Plant Demonstration Test at Minntac Using Pebble Lime, Coleraine Minerals Research Laboratory, Natural Resources Research Institute, University of Minnesota DuluthThere were two main goals to the second test; to determine the long tenn operability of
balling circuits using quicklime and to produce green balls equal in quality to those produced
using bentonite without allowing the mixed material to sit before balling. Modifications were
made to the 03-4 circuit after the May test in order to achieve both of the above and this test was
run from November 8 through November 12, 1994. A summary of the results is given below:
The test was a success for two reasons. The 03-4 circuit ran smoothly for 4 days using
quicklime instead ofbentonite. -.And, because the circuit ran smoothly, a lot of useful and
meaningful data was collected and evaluated.
The test was completed safely. There were no incidents or accidents reported during the
preparation for or during the test. Levels of ammonia and fugitive dust were monitored during
the test and found to be lower than during the May test. The levels detected in both tests were
well below MSHA requirements.
The green ball quality achieved during this test was higher than that achieved during the
May test but below desired levels. However, this test, the May test and pilot plant tests all
indicate that acceptable quality green balls can be produced using quicklime under the right
conditions. Good quality green balls were produced during the May test when the mixed
materials were allowed to sit after being mixed, during pilot plant tests when the materials were
mixed for 1 minute and during this test when the mixing time exceeded 110 seconds. There were no unloading or handling problems during the test despite the fact that the
pulverized quicklime was contaminated with pebble sized chunks. The supplier, Marblehead Lime
Company, indicated that the chunks represented contamination from loading bins at their plant.
The fired pellet quality on the entire line dropped during both tests despite the fact that
quicklime was being used on only one of the four circuits on the line. This appears to be
indirectly related to the use of quicklime. It appeared that, during the tests, quicklime reacted
with the water in the bentonite and negatively affected the water absorbing properties of the
bentonite. The circuits using the contaminated bentonite then produced poorer quality green balls
than the circuit using quicklime. The slightly lower quality green balls produced using quicklime
combined with the significantly lower quality green balls made with contaminated bentonite and
resulted in lower quality fired pellets. This was suspected in the May test and verified during this
test
