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.
University of Minnesota Duluth, Natural Resources Research Institute, 5013 Miller Trunk Highway, Duluth, Minnesota 55811; Coleraine Minerals Research Laboratory, One Gayley Avenue, PO Box 188, Coleraine, Minnesota 55722
Benner, Blair R; Hendrickson, David W.
Minnesota Ilmenite Processing Using High Pressure Rolls.
University of Minnesota Duluth.
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