 24%. Using a continuous-feed belt in a microwave applicator, samples heated more uniformly and quickly than in batch operations. In a microwave chamber designed to simulate a continuous-throughput operation at 3 kW, the grindability of a taconite ore was improved by 13% at a bulk temperature of 197 degrees C. Because stress cracking occurred at a lower temperature, less energy was consumed, thereby improving cost effectiveness. To further improve the economics, preliminary tests were conducted to increase heating rates by using higher microwave powers. The beneficial effects in the grinding circuit and in the extractive operation are discussed.<>