Minnesota Ilmenite Processing Using High Pressure Rolls

Abstract

With funding from the Minnesota Department of Natural Resources through the Minerals Coordinating Committee, a study was undertaken to determine the potential for the use of High Pressure Rolls (HPR) grinding to improve recovery and reduce grinding energy in the processing of ilmenite bearing material from the Duluth Complex. Several deposits in the Duluth Complex have been identified, and the potential ore reserves have been estimated at 50 million tons. Previous work on this material showed the potential for making a low-silica ilmenite concentrate; however, the recovery was only about 50 percent. Relatively low recovery was due to losses in the minus 200 mesh fraction. HPR has been shown to produce less minus 200 mesh material than the conventional rod mill that had been used previously. Two HPR grinding flowsheets were tested. The first involved two stages of HPR, with the first stage being closed by a three mesh screen. The second stage, which treated the minus 3 mesh material from stage one, was closed with a 14 mesh screen. The second flowsheet involved a single HPR stage closed by a 14 mesh screen. Both flowsheets produced significantly less minus 200 mesh material than the rod mill, with the single stage producing the least. Grinding energy for the single stage HPR was 3.28 kWh/mt of new feed, compared to the previous rod mill energy consumption of 13.59 kWh/mt. The minus 14 mesh material from the HPR grinding was concentrated in two stages of spirals with recirculation of the cleaner tails to new feed. The cleaner concentrate was passed through a single drum magnetic separator to remove any magnetite. The nonmagnetic fraction was dewatered in a screw classifier and stored for future upgrading. Ti02 recovery in the nonmagnetics averaged about 61 percent, compared to the average Ti02 recovery of about 50 percent in the previous study. Clearly, the HPR grinding resulted in improved recovery. The amount of Ti02 reporting to the magnetic concentrate was essentially the same for both this study and the previous study using the rod mill; 25. 07 percent and 25 .19 percent respectively. To determine the potential for recovering a portion of the Ti02 in the magnetic concentrate, a series of grinds followed by laboratory magnetic separation tests were run. Even a 90.6 passing 270 mesh grind was not sufficient to produce a magnetic concentrate suitable for pellet production. Elutriation tests run on selected size fractions from the nonmagnetic material from the 84.9 percent passing 270 mesh grind indicated that the Ti02 was well liberated in the plus 500 mesh fractions. A study funded by the Permanent University Trust Fund is currently under way to explore ways of reprocessing the primary magnetic concentrate to increase Ti02 recovery and to produce a suitable pellet feed material.