Blueman has the inquisitive post.
I had thoughts I left in his comments. Have a look.
A Google = taconite tailings density
gave additional interesting links I did not comment about at blueman's site, here, here, here and here.
That last one stands out like a sore thumb.
Why is that kind looking Mr. Hauck and his NRRI folks so reticent about this particular little hummer? The others are not so terse.
And that second to last item. Look at the project starting date: Feb. 1, 2002.
WHO WAS MnDOT HEAD HONCHO BACK THEN?
HOW ABOUT A TACONITE TACO FOR THE TACONITE TITAN, IF HE DECLINES "6T" DISCLOSURE?