From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Subject: Re: Hulett Iron Ore Unloaders
Date: Fri, 11 Jun 1999 12:33:19 GMT
On Thu, 10 Jun 1999 19:39:52 -0500, "Ray Henry" <firstname.lastname@example.org>
>Taconite is roughly fifty percent iron. The rest is clay. The pellets
>are baked in rotary ovens. There is some good stuff at both of these
50% ???? That seems a bit high. I worked on the Messabi Iron range as
an analytical chemist for 2.5 years back in the days when they were
shipping almost pure hematite. Fe203 is about 67% iron.
The Erie Mining Co. was still running the taconite process in a pilot
plant when I left for what I hoped would be greener pastures (they
My recollection is that Taconite is roughly 50% silica and a little
under 30% iron (with damned little if any clay).
Taconite was essentially one rock which was drilled and blasted to get
small enough chunks to load in those huge Euclid trucks. It then went
through a couple jaw crushers, a rod mill, and a ball mill to get a
powder which was 200 mesh. Once one got to that mesh size the silica
and hematite were pretty much separate particles.
I am not sure why the floatation method was not used here as it was
with many other low grade iron ores but the powder was run through a
reducing atmosphere in a furnace to convert the hematite to magnetite.
At this point it was run through a magnetic separator to produce a
fine powdered rather pure Fe304. It would have been nice to ship this
stuff because one would be shipping less oxygen than with hematite but
unfortunately 200 mesh powder would have been blown out of the rail
cars (& the blast furnace).
A bit of clay was added and the powder was run through a mill to
produce (soft) pellets about 3/4 inches in diameter. The last step was
to sinter the pellets in another furnace. The sinter process
unfortunately converted the magnetite back to hematite so the added
oxygen was shipped also.
After I left they built the big plants on the shore of Lake Superior.
It was convenient to dump the tailings in the Lake but later on of
course it was found that the tailings contained asbestos and it was
getting into the Duluth water supply.
All hell broke loose and it nearly closed down the mines.
This is recalled from an almost 50 year old past so some of the
details are a bit hazy.