The Application of the Vertimill to the Fine Grinding of Taconite

摘要

Since grinding energy consumption is a very significant cost to the taconite industry, a purportedly more energy efficient grinding device, the Vertimill, was installed outside of the concentrator at the Minntac plant. The initial test program called for testing hree plant streams, froth regrind, fine screen oversize and secondary ball mill feed, in the Vertimill. Only the tests on the froth regrind and the oversize were conducted. The system consisted of a 150 hp Vertimill charged with 1/2-inch balls, a recycle sump and pump, a cyclone feed sump and pump, a movable feed pump, and a return sump and pump. Power to the system was supplied by a portable generator. The tests on the froth regrind indicated that operating the Vertimill in open circuit used about 9 Kwh/lt less than either the plant ball mill or the pilot plant ball mill in open circuit. Running the Vertimill in closed circuit resulted in power savings close to 40 percent compared to the ball mills in open circuit. Feed rate was the only variable tested that made a significant difference in the amount of minus 500 mesh produced. Liberation was the same for both the Vertimill and the ball mill. Testing of the screen oversize, resulted in energy saving for the Vertimill when operated in closed circuit. Open circuit tests indicated poorer energy consumption compared to the ball mill. However, it is thought that the open circuit operation of the Vertimill was not optimized and that further testing will be conducted in the summer of 1997. As with the froth regrind, the mill type had no effect on liberation. The liberation test work did point out the substantial difference between laboratory (batch) ball milling and the continuous ball mill or Vertimill grinding. The test work also indicated potential grade and flotation operational improvements by grinding the screen oversize in a separate mill to produce a finer grind.